Serve uploaded files through get_uploaded_file in development.

Previously, uploaded files were served:
* With S3UploadBackend, via get_uploaded_file (redirects to S3)
* With LocalUploadBackend in production, via nginx directly
* With LocalUploadBackend in development, via Django's static file server

This changes that last case to use get_uploaded_file in development,
which is a key step towards being able to do proper access control
authorization.

Does not affect production.

zerver/views/upload.py

@@ -1,13 +1,14 @@
 from __future__ import absolute_import
 
-from django.http import HttpRequest, HttpResponse, HttpResponseForbidden
+from django.http import HttpRequest, HttpResponse, HttpResponseForbidden, FileResponse, \
+    HttpResponseNotFound
 from django.shortcuts import redirect
 from django.utils.translation import ugettext as _
 
 from zerver.decorator import authenticated_json_post_view, zulip_login_required
 from zerver.lib.request import has_request_variables, REQ
 from zerver.lib.response import json_success, json_error
-from zerver.lib.upload import upload_message_image_from_request, \
+from zerver.lib.upload import upload_message_image_from_request, get_local_file_path, \
     get_signed_upload_url, get_realm_for_filename
 from zerver.lib.validator import check_bool
 from zerver.models import UserProfile
@@ -35,7 +36,7 @@ def serve_s3(request, user_profile, realm_id_str, filename, redir):
         realm_id = get_realm_for_filename(url_path)
         if realm_id is None:
             # File does not exist
-            return json_error(_("That file does not exist."), status=404)
+            return HttpResponseNotFound('<p>File not found</p>')
     else:
         realm_id = int(realm_id_str)
 
@@ -49,10 +50,24 @@ def serve_s3(request, user_profile, realm_id_str, filename, redir):
     else:
         return HttpResponseForbidden()
 
+# TODO: Rewrite this once we have django-sendfile
+def serve_local(request, path_id):
+    # type: (HttpRequest, str) -> HttpResponse
+    import os
+    import mimetypes
+    local_path = get_local_file_path(path_id)
+    if local_path is None:
+        return HttpResponseNotFound('<p>File not found</p>')
+    filename = os.path.basename(local_path)
+    response = FileResponse(open(local_path, 'rb'), content_type = mimetypes.guess_type(filename))
+    return response
+    response['Content-Disposition'] = 'attachment; filename=%s' % (filename)
+
 def serve_file_backend(request, user_profile, realm_id_str, filename, redir):
     # type: (HttpRequest, UserProfile, str, str, bool) -> HttpResponse
+    path_id = "%s/%s" % (realm_id_str, filename)
     if settings.LOCAL_UPLOADS_DIR is not None:
-         return HttpResponseForbidden() # Should have been served by nginx
+        return serve_local(request, path_id)
 
     return serve_s3(request, user_profile, realm_id_str, filename, redir)
 
@@ -69,4 +84,3 @@ def get_uploaded_file(request, realm_id_str, filename,
     # type: (HttpRequest, str, str, bool) -> HttpResponse
     user_profile = request.user
     return serve_file_backend(request, user_profile, realm_id_str, filename, redir)
-