Record errors that trigger a data reduction proxy bypass

net/http/http_response_headers.cc

Index: net/http/http_response_headers.cc
diff --git a/net/http/http_response_headers.cc b/net/http/http_response_headers.cc
index 7ecf37a2352704f02685e9012c64a04c296999bd..676f16db5aa90156a743e77b99823903b67d2964 100644
--- a/net/http/http_response_headers.cc
+++ b/net/http/http_response_headers.cc
@@ -1504,6 +1504,19 @@ HttpResponseHeaders::GetDataReductionProxyBypassEventType(
     // 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.