chrome/browser/component_updater/component_updater_service.cc

// 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/component_updater/component_updater_service.h"

#include <algorithm>
#include <set>
#include <vector>

#include "base/at_exit.h"
#include "base/bind.h"
#include "base/compiler_specific.h"
#include "base/file_util.h"
#include "base/files/file_path.h"
#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/memory/weak_ptr.h"
#include "base/stl_util.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_piece.h"
#include "base/strings/string_util.h"
#include "base/strings/stringprintf.h"
#include "base/threading/sequenced_worker_pool.h"
#include "base/timer/timer.h"
#include "chrome/browser/browser_process.h"
#include "chrome/browser/component_updater/component_patcher.h"
#include "chrome/browser/component_updater/component_unpacker.h"
#include "chrome/browser/component_updater/component_updater_ping_manager.h"
#include "chrome/browser/component_updater/component_updater_utils.h"
#include "chrome/browser/component_updater/crx_downloader.h"
#include "chrome/browser/component_updater/crx_update_item.h"
#include "chrome/browser/component_updater/update_response.h"
#include "chrome/common/chrome_version_info.h"
#include "content/public/browser/browser_thread.h"
#include "content/public/browser/resource_controller.h"
#include "content/public/browser/resource_throttle.h"
#include "extensions/common/extension.h"
#include "net/base/escape.h"
#include "net/base/load_flags.h"
#include "net/base/net_errors.h"
#include "net/url_request/url_fetcher.h"
#include "net/url_request/url_fetcher_delegate.h"
#include "net/url_request/url_request.h"
#include "url/gurl.h"

using content::BrowserThread;

// The component updater is designed to live until process shutdown, so
// base::Bind() calls are not refcounted.

namespace {

// Produces an extension-like friendly |id|. This might be removed in the
// future if we roll our on packing tools.
static std::string HexStringToID(const std::string& hexstr) {
  std::string id;
  for (size_t i = 0; i < hexstr.size(); ++i) {
    int val(0);
    if (base::HexStringToInt(base::StringPiece(hexstr.begin() + i,
                                               hexstr.begin() + i + 1),
                             &val)) {
      id.append(1, val + 'a');
    } else {
      id.append(1, 'a');
    }
  }
  DCHECK(extensions::Extension::IdIsValid(id));
  return id;
}

// Returns true if the |proposed| version is newer than |current| version.
bool IsVersionNewer(const Version& current, const std::string& proposed) {
  Version proposed_ver(proposed);
  return proposed_ver.IsValid() && current.CompareTo(proposed_ver) < 0;
}

// Helper template class that allows our main class to have separate
// OnURLFetchComplete() callbacks for different types of url requests
// they are differentiated by the |Ctx| type.
template <typename Del, typename Ctx>
class DelegateWithContext : public net::URLFetcherDelegate {
 public:
  DelegateWithContext(Del* delegate, Ctx* context)
    : delegate_(delegate), context_(context) {}

  virtual void OnURLFetchComplete(const net::URLFetcher* source) OVERRIDE {
    delegate_->OnURLFetchComplete(source, context_);
    delete this;
  }

 private:
  ~DelegateWithContext() {}

  Del* delegate_;
  Ctx* context_;
};
// This function creates the right DelegateWithContext using template inference.
template <typename Del, typename Ctx>
net::URLFetcherDelegate* MakeContextDelegate(Del* delegate, Ctx* context) {
  return new DelegateWithContext<Del, Ctx>(delegate, context);
}

// Returns true if a differential update is available for the update item.
bool IsDiffUpdateAvailable(const CrxUpdateItem* update_item) {
  return update_item->diff_crx_url.is_valid();
}

// Returns true if a differential update is available, it has not failed yet,
// and the configuration allows it.
bool CanTryDiffUpdate(const CrxUpdateItem* update_item,
                      const ComponentUpdateService::Configurator& config) {
  return IsDiffUpdateAvailable(update_item) &&
         !update_item->diff_update_failed &&
         config.DeltasEnabled();
}

}  // namespace

CrxUpdateItem::CrxUpdateItem()
    : status(kNew),
      on_demand(false),
      diff_update_failed(false),
      error_category(0),
      error_code(0),
      extra_code1(0),
      diff_error_category(0),
      diff_error_code(0),
      diff_extra_code1(0) {
}

CrxUpdateItem::~CrxUpdateItem() {
}

CrxComponent::CrxComponent()
    : installer(NULL),
      observer(NULL) {
}

CrxComponent::~CrxComponent() {
}

std::string GetCrxComponentID(const CrxComponent& component) {
  return HexStringToID(StringToLowerASCII(base::HexEncode(&component.pk_hash[0],
                                          component.pk_hash.size()/2)));
}

