[translate] Add translate ranker model loader.

components/translate/core/browser/ranker_model_loader.cc

Index: components/translate/core/browser/ranker_model_loader.cc
diff --git a/components/translate/core/browser/ranker_model_loader.cc b/components/translate/core/browser/ranker_model_loader.cc
new file mode 100644
index 0000000000000000000000000000000000000000..900815b59dd4b0a8b8f6bd3f7c8b97f015cea3e3
--- /dev/null
+++ b/components/translate/core/browser/ranker_model_loader.cc
@@ -0,0 +1,420 @@
+// Copyright 2016 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 "components/translate/core/browser/ranker_model_loader.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/command_line.h"
+#include "base/files/file_path.h"
+#include "base/files/file_util.h"
+#include "base/files/important_file_writer.h"
+#include "base/macros.h"
+#include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/profiler/scoped_tracker.h"
+#include "base/sequenced_task_runner.h"
+#include "base/strings/string_util.h"
+#include "base/task_scheduler/post_task.h"
+#include "base/threading/sequenced_task_runner_handle.h"
+#include "components/translate/core/browser/proto/ranker_model.pb.h"
+#include "components/translate/core/browser/ranker_model.h"
+#include "components/translate/core/browser/translate_url_fetcher.h"
+#include "url/gurl.h"
+
+namespace translate {
+namespace {
+
+using chrome_intelligence::RankerModel;
+using chrome_intelligence::RankerModelProto;
+
+constexpr int kUrlFetcherId = 2;
+
+// The maximum number of model download attempts to make. Download may fail
+// due to server error or network availability issues.
+constexpr int kMaxRetryOn5xx = 8;
+
+// The minimum duration, in minutes, between download attempts.
+constexpr int kMinRetryDelayMins = 3;
+
+// Suffixes for the various histograms produced by the backend.
+const char kWriteTimerHistogram[] = ".Timer.WriteModel";
+const char kReadTimerHistogram[] = ".Timer.ReadModel";
+const char kDownloadTimerHistogram[] = ".Timer.DownloadModel";
+const char kParsetimerHistogram[] = ".Timer.ParseModel";
+const char kModelStatusHistogram[] = ".Model.Status";
+
+// A helper class to produce a scoped timer histogram that supports using a
+// non-static-const name.
+class MyScopedHistogramTimer {
+ public:
+  MyScopedHistogramTimer(const base::StringPiece& name)
+      : name_(name.begin(), name.end()), start_(base::TimeTicks::Now()) {}
+
+  ~MyScopedHistogramTimer() {
+    base::TimeDelta duration = base::TimeTicks::Now() - start_;
+    base::HistogramBase* counter = base::Histogram::FactoryTimeGet(
+        name_, base::TimeDelta::FromMilliseconds(10),
+        base::TimeDelta::FromMilliseconds(200000), 100,
+        base::HistogramBase::kUmaTargetedHistogramFlag);
+    if (counter)
+      counter->AddTime(duration);
+  }
+
+ private:
+  const std::string name_;
+  const base::TimeTicks start_;
+
+  DISALLOW_COPY_AND_ASSIGN(MyScopedHistogramTimer);
+};
+
+}  // namespace
+
+// =============================================================================
+// RankerModelLoader::Backend
+
+class RankerModelLoader::Backend {
+ public:
+  // An internal version of RankerModelLoader::OnModelAvailableCallback that
+  // bundles calling the real callback with a notification of whether or not
+  // tha backend is finished.
+  using InternalOnModelAvailableCallback =
+      base::Callback<void(std::unique_ptr<RankerModel>, bool)>;
+
+  Backend(const ValidateModelCallback& validate_model_cb,
+          const InternalOnModelAvailableCallback& on_model_available_cb,
+          const base::FilePath& model_path,
+          const GURL& model_url,
+          const std::string& uma_prefix);
+  ~Backend();
+
+  // Reads the model from |model_path_|.
+  void LoadFromFile();
+
+  // Reads the model from |model_url_|.
+  void AsyncLoadFromURL();
+
+ private:
+  // Log and return the result of loading a model to UMA.
+  RankerModelStatus ReportModelStatus(RankerModelStatus model_status);
+
+  // Constructs a model from the given |data|.
