daemon: Run 'guix substitute --substitute' as an agent.

This avoids spawning one substitute process per substitution.

* nix/libstore/build.cc (class Worker)[substituter]: New field.
[outPipe, logPipe, pid]: Remove.
(class SubstitutionGoal)[expectedHashStr, status, substituter]: New fields.
(SubstitutionGoal::timedOut): Adjust to check 'substituter'.
(SubstitutionGoal::tryToRun): Remove references to 'outPipe' and
'logPipe'.  Run "guix substitute --substitute" as an 'Agent'.  Send the
request with 'writeLine'.
(SubstitutionGoal::finished): Likewise.
(SubstitutionGoal::handleChildOutput): Change to fill in
'expectedHashStr' and 'status'.
(SubstitutionGoal::handleEOF): Call 'wakeUp' unconditionally.
(SubstitutionGoal::~SubstitutionGoal): Adjust to check 'substituter'.
* guix/scripts/substitute.scm (process-substitution): Write "success\n"
to stdout upon success.
(%error-to-file-descriptor-4?): New variable.
(guix-substitute): Set 'current-error-port' to file descriptor 4
unless (%error-to-file-descriptor-4?) is false.
Remove "--substitute" arguments.  Loop reading line from stdin.
* tests/substitute.scm <top level>: Call '%error-to-file-descriptor-4?'.
(request-substitution): New procedure.
("substitute, no signature")
("substitute, invalid hash")
("substitute, unauthorized key")
("substitute, authorized key")
("substitute, unauthorized narinfo comes first")
("substitute, unsigned narinfo comes first")
("substitute, first narinfo is unsigned and has wrong hash")
("substitute, first narinfo is unsigned and has wrong refs")
("substitute, two invalid narinfos")
("substitute, narinfo with several URLs"): Adjust to new "guix
substitute --substitute" calling convention.

guix/scripts/substitute.scm

@@ -88,6 +88,7 @@ (define-module (guix scripts substitute)
             write-narinfo
 
             %allow-unauthenticated-substitutes?
+            %error-to-file-descriptor-4?
 
             substitute-urls
             guix-substitute))
@@ -1016,7 +1017,10 @@ (define narinfo
 
       ;; Skip a line after what 'progress-reporter/file' printed, and another
       ;; one to visually separate substitutions.
-      (display "\n\n" (current-error-port)))))
+      (display "\n\n" (current-error-port))
+
+      ;; Tell the daemon that we're done.
+      (display "success\n" (current-output-port)))))
 
 
 ;;;
@@ -1127,6 +1131,11 @@ (define (validate-uri uri)
   (unless (string->uri uri)
     (leave (G_ "~a: invalid URI~%") uri)))
 
+(define %error-to-file-descriptor-4?
+  ;; Whether to direct 'current-error-port' to file descriptor 4 like
+  ;; 'guix-daemon' expects.
+  (make-parameter #t))
+
 (define-command (guix-substitute . args)
   (category internal)
   (synopsis "implement the build daemon's substituter protocol")
@@ -1140,9 +1149,9 @@ (define print-build-trace?
 
   ;; The daemon's agent code opens file descriptor 4 for us and this is where
   ;; stderr should go.
-  (parameterize ((current-error-port (match args
-                                       (("--query") (fdopen 4 "wl"))
-                                       (_ (current-error-port)))))
+  (parameterize ((current-error-port (if (%error-to-file-descriptor-4?)
+                                         (fdopen 4 "wl")
+                                         (current-error-port))))
     ;; Redirect diagnostics to file descriptor 4 as well.
     (guix-warning-port (current-error-port))
 
