// Copyright 2017 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 "content/public/common/simple_url_loader.h"

#include <stdint.h>

#include <algorithm>
#include <limits>

#include "base/bind.h"
#include "base/files/file_path.h"
#include "base/files/file_util.h"
#include "base/location.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/memory/ptr_util.h"
#include "base/memory/ref_counted.h"
#include "base/memory/weak_ptr.h"
#include "base/sequence_checker.h"
#include "base/sequenced_task_runner.h"
#include "base/task_scheduler/post_task.h"
#include "base/task_scheduler/task_traits.h"
#include "base/threading/sequenced_task_runner_handle.h"
#include "mojo/public/cpp/bindings/binding.h"
#include "mojo/public/cpp/bindings/binding_set.h"
#include "mojo/public/cpp/system/data_pipe.h"
#include "mojo/public/cpp/system/simple_watcher.h"
#include "net/base/net_errors.h"
#include "net/base/request_priority.h"
#include "net/http/http_request_headers.h"
#include "net/traffic_annotation/network_traffic_annotation.h"
#include "services/network/public/cpp/data_element.h"
#include "services/network/public/cpp/resource_request.h"
#include "services/network/public/cpp/resource_response.h"
#include "services/network/public/interfaces/data_pipe_getter.mojom.h"
#include "services/network/public/interfaces/url_loader.mojom.h"
#include "services/network/public/interfaces/url_loader_factory.mojom.h"

namespace content {

const size_t SimpleURLLoader::kMaxBoundedStringDownloadSize = 1024 * 1024;
const size_t SimpleURLLoader::kMaxUploadStringSizeToCopy = 256 * 1024;

namespace {

// This file contains SimpleURLLoaderImpl, several BodyHandler implementations,
// BodyReader, and StringUploadDataPipeGetter.
//
// SimpleURLLoaderImpl implements URLLoaderClient and drives the URLLoader.
//
// Each SimpleURLLoaderImpl creates a BodyHandler when the request is started.
// The BodyHandler drives the body pipe, handles body data as needed (writes it
// to a string, file, etc), and handles passing that data to the consumer's
// callback.
//
// BodyReader is a utility class that BodyHandler implementations use to drive
// the BodyPipe. This isn't handled by the SimpleURLLoader as some BodyHandlers
// consume data off thread, so having it as a separate class allows the data
// pipe to be used off thread, reducing use of the main thread.
//
// StringUploadDataPipeGetter is a class to stream a string upload body to the
// network service, rather than to copy it all at once.

class StringUploadDataPipeGetter : public network::mojom::DataPipeGetter {
 public:
  explicit StringUploadDataPipeGetter(const std::string& upload_string)
      : upload_string_(upload_string) {}
  ~StringUploadDataPipeGetter() override = default;

  // Returns a DataPipeGetterPtr for a new upload attempt, closing all
  // previously opened pipes.
  network::mojom::DataPipeGetterPtr GetPtrForNewUpload() {
    // If this is a retry, need to close all bindings, since only one consumer
    // can read from the data pipe at a time.
    binding_set_.CloseAllBindings();
    // Not strictly needed, but seems best to close the old body pipe and stop
    // any pending reads.
    ResetBodyPipe();

    network::mojom::DataPipeGetterPtr data_pipe_getter;
    binding_set_.AddBinding(this, mojo::MakeRequest(&data_pipe_getter));
    return data_pipe_getter;
  }

 private:
  // DataPipeGetter implementation:

  void Read(mojo::ScopedDataPipeProducerHandle pipe,
            ReadCallback callback) override {
    // Close any previous body pipe, to avoid confusion between the two, if the
    // consumer wants to restart reading from the file.
    ResetBodyPipe();

    std::move(callback).Run(net::OK, upload_string_.length());
    upload_body_pipe_ = std::move(pipe);
    handle_watcher_ = std::make_unique<mojo::SimpleWatcher>(
        FROM_HERE, mojo::SimpleWatcher::ArmingPolicy::MANUAL);
    handle_watcher_->Watch(
        upload_body_pipe_.get(),
        // Don't bother watching for close - rely on read pipes for errors.
        MOJO_HANDLE_SIGNAL_WRITABLE, MOJO_WATCH_CONDITION_SATISFIED,
        base::BindRepeating(&StringUploadDataPipeGetter::MojoReadyCallback,
                            base::Unretained(this)));
    WriteData();
  }

  void Clone(network::mojom::DataPipeGetterRequest request) override {
    binding_set_.AddBinding(this, std::move(request));
  }

  void MojoReadyCallback(MojoResult result,
                         const mojo::HandleSignalsState& state) {
    WriteData();
  }

  void WriteData() {
    DCHECK_LE(write_position_, upload_string_.length());

    while (true) {
      uint32_t write_size = static_cast<uint32_t>(
          std::min(static_cast<size_t>(32 * 1024),
                   upload_string_.length() - write_position_));
      if (write_size == 0) {
        // Upload is done. Close the uplaod body pipe and wait for another call
        // to Read().
        ResetBodyPipe();
        return;
      }

      int result =
          upload_body_pipe_->WriteData(upload_string_.data() + write_position_,
                                       &write_size, MOJO_WRITE_DATA_FLAG_NONE);
      if (result == MOJO_RESULT_SHOULD_WAIT) {
        handle_watcher_->ArmOrNotify();
        return;
      }

      if (result != MOJO_RESULT_OK) {
        // Ignore the pipe being closed - the upload may still be retried with
        // another call to Read.
        ResetBodyPipe();
        return;
      }

      write_position_ += write_size;
      DCHECK_LE(write_position_, upload_string_.length());
    }
  }

