Add 'third_party/nix/' from commit 'be66c7a6b24e3c3c6157fd37b86c7203d14acf10'

git-subtree-dir: third_party/nix
git-subtree-mainline: cf8cd640c1
git-subtree-split: be66c7a6b24e3c3c6157fd37b86c7203d14acf10

third_party/nix/src/libutil/affinity.cc

@@ -0,0 +1,55 @@
+#include "types.hh"
+#include "util.hh"
+#include "affinity.hh"
+
+#if __linux__
+#include <sched.h>
+#endif
+
+namespace nix {
+
+
+#if __linux__
+static bool didSaveAffinity = false;
+static cpu_set_t savedAffinity;
+#endif
+
+
+void setAffinityTo(int cpu)
+{
+#if __linux__
+    if (sched_getaffinity(0, sizeof(cpu_set_t), &savedAffinity) == -1) return;
+    didSaveAffinity = true;
+    debug(format("locking this thread to CPU %1%") % cpu);
+    cpu_set_t newAffinity;
+    CPU_ZERO(&newAffinity);
+    CPU_SET(cpu, &newAffinity);
+    if (sched_setaffinity(0, sizeof(cpu_set_t), &newAffinity) == -1)
+        printError(format("failed to lock thread to CPU %1%") % cpu);
+#endif
+}
+
+
+int lockToCurrentCPU()
+{
+#if __linux__
+    int cpu = sched_getcpu();
+    if (cpu != -1) setAffinityTo(cpu);
+    return cpu;
+#else
+    return -1;
+#endif
+}
+
+
+void restoreAffinity()
+{
+#if __linux__
+    if (!didSaveAffinity) return;
+    if (sched_setaffinity(0, sizeof(cpu_set_t), &savedAffinity) == -1)
+        printError("failed to restore affinity %1%");
+#endif
+}
+
+
+}

third_party/nix/src/libutil/affinity.hh

@@ -0,0 +1,9 @@
+#pragma once
+
+namespace nix {
+
+void setAffinityTo(int cpu);
+int lockToCurrentCPU();
+void restoreAffinity();
+
+}

third_party/nix/src/libutil/archive.cc

@@ -0,0 +1,378 @@
+#include <cerrno>
+#include <algorithm>
+#include <vector>
+#include <map>
+
+#include <strings.h> // for strcasecmp
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <dirent.h>
+#include <fcntl.h>
+
+#include "archive.hh"
+#include "util.hh"
+#include "config.hh"
+
+namespace nix {
+
+struct ArchiveSettings : Config
+{
+    Setting<bool> useCaseHack{this,
+        #if __APPLE__
+            true,
+        #else
+            false,
+        #endif
+        "use-case-hack",
+        "Whether to enable a Darwin-specific hack for dealing with file name collisions."};
+};
+
+static ArchiveSettings archiveSettings;
+
+static GlobalConfig::Register r1(&archiveSettings);
+
+const std::string narVersionMagic1 = "nix-archive-1";
+
+static string caseHackSuffix = "~nix~case~hack~";
+
+PathFilter defaultPathFilter = [](const Path &) { return true; };
+
+
+static void dumpContents(const Path & path, size_t size,
+    Sink & sink)
+{
+    sink << "contents" << size;
+
+    AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
+    if (!fd) throw SysError(format("opening file '%1%'") % path);
+
+    std::vector<unsigned char> buf(65536);
+    size_t left = size;
+
+    while (left > 0) {
+        auto n = std::min(left, buf.size());
+        readFull(fd.get(), buf.data(), n);
+        left -= n;
+        sink(buf.data(), n);
+    }
+
+    writePadding(size, sink);
+}
+
+
+static void dump(const Path & path, Sink & sink, PathFilter & filter)
+{
+    checkInterrupt();
+
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+        throw SysError(format("getting attributes of path '%1%'") % path);
+
+    sink << "(";
+
+    if (S_ISREG(st.st_mode)) {
+        sink << "type" << "regular";
+        if (st.st_mode & S_IXUSR)
+            sink << "executable" << "";
+        dumpContents(path, (size_t) st.st_size, sink);
+    }
+
+    else if (S_ISDIR(st.st_mode)) {
+        sink << "type" << "directory";
+
+        /* If we're on a case-insensitive system like macOS, undo
+           the case hack applied by restorePath(). */
+        std::map<string, string> unhacked;
+        for (auto & i : readDirectory(path))
+            if (archiveSettings.useCaseHack) {
+                string name(i.name);
+                size_t pos = i.name.find(caseHackSuffix);
+                if (pos != string::npos) {
+                    debug(format("removing case hack suffix from '%1%'") % (path + "/" + i.name));
+                    name.erase(pos);
+                }
+                if (unhacked.find(name) != unhacked.end())
+                    throw Error(format("file name collision in between '%1%' and '%2%'")
+                        % (path + "/" + unhacked[name]) % (path + "/" + i.name));
+                unhacked[name] = i.name;
+            } else
+                unhacked[i.name] = i.name;
+
+        for (auto & i : unhacked)
+            if (filter(path + "/" + i.first)) {
+                sink << "entry" << "(" << "name" << i.first << "node";
+                dump(path + "/" + i.second, sink, filter);
+                sink << ")";
+            }
+    }
+
+    else if (S_ISLNK(st.st_mode))
+        sink << "type" << "symlink" << "target" << readLink(path);
+
+    else throw Error(format("file '%1%' has an unsupported type") % path);
+
+    sink << ")";
+}
+
+
+void dumpPath(const Path & path, Sink & sink, PathFilter & filter)
+{
+    sink << narVersionMagic1;
+    dump(path, sink, filter);
+}
+
+
+void dumpString(const std::string & s, Sink & sink)
+{
+    sink << narVersionMagic1 << "(" << "type" << "regular" << "contents" << s << ")";
+}
+
+
+static SerialisationError badArchive(string s)
+{
+    return SerialisationError("bad archive: " + s);
+}
+
+
+#if 0
+static void skipGeneric(Source & source)
+{
+    if (readString(source) == "(") {
+        while (readString(source) != ")")
+            skipGeneric(source);
+    }
+}
+#endif
+
+
+static void parseContents(ParseSink & sink, Source & source, const Path & path)
+{
+    unsigned long long size = readLongLong(source);
+
+    sink.preallocateContents(size);
+
+    unsigned long long left = size;
+    std::vector<unsigned char> buf(65536);
+
+    while (left) {
+        checkInterrupt();
+        auto n = buf.size();
+        if ((unsigned long long)n > left) n = left;
+        source(buf.data(), n);
+        sink.receiveContents(buf.data(), n);
+        left -= n;
+    }
+
+    readPadding(size, source);
+}
+
+
+struct CaseInsensitiveCompare
+{
+    bool operator() (const string & a, const string & b) const
+    {
+        return strcasecmp(a.c_str(), b.c_str()) < 0;
+    }
+};
+
+
+static void parse(ParseSink & sink, Source & source, const Path & path)
+{
+    string s;
+
+    s = readString(source);
+    if (s != "(") throw badArchive("expected open tag");
+
+    enum { tpUnknown, tpRegular, tpDirectory, tpSymlink } type = tpUnknown;
+
+    std::map<Path, int, CaseInsensitiveCompare> names;
+
+    while (1) {
+        checkInterrupt();
+
+        s = readString(source);
+
+        if (s == ")") {
+            break;
+        }
+
+        else if (s == "type") {
+            if (type != tpUnknown)
+                throw badArchive("multiple type fields");
+            string t = readString(source);
+
+            if (t == "regular") {
+                type = tpRegular;
+                sink.createRegularFile(path);
+            }
+
+            else if (t == "directory") {
+                sink.createDirectory(path);
+                type = tpDirectory;
+            }
+
+            else if (t == "symlink") {
+                type = tpSymlink;
+            }
+
+            else throw badArchive("unknown file type " + t);
+
+        }
+
+        else if (s == "contents" && type == tpRegular) {
+            parseContents(sink, source, path);
+        }
+
+        else if (s == "executable" && type == tpRegular) {
+            auto s = readString(source);
+            if (s != "") throw badArchive("executable marker has non-empty value");
+            sink.isExecutable();
+        }
+
+        else if (s == "entry" && type == tpDirectory) {
+            string name, prevName;
+
+            s = readString(source);
+            if (s != "(") throw badArchive("expected open tag");
+
+            while (1) {
+                checkInterrupt();
+
+                s = readString(source);
+
+                if (s == ")") {
+                    break;
+                } else if (s == "name") {
+                    name = readString(source);
+                    if (name.empty() || name == "." || name == ".." || name.find('/') != string::npos || name.find((char) 0) != string::npos)
+                        throw Error(format("NAR contains invalid file name '%1%'") % name);
+                    if (name <= prevName)
+                        throw Error("NAR directory is not sorted");
+                    prevName = name;
+                    if (archiveSettings.useCaseHack) {
+                        auto i = names.find(name);
+                        if (i != names.end()) {
+                            debug(format("case collision between '%1%' and '%2%'") % i->first % name);
+                            name += caseHackSuffix;
+                            name += std::to_string(++i->second);
+                        } else
+                            names[name] = 0;
+                    }
+                } else if (s == "node") {
+                    if (s.empty()) throw badArchive("entry name missing");
+                    parse(sink, source, path + "/" + name);
+                } else
+                    throw badArchive("unknown field " + s);
+            }
+        }
+
+        else if (s == "target" && type == tpSymlink) {
+            string target = readString(source);
+            sink.createSymlink(path, target);
+        }
+
+        else
+            throw badArchive("unknown field " + s);
+    }
+}
+
+
+void parseDump(ParseSink & sink, Source & source)
+{
+    string version;
+    try {
+        version = readString(source, narVersionMagic1.size());
+    } catch (SerialisationError & e) {
+        /* This generally means the integer at the start couldn't be
+           decoded.  Ignore and throw the exception below. */
+    }
+    if (version != narVersionMagic1)
+        throw badArchive("input doesn't look like a Nix archive");
+    parse(sink, source, "");
+}
+
+
+struct RestoreSink : ParseSink
+{
+    Path dstPath;
+    AutoCloseFD fd;
+
+    void createDirectory(const Path & path)
+    {
+        Path p = dstPath + path;
+        if (mkdir(p.c_str(), 0777) == -1)
+            throw SysError(format("creating directory '%1%'") % p);
+    };
+
+    void createRegularFile(const Path & path)
+    {
+        Path p = dstPath + path;
+        fd = open(p.c_str(), O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC, 0666);
+        if (!fd) throw SysError(format("creating file '%1%'") % p);
+    }
+
+    void isExecutable()
+    {
+        struct stat st;
+        if (fstat(fd.get(), &st) == -1)
+            throw SysError("fstat");
+        if (fchmod(fd.get(), st.st_mode | (S_IXUSR | S_IXGRP | S_IXOTH)) == -1)
+            throw SysError("fchmod");
+    }
+
+    void preallocateContents(unsigned long long len)
+    {
+#if HAVE_POSIX_FALLOCATE
+        if (len) {
+            errno = posix_fallocate(fd.get(), 0, len);
+            /* Note that EINVAL may indicate that the underlying
+               filesystem doesn't support preallocation (e.g. on
+               OpenSolaris).  Since preallocation is just an
+               optimisation, ignore it. */
+            if (errno && errno != EINVAL && errno != EOPNOTSUPP && errno != ENOSYS)
+                throw SysError(format("preallocating file of %1% bytes") % len);
+        }
+#endif
+    }
+
+    void receiveContents(unsigned char * data, unsigned int len)
+    {
+        writeFull(fd.get(), data, len);
+    }
+
+    void createSymlink(const Path & path, const string & target)
+    {
+        Path p = dstPath + path;
+        nix::createSymlink(target, p);
+    }
+};
+
+
+void restorePath(const Path & path, Source & source)
+{
+    RestoreSink sink;
+    sink.dstPath = path;
+    parseDump(sink, source);
+}
+
+
+void copyNAR(Source & source, Sink & sink)
+{
+    // FIXME: if 'source' is the output of dumpPath() followed by EOF,
+    // we should just forward all data directly without parsing.
+
+    ParseSink parseSink; /* null sink; just parse the NAR */
+
+    LambdaSource wrapper([&](unsigned char * data, size_t len) {
+        auto n = source.read(data, len);
+        sink(data, n);
+        return n;
+    });
+
+    parseDump(parseSink, wrapper);
+}
+
+
+}

third_party/nix/src/libutil/archive.hh

@@ -0,0 +1,84 @@
+#pragma once
+
+#include "types.hh"
+#include "serialise.hh"
+
+
+namespace nix {
+
+
+/* dumpPath creates a Nix archive of the specified path.  The format
+   is as follows:
+
+   IF path points to a REGULAR FILE:
+     dump(path) = attrs(
+       [ ("type", "regular")
+       , ("contents", contents(path))
+       ])
+
+   IF path points to a DIRECTORY:
+     dump(path) = attrs(
+       [ ("type", "directory")
+       , ("entries", concat(map(f, sort(entries(path)))))
+       ])
+       where f(fn) = attrs(
+         [ ("name", fn)
+         , ("file", dump(path + "/" + fn))
+         ])
+
+   where:
+
+     attrs(as) = concat(map(attr, as)) + encN(0)
+     attrs((a, b)) = encS(a) + encS(b)
+
+     encS(s) = encN(len(s)) + s + (padding until next 64-bit boundary)
+
+     encN(n) = 64-bit little-endian encoding of n.
+
+     contents(path) = the contents of a regular file.
+
+     sort(strings) = lexicographic sort by 8-bit value (strcmp).
+
+     entries(path) = the entries of a directory, without `.' and
+     `..'.
+
+     `+' denotes string concatenation. */
+
+
+void dumpPath(const Path & path, Sink & sink,
+    PathFilter & filter = defaultPathFilter);
+
+void dumpString(const std::string & s, Sink & sink);
+
+/* FIXME: fix this API, it sucks. */
+struct ParseSink
+{
+    virtual void createDirectory(const Path & path) { };
+
+    virtual void createRegularFile(const Path & path) { };
+    virtual void isExecutable() { };
+    virtual void preallocateContents(unsigned long long size) { };
+    virtual void receiveContents(unsigned char * data, unsigned int len) { };
+
+    virtual void createSymlink(const Path & path, const string & target) { };
+};
+
+struct TeeSink : ParseSink
+{
+    TeeSource source;
+
+    TeeSink(Source & source) : source(source) { }
+};
+
+void parseDump(ParseSink & sink, Source & source);
+
+void restorePath(const Path & path, Source & source);
+
+/* Read a NAR from 'source' and write it to 'sink'. */
+void copyNAR(Source & source, Sink & sink);
+
+
+extern const std::string narVersionMagic1;
+
+
+}

third_party/nix/src/libutil/args.cc

@@ -0,0 +1,203 @@
+#include "args.hh"
+#include "hash.hh"
+
+namespace nix {
+
+Args::FlagMaker Args::mkFlag()
+{
+    return FlagMaker(*this);
+}
+
+Args::FlagMaker::~FlagMaker()
+{
+    assert(flag->longName != "");
+    args.longFlags[flag->longName] = flag;
+    if (flag->shortName) args.shortFlags[flag->shortName] = flag;
+}
+
+void Args::parseCmdline(const Strings & _cmdline)
+{
+    Strings pendingArgs;
+    bool dashDash = false;
+
+    Strings cmdline(_cmdline);
+
+    for (auto pos = cmdline.begin(); pos != cmdline.end(); ) {
+
+        auto arg = *pos;
+
+        /* Expand compound dash options (i.e., `-qlf' -> `-q -l -f',
+           `-j3` -> `-j 3`). */
+        if (!dashDash && arg.length() > 2 && arg[0] == '-' && arg[1] != '-' && isalpha(arg[1])) {
+            *pos = (string) "-" + arg[1];
+            auto next = pos; ++next;
+            for (unsigned int j = 2; j < arg.length(); j++)
+                if (isalpha(arg[j]))
+                    cmdline.insert(next, (string) "-" + arg[j]);
+                else {
+                    cmdline.insert(next, string(arg, j));
+                    break;
+                }
+            arg = *pos;
+        }
+
+        if (!dashDash && arg == "--") {
+            dashDash = true;
+            ++pos;
+        }
+        else if (!dashDash && std::string(arg, 0, 1) == "-") {
+            if (!processFlag(pos, cmdline.end()))
+                throw UsageError(format("unrecognised flag '%1%'") % arg);
+        }
+        else {
+            pendingArgs.push_back(*pos++);
+            if (processArgs(pendingArgs, false))
+                pendingArgs.clear();
+        }
+    }
+
+    processArgs(pendingArgs, true);
+}
+
+void Args::printHelp(const string & programName, std::ostream & out)
+{
+    std::cout << "Usage: " << programName << " <FLAGS>...";
+    for (auto & exp : expectedArgs) {
+        std::cout << renderLabels({exp.label});
+        // FIXME: handle arity > 1
+        if (exp.arity == 0) std::cout << "...";
+        if (exp.optional) std::cout << "?";
+    }
+    std::cout << "\n";
+
+    auto s = description();
+    if (s != "")
+        std::cout << "\nSummary: " << s << ".\n";
+
+    if (longFlags.size()) {
+        std::cout << "\n";
+        std::cout << "Flags:\n";
+        printFlags(out);
+    }
+}
+
+void Args::printFlags(std::ostream & out)
+{
+    Table2 table;
+    for (auto & flag : longFlags) {
+        if (hiddenCategories.count(flag.second->category)) continue;
+        table.push_back(std::make_pair(
+                (flag.second->shortName ? std::string("-") + flag.second->shortName + ", " : "    ")
+                + "--" + flag.first + renderLabels(flag.second->labels),
+                flag.second->description));
+    }
+    printTable(out, table);
+}
+
+bool Args::processFlag(Strings::iterator & pos, Strings::iterator end)
+{
+    assert(pos != end);
+
+    auto process = [&](const std::string & name, const Flag & flag) -> bool {
+        ++pos;
+        std::vector<std::string> args;
+        for (size_t n = 0 ; n < flag.arity; ++n) {
+            if (pos == end) {
+                if (flag.arity == ArityAny) break;
+                throw UsageError(format("flag '%1%' requires %2% argument(s)")
+                    % name % flag.arity);
+            }
+            args.push_back(*pos++);
+        }
+        flag.handler(std::move(args));
+        return true;
+    };
+
+    if (string(*pos, 0, 2) == "--") {
+        auto i = longFlags.find(string(*pos, 2));
+        if (i == longFlags.end()) return false;
+        return process("--" + i->first, *i->second);
+    }
+
+    if (string(*pos, 0, 1) == "-" && pos->size() == 2) {
+        auto c = (*pos)[1];
+        auto i = shortFlags.find(c);
+        if (i == shortFlags.end()) return false;
+        return process(std::string("-") + c, *i->second);
+    }
+
+    return false;
+}
+
+bool Args::processArgs(const Strings & args, bool finish)
+{
+    if (expectedArgs.empty()) {
+        if (!args.empty())
+            throw UsageError(format("unexpected argument '%1%'") % args.front());
+        return true;
+    }
+
+    auto & exp = expectedArgs.front();
+
+    bool res = false;
+
+    if ((exp.arity == 0 && finish) ||
+        (exp.arity > 0 && args.size() == exp.arity))
+    {
+        std::vector<std::string> ss;
+        for (auto & s : args) ss.push_back(s);
+        exp.handler(std::move(ss));
+        expectedArgs.pop_front();
+        res = true;
+    }
+
+    if (finish && !expectedArgs.empty() && !expectedArgs.front().optional)
+        throw UsageError("more arguments are required");
+
+    return res;
+}
+
+Args::FlagMaker & Args::FlagMaker::mkHashTypeFlag(HashType * ht)
+{
+    arity(1);
+    label("type");
+    description("hash algorithm ('md5', 'sha1', 'sha256', or 'sha512')");
+    handler([ht](std::string s) {
+        *ht = parseHashType(s);
+        if (*ht == htUnknown)
+            throw UsageError("unknown hash type '%1%'", s);
+    });
+    return *this;
+}
+
+Strings argvToStrings(int argc, char * * argv)
+{
+    Strings args;
+    argc--; argv++;
+    while (argc--) args.push_back(*argv++);
+    return args;
+}
+
+std::string renderLabels(const Strings & labels)
+{
+    std::string res;
+    for (auto label : labels) {
+        for (auto & c : label) c = std::toupper(c);
+        res += " <" + label + ">";
+    }
+    return res;
+}
+
+void printTable(std::ostream & out, const Table2 & table)
+{
+    size_t max = 0;
+    for (auto & row : table)
+        max = std::max(max, row.first.size());
+    for (auto & row : table) {
+        out << "  " << row.first
+            << std::string(max - row.first.size() + 2, ' ')
+            << row.second << "\n";
+    }
+}
+
+}

