Not allow compression when requesting multimedia

net/url_request/url_request_http_job.cc

 // Copyright (c) 2011 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.
 
 #include "net/url_request/url_request_http_job.h"
 
 #include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/file_util.h"
@@ skipping 380 matching lines @@
 
   // The transaction started synchronously, but we need to notify the
   // URLRequest delegate via the message loop.
   MessageLoop::current()->PostTask(
       FROM_HERE,
       method_factory_.NewRunnableMethod(
           &URLRequestHttpJob::OnStartCompleted, rv));
 }
 
 void URLRequestHttpJob::AddExtraHeaders() {
-  // TODO(jar): Consider optimizing away SDCH advertising bytes when the URL is
-  // probably an img or such (and SDCH encoding is not likely).
-  bool advertise_sdch = SdchManager::Global() &&
-      SdchManager::Global()->IsInSupportedDomain(request_->url());
-  std::string avail_dictionaries;
-  if (advertise_sdch) {
-    SdchManager::Global()->GetAvailDictionaryList(request_->url(),
-                                                  &avail_dictionaries);
+  // Supply Accept-Encoding field only if it is not already supplied.
+  if (!request_info_.extra_headers.HasHeader(
+      HttpRequestHeaders::kAcceptEncoding)) {
+    // TODO(jar): Consider optimizing away SDCH advertising bytes when the URL
+    // is probably an img or such (and SDCH encoding is not likely).

[jar (doing other things), 2011/06/09 21:24:37]

Do you think this Todo() is satisfied?  Perhaps it is not completely satisfied,
and so you should move it??

Perhaps you can improve your comment (line 401) to indicate that 

the Accept-encoding is provided IF the content is known to have restrictions on
potential encoding, such as multi-media. 


You could then add a TODO() around line 401 to suggest that jpeg files etc.
should set up a request header if possible.

[enal, 2011/06/09 21:55:03]

Done.

+    bool advertise_sdch = SdchManager::Global() &&
+        SdchManager::Global()->IsInSupportedDomain(request_->url());
+    std::string avail_dictionaries;
+    if (advertise_sdch) {
+      SdchManager::Global()->GetAvailDictionaryList(request_->url(),
+                                                    &avail_dictionaries);
 
-    // The AllowLatencyExperiment() is only true if we've successfully done a
-    // full SDCH compression recently in this browser session for this host.
-    // Note that for this path, there might be no applicable dictionaries, and
-    // hence we can't participate in the experiment.
-    if (!avail_dictionaries.empty() &&
-        SdchManager::Global()->AllowLatencyExperiment(request_->url())) {
-      // We are participating in the test (or control), and hence we'll
-      // eventually record statistics via either SDCH_EXPERIMENT_DECODE or
-      // SDCH_EXPERIMENT_HOLDBACK, and we'll need some packet timing data.
-      packet_timing_enabled_ = true;
-      if (base::RandDouble() < .01) {
-        sdch_test_control_ = true;  // 1% probability.
-        advertise_sdch = false;
-      } else {
-        sdch_test_activated_ = true;
+      // The AllowLatencyExperiment() is only true if we've successfully done a
+      // full SDCH compression recently in this browser session for this host.
+      // Note that for this path, there might be no applicable dictionaries,
+      // and hence we can't participate in the experiment.
+      if (!avail_dictionaries.empty() &&
+          SdchManager::Global()->AllowLatencyExperiment(request_->url())) {
+        // We are participating in the test (or control), and hence we'll
+        // eventually record statistics via either SDCH_EXPERIMENT_DECODE or
+        // SDCH_EXPERIMENT_HOLDBACK, and we'll need some packet timing data.
+        packet_timing_enabled_ = true;
+        if (base::RandDouble() < .01) {
+          sdch_test_control_ = true;  // 1% probability.
+          advertise_sdch = false;
+        } else {
+          sdch_test_activated_ = true;
+        }
+      }
+    }
+
+    // Supply Accept-Encoding headers first so that it is more likely that they
+    // will be in the first transmitted packet.  This can sometimes make it
+    // easier to filter and analyze the streams to assure that a proxy has not
+    // damaged these headers.  Some proxies deliberately corrupt Accept-Encoding
+    // headers.
+    if (!advertise_sdch) {
+      // Tell the server what compression formats we support (other than SDCH).
+      request_info_.extra_headers.SetHeader(
+          HttpRequestHeaders::kAcceptEncoding, "gzip,deflate");
+    } else {
+      // Include SDCH in acceptable list.
+      request_info_.extra_headers.SetHeader(
+          HttpRequestHeaders::kAcceptEncoding, "gzip,deflate,sdch");
+      if (!avail_dictionaries.empty()) {
+        request_info_.extra_headers.SetHeader(
+            kAvailDictionaryHeader,
+            avail_dictionaries);
+        sdch_dictionary_advertised_ = true;
+        // Since we're tagging this transaction as advertising a dictionary,
+        // we'll definitely employ an SDCH filter (or tentative sdch filter)
+        // when we get a response.  When done, we'll record histograms via
+        // SDCH_DECODE or SDCH_PASSTHROUGH.  Hence we need to record packet
+        // arrival times.
+        packet_timing_enabled_ = true;
       }
     }
   }
 
-  // Supply Accept-Encoding headers first so that it is more likely that they
-  // will be in the first transmitted packet.  This can sometimes make it easier
-  // to filter and analyze the streams to assure that a proxy has not damaged
-  // these headers.  Some proxies deliberately corrupt Accept-Encoding headers.
-  if (!advertise_sdch) {
-    // Tell the server what compression formats we support (other than SDCH).
-    request_info_.extra_headers.SetHeader(
-        HttpRequestHeaders::kAcceptEncoding, "gzip,deflate");
-  } else {
-    // Include SDCH in acceptable list.
-    request_info_.extra_headers.SetHeader(
-        HttpRequestHeaders::kAcceptEncoding, "gzip,deflate,sdch");
-    if (!avail_dictionaries.empty()) {
-      request_info_.extra_headers.SetHeader(
-          kAvailDictionaryHeader,
-          avail_dictionaries);
-      sdch_dictionary_advertised_ = true;
-      // Since we're tagging this transaction as advertising a dictionary, we'll
-      // definitely employ an SDCH filter (or tentative sdch filter) when we get
-      // a response.  When done, we'll record histograms via SDCH_DECODE or
-      // SDCH_PASSTHROUGH.  Hence we need to record packet arrival times.
-      packet_timing_enabled_ = true;
-    }
-  }
-
   URLRequestContext* context = request_->context();
   if (context) {
     // Only add default Accept-Language and Accept-Charset if the request
     // didn't have them specified.
     if (!context->accept_language().empty()) {
       request_info_.extra_headers.SetHeaderIfMissing(
           HttpRequestHeaders::kAcceptLanguage,
           context->accept_language());
     }
     if (!context->accept_charset().empty()) {
@@ skipping 945 matching lines @@
 }
 
 bool URLRequestHttpJob::IsCompressibleContent() const {
   std::string mime_type;
   return GetMimeType(&mime_type) &&
       (IsSupportedJavascriptMimeType(mime_type.c_str()) ||
        IsSupportedNonImageMimeType(mime_type.c_str()));
 }
 
 }  // namespace net