  // Closes the body pipe, and resets the position the class is writing from.
  // Should be called either when a new binding is created, or a new read
  // through the file is started.
  void ResetBodyPipe() {
    handle_watcher_.reset();
    upload_body_pipe_.reset();
    write_position_ = 0;
  }

  mojo::BindingSet<network::mojom::DataPipeGetter> binding_set_;

  mojo::ScopedDataPipeProducerHandle upload_body_pipe_;
  // Must be below |write_pipe_|, so it's deleted first.
  std::unique_ptr<mojo::SimpleWatcher> handle_watcher_;
  size_t write_position_ = 0;

  const std::string upload_string_;

  DISALLOW_COPY_AND_ASSIGN(StringUploadDataPipeGetter);
};

class BodyHandler;

class SimpleURLLoaderImpl : public SimpleURLLoader,
                            public network::mojom::URLLoaderClient {
 public:
  SimpleURLLoaderImpl(
      std::unique_ptr<network::ResourceRequest> resource_request,
      const net::NetworkTrafficAnnotationTag& annotation_tag);
  ~SimpleURLLoaderImpl() override;

  // SimpleURLLoader implementation.
  void DownloadToString(network::mojom::URLLoaderFactory* url_loader_factory,
                        BodyAsStringCallback body_as_string_callback,
                        size_t max_body_size) override;
  void DownloadToStringOfUnboundedSizeUntilCrashAndDie(
      network::mojom::URLLoaderFactory* url_loader_factory,
      BodyAsStringCallback body_as_string_callback) override;
  void DownloadToFile(
      network::mojom::URLLoaderFactory* url_loader_factory,
      DownloadToFileCompleteCallback download_to_file_complete_callback,
      const base::FilePath& file_path,
      int64_t max_body_size) override;
  void DownloadToTempFile(
      network::mojom::URLLoaderFactory* url_loader_factory,
      DownloadToFileCompleteCallback download_to_file_complete_callback,
      int64_t max_body_size) override;
  void SetOnRedirectCallback(
      const OnRedirectCallback& on_redirect_callback) override;
  void SetAllowPartialResults(bool allow_partial_results) override;
  void SetAllowHttpErrorResults(bool allow_http_error_results) override;
  void AttachStringForUpload(const std::string& upload_data,
                             const std::string& upload_content_type) override;
  void AttachFileForUpload(const base::FilePath& upload_file_path,
                           const std::string& upload_content_type) override;
  void SetRetryOptions(int max_retries, int retry_mode) override;
  int NetError() const override;
  const network::ResourceResponseHead* ResponseInfo() const override;

  // Called by BodyHandler when the BodyHandler body handler is done. If |error|
  // is not net::OK, some error occurred reading or consuming the body. If it is
  // net::OK, the pipe was closed and all data received was successfully
  // handled. This could indicate an error, concellation, or completion. To
  // determine which case this is, the size will also be compared to the size
  // reported in network::URLLoaderCompletionStatus(), if
  // network::URLLoaderCompletionStatus indicates a success.
  void OnBodyHandlerDone(net::Error error, int64_t received_body_size);

  // Finished the request with the provided error code, after freeing Mojo
  // resources. Closes any open pipes, so no URLLoader or BodyHandlers callbacks
  // will be invoked after this is called.
  void FinishWithResult(int net_error);

 private:
  // Per-request state values. This object is re-created for each retry.
  // Separating out the values makes re-initializing them on retry simpler.
  struct RequestState {
    RequestState() = default;
    ~RequestState() = default;

    bool request_completed = false;
    // The expected total size of the body, taken from
    // network::URLLoaderCompletionStatus.
    int64_t expected_body_size = 0;

    bool body_started = false;
    bool body_completed = false;
    // Final size of the body. Set once the body's Mojo pipe has been closed.
    int64_t received_body_size = 0;

    // Set to true when FinishWithResult() is called. Once that happens, the
    // consumer is informed of completion, and both pipes are closed.
    bool finished = false;

    // Result of the request.
    int net_error = net::ERR_IO_PENDING;

    std::unique_ptr<network::ResourceResponseHead> response_info;
  };

  // Prepares internal state to start a request, and then calls StartRequest().
  // Only used for the initial request (Not retries).
  void Start(network::mojom::URLLoaderFactory* url_loader_factory);

  // Starts a request. Used for both the initial request and retries, if any.
  void StartRequest(network::mojom::URLLoaderFactory* url_loader_factory);

  // Re-initializes state of |this| and |body_handler_| prior to retrying a
  // request.
  void Retry();

