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..b2248ec3c48afd8c64fbf16b2a033a5e1f07d98a 100644
--- a/net/http/http_response_headers.cc
+++ b/net/http/http_response_headers.cc
@@ -1504,6 +1504,15 @@ 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 (HasHeaderValue("Server", "GFE/2.0"))

[mef, 2014/05/28 15:39:57]

Um, why do you need to hardcode GFE here?

[bengr, 2014/05/29 16:09:48]

A missing via header with this server error indicates that the proxy front end
rejected the request. The proxy should be bypasses for any retry of this
request. In contrast, if a 4xx is returned that lacks the proxy via header and
lacks the proxy front end server header, something more serious is wrong with
the connection (e.g., a middle box is stripping headers). In that case, the
proxy should be bypassed for longer.

I added a comment to address concerns about deprecation.

Note: In the next few weeks, I plan to move all DataReductionProxy code from
HttpResponseHeaders to components/data_reduction_proxy.

+        return ProxyService::PROXY_4XX_BYPASS;
+      // Otherwise, bypass on the missing Via header.
+    }
     return ProxyService::MISSING_VIA_HEADER;
   }
   // There is no bypass event.