CrxComponentInfo::CrxComponentInfo() {
}

CrxComponentInfo::~CrxComponentInfo() {
}

///////////////////////////////////////////////////////////////////////////////
// In charge of blocking url requests until the |crx_id| component has been
// updated. This class is touched solely from the IO thread. The UI thread
// can post tasks to it via weak pointers. By default the request is blocked
// unless the CrxUpdateService calls Unblock().
// The lifetime is controlled by Chrome's resource loader so the component
// updater cannot touch objects from this class except via weak pointers.
class CUResourceThrottle
    : public content::ResourceThrottle,
      public base::SupportsWeakPtr<CUResourceThrottle> {
 public:
  explicit CUResourceThrottle(const net::URLRequest* request);
  virtual ~CUResourceThrottle();

  // Overriden from ResourceThrottle.
  virtual void WillStartRequest(bool* defer) OVERRIDE;
  virtual void WillRedirectRequest(const GURL& new_url, bool* defer) OVERRIDE;

  // Component updater calls this function via PostTask to unblock the request.
  void Unblock();

  typedef std::vector<base::WeakPtr<CUResourceThrottle> > WeakPtrVector;

 private:
  enum State {
    NEW,
    BLOCKED,
    UNBLOCKED
  };

  State state_;
};

void UnblockResourceThrottle(base::WeakPtr<CUResourceThrottle> rt) {
  BrowserThread::PostTask(
      BrowserThread::IO,
      FROM_HERE,
      base::Bind(&CUResourceThrottle::Unblock, rt));
}

void UnblockandReapAllThrottles(CUResourceThrottle::WeakPtrVector* throttles) {
  CUResourceThrottle::WeakPtrVector::iterator it;
  for (it = throttles->begin(); it != throttles->end(); ++it)
    UnblockResourceThrottle(*it);
  throttles->clear();
}

//////////////////////////////////////////////////////////////////////////////
// The one and only implementation of the ComponentUpdateService interface. In
// charge of running the show. The main method is ProcessPendingItems() which
// is called periodically to do the upgrades/installs or the update checks.
// An important consideration here is to be as "low impact" as we can to the
// rest of the browser, so even if we have many components registered and
// eligible for update, we only do one thing at a time with pauses in between
// the tasks. Also when we do network requests there is only one |url_fetcher_|
// in flight at a time.
// There are no locks in this code, the main structure |work_items_| is mutated
// only from the UI thread. The unpack and installation is done in the file
// thread and the network requests are done in the IO thread and in the file
// thread.
class CrxUpdateService : public ComponentUpdateService {
 public:
  explicit CrxUpdateService(ComponentUpdateService::Configurator* config);
  virtual ~CrxUpdateService();

  // Overrides for ComponentUpdateService.
  virtual Status Start() OVERRIDE;
  virtual Status Stop() OVERRIDE;
  virtual Status RegisterComponent(const CrxComponent& component) OVERRIDE;
  virtual Status OnDemandUpdate(const std::string& component_id) OVERRIDE;
  virtual void GetComponents(
      std::vector<CrxComponentInfo>* components) OVERRIDE;
  virtual content::ResourceThrottle* GetOnDemandResourceThrottle(
      net::URLRequest* request, const std::string& crx_id) OVERRIDE;

  // Context for a update check url request. See DelegateWithContext above.
  struct UpdateContext {
    base::Time start;
    UpdateContext() : start(base::Time::Now()) {}
  };

  // Context for a crx download url request. See DelegateWithContext above.
  struct CRXContext {
    ComponentInstaller* installer;
    std::vector<uint8> pk_hash;
    std::string id;
    std::string fingerprint;
    CRXContext() : installer(NULL) {}
  };

  void OnURLFetchComplete(const net::URLFetcher* source,
                          UpdateContext* context);

 private:
  enum ErrorCategory {
    kErrorNone = 0,
    kNetworkError,
    kUnpackError,
    kInstallError,
  };

  enum StepDelayInterval {
    kStepDelayShort = 0,
    kStepDelayMedium,
    kStepDelayLong,
  };

  void OnParseUpdateResponseSucceeded(
      const component_updater::UpdateResponse::Results& results);
  void OnParseUpdateResponseFailed(const std::string& error_message);

  void DownloadComplete(scoped_ptr<CRXContext> crx_context,
                        int error,
                        const base::FilePath& response);

  Status OnDemandUpdateInternal(CrxUpdateItem* item);

  void ProcessPendingItems();

  CrxUpdateItem* FindReadyComponent();

  void UpdateComponent(CrxUpdateItem* workitem);

  void AddItemToUpdateCheck(CrxUpdateItem* item,
                            std::string* update_check_items);

  void AddUpdateCheckItems(std::string* update_check_items);

  void DoUpdateCheck(const std::string& update_check_items);

  void ScheduleNextRun(StepDelayInterval step_delay);

  void ParseResponse(const std::string& xml);

  void Install(scoped_ptr<CRXContext> context, const base::FilePath& crx_path);

  void DoneInstalling(const std::string& component_id,
                      ComponentUnpacker::Error error,
                      int extended_error);

  void ChangeItemState(CrxUpdateItem* item, CrxUpdateItem::Status to);

  size_t ChangeItemStatus(CrxUpdateItem::Status from,
                          CrxUpdateItem::Status to);