  // network::mojom::URLLoaderClient implementation;
  void OnReceiveResponse(
      const network::ResourceResponseHead& response_head,
      const base::Optional<net::SSLInfo>& ssl_info,
      network::mojom::DownloadedTempFilePtr downloaded_file) override;
  void OnReceiveRedirect(
      const net::RedirectInfo& redirect_info,
      const network::ResourceResponseHead& response_head) override;
  void OnDataDownloaded(int64_t data_length, int64_t encoded_length) override;
  void OnReceiveCachedMetadata(const std::vector<uint8_t>& data) override;
  void OnTransferSizeUpdated(int32_t transfer_size_diff) override;
  void OnUploadProgress(int64_t current_position,
                        int64_t total_size,
                        OnUploadProgressCallback ack_callback) override;
  void OnStartLoadingResponseBody(
      mojo::ScopedDataPipeConsumerHandle body) override;
  void OnComplete(const network::URLLoaderCompletionStatus& status) override;

  // Choose the TaskPriority based on |resource_request_|'s net priority.
  // TODO(mmenke): Can something better be done here?
  base::TaskPriority GetTaskPriority() const {
    base::TaskPriority task_priority;
    if (resource_request_->priority >= net::MEDIUM) {
      task_priority = base::TaskPriority::USER_BLOCKING;
    } else if (resource_request_->priority >= net::LOW) {
      task_priority = base::TaskPriority::USER_VISIBLE;
    } else {
      task_priority = base::TaskPriority::BACKGROUND;
    }
    return task_priority;
  }

  // Bound to the URLLoaderClient message pipe (|client_binding_|) via
  // set_connection_error_handler.
  void OnConnectionError();

  // Completes the request by calling FinishWithResult() if OnComplete() was
  // called and either no body pipe was ever received, or the body pipe was
  // closed.
  void MaybeComplete();

  OnRedirectCallback on_redirect_callback_;
  bool allow_partial_results_ = false;
  bool allow_http_error_results_ = false;

  // Information related to retrying.
  int remaining_retries_ = 0;
  int retry_mode_ = RETRY_NEVER;

  // The next values contain all the information required to restart the
  // request.

  // Populated in the constructor, and cleared once no longer needed, when no
  // more retries are possible.
  std::unique_ptr<network::ResourceRequest> resource_request_;
  const net::NetworkTrafficAnnotationTag annotation_tag_;
  // Cloned from the input URLLoaderFactory if it may be needed to follow
  // redirects.
  network::mojom::URLLoaderFactoryPtr url_loader_factory_ptr_;
  std::unique_ptr<BodyHandler> body_handler_;

  mojo::Binding<network::mojom::URLLoaderClient> client_binding_;
  network::mojom::URLLoaderPtr url_loader_;

  std::unique_ptr<StringUploadDataPipeGetter> string_upload_data_pipe_getter_;

  // Per-request state. Always non-null, but re-created on redirect.
  std::unique_ptr<RequestState> request_state_;

  SEQUENCE_CHECKER(sequence_checker_);

  base::WeakPtrFactory<SimpleURLLoaderImpl> weak_ptr_factory_;

  DISALLOW_COPY_AND_ASSIGN(SimpleURLLoaderImpl);
};

// Utility class to drive the pipe reading a response body. Can be created on
// one thread and then used to read data on another. A BodyReader may only be
// used once. If a request is retried, a new one must be created.
class BodyReader {
 public:
  class Delegate {
   public:
    Delegate() {}

    // The specified amount of data was read from the pipe. The BodyReader must
    // not be deleted during this callback. The Delegate should return net::OK
    // to continue reading, or a value indicating an error if the pipe should be
    // closed.
    virtual net::Error OnDataRead(uint32_t length, const char* data) = 0;

    // Called when the pipe is closed by the remote size, the size limit is
    // reached, or OnDataRead returned an error. |error| is net::OK if the
    // pipe was closed, or an error value otherwise. It is safe to delete the
    // BodyReader during this callback.
    virtual void OnDone(net::Error error, int64_t total_bytes) = 0;

   protected:
    virtual ~Delegate() {}

   private:
    DISALLOW_COPY_AND_ASSIGN(Delegate);
  };

  BodyReader(Delegate* delegate, int64_t max_body_size)
      : delegate_(delegate), max_body_size_(max_body_size) {
    DCHECK_GE(max_body_size_, 0);
  }

  // Makes the reader start reading from |body_data_pipe|. May only be called
  // once. The reader will continuously to try to read from the pipe (without
  // blocking the thread), calling OnDataRead as data is read, until one of the
  // following happens:
  // * The size limit is reached.
  // * OnDataRead returns an error.
  // * The BodyReader is deleted.
  void Start(mojo::ScopedDataPipeConsumerHandle body_data_pipe) {
    DCHECK(!body_data_pipe_.is_valid());
    body_data_pipe_ = std::move(body_data_pipe);
    handle_watcher_ = std::make_unique<mojo::SimpleWatcher>(
        FROM_HERE, mojo::SimpleWatcher::ArmingPolicy::MANUAL);
    handle_watcher_->Watch(
        body_data_pipe_.get(),
        MOJO_HANDLE_SIGNAL_READABLE | MOJO_HANDLE_SIGNAL_PEER_CLOSED,
        MOJO_WATCH_CONDITION_SATISFIED,
        base::BindRepeating(&BodyReader::MojoReadyCallback,
                            base::Unretained(this)));
    ReadData();
  }

 private:
  void MojoReadyCallback(MojoResult result,
                         const mojo::HandleSignalsState& state) {
    ReadData();
  }

