daemon: Implement ‘substitute-urls’ RPC.

* nix/libstore/worker-protocol.hh (PROTOCOL_VERSION): Bump.
(WorkerOp): Add ‘wopSubstituteURLs’.
* nix/nix-daemon/nix-daemon.cc (performOp): Implement it.
* guix/store.scm (%protocol-version): Bump.
(operation-id): Add ‘substitute-urls’.
(substitute-urls): New procedure.
* tests/store.scm ("substitute-urls, default")
("substitute-urls, client-specified URLs")
("substitute-urls, disabled"): New tests.

Change-Id: I2c0119500c3a1eecfa5ebf32463ffb0f173161de

2 files changed, 20 insertions, 2 deletions

diff --git a/nix/libstore/worker-protocol.hh b/nix/libstore/worker-protocol.hh
index ea67b10a5b..ef259db2a0 100644
--- a/nix/libstore/worker-protocol.hh
+++ b/nix/libstore/worker-protocol.hh
@@ -6,7 +6,7 @@ namespace nix {
 #define WORKER_MAGIC_1 0x6e697863
 #define WORKER_MAGIC_2 0x6478696f
 
-#define PROTOCOL_VERSION 0x163
+#define PROTOCOL_VERSION 0x164
 #define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 #define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
 
@@ -44,7 +44,8 @@ typedef enum {
     wopQueryValidDerivers = 33,
     wopOptimiseStore = 34,
     wopVerifyStore = 35,
-    wopBuiltinBuilders = 80
+    wopBuiltinBuilders = 80,
+    wopSubstituteURLs = 81
 } WorkerOp;
 
 
diff --git a/nix/nix-daemon/nix-daemon.cc b/nix/nix-daemon/nix-daemon.cc
index 497de11a04..4cb05c802e 100644
--- a/nix/nix-daemon/nix-daemon.cc
+++ b/nix/nix-daemon/nix-daemon.cc
@@ -736,6 +736,23 @@ static void performOp(bool trusted, unsigned int clientVersion,
 	break;
     }
 
+    case wopSubstituteURLs: {
+	startWork();
+	Strings urls;
+	if (settings.get("build-use-substitutes", std::string("false")) == "true") {
+	    /* First check the client-provided substitute URLs, then those
+	       passed to the daemon.  */
+	    auto str = settings.get("untrusted-substitute-urls",  std::string(""));
+	    if (str.empty()) {
+		str = settings.get("substitute-urls",  std::string(""));
+	    }
+	    urls = tokenizeString<Strings>(str);
+	}
+	stopWork();
+	writeStrings(urls, to);
+	break;
+    }
+
     default:
         throw Error(format("invalid operation %1%") % op);
     }