@@ -1184,15 +1193,22 @@ (define print-build-trace?
                                    #:cache-urls (substitute-urls)
                                    #:acl acl)
                     (loop (read-line)))))))
-         (("--substitute" store-path destination)
+         (("--substitute")
           ;; Download STORE-PATH and store it as a Nar in file DESTINATION.
           ;; Specify the number of columns of the terminal so the progress
           ;; report displays nicely.
           (parameterize ((current-terminal-columns (client-terminal-columns)))
-            (process-substitution store-path destination
-                                  #:cache-urls (substitute-urls)
-                                  #:acl (current-acl)
-                                  #:print-build-trace? print-build-trace?)))
+            (let loop ()
+              (match (read-line)
+                ((? eof-object?)
+                 #t)
+                ((= string-tokenize ("substitute" store-path destination))
+                 (process-substitution store-path destination
+                                       #:cache-urls (substitute-urls)
+                                       #:acl (current-acl)
+                                       #:print-build-trace?
+                                       print-build-trace?)
+                 (loop))))))
          ((or ("-V") ("--version"))
           (show-version-and-exit "guix substitute"))
          (("--help")

nix/libstore/build.cc

@@ -262,6 +262,7 @@ public:
     LocalStore & store;
 
     std::shared_ptr<Agent> hook;
+    std::shared_ptr<Agent> substituter;
 
     Worker(LocalStore & store);
     ~Worker();
@@ -2773,15 +2774,6 @@ private:
     /* Path info returned by the substituter's query info operation. */
     SubstitutablePathInfo info;
 
-    /* Pipe for the substituter's standard output. */
-    Pipe outPipe;
-
-    /* Pipe for the substituter's standard error. */
-    Pipe logPipe;
-
-    /* The process ID of the builder. */
-    Pid pid;
-
     /* Lock on the store path. */
     std::shared_ptr<PathLocks> outputLock;
 
@@ -2795,6 +2787,17 @@ private:
     typedef void (SubstitutionGoal::*GoalState)();
     GoalState state;
 
+    /* The substituter. */
+    std::shared_ptr<Agent> substituter;
+
+    /* Either the empty string, or the expected hash as returned by the
+       substituter.  */
+    string expectedHashStr;
+
+    /* Either the empty string, or the status phrase returned by the
+       substituter.  */
+    string status;
+
     void tryNext();
 
 public:
@@ -2840,7 +2843,7 @@ SubstitutionGoal::SubstitutionGoal(const Path & storePath, Worker & worker, bool
 
 SubstitutionGoal::~SubstitutionGoal()
 {
-    if (pid != -1) worker.childTerminated(pid);
+    if (substituter) worker.childTerminated(substituter->pid);
 }
 
 
@@ -2848,9 +2851,9 @@ void SubstitutionGoal::timedOut()
 {
     if (settings.printBuildTrace)
         printMsg(lvlError, format("@ substituter-failed %1% timeout") % storePath);
-    if (pid != -1) {
-        pid_t savedPid = pid;
-        pid.kill();
+    if (substituter) {
+        pid_t savedPid = substituter->pid;
+	substituter.reset();
         worker.childTerminated(savedPid);
     }
     amDone(ecFailed);
@@ -2977,45 +2980,29 @@ void SubstitutionGoal::tryToRun()
 
     printMsg(lvlInfo, format("fetching path `%1%'...") % storePath);
 
-    outPipe.create();
-    logPipe.create();
-
     destPath = repair ? storePath + ".tmp" : storePath;
 
     /* Remove the (stale) output path if it exists. */
     if (pathExists(destPath))
         deletePath(destPath);
 
-    /* Fill in the arguments. */
-    Strings args;
-    args.push_back("guix");
-    args.push_back("substitute");
-    args.push_back("--substitute");
-    args.push_back(storePath);
-    args.push_back(destPath);
+    if (!worker.substituter) {
+	const Strings args = { "substitute", "--substitute" };
+	const std::map<string, string> env = { { "_NIX_OPTIONS", settings.pack() } };
+	worker.substituter = std::make_shared<Agent>(settings.guixProgram, args, env);
+    }
 