  CrxUpdateItem* FindUpdateItemById(const std::string& id);

  void NotifyComponentObservers(ComponentObserver::Events event,
                                int extra) const;

  bool HasOnDemandItems() const;

  void OnNewResourceThrottle(base::WeakPtr<CUResourceThrottle> rt,
                             const std::string& crx_id);

  scoped_ptr<ComponentUpdateService::Configurator> config_;

  scoped_ptr<ComponentPatcher> component_patcher_;

  scoped_ptr<net::URLFetcher> url_fetcher_;

  scoped_ptr<component_updater::PingManager> ping_manager_;

  scoped_ptr<component_updater::CrxDownloader> crx_downloader_;

  // A collection of every work item.
  typedef std::vector<CrxUpdateItem*> UpdateItems;
  UpdateItems work_items_;

  base::OneShotTimer<CrxUpdateService> timer_;

  scoped_refptr<base::SequencedTaskRunner> blocking_task_runner_;

  const Version chrome_version_;

  bool running_;

  DISALLOW_COPY_AND_ASSIGN(CrxUpdateService);
};

//////////////////////////////////////////////////////////////////////////////

CrxUpdateService::CrxUpdateService(ComponentUpdateService::Configurator* config)
    : config_(config),
      component_patcher_(config->CreateComponentPatcher()),
      ping_manager_(new component_updater::PingManager(
          config->PingUrl(),
          config->RequestContext())),
      blocking_task_runner_(BrowserThread::GetBlockingPool()->
          GetSequencedTaskRunnerWithShutdownBehavior(
              BrowserThread::GetBlockingPool()->GetSequenceToken(),
              base::SequencedWorkerPool::SKIP_ON_SHUTDOWN)),
      chrome_version_(chrome::VersionInfo().Version()),
      running_(false) {
}

CrxUpdateService::~CrxUpdateService() {
  // Because we are a singleton, at this point only the UI thread should be
  // alive, this simplifies the management of the work that could be in
  // flight in other threads.
  Stop();
  STLDeleteElements(&work_items_);
}

ComponentUpdateService::Status CrxUpdateService::Start() {
  // Note that RegisterComponent will call Start() when the first
  // component is registered, so it can be called twice. This way
  // we avoid scheduling the timer if there is no work to do.
  running_ = true;
  if (work_items_.empty())
    return kOk;

  NotifyComponentObservers(ComponentObserver::COMPONENT_UPDATER_STARTED, 0);

  timer_.Start(FROM_HERE, base::TimeDelta::FromSeconds(config_->InitialDelay()),
               this, &CrxUpdateService::ProcessPendingItems);
  return kOk;
}

// Stop the main check + update loop. In flight operations will be
// completed.
ComponentUpdateService::Status CrxUpdateService::Stop() {
  running_ = false;
  timer_.Stop();
  return kOk;
}

bool CrxUpdateService::HasOnDemandItems() const {
  class Helper {
   public:
    static bool IsOnDemand(CrxUpdateItem* item) {
      return item->on_demand;
    }
  };
  return std::find_if(work_items_.begin(),
                      work_items_.end(),
                      Helper::IsOnDemand) != work_items_.end();
}

// This function sets the timer which will call ProcessPendingItems() or
// ProcessRequestedItem() if there is an on_demand item.  There
// are three kinds of waits:
//  - a short delay, when there is immediate work to be done.
//  - a medium delay, when there are updates to be applied within the current
//    update cycle, or there are components that are still unchecked.
//  - a long delay when a full check/update cycle has completed for all
//    components.
void CrxUpdateService::ScheduleNextRun(StepDelayInterval step_delay) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  DCHECK(url_fetcher_.get() == NULL);
  CHECK(!timer_.IsRunning());
  // It could be the case that Stop() had been called while a url request
  // or unpacking was in flight, if so we arrive here but |running_| is
  // false. In that case do not loop again.
  if (!running_)
    return;

  // Keep the delay short if in the middle of an update (step_delay),
  // or there are new requested_work_items_ that have not been processed yet.
  int64 delay_seconds = 0;
  if (!HasOnDemandItems()) {
    switch (step_delay) {
      case kStepDelayShort:
        delay_seconds = config_->StepDelay();
        break;
      case kStepDelayMedium:
        delay_seconds = config_->StepDelayMedium();
        break;
      case kStepDelayLong:
        delay_seconds = config_->NextCheckDelay();
        break;
    }
  } else {
    delay_seconds = config_->StepDelay();
  }

  if (step_delay != kStepDelayShort) {
    NotifyComponentObservers(ComponentObserver::COMPONENT_UPDATER_SLEEPING, 0);