third_party/nix/src/libutil/args.hh

@@ -0,0 +1,201 @@
+#pragma once
+
+#include <iostream>
+#include <map>
+#include <memory>
+
+#include "util.hh"
+
+namespace nix {
+
+MakeError(UsageError, Error);
+
+enum HashType : char;
+
+class Args
+{
+public:
+
+    /* Parse the command line, throwing a UsageError if something goes
+       wrong. */
+    void parseCmdline(const Strings & cmdline);
+
+    virtual void printHelp(const string & programName, std::ostream & out);
+
+    virtual std::string description() { return ""; }
+
+protected:
+
+    static const size_t ArityAny = std::numeric_limits<size_t>::max();
+
+    /* Flags. */
+    struct Flag
+    {
+        typedef std::shared_ptr<Flag> ptr;
+        std::string longName;
+        char shortName = 0;
+        std::string description;
+        Strings labels;
+        size_t arity = 0;
+        std::function<void(std::vector<std::string>)> handler;
+        std::string category;
+    };
+
+    std::map<std::string, Flag::ptr> longFlags;
+    std::map<char, Flag::ptr> shortFlags;
+
+    virtual bool processFlag(Strings::iterator & pos, Strings::iterator end);
+
+    virtual void printFlags(std::ostream & out);
+
+    /* Positional arguments. */
+    struct ExpectedArg
+    {
+        std::string label;
+        size_t arity; // 0 = any
+        bool optional;
+        std::function<void(std::vector<std::string>)> handler;
+    };
+
+    std::list<ExpectedArg> expectedArgs;
+
+    virtual bool processArgs(const Strings & args, bool finish);
+
+    std::set<std::string> hiddenCategories;
+
+public:
+
+    class FlagMaker
+    {
+        Args & args;
+        Flag::ptr flag;
+        friend class Args;
+        FlagMaker(Args & args) : args(args), flag(std::make_shared<Flag>()) { };
+    public:
+        ~FlagMaker();
+        FlagMaker & longName(const std::string & s) { flag->longName = s; return *this; };
+        FlagMaker & shortName(char s) { flag->shortName = s; return *this; };
+        FlagMaker & description(const std::string & s) { flag->description = s; return *this; };
+        FlagMaker & label(const std::string & l) { flag->arity = 1; flag->labels = {l}; return *this; };
+        FlagMaker & labels(const Strings & ls) { flag->arity = ls.size(); flag->labels = ls; return *this; };
+        FlagMaker & arity(size_t arity) { flag->arity = arity; return *this; };
+        FlagMaker & handler(std::function<void(std::vector<std::string>)> handler) { flag->handler = handler; return *this; };
+        FlagMaker & handler(std::function<void()> handler) { flag->handler = [handler](std::vector<std::string>) { handler(); }; return *this; };
+        FlagMaker & handler(std::function<void(std::string)> handler) {
+            flag->arity = 1;
+            flag->handler = [handler](std::vector<std::string> ss) { handler(std::move(ss[0])); };
+            return *this;
+        };
+        FlagMaker & category(const std::string & s) { flag->category = s; return *this; };
+
+        template<class T>
+        FlagMaker & dest(T * dest)
+        {
+            flag->arity = 1;
+            flag->handler = [=](std::vector<std::string> ss) { *dest = ss[0]; };
+            return *this;
+        };
+
+        template<class T>
+        FlagMaker & set(T * dest, const T & val)
+        {
+            flag->arity = 0;
+            flag->handler = [=](std::vector<std::string> ss) { *dest = val; };
+            return *this;
+        };
+
+        FlagMaker & mkHashTypeFlag(HashType * ht);
+    };
+
+    FlagMaker mkFlag();
+
+    /* Helper functions for constructing flags / positional
+       arguments. */
+
+    void mkFlag1(char shortName, const std::string & longName,
+        const std::string & label, const std::string & description,
+        std::function<void(std::string)> fun)
+    {
+        mkFlag()
+            .shortName(shortName)
+            .longName(longName)
+            .labels({label})
+            .description(description)
+            .arity(1)
+            .handler([=](std::vector<std::string> ss) { fun(ss[0]); });
+    }
+
+    void mkFlag(char shortName, const std::string & name,
+        const std::string & description, bool * dest)
+    {
+        mkFlag(shortName, name, description, dest, true);
+    }
+
+    template<class T>
+    void mkFlag(char shortName, const std::string & longName, const std::string & description,
+        T * dest, const T & value)
+    {
+        mkFlag()
+            .shortName(shortName)
+            .longName(longName)
+            .description(description)
+            .handler([=](std::vector<std::string> ss) { *dest = value; });
+    }
+
+    template<class I>
+    void mkIntFlag(char shortName, const std::string & longName,
+        const std::string & description, I * dest)
+    {
+        mkFlag<I>(shortName, longName, description, [=](I n) {
+            *dest = n;
+        });
+    }
+
+    template<class I>
+    void mkFlag(char shortName, const std::string & longName,
+        const std::string & description, std::function<void(I)> fun)
+    {
+        mkFlag()
+            .shortName(shortName)
+            .longName(longName)
+            .labels({"N"})
+            .description(description)
+            .arity(1)
+            .handler([=](std::vector<std::string> ss) {
+                I n;
+                if (!string2Int(ss[0], n))
+                    throw UsageError("flag '--%s' requires a integer argument", longName);
+                fun(n);
+            });
+    }
+
+    /* Expect a string argument. */
+    void expectArg(const std::string & label, string * dest, bool optional = false)
+    {
+        expectedArgs.push_back(ExpectedArg{label, 1, optional, [=](std::vector<std::string> ss) {
+            *dest = ss[0];
+        }});
+    }
+
+    /* Expect 0 or more arguments. */
+    void expectArgs(const std::string & label, std::vector<std::string> * dest)
+    {
+        expectedArgs.push_back(ExpectedArg{label, 0, false, [=](std::vector<std::string> ss) {
+            *dest = std::move(ss);
+        }});
+    }
+
+    friend class MultiCommand;
+};
+
+Strings argvToStrings(int argc, char * * argv);
+
+/* Helper function for rendering argument labels. */
+std::string renderLabels(const Strings & labels);
+
+/* Helper function for printing 2-column tables. */
+typedef std::vector<std::pair<std::string, std::string>> Table2;
+
+void printTable(std::ostream & out, const Table2 & table);
+
+}

third_party/nix/src/libutil/compression.cc

@@ -0,0 +1,432 @@
+#include "compression.hh"
+#include "util.hh"
+#include "finally.hh"
+#include "logging.hh"
+
+#include <lzma.h>
+#include <bzlib.h>
+#include <cstdio>
+#include <cstring>
+
+#include <brotli/decode.h>
+#include <brotli/encode.h>
+
+#include <iostream>
+
+namespace nix {
+
+// Don't feed brotli too much at once.
+struct ChunkedCompressionSink : CompressionSink
+{
+    uint8_t outbuf[32 * 1024];
+
+    void write(const unsigned char * data, size_t len) override
+    {
+        const size_t CHUNK_SIZE = sizeof(outbuf) << 2;
+        while (len) {
+            size_t n = std::min(CHUNK_SIZE, len);
+            writeInternal(data, n);
+            data += n;
+            len -= n;
+        }
+    }
+
+    virtual void writeInternal(const unsigned char * data, size_t len) = 0;
+};
+
+struct NoneSink : CompressionSink
+{
+    Sink & nextSink;
+    NoneSink(Sink & nextSink) : nextSink(nextSink) { }
+    void finish() override { flush(); }
+    void write(const unsigned char * data, size_t len) override { nextSink(data, len); }
+};
+
+struct XzDecompressionSink : CompressionSink
+{
+    Sink & nextSink;
+    uint8_t outbuf[BUFSIZ];
+    lzma_stream strm = LZMA_STREAM_INIT;
+    bool finished = false;
+
+    XzDecompressionSink(Sink & nextSink) : nextSink(nextSink)
+    {
+        lzma_ret ret = lzma_stream_decoder(
+            &strm, UINT64_MAX, LZMA_CONCATENATED);
+        if (ret != LZMA_OK)
+            throw CompressionError("unable to initialise lzma decoder");
+
+        strm.next_out = outbuf;
+        strm.avail_out = sizeof(outbuf);
+    }
+
+    ~XzDecompressionSink()
+    {
+        lzma_end(&strm);
+    }
+
+    void finish() override
+    {
+        CompressionSink::flush();
+        write(nullptr, 0);
+    }
+
+    void write(const unsigned char * data, size_t len) override
+    {
+        strm.next_in = data;
+        strm.avail_in = len;
+
+        while (!finished && (!data || strm.avail_in)) {
+            checkInterrupt();
+
+            lzma_ret ret = lzma_code(&strm, data ? LZMA_RUN : LZMA_FINISH);
+            if (ret != LZMA_OK && ret != LZMA_STREAM_END)
+                throw CompressionError("error %d while decompressing xz file", ret);
+
+            finished = ret == LZMA_STREAM_END;
+
+            if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
+                nextSink(outbuf, sizeof(outbuf) - strm.avail_out);
+                strm.next_out = outbuf;
+                strm.avail_out = sizeof(outbuf);
+            }
+        }
+    }
+};
+
+struct BzipDecompressionSink : ChunkedCompressionSink
+{
+    Sink & nextSink;
+    bz_stream strm;
+    bool finished = false;
+
+    BzipDecompressionSink(Sink & nextSink) : nextSink(nextSink)
+    {
+        memset(&strm, 0, sizeof(strm));
+        int ret = BZ2_bzDecompressInit(&strm, 0, 0);
+        if (ret != BZ_OK)
+            throw CompressionError("unable to initialise bzip2 decoder");
+
+        strm.next_out = (char *) outbuf;
+        strm.avail_out = sizeof(outbuf);
+    }
+
+    ~BzipDecompressionSink()
+    {
+        BZ2_bzDecompressEnd(&strm);
+    }
+
+    void finish() override
+    {
+        flush();
+        write(nullptr, 0);
+    }
+
+    void writeInternal(const unsigned char * data, size_t len) override
+    {
+        assert(len <= std::numeric_limits<decltype(strm.avail_in)>::max());
+
+        strm.next_in = (char *) data;
+        strm.avail_in = len;
+
+        while (strm.avail_in) {
+            checkInterrupt();
+
+            int ret = BZ2_bzDecompress(&strm);
+            if (ret != BZ_OK && ret != BZ_STREAM_END)
+                throw CompressionError("error while decompressing bzip2 file");
+
+            finished = ret == BZ_STREAM_END;
+
+            if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
+                nextSink(outbuf, sizeof(outbuf) - strm.avail_out);
+                strm.next_out = (char *) outbuf;
+                strm.avail_out = sizeof(outbuf);
+            }
+        }
+    }
+};
+
+struct BrotliDecompressionSink : ChunkedCompressionSink
+{
+    Sink & nextSink;
+    BrotliDecoderState * state;
+    bool finished = false;
+
+    BrotliDecompressionSink(Sink & nextSink) : nextSink(nextSink)
+    {
+        state = BrotliDecoderCreateInstance(nullptr, nullptr, nullptr);
+        if (!state)
+            throw CompressionError("unable to initialize brotli decoder");
+    }
+
+    ~BrotliDecompressionSink()
+    {
+        BrotliDecoderDestroyInstance(state);
+    }
+
+    void finish() override
+    {
+        flush();
+        writeInternal(nullptr, 0);
+    }
+
+    void writeInternal(const unsigned char * data, size_t len) override
+    {
+        const uint8_t * next_in = data;
+        size_t avail_in = len;
+        uint8_t * next_out = outbuf;
+        size_t avail_out = sizeof(outbuf);
+
+        while (!finished && (!data || avail_in)) {
+            checkInterrupt();
+
+            if (!BrotliDecoderDecompressStream(state,
+                    &avail_in, &next_in,
+                    &avail_out, &next_out,
+                    nullptr))
+                throw CompressionError("error while decompressing brotli file");
+
+            if (avail_out < sizeof(outbuf) || avail_in == 0) {
+                nextSink(outbuf, sizeof(outbuf) - avail_out);
+                next_out = outbuf;
+                avail_out = sizeof(outbuf);
+            }
+
+            finished = BrotliDecoderIsFinished(state);
+        }
+    }
+};
+
+ref<std::string> decompress(const std::string & method, const std::string & in)
+{
+    StringSink ssink;
+    auto sink = makeDecompressionSink(method, ssink);
+    (*sink)(in);
+    sink->finish();
+    return ssink.s;
+}
+
+ref<CompressionSink> makeDecompressionSink(const std::string & method, Sink & nextSink)
+{
+    if (method == "none" || method == "")
+        return make_ref<NoneSink>(nextSink);
+    else if (method == "xz")
+        return make_ref<XzDecompressionSink>(nextSink);
+    else if (method == "bzip2")
+        return make_ref<BzipDecompressionSink>(nextSink);
+    else if (method == "br")
+        return make_ref<BrotliDecompressionSink>(nextSink);
+    else
+        throw UnknownCompressionMethod("unknown compression method '%s'", method);
+}
+
+struct XzCompressionSink : CompressionSink
+{
+    Sink & nextSink;
+    uint8_t outbuf[BUFSIZ];
+    lzma_stream strm = LZMA_STREAM_INIT;
+    bool finished = false;
+
+    XzCompressionSink(Sink & nextSink, bool parallel) : nextSink(nextSink)
+    {
+        lzma_ret ret;
+        bool done = false;
+
+        if (parallel) {
+#ifdef HAVE_LZMA_MT
+            lzma_mt mt_options = {};
+            mt_options.flags = 0;
+            mt_options.timeout = 300; // Using the same setting as the xz cmd line
+            mt_options.preset = LZMA_PRESET_DEFAULT;
+            mt_options.filters = NULL;
+            mt_options.check = LZMA_CHECK_CRC64;
+            mt_options.threads = lzma_cputhreads();
+            mt_options.block_size = 0;
+            if (mt_options.threads == 0)
+                mt_options.threads = 1;
+            // FIXME: maybe use lzma_stream_encoder_mt_memusage() to control the
+            // number of threads.
+            ret = lzma_stream_encoder_mt(&strm, &mt_options);
+            done = true;
+#else
+            printMsg(lvlError, "warning: parallel XZ compression requested but not supported, falling back to single-threaded compression");
+#endif
+        }
+
+        if (!done)
+            ret = lzma_easy_encoder(&strm, 6, LZMA_CHECK_CRC64);
+
+        if (ret != LZMA_OK)
+            throw CompressionError("unable to initialise lzma encoder");
+
+        // FIXME: apply the x86 BCJ filter?
+
+        strm.next_out = outbuf;
+        strm.avail_out = sizeof(outbuf);
+    }
+
+    ~XzCompressionSink()
+    {
+        lzma_end(&strm);
+    }
+
+    void finish() override
+    {
+        CompressionSink::flush();
+        write(nullptr, 0);
+    }
+
+    void write(const unsigned char * data, size_t len) override
+    {
+        strm.next_in = data;
+        strm.avail_in = len;
+
+        while (!finished && (!data || strm.avail_in)) {
+            checkInterrupt();
+
+            lzma_ret ret = lzma_code(&strm, data ? LZMA_RUN : LZMA_FINISH);
+            if (ret != LZMA_OK && ret != LZMA_STREAM_END)
+                throw CompressionError("error %d while compressing xz file", ret);
+
+            finished = ret == LZMA_STREAM_END;
+
+            if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
+                nextSink(outbuf, sizeof(outbuf) - strm.avail_out);
+                strm.next_out = outbuf;
+                strm.avail_out = sizeof(outbuf);
+            }
+        }
+    }
+};
+
+struct BzipCompressionSink : ChunkedCompressionSink
+{
+    Sink & nextSink;
+    bz_stream strm;
+    bool finished = false;
+
+    BzipCompressionSink(Sink & nextSink) : nextSink(nextSink)
+    {
+        memset(&strm, 0, sizeof(strm));
+        int ret = BZ2_bzCompressInit(&strm, 9, 0, 30);
+        if (ret != BZ_OK)
+            throw CompressionError("unable to initialise bzip2 encoder");
+
+        strm.next_out = (char *) outbuf;
+        strm.avail_out = sizeof(outbuf);
+    }
+
+    ~BzipCompressionSink()
+    {
+        BZ2_bzCompressEnd(&strm);
+    }
+
+    void finish() override
+    {
+        flush();
+        writeInternal(nullptr, 0);
+    }
+
+    void writeInternal(const unsigned char * data, size_t len) override
+    {
+        assert(len <= std::numeric_limits<decltype(strm.avail_in)>::max());
+
+        strm.next_in = (char *) data;
+        strm.avail_in = len;
+
+        while (!finished && (!data || strm.avail_in)) {
+            checkInterrupt();
+
+            int ret = BZ2_bzCompress(&strm, data ? BZ_RUN : BZ_FINISH);
+            if (ret != BZ_RUN_OK && ret != BZ_FINISH_OK && ret != BZ_STREAM_END)
+                throw CompressionError("error %d while compressing bzip2 file", ret);
+
+            finished = ret == BZ_STREAM_END;
+
+            if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
+                nextSink(outbuf, sizeof(outbuf) - strm.avail_out);
+                strm.next_out = (char *) outbuf;
+                strm.avail_out = sizeof(outbuf);
+            }
+        }
+    }
+};
+
+struct BrotliCompressionSink : ChunkedCompressionSink
+{
+    Sink & nextSink;
+    uint8_t outbuf[BUFSIZ];
+    BrotliEncoderState *state;
+    bool finished = false;
+
+    BrotliCompressionSink(Sink & nextSink) : nextSink(nextSink)
+    {
+        state = BrotliEncoderCreateInstance(nullptr, nullptr, nullptr);
+        if (!state)
+            throw CompressionError("unable to initialise brotli encoder");
+    }
+
+    ~BrotliCompressionSink()
+    {
+        BrotliEncoderDestroyInstance(state);
+    }
+
+    void finish() override
+    {
+        flush();
+        writeInternal(nullptr, 0);
+    }
+
+    void writeInternal(const unsigned char * data, size_t len) override
+    {
+        const uint8_t * next_in = data;
+        size_t avail_in = len;
+        uint8_t * next_out = outbuf;
+        size_t avail_out = sizeof(outbuf);
+
+        while (!finished && (!data || avail_in)) {
+            checkInterrupt();
+
+            if (!BrotliEncoderCompressStream(state,
+                    data ? BROTLI_OPERATION_PROCESS : BROTLI_OPERATION_FINISH,
+                    &avail_in, &next_in,
+                    &avail_out, &next_out,
+                    nullptr))
+                throw CompressionError("error while compressing brotli compression");
+
+            if (avail_out < sizeof(outbuf) || avail_in == 0) {
+                nextSink(outbuf, sizeof(outbuf) - avail_out);
+                next_out = outbuf;
+                avail_out = sizeof(outbuf);
+            }
+
+            finished = BrotliEncoderIsFinished(state);
+        }
+    }
+};
+
+ref<CompressionSink> makeCompressionSink(const std::string & method, Sink & nextSink, const bool parallel)
+{
+    if (method == "none")
+        return make_ref<NoneSink>(nextSink);
+    else if (method == "xz")
+        return make_ref<XzCompressionSink>(nextSink, parallel);
+    else if (method == "bzip2")
+        return make_ref<BzipCompressionSink>(nextSink);
+    else if (method == "br")
+        return make_ref<BrotliCompressionSink>(nextSink);
+    else
+        throw UnknownCompressionMethod(format("unknown compression method '%s'") % method);
+}
+
+ref<std::string> compress(const std::string & method, const std::string & in, const bool parallel)
+{
+    StringSink ssink;
+    auto sink = makeCompressionSink(method, ssink, parallel);
+    (*sink)(in);
+    sink->finish();
+    return ssink.s;
+}
+
+}