+  std::unique_ptr<chrome_intelligence::RankerModel> CreateModel(
+      const std::string& data);
+
+  // Accepts downloaded model data. This signature is mandated by the callback
+  // defined by TransalteURLFetcher.
+  //
+  // id - the id given to the TranslateURLFetcher on creation
+  // success - true of the download was successful
+  // data - the body of the downloads response
+  void OnDownloadComplete(int id, bool success, const std::string& data);
+
+  // Transfers ownership of |model| to the client using the
+  // |internal_on_model_available_cb_|. |is_finished| denotes whether the
+  // backend is finished (or has given up on) loading the model.
+  void TransferModelToClient(
+      std::unique_ptr<chrome_intelligence::RankerModel> model,
+      bool is_finished);
+
+  // Validates that ranker model loader backend tasks are all performed on the
+  // same sequence.
+  base::SequenceChecker sequence_checker_;
+
+  // The TaskRunner on which |this| was constructed.
+  const scoped_refptr<base::SequencedTaskRunner> origin_task_runner_;
+
+  // Validates a ranker model on behalf of the model loader client. This may
+  // be called on any sequence and must, therefore, be thread-safe.
+  const ValidateModelCallback validate_model_cb_;
+
+  // Transfers ownership of a loaded model back to the model loader client.
+  // This will be called on the sequence on which the model loader was
+  // constructed.
+  const InternalOnModelAvailableCallback internal_on_model_available_cb_;
+
+  // The path at which the model is (or should be) cached.
+  const base::FilePath model_path_;
+
+  // The URL from which to download the model if the model is not in the cache
+  // or the cached model is invalid/expired.
+  const GURL model_url_;
+
+  // This will prefix all UMA metrics generated by the model loader.
+  const std::string uma_prefix_;
+
+  // Used to download model data from |model_url_|.
+  // TODO(rogerm): Use net::URLFetcher directly?
+  std::unique_ptr<TranslateURLFetcher> url_fetcher_;
+
+  // The next time before which no new attempts to download the model should be
+  // attempted.
+  base::TimeTicks next_earliest_download_time_;
+
+  // Tracks the last time of the last attempt to download a model. Used for UMA
+  // reporting of download duration.
+  base::TimeTicks download_start_time_;
+
+  DISALLOW_COPY_AND_ASSIGN(Backend);
+};
+
+RankerModelLoader::Backend::Backend(
+    const ValidateModelCallback& validate_model_cb,
+    const InternalOnModelAvailableCallback& internal_on_model_available_cb,
+    const base::FilePath& model_path,
+    const GURL& model_url,
+    const std::string& uma_prefix)
+    : origin_task_runner_(base::SequencedTaskRunnerHandle::Get()),
+      validate_model_cb_(validate_model_cb),
+      internal_on_model_available_cb_(internal_on_model_available_cb),
+      model_path_(model_path),
+      model_url_(model_url),
+      uma_prefix_(uma_prefix) {
+  sequence_checker_.DetachFromSequence();
+}
+
+RankerModelLoader::Backend::~Backend() {}
+
+RankerModelStatus RankerModelLoader::Backend::ReportModelStatus(
+    RankerModelStatus model_status) {
+  base::HistogramBase* histogram = base::LinearHistogram::FactoryGet(
+      uma_prefix_ + kModelStatusHistogram, 1,
+      static_cast<int>(RankerModelStatus::MAX),
+      static_cast<int>(RankerModelStatus::MAX) + 1,
+      base::HistogramBase::kUmaTargetedHistogramFlag);
+  if (histogram)
+    histogram->Add(static_cast<int>(model_status));
+  return model_status;
+}
+
+std::unique_ptr<chrome_intelligence::RankerModel>
+RankerModelLoader::Backend::CreateModel(const std::string& data) {
+  DCHECK(sequence_checker_.CalledOnValidSequence());
+  MyScopedHistogramTimer timer(uma_prefix_ + kParsetimerHistogram);
+  auto model = RankerModel::FromString(data);
+  if (ReportModelStatus(model ? validate_model_cb_.Run(*model)
+                              : RankerModelStatus::PARSE_FAILED) !=
+      RankerModelStatus::OK) {
+    return nullptr;
+  }
+  return model;
+}
+
+void RankerModelLoader::Backend::LoadFromFile() {
+  DCHECK(sequence_checker_.CalledOnValidSequence());
+
+  // If there is not cache path set, move on to loading the model by URL.
