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diff --git a/guix/nar.scm b/guix/nar.scm
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+;;; 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 (guix nar)
+  #:use-module (guix utils)
+  #:use-module (guix serialization)
+  #:use-module (rnrs bytevectors)
+  #:use-module (rnrs io ports)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:use-module (ice-9 ftw)
+  #:export (write-file))
+
+;;; Comment:
+;;;
+;;; Read and write Nix archives, aka. ‘nar’.
+;;;
+;;; Code:
+
+(define (write-contents file p size)
+  "Write SIZE bytes from FILE to output port P."
+  (define (call-with-binary-input-file file proc)
+    ;; Open FILE as a binary file.  This avoids scan-for-encoding, and thus
+    ;; avoids any initial buffering.  Disable file name canonicalization to
+    ;; avoid stat'ing like crazy.
+    (with-fluids ((%file-port-name-canonicalization #f))
+      (let ((port (open-file file "rb")))
+        (catch #t (cut proc port)
+          (lambda args
+            (close-port port)
+            (apply throw args))))))
+
+  (define (dump in size)
+    (define buf-size 65536)
+    (define buf (make-bytevector buf-size))
+
+    (let loop ((left size))
+      (if (<= left 0)
+          0
+          (let ((read (get-bytevector-n! in buf 0 buf-size)))
+            (if (eof-object? read)
+                left
+                (begin
+                  (put-bytevector p buf 0 read)
+                  (loop (- left read))))))))
+
+  (write-string "contents" p)
+  (write-long-long size p)
+  (call-with-binary-input-file file
+    ;; Use `sendfile' when available (Guile 2.0.8+).
+    (if (compile-time-value (defined? 'sendfile))
+        (cut sendfile p <> size 0)
+        (cut dump <> size)))
+  (write-padding size p))
+
+(define (write-file file port)
+  "Write the contents of FILE to PORT in Nar format, recursing into
+sub-directories of FILE as needed."
+  (define %archive-version-1 "nix-archive-1")
+  (define p port)
+
+  (write-string %archive-version-1 p)
+
+  (let dump ((f file))
+    (let ((s (lstat f)))
+      (write-string "(" p)
+      (case (stat:type s)
+        ((regular)
+         (write-string "type" p)
+         (write-string "regular" p)
+         (if (not (zero? (logand (stat:mode s) #o100)))
+             (begin
+               (write-string "executable" p)
+               (write-string "" p)))
+         (write-contents f p (stat:size s)))
+        ((directory)
+         (write-string "type" p)
+         (write-string "directory" p)
+         (let ((entries (remove (cut member <> '("." ".."))
+                                (scandir f))))
+           (for-each (lambda (e)
+                       (let ((f (string-append f "/" e)))
+                         (write-string "entry" p)
+                         (write-string "(" p)
+                         (write-string "name" p)
+                         (write-string e p)
+                         (write-string "node" p)
+                         (dump f)
+                         (write-string ")" p)))
+                     entries)))
+        (else
+         (error "ENOSYS")))
+      (write-string ")" p))))
+
+;;; nar.scm ends here