    // Zero is only used for unit tests.
    if (0 == delay_seconds)
      return;
  }

  timer_.Start(FROM_HERE, base::TimeDelta::FromSeconds(delay_seconds),
               this, &CrxUpdateService::ProcessPendingItems);
}

// Given a extension-like component id, find the associated component.
CrxUpdateItem* CrxUpdateService::FindUpdateItemById(const std::string& id) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  CrxUpdateItem::FindById finder(id);
  UpdateItems::iterator it = std::find_if(work_items_.begin(),
                                          work_items_.end(),
                                          finder);
  if (it == work_items_.end())
    return NULL;
  return (*it);
}

// Changes a component's status, clearing on_demand and firing notifications as
// necessary. By convention, this is the only function that can change a
// CrxUpdateItem's |status|.
// TODO(waffles): Do we want to add DCHECKS for valid state transitions here?
void CrxUpdateService::ChangeItemState(CrxUpdateItem* item,
                                       CrxUpdateItem::Status to) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  if (to == CrxUpdateItem::kNoUpdate ||
      to == CrxUpdateItem::kUpdated ||
      to == CrxUpdateItem::kUpToDate) {
    item->on_demand = false;
  }

  item->status = to;

  ComponentObserver* observer = item->component.observer;
  if (observer) {
    switch (to) {
      case CrxUpdateItem::kCanUpdate:
        observer->OnEvent(ComponentObserver::COMPONENT_UPDATE_FOUND, 0);
        break;
      case CrxUpdateItem::kUpdatingDiff:
      case CrxUpdateItem::kUpdating:
        observer->OnEvent(ComponentObserver::COMPONENT_UPDATE_READY, 0);
        break;
      case CrxUpdateItem::kUpdated:
        observer->OnEvent(ComponentObserver::COMPONENT_UPDATED, 0);
        break;
      case CrxUpdateItem::kUpToDate:
      case CrxUpdateItem::kNoUpdate:
        observer->OnEvent(ComponentObserver::COMPONENT_NOT_UPDATED, 0);
        break;
      case CrxUpdateItem::kNew:
      case CrxUpdateItem::kChecking:
      case CrxUpdateItem::kDownloading:
      case CrxUpdateItem::kDownloadingDiff:
      case CrxUpdateItem::kLastStatus:
        // No notification for these states.
        break;
    }
  }

  // Free possible pending network requests.
  if ((to == CrxUpdateItem::kUpdated) ||
      (to == CrxUpdateItem::kUpToDate) ||
      (to == CrxUpdateItem::kNoUpdate)) {
    UnblockandReapAllThrottles(&item->throttles);
  }
}

// Changes all the components in |work_items_| that have |from| status to
// |to| status and returns how many have been changed.
size_t CrxUpdateService::ChangeItemStatus(CrxUpdateItem::Status from,
                                          CrxUpdateItem::Status to) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  size_t count = 0;
  for (UpdateItems::iterator it = work_items_.begin();
       it != work_items_.end(); ++it) {
    CrxUpdateItem* item = *it;
    if (item->status != from)
      continue;
    ChangeItemState(item, to);
    ++count;
  }
  return count;
}

// Adds a component to be checked for upgrades. If the component exists it
// it will be replaced and the return code is kReplaced.
//
// TODO(cpu): Evaluate if we want to support un-registration.
ComponentUpdateService::Status CrxUpdateService::RegisterComponent(
    const CrxComponent& component) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  if (component.pk_hash.empty() ||
      !component.version.IsValid() ||
      !component.installer)
    return kError;

  std::string id =
    HexStringToID(StringToLowerASCII(base::HexEncode(&component.pk_hash[0],
                                     component.pk_hash.size()/2)));
  CrxUpdateItem* uit;
  uit = FindUpdateItemById(id);
  if (uit) {
    uit->component = component;
    return kReplaced;
  }

  uit = new CrxUpdateItem;
  uit->id.swap(id);
  uit->component = component;

  work_items_.push_back(uit);
  // If this is the first component registered we call Start to
  // schedule the first timer.
  if (running_ && (work_items_.size() == 1))
    Start();

  return kOk;
}

// Start the process of checking for an update, for a particular component
// that was previously registered.
// |component_id| is a value returned from GetCrxComponentID().
ComponentUpdateService::Status CrxUpdateService::OnDemandUpdate(
    const std::string& component_id) {
  return OnDemandUpdateInternal(FindUpdateItemById(component_id));
}

ComponentUpdateService::Status CrxUpdateService::OnDemandUpdateInternal(
    CrxUpdateItem* uit) {
  if (!uit)
    return kError;

