10 files changed, 42 insertions, 16 deletions
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 5c8b31cf6a6b..e300292e96cf 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1065,7 +1065,7 @@ static string makeValidityRegistration(const PathSet & paths,
     for (PathSet::iterator i = paths.begin(); i != paths.end(); ++i) {
         s += *i + "\n";
 
-        Path deriver = showDerivers ? queryDeriver(noTxn, *i) : "";
+        Path deriver = showDerivers ? store->queryDeriver(*i) : "";
         s += deriver + "\n";
 
         PathSet references;
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 2ad52d8bf4ea..3699b234402f 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -482,7 +482,7 @@ void LocalStore::collectGarbage(GCAction action, const PathSet & pathsToDelete,
             /* Note that the deriver need not be valid (e.g., if we
                previously ran the collector with `gcKeepDerivations'
                turned off). */
-            Path deriver = queryDeriver(noTxn, *i);
+            Path deriver = store->queryDeriver(*i);
             if (deriver != "" && store->isValidPath(deriver))
                 computeFSClosure(deriver, livePaths);
         }
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index cd8bc1a3394f..1165335125b9 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -399,7 +399,7 @@ void setDeriver(const Transaction & txn, const Path & storePath,
 }
 
 
-Path queryDeriver(const Transaction & txn, const Path & storePath)
+static Path queryDeriver(const Transaction & txn, const Path & storePath)
 {
     if (!isRealisablePath(txn, storePath))
         throw Error(format("path `%1%' is not valid") % storePath);
@@ -411,6 +411,12 @@ Path queryDeriver(const Transaction & txn, const Path & storePath)
 }
 
 
+Path LocalStore::queryDeriver(const Path & path)
+{
+    return nix::queryDeriver(noTxn, path);
+}
+
+
 const int substituteVersion = 2;
 
 
@@ -756,7 +762,7 @@ void LocalStore::exportPath(const Path & path, bool sign,
     nix::queryReferences(txn, path, references);
     writeStringSet(references, hashAndWriteSink);
 
-    Path deriver = queryDeriver(txn, path);
+    Path deriver = nix::queryDeriver(txn, path);
     writeString(deriver, hashAndWriteSink);
 
     if (sign) {
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index 099be2efcd1a..7c5cd2668405 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -49,6 +49,8 @@ public:
 
     void queryReferrers(const Path & path, PathSet & referrers);
 
+    Path queryDeriver(const Path & path);
+    
     Path addToStore(const Path & srcPath, bool fixed = false,
         bool recursive = false, string hashAlgo = "",
         PathFilter & filter = defaultPathFilter);
@@ -136,10 +138,6 @@ void setReferences(const Transaction & txn, const Path & path,
 void setDeriver(const Transaction & txn, const Path & path,
     const Path & deriver);
 
-/* Query the deriver of a store path.  Return the empty string if no
-   deriver has been set. */
-Path queryDeriver(const Transaction & txn, const Path & path);
-
 /* Delete a value from the nixStore directory. */
 void deleteFromStore(const Path & path, unsigned long long & bytesFreed);
 
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 449a4c448f0f..820bf66ad99a 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -212,6 +212,15 @@ void RemoteStore::queryReferrers(const Path & path,
 }
 
 
+Path RemoteStore::queryDeriver(const Path & path)
+{
+    writeInt(wopQueryDeriver, to);
+    writeString(path, to);
+    processStderr();
+    return readStorePath(from);
+}
+
+
 Path RemoteStore::addToStore(const Path & _srcPath, bool fixed,
     bool recursive, string hashAlgo, PathFilter & filter)
 {
@@ -224,8 +233,7 @@ Path RemoteStore::addToStore(const Path & _srcPath, bool fixed,
     writeString(hashAlgo, to);
     dumpPath(srcPath, to, filter);
     processStderr();
-    Path path = readStorePath(from);
-    return path;
+    return readStorePath(from);
 }
 
 
@@ -238,8 +246,7 @@ Path RemoteStore::addTextToStore(const string & suffix, const string & s,
     writeStringSet(references, to);
     
     processStderr();
-    Path path = readStorePath(from);
-    return path;
+    return readStorePath(from);
 }
 
 
@@ -261,8 +268,7 @@ Path RemoteStore::importPath(bool requireSignature, Source & source)
        anyway. */
     
     processStderr(0, &source);
-    Path path = readStorePath(from);
-    return path;
+    return readStorePath(from);
 }
 
 
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index 19af8c0bed7f..29b4a88f9a4b 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -37,6 +37,8 @@ public:
 
     void queryReferrers(const Path & path, PathSet & referrers);
 
+    Path queryDeriver(const Path & path);
+    
     Path addToStore(const Path & srcPath, bool fixed = false,
         bool recursive = false, string hashAlgo = "",
         PathFilter & filter = defaultPathFilter);
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 8531eb040496..01b561e9d496 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -77,6 +77,10 @@ public:
     virtual void queryReferrers(const Path & path,
         PathSet & referrers) = 0;
 
+    /* Query the deriver of a store path.  Return the empty string if
+       no deriver has been set. */
+    virtual Path queryDeriver(const Path & path) = 0;
+
     /* Copy the contents of a path to the store and register the
        validity the resulting path.  The resulting path is returned.
        If `fixed' is true, then the output of a fixed-output
diff --git a/src/libstore/worker-protocol.hh b/src/libstore/worker-protocol.hh
index 0126c8d59db9..4a2e8b6942cf 100644
--- a/src/libstore/worker-protocol.hh
+++ b/src/libstore/worker-protocol.hh
@@ -28,6 +28,7 @@ typedef enum {
     wopCollectGarbage,
     wopExportPath,
     wopImportPath,
+    wopQueryDeriver,
 } WorkerOp;
 
 
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 88acc79aa162..c600a5b9a7dc 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -46,7 +46,7 @@ static Path fixPath(Path path)
 static Path useDeriver(Path path)
 {       
     if (!isDerivation(path)) {
-        path = queryDeriver(noTxn, path);
+        path = store->queryDeriver(path);
         if (path == "")
             throw Error(format("deriver of path `%1%' is not known") % path);
     }
@@ -330,7 +330,7 @@ static void opQuery(Strings opFlags, Strings opArgs)
             for (Strings::iterator i = opArgs.begin();
                  i != opArgs.end(); ++i)
             {
-                Path deriver = queryDeriver(noTxn, fixPath(*i));
+                Path deriver = store->queryDeriver(fixPath(*i));
                 cout << format("%1%\n") %
                     (deriver == "" ? "unknown-deriver" : deriver);
             }
diff --git a/src/nix-worker/nix-worker.cc b/src/nix-worker/nix-worker.cc
index 078362e9c37b..6ddf01bd017d 100644
--- a/src/nix-worker/nix-worker.cc
+++ b/src/nix-worker/nix-worker.cc
@@ -277,6 +277,15 @@ static void performOp(Source & from, Sink & to, unsigned int op)
         break;
     }
 
+    case wopQueryDeriver: {
+        Path path = readStorePath(from);
+        startWork();
+        Path deriver = store->queryDeriver(path);
+        stopWork();
+        writeString(deriver, to);
+        break;
+    }
+
     case wopAddToStore: {
         /* !!! uberquick hack */
         string baseName = readString(from);