  // Reads as much data as possible from |body_data_pipe_|, copying it to
  // |body_|. Arms |handle_watcher_| when data is not currently available.
  void ReadData() {
    while (true) {
      const void* body_data;
      uint32_t read_size;
      MojoResult result = body_data_pipe_->BeginReadData(
          &body_data, &read_size, MOJO_READ_DATA_FLAG_NONE);
      if (result == MOJO_RESULT_SHOULD_WAIT) {
        handle_watcher_->ArmOrNotify();
        return;
      }

      // If the pipe was closed, unclear if it was an error or success. Notify
      // the consumer of how much data was received.
      if (result != MOJO_RESULT_OK) {
        // The only error other than MOJO_RESULT_SHOULD_WAIT this should fail
        // with is MOJO_RESULT_FAILED_PRECONDITION, in the case the pipe was
        // closed.
        DCHECK_EQ(MOJO_RESULT_FAILED_PRECONDITION, result);
        ClosePipe();
        delegate_->OnDone(net::OK, total_bytes_read_);
        return;
      }

      // Check size against the limit.
      uint32_t copy_size = read_size;
      if (static_cast<int64_t>(copy_size) > max_body_size_ - total_bytes_read_)
        copy_size = max_body_size_ - total_bytes_read_;

      total_bytes_read_ += copy_size;
      net::Error error =
          delegate_->OnDataRead(copy_size, static_cast<const char*>(body_data));
      body_data_pipe_->EndReadData(read_size);
      // Handling reads asynchronously is currently not supported.
      DCHECK_NE(error, net::ERR_IO_PENDING);
      if (error == net::OK && copy_size < read_size)
        error = net::ERR_INSUFFICIENT_RESOURCES;

      if (error) {
        ClosePipe();
        delegate_->OnDone(error, total_bytes_read_);
        return;
      }
    }
  }

  // Frees Mojo resources and prevents any more Mojo messages from arriving.
  void ClosePipe() {
    handle_watcher_.reset();
    body_data_pipe_.reset();
  }

  mojo::ScopedDataPipeConsumerHandle body_data_pipe_;
  std::unique_ptr<mojo::SimpleWatcher> handle_watcher_;

  Delegate* const delegate_;

  const int64_t max_body_size_;
  int64_t total_bytes_read_ = 0;

  DISALLOW_COPY_AND_ASSIGN(BodyReader);
};

// Class to drive the pipe for reading the body, handle the results of the body
// read as appropriate, and invoke the consumer's callback to notify it of
// request completion. Implementations typically use a BodyReader to to manage
// reads from the body data pipe.
class BodyHandler {
 public:
  // A raw pointer is safe, since |simple_url_loader| owns the BodyHandler.
  explicit BodyHandler(SimpleURLLoaderImpl* simple_url_loader)
      : simple_url_loader_(simple_url_loader) {}
  virtual ~BodyHandler() {}

  // Called by SimpleURLLoader with the data pipe received from the URLLoader.
  // The BodyHandler is responsible for reading from it and monitoring it for
  // closure. Should call SimpleURLLoaderImpl::OnBodyHandlerDone(), once either
  // when the body pipe is closed or when an error occurs, like a write to a
  // file fails.
  virtual void OnStartLoadingResponseBody(
      mojo::ScopedDataPipeConsumerHandle body_data_pipe) = 0;

  // Called by SimpleURLLoader. Notifies the SimpleURLLoader's consumer that the
  // request has completed, either successfully or with an error. May be invoked
  // before OnStartLoadingResponseBody(), or before the BodyHandler has notified
  // SimplerURLLoader of completion or an error. Once this is called, the
  // BodyHandler must not invoke any of SimpleURLLoaderImpl's callbacks. If
  // |destroy_results| is true, any received data should be destroyed instead of
  // being sent to the consumer.
  virtual void NotifyConsumerOfCompletion(bool destroy_results) = 0;

  // Called before retrying a request. Only called either before receiving a
  // body pipe, or after the body pipe has been closed, so there should be no
  // pending callbacks when invoked. |retry_callback| should be invoked when
  // the BodyHandler is ready for the request to be retried. Callback may be
  // invoked synchronously.
  virtual void PrepareToRetry(base::OnceClosure retry_callback) = 0;

 protected:
  SimpleURLLoaderImpl* simple_url_loader() { return simple_url_loader_; }

 private:
  SimpleURLLoaderImpl* const simple_url_loader_;

  DISALLOW_COPY_AND_ASSIGN(BodyHandler);
};

// BodyHandler implementation for consuming the response as a string.
class SaveToStringBodyHandler : public BodyHandler,
                                public BodyReader::Delegate {
 public:
  SaveToStringBodyHandler(
      SimpleURLLoaderImpl* simple_url_loader,
      SimpleURLLoader::BodyAsStringCallback body_as_string_callback,
      int64_t max_body_size)
      : BodyHandler(simple_url_loader),
        max_body_size_(max_body_size),
        body_as_string_callback_(std::move(body_as_string_callback)) {}

