Issue 2956 - Ensure the correct version of jsshell is present

utils.py

 # coding: utf-8
 
 # This Source Code is subject to the terms of the Mozilla Public License
 # version 2.0 (the "License"). You can obtain a copy of the License at
 # http://mozilla.org/MPL/2.0/.
 
+from contextlib import closing
 import os
 import platform
 from StringIO import StringIO
 import sys
 import urllib
 import zipfile
 
+JSSHELL_DIR = "mozilla-esr31"
+JSSHELL_URL = ("https://ftp.mozilla.org/pub/mozilla.org/firefox/nightly"
+               "/2015/02/2015-02-25-00-22-19-%s/jsshell-%%s.zip" % JSSHELL_DIR)
+
+JSSHELL_SUPPORTED_PLATFORMS = {
+  "win32": "win32",
+  "linux2": {
+    "i686": "linux-i686",
+    "x86_64": "linux-x86_64"
+  },
+  "darwin": "mac"
+}
+
 def ensureJSShell():
   baseDir = os.path.dirname(__file__)
-  shell_dir = os.path.join(baseDir, 'mozilla')
+  shell_dir = os.path.join(baseDir, JSSHELL_DIR)
+
   if not os.path.exists(shell_dir):
     os.makedirs(shell_dir)
   if sys.platform == 'win32':
     path = os.path.join(shell_dir, 'js.exe')
   else:
     path = os.path.join(shell_dir, 'js')
+
   if os.path.exists(path):
     return path
 
-  supported_platforms = {
-    'win32': 'win32',
-    'linux2': {
-      'i686': 'linux-i686',
-      'x86_64': 'linux-x86_64'
-    },
-    'darwin': 'mac',
-  }
   try:
-    build = supported_platforms[sys.platform]
+    build = JSSHELL_SUPPORTED_PLATFORMS[sys.platform]
     if isinstance(build, dict):
       build = build[platform.machine()]
   except KeyError:
     raise Exception('Platform %s (%s) not supported by JS shell' % (
       sys.platform, platform.machine()
     ))
 
-  download_url = 'https://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/2015/02/2015-02-25-00-22-19-mozilla-esr31/jsshell-%s.zip' % build
-  data = StringIO(urllib.urlopen(download_url).read())
-  zip = zipfile.ZipFile(data)
-  zip.extractall(shell_dir)
-  zip.close()
+  with closing(urllib.urlopen(JSSHELL_URL % build)) as response, \
+       zipfile.ZipFile(StringIO(response.read())) as zip:
+    zip.extractall(shell_dir)
 
   if not os.path.exists(path):
     raise Exception('Downloaded package didn\'t contain JS shell executable')
 
   try:
     os.chmod(path, 0700)
   except:
     pass
 
   return path