HPACK optimal Huffman code instrumentation and UMA collection.

net/spdy/hpack_huffman_aggregator.h

Index: net/spdy/hpack_huffman_aggregator.h
diff --git a/net/spdy/hpack_huffman_aggregator.h b/net/spdy/hpack_huffman_aggregator.h
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+// Copyright 2014 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 <list>
+#include <vector>
+
+#include "net/base/net_export.h"
+#include "net/spdy/spdy_header_block.h"
+#include "net/spdy/spdy_protocol.h"
+#include "net/spdy/spdy_session_key.h"
+
+namespace net {
+
+class HpackEncoder;
+class HttpRequestHeaders;
+struct HttpRequestInfo;
+class HttpResponseHeaders;
+class ProxyServer;
+
+namespace test {
+class HpackHuffmanAggregatorPeer;
+}  // namespace test
+
+class NET_EXPORT_PRIVATE HpackHuffmanAggregator {
+ public:
+  friend class test::HpackHuffmanAggregatorPeer;
+
+  HpackHuffmanAggregator();
+  ~HpackHuffmanAggregator();
+
+  // Encodes the request and response headers of the transaction with an
+  // HpackEncoder keyed on the transaction's SpdySessionKey. Literal headers
+  // emitted by that encoder are aggregated into internal character counts,
+  // which are periodically published to a UMA histogram.
+  void AggregateTransactionCharacterCounts(
+    const HttpRequestInfo& request,
+    const HttpRequestHeaders& request_headers,
+    const ProxyServer& proxy,
+    const HttpResponseHeaders& response_headers);
+
+  // Returns whether the aggregator is enabled for the session by a field trial.
+  static bool UseAggregator();
+
+ private:
+  // Returns true if the request is considered cross-origin,
+  // and should not be aggregated.
+  static bool IsCrossOrigin(const HttpRequestInfo& request);
+
+  // Converts |headers| into SPDY headers block |headers_out|.
+  static void CreateSpdyHeadersFromHttpResponse(
+      const HttpResponseHeaders& headers,
+      SpdyHeaderBlock* headers_out);
+
+  // Creates or returns an encoder for the origin key.
+  HpackEncoder* ObtainEncoder(const SpdySessionKey& key);
+
+  // Publishes aggregated counts to a UMA histogram.
+  void PublishCounts();
+
+  typedef std::pair<SpdySessionKey, HpackEncoder*> OriginEncoder;
+  typedef std::list<OriginEncoder> OriginEncoders;
+
+  std::vector<size_t> counts_;
+  size_t total_counts_;
+
+  OriginEncoders encoders_;
+  size_t max_encoders_;
+};
+
+}  // namespace net