  // Check if the request is too soon.
  base::TimeDelta delta = base::Time::Now() - uit->last_check;
  if (delta < base::TimeDelta::FromSeconds(config_->OnDemandDelay()))
    return kError;

  switch (uit->status) {
    // If the item is already in the process of being updated, there is
    // no point in this call, so return kInProgress.
    case CrxUpdateItem::kChecking:
    case CrxUpdateItem::kCanUpdate:
    case CrxUpdateItem::kDownloadingDiff:
    case CrxUpdateItem::kDownloading:
    case CrxUpdateItem::kUpdatingDiff:
    case CrxUpdateItem::kUpdating:
      return kInProgress;
    // Otherwise the item was already checked a while back (or it is new),
    // set its status to kNew to give it a slightly higher priority.
    case CrxUpdateItem::kNew:
    case CrxUpdateItem::kUpdated:
    case CrxUpdateItem::kUpToDate:
    case CrxUpdateItem::kNoUpdate:
      ChangeItemState(uit, CrxUpdateItem::kNew);
      uit->on_demand = true;
      break;
    case CrxUpdateItem::kLastStatus:
      NOTREACHED() << uit->status;
  }

  // In case the current delay is long, set the timer to a shorter value
  // to get the ball rolling.
  if (timer_.IsRunning()) {
    timer_.Stop();
    timer_.Start(FROM_HERE, base::TimeDelta::FromSeconds(config_->StepDelay()),
                 this, &CrxUpdateService::ProcessPendingItems);
  }

  return kOk;
}

void CrxUpdateService::GetComponents(
    std::vector<CrxComponentInfo>* components) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  for (UpdateItems::const_iterator it = work_items_.begin();
       it != work_items_.end(); ++it) {
    const CrxUpdateItem* item = *it;
    CrxComponentInfo info;
    info.id = GetCrxComponentID(item->component);
    info.version = item->component.version.GetString();
    info.name = item->component.name;
    components->push_back(info);
  }
}

// This is the main loop of the component updater.
void CrxUpdateService::ProcessPendingItems() {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  CrxUpdateItem* ready_upgrade = FindReadyComponent();
  if (ready_upgrade) {
    UpdateComponent(ready_upgrade);
    return;
  }
  std::string update_check_items;
  AddUpdateCheckItems(&update_check_items);
  if (!update_check_items.empty()) {
    DoUpdateCheck(update_check_items);
    return;
  }
  // No components to update. The next check will be after a long sleep.
  ScheduleNextRun(kStepDelayLong);
}

CrxUpdateItem* CrxUpdateService::FindReadyComponent() {
  class Helper {
   public:
    static bool IsReadyOnDemand(CrxUpdateItem* item) {
      return item->on_demand && IsReady(item);
    }
    static bool IsReady(CrxUpdateItem* item) {
      return item->status == CrxUpdateItem::kCanUpdate;
    }
  };

  std::vector<CrxUpdateItem*>::iterator it = std::find_if(
      work_items_.begin(), work_items_.end(), Helper::IsReadyOnDemand);
  if (it != work_items_.end())
    return *it;
  it = std::find_if(work_items_.begin(), work_items_.end(), Helper::IsReady);
  if (it != work_items_.end())
    return *it;
  return NULL;
}

void CrxUpdateService::UpdateComponent(CrxUpdateItem* workitem) {
  scoped_ptr<CRXContext> crx_context(new CRXContext);
  crx_context->pk_hash = workitem->component.pk_hash;
  crx_context->id = workitem->id;
  crx_context->installer = workitem->component.installer;
  crx_context->fingerprint = workitem->next_fp;
  GURL package_url;
  if (CanTryDiffUpdate(workitem, *config_)) {
    package_url = workitem->diff_crx_url;
    ChangeItemState(workitem, CrxUpdateItem::kDownloadingDiff);
  } else {
    package_url = workitem->crx_url;
    ChangeItemState(workitem, CrxUpdateItem::kDownloading);
  }
  crx_downloader_.reset(component_updater::CrxDownloader::Create(
      config_->RequestContext(),
      blocking_task_runner_,
      base::Bind(&CrxUpdateService::DownloadComplete,
                 base::Unretained(this),
                 base::Passed(&crx_context))));
  crx_downloader_->StartDownloadFromUrl(package_url);
}

// Sets the state of the component to be checked for updates. After the
// function is called, the <app> element corresponding to the |item| parameter
// is appended to the |update_check_items|.
void CrxUpdateService::AddItemToUpdateCheck(CrxUpdateItem* item,
                                            std::string* update_check_items) {
  // The app element corresponding to an update items looks like this:
  //    <app appid="hnimpnehoodheedghdeeijklkeaacbdc"
  //         version="0.1.2.3" installsource="ondemand">
  //    <updatecheck />
  //    <packages>
  //        <package fp="abcd" />
  //    </packages>
  //    </app>
  std::string app_attributes;
  base::StringAppendF(&app_attributes,
                      "appid=\"%s\" version=\"%s\"",
                      item->id.c_str(),
                      item->component.version.GetString().c_str());
  if (item->on_demand)
    base::StringAppendF(&app_attributes, " installsource=\"ondemand\"");

  std::string app;
  if (item->component.fingerprint.empty())
    base::StringAppendF(&app,
                        "<app %s>"
                        "<updatecheck />"
                        "</app>",
                        app_attributes.c_str());
  else
    base::StringAppendF(&app,
                        "<app %s>"
                        "<updatecheck />"
                        "<packages>"
                        "<package fp=\"%s\"/>"
                        "</packages>"
                        "</app>",
                        app_attributes.c_str(),
                        item->component.fingerprint.c_str());

  update_check_items->append(app);

