backends-nginx: Add support for Nginx versions older than 1.5.9.

In this commit we are adding support for Nginx version older than
1.5.9. This is achieved through conditionally quoting the URL's in
X-Accel-Redirect headers according to compatibility with Nginx.
Since newer versions of Nginx expect URL's in X-Accel-Redirect to
be quoted unlike the versions older that Nginx 1.5.9. In this commit
we start to check the Nginx version using 'nginx -v' and then caching
the result be making use of a decorator. Using this result we decide
whether the outgoing URL should be quoted or not.
Fixes: johnsensible#56, johnsensible#58. Closes johnsensible#45.

Author: adnrs96

sendfile/backends/_internalredirect.py

@@ -1,14 +1,43 @@
 import os.path
+import subprocess
 
 from django.conf import settings
 from django.utils.encoding import smart_text, smart_bytes
+from django.conf import settings
 
 try:
     from urllib.parse import quote
 except ImportError:
     from urllib import quote
 
 
+def _decision(fn):
+    _cached_decision = []
+    def _decorated():
+        if not _cached_decision:
+            _cached_decision.append(fn())
+        return _cached_decision[0]
+    return _decorated
+
+@_decision
+def should_be_quoted():
+    backend = getattr(settings, 'SENDFILE_BACKEND', None)
+    if backend == 'sendfile.backends.nginx':
+        try:
+            nginx_version = subprocess.Popen(['nginx','-v'],
+                                             stdout=subprocess.PIPE,
+                                             stderr=subprocess.STDOUT).stdout.read()
+            nginx_version = nginx_version.split('/')[1].split(' ')[0].split('.')
+            nginx_version = map(int, nginx_version)
+            # Since Starting with Nginx 1.5.9, quoted url's are expected to be
+            # sent with X-Accel-Redirect headers, we will not quote url's for
+            # versions of Nginx before 1.5.9
+            if nginx_version < [1, 5, 9]:
+                return False
+        except:
+            return True
+    return True
+
 def _convert_file_to_url(filename):
     relpath = os.path.relpath(filename, settings.SENDFILE_ROOT)
 
@@ -21,4 +50,7 @@ def _convert_file_to_url(filename):
     # Python3 urllib.parse.quote accepts both unicode and bytes, while Python2 urllib.quote only accepts bytes.
     # So use bytes for quoting and then go back to unicode.
     url = [smart_bytes(url_component) for url_component in url]
-    return smart_text(quote(b'/'.join(url)))
+    if should_be_quoted():
+        return smart_text(quote(b'/'.join(url)))
+    else:
+        return smart_text(b'/'.join(url))