  ~SaveToStringBodyHandler() override {}

  // BodyHandler implementation:

  void OnStartLoadingResponseBody(
      mojo::ScopedDataPipeConsumerHandle body_data_pipe) override {
    DCHECK(!body_);
    DCHECK(!body_reader_);

    body_ = std::make_unique<std::string>();
    body_reader_ = std::make_unique<BodyReader>(this, max_body_size_);
    body_reader_->Start(std::move(body_data_pipe));
  }

  void NotifyConsumerOfCompletion(bool destroy_results) override {
    body_reader_.reset();
    if (destroy_results)
      body_.reset();

    std::move(body_as_string_callback_).Run(std::move(body_));
  }

  void PrepareToRetry(base::OnceClosure retry_callback) override {
    body_.reset();
    body_reader_.reset();
    std::move(retry_callback).Run();
  }

 private:
  // BodyReader::Delegate implementation.

  net::Error OnDataRead(uint32_t length, const char* data) override {
    body_->append(data, length);
    return net::OK;
  }

  void OnDone(net::Error error, int64_t total_bytes) override {
    DCHECK_EQ(body_->size(), static_cast<size_t>(total_bytes));
    simple_url_loader()->OnBodyHandlerDone(error, total_bytes);
  }

  const int64_t max_body_size_;

  std::unique_ptr<std::string> body_;
  SimpleURLLoader::BodyAsStringCallback body_as_string_callback_;

  std::unique_ptr<BodyReader> body_reader_;

  DISALLOW_COPY_AND_ASSIGN(SaveToStringBodyHandler);
};

// BodyHandler implementation for saving the response to a file
class SaveToFileBodyHandler : public BodyHandler {
 public:
  // |net_priority| is the priority from the ResourceRequest, and is used to
  // determine the TaskPriority of the sequence used to read from the response
  // body and write to the file. If |create_temp_file| is true, a temp file is
  // created instead of using |path|.
  SaveToFileBodyHandler(SimpleURLLoaderImpl* simple_url_loader,
                        SimpleURLLoader::DownloadToFileCompleteCallback
                            download_to_file_complete_callback,
                        const base::FilePath& path,
                        bool create_temp_file,
                        uint64_t max_body_size,
                        base::TaskPriority task_priority)
      : BodyHandler(simple_url_loader),
        download_to_file_complete_callback_(
            std::move(download_to_file_complete_callback)),
        weak_ptr_factory_(this) {
    DCHECK(create_temp_file || !path.empty());

    // Can only do this after initializing the WeakPtrFactory.
    file_writer_ = std::make_unique<FileWriter>(path, create_temp_file,
                                                max_body_size, task_priority);
  }

  ~SaveToFileBodyHandler() override {
    DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
    if (file_writer_) {
      // |file_writer_| is only non-null at this point if any downloaded file
      // wasn't passed to the consumer. Destroy any partially downloaded file.
      file_writer_->DeleteFile(base::OnceClosure());
      FileWriter::Destroy(std::move(file_writer_));
    }
  }

  // BodyHandler implementation:
  void OnStartLoadingResponseBody(
      mojo::ScopedDataPipeConsumerHandle body_data_pipe) override {
    DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
    file_writer_->StartWriting(std::move(body_data_pipe),
                               base::BindOnce(&SaveToFileBodyHandler::OnDone,
                                              weak_ptr_factory_.GetWeakPtr()));
  }

  void NotifyConsumerOfCompletion(bool destroy_results) override {
    DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
    DCHECK(!download_to_file_complete_callback_.is_null());

    if (destroy_results) {
      // Prevent the FileWriter from calling OnDone().
      weak_ptr_factory_.InvalidateWeakPtrs();

      // To avoid any issues if the consumer tries to re-download a file to the
      // same location, don't invoke the callback until any partially downloaded
      // file has been destroyed.
      file_writer_->DeleteFile(
          base::BindOnce(&SaveToFileBodyHandler::InvokeCallbackAsynchronously,
                         weak_ptr_factory_.GetWeakPtr()));
      FileWriter::Destroy(std::move(file_writer_));
      return;
    }

    // Destroy the |file_writer_|, so the file won't be destroyed in |this|'s
    // destructor.
    FileWriter::Destroy(std::move(file_writer_));

    std::move(download_to_file_complete_callback_).Run(path_);
  }

  void PrepareToRetry(base::OnceClosure retry_callback) override {
    // |file_writer_| is only destroyed when notifying the consumer of
    // completion and in the destructor. After either of those happens, a
    // request should not be retried.
    DCHECK(file_writer_);

    // Delete file and wait for it to be destroyed, so if the retry fails
    // before trying to create a new file, the consumer will still only be
    // notified of completion after the file is destroyed.
    file_writer_->DeleteFile(std::move(retry_callback));
  }

 private:
  // Class to read from a mojo::ScopedDataPipeConsumerHandle and write the
  // contents to a file. Does all reading and writing on a separate file
  // SequencedTaskRunner. All public methods except the destructor are called on
  // BodyHandler's TaskRunner.  All private methods and the destructor are run
  // on the file TaskRunner.
  //
  // FileWriter is owned by the SaveToFileBodyHandler and destroyed by a task
  // moving its unique_ptr to the |file_writer_task_runner_|. As a result, tasks
  // posted to |file_writer_task_runner_| can always use base::Unretained. Tasks
  // posted the other way, however, require the SaveToFileBodyHandler to use
  // WeakPtrs, since the SaveToFileBodyHandler can be destroyed at any time.
  //
  // When a request is retried, the FileWriter deletes any partially downloaded
  // file, and is then reused.
  class FileWriter : public BodyReader::Delegate {
   public:
    using OnDoneCallback = base::OnceCallback<void(net::Error error,
                                                   int64_t total_bytes,
                                                   const base::FilePath& path)>;

