build-remote.pl: Use ‘nix-store --serve’ on the remote side

This makes things more efficient (we don't need to use an SSH master
connection, and we only start a single remote process) and gets rid of
locking issues (the remote nix-store process will keep inputs and
outputs locked as long as they're needed).

It also makes it more or less secure to connect directly to the root
account on the build machine, using a forced command
(e.g. ‘command="nix-store --serve --write"’). This bypasses the Nix
daemon and is therefore more efficient.

Also, don't call nix-store to import the output paths.

2 files changed, 34 insertions, 5 deletions

diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index f31eb0e29a36..0196c2fc1873 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -928,7 +928,6 @@ static void opServe(Strings opFlags, Strings opArgs)
                 }
 
                 writeStrings(store->queryValidPaths(paths), out);
-                out.flush();
                 break;
             }
 
@@ -947,17 +946,15 @@ static void opServe(Strings opFlags, Strings opArgs)
                     writeLongLong(info.narSize, out);
                 }
                 writeString("", out);
-                out.flush();
                 break;
             }
 
             case cmdDumpStorePath:
                 dumpPath(readStorePath(in), out);
-                out.flush();
                 break;
 
             case cmdImportPaths: {
-                if (!writeAllowed) throw Error("importing paths not allowed");
+                if (!writeAllowed) throw Error("importing paths is not allowed");
                 string compression = readString(in);
 
                 if (compression != "") {
@@ -986,7 +983,6 @@ static void opServe(Strings opFlags, Strings opArgs)
                     store->importPaths(false, in);
 
                 writeInt(1, out); // indicate success
-                out.flush();
 
                 /* The decompressor will have left stdin in an
                    undefined state, so we can't continue. */
@@ -995,9 +991,40 @@ static void opServe(Strings opFlags, Strings opArgs)
                 break;
             }
 
+            case cmdExportPaths: {
+                exportPaths(*store, readStorePaths<Paths>(in), false, out);
+                break;
+            }
+
+            case cmdBuildPaths: {
+                /* Used by build-remote.pl. */
+                if (!writeAllowed) throw Error("building paths is not allowed");
+                PathSet paths = readStorePaths<PathSet>(in);
+
+                // FIXME: changing options here doesn't work if we're
+                // building through the daemon.
+                verbosity = lvlError;
+                settings.keepLog = false;
+                settings.useSubstitutes = false;
+                settings.maxSilentTime = readInt(in);
+                settings.buildTimeout = readInt(in);
+
+                int res = 0;
+                try {
+                    store->buildPaths(paths);
+                } catch (Error & e) {
+                    printMsg(lvlError, format("error: %1%") % e.msg());
+                    res = e.status;
+                }
+                writeInt(res, out);
+                break;
+            }
+
             default:
                 throw Error(format("unknown serve command %1%") % cmd);
         }
+
+        out.flush();
     }
 }
 
diff --git a/src/nix-store/serve-protocol.hh b/src/nix-store/serve-protocol.hh
index 07ff4f7a7cc4..eb13b46e51bd 100644
--- a/src/nix-store/serve-protocol.hh
+++ b/src/nix-store/serve-protocol.hh
@@ -14,6 +14,8 @@ typedef enum {
     cmdQueryPathInfos = 2,
     cmdDumpStorePath = 3,
     cmdImportPaths = 4,
+    cmdExportPaths = 5,
+    cmdBuildPaths = 6,
 } ServeCommand;
 
 }