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.

1 files changed, 132 insertions, 18 deletions

diff --git a/guix/nar.scm b/guix/nar.scm
index b42f03c514..9ae76ff2a9 100644
--- a/guix/nar.scm
+++ b/guix/nar.scm
@@ -19,12 +19,23 @@
 (define-module (guix nar)
   #:use-module (guix utils)
   #:use-module (guix serialization)
+  #:use-module ((guix build utils) #:select (with-directory-excursion))
   #:use-module (rnrs bytevectors)
   #:use-module (rnrs io ports)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-34)
+  #:use-module (srfi srfi-35)
   #:use-module (ice-9 ftw)
-  #:export (write-file))
+  #:use-module (ice-9 match)
+  #:export (nar-error?
+            nar-read-error?
+            nar-read-error-file
+            nar-read-error-port
+            nar-read-error-token
+
+            write-file
+            restore-file))
 
 ;;; Comment:
 ;;;
@@ -32,6 +43,31 @@
 ;;;
 ;;; Code:
 
+(define-condition-type &nar-error &error      ; XXX: inherit from &nix-error ?
+  nar-error?)
+
+(define-condition-type &nar-read-error &nar-error
+  nar-read-error?
+  (port  nar-read-error-port)                   ; port from which we read
+  (file  nar-read-error-file)                   ; file we were restoring, or #f
+  (token nar-read-error-token))                 ; faulty token, or #f
+
+
+(define (dump in out size)
+  "Copy SIZE bytes from IN to OUT."
+  (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 (min left buf-size))))
+          (if (eof-object? read)
+              left
+              (begin
+                (put-bytevector out buf 0 read)
+                (loop (- left read))))))))
+
 (define (write-contents file p size)
   "Write SIZE bytes from FILE to output port P."
   (define (call-with-binary-input-file file proc)
@@ -45,33 +81,55 @@
             (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)))
+        (cut dump <> p size)))
   (write-padding size p))
 
+(define (read-contents in out)
+  "Read the contents of a file from the Nar at IN, write it to OUT, and return
+the size in bytes."
+  (define executable?
+    (match (read-string in)
+      ("contents"
+       #f)
+      ("executable"
+       (match (list (read-string in) (read-string in))
+         (("" "contents") #t)
+         (x (raise
+             (condition (&message
+                         (message "unexpected executable file marker"))
+                        (&nar-read-error (port in)
+                                         (file #f)
+                                         (token x))))))
+       #t)
+      (x
+       (raise
+        (condition (&message (message "unsupported nar file type"))
+                   (&nar-read-error (port in) (file #f) (token x)))))))
+
+  (let ((size (read-long-long in)))
+    ;; Note: `sendfile' cannot be used here because of port buffering on IN.
+    (dump in out size)
+
+    (when executable?
+      (chmod out #o755))
+    (let ((m (modulo size 8)))
+      (unless (zero? m)
+        (get-bytevector-n in (- 8 m))))
+    size))
+
+(define %archive-version-1
+  ;; Magic cookie for Nix archives.
+  "nix-archive-1")
+
 (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)
@@ -104,7 +162,63 @@ sub-directories of FILE as needed."
                          (write-string ")" p)))
                      entries)))
         (else
-         (error "ENOSYS")))
+         (raise (condition (&message (message "ENOSYS"))
+                           (&nar-error)))))
       (write-string ")" p))))
 
+(define (restore-file port file)
+  "Read a file (possibly a directory structure) in Nar format from PORT.
+Restore it as FILE."
+  (let ((signature (read-string port)))
+    (unless (equal? signature %archive-version-1)
+      (raise
+       (condition (&message (message "invalid nar signature"))
+                  (&nar-read-error (port port)
+                                   (token signature)
+                                   (file #f))))))
+
+  (let restore ((file file))
+    (match (list (read-string port) (read-string port) (read-string port))
+      (("(" "type" "regular")
+       (call-with-output-file file (cut read-contents port <>))
+       (match (read-string port)
+         (")" #t)
+         (x (raise
+             (condition
+              (&message (message "invalid nar end-of-file marker"))
+              (&nar-read-error (port port) (file file) (token x)))))))
+      (("(" "type" "directory")
+       (let ((dir file))
+         (mkdir dir)
+         (let loop ((prefix (read-string port)))
+           (match prefix
+             ("entry"
+              (match (list (read-string port)
+                           (read-string port) (read-string port)
+                           (read-string port))
+                (("(" "name" file "node")
+                 (restore (string-append dir "/" file))
+                 (match (read-string port)
+                   (")" #t)
+                   (x
+                    (raise
+                     (condition
+                      (&message
+                       (message "unexpected directory entry termination"))
+                      (&nar-read-error (port port)
+                                       (file file)
+                                       (token x))))))
+                 (loop (read-string port)))))
+             (")" #t)                             ; done with DIR
+             (x
+              (raise
+               (condition
+                (&message (message "unexpected directory inter-entry marker"))
+                (&nar-read-error (port port) (file file) (token x)))))))))
+      (x
+       (raise
+        (condition
+         (&message (message "unsupported nar entry type"))
+         (&nar-read-error (port port) (file file) (token x))))))))
+
 ;;; nar.scm ends here