    FileWriter(const base::FilePath& path,
               bool create_temp_file,
               int64_t max_body_size,
               base::TaskPriority priority)
        : body_handler_task_runner_(base::SequencedTaskRunnerHandle::Get()),
          file_writer_task_runner_(base::CreateSequencedTaskRunnerWithTraits(
              {base::MayBlock(), priority,
               base::TaskShutdownBehavior::BLOCK_SHUTDOWN})),
          path_(path),
          create_temp_file_(create_temp_file),
          max_body_size_(max_body_size) {
      DCHECK(body_handler_task_runner_->RunsTasksInCurrentSequence());
      DCHECK(create_temp_file_ || !path_.empty());
    }

    // Starts reading from |body_data_pipe| and writing to the file.
    void StartWriting(mojo::ScopedDataPipeConsumerHandle body_data_pipe,
                      OnDoneCallback on_done_callback) {
      DCHECK(body_handler_task_runner_->RunsTasksInCurrentSequence());
      file_writer_task_runner_->PostTask(
          FROM_HERE,
          base::BindOnce(&FileWriter::StartWritingOnFileSequence,
                         base::Unretained(this), std::move(body_data_pipe),
                         std::move(on_done_callback)));
    }

    // Deletes any partially downloaded file, and closes the body pipe, if open.
    // Must be called if SaveToFileBodyHandler's OnDone() method is never
    // invoked, to avoid keeping around partial downloads that were never passed
    // to the consumer.
    //
    // If |on_file_deleted_closure| is non-null, it will be invoked on the
    // caller's task runner once the file has been deleted.
    void DeleteFile(base::OnceClosure on_file_deleted_closure) {
      DCHECK(body_handler_task_runner_->RunsTasksInCurrentSequence());
      file_writer_task_runner_->PostTask(
          FROM_HERE, base::BindOnce(&FileWriter::DeleteFileOnFileSequence,
                                    base::Unretained(this),
                                    std::move(on_file_deleted_closure)));
    }

    // Destroys the FileWriter on the file TaskRunner.
    static void Destroy(std::unique_ptr<FileWriter> file_writer) {
      DCHECK(
          file_writer->body_handler_task_runner_->RunsTasksInCurrentSequence());

      // Have to stash this pointer before posting a task, since |file_writer|
      // is bound to the callback that's posted to the TaskRunner.
      base::SequencedTaskRunner* task_runner =
          file_writer->file_writer_task_runner_.get();
      task_runner->DeleteSoon(FROM_HERE, std::move(file_writer));
    }

    // Destructor is only public so the consumer can keep it in a unique_ptr.
    // Class must be destroyed by using Destroy().
    ~FileWriter() override {
      DCHECK(file_writer_task_runner_->RunsTasksInCurrentSequence());
    }

   private:
    void StartWritingOnFileSequence(
        mojo::ScopedDataPipeConsumerHandle body_data_pipe,
        OnDoneCallback on_done_callback) {
      DCHECK(file_writer_task_runner_->RunsTasksInCurrentSequence());
      DCHECK(!file_.IsValid());
      DCHECK(!body_reader_);

      bool have_path = !create_temp_file_;
      if (!have_path) {
        DCHECK(create_temp_file_);
        have_path = base::CreateTemporaryFile(&path_);
        // CreateTemporaryFile() creates an empty file.
        if (have_path)
          owns_file_ = true;
      }

      if (have_path) {
        // Try to initialize |file_|, creating the file if needed.
        file_.Initialize(
            path_, base::File::FLAG_WRITE | base::File::FLAG_CREATE_ALWAYS);
      }

      // If CreateTemporaryFile() or File::Initialize() failed, report failure.
      if (!file_.IsValid()) {
        body_handler_task_runner_->PostTask(
            FROM_HERE, base::BindOnce(std::move(on_done_callback),
                                      net::MapSystemError(
                                          logging::GetLastSystemErrorCode()),
                                      0, base::FilePath()));
        return;
      }

      on_done_callback_ = std::move(on_done_callback);
      owns_file_ = true;
      body_reader_ = std::make_unique<BodyReader>(this, max_body_size_);
      body_reader_->Start(std::move(body_data_pipe));
    }

    // BodyReader::Delegate implementation:
    net::Error OnDataRead(uint32_t length, const char* data) override {
      DCHECK(file_writer_task_runner_->RunsTasksInCurrentSequence());
      while (length > 0) {
        int written = file_.WriteAtCurrentPos(
            data, std::min(length, static_cast<uint32_t>(
                                       std::numeric_limits<int>::max())));
        if (written < 0)
          return net::MapSystemError(logging::GetLastSystemErrorCode());
        length -= written;
        data += written;
      }

      return net::OK;
    }

    void OnDone(net::Error error, int64_t total_bytes) override {
      DCHECK(file_writer_task_runner_->RunsTasksInCurrentSequence());
      // This should only be called if the file was successfully created.
      DCHECK(file_.IsValid());