third_party/nix/src/libutil/compression.hh

@@ -0,0 +1,28 @@
+#pragma once
+
+#include "ref.hh"
+#include "types.hh"
+#include "serialise.hh"
+
+#include <string>
+
+namespace nix {
+
+struct CompressionSink : BufferedSink
+{
+    virtual void finish() = 0;
+};
+
+ref<std::string> decompress(const std::string & method, const std::string & in);
+
+ref<CompressionSink> makeDecompressionSink(const std::string & method, Sink & nextSink);
+
+ref<std::string> compress(const std::string & method, const std::string & in, const bool parallel = false);
+
+ref<CompressionSink> makeCompressionSink(const std::string & method, Sink & nextSink, const bool parallel = false);
+
+MakeError(UnknownCompressionMethod, Error);
+
+MakeError(CompressionError, Error);
+
+}

third_party/nix/src/libutil/config.cc

@@ -0,0 +1,338 @@
+#include "config.hh"
+#include "args.hh"
+#include "json.hh"
+
+namespace nix {
+
+bool Config::set(const std::string & name, const std::string & value)
+{
+    auto i = _settings.find(name);
+    if (i == _settings.end()) return false;
+    i->second.setting->set(value);
+    i->second.setting->overriden = true;
+    return true;
+}
+
+void Config::addSetting(AbstractSetting * setting)
+{
+    _settings.emplace(setting->name, Config::SettingData(false, setting));
+    for (auto & alias : setting->aliases)
+        _settings.emplace(alias, Config::SettingData(true, setting));
+
+    bool set = false;
+
+    auto i = unknownSettings.find(setting->name);
+    if (i != unknownSettings.end()) {
+        setting->set(i->second);
+        setting->overriden = true;
+        unknownSettings.erase(i);
+        set = true;
+    }
+
+    for (auto & alias : setting->aliases) {
+        auto i = unknownSettings.find(alias);
+        if (i != unknownSettings.end()) {
+            if (set)
+                warn("setting '%s' is set, but it's an alias of '%s' which is also set",
+                    alias, setting->name);
+            else {
+                setting->set(i->second);
+                setting->overriden = true;
+                unknownSettings.erase(i);
+                set = true;
+            }
+        }
+    }
+}
+
+void AbstractConfig::warnUnknownSettings()
+{
+    for (auto & s : unknownSettings)
+        warn("unknown setting '%s'", s.first);
+}
+
+void AbstractConfig::reapplyUnknownSettings()
+{
+    auto unknownSettings2 = std::move(unknownSettings);
+    for (auto & s : unknownSettings2)
+        set(s.first, s.second);
+}
+
+void Config::getSettings(std::map<std::string, SettingInfo> & res, bool overridenOnly)
+{
+    for (auto & opt : _settings)
+        if (!opt.second.isAlias && (!overridenOnly || opt.second.setting->overriden))
+            res.emplace(opt.first, SettingInfo{opt.second.setting->to_string(), opt.second.setting->description});
+}
+
+void AbstractConfig::applyConfigFile(const Path & path)
+{
+    try {
+        string contents = readFile(path);
+
+        unsigned int pos = 0;
+
+        while (pos < contents.size()) {
+            string line;
+            while (pos < contents.size() && contents[pos] != '\n')
+                line += contents[pos++];
+            pos++;
+
+            string::size_type hash = line.find('#');
+            if (hash != string::npos)
+                line = string(line, 0, hash);
+
+            vector<string> tokens = tokenizeString<vector<string> >(line);
+            if (tokens.empty()) continue;
+
+            if (tokens.size() < 2)
+                throw UsageError("illegal configuration line '%1%' in '%2%'", line, path);
+
+            auto include = false;
+            auto ignoreMissing = false;
+            if (tokens[0] == "include")
+                include = true;
+            else if (tokens[0] == "!include") {
+                include = true;
+                ignoreMissing = true;
+            }
+
+            if (include) {
+                if (tokens.size() != 2)
+                    throw UsageError("illegal configuration line '%1%' in '%2%'", line, path);
+                auto p = absPath(tokens[1], dirOf(path));
+                if (pathExists(p)) {
+                    applyConfigFile(p);
+                } else if (!ignoreMissing) {
+                    throw Error("file '%1%' included from '%2%' not found", p, path);
+                }
+                continue;
+            }
+
+            if (tokens[1] != "=")
+                throw UsageError("illegal configuration line '%1%' in '%2%'", line, path);
+
+            string name = tokens[0];
+
+            vector<string>::iterator i = tokens.begin();
+            advance(i, 2);
+
+            set(name, concatStringsSep(" ", Strings(i, tokens.end()))); // FIXME: slow
+        };
+    } catch (SysError &) { }
+}
+
+void Config::resetOverriden()
+{
+    for (auto & s : _settings)
+        s.second.setting->overriden = false;
+}
+
+void Config::toJSON(JSONObject & out)
+{
+    for (auto & s : _settings)
+        if (!s.second.isAlias) {
+            JSONObject out2(out.object(s.first));
+            out2.attr("description", s.second.setting->description);
+            JSONPlaceholder out3(out2.placeholder("value"));
+            s.second.setting->toJSON(out3);
+        }
+}
+
+void Config::convertToArgs(Args & args, const std::string & category)
+{
+    for (auto & s : _settings)
+        if (!s.second.isAlias)
+            s.second.setting->convertToArg(args, category);
+}
+
+AbstractSetting::AbstractSetting(
+    const std::string & name,
+    const std::string & description,
+    const std::set<std::string> & aliases)
+    : name(name), description(description), aliases(aliases)
+{
+}
+
+void AbstractSetting::toJSON(JSONPlaceholder & out)
+{
+    out.write(to_string());
+}
+
+void AbstractSetting::convertToArg(Args & args, const std::string & category)
+{
+}
+
+template<typename T>
+void BaseSetting<T>::toJSON(JSONPlaceholder & out)
+{
+    out.write(value);
+}
+
+template<typename T>
+void BaseSetting<T>::convertToArg(Args & args, const std::string & category)
+{
+    args.mkFlag()
+        .longName(name)
+        .description(description)
+        .arity(1)
+        .handler([=](std::vector<std::string> ss) { overriden = true; set(ss[0]); })
+        .category(category);
+}
+
+template<> void BaseSetting<std::string>::set(const std::string & str)
+{
+    value = str;
+}
+
+template<> std::string BaseSetting<std::string>::to_string()
+{
+    return value;
+}
+
+template<typename T>
+void BaseSetting<T>::set(const std::string & str)
+{
+    static_assert(std::is_integral<T>::value, "Integer required.");
+    if (!string2Int(str, value))
+        throw UsageError("setting '%s' has invalid value '%s'", name, str);
+}
+
+template<typename T>
+std::string BaseSetting<T>::to_string()
+{
+    static_assert(std::is_integral<T>::value, "Integer required.");
+    return std::to_string(value);
+}
+
+template<> void BaseSetting<bool>::set(const std::string & str)
+{
+    if (str == "true" || str == "yes" || str == "1")
+        value = true;
+    else if (str == "false" || str == "no" || str == "0")
+        value = false;
+    else
+        throw UsageError("Boolean setting '%s' has invalid value '%s'", name, str);
+}
+
+template<> std::string BaseSetting<bool>::to_string()
+{
+    return value ? "true" : "false";
+}
+
+template<> void BaseSetting<bool>::convertToArg(Args & args, const std::string & category)
+{
+    args.mkFlag()
+        .longName(name)
+        .description(description)
+        .handler([=](std::vector<std::string> ss) { override(true); })
+        .category(category);
+    args.mkFlag()
+        .longName("no-" + name)
+        .description(description)
+        .handler([=](std::vector<std::string> ss) { override(false); })
+        .category(category);
+}
+
+template<> void BaseSetting<Strings>::set(const std::string & str)
+{
+    value = tokenizeString<Strings>(str);
+}
+
+template<> std::string BaseSetting<Strings>::to_string()
+{
+    return concatStringsSep(" ", value);
+}
+
+template<> void BaseSetting<Strings>::toJSON(JSONPlaceholder & out)
+{
+    JSONList list(out.list());
+    for (auto & s : value)
+        list.elem(s);
+}
+
+template<> void BaseSetting<StringSet>::set(const std::string & str)
+{
+    value = tokenizeString<StringSet>(str);
+}
+
+template<> std::string BaseSetting<StringSet>::to_string()
+{
+    return concatStringsSep(" ", value);
+}
+
+template<> void BaseSetting<StringSet>::toJSON(JSONPlaceholder & out)
+{
+    JSONList list(out.list());
+    for (auto & s : value)
+        list.elem(s);
+}
+
+template class BaseSetting<int>;
+template class BaseSetting<unsigned int>;
+template class BaseSetting<long>;
+template class BaseSetting<unsigned long>;
+template class BaseSetting<long long>;
+template class BaseSetting<unsigned long long>;
+template class BaseSetting<bool>;
+template class BaseSetting<std::string>;
+template class BaseSetting<Strings>;
+template class BaseSetting<StringSet>;
+
+void PathSetting::set(const std::string & str)
+{
+    if (str == "") {
+        if (allowEmpty)
+            value = "";
+        else
+            throw UsageError("setting '%s' cannot be empty", name);
+    } else
+        value = canonPath(str);
+}
+
+bool GlobalConfig::set(const std::string & name, const std::string & value)
+{
+    for (auto & config : *configRegistrations)
+        if (config->set(name, value)) return true;
+
+    unknownSettings.emplace(name, value);
+
+    return false;
+}
+
+void GlobalConfig::getSettings(std::map<std::string, SettingInfo> & res, bool overridenOnly)
+{
+    for (auto & config : *configRegistrations)
+        config->getSettings(res, overridenOnly);
+}
+
+void GlobalConfig::resetOverriden()
+{
+    for (auto & config : *configRegistrations)
+        config->resetOverriden();
+}
+
+void GlobalConfig::toJSON(JSONObject & out)
+{
+    for (auto & config : *configRegistrations)
+        config->toJSON(out);
+}
+
+void GlobalConfig::convertToArgs(Args & args, const std::string & category)
+{
+    for (auto & config : *configRegistrations)
+        config->convertToArgs(args, category);
+}
+
+GlobalConfig globalConfig;
+
+GlobalConfig::ConfigRegistrations * GlobalConfig::configRegistrations;
+
+GlobalConfig::Register::Register(Config * config)
+{
+    if (!configRegistrations)
+        configRegistrations = new ConfigRegistrations;
+    configRegistrations->emplace_back(config);
+}
+
+}

third_party/nix/src/libutil/config.hh

@@ -0,0 +1,261 @@
+#include <map>
+#include <set>
+
+#include "types.hh"
+
+#pragma once
+
+namespace nix {
+
+class Args;
+class AbstractSetting;
+class JSONPlaceholder;
+class JSONObject;
+
+class AbstractConfig
+{
+protected:
+    StringMap unknownSettings;
+
+    AbstractConfig(const StringMap & initials = {})
+        : unknownSettings(initials)
+    { }
+
+public:
+
+    virtual bool set(const std::string & name, const std::string & value) = 0;
+
+    struct SettingInfo
+    {
+        std::string value;
+        std::string description;
+    };
+
+    virtual void getSettings(std::map<std::string, SettingInfo> & res, bool overridenOnly = false) = 0;
+
+    void applyConfigFile(const Path & path);
+
+    virtual void resetOverriden() = 0;
+
+    virtual void toJSON(JSONObject & out) = 0;
+
+    virtual void convertToArgs(Args & args, const std::string & category) = 0;
+
+    void warnUnknownSettings();
+
+    void reapplyUnknownSettings();
+};
+
+/* A class to simplify providing configuration settings. The typical
+   use is to inherit Config and add Setting<T> members:
+
+   class MyClass : private Config
+   {
+     Setting<int> foo{this, 123, "foo", "the number of foos to use"};
+     Setting<std::string> bar{this, "blabla", "bar", "the name of the bar"};
+
+     MyClass() : Config(readConfigFile("/etc/my-app.conf"))
+     {
+       std::cout << foo << "\n"; // will print 123 unless overriden
+     }
+   };
+*/
+
+class Config : public AbstractConfig
+{
+    friend class AbstractSetting;
+
+public:
+
+    struct SettingData
+    {
+        bool isAlias;
+        AbstractSetting * setting;
+        SettingData(bool isAlias, AbstractSetting * setting)
+            : isAlias(isAlias), setting(setting)
+        { }
+    };
+
+    typedef std::map<std::string, SettingData> Settings;
+
+private:
+
+    Settings _settings;
+
+public:
+
+    Config(const StringMap & initials = {})
+        : AbstractConfig(initials)
+    { }
+
+    bool set(const std::string & name, const std::string & value) override;
+
+    void addSetting(AbstractSetting * setting);
+
+    void getSettings(std::map<std::string, SettingInfo> & res, bool overridenOnly = false) override;
+
+    void resetOverriden() override;
+
+    void toJSON(JSONObject & out) override;
+
+    void convertToArgs(Args & args, const std::string & category) override;
+};
+
+class AbstractSetting
+{
+    friend class Config;
+
+public:
+
+    const std::string name;
+    const std::string description;
+    const std::set<std::string> aliases;
+
+    int created = 123;
+
+    bool overriden = false;
+
+protected:
+
+    AbstractSetting(
+        const std::string & name,
+        const std::string & description,
+        const std::set<std::string> & aliases);
+
+    virtual ~AbstractSetting()
+    {
+        // Check against a gcc miscompilation causing our constructor
+        // not to run (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80431).
+        assert(created == 123);
+    }
+
+    virtual void set(const std::string & value) = 0;
+
+    virtual std::string to_string() = 0;
+
+    virtual void toJSON(JSONPlaceholder & out);
+
+    virtual void convertToArg(Args & args, const std::string & category);
+
+    bool isOverriden() { return overriden; }
+};
+
+/* A setting of type T. */
+template<typename T>
+class BaseSetting : public AbstractSetting
+{
+protected:
+
+    T value;
+
+public:
+
+    BaseSetting(const T & def,
+        const std::string & name,
+        const std::string & description,
+        const std::set<std::string> & aliases = {})
+        : AbstractSetting(name, description, aliases)
+        , value(def)
+    { }
+
+    operator const T &() const { return value; }
+    operator T &() { return value; }
+    const T & get() const { return value; }
+    bool operator ==(const T & v2) const { return value == v2; }
+    bool operator !=(const T & v2) const { return value != v2; }
+    void operator =(const T & v) { assign(v); }
+    virtual void assign(const T & v) { value = v; }
+
+    void set(const std::string & str) override;
+
+    virtual void override(const T & v)
+    {
+        overriden = true;
+        value = v;
+    }
+
+    std::string to_string() override;
+
+    void convertToArg(Args & args, const std::string & category) override;
+
+    void toJSON(JSONPlaceholder & out) override;
+};
+
+template<typename T>
+std::ostream & operator <<(std::ostream & str, const BaseSetting<T> & opt)
+{
+    str << (const T &) opt;
+    return str;
+}
+
+template<typename T>
+bool operator ==(const T & v1, const BaseSetting<T> & v2) { return v1 == (const T &) v2; }
+
+template<typename T>
+class Setting : public BaseSetting<T>
+{
+public:
+    Setting(Config * options,
+        const T & def,
+        const std::string & name,
+        const std::string & description,
+        const std::set<std::string> & aliases = {})
+        : BaseSetting<T>(def, name, description, aliases)
+    {
+        options->addSetting(this);
+    }
+
+    void operator =(const T & v) { this->assign(v); }
+};
+
+/* A special setting for Paths. These are automatically canonicalised
+   (e.g. "/foo//bar/" becomes "/foo/bar"). */
+class PathSetting : public BaseSetting<Path>
+{
+    bool allowEmpty;
+
+public:
+
+    PathSetting(Config * options,
+        bool allowEmpty,
+        const Path & def,
+        const std::string & name,
+        const std::string & description,
+        const std::set<std::string> & aliases = {})
+        : BaseSetting<Path>(def, name, description, aliases)
+        , allowEmpty(allowEmpty)
+    {
+        options->addSetting(this);
+    }
+
+    void set(const std::string & str) override;
+
+    Path operator +(const char * p) const { return value + p; }
+
+    void operator =(const Path & v) { this->assign(v); }
+};
+
+struct GlobalConfig : public AbstractConfig
+{
+    typedef std::vector<Config*> ConfigRegistrations;
+    static ConfigRegistrations * configRegistrations;
+
+    bool set(const std::string & name, const std::string & value) override;
+
+    void getSettings(std::map<std::string, SettingInfo> & res, bool overridenOnly = false) override;
+
+    void resetOverriden() override;
+
+    void toJSON(JSONObject & out) override;
+
+    void convertToArgs(Args & args, const std::string & category) override;
+
+    struct Register
+    {
+        Register(Config * config);
+    };
+};
+
+extern GlobalConfig globalConfig;
+
+}

third_party/nix/src/libutil/finally.hh

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <functional>
+
+/* A trivial class to run a function at the end of a scope. */
+class Finally
+{
+private:
+    std::function<void()> fun;
+
+public:
+    Finally(std::function<void()> fun) : fun(fun) { }
+    ~Finally() { fun(); }
+};