+  if (model_path_.empty()) {
+    AsyncLoadFromURL();
+    return;
+  }
+
+  DVLOG(2) << "Attempting to load model from: " << model_path_.value();
+
+  std::string data;
+
+  {
+    MyScopedHistogramTimer timer(uma_prefix_ + kReadTimerHistogram);
+    if (!base::ReadFileToString(model_path_, &data) || data.empty()) {
+      DVLOG(2) << "Failed to read model from: " << model_path_.value();
+      data.clear();
+    }
+  }
+
+  // If model data was loaded, check if it can be parsed to a valid model.
+  if (!data.empty()) {
+    auto model = CreateModel(data);
+    if (model) {
+      // The model is valid. The client is willing/able to use it. Keep track
+      // of where it originated and whether or not is has expired.
+      std::string url_spec = model->GetSourceURL();
+      bool is_expired = model->IsExpired();
+      bool is_finished = url_spec == model_url_.spec() && !is_expired;
+
+      DVLOG(2) << (is_expired ? "Expired m" : "M") << "odel in '"
+               << model_path_.value() << "' was originally downloaded from '"
+               << url_spec << "'.";
+
+      // Transfer the model to the client. Beyond this line, |model| is invalid.
+      TransferModelToClient(std::move(model), is_finished);
+
+      // If the cached model came from currently configured |model_url_| and has
+      // not expired, there is no need schedule a model download.
+      if (is_finished)
+        return;
+
+      // Otherwise, fall out of this block to schedule a download. The client
+      // can continue to use the valid but expired model until the download
+      // completes.
+    }
+  }
+
+  // Reaching this point means that a model download is required. If there is
+  // no download URL configured, then there is nothing further to do.
+  AsyncLoadFromURL();
+}
+
+void RankerModelLoader::Backend::AsyncLoadFromURL() {
+  DCHECK(sequence_checker_.CalledOnValidSequence());
+
+  if (!model_url_.is_valid())
+    return;
+
+  // Do nothing if the download attempts should be throttled.
+  if (base::TimeTicks::Now() < next_earliest_download_time_) {
+    DVLOG(2) << "Last download attempt was too recent.";
+    return;
+  }
+
+  // Otherwise, initialize the model fetcher to be non-null and trigger an
+  // initial download attempt.
+  if (!url_fetcher_) {
+    url_fetcher_ = base::MakeUnique<TranslateURLFetcher>(kUrlFetcherId);
+    url_fetcher_->set_max_retry_on_5xx(kMaxRetryOn5xx);
+  }
+
+  // If a request is already in flight, do not issue a new one.
+  if (url_fetcher_->state() == TranslateURLFetcher::REQUESTING) {
+    DVLOG(2) << "Download is in progress.";
+    return;
+  }
+
+  DVLOG(2) << "Downloading model from: " << model_url_;
+
+  // Reset the time of the next earliest allowable download attempt.
+  next_earliest_download_time_ =
+      base::TimeTicks::Now() + base::TimeDelta::FromMinutes(kMinRetryDelayMins);
+
+  // Kick off the next download attempt.
+  download_start_time_ = base::TimeTicks::Now();
+  bool result = url_fetcher_->Request(
+      model_url_, base::Bind(&RankerModelLoader::Backend::OnDownloadComplete,
+                             base::Unretained(this)));
+
+  // The maximum number of download attempts has been surpassed. Don't make
+  // any further attempts.
+  if (!result) {
+    DVLOG(2) << "Model download abandoned.";
+    ReportModelStatus(RankerModelStatus::DOWNLOAD_FAILED);
+    url_fetcher_.reset();
+
+    // Notify the loader that model loading has been abandoned.
+    TransferModelToClient(nullptr, true);
+  }
+}
+
+void RankerModelLoader::Backend::OnDownloadComplete(int /* id */,
+                                                    bool success,
+                                                    const std::string& data) {
+  DCHECK(sequence_checker_.CalledOnValidSequence());
+
+  // Record the duration of the download.
+  base::TimeDelta duration = base::TimeTicks::Now() - download_start_time_;
+  base::HistogramBase* counter = base::Histogram::FactoryTimeGet(
+      uma_prefix_ + kDownloadTimerHistogram,
+      base::TimeDelta::FromMilliseconds(10),
+      base::TimeDelta::FromMilliseconds(200000), 100,
+      base::HistogramBase::kUmaTargetedHistogramFlag);
+  if (counter)
+    counter->AddTime(duration);
+
+  // On failure, we just abort. The TranslateRanker will retry on a subsequent
+  // translation opportunity. The TranslateURLFetcher enforces a limit for
+  // retried requests.
