nix-copy-closure: Implement in C++.

Tests fail currently because the database is not given proper hashes in the VM

src/libstore/ssh-store.cc

@@ -39,6 +39,8 @@ private:
     string uri;
 
     Path key;
+
+    bool compress;
 };
 
 SSHStore::SSHStore(string uri, const Params & params, size_t maxConnections)
@@ -48,6 +50,7 @@ SSHStore::SSHStore(string uri, const Params & params, size_t maxConnections)
     , socketPath((Path) tmpDir + "/ssh.sock")
     , uri(std::move(uri))
     , key(get(params, "ssh-key", ""))
+    , compress(get(params, "compress", "") == "true")
 {
     /* open a connection and perform the handshake to verify all is well */
     connections->get();
@@ -90,11 +93,12 @@ ref<FSAccessor> SSHStore::getFSAccessor()
 ref<RemoteStore::Connection> SSHStore::openConnection()
 {
     if ((pid_t) sshMaster == -1) {
+        auto flags = compress ? "-NMCS" : "-NMS";
         sshMaster = startProcess([&]() {
             if (key.empty())
-                execlp("ssh", "ssh", "-N", "-M", "-S", socketPath.c_str(), uri.c_str(), NULL);
+                execlp("ssh", "ssh", flags, socketPath.c_str(), uri.c_str(), NULL);
             else
-                execlp("ssh", "ssh", "-N", "-M", "-S", socketPath.c_str(), "-i", key.c_str(), uri.c_str(), NULL);
+                execlp("ssh", "ssh", flags, socketPath.c_str(), "-i", key.c_str(), uri.c_str(), NULL);
             throw SysError("starting ssh master");
         });
     }

src/libstore/store-api.cc

@@ -4,6 +4,7 @@
 #include "util.hh"
 #include "nar-info-disk-cache.hh"
 #include "thread-pool.hh"
+#include "derivations.hh"
 
 #include <future>
 
@@ -699,8 +700,27 @@ std::list<ref<Store>> getDefaultSubstituters()
 }
 
 
-void copyPaths(ref<Store> from, ref<Store> to, const Paths & storePaths)
+void copyPaths(ref<Store> from, ref<Store> to, const Paths & storePaths, bool substitute)
 {
+    if (substitute) {
+        /* Filter out .drv files (we don't want to build anything). */
+        PathSet paths2;
+        for (auto & path : storePaths)
+            if (!isDerivation(path)) paths2.insert(path);
+        unsigned long long downloadSize, narSize;
+        PathSet willBuild, willSubstitute, unknown;
+        to->queryMissing(PathSet(paths2.begin(), paths2.end()),
+            willBuild, willSubstitute, unknown, downloadSize, narSize);
+        /* FIXME: should use ensurePath(), but it only
+           does one path at a time. */
+        if (!willSubstitute.empty())
+            try {
+                to->buildPaths(willSubstitute);
+            } catch (Error & e) {
+                printMsg(lvlError, format("warning: %1%") % e.msg());
+            }
+    }
+
     std::string copiedLabel = "copied";
 
     logger->setExpected(copiedLabel, storePaths.size());

src/libstore/store-api.hh

@@ -625,7 +625,7 @@ void removeTempRoots();
 ref<Store> openStore(const std::string & uri = getEnv("NIX_REMOTE"));
 
 
-void copyPaths(ref<Store> from, ref<Store> to, const Paths & storePaths);
+void copyPaths(ref<Store> from, ref<Store> to, const Paths & storePaths, bool substitute = false);
 
 enum StoreType {
     tDaemon,