store: 'GUIX_DAEMON_SOCKET' can now be a URI.

* guix/store.scm (%daemon-socket-file): Rename to...
(%daemon-socket-uri): ... this.
(connect-to-daemon): New procedure.
(open-connection): Rename 'file' to 'uri'.  Use 'connect-to-daemon'
instead of 'open-unix-domain-socket'.
* guix/tests.scm (open-connection-for-tests): Rename 'file' to 'uri'.
* tests/guix-build.sh: Add tests.
* tests/store.scm ("open-connection with file:// URI"): New tests.

doc/guix.texi

@@ -3666,10 +3666,30 @@ accidental modifications.
 @end quotation
 
 The @code{(guix store)} module provides procedures to connect to the
-daemon, and to perform RPCs.  These are described below.
+daemon, and to perform RPCs.  These are described below.  By default,
+@code{open-connection}, and thus all the @command{guix} commands,
+connect to the local daemon or to the URI specified by the
+@code{GUIX_DAEMON_SOCKET} environment variable.
 
-@deffn {Scheme Procedure} open-connection [@var{file}] [#:reserve-space? #t]
+@defvr {Environment Variable} GUIX_DAEMON_SOCKET
-Connect to the daemon over the Unix-domain socket at @var{file}.  When
+When set, the value of this variable should be a file name or a URI
+designating the daemon endpoint.  When it is a file name, it denotes a
+Unix-domain socket to connect to.  In addition to file names, the
+supported URI schemes are:
+
+@table @code
+@item file
+@itemx unix
+These are for Unix-domain sockets.
+@code{file:///var/guix/daemon-socket/socket} is equivalent to
+@file{/var/guix/daemon-socket/socket}.
+@end table
+
+Additional URI schemes may be supported in the future.
+@end defvr
+
+@deffn {Scheme Procedure} open-connection [@var{uri}] [#:reserve-space? #t]
+Connect to the daemon over the Unix-domain socket at @var{uri} (a string).  When
 @var{reserve-space?} is true, instruct it to reserve a little bit of
 extra space on the file system so that the garbage collector can still
 operate should the disk become full.  Return a server object.

guix/store.scm

@@ -39,7 +39,8 @@
   #:use-module (ice-9 regex)
   #:use-module (ice-9 vlist)
   #:use-module (ice-9 popen)
-  #:export (%daemon-socket-file
+  #:use-module (web uri)
+  #:export (%daemon-socket-uri
             %gc-roots-directory
             %default-substitute-urls
 
@@ -216,8 +217,8 @@
 (define %default-socket-path
   (string-append %state-directory "/daemon-socket/socket"))
 
-(define %daemon-socket-file
+(define %daemon-socket-uri
-  ;; File name of the socket the daemon listens too.
+  ;; URI or file name of the socket the daemon listens too.
   (make-parameter (or (getenv "GUIX_DAEMON_SOCKET")
                       %default-socket-path)))
 
@@ -369,10 +370,29 @@
                              (file file)
                              (errno errno)))))))))
 
-(define* (open-connection #:optional (file (%daemon-socket-file))
+(define (connect-to-daemon uri)
+  "Connect to the daemon at URI, a string that may be an actual URI or a file
+name."
+  (define connect
+    (match (string->uri uri)
+      (#f                                         ;URI is a file name
+       open-unix-domain-socket)
+      ((? uri? uri)
+       (match (uri-scheme uri)
+         ((or #f 'file 'unix)
+          (lambda (_)
+            (open-unix-domain-socket (uri-path uri))))
+         (x
+          (raise (condition (&nix-connection-error
+                             (file (uri->string uri))
+                             (errno ENOTSUP)))))))))
+
+  (connect uri))
+
+(define* (open-connection #:optional (uri (%daemon-socket-uri))
                           #:key port (reserve-space? #t) cpu-affinity)
-  "Connect to the daemon over the Unix-domain socket at FILE, or, if PORT is
+  "Connect to the daemon at URI (a string), or, if PORT is not #f, use it as
-not #f, use it as the I/O port over which to communicate to a build daemon.
+the I/O port over which to communicate to a build daemon.
 
 When RESERVE-SPACE? is true, instruct it to reserve a little bit of extra
 space on the file system so that the garbage collector can still operate,
@@ -383,10 +403,10 @@ for this connection will be pinned.  Return a server object."
              ;; One of the 'write-' or 'read-' calls below failed, but this is
              ;; really a connection error.
              (raise (condition
-                     (&nix-connection-error (file (or port file))
+                     (&nix-connection-error (file (or port uri))
                                             (errno EPROTO))
                      (&message (message "build daemon handshake failed"))))))
-    (let ((port (or port (open-unix-domain-socket file))))
+    (let ((port (or port (connect-to-daemon uri))))
       (write-int %worker-magic-1 port)
       (let ((r (read-int port)))
         (and (eqv? r %worker-magic-2)

guix/tests.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2013, 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013, 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -56,13 +56,13 @@
    (or (and=> (getenv "GUIX_BINARY_SUBSTITUTE_URL") list)
        '())))
 
-(define* (open-connection-for-tests #:optional (file (%daemon-socket-file)))
+(define* (open-connection-for-tests #:optional (uri (%daemon-socket-uri)))
   "Open a connection to the build daemon for tests purposes and return it."
   (guard (c ((nix-error? c)
              (format (current-error-port)
                      "warning: build daemon error: ~s~%" c)
              #f))
-    (let ((store (open-connection file)))
+    (let ((store (open-connection uri)))
       ;; Make sure we build everything by ourselves.
       (set-build-options store
                          #:use-substitutes? #f

tests/guix-build.sh

@@ -36,6 +36,14 @@ guix build -e '(@@ (gnu packages bootstrap) %bootstrap-guile)' |	\
 guix build hello -d |				\
     grep -e '-hello-[0-9\.]\+\.drv$'
 
+# Passing a URI.
+GUIX_DAEMON_SOCKET="file://$NIX_STATE_DIR/daemon-socket/socket"	\
+guix build -e '(@@ (gnu packages bootstrap) %bootstrap-guile)'
+
+( if GUIX_DAEMON_SOCKET="weird://uri"					\
+     guix build -e '(@@ (gnu packages bootstrap) %bootstrap-guile)';	\
+  then exit 1; fi )
+
 # Check --sources option with its arguments
 module_dir="t-guix-build-$$"
 mkdir "$module_dir"

tests/store.scm

@@ -48,6 +48,14 @@
 
 (test-begin "store")
 
+(test-assert "open-connection with file:// URI"
+  (let ((store (open-connection (string-append "file://"
+                                               (%daemon-socket-uri)))))
+    (and (add-text-to-store store "foo" "bar")
+         (begin
+           (close-connection store)
+           #t))))
+
 (test-equal "connection handshake error"
   EPROTO
   (let ((port (%make-void-port "rw")))