import: json: Silence json-fetch output.

* guix/import/json.scm (json-fetch): Use http-fetch instead of url-fetch
to avoid writing to stdout and a temporary file for each invocation.
* guix/import/gem.scm (rubygems-fetch): Do not redirect json-fetch
output to /dev/null.
* guix/import/pypi.scm (pypi-fetch): Likewise.

guix/import/gem.scm

@@ -38,14 +38,8 @@
 (define (rubygems-fetch name)
   "Return an alist representation of the RubyGems metadata for the package NAME,
 or #f on failure."
-  ;; XXX: We want to silence the download progress report, which is especially
-  ;; annoying for 'guix refresh', but we have to use a file port.
-  (call-with-output-file "/dev/null"
-    (lambda (null)
-      (with-error-to-port null
-        (lambda ()
-          (json-fetch
-           (string-append "https://rubygems.org/api/v1/gems/" name ".json")))))))
+  (json-fetch
+   (string-append "https://rubygems.org/api/v1/gems/" name ".json")))
 
 (define (ruby-package-name name)
   "Given the NAME of a package on RubyGems, return a Guix-compliant name for

guix/import/json.scm

@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2014 David Thompson <davet@gnu.org>
-;;; Copyright © 2015 Eric Bavier <bavier@member.fsf.org>
+;;; Copyright © 2015, 2016 Eric Bavier <bavier@member.fsf.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -19,14 +19,17 @@
 
 (define-module (guix import json)
   #:use-module (json)
-  #:use-module (guix utils)
+  #:use-module (guix http-client)
   #:use-module (guix import utils)
+  #:use-module (srfi srfi-34)
   #:export (json-fetch))
 
 (define (json-fetch url)
   "Return an alist representation of the JSON resource URL, or #f on failure."
-  (call-with-temporary-output-file
-   (lambda (temp port)
-     (and (url-fetch url temp)
-          (hash-table->alist
-           (call-with-input-file temp json->scm))))))
+  (guard (c ((and (http-get-error? c)
+                  (= 404 (http-get-error-code c)))
+             #f))                       ;"expected" if package is unknown
+    (let* ((port (http-fetch url))
+           (result (hash-table->alist (json->scm port))))
+      (close-port port)
+      result)))

guix/import/pypi.scm

@@ -51,14 +51,8 @@
 (define (pypi-fetch name)
   "Return an alist representation of the PyPI metadata for the package NAME,
 or #f on failure."
-  ;; XXX: We want to silence the download progress report, which is especially
-  ;; annoying for 'guix refresh', but we have to use a file port.
-  (call-with-output-file "/dev/null"
-    (lambda (null)
-      (with-error-to-port null
-        (lambda ()
-          (json-fetch (string-append "https://pypi.python.org/pypi/"
-                                     name "/json")))))))
+  (json-fetch (string-append "https://pypi.python.org/pypi/"
+                             name "/json")))
 
 ;; For packages found on PyPI that lack a source distribution.
 (define-condition-type &missing-source-error &error