snix/third_party/nix/src/libutil/util.hh

#pragma once

#include <cstdio>
#include <functional>
#include <future>
#include <limits>
#include <map>
#include <optional>
#include <sstream>

#include <absl/strings/string_view.h>
#include <dirent.h>
#include <signal.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include "libutil/types.hh"

namespace nix {

struct Sink;
struct Source;

/* The system for which Nix is compiled. */
extern const std::string nativeSystem;

/* Return an environment variable. */
std::optional<std::string> getEnv(const std::string& key);

/* 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(absl::string_view path);

/* Return the base name of the given canonical path, i.e., everything
   following the final `/'. */
std::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 {
  std::string name;
  ino_t ino;
  unsigned char type;  // one of DT_*
  DirEntry(const std::string& name, ino_t ino, unsigned char type)
      : name(name), ino(ino), type(type) {}
};

typedef std::vector<DirEntry> DirEntries;

DirEntries readDirectory(const Path& path);

unsigned char getFileType(const Path& path);

/* Read the contents of a file into a string. */
std::string readFile(int fd);
std::string readFile(absl::string_view path, bool drain = false);
void readFile(absl::string_view path, Sink& sink);

/* Write a string to a file. */
void writeFile(const Path& path, const std::string& s, mode_t mode = 0666);

void writeFile(const Path& path, Source& source, mode_t mode = 0666);

/* Read a line from a file descriptor. */
std::string readLine(int fd);

/* Write a line to a file descriptor. */
void writeLine(int fd, std::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 std::string& s, bool allowInterrupts = true);

MakeError(EndOfFile, Error);

/* Read a file descriptor until EOF occurs. */
std::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();
  explicit AutoDelete(Path p, bool recursive = true);
  ~AutoDelete();
  void cancel();
  void reset(const Path& p, bool recursive = true);
  explicit operator Path() const { return path; }
};

class AutoCloseFD {
  int fd;
  void close();

 public:
  AutoCloseFD();
  explicit AutoCloseFD(int fd);
  AutoCloseFD(const AutoCloseFD& fd) = delete;
  AutoCloseFD(AutoCloseFD&& that);
  ~AutoCloseFD();
  AutoCloseFD& operator=(const AutoCloseFD& fd) = delete;
  AutoCloseFD& operator=(AutoCloseFD&& that);
  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); }
};

using AutoCloseDir = std::unique_ptr<DIR, DIRDeleter>;

class Pid {
  pid_t pid = -1;
  bool separatePG = false;
  int killSignal = SIGKILL;

 public:
  Pid();
  explicit Pid(pid_t pid);
  ~Pid();
  void operator=(pid_t pid);
  explicit operator pid_t();
  int kill();
  int wait();

  void setSeparatePG(bool separatePG);
  void setKillSignal(int signal);
  pid_t release();

  friend bool operator==(const Pid& lhs, const Pid& rhs) {
    return lhs.pid == rhs.pid;
  }

  friend bool operator!=(const Pid& lhs, const Pid& rhs) {
    return !(lhs == rhs);
  }
};

/* 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 {
  std::string errorPrefix = "error: ";
  bool dieWithParent = true;
  bool runExitHandlers = false;
};

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). */
std::string runProgram(const 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>
  explicit 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 std::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);

/* Concatenate the given strings with a separator between the
   elements. */
std::string concatStringsSep(const std::string& sep, const Strings& ss);
std::string concatStringsSep(const std::string& sep, const StringSet& ss);

/* Replace all occurrences of a string inside another string. */
std::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. */
std::string statusToString(int status);

bool statusOk(int status);

/* Parse a string into a float. */
template <class N>
bool string2Float(const std::string& s, N& n) {
  std::istringstream str(s);
  str >> n;
  return str && str.get() == EOF;
}

/* 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());

/* Get a value for the specified key from an associate container, or a
   default value if the key doesn't exist. */
template <class T>
std::string get(const T& map, const std::string& key,
                const std::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:
  explicit 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();
    }
  }

// The unused-variable assert is disabled in this block because the
// `prev` variables are only used in debug mode (in the asserts).
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunused-variable"

  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());
  }

#pragma clang diagnostic pop
};

/* 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(
    const 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;
  explicit 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. */
using PathFilter = std::function<bool(const Path&)>;

extern PathFilter defaultPathFilter;

}  // namespace nix