-    /* Fork the substitute program. */
-    pid = startProcess([&]() {
+    /* Borrow the worker's substituter.  */
+    if (!substituter) substituter.swap(worker.substituter);
 
-	/* Communicate substitute-urls & co. to 'guix substitute'.  */
-        setenv("_NIX_OPTIONS", settings.pack().c_str(), 1);
+    /* Send the request to the substituter.  */
+    writeLine(substituter->toAgent.writeSide,
+	      (format("substitute %1% %2%") % storePath % destPath).str());
 
-        commonChildInit(logPipe);
-
-        if (dup2(outPipe.writeSide, STDOUT_FILENO) == -1)
-            throw SysError("cannot dup output pipe into stdout");
-
-        execv(settings.guixProgram.c_str(), stringsToCharPtrs(args).data());
-
-        throw SysError(format("executing `%1% substitute'") % settings.guixProgram);
-    });
-
-    pid.setSeparatePG(true);
-    pid.setKillSignal(SIGTERM);
-    outPipe.writeSide.close();
-    logPipe.writeSide.close();
-    worker.childStarted(shared_from_this(),
-        pid, singleton<set<int> >(logPipe.readSide), true, true);
+    set<int> fds;
+    fds.insert(substituter->fromAgent.readSide);
+    fds.insert(substituter->builderOut.readSide);
+    worker.childStarted(shared_from_this(), substituter->pid, fds, true, true);
 
     state = &SubstitutionGoal::finished;
 
@@ -3030,28 +3017,25 @@ void SubstitutionGoal::finished()
 {
     trace("substitute finished");
 
-    /* Since we got an EOF on the logger pipe, the substitute is
-       presumed to have terminated.  */
-    pid_t savedPid = pid;
-    int status = pid.wait(true);
+    /* Remove the 'guix substitute' process from the list of children.  */
+    worker.childTerminated(substituter->pid);
 
-    /* So the child is gone now. */
-    worker.childTerminated(savedPid);
-
-    /* Close the read side of the logger pipe. */
-    logPipe.readSide.close();
-
-    /* Get the hash info from stdout. */
-    string expectedHashStr = statusOk(status) ? readLine(outPipe.readSide) : "";
-    outPipe.readSide.close();
+    /* If max-jobs > 1, the worker might have created a new 'substitute'
+       process in the meantime.  If that is the case, terminate ours;
+       otherwise, give it back to the worker.  */
+    if (worker.substituter) {
+	substituter.reset ();
+    } else {
+	worker.substituter.swap(substituter);
+    }
 
     /* Check the exit status and the build result. */
     HashResult hash;
     try {
 
-        if (!statusOk(status))
-            throw SubstError(format("fetching path `%1%' %2%")
-                % storePath % statusToString(status));
+        if (status != "success")
+            throw SubstError(format("fetching path `%1%' (status: '%2%')")
+                % storePath % status);
 
         if (!pathExists(destPath))
             throw SubstError(format("substitute did not produce path `%1%'") % destPath);
@@ -3122,16 +3106,33 @@ void SubstitutionGoal::finished()
 
 void SubstitutionGoal::handleChildOutput(int fd, const string & data)
 {
-    assert(fd == logPipe.readSide);
-    if (verbosity >= settings.buildVerbosity) writeToStderr(data);
-    /* Don't write substitution output to a log file for now.  We
-       probably should, though. */
+    if (verbosity >= settings.buildVerbosity
+	&& fd == substituter->builderOut.readSide) {
+	writeToStderr(data);
+	/* Don't write substitution output to a log file for now.  We
+	   probably should, though. */
+    }
+
+    if (fd == substituter->fromAgent.readSide) {
+	/* Trim whitespace to the right.  */
+	size_t end = data.find_last_not_of(" \t\n");
+	string trimmed = (end != string::npos) ? data.substr(0, end + 1) : data;
+
+	if (expectedHashStr == "") {
+	    expectedHashStr = trimmed;
+	} else if (status == "") {
+	    status = trimmed;
+	    worker.wakeUp(shared_from_this());
+	} else {
+	    printMsg(lvlError, format("unexpected substituter message '%1%'") % data);
+	}
+    }
 }
 
 
 void SubstitutionGoal::handleEOF(int fd)
 {
-    if (fd == logPipe.readSide) worker.wakeUp(shared_from_this());
+    worker.wakeUp(shared_from_this());
 }
 