+  if (!success || data.empty()) {
+    DVLOG(2) << "Download from '" << model_url_ << "'' failed.";
+    return;
+  }
+
+  auto model = CreateModel(data);
+  if (!model) {
+    DVLOG(2) << "Model from '" << model_url_ << "'' not valid.";
+    return;
+  }
+
+  url_fetcher_.reset();
+
+  auto* metadata = model->mutable_proto()->mutable_metadata();
+  metadata->set_source(model_url_.spec());
+  metadata->set_last_modified_sec(
+      (base::Time::Now() - base::Time()).InSeconds());
+
+  if (!model_path_.empty()) {
+    DVLOG(2) << "Saving model from '" << model_url_ << "'' to '"
+             << model_path_.value() << "'.";
+    MyScopedHistogramTimer timer(uma_prefix_ + kWriteTimerHistogram);
+    base::ImportantFileWriter::WriteFileAtomically(model_path_,
+                                                   model->SerializeAsString());
+  }
+
+  // Notify the owner that a compatible model is available.
+  TransferModelToClient(std::move(model), true);
+}
+
+void RankerModelLoader::Backend::TransferModelToClient(
+    std::unique_ptr<chrome_intelligence::RankerModel> model,
+    bool is_finished) {
+  DCHECK(sequence_checker_.CalledOnValidSequence());
+  origin_task_runner_->PostTask(
+      FROM_HERE, base::Bind(internal_on_model_available_cb_,
+                            base::Passed(std::move(model)), is_finished));
+}
+
+// =============================================================================
+// RankerModelLoader
+
+RankerModelLoader::RankerModelLoader(
+    const ValidateModelCallback& validate_model_cb,
+    const OnModelAvailableCallback& on_model_available_cb,
+    const base::FilePath& model_path,
+    const GURL& model_url,
+    const std::string& uma_prefix)
+    : backend_task_runner_(base::CreateSequencedTaskRunnerWithTraits(
+          base::TaskTraits().MayBlock().WithShutdownBehavior(
+              base::TaskShutdownBehavior::SKIP_ON_SHUTDOWN))),
+      weak_ptr_factory_(this) {
+  auto internal_on_model_available_cb =
+      base::Bind(&RankerModelLoader::InternalOnModelAvailable,
+                 weak_ptr_factory_.GetWeakPtr(), on_model_available_cb);
+  backend_ = base::MakeUnique<Backend>(validate_model_cb,
+                                       internal_on_model_available_cb,
+                                       model_path, model_url, uma_prefix);
+}
+
+RankerModelLoader::~RankerModelLoader() {
+  DCHECK(sequence_checker_.CalledOnValidSequence());
+  // This is guaranteed to be sequenced after any pending backend operation.
+  backend_task_runner_->DeleteSoon(FROM_HERE, backend_.release());
+}
+
+void RankerModelLoader::Start() {
+  DCHECK(sequence_checker_.CalledOnValidSequence());
+  DCHECK_EQ(state_, LoaderState::NOT_STARTED);
+  state_ = LoaderState::RUNNING;
+  backend_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&RankerModelLoader::Backend::LoadFromFile,
+                            base::Unretained(backend_.get())));
+}
+
+void RankerModelLoader::NotifyOfRankerActivity() {
+  DCHECK(sequence_checker_.CalledOnValidSequence());
+  if (state_ == LoaderState::RUNNING) {
+    backend_task_runner_->PostTask(
+        FROM_HERE, base::Bind(&RankerModelLoader::Backend::AsyncLoadFromURL,
+                              base::Unretained(backend_.get())));
+  }
+}
+
+void RankerModelLoader::InternalOnModelAvailable(
+    const OnModelAvailableCallback& callback,
+    std::unique_ptr<RankerModel> model,
+    bool finished) {
+  DCHECK(sequence_checker_.CalledOnValidSequence());
+  if (finished)
+    state_ = LoaderState::FINISHED;
+  if (model)
+    callback.Run(std::move(model));
+}
+
+}  // namespace translate