root/chrome/browser/metrics/extension_metrics.cc

DEFINITIONS

1. cached_profile_
2. HashExtension
3. GetMetricsProfile
4. GetInstalledExtensions
5. WriteExtensionList

// 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 "chrome/browser/metrics/extension_metrics.h"

#include <set>

#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/strings/stringprintf.h"
#include "chrome/browser/browser_process.h"
#include "chrome/browser/profiles/profile_manager.h"
#include "chrome/common/metrics/proto/system_profile.pb.h"
#include "extensions/browser/extension_registry.h"
#include "extensions/common/extension_set.h"

// From third_party/smhasher/src/City.h; that file can't be included here due
// to macro redefinitions (of UINT8_C, etc.) on Windows.
// TODO(mvrable): Clean up City.h so it can be included directly.
uint64 CityHash64(const char *buf, size_t len);

namespace {

// The number of possible hash keys that a client may use.  The UMA client_id
// value is reduced modulo this value to produce the key used by that
// particular client.
const size_t kExtensionListClientKeys = 4096;

// The number of hash buckets into which extension IDs are mapped.  This sets
// the possible output range of the HashExtension function.
const size_t kExtensionListBuckets = 1024;

}  // namespace

HashedExtensionMetrics::HashedExtensionMetrics(uint64 client_id)
    : client_key_(client_id % kExtensionListClientKeys),
      cached_profile_(NULL) {}
HashedExtensionMetrics::~HashedExtensionMetrics() {}

// static
int HashedExtensionMetrics::HashExtension(const std::string& extension_id,
                                          uint32 client_key) {
  DCHECK_LE(client_key, kExtensionListClientKeys);
  std::string message =
      base::StringPrintf("%u:%s", client_key, extension_id.c_str());
  uint64 output = CityHash64(message.data(), message.size());
  return output % kExtensionListBuckets;
}

Profile* HashedExtensionMetrics::GetMetricsProfile() {
  ProfileManager* profile_manager = g_browser_process->profile_manager();
  if (!profile_manager)
    return NULL;

  // If there is a cached profile, reuse that.  However, check that it is still
  // valid first.
  if (cached_profile_ && profile_manager->IsValidProfile(cached_profile_))
    return cached_profile_;

  // Find a suitable profile to use, and cache it so that we continue to report
  // statistics on the same profile.
  cached_profile_ = ProfileManager::GetLastUsedProfile();
  if (cached_profile_) {
    // Ensure that the returned profile is not an incognito profile.
    cached_profile_ = cached_profile_->GetOriginalProfile();
  }
  return cached_profile_;
}

scoped_ptr<extensions::ExtensionSet>
HashedExtensionMetrics::GetInstalledExtensions() {
#if defined(ENABLE_EXTENSIONS)
  // UMA reports do not support multiple profiles, but extensions are installed
  // per-profile.  We return the extensions installed in the primary profile.
  // In the future, we might consider reporting data about extensions in all
  // profiles.
  Profile* profile = GetMetricsProfile();
  if (profile) {
    return extensions::ExtensionRegistry::Get(profile)
        ->GenerateInstalledExtensionsSet();
  }
#endif  // defined(ENABLE_EXTENSIONS)
  return scoped_ptr<extensions::ExtensionSet>();
}

void HashedExtensionMetrics::WriteExtensionList(
    metrics::SystemProfileProto* system_profile) {
  scoped_ptr<extensions::ExtensionSet> extensions(GetInstalledExtensions());
  if (!extensions)
    return;

  std::set<int> buckets;
  for (extensions::ExtensionSet::const_iterator it = extensions->begin();
       it != extensions->end(); ++it) {
    buckets.insert(HashExtension((*it)->id(), client_key_));
  }

  for (std::set<int>::const_iterator it = buckets.begin();
       it != buckets.end(); ++it) {
    system_profile->add_occupied_extension_bucket(*it);
  }
}