Record errors that trigger a data reduction proxy bypass

net/http/http_response_headers.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // The rules for header parsing were borrowed from Firefox:
 // http://lxr.mozilla.org/seamonkey/source/netwerk/protocol/http/src/nsHttpResponseHead.cpp
 // The rules for parsing content-types were also borrowed from Firefox:
 // http://lxr.mozilla.org/mozilla/source/netwerk/base/src/nsURLHelper.cpp#834
 
 #include "net/http/http_response_headers.h"
@@ skipping 1486 matching lines @@
       response_code() == HTTP_SERVICE_UNAVAILABLE) {
     // Fall back if a 500, 502 or 503 is returned.
     return ProxyService::INTERNAL_SERVER_ERROR_BYPASS;
   }
   if (!IsDataReductionProxyResponse() &&
       (response_code() != HTTP_NOT_MODIFIED)) {
     // A Via header might not be present in a 304. Since the goal of a 304
     // response is to minimize information transfer, a sender in general
     // should not generate representation metadata other than Cache-Control,
     // Content-Location, Date, ETag, Expires, and Vary.
+
+    // A Via header might also not be present in a 4xx response. If there is
+    // evidence that the 4xx response was generated by the proxy, bypass it.
+    if (response_code() >= HTTP_BAD_REQUEST &&
+        response_code() < HTTP_INTERNAL_SERVER_ERROR) {
+      // If the data reduction proxy ever deprecates use of this "Server"
+      // header, a 4xx response from the proxy will be interpreted as
+      // a response that is missing a "Via" header. Either way, the proxy will
+      // be bypassed.
+      if (HasHeaderValue("Server", "GFE/2.0"))
+        return ProxyService::PROXY_4XX_BYPASS;

[mef, 2014/05/29 16:41:38]

I'm still uneasy about hardcoded "GFE/2.0", and I'm looking for suggestions.

[bengr, 2014/05/29 18:46:19]

OK

+      // Otherwise, bypass on the missing Via header.
+    }
     return ProxyService::MISSING_VIA_HEADER;
   }
   // There is no bypass event.
   return ProxyService::BYPASS_EVENT_TYPE_MAX;
 }
 #endif  // defined(SPDY_PROXY_AUTH_ORIGIN)
 
 }  // namespace net