Suppress pause-and-buffer behavior when the HTTP response won't satisfy future requests via cache.

webkit/media/buffered_resource_loader.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.
 
 #include "webkit/media/buffered_resource_loader.h"
 
 #include "base/callback_helpers.h"
 #include "base/format_macros.h"
+#include "base/metrics/histogram.h"
 #include "base/string_number_conversions.h"
 #include "base/string_util.h"
 #include "base/stringprintf.h"
 #include "media/base/media_log.h"
 #include "net/http/http_request_headers.h"
+#include "webkit/media/cache_util.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebKit.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebURLLoaderOptions.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/platform/WebKitPlatformSupport.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/platform/WebString.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/platform/WebURLError.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/platform/WebURLResponse.h"
 
 using WebKit::WebFrame;
 using WebKit::WebString;
 using WebKit::WebURLError;
@@ skipping 80 matching lines @@
     const GURL& url,
     int64 first_byte_position,
     int64 last_byte_position,
     DeferStrategy strategy,
     int bitrate,
     float playback_rate,
     media::MediaLog* media_log)
     : buffer_(kMinBufferCapacity, kMinBufferCapacity),
       loader_failed_(false),
       defer_strategy_(strategy),
+      might_be_reused_from_cache_in_future_(true),
       range_supported_(false),
       saved_forward_capacity_(0),
       url_(url),
       first_byte_position_(first_byte_position),
       last_byte_position_(last_byte_position),
       single_origin_(true),
       offset_(0),
       content_length_(kPositionNotSpecified),
       instance_size_(kPositionNotSpecified),
       read_position_(0),
@@ skipping 237 matching lines @@
                response.httpVersion() == WebURLResponse::HTTP_1_1 ? "1.1" :
                "Unknown")
            << " " << response.httpStatusCode();
   DCHECK(active_loader_.get());
 
   // The loader may have been stopped and |start_cb| is destroyed.
   // In this case we shouldn't do anything.
   if (start_cb_.is_null())
     return;
 
+  std::vector<UncacheableReason> reasons =
+      GetReasonsForUncacheability(response);
+  might_be_reused_from_cache_in_future_ = reasons.empty();
+  UMA_HISTOGRAM_BOOLEAN("Media.CacheUseful", reasons.empty());
+  for (size_t i = 0; i < reasons.size(); ++i) {
+    UMA_HISTOGRAM_ENUMERATION(
+        "Media.UncacheableReason", reasons[i], kMaxReason);

[scherkus (not reviewing), 2012/05/23 01:16:03]

one nit: we would increment counts every time we recreated a connection for a
single media source as opposed to the element (think about an ogg file doing a
binary search when seeking! that's like ~8 HTTP connections!)

I'd prefer to drop this code into the initial connection callback code inside
BDS but I suspect that may have to wait until we break down BRL into two pieces
(a piece that handles sending request + receiving response, and piece that
handles the sliding window reading + buffering)

[Ami GONE FROM CHROMIUM, 2012/05/23 01:27:28]

But the whole idea is to classify reusability of individual responses!

[scherkus (not reviewing), 2012/05/23 01:34:19]

I suppose so but how could we answer that out of N people who set the src to
"http://foo.com/bar.wav" they got something cacheable?

Can we solve this with more histograms!? (first response vs all responses!?)

[Ami GONE FROM CHROMIUM, 2012/05/23 01:38:25]

UMA is by its nature not per-site (aggregated along different dimension).
Could do.  

What I'm actually after is characterizing the useful-vs-unuseful as a first cut
(l.377).  l.380 is more about digging into the unuseful, if that turns out to be
a sizeable population.  I suspect we'll want to refine if that's the case, but
this seems like a useful first cut to me.

[scherkus (not reviewing), 2012/05/23 01:43:01]

I'm not interested in the domain but setting the src attribute has a 1:1 mapping
to creating a media engine + loading a URL, which makes for easier to comprehend
numbers (at least for me!)
Agreed. I'm more interested in collecting some data over no data and refining
later along w/ subsequent code shuffling, but taking this opportunity to
mini-brainstorm about said possible refinements!

+  }
+
   // Expected content length can be |kPositionNotSpecified|, in that case
   // |content_length_| is not specified and this is a streaming response.
   content_length_ = response.expectedContentLength();
 
   // We make a strong assumption that when we reach here we have either
   // received a response from HTTP/HTTPS protocol or the request was
   // successful (in particular range request). So we only verify the partial
   // response for HTTP and HTTPS protocol.
   if (url_.SchemeIs(kHttpScheme) || url_.SchemeIs(kHttpsScheme)) {
     bool partial_response = (response.httpStatusCode() == kHttpPartialContent);
@@ skipping 152 matching lines @@
   }
 }
 
 bool BufferedResourceLoader::HasSingleOrigin() const {
   DCHECK(start_cb_.is_null())
       << "Start() must complete before calling HasSingleOrigin()";
   return single_origin_;
 }
 
 void BufferedResourceLoader::UpdateDeferStrategy(DeferStrategy strategy) {
+  if (!might_be_reused_from_cache_in_future_ && strategy == kNeverDefer)
+    strategy = kThresholdDefer;
   defer_strategy_ = strategy;
   UpdateDeferBehavior();
 }
 
 void BufferedResourceLoader::SetPlaybackRate(float playback_rate) {
   playback_rate_ = playback_rate;
 
   // This is a pause so don't bother updating the buffer window as we'll likely
   // get unpaused in the future.
   if (playback_rate_ == 0.0)
@@ skipping 260 matching lines @@
 
 void BufferedResourceLoader::Log() {
   media_log_->AddEvent(
       media_log_->CreateBufferedExtentsChangedEvent(
           offset_ - buffer_.backward_bytes(),
           offset_,
           offset_ + buffer_.forward_bytes()));
 }
 
 }  // namespace webkit_media