web: Backport chunked encoding support for Guile <= 2.0.5.

* guix/web.scm (when-guile<=2.0.5): New macro.
  (read-chunk-header, read-chunk, read-chunk-body,
  make-chunked-input-port, read-response-body*)[when-guile<=2.0.5]: New
  procedures.
  (http-fetch): Clarify message when (not data).

guix/web.scm

@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012 Free Software Foundation, Inc.
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -17,6 +18,7 @@
 ;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
 
 (define-module (guix web)
+  #:use-module (guix utils)
   #:use-module (web uri)
   #:use-module (web client)
   #:use-module (web response)
@@ -33,6 +35,105 @@
 ;;;
 ;;; Code:
 
+(define-syntax when-guile<=2.0.5
+  (lambda (s)
+    (syntax-case s ()
+      ((_ body ...)
+       ;; Always emit BODY, regardless of VERSION, because sometimes this code
+       ;; might be compiled with a recent Guile and run with 2.0.5---e.g.,
+       ;; when using "guix pull".
+       #'(begin body ...)))))
+
+(when-guile<=2.0.5
+ ;; Backport of Guile commit 312e79f8 ("Add HTTP Chunked Encoding support to
+ ;; web modules.").
+
+ (use-modules (ice-9 rdelim))
+
+ ;; Chunked Responses
+ (define (read-chunk-header port)
+   (let* ((str (read-line port))
+          (extension-start (string-index str (lambda (c) (or (char=? c #\;)
+                                                             (char=? c #\return)))))
+          (size (string->number (if extension-start ; unnecessary?
+                                    (substring str 0 extension-start)
+                                    str)
+                                16)))
+     size))
+
+ (define (read-chunk port)
+   (let ((size (read-chunk-header port)))
+     (read-chunk-body port size)))
+
+ (define (read-chunk-body port size)
+   (let ((bv (get-bytevector-n port size)))
+     (get-u8 port)                                ; CR
+     (get-u8 port)                                ; LF
+     bv))
+
+ (define* (make-chunked-input-port port #:key (keep-alive? #f))
+   "Returns a new port which translates HTTP chunked transfer encoded
+data from PORT into a non-encoded format. Returns eof when it has
+read the final chunk from PORT. This does not necessarily mean
+that there is no more data on PORT. When the returned port is
+closed it will also close PORT, unless the KEEP-ALIVE? is true."
+   (define (next-chunk)
+     (read-chunk port))
+   (define finished? #f)
+   (define (close)
+     (unless keep-alive?
+       (close-port port)))
+   (define buffer #vu8())
+   (define buffer-size 0)
+   (define buffer-pointer 0)
+   (define (read! bv idx to-read)
+     (define (loop to-read num-read)
+       (cond ((or finished? (zero? to-read))
+              num-read)
+             ((<= to-read (- buffer-size buffer-pointer))
+              (bytevector-copy! buffer buffer-pointer
+                                bv (+ idx num-read)
+                                to-read)
+              (set! buffer-pointer (+ buffer-pointer to-read))
+              (loop 0 (+ num-read to-read)))
+             (else
+              (let ((n (- buffer-size buffer-pointer)))
+                (bytevector-copy! buffer buffer-pointer
+                                  bv (+ idx num-read)
+                                  n)
+                (set! buffer (next-chunk))
+                (set! buffer-pointer 0)
+                (set! buffer-size (bytevector-length buffer))
+                (set! finished? (= buffer-size 0))
+                (loop (- to-read n)
+                      (+ num-read n))))))
+     (loop to-read 0))
+   (make-custom-binary-input-port "chunked input port" read! #f #f close))
+
+ (define (read-response-body* r)
+   "Reads the response body from @var{r}, as a bytevector.  Returns
+ @code{#f} if there was no response body."
+   (define bad-response
+     (@@ (web response) bad-response))
+
+   (if (member '(chunked) (response-transfer-encoding r))
+       (let ((chunk-port (make-chunked-input-port (response-port r)
+                                                  #:keep-alive? #t)))
+         (get-bytevector-all chunk-port))
+       (let ((nbytes (response-content-length r)))
+         (and nbytes
+              (let ((bv (get-bytevector-n (response-port r) nbytes)))
+                (if (= (bytevector-length bv) nbytes)
+                    bv
+                    (bad-response "EOF while reading response body: ~a bytes of ~a"
+                                  (bytevector-length bv) nbytes)))))))
+
+ ;; Install this patch only on Guile 2.0.5.
+ (when (version>? "2.0.6" (version))
+   (module-set! (resolve-module '(web response))
+                'read-response-body read-response-body*)))
+
+
 (define* (http-fetch uri #:key (text? #f))
   "Return an input port containing the data at URI, and the expected number of
 bytes available or #f.  If TEXT? is true, the data at URI is considered to be
@@ -54,15 +155,14 @@ textual.  Follow any HTTP redirection."
          (let ((len (response-content-length resp)))
            (cond ((not data)
                   (begin
-                    ;; XXX: Guile 2.0.5 and earlier did not support chunked
+                    ;; Guile 2.0.5 and earlier did not support chunked
                     ;; transfer encoding, which is required for instance when
                     ;; fetching %PACKAGE-LIST-URL (see
                     ;; <http://lists.gnu.org/archive/html/guile-devel/2011-09/msg00089.html>).
-                    ;; Since users may still be using these versions, warn them
+                    ;; Normally the `when-guile<=2.0.5' block above fixes
-                    ;; and bail out.
+                    ;; that, but who knows what could happen.
-                    (warning (_ "using Guile ~a, ~a ~s encoding~%")
+                    (warning (_ "using Guile ~a, which does not support ~s encoding~%")
                              (version)
-                             "which does not support HTTP"
                              (response-transfer-encoding resp))
                     (leave (_ "download failed; use a newer Guile~%")
                            uri resp)))