third_party/nix/src/libutil/hash.cc

@@ -0,0 +1,355 @@
+#include <iostream>
+#include <cstring>
+
+#include <openssl/md5.h>
+#include <openssl/sha.h>
+
+#include "hash.hh"
+#include "archive.hh"
+#include "util.hh"
+#include "istringstream_nocopy.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+namespace nix {
+
+
+void Hash::init()
+{
+    if (type == htMD5) hashSize = md5HashSize;
+    else if (type == htSHA1) hashSize = sha1HashSize;
+    else if (type == htSHA256) hashSize = sha256HashSize;
+    else if (type == htSHA512) hashSize = sha512HashSize;
+    else abort();
+    assert(hashSize <= maxHashSize);
+    memset(hash, 0, maxHashSize);
+}
+
+
+bool Hash::operator == (const Hash & h2) const
+{
+    if (hashSize != h2.hashSize) return false;
+    for (unsigned int i = 0; i < hashSize; i++)
+        if (hash[i] != h2.hash[i]) return false;
+    return true;
+}
+
+
+bool Hash::operator != (const Hash & h2) const
+{
+    return !(*this == h2);
+}
+
+
+bool Hash::operator < (const Hash & h) const
+{
+    if (hashSize < h.hashSize) return true;
+    if (hashSize > h.hashSize) return false;
+    for (unsigned int i = 0; i < hashSize; i++) {
+        if (hash[i] < h.hash[i]) return true;
+        if (hash[i] > h.hash[i]) return false;
+    }
+    return false;
+}
+
+
+const string base16Chars = "0123456789abcdef";
+
+
+static string printHash16(const Hash & hash)
+{
+    char buf[hash.hashSize * 2];
+    for (unsigned int i = 0; i < hash.hashSize; i++) {
+        buf[i * 2] = base16Chars[hash.hash[i] >> 4];
+        buf[i * 2 + 1] = base16Chars[hash.hash[i] & 0x0f];
+    }
+    return string(buf, hash.hashSize * 2);
+}
+
+
+// omitted: E O U T
+const string base32Chars = "0123456789abcdfghijklmnpqrsvwxyz";
+
+
+static string printHash32(const Hash & hash)
+{
+    assert(hash.hashSize);
+    size_t len = hash.base32Len();
+    assert(len);
+
+    string s;
+    s.reserve(len);
+
+    for (int n = (int) len - 1; n >= 0; n--) {
+        unsigned int b = n * 5;
+        unsigned int i = b / 8;
+        unsigned int j = b % 8;
+        unsigned char c =
+            (hash.hash[i] >> j)
+            | (i >= hash.hashSize - 1 ? 0 : hash.hash[i + 1] << (8 - j));
+        s.push_back(base32Chars[c & 0x1f]);
+    }
+
+    return s;
+}
+
+
+string printHash16or32(const Hash & hash)
+{
+    return hash.to_string(hash.type == htMD5 ? Base16 : Base32, false);
+}
+
+
+std::string Hash::to_string(Base base, bool includeType) const
+{
+    std::string s;
+    if (base == SRI || includeType) {
+        s += printHashType(type);
+        s += base == SRI ? '-' : ':';
+    }
+    switch (base) {
+    case Base16:
+        s += printHash16(*this);
+        break;
+    case Base32:
+        s += printHash32(*this);
+        break;
+    case Base64:
+    case SRI:
+        s += base64Encode(std::string((const char *) hash, hashSize));
+        break;
+    }
+    return s;
+}
+
+
+Hash::Hash(const std::string & s, HashType type)
+    : type(type)
+{
+    size_t pos = 0;
+    bool isSRI = false;
+
+    auto sep = s.find(':');
+    if (sep == string::npos) {
+        sep = s.find('-');
+        if (sep != string::npos) {
+            isSRI = true;
+        } else if (type == htUnknown)
+            throw BadHash("hash '%s' does not include a type", s);
+    }
+
+    if (sep != string::npos) {
+        string hts = string(s, 0, sep);
+        this->type = parseHashType(hts);
+        if (this->type == htUnknown)
+            throw BadHash("unknown hash type '%s'", hts);
+        if (type != htUnknown && type != this->type)
+            throw BadHash("hash '%s' should have type '%s'", s, printHashType(type));
+        pos = sep + 1;
+    }
+
+    init();
+
+    size_t size = s.size() - pos;
+
+    if (!isSRI && size == base16Len()) {
+
+        auto parseHexDigit = [&](char c) {
+            if (c >= '0' && c <= '9') return c - '0';
+            if (c >= 'A' && c <= 'F') return c - 'A' + 10;
+            if (c >= 'a' && c <= 'f') return c - 'a' + 10;
+            throw BadHash("invalid base-16 hash '%s'", s);
+        };
+
+        for (unsigned int i = 0; i < hashSize; i++) {
+            hash[i] =
+                parseHexDigit(s[pos + i * 2]) << 4
+                | parseHexDigit(s[pos + i * 2 + 1]);
+        }
+    }
+
+    else if (!isSRI && size == base32Len()) {
+
+        for (unsigned int n = 0; n < size; ++n) {
+            char c = s[pos + size - n - 1];
+            unsigned char digit;
+            for (digit = 0; digit < base32Chars.size(); ++digit) /* !!! slow */
+                if (base32Chars[digit] == c) break;
+            if (digit >= 32)
+                throw BadHash("invalid base-32 hash '%s'", s);
+            unsigned int b = n * 5;
+            unsigned int i = b / 8;
+            unsigned int j = b % 8;
+            hash[i] |= digit << j;
+
+            if (i < hashSize - 1) {
+                hash[i + 1] |= digit >> (8 - j);
+            } else {
+                if (digit >> (8 - j))
+                    throw BadHash("invalid base-32 hash '%s'", s);
+            }
+        }
+    }
+
+    else if (isSRI || size == base64Len()) {
+        auto d = base64Decode(std::string(s, pos));
+        if (d.size() != hashSize)
+            throw BadHash("invalid %s hash '%s'", isSRI ? "SRI" : "base-64", s);
+        assert(hashSize);
+        memcpy(hash, d.data(), hashSize);
+    }
+
+    else
+        throw BadHash("hash '%s' has wrong length for hash type '%s'", s, printHashType(type));
+}
+
+
+union Ctx
+{
+    MD5_CTX md5;
+    SHA_CTX sha1;
+    SHA256_CTX sha256;
+    SHA512_CTX sha512;
+};
+
+
+static void start(HashType ht, Ctx & ctx)
+{
+    if (ht == htMD5) MD5_Init(&ctx.md5);
+    else if (ht == htSHA1) SHA1_Init(&ctx.sha1);
+    else if (ht == htSHA256) SHA256_Init(&ctx.sha256);
+    else if (ht == htSHA512) SHA512_Init(&ctx.sha512);
+}
+
+
+static void update(HashType ht, Ctx & ctx,
+    const unsigned char * bytes, size_t len)
+{
+    if (ht == htMD5) MD5_Update(&ctx.md5, bytes, len);
+    else if (ht == htSHA1) SHA1_Update(&ctx.sha1, bytes, len);
+    else if (ht == htSHA256) SHA256_Update(&ctx.sha256, bytes, len);
+    else if (ht == htSHA512) SHA512_Update(&ctx.sha512, bytes, len);
+}
+
+
+static void finish(HashType ht, Ctx & ctx, unsigned char * hash)
+{
+    if (ht == htMD5) MD5_Final(hash, &ctx.md5);
+    else if (ht == htSHA1) SHA1_Final(hash, &ctx.sha1);
+    else if (ht == htSHA256) SHA256_Final(hash, &ctx.sha256);
+    else if (ht == htSHA512) SHA512_Final(hash, &ctx.sha512);
+}
+
+
+Hash hashString(HashType ht, const string & s)
+{
+    Ctx ctx;
+    Hash hash(ht);
+    start(ht, ctx);
+    update(ht, ctx, (const unsigned char *) s.data(), s.length());
+    finish(ht, ctx, hash.hash);
+    return hash;
+}
+
+
+Hash hashFile(HashType ht, const Path & path)
+{
+    Ctx ctx;
+    Hash hash(ht);
+    start(ht, ctx);
+
+    AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
+    if (!fd) throw SysError(format("opening file '%1%'") % path);
+
+    std::vector<unsigned char> buf(8192);
+    ssize_t n;
+    while ((n = read(fd.get(), buf.data(), buf.size()))) {
+        checkInterrupt();
+        if (n == -1) throw SysError(format("reading file '%1%'") % path);
+        update(ht, ctx, buf.data(), n);
+    }
+
+    finish(ht, ctx, hash.hash);
+    return hash;
+}
+
+
+HashSink::HashSink(HashType ht) : ht(ht)
+{
+    ctx = new Ctx;
+    bytes = 0;
+    start(ht, *ctx);
+}
+
+HashSink::~HashSink()
+{
+    bufPos = 0;
+    delete ctx;
+}
+
+void HashSink::write(const unsigned char * data, size_t len)
+{
+    bytes += len;
+    update(ht, *ctx, data, len);
+}
+
+HashResult HashSink::finish()
+{
+    flush();
+    Hash hash(ht);
+    nix::finish(ht, *ctx, hash.hash);
+    return HashResult(hash, bytes);
+}
+
+HashResult HashSink::currentHash()
+{
+    flush();
+    Ctx ctx2 = *ctx;
+    Hash hash(ht);
+    nix::finish(ht, ctx2, hash.hash);
+    return HashResult(hash, bytes);
+}
+
+
+HashResult hashPath(
+    HashType ht, const Path & path, PathFilter & filter)
+{
+    HashSink sink(ht);
+    dumpPath(path, sink, filter);
+    return sink.finish();
+}
+
+
+Hash compressHash(const Hash & hash, unsigned int newSize)
+{
+    Hash h;
+    h.hashSize = newSize;
+    for (unsigned int i = 0; i < hash.hashSize; ++i)
+        h.hash[i % newSize] ^= hash.hash[i];
+    return h;
+}
+
+
+HashType parseHashType(const string & s)
+{
+    if (s == "md5") return htMD5;
+    else if (s == "sha1") return htSHA1;
+    else if (s == "sha256") return htSHA256;
+    else if (s == "sha512") return htSHA512;
+    else return htUnknown;
+}
+
+
+string printHashType(HashType ht)
+{
+    if (ht == htMD5) return "md5";
+    else if (ht == htSHA1) return "sha1";
+    else if (ht == htSHA256) return "sha256";
+    else if (ht == htSHA512) return "sha512";
+    else abort();
+}
+
+
+}

third_party/nix/src/libutil/hash.hh

@@ -0,0 +1,131 @@
+#pragma once
+
+#include "types.hh"
+#include "serialise.hh"
+
+
+namespace nix {
+
+
+MakeError(BadHash, Error);
+
+
+enum HashType : char { htUnknown, htMD5, htSHA1, htSHA256, htSHA512 };
+
+
+const int md5HashSize = 16;
+const int sha1HashSize = 20;
+const int sha256HashSize = 32;
+const int sha512HashSize = 64;
+
+extern const string base32Chars;
+
+enum Base : int { Base64, Base32, Base16, SRI };
+
+
+struct Hash
+{
+    static const unsigned int maxHashSize = 64;
+    unsigned int hashSize = 0;
+    unsigned char hash[maxHashSize] = {};
+
+    HashType type = htUnknown;
+
+    /* Create an unset hash object. */
+    Hash() { };
+
+    /* Create a zero-filled hash object. */
+    Hash(HashType type) : type(type) { init(); };
+
+    /* Initialize the hash from a string representation, in the format
+       "[<type>:]<base16|base32|base64>" or "<type>-<base64>" (a
+       Subresource Integrity hash expression). If the 'type' argument
+       is htUnknown, then the hash type must be specified in the
+       string. */
+    Hash(const std::string & s, HashType type = htUnknown);
+
+    void init();
+
+    /* Check whether a hash is set. */
+    operator bool () const { return type != htUnknown; }
+
+    /* Check whether two hash are equal. */
+    bool operator == (const Hash & h2) const;
+
+    /* Check whether two hash are not equal. */
+    bool operator != (const Hash & h2) const;
+
+    /* For sorting. */
+    bool operator < (const Hash & h) const;
+
+    /* Returns the length of a base-16 representation of this hash. */
+    size_t base16Len() const
+    {
+        return hashSize * 2;
+    }
+
+    /* Returns the length of a base-32 representation of this hash. */
+    size_t base32Len() const
+    {
+        return (hashSize * 8 - 1) / 5 + 1;
+    }
+
+    /* Returns the length of a base-64 representation of this hash. */
+    size_t base64Len() const
+    {
+        return ((4 * hashSize / 3) + 3) & ~3;
+    }
+
+    /* Return a string representation of the hash, in base-16, base-32
+       or base-64. By default, this is prefixed by the hash type
+       (e.g. "sha256:"). */
+    std::string to_string(Base base = Base32, bool includeType = true) const;
+};
+
+
+/* Print a hash in base-16 if it's MD5, or base-32 otherwise. */
+string printHash16or32(const Hash & hash);
+
+/* Compute the hash of the given string. */
+Hash hashString(HashType ht, const string & s);
+
+/* Compute the hash of the given file. */
+Hash hashFile(HashType ht, const Path & path);
+
+/* Compute the hash of the given path.  The hash is defined as
+   (essentially) hashString(ht, dumpPath(path)). */
+typedef std::pair<Hash, unsigned long long> HashResult;
+HashResult hashPath(HashType ht, const Path & path,
+    PathFilter & filter = defaultPathFilter);
+
+/* Compress a hash to the specified number of bytes by cyclically
+   XORing bytes together. */
+Hash compressHash(const Hash & hash, unsigned int newSize);
+
+/* Parse a string representing a hash type. */
+HashType parseHashType(const string & s);
+
+/* And the reverse. */
+string printHashType(HashType ht);
+
+
+union Ctx;
+
+class HashSink : public BufferedSink
+{
+private:
+    HashType ht;
+    Ctx * ctx;
+    unsigned long long bytes;
+
+public:
+    HashSink(HashType ht);
+    HashSink(const HashSink & h);
+    ~HashSink();
+    void write(const unsigned char * data, size_t len);
+    HashResult finish();
+    HashResult currentHash();
+};
+
+
+}

third_party/nix/src/libutil/istringstream_nocopy.hh

@@ -0,0 +1,92 @@
+/* This file provides a variant of std::istringstream that doesn't
+   copy its string argument. This is useful for large strings. The
+   caller must ensure that the string object is not destroyed while
+   it's referenced by this object. */
+
+#pragma once
+
+#include <string>
+#include <iostream>
+
+template <class CharT, class Traits = std::char_traits<CharT>, class Allocator = std::allocator<CharT>>
+class basic_istringbuf_nocopy : public std::basic_streambuf<CharT, Traits>
+{
+public:
+    typedef std::basic_string<CharT, Traits, Allocator> string_type;
+
+    typedef typename std::basic_streambuf<CharT, Traits>::off_type off_type;
+
+    typedef typename std::basic_streambuf<CharT, Traits>::pos_type pos_type;
+
+    typedef typename std::basic_streambuf<CharT, Traits>::int_type int_type;
+
+    typedef typename std::basic_streambuf<CharT, Traits>::traits_type traits_type;
+
+private:
+    const string_type & s;
+
+    off_type off;
+
+public:
+    basic_istringbuf_nocopy(const string_type & s) : s{s}, off{0}
+    {
+    }
+
+private:
+    pos_type seekoff(off_type off, std::ios_base::seekdir dir, std::ios_base::openmode which)
+    {
+        if (which & std::ios_base::in) {
+            this->off = dir == std::ios_base::beg
+                ? off
+                : (dir == std::ios_base::end
+                    ? s.size() + off
+                    : this->off + off);
+        }
+        return pos_type(this->off);
+    }
+
+    pos_type seekpos(pos_type pos, std::ios_base::openmode which)
+    {
+        return seekoff(pos, std::ios_base::beg, which);
+    }
+
+    std::streamsize showmanyc()
+    {
+        return s.size() - off;
+    }
+
+    int_type underflow()
+    {
+        if (typename string_type::size_type(off) == s.size())
+            return traits_type::eof();
+        return traits_type::to_int_type(s[off]);
+    }
+
+    int_type uflow()
+    {
+        if (typename string_type::size_type(off) == s.size())
+            return traits_type::eof();
+        return traits_type::to_int_type(s[off++]);
+    }
+
+    int_type pbackfail(int_type ch)
+    {
+        if (off == 0 || (ch != traits_type::eof() && ch != s[off - 1]))
+            return traits_type::eof();
+
+        return traits_type::to_int_type(s[--off]);
+    }
+
+};
+
+template <class CharT, class Traits = std::char_traits<CharT>, class Allocator = std::allocator<CharT>>
+class basic_istringstream_nocopy : public std::basic_iostream<CharT, Traits>
+{
+    typedef basic_istringbuf_nocopy<CharT, Traits, Allocator> buf_type;
+    buf_type buf;
+public:
+    basic_istringstream_nocopy(const typename buf_type::string_type & s) :
+        std::basic_iostream<CharT, Traits>(&buf), buf(s) {};
+};
+
+typedef basic_istringstream_nocopy<char> istringstream_nocopy;

third_party/nix/src/libutil/json.cc

@@ -0,0 +1,174 @@
+#include "json.hh"
+
+#include <iomanip>
+#include <cstring>
+
+namespace nix {
+
+void toJSON(std::ostream & str, const char * start, const char * end)
+{
+    str << '"';
+    for (auto i = start; i != end; i++)
+        if (*i == '\"' || *i == '\\') str << '\\' << *i;
+        else if (*i == '\n') str << "\\n";
+        else if (*i == '\r') str << "\\r";
+        else if (*i == '\t') str << "\\t";
+        else if (*i >= 0 && *i < 32)
+            str << "\\u" << std::setfill('0') << std::setw(4) << std::hex << (uint16_t) *i << std::dec;
+        else str << *i;
+    str << '"';
+}
+
+void toJSON(std::ostream & str, const char * s)
+{
+    if (!s) str << "null"; else toJSON(str, s, s + strlen(s));
+}
+
+template<> void toJSON<int>(std::ostream & str, const int & n) { str << n; }
+template<> void toJSON<unsigned int>(std::ostream & str, const unsigned int & n) { str << n; }
+template<> void toJSON<long>(std::ostream & str, const long & n) { str << n; }
+template<> void toJSON<unsigned long>(std::ostream & str, const unsigned long & n) { str << n; }
+template<> void toJSON<long long>(std::ostream & str, const long long & n) { str << n; }
+template<> void toJSON<unsigned long long>(std::ostream & str, const unsigned long long & n) { str << n; }
+template<> void toJSON<float>(std::ostream & str, const float & n) { str << n; }
+template<> void toJSON<double>(std::ostream & str, const double & n) { str << n; }
+
+template<> void toJSON<std::string>(std::ostream & str, const std::string & s)
+{
+    toJSON(str, s.c_str(), s.c_str() + s.size());
+}
+
+template<> void toJSON<bool>(std::ostream & str, const bool & b)
+{
+    str << (b ? "true" : "false");
+}
+
+template<> void toJSON<std::nullptr_t>(std::ostream & str, const std::nullptr_t & b)
+{
+    str << "null";
+}
+
+JSONWriter::JSONWriter(std::ostream & str, bool indent)
+    : state(new JSONState(str, indent))
+{
+    state->stack++;
+}
+
+JSONWriter::JSONWriter(JSONState * state)
+    : state(state)
+{
+    state->stack++;
+}
+
+JSONWriter::~JSONWriter()
+{
+    if (state) {
+        assertActive();
+        state->stack--;
+        if (state->stack == 0) delete state;
+    }
+}
+
+void JSONWriter::comma()
+{
+    assertActive();
+    if (first) {
+        first = false;
+    } else {
+        state->str << ',';
+    }
+    if (state->indent) indent();
+}
+
+void JSONWriter::indent()
+{
+    state->str << '\n' << std::string(state->depth * 2, ' ');
+}
+
+void JSONList::open()
+{
+    state->depth++;
+    state->str << '[';
+}
+
+JSONList::~JSONList()
+{
+    state->depth--;
+    if (state->indent && !first) indent();
+    state->str << "]";
+}
+
+JSONList JSONList::list()
+{
+    comma();
+    return JSONList(state);
+}
+
+JSONObject JSONList::object()
+{
+    comma();
+    return JSONObject(state);
+}
+
+JSONPlaceholder JSONList::placeholder()
+{
+    comma();
+    return JSONPlaceholder(state);
+}
+
+void JSONObject::open()
+{
+    state->depth++;
+    state->str << '{';
+}
+
+JSONObject::~JSONObject()
+{
+    if (state) {
+        state->depth--;
+        if (state->indent && !first) indent();
+        state->str << "}";
+    }
+}
+
+void JSONObject::attr(const std::string & s)
+{
+    comma();
+    toJSON(state->str, s);
+    state->str << ':';
+    if (state->indent) state->str << ' ';
+}
+
+JSONList JSONObject::list(const std::string & name)
+{
+    attr(name);
+    return JSONList(state);
+}
+
+JSONObject JSONObject::object(const std::string & name)
+{
+    attr(name);
+    return JSONObject(state);
+}
+
+JSONPlaceholder JSONObject::placeholder(const std::string & name)
+{
+    attr(name);
+    return JSONPlaceholder(state);
+}
+
+JSONList JSONPlaceholder::list()
+{
+    assertValid();
+    first = false;
+    return JSONList(state);
+}
+
+JSONObject JSONPlaceholder::object()
+{
+    assertValid();
+    first = false;
+    return JSONObject(state);
+}
+
+}

