Issue 4097 - Make JSHydra use SpiderMonkey location from an environment variable if available

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():
+    path = os.environ.get('SPIDERMONKEY_BINARY')
+    if path and os.path.isfile(path):
+        return path
+
     baseDir = os.path.dirname(__file__)
 
     try:
         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()
         ))
 
     shell_dir = os.path.join(baseDir, JSSHELL_DIR + "-" + build)
     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
-    
+
     with closing(urllib.urlopen(JSSHELL_URL % build)) as response:
         data = response.read()
 
     with zipfile.ZipFile(StringIO(data)) 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