  ChangeItemState(item, CrxUpdateItem::kChecking);
  item->last_check = base::Time::Now();
  item->crx_url = GURL();
  item->diff_crx_url = GURL();
  item->previous_version = item->component.version;
  item->next_version = Version();
  item->previous_fp = item->component.fingerprint;
  item->next_fp.clear();
  item->diff_update_failed = false;
  item->error_category = 0;
  item->error_code = 0;
  item->extra_code1 = 0;
  item->diff_error_category = 0;
  item->diff_error_code = 0;
  item->diff_extra_code1 = 0;
}

// Builds the sequence of <app> elements in the update check and returns it
// in the |update_check_items| parameter.
void CrxUpdateService::AddUpdateCheckItems(std::string* update_check_items) {
  // Given that our |work_items_| list is expected to contain relatively few
  // items, we simply loop several times.
  for (UpdateItems::const_iterator it = work_items_.begin();
       it != work_items_.end(); ++it) {
    CrxUpdateItem* item = *it;
    if (item->status != CrxUpdateItem::kNew)
      continue;
    AddItemToUpdateCheck(item, update_check_items);
  }

  // Next we can go back to components we already checked, here
  // we can also batch them in a single url request, as long as
  // we have not checked them recently.
  const base::TimeDelta min_delta_time =
      base::TimeDelta::FromSeconds(config_->MinimumReCheckWait());

  for (UpdateItems::const_iterator it = work_items_.begin();
       it != work_items_.end(); ++it) {
    CrxUpdateItem* item = *it;
    if ((item->status != CrxUpdateItem::kNoUpdate) &&
        (item->status != CrxUpdateItem::kUpToDate))
      continue;
    base::TimeDelta delta = base::Time::Now() - item->last_check;
    if (delta < min_delta_time)
      continue;
    AddItemToUpdateCheck(item, update_check_items);
  }

  // Finally, we check components that we already updated as long as
  // we have not checked them recently.
  for (UpdateItems::const_iterator it = work_items_.begin();
       it != work_items_.end(); ++it) {
    CrxUpdateItem* item = *it;
    if (item->status != CrxUpdateItem::kUpdated)
      continue;
    base::TimeDelta delta = base::Time::Now() - item->last_check;
    if (delta < min_delta_time)
      continue;
    AddItemToUpdateCheck(item, update_check_items);
  }
}

// Sends an update request. The |update_check_items| parameter
// contains the sequence of <app> xml elements of the update check.
void CrxUpdateService::DoUpdateCheck(const std::string& update_check_items) {
  using component_updater::BuildProtocolRequest;
  url_fetcher_.reset(component_updater::SendProtocolRequest(
      config_->UpdateUrl(),
      BuildProtocolRequest(update_check_items),
      MakeContextDelegate(this, new UpdateContext()),
      config_->RequestContext()));
}

// Called when we got a response from the update server. It consists of an xml
// document following the omaha update scheme.
void CrxUpdateService::OnURLFetchComplete(const net::URLFetcher* source,
                                          UpdateContext* context) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  if (component_updater::FetchSuccess(*source)) {
    std::string xml;
    source->GetResponseAsString(&xml);
    url_fetcher_.reset();
    ParseResponse(xml);
  } else {
    url_fetcher_.reset();
    CrxUpdateService::OnParseUpdateResponseFailed("network error");
  }
  delete context;
}

void CrxUpdateService::ParseResponse(const std::string& xml) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  component_updater::UpdateResponse update_response;
  if (update_response.Parse(xml))
    CrxUpdateService::OnParseUpdateResponseSucceeded(update_response.results());
  else
    CrxUpdateService::OnParseUpdateResponseFailed(update_response.errors());
}

// A valid Omaha update check has arrived, from only the list of components that
// we are currently upgrading we check for a match in which the server side
// version is newer, if so we queue them for an upgrade. The next time we call
// ProcessPendingItems() one of them will be drafted for the upgrade process.
void CrxUpdateService::OnParseUpdateResponseSucceeded(
    const component_updater::UpdateResponse::Results& results) {
  size_t num_updates_pending = 0;
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  std::vector<component_updater::UpdateResponse::Result>::const_iterator it;
  for (it = results.list.begin(); it != results.list.end(); ++it) {
    CrxUpdateItem* crx = FindUpdateItemById(it->extension_id);
    if (!crx)
      continue;

    if (crx->status != CrxUpdateItem::kChecking) {
      NOTREACHED();
      continue;  // Not updating this component now.
    }

