copyPaths(): Use queryValidPaths() to reduce SSH latency

src/build-remote/build-remote.cc

@@ -252,10 +252,10 @@ connected:
         string line;
         if (!getline(cin, line))
             throw Error("hook caller didn't send inputs");
-        auto inputs = tokenizeString<std::list<string>>(line);
+        auto inputs = tokenizeString<PathSet>(line);
         if (!getline(cin, line))
             throw Error("hook caller didn't send outputs");
-        auto outputs = tokenizeString<Strings>(line);
+        auto outputs = tokenizeString<PathSet>(line);
         AutoCloseFD uploadLock = openLockFile(currentLoad + "/" + hostName + ".upload-lock", true);
         auto old = signal(SIGALRM, handleAlarm);
         alarm(15 * 60);
@@ -269,11 +269,15 @@ connected:
         printError("building ‘%s’ on ‘%s’", drvPath, hostName);
         sshStore->buildDerivation(drvPath, readDerivation(drvPath));
 
-        std::remove_if(outputs.begin(), outputs.end(), [=](const Path & path) { return store->isValidPath(path); });
-        if (!outputs.empty()) {
-            setenv("NIX_HELD_LOCKS", concatStringsSep(" ", outputs).c_str(), 1); /* FIXME: ugly */
-            copyPaths(ref<Store>(sshStore), store, outputs);
+        PathSet missing;
+        for (auto & path : outputs)
+            if (!store->isValidPath(path)) missing.insert(path);
+
+        if (!missing.empty()) {
+            setenv("NIX_HELD_LOCKS", concatStringsSep(" ", missing).c_str(), 1); /* FIXME: ugly */
+            copyPaths(ref<Store>(sshStore), store, missing);
         }
+
         return;
     });
 }

src/libstore/legacy-ssh-store.cc

@@ -226,6 +226,19 @@ struct LegacySSHStore : public Store
         out.insert(res.begin(), res.end());
     }
 
+    PathSet queryValidPaths(const PathSet & paths, bool maybeSubstitute = false) override
+    {
+        auto conn(connections->get());
+
+        conn->to
+            << cmdQueryValidPaths
+            << false // lock
+            << maybeSubstitute
+            << paths;
+        conn->to.flush();
+
+        return readStorePaths<PathSet>(*this, conn->from);
+    }
 };
 
 static RegisterStoreImplementation regStore([](

src/libstore/local-store.cc

@@ -669,7 +669,7 @@ bool LocalStore::isValidPathUncached(const Path & path)
 }
 
 
-PathSet LocalStore::queryValidPaths(const PathSet & paths)
+PathSet LocalStore::queryValidPaths(const PathSet & paths, bool maybeSubstitute)
 {
     PathSet res;
     for (auto & i : paths)

src/libstore/local-store.hh

@@ -99,7 +99,7 @@ public:
 
     bool isValidPathUncached(const Path & path) override;
 
-    PathSet queryValidPaths(const PathSet & paths) override;
+    PathSet queryValidPaths(const PathSet & paths, bool maybeSubstitute = false) override;
 
     PathSet queryAllValidPaths() override;
 

src/libstore/remote-store.cc

@@ -187,7 +187,7 @@ bool RemoteStore::isValidPathUncached(const Path & path)
 }
 
 
-PathSet RemoteStore::queryValidPaths(const PathSet & paths)
+PathSet RemoteStore::queryValidPaths(const PathSet & paths, bool maybeSubstitute)
 {
     auto conn(connections->get());
     if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 12) {

src/libstore/remote-store.hh

@@ -28,7 +28,7 @@ public:
 
     bool isValidPathUncached(const Path & path) override;
 
-    PathSet queryValidPaths(const PathSet & paths) override;
+    PathSet queryValidPaths(const PathSet & paths, bool maybeSubstitute = false) override;
 
     PathSet queryAllValidPaths() override;
 

src/libstore/store-api.cc

@@ -377,7 +377,7 @@ void Store::queryPathInfo(const Path & storePath,
 }
 
 
-PathSet Store::queryValidPaths(const PathSet & paths)
+PathSet Store::queryValidPaths(const PathSet & paths, bool maybeSubstitute)
 {
     struct State
     {
@@ -550,6 +550,8 @@ void copyClosure(ref<Store> srcStore, ref<Store> dstStore,
     for (auto & path : storePaths)
         srcStore->computeFSClosure(path, closure);
 
+    // FIXME: use copyStorePaths()
+
     PathSet valid = dstStore->queryValidPaths(closure);
 
     if (valid.size() == closure.size()) return;
@@ -791,35 +793,22 @@ std::list<ref<Store>> getDefaultSubstituters()
 }
 
 
-void copyPaths(ref<Store> from, ref<Store> to, const Paths & storePaths, bool substitute)
+void copyPaths(ref<Store> from, ref<Store> to, const PathSet & storePaths, bool substitute)
 {
-    if (substitute) {
-        /* Filter out .drv files (we don't want to build anything). */
-        PathSet paths2;
+    PathSet valid = to->queryValidPaths(storePaths, substitute);
+
+    PathSet missing;
     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());
-            }
-    }
+        if (!valid.count(path)) missing.insert(path);
 
     std::string copiedLabel = "copied";
 
-    logger->setExpected(copiedLabel, storePaths.size());
+    logger->setExpected(copiedLabel, missing.size());
 
     ThreadPool pool;
 
     processGraph<Path>(pool,
-        PathSet(storePaths.begin(), storePaths.end()),
+        PathSet(missing.begin(), missing.end()),
 
         [&](const Path & storePath) {
             if (to->isValidPath(storePath)) return PathSet();

src/libstore/store-api.hh

@@ -324,8 +324,10 @@ protected:
 
 public:
 
-    /* Query which of the given paths is valid. */
-    virtual PathSet queryValidPaths(const PathSet & paths);
+    /* Query which of the given paths is valid. Optionally, try to
+       substitute missing paths. */
+    virtual PathSet queryValidPaths(const PathSet & paths,
+        bool maybeSubstitute = false);
 
     /* Query the set of all valid paths. Note that for some store
        backends, the name part of store paths may be omitted
@@ -653,7 +655,7 @@ ref<Store> openStore(const std::string & uri = getEnv("NIX_REMOTE"));
 ref<Store> openStore(const std::string & uri, const Store::Params & params);
 
 
-void copyPaths(ref<Store> from, ref<Store> to, const Paths & storePaths, bool substitute = false);
+void copyPaths(ref<Store> from, ref<Store> to, const PathSet & storePaths, bool substitute = false);
 
 enum StoreType {
     tDaemon,

src/nix-copy-closure/nix-copy-closure.cc

@@ -58,6 +58,6 @@ int main(int argc, char ** argv)
         PathSet closure;
         from->computeFSClosure(storePaths2, closure, false, includeOutputs);
 
-        copyPaths(from, to, Paths(closure.begin(), closure.end()), useSubstitutes);
+        copyPaths(from, to, closure, useSubstitutes);
     });
 }

src/nix/copy.cc

@@ -46,7 +46,7 @@ struct CmdCopy : StorePathsCommand
         ref<Store> srcStore = srcUri.empty() ? store : openStore(srcUri);
         ref<Store> dstStore = dstUri.empty() ? store : openStore(dstUri);
 
-        copyPaths(srcStore, dstStore, storePaths);
+        copyPaths(srcStore, dstStore, PathSet(storePaths.begin(), storePaths.end()));
     }
 };