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

1 files changed, 17 insertions, 0 deletions

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);
     }