Hand craft an A/B test of SDCH compression...

net/url_request/url_request_job.h

 // Copyright (c) 2006-2008 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.
 
 #ifndef NET_URL_REQUEST_URL_REQUEST_JOB_H_
 #define NET_URL_REQUEST_URL_REQUEST_JOB_H_
 
 #include <string>
 #include <vector>
 
 #include "base/ref_counted.h"
 #include "base/scoped_ptr.h"
+#include "base/time.h"
 #include "net/base/filter.h"
 #include "net/base/load_states.h"
 
 namespace net {
 class AuthChallengeInfo;
 class HttpResponseInfo;
 class IOBuffer;
 class UploadData;
 }
 
 class GURL;
 class URLRequest;
 class URLRequestStatus;
 class URLRequestJobMetrics;
 
 // The URLRequestJob is using RefCounterThreadSafe because some sub classes
 // can be destroyed on multiple threads. This is the case of the
 // UrlRequestFileJob.
 class URLRequestJob : public base::RefCountedThreadSafe<URLRequestJob>,
                       public FilterContext {
  public:
+  // When histogramming results related to SDCH and/or an SDCH latency test, the
+  // number of packets for which we need to record arrival times so as to
+  // calculate interpacket latencies.  We currently are only looking at the
+  // first few packets, as we're monitoring the impact of the initial TCP
+  // congestion window on stalling of transmissions.
+  static const size_t kSdchPacketHistogramCount = 5;
+
   explicit URLRequestJob(URLRequest* request);
   virtual ~URLRequestJob();
 
   // Returns the request that owns this job. THIS POINTER MAY BE NULL if the
   // request was destroyed.
   URLRequest* request() const {
     return request_;
   }
 
   // Sets the upload data, most requests have no upload data, so this is a NOP.
@@ skipping 150 matching lines @@
 
   // FilterContext methods:
   // These methods are not applicable to all connections.
   virtual bool GetMimeType(std::string* mime_type) const { return false; }
   virtual bool GetURL(GURL* gurl) const;
   virtual base::Time GetRequestTime() const;
   virtual bool IsCachedContent() const;
   virtual int64 GetByteReadCount() const;
   virtual int GetResponseCode() const { return -1; }
   virtual int GetInputStreamBufferSize() const { return kFilterBufSize; }
+  virtual void RecordPacketStats(StatisticSelector statistic) const;
 
  protected:
   // Notifies the job that headers have been received.
   void NotifyHeadersComplete();
 
   // Notifies the request that the job has completed a Read operation.
   void NotifyReadComplete(int bytes_read);
 
   // Notifies the request that a start error has occurred.
   void NotifyStartError(const URLRequestStatus& status);
@@ skipping 51 matching lines @@
 
   // Set the status of the job.
   void SetStatus(const URLRequestStatus& status);
 
   // Whether the job is doing performance profiling
   bool is_profiling_;
 
   // Contains IO performance measurement when profiling is enabled.
   scoped_ptr<URLRequestJobMetrics> metrics_;
 
+  // Facilitate histogramming by turning on packet counting.
+  // If called more than once, the largest value will be used.
+  void EnablePacketCounting(size_t max_packets_timed);
+
  private:
   // Size of filter input buffers used by this class.
   static const int kFilterBufSize;
 
   // When data filtering is enabled, this function is used to read data
   // for the filter.  Returns true if raw data was read.  Returns false if
   // an error occurred (or we are waiting for IO to complete).
   bool ReadRawDataForFilter(int *bytes_read);
 
   // Called in response to a redirect that was not canceled to follow the
   // redirect. The current job will be replaced with a new job loading the
   // given redirect destination.
   void FollowRedirect(const GURL& location, int http_status_code);
 
   // Updates the profiling info and notifies observers that bytes_read bytes
   // have been read.
   void RecordBytesRead(int bytes_read);
 
- private:
   // Called to query whether there is data available in the filter to be read
   // out.
   bool FilterHasData();
 
+  // Record packet arrival times for possible use in histograms.
+  void UpdatePacketReadTimes();
+
   // Indicates that the job is done producing data, either it has completed
   // all the data or an error has been encountered. Set exclusively by
   // NotifyDone so that it is kept in sync with the request.
   bool done_;
 
   // Cache the load flags from request_ because it might go away.
   int load_flags_;
 
   // The data stream filter which is enabled on demand.
   scoped_ptr<Filter> filter_;
 
   // If the filter filled its output buffer, then there is a change that it
   // still has internal data to emit, and this flag is set.
   bool filter_needs_more_output_space_;
 
   // When we filter data, we receive data into the filter buffers.  After
   // processing the filtered data, we return the data in the caller's buffer.
   // While the async IO is in progress, we save the user buffer here, and
   // when the IO completes, we fill this in.
   net::IOBuffer *read_buffer_;
   int read_buffer_len_;
 
   // Used by HandleResponseIfNecessary to track whether we've sent the
   // OnResponseStarted callback and potentially redirect callbacks as well.
   bool has_handled_response_;
 
   // Expected content size
   int64 expected_content_size_;
 
+  //----------------------------------------------------------------------------
+  // Data used for statistics gathering in some instances.  This data is only
+  // used for histograms etc., and is not required.  It is optionally gathered
+  // based on the settings of several control variables.
+
+  // Enable recording of packet arrival times for histogramming.
+  bool packet_timing_enabled_;
+
+  // TODO(jar): improve the quality of the gathered info by gathering most times
+  // at a lower point in the network stack, assuring we have actual packet
+  // boundaries, rather than approximations.  Also note that input byte count
+  // as gathered here is post-SSL, and post-cache-fetch, and does not reflect
+  // true packet arrival times in such cases.
+
   // Total number of bytes read from network (or cache) and and typically handed
   // to filter to process.  Used to histogram compression ratios, and error
   // recovery scenarios in filters.
   int64 filter_input_byte_count_;
 
+  // The number of bytes that have been accounted for in packets (where some of
+  // those packets may possibly have had their time of arrival recorded).
+  int64 bytes_observed_in_packets_;
+
+  // Limit on the size of the array packet_times_.  This can be set to
+  // zero, and then no packet times will be gathered.
+  size_t max_packets_timed_;
+
+  // Arrival times for some of the first few packets.
+  std::vector<base::Time> packet_times_;
+
+  // The request time may not be available when we are being destroyed, so we
+  // snapshot it early on.
+  base::Time request_time_snapshot_;
+
+  // Since we don't save all packet times in packet_times_, we save the
+  // last time for use in histograms.
+  base::Time final_packet_time_;
+
+  // The count of the number of packets, some of which may not have been timed.
+  // We're ignoring overflow, as 1430 x 2^31 is a LOT of bytes.
+  int observed_packet_count_;
+
   DISALLOW_COPY_AND_ASSIGN(URLRequestJob);
 };
 
 #endif  // NET_URL_REQUEST_URL_REQUEST_JOB_H_