      // Close the file so that there's no ownership contention when the
      // consumer uses it.
      file_.Close();
      body_reader_.reset();

      body_handler_task_runner_->PostTask(
          FROM_HERE, base::BindOnce(std::move(on_done_callback_), error,
                                    total_bytes, path_));
    }

    void DeleteFileOnFileSequence(base::OnceClosure on_file_deleted_closure) {
      DCHECK(file_writer_task_runner_->RunsTasksInCurrentSequence());

      if (owns_file_) {
        // Close the file before deleting it, if it's still open.
        file_.Close();

        // Close the body pipe.
        body_reader_.reset();

        // May as well clean this up, too.
        on_done_callback_.Reset();

        DCHECK(!path_.empty());
        base::DeleteFile(path_, false /* recursive */);

        owns_file_ = false;
      }

      if (on_file_deleted_closure) {
        body_handler_task_runner_->PostTask(FROM_HERE,
                                            std::move(on_file_deleted_closure));
      }
    }

    // These are set on cosntruction and accessed on both task runners.
    const scoped_refptr<base::SequencedTaskRunner> body_handler_task_runner_;
    const scoped_refptr<base::SequencedTaskRunner> file_writer_task_runner_;

    // After construction, all other values are only read and written on the
    // |file_writer_task_runner_|.

    base::FilePath path_;
    const bool create_temp_file_;
    const int64_t max_body_size_;

    // File being downloaded to. Created just before reading from the data pipe.
    base::File file_;

    OnDoneCallback on_done_callback_;

    std::unique_ptr<BodyReader> body_reader_;

    // True if a file was successfully created. Set to false when the file is
    // destroyed.
    bool owns_file_ = false;

    DISALLOW_COPY_AND_ASSIGN(FileWriter);
  };

  // Called by FileWriter::Destroy after deleting a partially downloaded file.
  void InvokeCallbackAsynchronously() {
    DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
    std::move(download_to_file_complete_callback_).Run(base::FilePath());
  }

  void OnDone(net::Error error,
              int64_t total_bytes,
              const base::FilePath& path) {
    path_ = path;
    simple_url_loader()->OnBodyHandlerDone(error, total_bytes);
  }

  // Path of the file. Set in OnDone().
  base::FilePath path_;

  SimpleURLLoader::DownloadToFileCompleteCallback
      download_to_file_complete_callback_;

  std::unique_ptr<FileWriter> file_writer_;

  SEQUENCE_CHECKER(sequence_checker_);

  base::WeakPtrFactory<SaveToFileBodyHandler> weak_ptr_factory_;

  DISALLOW_COPY_AND_ASSIGN(SaveToFileBodyHandler);
};

SimpleURLLoaderImpl::SimpleURLLoaderImpl(
    std::unique_ptr<network::ResourceRequest> resource_request,
    const net::NetworkTrafficAnnotationTag& annotation_tag)
    : resource_request_(std::move(resource_request)),
      annotation_tag_(annotation_tag),
      client_binding_(this),
      request_state_(std::make_unique<RequestState>()),
      weak_ptr_factory_(this) {
  // Allow creation and use on different threads.
  DETACH_FROM_SEQUENCE(sequence_checker_);
#if DCHECK_IS_ON()
  if (resource_request_->request_body) {
    for (const network::DataElement& element :
         *resource_request_->request_body->elements()) {
      // Files should be attached with AttachFileForUpload, so that (Once
      // supported) they can be opened in the current process.
      //
      // TODO(mmenke): Add a similar method for bytes, to allow streaming of
      // large byte buffers to the network process when uploading.
      DCHECK(element.type() != network::DataElement::TYPE_FILE &&
             element.type() != network::DataElement::TYPE_BYTES);
    }
  }
#endif  // DCHECK_IS_ON()
}

SimpleURLLoaderImpl::~SimpleURLLoaderImpl() {}

void SimpleURLLoaderImpl::DownloadToString(
    network::mojom::URLLoaderFactory* url_loader_factory,
    BodyAsStringCallback body_as_string_callback,
    size_t max_body_size) {
  DCHECK_LE(max_body_size, kMaxBoundedStringDownloadSize);
  body_handler_ = std::make_unique<SaveToStringBodyHandler>(
      this, std::move(body_as_string_callback), max_body_size);
  Start(url_loader_factory);
}

void SimpleURLLoaderImpl::DownloadToStringOfUnboundedSizeUntilCrashAndDie(
    network::mojom::URLLoaderFactory* url_loader_factory,
    BodyAsStringCallback body_as_string_callback) {
  body_handler_ = std::make_unique<SaveToStringBodyHandler>(
      this, std::move(body_as_string_callback),
      // int64_t because network::URLLoaderCompletionStatus::decoded_body_length
      // is an int64_t, not a size_t.
      std::numeric_limits<int64_t>::max());
  Start(url_loader_factory);
}

void SimpleURLLoaderImpl::DownloadToFile(
    network::mojom::URLLoaderFactory* url_loader_factory,
    DownloadToFileCompleteCallback download_to_file_complete_callback,
    const base::FilePath& file_path,
    int64_t max_body_size) {
  DCHECK(!file_path.empty());
  body_handler_ = std::make_unique<SaveToFileBodyHandler>(
      this, std::move(download_to_file_complete_callback), file_path,
      false /* create_temp_file */, max_body_size, GetTaskPriority());
  Start(url_loader_factory);
}

