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

guix/store.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012-2022 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012-2023 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2018 Jan Nieuwenhuizen <janneke@gnu.org>
 ;;; Copyright © 2019, 2020 Mathieu Othacehe <m.othacehe@gmail.com>
 ;;; Copyright © 2020 Florian Pelz <pelzflorian@pelzflorian.de>
@@ -145,6 +145,7 @@
             path-info-nar-size
 
             built-in-builders
+            substitute-urls
             references
             references/cached
             references*
@@ -199,7 +200,7 @@
             derivation-log-file
             log-file))
 
-(define %protocol-version #x163)
+(define %protocol-version #x164)
 
 (define %worker-magic-1 #x6e697863)               ; "nixc"
 (define %worker-magic-2 #x6478696f)               ; "dxio"
@@ -253,7 +254,8 @@
   (query-valid-derivers 33)
   (optimize-store 34)
   (verify-store 35)
-  (built-in-builders 80))
+  (built-in-builders 80)
+  (substitute-urls 81))
 
 (define-enumerate-type hash-algo
   ;; hash.hh
@@ -1780,6 +1782,16 @@ The result is always the empty list unless the daemon was started with
 This makes sense only when the daemon was started with '--cache-failures'."
   boolean)
 
+(define substitute-urls
+  (let ((urls (operation (substitute-urls)
+                         #f
+                         string-list)))
+    (lambda (store)
+      "Return the list of currently configured substitutes URLs for STORE, or
+#f if the daemon is too old and does not implement this RPC."
+      (and (>= (store-connection-version store) #x164)
+           (urls store)))))
+
 
 ;;;
 ;;; Per-connection caches.

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;
 
 

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);
     }

tests/store.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012-2021, 2023 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -105,7 +105,28 @@
               "/283gqy39v3g9dxjy26rynl0zls82fmcg-guile-2.0.7/bin/guile")))
        (not (direct-store-path? (%store-prefix)))))
 
-(test-skip (if %store 0 15))
+(test-skip (if %store 0 18))
+
+(test-equal "substitute-urls, default"
+  (list (getenv "GUIX_BINARY_SUBSTITUTE_URL"))
+  (with-store store
+    (set-build-options store #:use-substitutes? #t)
+    (substitute-urls store)))
+
+(test-equal "substitute-urls, client-specified URLs"
+  '("http://substitutes.example.org"
+    "http://other.example.org")
+  (with-store store
+    (set-build-options store #:use-substitutes? #t
+                       #:substitute-urls '("http://substitutes.example.org"
+                                           "http://other.example.org"))
+    (substitute-urls store)))
+
+(test-equal "substitute-urls, disabled"
+  '()
+  (with-store store
+    (set-build-options store #:use-substitutes? #f)
+    (substitute-urls store)))
 
 (test-equal "profiles/per-user exists and is not writable"
   #o755