third_party/nix/src/libutil/json.hh

@@ -0,0 +1,189 @@
+#pragma once
+
+#include <iostream>
+#include <vector>
+#include <cassert>
+
+namespace nix {
+
+void toJSON(std::ostream & str, const char * start, const char * end);
+void toJSON(std::ostream & str, const char * s);
+
+template<typename T>
+void toJSON(std::ostream & str, const T & n);
+
+class JSONWriter
+{
+protected:
+
+    struct JSONState
+    {
+        std::ostream & str;
+        bool indent;
+        size_t depth = 0;
+        size_t stack = 0;
+        JSONState(std::ostream & str, bool indent) : str(str), indent(indent) { }
+        ~JSONState()
+        {
+            assert(stack == 0);
+        }
+    };
+
+    JSONState * state;
+
+    bool first = true;
+
+    JSONWriter(std::ostream & str, bool indent);
+
+    JSONWriter(JSONState * state);
+
+    ~JSONWriter();
+
+    void assertActive()
+    {
+        assert(state->stack != 0);
+    }
+
+    void comma();
+
+    void indent();
+};
+
+class JSONObject;
+class JSONPlaceholder;
+
+class JSONList : JSONWriter
+{
+private:
+
+    friend class JSONObject;
+    friend class JSONPlaceholder;
+
+    void open();
+
+    JSONList(JSONState * state)
+        : JSONWriter(state)
+    {
+        open();
+    }
+
+public:
+
+    JSONList(std::ostream & str, bool indent = false)
+        : JSONWriter(str, indent)
+    {
+        open();
+    }
+
+    ~JSONList();
+
+    template<typename T>
+    JSONList & elem(const T & v)
+    {
+        comma();
+        toJSON(state->str, v);
+        return *this;
+    }
+
+    JSONList list();
+
+    JSONObject object();
+
+    JSONPlaceholder placeholder();
+};
+
+class JSONObject : JSONWriter
+{
+private:
+
+    friend class JSONList;
+    friend class JSONPlaceholder;
+
+    void open();
+
+    JSONObject(JSONState * state)
+        : JSONWriter(state)
+    {
+        open();
+    }
+
+    void attr(const std::string & s);
+
+public:
+
+    JSONObject(std::ostream & str, bool indent = false)
+        : JSONWriter(str, indent)
+    {
+        open();
+    }
+
+    JSONObject(const JSONObject & obj) = delete;
+
+    JSONObject(JSONObject && obj)
+        : JSONWriter(obj.state)
+    {
+        obj.state = 0;
+    }
+
+    ~JSONObject();
+
+    template<typename T>
+    JSONObject & attr(const std::string & name, const T & v)
+    {
+        attr(name);
+        toJSON(state->str, v);
+        return *this;
+    }
+
+    JSONList list(const std::string & name);
+
+    JSONObject object(const std::string & name);
+
+    JSONPlaceholder placeholder(const std::string & name);
+};
+
+class JSONPlaceholder : JSONWriter
+{
+
+private:
+
+    friend class JSONList;
+    friend class JSONObject;
+
+    JSONPlaceholder(JSONState * state)
+        : JSONWriter(state)
+    {
+    }
+
+    void assertValid()
+    {
+        assertActive();
+        assert(first);
+    }
+
+public:
+
+    JSONPlaceholder(std::ostream & str, bool indent = false)
+        : JSONWriter(str, indent)
+    {
+    }
+
+    ~JSONPlaceholder()
+    {
+        assert(!first || std::uncaught_exception());
+    }
+
+    template<typename T>
+    void write(const T & v)
+    {
+        assertValid();
+        first = false;
+        toJSON(state->str, v);
+    }
+
+    JSONList list();
+
+    JSONObject object();
+};
+
+}

third_party/nix/src/libutil/lazy.hh

@@ -0,0 +1,48 @@
+#include <exception>
+#include <functional>
+#include <mutex>
+
+namespace nix {
+
+/* A helper class for lazily-initialized variables.
+
+     Lazy<T> var([]() { return value; });
+
+   declares a variable of type T that is initialized to 'value' (in a
+   thread-safe way) on first use, that is, when var() is first
+   called. If the initialiser code throws an exception, then all
+   subsequent calls to var() will rethrow that exception. */
+template<typename T>
+class Lazy
+{
+
+    typedef std::function<T()> Init;
+
+    Init init;
+
+    std::once_flag done;
+
+    T value;
+
+    std::exception_ptr ex;
+
+public:
+
+    Lazy(Init init) : init(init)
+    { }
+
+    const T & operator () ()
+    {
+        std::call_once(done, [&]() {
+            try {
+                value = init();
+            } catch (...) {
+                ex = std::current_exception();
+            }
+        });
+        if (ex) std::rethrow_exception(ex);
+        return value;
+    }
+};
+
+}

third_party/nix/src/libutil/local.mk

@@ -0,0 +1,9 @@
+libraries += libutil
+
+libutil_NAME = libnixutil
+
+libutil_DIR := $(d)
+
+libutil_SOURCES := $(wildcard $(d)/*.cc)
+
+libutil_LDFLAGS = $(LIBLZMA_LIBS) -lbz2 -pthread $(OPENSSL_LIBS) $(LIBBROTLI_LIBS) $(BOOST_LDFLAGS) -lboost_context

third_party/nix/src/libutil/logging.cc

@@ -0,0 +1,242 @@
+#include "logging.hh"
+#include "util.hh"
+
+#include <atomic>
+#include <nlohmann/json.hpp>
+
+namespace nix {
+
+static thread_local ActivityId curActivity = 0;
+
+ActivityId getCurActivity()
+{
+    return curActivity;
+}
+void setCurActivity(const ActivityId activityId)
+{
+    curActivity = activityId;
+}
+
+Logger * logger = makeDefaultLogger();
+
+void Logger::warn(const std::string & msg)
+{
+    log(lvlWarn, ANSI_RED "warning:" ANSI_NORMAL " " + msg);
+}
+
+class SimpleLogger : public Logger
+{
+public:
+
+    bool systemd, tty;
+
+    SimpleLogger()
+    {
+        systemd = getEnv("IN_SYSTEMD") == "1";
+        tty = isatty(STDERR_FILENO);
+    }
+
+    void log(Verbosity lvl, const FormatOrString & fs) override
+    {
+        if (lvl > verbosity) return;
+
+        std::string prefix;
+
+        if (systemd) {
+            char c;
+            switch (lvl) {
+            case lvlError: c = '3'; break;
+            case lvlWarn: c = '4'; break;
+            case lvlInfo: c = '5'; break;
+            case lvlTalkative: case lvlChatty: c = '6'; break;
+            default: c = '7';
+            }
+            prefix = std::string("<") + c + ">";
+        }
+
+        writeToStderr(prefix + filterANSIEscapes(fs.s, !tty) + "\n");
+    }
+
+    void startActivity(ActivityId act, Verbosity lvl, ActivityType type,
+        const std::string & s, const Fields & fields, ActivityId parent)
+        override
+    {
+        if (lvl <= verbosity && !s.empty())
+            log(lvl, s + "...");
+    }
+};
+
+Verbosity verbosity = lvlInfo;
+
+void warnOnce(bool & haveWarned, const FormatOrString & fs)
+{
+    if (!haveWarned) {
+        warn(fs.s);
+        haveWarned = true;
+    }
+}
+
+void writeToStderr(const string & s)
+{
+    try {
+        writeFull(STDERR_FILENO, s, false);
+    } catch (SysError & e) {
+        /* Ignore failing writes to stderr.  We need to ignore write
+           errors to ensure that cleanup code that logs to stderr runs
+           to completion if the other side of stderr has been closed
+           unexpectedly. */
+    }
+}
+
+Logger * makeDefaultLogger()
+{
+    return new SimpleLogger();
+}
+
+std::atomic<uint64_t> nextId{(uint64_t) getpid() << 32};
+
+Activity::Activity(Logger & logger, Verbosity lvl, ActivityType type,
+    const std::string & s, const Logger::Fields & fields, ActivityId parent)
+    : logger(logger), id(nextId++)
+{
+    logger.startActivity(id, lvl, type, s, fields, parent);
+}
+
+struct JSONLogger : Logger
+{
+    Logger & prevLogger;
+
+    JSONLogger(Logger & prevLogger) : prevLogger(prevLogger) { }
+
+    void addFields(nlohmann::json & json, const Fields & fields)
+    {
+        if (fields.empty()) return;
+        auto & arr = json["fields"] = nlohmann::json::array();
+        for (auto & f : fields)
+            if (f.type == Logger::Field::tInt)
+                arr.push_back(f.i);
+            else if (f.type == Logger::Field::tString)
+                arr.push_back(f.s);
+            else
+                abort();
+    }
+
+    void write(const nlohmann::json & json)
+    {
+        prevLogger.log(lvlError, "@nix " + json.dump());
+    }
+
+    void log(Verbosity lvl, const FormatOrString & fs) override
+    {
+        nlohmann::json json;
+        json["action"] = "msg";
+        json["level"] = lvl;
+        json["msg"] = fs.s;
+        write(json);
+    }
+
+    void startActivity(ActivityId act, Verbosity lvl, ActivityType type,
+        const std::string & s, const Fields & fields, ActivityId parent) override
+    {
+        nlohmann::json json;
+        json["action"] = "start";
+        json["id"] = act;
+        json["level"] = lvl;
+        json["type"] = type;
+        json["text"] = s;
+        addFields(json, fields);
+        // FIXME: handle parent
+        write(json);
+    }
+
+    void stopActivity(ActivityId act) override
+    {
+        nlohmann::json json;
+        json["action"] = "stop";
+        json["id"] = act;
+        write(json);
+    }
+
+    void result(ActivityId act, ResultType type, const Fields & fields) override
+    {
+        nlohmann::json json;
+        json["action"] = "result";
+        json["id"] = act;
+        json["type"] = type;
+        addFields(json, fields);
+        write(json);
+    }
+};
+
+Logger * makeJSONLogger(Logger & prevLogger)
+{
+    return new JSONLogger(prevLogger);
+}
+
+static Logger::Fields getFields(nlohmann::json & json)
+{
+    Logger::Fields fields;
+    for (auto & f : json) {
+        if (f.type() == nlohmann::json::value_t::number_unsigned)
+            fields.emplace_back(Logger::Field(f.get<uint64_t>()));
+        else if (f.type() == nlohmann::json::value_t::string)
+            fields.emplace_back(Logger::Field(f.get<std::string>()));
+        else throw Error("unsupported JSON type %d", (int) f.type());
+    }
+    return fields;
+}
+
+bool handleJSONLogMessage(const std::string & msg,
+    const Activity & act, std::map<ActivityId, Activity> & activities, bool trusted)
+{
+    if (!hasPrefix(msg, "@nix ")) return false;
+
+    try {
+        auto json = nlohmann::json::parse(std::string(msg, 5));
+
+        std::string action = json["action"];
+
+        if (action == "start") {
+            auto type = (ActivityType) json["type"];
+            if (trusted || type == actDownload)
+                activities.emplace(std::piecewise_construct,
+                    std::forward_as_tuple(json["id"]),
+                    std::forward_as_tuple(*logger, (Verbosity) json["level"], type,
+                        json["text"], getFields(json["fields"]), act.id));
+        }
+
+        else if (action == "stop")
+            activities.erase((ActivityId) json["id"]);
+
+        else if (action == "result") {
+            auto i = activities.find((ActivityId) json["id"]);
+            if (i != activities.end())
+                i->second.result((ResultType) json["type"], getFields(json["fields"]));
+        }
+
+        else if (action == "setPhase") {
+            std::string phase = json["phase"];
+            act.result(resSetPhase, phase);
+        }
+
+        else if (action == "msg") {
+            std::string msg = json["msg"];
+            logger->log((Verbosity) json["level"], msg);
+        }
+
+    } catch (std::exception & e) {
+        printError("bad log message from builder: %s", e.what());
+    }
+
+    return true;
+}
+
+Activity::~Activity() {
+    try {
+        logger.stopActivity(id);
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+}

third_party/nix/src/libutil/logging.hh

@@ -0,0 +1,172 @@
+#pragma once
+
+#include "types.hh"
+
+namespace nix {
+
+typedef enum {
+    lvlError = 0,
+    lvlWarn,
+    lvlInfo,
+    lvlTalkative,
+    lvlChatty,
+    lvlDebug,
+    lvlVomit
+} Verbosity;
+
+typedef enum {
+    actUnknown = 0,
+    actCopyPath = 100,
+    actDownload = 101,
+    actRealise = 102,
+    actCopyPaths = 103,
+    actBuilds = 104,
+    actBuild = 105,
+    actOptimiseStore = 106,
+    actVerifyPaths = 107,
+    actSubstitute = 108,
+    actQueryPathInfo = 109,
+    actPostBuildHook = 110,
+} ActivityType;
+
+typedef enum {
+    resFileLinked = 100,
+    resBuildLogLine = 101,
+    resUntrustedPath = 102,
+    resCorruptedPath = 103,
+    resSetPhase = 104,
+    resProgress = 105,
+    resSetExpected = 106,
+    resPostBuildLogLine = 107,
+} ResultType;
+
+typedef uint64_t ActivityId;
+
+class Logger
+{
+    friend struct Activity;
+
+public:
+
+    struct Field
+    {
+        // FIXME: use std::variant.
+        enum { tInt = 0, tString = 1 } type;
+        uint64_t i = 0;
+        std::string s;
+        Field(const std::string & s) : type(tString), s(s) { }
+        Field(const char * s) : type(tString), s(s) { }
+        Field(const uint64_t & i) : type(tInt), i(i) { }
+    };
+
+    typedef std::vector<Field> Fields;
+
+    virtual ~Logger() { }
+
+    virtual void log(Verbosity lvl, const FormatOrString & fs) = 0;
+
+    void log(const FormatOrString & fs)
+    {
+        log(lvlInfo, fs);
+    }
+
+    virtual void warn(const std::string & msg);
+
+    virtual void startActivity(ActivityId act, Verbosity lvl, ActivityType type,
+        const std::string & s, const Fields & fields, ActivityId parent) { };
+
+    virtual void stopActivity(ActivityId act) { };
+
+    virtual void result(ActivityId act, ResultType type, const Fields & fields) { };
+};
+
+ActivityId getCurActivity();
+void setCurActivity(const ActivityId activityId);
+
+struct Activity
+{
+    Logger & logger;
+
+    const ActivityId id;
+
+    Activity(Logger & logger, Verbosity lvl, ActivityType type, const std::string & s = "",
+        const Logger::Fields & fields = {}, ActivityId parent = getCurActivity());
+
+    Activity(Logger & logger, ActivityType type,
+        const Logger::Fields & fields = {}, ActivityId parent = getCurActivity())
+        : Activity(logger, lvlError, type, "", fields, parent) { };
+
+    Activity(const Activity & act) = delete;
+
+    ~Activity();
+
+    void progress(uint64_t done = 0, uint64_t expected = 0, uint64_t running = 0, uint64_t failed = 0) const
+    { result(resProgress, done, expected, running, failed); }
+
+    void setExpected(ActivityType type2, uint64_t expected) const
+    { result(resSetExpected, type2, expected); }
+
+    template<typename... Args>
+    void result(ResultType type, const Args & ... args) const
+    {
+        Logger::Fields fields;
+        nop{(fields.emplace_back(Logger::Field(args)), 1)...};
+        result(type, fields);
+    }
+
+    void result(ResultType type, const Logger::Fields & fields) const
+    {
+        logger.result(id, type, fields);
+    }
+
+    friend class Logger;
+};
+
+struct PushActivity
+{
+    const ActivityId prevAct;
+    PushActivity(ActivityId act) : prevAct(getCurActivity()) { setCurActivity(act); }
+    ~PushActivity() { setCurActivity(prevAct); }
+};
+
+extern Logger * logger;
+
+Logger * makeDefaultLogger();
+
+Logger * makeJSONLogger(Logger & prevLogger);
+
+bool handleJSONLogMessage(const std::string & msg,
+    const Activity & act, std::map<ActivityId, Activity> & activities,
+    bool trusted);
+
+extern Verbosity verbosity; /* suppress msgs > this */
+
+/* Print a message if the current log level is at least the specified
+   level. Note that this has to be implemented as a macro to ensure
+   that the arguments are evaluated lazily. */
+#define printMsg(level, args...) \
+    do { \
+        if (level <= nix::verbosity) { \
+            logger->log(level, fmt(args)); \
+        } \
+    } while (0)
+
+#define printError(args...) printMsg(lvlError, args)
+#define printInfo(args...) printMsg(lvlInfo, args)
+#define printTalkative(args...) printMsg(lvlTalkative, args)
+#define debug(args...) printMsg(lvlDebug, args)
+#define vomit(args...) printMsg(lvlVomit, args)
+
+template<typename... Args>
+inline void warn(const std::string & fs, Args... args)
+{
+    boost::format f(fs);
+    nop{boost::io::detail::feed(f, args)...};
+    logger->warn(f.str());
+}
+
+void warnOnce(bool & haveWarned, const FormatOrString & fs);
+
+void writeToStderr(const string & s);
+
+}

third_party/nix/src/libutil/lru-cache.hh

@@ -0,0 +1,92 @@
+#pragma once
+
+#include <map>
+#include <list>
+#include <optional>
+
+namespace nix {
+
+/* A simple least-recently used cache. Not thread-safe. */
+template<typename Key, typename Value>
+class LRUCache
+{
+private:
+
+    size_t capacity;
+
+    // Stupid wrapper to get around circular dependency between Data
+    // and LRU.
+    struct LRUIterator;
+
+    using Data = std::map<Key, std::pair<LRUIterator, Value>>;
+    using LRU = std::list<typename Data::iterator>;
+
+    struct LRUIterator { typename LRU::iterator it; };
+
+    Data data;
+    LRU lru;
+
+public:
+
+    LRUCache(size_t capacity) : capacity(capacity) { }
+
+    /* Insert or upsert an item in the cache. */
+    void upsert(const Key & key, const Value & value)
+    {
+        if (capacity == 0) return;
+
+        erase(key);
+
+        if (data.size() >= capacity) {
+            /* Retire the oldest item. */
+            auto oldest = lru.begin();
+            data.erase(*oldest);
+            lru.erase(oldest);
+        }
+
+        auto res = data.emplace(key, std::make_pair(LRUIterator(), value));
+        assert(res.second);
+        auto & i(res.first);
+
+        auto j = lru.insert(lru.end(), i);
+
+        i->second.first.it = j;
+    }
+
+    bool erase(const Key & key)
+    {
+        auto i = data.find(key);
+        if (i == data.end()) return false;
+        lru.erase(i->second.first.it);
+        data.erase(i);
+        return true;
+    }
+
+    /* Look up an item in the cache. If it exists, it becomes the most
+       recently used item. */
+    std::optional<Value> get(const Key & key)
+    {
+        auto i = data.find(key);
+        if (i == data.end()) return {};
+
+        /* Move this item to the back of the LRU list. */
+        lru.erase(i->second.first.it);
+        auto j = lru.insert(lru.end(), i);
+        i->second.first.it = j;
+
+        return i->second.second;
+    }
+
+    size_t size()
+    {
+        return data.size();
+    }
+
+    void clear()
+    {
+        data.clear();
+        lru.clear();
+    }
+};
+
+}