 

tests/substitute.scm

@@ -58,6 +58,14 @@ (define-syntax-rule (test-quit name error-rx exp)
                   (let ((message (get-output-string error-output)))
                     (->bool (string-match error-rx message))))))))))
 
+(define (request-substitution item destination)
+  "Run 'guix substitute --substitute' to fetch ITEM to DESTINATION."
+  (parameterize ((guix-warning-port (current-error-port)))
+    (with-input-from-string (string-append "substitute " item " "
+                                           destination "\n")
+      (lambda ()
+        (guix-substitute "--substitute")))))
+
 (define %public-key
   ;; This key is known to be in the ACL by default.
   (call-with-input-file (string-append %config-directory "/signing-key.pub")
@@ -184,6 +192,11 @@ (define-syntax-rule (with-narinfo* narinfo directory body ...)
 ;; Transmit these options to 'guix substitute'.
 (substitute-urls (list (getenv "GUIX_BINARY_SUBSTITUTE_URL")))
 
+;; Never use file descriptor 4, unlike what happens when invoked by the
+;; daemon.
+(%error-to-file-descriptor-4? #f)
+
+
 (test-equal "query narinfo without signature"
   ""                                              ; not substitutable
 
@@ -284,10 +297,12 @@ (define-syntax-rule (with-narinfo* narinfo directory body ...)
 (test-quit "substitute, no signature"
     "no valid substitute"
   (with-narinfo %narinfo
-    (guix-substitute "--substitute"
-                     (string-append (%store-prefix)
-                                    "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
-                     "foo")))
+    (with-input-from-string (string-append "substitute "
+                                           (%store-prefix)
+                                           "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo"
+                                           " foo\n")
+      (lambda ()
+        (guix-substitute "--substitute")))))
 
 (test-quit "substitute, invalid hash"
     "no valid substitute"
@@ -295,10 +310,12 @@ (define-syntax-rule (with-narinfo* narinfo directory body ...)
   (with-narinfo (string-append %narinfo "Signature: "
                                (signature-field "different body")
                                "\n")
-    (guix-substitute "--substitute"
-                     (string-append (%store-prefix)
-                                    "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
-                     "foo")))
+    (with-input-from-string (string-append "substitute "
+                                           (%store-prefix)
+                                           "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo"
+                                           " foo\n")
+      (lambda ()
+        (guix-substitute "--substitute")))))
 
 (test-quit "substitute, unauthorized key"
     "no valid substitute"
@@ -307,10 +324,12 @@ (define-syntax-rule (with-narinfo* narinfo directory body ...)
                                 %narinfo
                                 #:public-key %wrong-public-key)
                                "\n")
-    (guix-substitute "--substitute"
-                     (string-append (%store-prefix)
-                                    "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
-                     "foo")))
+    (with-input-from-string (string-append "substitute "
+                                           (%store-prefix)
+                                           "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo"
+                                           " foo\n")
+      (lambda ()
+        (guix-substitute "--substitute")))))
 
