Add a function queryValidPaths()

queryValidPaths() combines multiple calls to isValidPath() in one.
This matters when using the Nix daemon because it reduces latency.
For instance, on "nix-env -qas \*" it reduces execution time from 5.7s
to 4.7s (which is indistinguishable from the non-daemon case).

src/libstore/local-store.cc

@@ -744,6 +744,15 @@ bool LocalStore::isValidPath(const Path & path)
 }
 
 
+PathSet LocalStore::queryValidPaths(const PathSet & paths)
+{
+    PathSet res;
+    foreach (PathSet::const_iterator, i, paths)
+        if (isValidPath(*i)) res.insert(*i);
+    return res;
+}
+
+
 PathSet LocalStore::queryAllValidPaths()
 {
     SQLiteStmt stmt;

src/libstore/local-store.hh

@@ -99,6 +99,8 @@ public:
     
     bool isValidPath(const Path & path);
 
+    PathSet queryValidPaths(const PathSet & paths);
+    
     PathSet queryAllValidPaths();
     
     ValidPathInfo queryPathInfo(const Path & path);

src/libstore/remote-store.cc

@@ -217,6 +217,23 @@ bool RemoteStore::isValidPath(const Path & path)
 }
 
 
+PathSet RemoteStore::queryValidPaths(const PathSet & paths)
+{
+    if (GET_PROTOCOL_MINOR(daemonVersion) < 12) {
+        PathSet res;
+        foreach (PathSet::const_iterator, i, paths)
+            if (isValidPath(*i)) res.insert(*i);
+        return res;
+    } else {
+        openConnection();
+        writeInt(wopQueryValidPaths, to);
+        writeStrings(paths, to);
+        processStderr();
+        return readStorePaths<PathSet>(from);
+    }
+}
+
+
 PathSet RemoteStore::queryAllValidPaths()
 {
     openConnection();

src/libstore/remote-store.hh

@@ -27,6 +27,8 @@ public:
     
     bool isValidPath(const Path & path);
 
+    PathSet queryValidPaths(const PathSet & paths);
+    
     PathSet queryAllValidPaths();
     
     ValidPathInfo queryPathInfo(const Path & path);

src/libstore/store-api.hh

@@ -113,6 +113,9 @@ public:
     /* Check whether a path is valid. */ 
     virtual bool isValidPath(const Path & path) = 0;
 
+    /* Query which of the given paths is valid. */
+    virtual PathSet queryValidPaths(const PathSet & paths) = 0;
+
     /* Query the set of all valid paths. */
     virtual PathSet queryAllValidPaths() = 0;
 

src/libstore/worker-protocol.hh

@@ -41,6 +41,7 @@ typedef enum {
     wopImportPaths = 27,
     wopQueryDerivationOutputNames = 28,
     wopQuerySubstitutablePathInfos = 29,
+    wopQueryValidPaths = 30,
 } WorkerOp;