third_party/nix/src/libutil/monitor-fd.hh

@@ -0,0 +1,58 @@
+#pragma once
+
+#include <thread>
+#include <atomic>
+
+#include <cstdlib>
+#include <poll.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <signal.h>
+
+namespace nix {
+
+
+class MonitorFdHup
+{
+private:
+    std::thread thread;
+
+public:
+    MonitorFdHup(int fd)
+    {
+        thread = std::thread([fd]() {
+            while (true) {
+              /* Wait indefinitely until a POLLHUP occurs. */
+              struct pollfd fds[1];
+              fds[0].fd = fd;
+              /* This shouldn't be necessary, but macOS doesn't seem to
+                 like a zeroed out events field.
+                 See rdar://37537852.
+              */
+              fds[0].events = POLLHUP;
+              auto count = poll(fds, 1, -1);
+              if (count == -1) abort(); // can't happen
+              /* This shouldn't happen, but can on macOS due to a bug.
+                 See rdar://37550628.
+
+                 This may eventually need a delay or further
+                 coordination with the main thread if spinning proves
+                 too harmful.
+               */
+              if (count == 0) continue;
+              assert(fds[0].revents & POLLHUP);
+              triggerInterrupt();
+              break;
+            }
+        });
+    };
+
+    ~MonitorFdHup()
+    {
+        pthread_cancel(thread.native_handle());
+        thread.join();
+    }
+};
+
+
+}

third_party/nix/src/libutil/pool.hh

@@ -0,0 +1,187 @@
+#pragma once
+
+#include <functional>
+#include <limits>
+#include <list>
+#include <memory>
+#include <cassert>
+
+#include "sync.hh"
+#include "ref.hh"
+
+namespace nix {
+
+/* This template class implements a simple pool manager of resources
+   of some type R, such as database connections. It is used as
+   follows:
+
+     class Connection { ... };
+
+     Pool<Connection> pool;
+
+     {
+       auto conn(pool.get());
+       conn->exec("select ...");
+     }
+
+   Here, the Connection object referenced by ‘conn’ is automatically
+   returned to the pool when ‘conn’ goes out of scope.
+*/
+
+template <class R>
+class Pool
+{
+public:
+
+    /* A function that produces new instances of R on demand. */
+    typedef std::function<ref<R>()> Factory;
+
+    /* A function that checks whether an instance of R is still
+       usable. Unusable instances are removed from the pool. */
+    typedef std::function<bool(const ref<R> &)> Validator;
+
+private:
+
+    Factory factory;
+    Validator validator;
+
+    struct State
+    {
+        size_t inUse = 0;
+        size_t max;
+        std::vector<ref<R>> idle;
+    };
+
+    Sync<State> state;
+
+    std::condition_variable wakeup;
+
+public:
+
+    Pool(size_t max = std::numeric_limits<size_t>::max(),
+        const Factory & factory = []() { return make_ref<R>(); },
+        const Validator & validator = [](ref<R> r) { return true; })
+        : factory(factory)
+        , validator(validator)
+    {
+        auto state_(state.lock());
+        state_->max = max;
+    }
+
+    void incCapacity()
+    {
+        auto state_(state.lock());
+        state_->max++;
+        /* we could wakeup here, but this is only used when we're
+         * about to nest Pool usages, and we want to save the slot for
+         * the nested use if we can
+         */
+    }
+
+    void decCapacity()
+    {
+        auto state_(state.lock());
+        state_->max--;
+    }
+
+    ~Pool()
+    {
+        auto state_(state.lock());
+        assert(!state_->inUse);
+        state_->max = 0;
+        state_->idle.clear();
+    }
+
+    class Handle
+    {
+    private:
+        Pool & pool;
+        std::shared_ptr<R> r;
+        bool bad = false;
+
+        friend Pool;
+
+        Handle(Pool & pool, std::shared_ptr<R> r) : pool(pool), r(r) { }
+
+    public:
+        Handle(Handle && h) : pool(h.pool), r(h.r) { h.r.reset(); }
+
+        Handle(const Handle & l) = delete;
+
+        ~Handle()
+        {
+            if (!r) return;
+            {
+                auto state_(pool.state.lock());
+                if (!bad)
+                    state_->idle.push_back(ref<R>(r));
+                assert(state_->inUse);
+                state_->inUse--;
+            }
+            pool.wakeup.notify_one();
+        }
+
+        R * operator -> () { return &*r; }
+        R & operator * () { return *r; }
+
+        void markBad() { bad = true; }
+    };
+
+    Handle get()
+    {
+        {
+            auto state_(state.lock());
+
+            /* If we're over the maximum number of instance, we need
+               to wait until a slot becomes available. */
+            while (state_->idle.empty() && state_->inUse >= state_->max)
+                state_.wait(wakeup);
+
+            while (!state_->idle.empty()) {
+                auto p = state_->idle.back();
+                state_->idle.pop_back();
+                if (validator(p)) {
+                    state_->inUse++;
+                    return Handle(*this, p);
+                }
+            }
+
+            state_->inUse++;
+        }
+
+        /* We need to create a new instance. Because that might take a
+           while, we don't hold the lock in the meantime. */
+        try {
+            Handle h(*this, factory());
+            return h;
+        } catch (...) {
+            auto state_(state.lock());
+            state_->inUse--;
+            wakeup.notify_one();
+            throw;
+        }
+    }
+
+    size_t count()
+    {
+        auto state_(state.lock());
+        return state_->idle.size() + state_->inUse;
+    }
+
+    size_t capacity()
+    {
+        return state.lock()->max;
+    }
+
+    void flushBad()
+    {
+        auto state_(state.lock());
+        std::vector<ref<R>> left;
+        for (auto & p : state_->idle)
+            if (validator(p))
+                left.push_back(p);
+        std::swap(state_->idle, left);
+    }
+};
+
+}

third_party/nix/src/libutil/ref.hh

@@ -0,0 +1,92 @@
+#pragma once
+
+#include <memory>
+#include <exception>
+#include <stdexcept>
+
+namespace nix {
+
+/* A simple non-nullable reference-counted pointer. Actually a wrapper
+   around std::shared_ptr that prevents non-null constructions. */
+template<typename T>
+class ref
+{
+private:
+
+    std::shared_ptr<T> p;
+
+public:
+
+    ref<T>(const ref<T> & r)
+        : p(r.p)
+    { }
+
+    explicit ref<T>(const std::shared_ptr<T> & p)
+        : p(p)
+    {
+        if (!p)
+            throw std::invalid_argument("null pointer cast to ref");
+    }
+
+    explicit ref<T>(T * p)
+        : p(p)
+    {
+        if (!p)
+            throw std::invalid_argument("null pointer cast to ref");
+    }
+
+    T* operator ->() const
+    {
+        return &*p;
+    }
+
+    T& operator *() const
+    {
+        return *p;
+    }
+
+    operator std::shared_ptr<T> () const
+    {
+        return p;
+    }
+
+    std::shared_ptr<T> get_ptr() const
+    {
+        return p;
+    }
+
+    template<typename T2>
+    ref<T2> cast() const
+    {
+        return ref<T2>(std::dynamic_pointer_cast<T2>(p));
+    }
+
+    template<typename T2>
+    std::shared_ptr<T2> dynamic_pointer_cast() const
+    {
+        return std::dynamic_pointer_cast<T2>(p);
+    }
+
+    template<typename T2>
+    operator ref<T2> () const
+    {
+        return ref<T2>((std::shared_ptr<T2>) p);
+    }
+
+private:
+
+    template<typename T2, typename... Args>
+    friend ref<T2>
+    make_ref(Args&&... args);
+
+};
+
+template<typename T, typename... Args>
+inline ref<T>
+make_ref(Args&&... args)
+{
+    auto p = std::make_shared<T>(std::forward<Args>(args)...);
+    return ref<T>(p);
+}
+
+}

third_party/nix/src/libutil/serialise.cc

@@ -0,0 +1,323 @@
+#include "serialise.hh"
+#include "util.hh"
+
+#include <cstring>
+#include <cerrno>
+#include <memory>
+
+#include <boost/coroutine2/coroutine.hpp>
+
+
+namespace nix {
+
+
+void BufferedSink::operator () (const unsigned char * data, size_t len)
+{
+    if (!buffer) buffer = decltype(buffer)(new unsigned char[bufSize]);
+
+    while (len) {
+        /* Optimisation: bypass the buffer if the data exceeds the
+           buffer size. */
+        if (bufPos + len >= bufSize) {
+            flush();
+            write(data, len);
+            break;
+        }
+        /* Otherwise, copy the bytes to the buffer.  Flush the buffer
+           when it's full. */
+        size_t n = bufPos + len > bufSize ? bufSize - bufPos : len;
+        memcpy(buffer.get() + bufPos, data, n);
+        data += n; bufPos += n; len -= n;
+        if (bufPos == bufSize) flush();
+    }
+}
+
+
+void BufferedSink::flush()
+{
+    if (bufPos == 0) return;
+    size_t n = bufPos;
+    bufPos = 0; // don't trigger the assert() in ~BufferedSink()
+    write(buffer.get(), n);
+}
+
+
+FdSink::~FdSink()
+{
+    try { flush(); } catch (...) { ignoreException(); }
+}
+
+
+size_t threshold = 256 * 1024 * 1024;
+
+static void warnLargeDump()
+{
+    printError("warning: dumping very large path (> 256 MiB); this may run out of memory");
+}
+
+
+void FdSink::write(const unsigned char * data, size_t len)
+{
+    written += len;
+    static bool warned = false;
+    if (warn && !warned) {
+        if (written > threshold) {
+            warnLargeDump();
+            warned = true;
+        }
+    }
+    try {
+        writeFull(fd, data, len);
+    } catch (SysError & e) {
+        _good = false;
+        throw;
+    }
+}
+
+
+bool FdSink::good()
+{
+    return _good;
+}
+
+
+void Source::operator () (unsigned char * data, size_t len)
+{
+    while (len) {
+        size_t n = read(data, len);
+        data += n; len -= n;
+    }
+}
+
+
+std::string Source::drain()
+{
+    std::string s;
+    std::vector<unsigned char> buf(8192);
+    while (true) {
+        size_t n;
+        try {
+            n = read(buf.data(), buf.size());
+            s.append((char *) buf.data(), n);
+        } catch (EndOfFile &) {
+            break;
+        }
+    }
+    return s;
+}
+
+
+size_t BufferedSource::read(unsigned char * data, size_t len)
+{
+    if (!buffer) buffer = decltype(buffer)(new unsigned char[bufSize]);
+
+    if (!bufPosIn) bufPosIn = readUnbuffered(buffer.get(), bufSize);
+
+    /* Copy out the data in the buffer. */
+    size_t n = len > bufPosIn - bufPosOut ? bufPosIn - bufPosOut : len;
+    memcpy(data, buffer.get() + bufPosOut, n);
+    bufPosOut += n;
+    if (bufPosIn == bufPosOut) bufPosIn = bufPosOut = 0;
+    return n;
+}
+
+
+bool BufferedSource::hasData()
+{
+    return bufPosOut < bufPosIn;
+}
+
+
+size_t FdSource::readUnbuffered(unsigned char * data, size_t len)
+{
+    ssize_t n;
+    do {
+        checkInterrupt();
+        n = ::read(fd, (char *) data, len);
+    } while (n == -1 && errno == EINTR);
+    if (n == -1) { _good = false; throw SysError("reading from file"); }
+    if (n == 0) { _good = false; throw EndOfFile("unexpected end-of-file"); }
+    read += n;
+    return n;
+}
+
+
+bool FdSource::good()
+{
+    return _good;
+}
+
+
+size_t StringSource::read(unsigned char * data, size_t len)
+{
+    if (pos == s.size()) throw EndOfFile("end of string reached");
+    size_t n = s.copy((char *) data, len, pos);
+    pos += n;
+    return n;
+}
+
+
+#if BOOST_VERSION >= 106300 && BOOST_VERSION < 106600
+#error Coroutines are broken in this version of Boost!
+#endif
+
+std::unique_ptr<Source> sinkToSource(
+    std::function<void(Sink &)> fun,
+    std::function<void()> eof)
+{
+    struct SinkToSource : Source
+    {
+        typedef boost::coroutines2::coroutine<std::string> coro_t;
+
+        std::function<void(Sink &)> fun;
+        std::function<void()> eof;
+        std::optional<coro_t::pull_type> coro;
+        bool started = false;
+
+        SinkToSource(std::function<void(Sink &)> fun, std::function<void()> eof)
+            : fun(fun), eof(eof)
+        {
+        }
+
+        std::string cur;
+        size_t pos = 0;
+
+        size_t read(unsigned char * data, size_t len) override
+        {
+            if (!coro)
+                coro = coro_t::pull_type([&](coro_t::push_type & yield) {
+                    LambdaSink sink([&](const unsigned char * data, size_t len) {
+                            if (len) yield(std::string((const char *) data, len));
+                        });
+                    fun(sink);
+                });
+
+            if (!*coro) { eof(); abort(); }
+
+            if (pos == cur.size()) {
+                if (!cur.empty()) (*coro)();
+                cur = coro->get();
+                pos = 0;
+            }
+
+            auto n = std::min(cur.size() - pos, len);
+            memcpy(data, (unsigned char *) cur.data() + pos, n);
+            pos += n;
+
+            return n;
+        }
+    };
+
+    return std::make_unique<SinkToSource>(fun, eof);
+}
+
+
+void writePadding(size_t len, Sink & sink)
+{
+    if (len % 8) {
+        unsigned char zero[8];
+        memset(zero, 0, sizeof(zero));
+        sink(zero, 8 - (len % 8));
+    }
+}
+
+
+void writeString(const unsigned char * buf, size_t len, Sink & sink)
+{
+    sink << len;
+    sink(buf, len);
+    writePadding(len, sink);
+}
+
+
+Sink & operator << (Sink & sink, const string & s)
+{
+    writeString((const unsigned char *) s.data(), s.size(), sink);
+    return sink;
+}
+
+
+template<class T> void writeStrings(const T & ss, Sink & sink)
+{
+    sink << ss.size();
+    for (auto & i : ss)
+        sink << i;
+}
+
+Sink & operator << (Sink & sink, const Strings & s)
+{
+    writeStrings(s, sink);
+    return sink;
+}
+
+Sink & operator << (Sink & sink, const StringSet & s)
+{
+    writeStrings(s, sink);
+    return sink;
+}
+
+
+void readPadding(size_t len, Source & source)
+{
+    if (len % 8) {
+        unsigned char zero[8];
+        size_t n = 8 - (len % 8);
+        source(zero, n);
+        for (unsigned int i = 0; i < n; i++)
+            if (zero[i]) throw SerialisationError("non-zero padding");
+    }
+}
+
+
+size_t readString(unsigned char * buf, size_t max, Source & source)
+{
+    auto len = readNum<size_t>(source);
+    if (len > max) throw SerialisationError("string is too long");
+    source(buf, len);
+    readPadding(len, source);
+    return len;
+}
+
+
+string readString(Source & source, size_t max)
+{
+    auto len = readNum<size_t>(source);
+    if (len > max) throw SerialisationError("string is too long");
+    std::string res(len, 0);
+    source((unsigned char*) res.data(), len);
+    readPadding(len, source);
+    return res;
+}
+
+Source & operator >> (Source & in, string & s)
+{
+    s = readString(in);
+    return in;
+}
+
+
+template<class T> T readStrings(Source & source)
+{
+    auto count = readNum<size_t>(source);
+    T ss;
+    while (count--)
+        ss.insert(ss.end(), readString(source));
+    return ss;
+}
+
+template Paths readStrings(Source & source);
+template PathSet readStrings(Source & source);
+
+
+void StringSink::operator () (const unsigned char * data, size_t len)
+{
+    static bool warned = false;
+    if (!warned && s->size() > threshold) {
+        warnLargeDump();
+        warned = true;
+    }
+    s->append((const char *) data, len);
+}
+
+
+}