 (test-equal "substitute, authorized key"
   "Substitutable data."
@@ -319,10 +338,9 @@ (define-syntax-rule (with-narinfo* narinfo directory body ...)
     (dynamic-wind
       (const #t)
       (lambda ()
-        (guix-substitute "--substitute"
-                         (string-append (%store-prefix)
-                                        "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
-                         "substitute-retrieved")
+        (request-substitution (string-append (%store-prefix)
+                                             "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
+                              "substitute-retrieved")
         (call-with-input-file "substitute-retrieved" get-string-all))
       (lambda ()
         (false-if-exception (delete-file "substitute-retrieved"))))))
@@ -352,10 +370,9 @@ (define-syntax-rule (with-narinfo* narinfo directory body ...)
                           (map (cut string-append "file://" <>)
                                (list %alternate-substitute-directory
                                      %main-substitute-directory))))
-            (guix-substitute "--substitute"
-                             (string-append (%store-prefix)
-                                            "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
-                             "substitute-retrieved"))
+            (request-substitution (string-append (%store-prefix)
+                                                 "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
+                                  "substitute-retrieved"))
           (call-with-input-file "substitute-retrieved" get-string-all))
         (lambda ()
           (false-if-exception (delete-file "substitute-retrieved")))))))
@@ -381,10 +398,9 @@ (define-syntax-rule (with-narinfo* narinfo directory body ...)
                           (map (cut string-append "file://" <>)
                                (list %alternate-substitute-directory
                                      %main-substitute-directory))))
-            (guix-substitute "--substitute"
-                             (string-append (%store-prefix)
-                                            "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
-                             "substitute-retrieved"))
+            (request-substitution (string-append (%store-prefix)
+                                                 "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
+                                  "substitute-retrieved"))
           (call-with-input-file "substitute-retrieved" get-string-all))
         (lambda ()
           (false-if-exception (delete-file "substitute-retrieved")))))))
@@ -417,10 +433,9 @@ (define-syntax-rule (with-narinfo* narinfo directory body ...)
                           (map (cut string-append "file://" <>)
                                (list %alternate-substitute-directory
                                      %main-substitute-directory))))
-            (guix-substitute "--substitute"
-                             (string-append (%store-prefix)
-                                            "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
-                             "substitute-retrieved"))
+            (request-substitution (string-append (%store-prefix)
+                                                 "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
+                                  "substitute-retrieved"))
           (call-with-input-file "substitute-retrieved" get-string-all))
         (lambda ()
           (false-if-exception (delete-file "substitute-retrieved")))))))
@@ -451,10 +466,9 @@ (define-syntax-rule (with-narinfo* narinfo directory body ...)
                           (map (cut string-append "file://" <>)
                                (list %alternate-substitute-directory
                                      %main-substitute-directory))))
-            (guix-substitute "--substitute"
-                             (string-append (%store-prefix)
-                                            "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
-                             "substitute-retrieved"))
+            (request-substitution (string-append (%store-prefix)
+                                                 "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
+                                  "substitute-retrieved"))
           (call-with-input-file "substitute-retrieved" get-string-all))
         (lambda ()
           (false-if-exception (delete-file "substitute-retrieved")))))))
@@ -470,10 +484,12 @@ (define-syntax-rule (with-narinfo* narinfo directory body ...)
                                    #:public-key %wrong-public-key))
         %main-substitute-directory
 
-      (guix-substitute "--substitute"
-                       (string-append (%store-prefix)
-                                      "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
-                       "substitute-retrieved"))))
+      (with-input-from-string (string-append "substitute "
+                                             (%store-prefix)
+                                             "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo"
+                                             " substitute-retrieved\n")
+        (lambda ()
+          (guix-substitute "--substitute"))))))
 
 (test-equal "substitute, narinfo with several URLs"
   "Substitutable data."
@@ -513,10 +529,9 @@ (define (compress input output compression)
           (parameterize ((substitute-urls
                           (list (string-append "file://"
                                                %main-substitute-directory))))
-            (guix-substitute "--substitute"
-                             (string-append (%store-prefix)
-                                            "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
-                             "substitute-retrieved"))
+            (request-substitution (string-append (%store-prefix)
+                                                 "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-foo")
+                                  "substitute-retrieved"))
           (call-with-input-file "substitute-retrieved" get-string-all))
         (lambda ()
           (false-if-exception (delete-file "substitute-retrieved")))))))