X-Chrome-Variations logic refactoring

chrome/browser/chrome_metrics_helper.cc

Index: chrome/browser/chrome_metrics_helper.cc
diff --git a/chrome/browser/chrome_metrics_helper.cc b/chrome/browser/chrome_metrics_helper.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ee6cbd439a381e7b3f60210e9d6d6859ac7d14c9
--- /dev/null
+++ b/chrome/browser/chrome_metrics_helper.cc
@@ -0,0 +1,132 @@
+// 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 "chrome/browser/chrome_metrics_helper.h"
+
+#include "base/base64.h"
+#include "base/memory/singleton.h"
+#include "chrome/browser/google/google_util.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/profiles/profile_io_data.h"
+#include "chrome/common/metrics/proto/chrome_experiments.pb.h"
+#include "chrome/common/metrics/variations/variations_util.h"
+#include "content/public/browser/browser_thread.h"
+#include "net/http/http_request_headers.h"
+
+using content::BrowserThread;
+
+ChromeMetricsHelper* ChromeMetricsHelper::GetInstance() {
+  return Singleton<ChromeMetricsHelper>::get();
+}
+
+void ChromeMetricsHelper::AppendHeaders(const GURL& url,
+                                        bool incognito,
+                                        bool uma_enabled,
+                                        net::HttpRequestHeaders* headers) {
+  // Note the criteria for attaching Chrome experiment headers:
+  // 1. We only transmit to *.google.<TLD> domains. NOTE that this use of
+  //    google_util helpers to check this does not guarantee that the URL is
+  //    Google-owned, only that it is of the form *.google.<TLD>. In the future
+  //    we may choose to reinforce this check.
+  // 2. Only transmit for non-Incognito profiles.
+  // 3. For the X-Chrome-UMA-Enabled bit, only set it if UMA is in fact enabled
+  //    for this install of Chrome.
+  // 4. For the X-Chrome-Variations, only include non-empty variation IDs.
+  if (incognito ||
+      !google_util::IsGoogleDomainUrl(url.spec(),
+                                      google_util::ALLOW_SUBDOMAIN,
+                                      google_util::ALLOW_NON_STANDARD_PORTS))
+    return;

[SteveT, 2012/12/14 18:35:41]

nit: I think we prefer curlies around a single line statement if the "if"
condition spans multiple lines.

[Bart N., 2012/12/16 00:09:10]

Done.

+
+  if (uma_enabled)
+    headers->SetHeaderIfMissing("X-Chrome-UMA-Enabled", "1");
+
+  // Lazily initialize the header, if not already done, before attempting to
+  // transmit it.
+  InitVariationIDsCacheIfNeeded();
+  base::AutoLock scoped_lock(lock_);
+  if (!variation_ids_header_.empty())
+    headers->SetHeaderIfMissing("X-Chrome-Variations", variation_ids_header_);
+}
+
+ChromeMetricsHelper::ChromeMetricsHelper()
+    : variation_ids_cache_initialized_(false) {
+}
+
+ChromeMetricsHelper::~ChromeMetricsHelper() {
+}
+
+void ChromeMetricsHelper::OnFieldTrialGroupFinalized(
+    const std::string& trial_name,
+    const std::string& group_name) {
+  chrome_variations::VariationID new_id =
+      chrome_variations::GetGoogleVariationID(
+          chrome_variations::GOOGLE_WEB_PROPERTIES, trial_name, group_name);
+  if (new_id == chrome_variations::kEmptyID)
+    return;
+  base::AutoLock scoped_lock(lock_);
+  variation_ids_set_.insert(new_id);
+  UpdateVariationIDsHeaderValue();
+}
+
+void ChromeMetricsHelper::InitVariationIDsCacheIfNeeded() {
+  base::AutoLock scoped_lock(lock_);
+  if (variation_ids_cache_initialized_)
+    return;
+
+  // Register for additional cache updates. This is done first to avoid a race
+  // that could cause registered FieldTrials to be missed.
+  base::FieldTrialList::AddObserver(this);
+
+  base::FieldTrial::ActiveGroups initial_groups;
+  base::FieldTrialList::GetActiveFieldTrialGroups(&initial_groups);
+  for (base::FieldTrial::ActiveGroups::const_iterator it =
+       initial_groups.begin(); it != initial_groups.end(); ++it) {
+    const chrome_variations::VariationID id =
+        chrome_variations::GetGoogleVariationID(
+            chrome_variations::GOOGLE_WEB_PROPERTIES, it->trial_name,
+            it->group_name);
+    if (id != chrome_variations::kEmptyID)
+      variation_ids_set_.insert(id);
+  }
+  UpdateVariationIDsHeaderValue();
+
+  variation_ids_cache_initialized_ = true;
+}
+
+void ChromeMetricsHelper::UpdateVariationIDsHeaderValue() {
+  // The header value is a serialized protobuffer of Variation IDs which is
+  // base64 encoded before transmitting as a string.
+  if (variation_ids_set_.empty())
+    return;
+
+  // This is the bottleneck for the creation of the header, so validate the size
+  // here. Force a hard maximum on the ID count in case the Variations server
+  // returns too many IDs and DOSs receiving servers with large requests.
+  DCHECK_LE(variation_ids_set_.size(), 10U);
+  if (variation_ids_set_.size() > 20) {
+    variation_ids_header_.clear();
+    return;
+  }
+
+  metrics::ChromeVariations proto;
+  for (std::set<chrome_variations::VariationID>::const_iterator it =
+      variation_ids_set_.begin(); it != variation_ids_set_.end(); ++it)
+    proto.add_variation_id(*it);
+
+  std::string serialized;
+  proto.SerializeToString(&serialized);
+
+  std::string hashed;
+  if (base::Base64Encode(serialized, &hashed)) {
+    // If successful, swap the header value with the new one.
+    // Note that the list of IDs and the header could be temporarily out of sync
+    // if IDs are added as the header is recreated. The receiving servers are OK
+    // with such descrepancies.
+    variation_ids_header_ = hashed;
+  } else {
+    NOTREACHED() << "Failed to base64 encode Variation IDs value: "
+                 << serialized;
+  }
+}