third_party/nix/src/libutil/serialise.hh

@@ -0,0 +1,337 @@
+#pragma once
+
+#include <memory>
+
+#include "types.hh"
+#include "util.hh"
+
+
+namespace nix {
+
+
+/* Abstract destination of binary data. */
+struct Sink
+{
+    virtual ~Sink() { }
+    virtual void operator () (const unsigned char * data, size_t len) = 0;
+    virtual bool good() { return true; }
+
+    void operator () (const std::string & s)
+    {
+        (*this)((const unsigned char *) s.data(), s.size());
+    }
+};
+
+
+/* A buffered abstract sink. */
+struct BufferedSink : Sink
+{
+    size_t bufSize, bufPos;
+    std::unique_ptr<unsigned char[]> buffer;
+
+    BufferedSink(size_t bufSize = 32 * 1024)
+        : bufSize(bufSize), bufPos(0), buffer(nullptr) { }
+
+    void operator () (const unsigned char * data, size_t len) override;
+
+    void operator () (const std::string & s)
+    {
+        Sink::operator()(s);
+    }
+
+    void flush();
+
+    virtual void write(const unsigned char * data, size_t len) = 0;
+};
+
+
+/* Abstract source of binary data. */
+struct Source
+{
+    virtual ~Source() { }
+
+    /* Store exactly ‘len’ bytes in the buffer pointed to by ‘data’.
+       It blocks until all the requested data is available, or throws
+       an error if it is not going to be available.   */
+    void operator () (unsigned char * data, size_t len);
+
+    /* Store up to ‘len’ in the buffer pointed to by ‘data’, and
+       return the number of bytes stored.  It blocks until at least
+       one byte is available. */
+    virtual size_t read(unsigned char * data, size_t len) = 0;
+
+    virtual bool good() { return true; }
+
+    std::string drain();
+};
+
+
+/* A buffered abstract source. */
+struct BufferedSource : Source
+{
+    size_t bufSize, bufPosIn, bufPosOut;
+    std::unique_ptr<unsigned char[]> buffer;
+
+    BufferedSource(size_t bufSize = 32 * 1024)
+        : bufSize(bufSize), bufPosIn(0), bufPosOut(0), buffer(nullptr) { }
+
+    size_t read(unsigned char * data, size_t len) override;
+
+
+    bool hasData();
+
+protected:
+    /* Underlying read call, to be overridden. */
+    virtual size_t readUnbuffered(unsigned char * data, size_t len) = 0;
+};
+
+
+/* A sink that writes data to a file descriptor. */
+struct FdSink : BufferedSink
+{
+    int fd;
+    bool warn = false;
+    size_t written = 0;
+
+    FdSink() : fd(-1) { }
+    FdSink(int fd) : fd(fd) { }
+    FdSink(FdSink&&) = default;
+
+    FdSink& operator=(FdSink && s)
+    {
+        flush();
+        fd = s.fd;
+        s.fd = -1;
+        warn = s.warn;
+        written = s.written;
+        return *this;
+    }
+
+    ~FdSink();
+
+    void write(const unsigned char * data, size_t len) override;
+
+    bool good() override;
+
+private:
+    bool _good = true;
+};
+
+
+/* A source that reads data from a file descriptor. */
+struct FdSource : BufferedSource
+{
+    int fd;
+    size_t read = 0;
+
+    FdSource() : fd(-1) { }
+    FdSource(int fd) : fd(fd) { }
+    FdSource(FdSource&&) = default;
+
+    FdSource& operator=(FdSource && s)
+    {
+        fd = s.fd;
+        s.fd = -1;
+        read = s.read;
+        return *this;
+    }
+
+    bool good() override;
+protected:
+    size_t readUnbuffered(unsigned char * data, size_t len) override;
+private:
+    bool _good = true;
+};
+
+
+/* A sink that writes data to a string. */
+struct StringSink : Sink
+{
+    ref<std::string> s;
+    StringSink() : s(make_ref<std::string>()) { };
+    StringSink(ref<std::string> s) : s(s) { };
+    void operator () (const unsigned char * data, size_t len) override;
+};
+
+
+/* A source that reads data from a string. */
+struct StringSource : Source
+{
+    const string & s;
+    size_t pos;
+    StringSource(const string & _s) : s(_s), pos(0) { }
+    size_t read(unsigned char * data, size_t len) override;
+};
+
+
+/* Adapter class of a Source that saves all data read to `s'. */
+struct TeeSource : Source
+{
+    Source & orig;
+    ref<std::string> data;
+    TeeSource(Source & orig)
+        : orig(orig), data(make_ref<std::string>()) { }
+    size_t read(unsigned char * data, size_t len)
+    {
+        size_t n = orig.read(data, len);
+        this->data->append((const char *) data, n);
+        return n;
+    }
+};
+
+/* A reader that consumes the original Source until 'size'. */
+struct SizedSource : Source
+{
+    Source & orig;
+    size_t remain;
+    SizedSource(Source & orig, size_t size)
+        : orig(orig), remain(size) { }
+    size_t read(unsigned char * data, size_t len)
+    {
+        if (this->remain <= 0) {
+            throw EndOfFile("sized: unexpected end-of-file");
+        }
+        len = std::min(len, this->remain);
+        size_t n = this->orig.read(data, len);
+        this->remain -= n;
+        return n;
+    }
+
+    /* Consume the original source until no remain data is left to consume. */
+    size_t drainAll()
+    {
+        std::vector<unsigned char> buf(8192);
+        size_t sum = 0;
+        while (this->remain > 0) {
+            size_t n = read(buf.data(), buf.size());
+            sum += n;
+        }
+        return sum;
+    }
+};
+
+/* Convert a function into a sink. */
+struct LambdaSink : Sink
+{
+    typedef std::function<void(const unsigned char *, size_t)> lambda_t;
+
+    lambda_t lambda;
+
+    LambdaSink(const lambda_t & lambda) : lambda(lambda) { }
+
+    virtual void operator () (const unsigned char * data, size_t len)
+    {
+        lambda(data, len);
+    }
+};
+
+
+/* Convert a function into a source. */
+struct LambdaSource : Source
+{
+    typedef std::function<size_t(unsigned char *, size_t)> lambda_t;
+
+    lambda_t lambda;
+
+    LambdaSource(const lambda_t & lambda) : lambda(lambda) { }
+
+    size_t read(unsigned char * data, size_t len) override
+    {
+        return lambda(data, len);
+    }
+};
+
+
+/* Convert a function that feeds data into a Sink into a Source. The
+   Source executes the function as a coroutine. */
+std::unique_ptr<Source> sinkToSource(
+    std::function<void(Sink &)> fun,
+    std::function<void()> eof = []() {
+        throw EndOfFile("coroutine has finished");
+    });
+
+
+void writePadding(size_t len, Sink & sink);
+void writeString(const unsigned char * buf, size_t len, Sink & sink);
+
+inline Sink & operator << (Sink & sink, uint64_t n)
+{
+    unsigned char buf[8];
+    buf[0] = n & 0xff;
+    buf[1] = (n >> 8) & 0xff;
+    buf[2] = (n >> 16) & 0xff;
+    buf[3] = (n >> 24) & 0xff;
+    buf[4] = (n >> 32) & 0xff;
+    buf[5] = (n >> 40) & 0xff;
+    buf[6] = (n >> 48) & 0xff;
+    buf[7] = (unsigned char) (n >> 56) & 0xff;
+    sink(buf, sizeof(buf));
+    return sink;
+}
+
+Sink & operator << (Sink & sink, const string & s);
+Sink & operator << (Sink & sink, const Strings & s);
+Sink & operator << (Sink & sink, const StringSet & s);
+
+
+MakeError(SerialisationError, Error)
+
+
+template<typename T>
+T readNum(Source & source)
+{
+    unsigned char buf[8];
+    source(buf, sizeof(buf));
+
+    uint64_t n =
+        ((unsigned long long) buf[0]) |
+        ((unsigned long long) buf[1] << 8) |
+        ((unsigned long long) buf[2] << 16) |
+        ((unsigned long long) buf[3] << 24) |
+        ((unsigned long long) buf[4] << 32) |
+        ((unsigned long long) buf[5] << 40) |
+        ((unsigned long long) buf[6] << 48) |
+        ((unsigned long long) buf[7] << 56);
+
+    if (n > std::numeric_limits<T>::max())
+        throw SerialisationError("serialised integer %d is too large for type '%s'", n, typeid(T).name());
+
+    return (T) n;
+}
+
+
+inline unsigned int readInt(Source & source)
+{
+    return readNum<unsigned int>(source);
+}
+
+
+inline uint64_t readLongLong(Source & source)
+{
+    return readNum<uint64_t>(source);
+}
+
+
+void readPadding(size_t len, Source & source);
+size_t readString(unsigned char * buf, size_t max, Source & source);
+string readString(Source & source, size_t max = std::numeric_limits<size_t>::max());
+template<class T> T readStrings(Source & source);
+
+Source & operator >> (Source & in, string & s);
+
+template<typename T>
+Source & operator >> (Source & in, T & n)
+{
+    n = readNum<T>(in);
+    return in;
+}
+
+template<typename T>
+Source & operator >> (Source & in, bool & b)
+{
+    b = readNum<uint64_t>(in);
+    return in;
+}
+
+
+}

third_party/nix/src/libutil/sync.hh

@@ -0,0 +1,88 @@
+#pragma once
+
+#include <cstdlib>
+#include <mutex>
+#include <condition_variable>
+#include <cassert>
+
+namespace nix {
+
+/* This template class ensures synchronized access to a value of type
+   T. It is used as follows:
+
+     struct Data { int x; ... };
+
+     Sync<Data> data;
+
+     {
+       auto data_(data.lock());
+       data_->x = 123;
+     }
+
+   Here, "data" is automatically unlocked when "data_" goes out of
+   scope.
+*/
+
+template<class T, class M = std::mutex>
+class Sync
+{
+private:
+    M mutex;
+    T data;
+
+public:
+
+    Sync() { }
+    Sync(const T & data) : data(data) { }
+    Sync(T && data) noexcept : data(std::move(data)) { }
+
+    class Lock
+    {
+    private:
+        Sync * s;
+        std::unique_lock<M> lk;
+        friend Sync;
+        Lock(Sync * s) : s(s), lk(s->mutex) { }
+    public:
+        Lock(Lock && l) : s(l.s) { abort(); }
+        Lock(const Lock & l) = delete;
+        ~Lock() { }
+        T * operator -> () { return &s->data; }
+        T & operator * () { return s->data; }
+
+        void wait(std::condition_variable & cv)
+        {
+            assert(s);
+            cv.wait(lk);
+        }
+
+        template<class Rep, class Period>
+        std::cv_status wait_for(std::condition_variable & cv,
+            const std::chrono::duration<Rep, Period> & duration)
+        {
+            assert(s);
+            return cv.wait_for(lk, duration);
+        }
+
+        template<class Rep, class Period, class Predicate>
+        bool wait_for(std::condition_variable & cv,
+            const std::chrono::duration<Rep, Period> & duration,
+            Predicate pred)
+        {
+            assert(s);
+            return cv.wait_for(lk, duration, pred);
+        }
+
+        template<class Clock, class Duration>
+        std::cv_status wait_until(std::condition_variable & cv,
+            const std::chrono::time_point<Clock, Duration> & duration)
+        {
+            assert(s);
+            return cv.wait_until(lk, duration);
+        }
+    };
+
+    Lock lock() { return Lock(this); }
+};
+
+}

third_party/nix/src/libutil/thread-pool.cc

@@ -0,0 +1,156 @@
+#include "thread-pool.hh"
+#include "affinity.hh"
+
+namespace nix {
+
+ThreadPool::ThreadPool(size_t _maxThreads)
+    : maxThreads(_maxThreads)
+{
+    restoreAffinity(); // FIXME
+
+    if (!maxThreads) {
+        maxThreads = std::thread::hardware_concurrency();
+        if (!maxThreads) maxThreads = 1;
+    }
+
+    debug("starting pool of %d threads", maxThreads - 1);
+}
+
+ThreadPool::~ThreadPool()
+{
+    shutdown();
+}
+
+void ThreadPool::shutdown()
+{
+    std::vector<std::thread> workers;
+    {
+        auto state(state_.lock());
+        quit = true;
+        std::swap(workers, state->workers);
+    }
+
+    if (workers.empty()) return;
+
+    debug("reaping %d worker threads", workers.size());
+
+    work.notify_all();
+
+    for (auto & thr : workers)
+        thr.join();
+}
+
+void ThreadPool::enqueue(const work_t & t)
+{
+    auto state(state_.lock());
+    if (quit)
+        throw ThreadPoolShutDown("cannot enqueue a work item while the thread pool is shutting down");
+    state->pending.push(t);
+    /* Note: process() also executes items, so count it as a worker. */
+    if (state->pending.size() > state->workers.size() + 1 && state->workers.size() + 1 < maxThreads)
+        state->workers.emplace_back(&ThreadPool::doWork, this, false);
+    work.notify_one();
+}
+
+void ThreadPool::process()
+{
+    state_.lock()->draining = true;
+
+    /* Do work until no more work is pending or active. */
+    try {
+        doWork(true);
+
+        auto state(state_.lock());
+
+        assert(quit);
+
+        if (state->exception)
+            std::rethrow_exception(state->exception);
+
+    } catch (...) {
+        /* In the exceptional case, some workers may still be
+           active. They may be referencing the stack frame of the
+           caller. So wait for them to finish. (~ThreadPool also does
+           this, but it might be destroyed after objects referenced by
+           the work item lambdas.) */
+        shutdown();
+        throw;
+    }
+}
+
+void ThreadPool::doWork(bool mainThread)
+{
+    if (!mainThread)
+        interruptCheck = [&]() { return (bool) quit; };
+
+    bool didWork = false;
+    std::exception_ptr exc;
+
+    while (true) {
+        work_t w;
+        {
+            auto state(state_.lock());
+
+            if (didWork) {
+                assert(state->active);
+                state->active--;
+
+                if (exc) {
+
+                    if (!state->exception) {
+                        state->exception = exc;
+                        // Tell the other workers to quit.
+                        quit = true;
+                        work.notify_all();
+                    } else {
+                        /* Print the exception, since we can't
+                           propagate it. */
+                        try {
+                            std::rethrow_exception(exc);
+                        } catch (std::exception & e) {
+                            if (!dynamic_cast<Interrupted*>(&e) &&
+                                !dynamic_cast<ThreadPoolShutDown*>(&e))
+                                ignoreException();
+                        } catch (...) {
+                        }
+                    }
+                }
+            }
+
+            /* Wait until a work item is available or we're asked to
+               quit. */
+            while (true) {
+                if (quit) return;
+
+                if (!state->pending.empty()) break;
+
+                /* If there are no active or pending items, and the
+                   main thread is running process(), then no new items
+                   can be added. So exit. */
+                if (!state->active && state->draining) {
+                    quit = true;
+                    work.notify_all();
+                    return;
+                }
+
+                state.wait(work);
+            }
+
+            w = std::move(state->pending.front());
+            state->pending.pop();
+            state->active++;
+        }
+
+        try {
+            w();
+        } catch (...) {
+            exc = std::current_exception();
+        }
+
+        didWork = true;
+    }
+}
+
+}
+
+

third_party/nix/src/libutil/thread-pool.hh

@@ -0,0 +1,143 @@
+#pragma once
+
+#include "sync.hh"
+#include "util.hh"
+
+#include <queue>
+#include <functional>
+#include <thread>
+#include <map>
+#include <atomic>
+
+namespace nix {
+
+MakeError(ThreadPoolShutDown, Error)
+
+/* A simple thread pool that executes a queue of work items
+   (lambdas). */
+class ThreadPool
+{
+public:
+
+    ThreadPool(size_t maxThreads = 0);
+
+    ~ThreadPool();
+
+    // FIXME: use std::packaged_task?
+    typedef std::function<void()> work_t;
+
+    /* Enqueue a function to be executed by the thread pool. */
+    void enqueue(const work_t & t);
+
+    /* Execute work items until the queue is empty. Note that work
+       items are allowed to add new items to the queue; this is
+       handled correctly. Queue processing stops prematurely if any
+       work item throws an exception. This exception is propagated to
+       the calling thread. If multiple work items throw an exception
+       concurrently, only one item is propagated; the others are
+       printed on stderr and otherwise ignored. */
+    void process();
+
+private:
+
+    size_t maxThreads;
+
+    struct State
+    {
+        std::queue<work_t> pending;
+        size_t active = 0;
+        std::exception_ptr exception;
+        std::vector<std::thread> workers;
+        bool draining = false;
+    };
+
+    std::atomic_bool quit{false};
+
+    Sync<State> state_;
+
+    std::condition_variable work;
+
+    void doWork(bool mainThread);
+
+    void shutdown();
+};
+
+/* Process in parallel a set of items of type T that have a partial
+   ordering between them. Thus, any item is only processed after all
+   its dependencies have been processed. */
+template<typename T>
+void processGraph(
+    ThreadPool & pool,
+    const std::set<T> & nodes,
+    std::function<std::set<T>(const T &)> getEdges,
+    std::function<void(const T &)> processNode)
+{
+    struct Graph {
+        std::set<T> left;
+        std::map<T, std::set<T>> refs, rrefs;
+    };
+
+    Sync<Graph> graph_(Graph{nodes, {}, {}});
+
+    std::function<void(const T &)> worker;
+
+    worker = [&](const T & node) {
+
+        {
+            auto graph(graph_.lock());
+            auto i = graph->refs.find(node);
+            if (i == graph->refs.end())
+                goto getRefs;
+            goto doWork;
+        }
+
+    getRefs:
+        {
+            auto refs = getEdges(node);
+            refs.erase(node);
+
+            {
+                auto graph(graph_.lock());
+                for (auto & ref : refs)
+                    if (graph->left.count(ref)) {
+                        graph->refs[node].insert(ref);
+                        graph->rrefs[ref].insert(node);
+                    }
+                if (graph->refs[node].empty())
+                    goto doWork;
+            }
+        }
+
+        return;
+
+    doWork:
+        processNode(node);
+
+        /* Enqueue work for all nodes that were waiting on this one
+           and have no unprocessed dependencies. */
+        {
+            auto graph(graph_.lock());
+            for (auto & rref : graph->rrefs[node]) {
+                auto & refs(graph->refs[rref]);
+                auto i = refs.find(node);
+                assert(i != refs.end());
+                refs.erase(i);
+                if (refs.empty())
+                    pool.enqueue(std::bind(worker, rref));
+            }
+            graph->left.erase(node);
+            graph->refs.erase(node);
+            graph->rrefs.erase(node);
+        }
+    };
+
+    for (auto & node : nodes)
+        pool.enqueue(std::bind(worker, std::ref(node)));
+
+    pool.process();
+
+    if (!graph_.lock()->left.empty())
+        throw Error("graph processing incomplete (cyclic reference?)");
+}
+
+}

third_party/nix/src/libutil/types.hh

@@ -0,0 +1,150 @@
+#pragma once
+
+
+#include "ref.hh"
+
+#include <string>
+#include <list>
+#include <set>
+#include <memory>
+#include <map>
+
+#include <boost/format.hpp>
+
+/* Before 4.7, gcc's std::exception uses empty throw() specifiers for
+ * its (virtual) destructor and what() in c++11 mode, in violation of spec
+ */
+#ifdef __GNUC__
+#if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 7)
+#define EXCEPTION_NEEDS_THROW_SPEC
+#endif
+#endif
+
+
+namespace nix {
+
+
+/* Inherit some names from other namespaces for convenience. */
+using std::string;
+using std::list;
+using std::set;
+using std::vector;
+using boost::format;
+
+
+/* A variadic template that does nothing. Useful to call a function
+   for all variadic arguments but ignoring the result. */
+struct nop { template<typename... T> nop(T...) {} };
+
+
+struct FormatOrString
+{
+    string s;
+    FormatOrString(const string & s) : s(s) { };
+    FormatOrString(const format & f) : s(f.str()) { };
+    FormatOrString(const char * s) : s(s) { };
+};
+
+
+/* A helper for formatting strings. ‘fmt(format, a_0, ..., a_n)’ is
+   equivalent to ‘boost::format(format) % a_0 % ... %
+   ... a_n’. However, ‘fmt(s)’ is equivalent to ‘s’ (so no %-expansion
+   takes place). */
+
+inline std::string fmt(const std::string & s)
+{
+    return s;
+}
+
+inline std::string fmt(const char * s)
+{
+    return s;
+}
+
+inline std::string fmt(const FormatOrString & fs)
+{
+    return fs.s;
+}
+
+template<typename... Args>
+inline std::string fmt(const std::string & fs, Args... args)
+{
+    boost::format f(fs);
+    f.exceptions(boost::io::all_error_bits ^ boost::io::too_many_args_bit);
+    nop{boost::io::detail::feed(f, args)...};
+    return f.str();
+}
+
+
+/* BaseError should generally not be caught, as it has Interrupted as
+   a subclass. Catch Error instead. */
+class BaseError : public std::exception
+{
+protected:
+    string prefix_; // used for location traces etc.
+    string err;
+public:
+    unsigned int status = 1; // exit status
+
+    template<typename... Args>
+    BaseError(unsigned int status, Args... args)
+        : err(fmt(args...))
+        , status(status)
+    {
+    }
+
+    template<typename... Args>
+    BaseError(Args... args)
+        : err(fmt(args...))
+    {
+    }
+
+#ifdef EXCEPTION_NEEDS_THROW_SPEC
+    ~BaseError() throw () { };
+    const char * what() const throw () { return err.c_str(); }
+#else
+    const char * what() const noexcept { return err.c_str(); }
+#endif
+
+    const string & msg() const { return err; }
+    const string & prefix() const { return prefix_; }
+    BaseError & addPrefix(const FormatOrString & fs);
+};
+
+#define MakeError(newClass, superClass) \
+    class newClass : public superClass                  \
+    {                                                   \
+    public:                                             \
+        using superClass::superClass;                   \
+    };
+
+MakeError(Error, BaseError)
+
+class SysError : public Error
+{
+public:
+    int errNo;
+
+    template<typename... Args>
+    SysError(Args... args)
+        : Error(addErrno(fmt(args...)))
+    { }
+
+private:
+
+    std::string addErrno(const std::string & s);
+};
+
+
+typedef list<string> Strings;
+typedef set<string> StringSet;
+typedef std::map<std::string, std::string> StringMap;
+
+
+/* Paths are just strings. */
+typedef string Path;
+typedef list<Path> Paths;
+typedef set<Path> PathSet;
+
+
+}