    if (it->manifest.version.empty()) {
      // No version means no update available.
      ChangeItemState(crx, CrxUpdateItem::kNoUpdate);
      continue;
    }

    if (!IsVersionNewer(crx->component.version, it->manifest.version)) {
      // The component is up to date.
      ChangeItemState(crx, CrxUpdateItem::kUpToDate);
      continue;
    }

    if (!it->manifest.browser_min_version.empty()) {
      if (IsVersionNewer(chrome_version_, it->manifest.browser_min_version)) {
        // The component is not compatible with this Chrome version.
        ChangeItemState(crx, CrxUpdateItem::kNoUpdate);
        continue;
      }
    }

    if (it->manifest.packages.size() != 1) {
      // Assume one and only one package per component.
      ChangeItemState(crx, CrxUpdateItem::kNoUpdate);
      continue;
    }

    // Parse the members of the result and queue an upgrade for this component.
    crx->next_version = Version(it->manifest.version);

    typedef component_updater::
        UpdateResponse::Result::Manifest::Package Package;
    const Package& package(it->manifest.packages[0]);
    crx->next_fp = package.fingerprint;

    // Select the first url from the list of urls until support for
    // fall back urls is implemented.
    if (!it->crx_urls.empty())
      crx->crx_url = it->crx_urls[0].Resolve(package.name);
    if (!it->crx_diffurls.empty())
      crx->diff_crx_url = it->crx_diffurls[0].Resolve(package.namediff);

    ChangeItemState(crx, CrxUpdateItem::kCanUpdate);
    ++num_updates_pending;
  }

  // All components that are not included in the update response are
  // considered up to date.
  ChangeItemStatus(CrxUpdateItem::kChecking, CrxUpdateItem::kUpToDate);

  // If there are updates pending we do a short wait, otherwise we take
  // a longer delay until we check the components again.
  ScheduleNextRun(num_updates_pending > 0 ? kStepDelayShort : kStepDelayMedium);
}

void CrxUpdateService::OnParseUpdateResponseFailed(
    const std::string& error_message) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  size_t count = ChangeItemStatus(CrxUpdateItem::kChecking,
                                  CrxUpdateItem::kNoUpdate);
  DCHECK_GT(count, 0ul);
  ScheduleNextRun(kStepDelayLong);
}

// Called when the CRX package has been downloaded to a temporary location.
// Here we fire the notifications and schedule the component-specific installer
// to be called in the file thread.
void CrxUpdateService::DownloadComplete(scoped_ptr<CRXContext> crx_context,
                                        int error,
                                        const base::FilePath& temp_crx_path) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));

  CrxUpdateItem* crx = FindUpdateItemById(crx_context->id);
  DCHECK(crx->status == CrxUpdateItem::kDownloadingDiff ||
         crx->status == CrxUpdateItem::kDownloading);

  if (error) {
    if (crx->status == CrxUpdateItem::kDownloadingDiff) {
      crx->diff_error_category = kNetworkError;
      crx->diff_error_code = error;
      crx->diff_update_failed = true;
      size_t count = ChangeItemStatus(CrxUpdateItem::kDownloadingDiff,
                                      CrxUpdateItem::kCanUpdate);
      DCHECK_EQ(count, 1ul);
      crx_downloader_.reset();

      ScheduleNextRun(kStepDelayShort);
      return;
    }
    crx->error_category = kNetworkError;
    crx->error_code = error;
    size_t count = ChangeItemStatus(CrxUpdateItem::kDownloading,
                                    CrxUpdateItem::kNoUpdate);
    DCHECK_EQ(count, 1ul);
    crx_downloader_.reset();

    // At this point, since both the differential and the full downloads failed,
    // the update for this component has finished with an error.
    ping_manager_->OnUpdateComplete(crx);

    // Move on to the next update, if there is one available.
    ScheduleNextRun(kStepDelayMedium);
  } else {
    size_t count = 0;
    if (crx->status == CrxUpdateItem::kDownloadingDiff) {
      count = ChangeItemStatus(CrxUpdateItem::kDownloadingDiff,
                               CrxUpdateItem::kUpdatingDiff);
    } else {
      count = ChangeItemStatus(CrxUpdateItem::kDownloading,
                               CrxUpdateItem::kUpdating);
    }
    DCHECK_EQ(count, 1ul);

    crx_downloader_.reset();

    // Why unretained? See comment at top of file.
    blocking_task_runner_->PostDelayedTask(
        FROM_HERE,
        base::Bind(&CrxUpdateService::Install,
                   base::Unretained(this),
                   base::Passed(&crx_context),
                   temp_crx_path),
        base::TimeDelta::FromMilliseconds(config_->StepDelay()));
  }
}

