HPACK optimal Huffman code instrumentation and UMA collection.

net/spdy/hpack_huffman_aggregator.cc

+// 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 "net/spdy/hpack_huffman_aggregator.h"
+
+#include "base/metrics/bucket_ranges.h"
+#include "base/metrics/field_trial.h"
+#include "base/metrics/histogram.h"
+#include "base/metrics/sample_vector.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
+#include "net/base/load_flags.h"
+#include "net/http/http_request_headers.h"
+#include "net/http/http_request_info.h"
+#include "net/http/http_response_headers.h"
+#include "net/spdy/hpack_encoder.h"
+#include "net/spdy/spdy_http_utils.h"
+
+namespace net {
+
+namespace {
+
+const char kHistogramName[] = "Net.SpdyHpackEncodedCharacterFrequency";
+
+const size_t kTotalCountsPublishThreshold = 10000;
+
+// Each encoder uses the default dynamic table size of 4096 total bytes.
+const size_t kMaxEncoders = 20;
+
+}  // namespace
+
+HpackHuffmanAggregator::HpackHuffmanAggregator()
+  : counts_(256, 0),
+    total_counts_(0),
+    max_encoders_(kMaxEncoders) {
+}
+
+HpackHuffmanAggregator::~HpackHuffmanAggregator() {
+}
+
+void HpackHuffmanAggregator::AggregateTransactionCharacterCounts(
+    const HttpRequestInfo& request,
+    const HttpRequestHeaders& request_headers,
+    const ProxyServer& proxy,
+    const HttpResponseHeaders& response_headers) {
+  if (IsCrossOrigin(request)) {
+    return;
+  }
+  HostPortPair endpoint = HostPortPair(request.url.HostNoBrackets(),
+                                       request.url.EffectiveIntPort());
+  HpackEncoder* encoder = ObtainEncoder(
+      SpdySessionKey(endpoint, proxy, request.privacy_mode));
+
+  // Convert and encode the request and response header sets.
+  {
+    SpdyHeaderBlock headers;
+    CreateSpdyHeadersFromHttpRequest(
+        request, request_headers, &headers, SPDY4, false);
+
+    std::string tmp_out;
+    encoder->EncodeHeaderSet(headers, &tmp_out);
+  }
+  {
+    SpdyHeaderBlock headers;
+    CreateSpdyHeadersFromHttpResponse(response_headers, &headers);
+
+    std::string tmp_out;
+    encoder->EncodeHeaderSet(headers, &tmp_out);
+  }
+  if (total_counts_ >= kTotalCountsPublishThreshold) {
+    PublishCounts();
+  }
+}
+
+// static
+bool HpackHuffmanAggregator::UseAggregator() {
+  const std::string group_name =
+      base::FieldTrialList::FindFullName("HpackHuffmanAggregator");
+  if (group_name == "Enabled") {
+    return true;
+  }
+  // HACK(jgraettinger): To be removed before submission.

[jar (doing other things), 2014/04/18 21:14:53]

hmmmm.... this seems like a bad plan.... and subject to landing without removing
it by accident.

Is this the "approved" way of doing this??

+  // This is here to enable by-default on try-bots.
+  if (group_name.empty()) {
+    return true;
+  }
+  return false;
+}
+
+// static
+void HpackHuffmanAggregator::CreateSpdyHeadersFromHttpResponse(
+    const HttpResponseHeaders& headers,
+    SpdyHeaderBlock* headers_out) {
+  // Lower-case header names, and coalesce multiple values delimited by \0.
+  // Also add the fixed status header.
+  std::string name, value;
+  void* it = NULL;
+  while (headers.EnumerateHeaderLines(&it, &name, &value)) {
+    StringToLowerASCII(&name);
+    if (headers_out->find(name) == headers_out->end()) {
+      (*headers_out)[name] = value;
+    } else {
+      (*headers_out)[name] += std::string(1, '\0') + value;
+    }
+  }
+  (*headers_out)[":status"] = base::IntToString(headers.response_code());
+}
+
+// static
+bool HpackHuffmanAggregator::IsCrossOrigin(const HttpRequestInfo& request) {
+  // Require that the request is top-level, or that it shares
+  // an origin with its referer.
+  HostPortPair endpoint = HostPortPair(request.url.HostNoBrackets(),
+                                       request.url.EffectiveIntPort());
+  if ((request.load_flags & LOAD_MAIN_FRAME) == 0) {
+    std::string referer_str;
+    if (!request.extra_headers.GetHeader(HttpRequestHeaders::kReferer,
+                                         &referer_str)) {
+      // Require a referer.
+      return true;
+    }
+    GURL referer(referer_str);
+    HostPortPair referer_endpoint = HostPortPair(referer.HostNoBrackets(),
+                                                 referer.EffectiveIntPort());
+    if (!endpoint.Equals(referer_endpoint)) {
+      // Cross-origin request.
+      return true;
+    }
+  }
+  return false;
+}
+
+HpackEncoder* HpackHuffmanAggregator::ObtainEncoder(const SpdySessionKey& key) {
+  for (OriginEncoders::iterator it = encoders_.begin();
+       it != encoders_.end(); ++it) {
+    if (key.Equals(it->first)) {
+      // Move to head of list and return.
+      OriginEncoder origin_encoder = *it;
+      encoders_.erase(it);
+      encoders_.push_front(origin_encoder);
+      return origin_encoder.second;
+    }
+  }
+  // Not found. Create a new encoder, evicting one if needed.
+  encoders_.push_front(std::make_pair(key, new HpackEncoder()));
+  if (encoders_.size() > max_encoders_) {
+    delete encoders_.back().second;
+    encoders_.pop_back();
+  }
+  encoders_.front().second->SetCharCountsStorage(&counts_, &total_counts_);
+  return encoders_.front().second;
+}
+
+void HpackHuffmanAggregator::PublishCounts() {
+  // base::Histogram requires that values be 1-indexed.
+  const size_t kRangeMin = 1;
+  const size_t kRangeMax = counts_.size() + 1;
+  const size_t kBucketCount = kRangeMax + 1;
+
+  base::BucketRanges ranges(kBucketCount + 1);
+  for (size_t i = 0; i != ranges.size(); ++i) {
+    ranges.set_range(i, i);
+  }
+  ranges.ResetChecksum();
+
+  // Copy |counts_| into a SampleVector.
+  base::SampleVector samples(&ranges);
+  for (size_t i = 0; i != counts_.size(); ++i) {
+    samples.Accumulate(i + 1, counts_[i]);

[jar (doing other things), 2014/04/18 21:14:53]

Why are you putting samples into your personal histogram, and then copying them
over to the global histogram??

Why don't you just use a standard histogram?  They are plenty efficient. Are you
fearful that you wont get an atomic group of all samples?  Even with this
approach it will not be atomic :-/.

+  }
+
+  STATIC_HISTOGRAM_POINTER_BLOCK(
+      kHistogramName,
+      AddSamples(samples),
+      base::LinearHistogram::FactoryGet(
+          kHistogramName, kRangeMin, kRangeMax, kBucketCount,
+          base::HistogramBase::kUmaTargetedHistogramFlag));
+
+  // Clear counts.
+  counts_.assign(counts_.size(), 0);
+  total_counts_ = 0;
+}
+
+}  // namespace net