third_party/nix/src/libutil/util.hh

@@ -0,0 +1,542 @@
+#pragma once
+
+#include "types.hh"
+#include "logging.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <dirent.h>
+#include <unistd.h>
+#include <signal.h>
+
+#include <functional>
+#include <limits>
+#include <cstdio>
+#include <map>
+#include <sstream>
+#include <optional>
+#include <future>
+
+#ifndef HAVE_STRUCT_DIRENT_D_TYPE
+#define DT_UNKNOWN 0
+#define DT_REG 1
+#define DT_LNK 2
+#define DT_DIR 3
+#endif
+
+namespace nix {
+
+struct Sink;
+struct Source;
+
+
+/* The system for which Nix is compiled. */
+extern const std::string nativeSystem;
+
+
+/* Return an environment variable. */
+string getEnv(const string & key, const string & def = "");
+
+/* Get the entire environment. */
+std::map<std::string, std::string> getEnv();
+
+/* Clear the environment. */
+void clearEnv();
+
+/* Return an absolutized path, resolving paths relative to the
+   specified directory, or the current directory otherwise.  The path
+   is also canonicalised. */
+Path absPath(Path path, Path dir = "");
+
+/* Canonicalise a path by removing all `.' or `..' components and
+   double or trailing slashes.  Optionally resolves all symlink
+   components such that each component of the resulting path is *not*
+   a symbolic link. */
+Path canonPath(const Path & path, bool resolveSymlinks = false);
+
+/* Return the directory part of the given canonical path, i.e.,
+   everything before the final `/'.  If the path is the root or an
+   immediate child thereof (e.g., `/foo'), this means an empty string
+   is returned. */
+Path dirOf(const Path & path);
+
+/* Return the base name of the given canonical path, i.e., everything
+   following the final `/'. */
+string baseNameOf(const Path & path);
+
+/* Check whether 'path' is a descendant of 'dir'. */
+bool isInDir(const Path & path, const Path & dir);
+
+/* Check whether 'path' is equal to 'dir' or a descendant of 'dir'. */
+bool isDirOrInDir(const Path & path, const Path & dir);
+
+/* Get status of `path'. */
+struct stat lstat(const Path & path);
+
+/* Return true iff the given path exists. */
+bool pathExists(const Path & path);
+
+/* Read the contents (target) of a symbolic link.  The result is not
+   in any way canonicalised. */
+Path readLink(const Path & path);
+
+bool isLink(const Path & path);
+
+/* Read the contents of a directory.  The entries `.' and `..' are
+   removed. */
+struct DirEntry
+{
+    string name;
+    ino_t ino;
+    unsigned char type; // one of DT_*
+    DirEntry(const string & name, ino_t ino, unsigned char type)
+        : name(name), ino(ino), type(type) { }
+};
+
+typedef vector<DirEntry> DirEntries;
+
+DirEntries readDirectory(const Path & path);
+
+unsigned char getFileType(const Path & path);
+
+/* Read the contents of a file into a string. */
+string readFile(int fd);
+string readFile(const Path & path, bool drain = false);
+void readFile(const Path & path, Sink & sink);
+
+/* Write a string to a file. */
+void writeFile(const Path & path, const string & s, mode_t mode = 0666);
+
+void writeFile(const Path & path, Source & source, mode_t mode = 0666);
+
+/* Read a line from a file descriptor. */
+string readLine(int fd);
+
+/* Write a line to a file descriptor. */
+void writeLine(int fd, string s);
+
+/* Delete a path; i.e., in the case of a directory, it is deleted
+   recursively. It's not an error if the path does not exist. The
+   second variant returns the number of bytes and blocks freed. */
+void deletePath(const Path & path);
+
+void deletePath(const Path & path, unsigned long long & bytesFreed);
+
+/* Create a temporary directory. */
+Path createTempDir(const Path & tmpRoot = "", const Path & prefix = "nix",
+    bool includePid = true, bool useGlobalCounter = true, mode_t mode = 0755);
+
+std::string getUserName();
+
+/* Return $HOME or the user's home directory from /etc/passwd. */
+Path getHome();
+
+/* Return $XDG_CACHE_HOME or $HOME/.cache. */
+Path getCacheDir();
+
+/* Return $XDG_CONFIG_HOME or $HOME/.config. */
+Path getConfigDir();
+
+/* Return the directories to search for user configuration files */
+std::vector<Path> getConfigDirs();
+
+/* Return $XDG_DATA_HOME or $HOME/.local/share. */
+Path getDataDir();
+
+/* Create a directory and all its parents, if necessary.  Returns the
+   list of created directories, in order of creation. */
+Paths createDirs(const Path & path);
+
+/* Create a symlink. */
+void createSymlink(const Path & target, const Path & link);
+
+/* Atomically create or replace a symlink. */
+void replaceSymlink(const Path & target, const Path & link);
+
+
+/* Wrappers arount read()/write() that read/write exactly the
+   requested number of bytes. */
+void readFull(int fd, unsigned char * buf, size_t count);
+void writeFull(int fd, const unsigned char * buf, size_t count, bool allowInterrupts = true);
+void writeFull(int fd, const string & s, bool allowInterrupts = true);
+
+MakeError(EndOfFile, Error)
+
+
+/* Read a file descriptor until EOF occurs. */
+string drainFD(int fd, bool block = true);
+
+void drainFD(int fd, Sink & sink, bool block = true);
+
+
+/* Automatic cleanup of resources. */
+
+
+class AutoDelete
+{
+    Path path;
+    bool del;
+    bool recursive;
+public:
+    AutoDelete();
+    AutoDelete(const Path & p, bool recursive = true);
+    ~AutoDelete();
+    void cancel();
+    void reset(const Path & p, bool recursive = true);
+    operator Path() const { return path; }
+};
+
+
+class AutoCloseFD
+{
+    int fd;
+    void close();
+public:
+    AutoCloseFD();
+    AutoCloseFD(int fd);
+    AutoCloseFD(const AutoCloseFD & fd) = delete;
+    AutoCloseFD(AutoCloseFD&& fd);
+    ~AutoCloseFD();
+    AutoCloseFD& operator =(const AutoCloseFD & fd) = delete;
+    AutoCloseFD& operator =(AutoCloseFD&& fd);
+    int get() const;
+    explicit operator bool() const;
+    int release();
+};
+
+
+class Pipe
+{
+public:
+    AutoCloseFD readSide, writeSide;
+    void create();
+};
+
+
+struct DIRDeleter
+{
+    void operator()(DIR * dir) const {
+        closedir(dir);
+    }
+};
+
+typedef std::unique_ptr<DIR, DIRDeleter> AutoCloseDir;
+
+
+class Pid
+{
+    pid_t pid = -1;
+    bool separatePG = false;
+    int killSignal = SIGKILL;
+public:
+    Pid();
+    Pid(pid_t pid);
+    ~Pid();
+    void operator =(pid_t pid);
+    operator pid_t();
+    int kill();
+    int wait();
+
+    void setSeparatePG(bool separatePG);
+    void setKillSignal(int signal);
+    pid_t release();
+};
+
+
+/* Kill all processes running under the specified uid by sending them
+   a SIGKILL. */
+void killUser(uid_t uid);
+
+
+/* Fork a process that runs the given function, and return the child
+   pid to the caller. */
+struct ProcessOptions
+{
+    string errorPrefix = "error: ";
+    bool dieWithParent = true;
+    bool runExitHandlers = false;
+    bool allowVfork = true;
+};
+
+pid_t startProcess(std::function<void()> fun, const ProcessOptions & options = ProcessOptions());
+
+
+/* Run a program and return its stdout in a string (i.e., like the
+   shell backtick operator). */
+string runProgram(Path program, bool searchPath = false,
+    const Strings & args = Strings(),
+    const std::optional<std::string> & input = {});
+
+struct RunOptions
+{
+    std::optional<uid_t> uid;
+    std::optional<uid_t> gid;
+    std::optional<Path> chdir;
+    std::optional<std::map<std::string, std::string>> environment;
+    Path program;
+    bool searchPath = true;
+    Strings args;
+    std::optional<std::string> input;
+    Source * standardIn = nullptr;
+    Sink * standardOut = nullptr;
+    bool mergeStderrToStdout = false;
+    bool _killStderr = false;
+
+    RunOptions(const Path & program, const Strings & args)
+        : program(program), args(args) { };
+
+    RunOptions & killStderr(bool v) { _killStderr = true; return *this; }
+};
+
+std::pair<int, std::string> runProgram(const RunOptions & options);
+
+void runProgram2(const RunOptions & options);
+
+
+class ExecError : public Error
+{
+public:
+    int status;
+
+    template<typename... Args>
+    ExecError(int status, Args... args)
+        : Error(args...), status(status)
+    { }
+};
+
+/* Convert a list of strings to a null-terminated vector of char
+   *'s. The result must not be accessed beyond the lifetime of the
+   list of strings. */
+std::vector<char *> stringsToCharPtrs(const Strings & ss);
+
+/* Close all file descriptors except those listed in the given set.
+   Good practice in child processes. */
+void closeMostFDs(const set<int> & exceptions);
+
+/* Set the close-on-exec flag for the given file descriptor. */
+void closeOnExec(int fd);
+
+
+/* User interruption. */
+
+extern bool _isInterrupted;
+
+extern thread_local std::function<bool()> interruptCheck;
+
+void setInterruptThrown();
+
+void _interrupted();
+
+void inline checkInterrupt()
+{
+    if (_isInterrupted || (interruptCheck && interruptCheck()))
+        _interrupted();
+}
+
+MakeError(Interrupted, BaseError)
+
+
+MakeError(FormatError, Error)
+
+
+/* String tokenizer. */
+template<class C> C tokenizeString(const string & s, const string & separators = " \t\n\r");
+
+
+/* Concatenate the given strings with a separator between the
+   elements. */
+string concatStringsSep(const string & sep, const Strings & ss);
+string concatStringsSep(const string & sep, const StringSet & ss);
+
+
+/* Remove trailing whitespace from a string. */
+string chomp(const string & s);
+
+
+/* Remove whitespace from the start and end of a string. */
+string trim(const string & s, const string & whitespace = " \n\r\t");
+
+
+/* Replace all occurrences of a string inside another string. */
+string replaceStrings(const std::string & s,
+    const std::string & from, const std::string & to);
+
+
+/* Convert the exit status of a child as returned by wait() into an
+   error string. */
+string statusToString(int status);
+
+bool statusOk(int status);
+
+
+/* Parse a string into an integer. */
+template<class N> bool string2Int(const string & s, N & n)
+{
+    if (string(s, 0, 1) == "-" && !std::numeric_limits<N>::is_signed)
+        return false;
+    std::istringstream str(s);
+    str >> n;
+    return str && str.get() == EOF;
+}
+
+/* Parse a string into a float. */
+template<class N> bool string2Float(const string & s, N & n)
+{
+    std::istringstream str(s);
+    str >> n;
+    return str && str.get() == EOF;
+}
+
+
+/* Return true iff `s' starts with `prefix'. */
+bool hasPrefix(const string & s, const string & prefix);
+
+
+/* Return true iff `s' ends in `suffix'. */
+bool hasSuffix(const string & s, const string & suffix);
+
+
+/* Convert a string to lower case. */
+std::string toLower(const std::string & s);
+
+
+/* Escape a string as a shell word. */
+std::string shellEscape(const std::string & s);
+
+
+/* Exception handling in destructors: print an error message, then
+   ignore the exception. */
+void ignoreException();
+
+
+/* Some ANSI escape sequences. */
+#define ANSI_NORMAL "\e[0m"
+#define ANSI_BOLD "\e[1m"
+#define ANSI_FAINT "\e[2m"
+#define ANSI_RED "\e[31;1m"
+#define ANSI_GREEN "\e[32;1m"
+#define ANSI_BLUE "\e[34;1m"
+
+
+/* Truncate a string to 'width' printable characters. If 'filterAll'
+   is true, all ANSI escape sequences are filtered out. Otherwise,
+   some escape sequences (such as colour setting) are copied but not
+   included in the character count. Also, tabs are expanded to
+   spaces. */
+std::string filterANSIEscapes(const std::string & s,
+    bool filterAll = false,
+    unsigned int width = std::numeric_limits<unsigned int>::max());
+
+
+/* Base64 encoding/decoding. */
+string base64Encode(const string & s);
+string base64Decode(const string & s);
+
+
+/* Get a value for the specified key from an associate container, or a
+   default value if the key doesn't exist. */
+template <class T>
+string get(const T & map, const string & key, const string & def = "")
+{
+    auto i = map.find(key);
+    return i == map.end() ? def : i->second;
+}
+
+
+/* A callback is a wrapper around a lambda that accepts a valid of
+   type T or an exception. (We abuse std::future<T> to pass the value or
+   exception.) */
+template<typename T>
+class Callback
+{
+    std::function<void(std::future<T>)> fun;
+    std::atomic_flag done = ATOMIC_FLAG_INIT;
+
+public:
+
+    Callback(std::function<void(std::future<T>)> fun) : fun(fun) { }
+
+    Callback(Callback && callback) : fun(std::move(callback.fun))
+    {
+        auto prev = callback.done.test_and_set();
+        if (prev) done.test_and_set();
+    }
+
+    void operator()(T && t) noexcept
+    {
+        auto prev = done.test_and_set();
+        assert(!prev);
+        std::promise<T> promise;
+        promise.set_value(std::move(t));
+        fun(promise.get_future());
+    }
+
+    void rethrow(const std::exception_ptr & exc = std::current_exception()) noexcept
+    {
+        auto prev = done.test_and_set();
+        assert(!prev);
+        std::promise<T> promise;
+        promise.set_exception(exc);
+        fun(promise.get_future());
+    }
+};
+
+
+/* Start a thread that handles various signals. Also block those signals
+   on the current thread (and thus any threads created by it). */
+void startSignalHandlerThread();
+
+/* Restore default signal handling. */
+void restoreSignals();
+
+struct InterruptCallback
+{
+    virtual ~InterruptCallback() { };
+};
+
+/* Register a function that gets called on SIGINT (in a non-signal
+   context). */
+std::unique_ptr<InterruptCallback> createInterruptCallback(
+    std::function<void()> callback);
+
+void triggerInterrupt();
+
+/* A RAII class that causes the current thread to receive SIGUSR1 when
+   the signal handler thread receives SIGINT. That is, this allows
+   SIGINT to be multiplexed to multiple threads. */
+struct ReceiveInterrupts
+{
+    pthread_t target;
+    std::unique_ptr<InterruptCallback> callback;
+
+    ReceiveInterrupts()
+        : target(pthread_self())
+        , callback(createInterruptCallback([&]() { pthread_kill(target, SIGUSR1); }))
+    { }
+};
+
+
+
+/* A RAII helper that increments a counter on construction and
+   decrements it on destruction. */
+template<typename T>
+struct MaintainCount
+{
+    T & counter;
+    long delta;
+    MaintainCount(T & counter, long delta = 1) : counter(counter), delta(delta) { counter += delta; }
+    ~MaintainCount() { counter -= delta; }
+};
+
+
+/* Return the number of rows and columns of the terminal. */
+std::pair<unsigned short, unsigned short> getWindowSize();
+
+
+/* Used in various places. */
+typedef std::function<bool(const Path & path)> PathFilter;
+
+extern PathFilter defaultPathFilter;
+
+
+}

third_party/nix/src/libutil/xml-writer.cc

@@ -0,0 +1,94 @@
+#include <assert.h>
+
+#include "xml-writer.hh"
+
+
+namespace nix {
+    
+
+XMLWriter::XMLWriter(bool indent, std::ostream & output)
+    : output(output), indent(indent)
+{
+    output << "<?xml version='1.0' encoding='utf-8'?>" << std::endl;
+    closed = false;
+}
+
+
+XMLWriter::~XMLWriter()
+{
+    close();
+}
+
+
+void XMLWriter::close()
+{
+    if (closed) return;
+    while (!pendingElems.empty()) closeElement();
+    closed = true;
+}
+
+
+void XMLWriter::indent_(size_t depth)
+{
+    if (!indent) return;
+    output << string(depth * 2, ' ');
+}
+
+
+void XMLWriter::openElement(const string & name,
+    const XMLAttrs & attrs)
+{
+    assert(!closed);
+    indent_(pendingElems.size());
+    output << "<" << name;
+    writeAttrs(attrs);
+    output << ">";
+    if (indent) output << std::endl;
+    pendingElems.push_back(name);
+}
+
+
+void XMLWriter::closeElement()
+{
+    assert(!pendingElems.empty());
+    indent_(pendingElems.size() - 1);
+    output << "</" << pendingElems.back() << ">";
+    if (indent) output << std::endl;
+    pendingElems.pop_back();
+    if (pendingElems.empty()) closed = true;
+}
+
+
+void XMLWriter::writeEmptyElement(const string & name,
+    const XMLAttrs & attrs)
+{
+    assert(!closed);
+    indent_(pendingElems.size());
+    output << "<" << name;
+    writeAttrs(attrs);
+    output << " />";
+    if (indent) output << std::endl;
+}
+
+
+void XMLWriter::writeAttrs(const XMLAttrs & attrs)
+{
+    for (auto & i : attrs) {
+        output << " " << i.first << "=\"";
+        for (size_t j = 0; j < i.second.size(); ++j) {
+            char c = i.second[j];
+            if (c == '"') output << "&quot;";
+            else if (c == '<') output << "&lt;";
+            else if (c == '>') output << "&gt;";
+            else if (c == '&') output << "&amp;";
+            /* Escape newlines to prevent attribute normalisation (see
+               XML spec, section 3.3.3. */
+            else if (c == '\n') output << "&#xA;";
+            else output << c;
+        }
+        output << "\"";
+    }
+}
+
+
+}

third_party/nix/src/libutil/xml-writer.hh

@@ -0,0 +1,69 @@
+#pragma once
+
+#include <iostream>
+#include <string>
+#include <list>
+#include <map>
+
+
+namespace nix {
+
+using std::string;
+using std::map;
+using std::list;
+
+
+typedef map<string, string> XMLAttrs;
+
+
+class XMLWriter
+{
+private:
+
+    std::ostream & output;
+
+    bool indent;
+    bool closed;
+
+    list<string> pendingElems;
+
+public:
+
+    XMLWriter(bool indent, std::ostream & output);
+    ~XMLWriter();
+
+    void close();
+
+    void openElement(const string & name,
+        const XMLAttrs & attrs = XMLAttrs());
+    void closeElement();
+
+    void writeEmptyElement(const string & name,
+        const XMLAttrs & attrs = XMLAttrs());
+
+private:
+    void writeAttrs(const XMLAttrs & attrs);
+
+    void indent_(size_t depth);
+};
+
+
+class XMLOpenElement
+{
+private:
+    XMLWriter & writer;
+public:
+    XMLOpenElement(XMLWriter & writer, const string & name,
+        const XMLAttrs & attrs = XMLAttrs())
+        : writer(writer)
+    {
+        writer.openElement(name, attrs);
+    }
+    ~XMLOpenElement()
+    {
+        writer.closeElement();
+    }
+};
+
+
+}