nar: Implement restoration from Nar.

* guix/nar.scm (&nar-error, &nar-read-error): New condition types.
  (dump): New procedure.
  (write-contents)[dump]: Remove.  Use the one above instead.
  (read-contents, write-file, restore-file): New procedures.
  (%archive-version-1): New variable.

tests/nar.scm

@@ -0,0 +1,95 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (test-nar)
+  #:use-module (guix nar)
+  #:use-module (rnrs bytevectors)
+  #:use-module (rnrs io ports)
+  #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-64)
+  #:use-module (ice-9 ftw))
+
+;; Test the (guix nar) module.
+
+(define (rm-rf dir)
+  (file-system-fold (const #t)                    ; enter?
+                    (lambda (file stat result)    ; leaf
+                      (delete-file file))
+                    (const #t)                    ; down
+                    (lambda (dir stat result)     ; up
+                      (rmdir dir))
+                    (const #t)                    ; skip
+                    (const #t)                    ; error
+                    #t
+                    dir
+                    lstat))
+
+
+(test-begin "nar")
+
+(test-assert "write-file + restore-file"
+  (let* ((input  (string-append (dirname (search-path %load-path "guix.scm"))
+                                "/guix"))
+         (output (string-append (dirname input)
+                                "/test-nar-"
+                                (number->string (getpid))))
+         (nar    (string-append output ".nar")))
+    (dynamic-wind
+      (lambda () #t)
+      (lambda ()
+        (call-with-output-file nar
+          (cut write-file input <>))
+        (call-with-input-file nar
+          (cut restore-file <> output))
+        (let* ((strip   (cute string-drop <> (string-length input)))
+               (sibling (compose (cut string-append output <>) strip))
+               (file=?  (lambda (a b)
+                          (and (eq? (stat:type (lstat a)) (stat:type (lstat b)))
+                               (case (stat:type (lstat a))
+                                 ((regular)
+                                  (equal?
+                                   (call-with-input-file a get-bytevector-all)
+                                   (call-with-input-file b get-bytevector-all)))
+                                 ((symlink)
+                                  (string=? (readlink a) (readlink b)))
+                                 (else
+                                  (error "what?" (lstat a))))))))
+          (file-system-fold (const #t)
+                            (lambda (name stat result) ; leaf
+                              (and result
+                                   (file=? name (sibling name))))
+                            (lambda (name stat result) ; down
+                              result)
+                            (lambda (name stat result) ; up
+                              result)
+                            (const #f)                 ; skip
+                            (lambda (name stat errno result)
+                              (pk 'error name stat errno)
+                              #f)
+                            (> (stat:nlink (stat output)) 2)
+                            input
+                            lstat)))
+      (lambda ()
+        (false-if-exception (delete-file nar))
+        (false-if-exception (rm-rf output))
+        ))))
+
+(test-end "nar")
+
+
+(exit (= (test-runner-fail-count (test-runner-current)) 0))