// Install consists of digital signature verification, unpacking and then
// calling the component specific installer. All that is handled by the
// |unpacker|. If there is an error this function is in charge of deleting
// the files created.
void CrxUpdateService::Install(scoped_ptr<CRXContext> context,
                               const base::FilePath& crx_path) {
  // This function owns the file at |crx_path| and the |context| object.
  ComponentUnpacker unpacker(context->pk_hash,
                             crx_path,
                             context->fingerprint,
                             component_patcher_.get(),
                             context->installer);
  if (!base::DeleteFile(crx_path, false))
    NOTREACHED() << crx_path.value();
  // Why unretained? See comment at top of file.
  BrowserThread::PostDelayedTask(
      BrowserThread::UI,
      FROM_HERE,
      base::Bind(&CrxUpdateService::DoneInstalling, base::Unretained(this),
                 context->id, unpacker.error(), unpacker.extended_error()),
      base::TimeDelta::FromMilliseconds(config_->StepDelay()));
}

// Installation has been completed. Adjust the component status and
// schedule the next check. Schedule a short delay before trying the full
// update when the differential update failed.
void CrxUpdateService::DoneInstalling(const std::string& component_id,
                                      ComponentUnpacker::Error error,
                                      int extra_code) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));

  ErrorCategory error_category = kErrorNone;
  switch (error) {
    case ComponentUnpacker::kNone:
      break;
    case ComponentUnpacker::kInstallerError:
      error_category = kInstallError;
      break;
    default:
      error_category = kUnpackError;
      break;
  }

  const bool is_success = error == ComponentUnpacker::kNone;

  CrxUpdateItem* item = FindUpdateItemById(component_id);
  if (item->status == CrxUpdateItem::kUpdatingDiff && !is_success) {
    item->diff_error_category = error_category;
    item->diff_error_code = error;
    item->diff_extra_code1 = extra_code;
    item->diff_update_failed = true;
    size_t count = ChangeItemStatus(CrxUpdateItem::kUpdatingDiff,
                                    CrxUpdateItem::kCanUpdate);
    DCHECK_EQ(count, 1ul);
    ScheduleNextRun(kStepDelayShort);
    return;
    }

  if (is_success) {
    ChangeItemState(item, CrxUpdateItem::kUpdated);
    item->component.version = item->next_version;
    item->component.fingerprint = item->next_fp;
  } else {
    ChangeItemState(item, CrxUpdateItem::kNoUpdate);
    item->error_category = error_category;
    item->error_code = error;
    item->extra_code1 = extra_code;
  }

  ping_manager_->OnUpdateComplete(item);

  // Move on to the next update, if there is one available.
  ScheduleNextRun(kStepDelayMedium);
}

void CrxUpdateService::NotifyComponentObservers(
    ComponentObserver::Events event, int extra) const {
  for (UpdateItems::const_iterator it = work_items_.begin();
       it != work_items_.end(); ++it) {
    ComponentObserver* observer = (*it)->component.observer;
    if (observer)
      observer->OnEvent(event, 0);
  }
}

content::ResourceThrottle* CrxUpdateService::GetOnDemandResourceThrottle(
     net::URLRequest* request, const std::string& crx_id) {
  // We give the raw pointer to the caller, who will delete it at will
  // and we keep for ourselves a weak pointer to it so we can post tasks
  // from the UI thread without having to track lifetime directly.
  CUResourceThrottle* rt = new CUResourceThrottle(request);
  BrowserThread::PostTask(
      BrowserThread::UI,
      FROM_HERE,
      base::Bind(&CrxUpdateService::OnNewResourceThrottle,
                 base::Unretained(this),
                 rt->AsWeakPtr(),
                 crx_id));
  return rt;
}

void CrxUpdateService::OnNewResourceThrottle(
    base::WeakPtr<CUResourceThrottle> rt, const std::string& crx_id) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  // Check if we can on-demand update, else unblock the request anyway.
  CrxUpdateItem* item = FindUpdateItemById(crx_id);
  Status status = OnDemandUpdateInternal(item);
  if (status == kOk || status == kInProgress) {
    item->throttles.push_back(rt);
    return;
  }
  UnblockResourceThrottle(rt);
}

///////////////////////////////////////////////////////////////////////////////

CUResourceThrottle::CUResourceThrottle(const net::URLRequest* request)
    : state_(NEW) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
}

CUResourceThrottle::~CUResourceThrottle() {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
}

void CUResourceThrottle::WillStartRequest(bool* defer) {
  if (state_ != UNBLOCKED) {
    state_ = BLOCKED;
    *defer = true;
  } else {
    *defer = false;
  }
}

void CUResourceThrottle::WillRedirectRequest(const GURL& new_url, bool* defer) {
  WillStartRequest(defer);
}

void CUResourceThrottle::Unblock() {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
  if (state_ == BLOCKED)
    controller()->Resume();
  state_ = UNBLOCKED;
}

// The component update factory. Using the component updater as a singleton
// is the job of the browser process.
ComponentUpdateService* ComponentUpdateServiceFactory(
    ComponentUpdateService::Configurator* config) {
  DCHECK(config);
  return new CrxUpdateService(config);
}