void SimpleURLLoaderImpl::DownloadToTempFile(
    network::mojom::URLLoaderFactory* url_loader_factory,
    DownloadToFileCompleteCallback download_to_file_complete_callback,
    int64_t max_body_size) {
  body_handler_ = std::make_unique<SaveToFileBodyHandler>(
      this, std::move(download_to_file_complete_callback), base::FilePath(),
      true /* create_temp_file */, max_body_size, GetTaskPriority());
  Start(url_loader_factory);
}

void SimpleURLLoaderImpl::SetOnRedirectCallback(
    const OnRedirectCallback& on_redirect_callback) {
  on_redirect_callback_ = on_redirect_callback;
}

void SimpleURLLoaderImpl::SetAllowPartialResults(bool allow_partial_results) {
  // Check if a request has not yet been started.
  DCHECK(!body_handler_);
  allow_partial_results_ = allow_partial_results;
}

void SimpleURLLoaderImpl::SetAllowHttpErrorResults(
    bool allow_http_error_results) {
  // Check if a request has not yet been started.
  DCHECK(!body_handler_);
  allow_http_error_results_ = allow_http_error_results;
}

void SimpleURLLoaderImpl::AttachStringForUpload(
    const std::string& upload_data,
    const std::string& upload_content_type) {
  // Currently only allow a single string to be attached.
  DCHECK(!resource_request_->request_body);
  DCHECK(resource_request_->method != "GET" &&
         resource_request_->method != "HEAD");

  resource_request_->request_body = new network::ResourceRequestBody();

  if (upload_data.length() <= kMaxUploadStringSizeToCopy) {
    int copy_length = static_cast<int>(upload_data.length());
    DCHECK_EQ(static_cast<size_t>(copy_length), upload_data.length());
    resource_request_->request_body->AppendBytes(upload_data.c_str(),
                                                 copy_length);
  } else {
    // Don't attach the upload body here.  A new pipe will need to be created
    // each time the request is tried.
    string_upload_data_pipe_getter_ =
        std::make_unique<StringUploadDataPipeGetter>(upload_data);
  }

  resource_request_->headers.SetHeader(net::HttpRequestHeaders::kContentType,
                                       upload_content_type);
}

void SimpleURLLoaderImpl::AttachFileForUpload(
    const base::FilePath& upload_file_path,
    const std::string& upload_content_type) {
  DCHECK(!upload_file_path.empty());

  // Currently only allow a single file to be attached.
  DCHECK(!resource_request_->request_body);
  DCHECK(resource_request_->method != "GET" &&
         resource_request_->method != "HEAD");

  // Create an empty body to make DCHECKing that there's no upload body yet
  // simpler.
  resource_request_->request_body = new network::ResourceRequestBody();
  // TODO(mmenke): Open the file in the current process and append the file
  // handle instead of the file path.
  resource_request_->request_body->AppendFileRange(
      upload_file_path, 0, std::numeric_limits<uint64_t>::max(), base::Time());

  resource_request_->headers.SetHeader(net::HttpRequestHeaders::kContentType,
                                       upload_content_type);
}

void SimpleURLLoaderImpl::SetRetryOptions(int max_retries, int retry_mode) {
  // Check if a request has not yet been started.
  DCHECK(!body_handler_);
  DCHECK_GE(max_retries, 0);
  // Non-zero |max_retries| makes no sense when retries are disabled.
  DCHECK(max_retries > 0 || retry_mode == RETRY_NEVER);

  remaining_retries_ = max_retries;
  retry_mode_ = retry_mode;

#if DCHECK_IS_ON()
  if (max_retries > 0 && resource_request_->request_body) {
    for (const network::DataElement& element :
         *resource_request_->request_body->elements()) {
      // Data pipes are single-use, so can't retry uploads when there's a data
      // pipe.
      // TODO(mmenke):  Data pipes can be Cloned(), though, so maybe update code
      // to do that?
      DCHECK(element.type() != network::DataElement::TYPE_DATA_PIPE);
    }
  }
#endif  // DCHECK_IS_ON()
}

int SimpleURLLoaderImpl::NetError() const {
  // Should only be called once the request is compelete.
  DCHECK(request_state_->finished);
  DCHECK_NE(net::ERR_IO_PENDING, request_state_->net_error);
  return request_state_->net_error;
}

const network::ResourceResponseHead* SimpleURLLoaderImpl::ResponseInfo() const {
  // Should only be called once the request is compelete.
  DCHECK(request_state_->finished);
  return request_state_->response_info.get();
}

void SimpleURLLoaderImpl::OnBodyHandlerDone(net::Error error,
                                            int64_t received_body_size) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK(request_state_->body_started);
  DCHECK(!request_state_->body_completed);

  // If there's an error, fail request and report it immediately.
  if (error != net::OK) {
    FinishWithResult(error);
    return;
  }

  // Otherwise, need to wait until the URLRequestClient pipe receives a complete
  // message or is closed, to determine if the entire body was received.
  request_state_->body_completed = true;
  request_state_->received_body_size = received_body_size;
  MaybeComplete();
}

void SimpleURLLoaderImpl::FinishWithResult(int net_error) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK(!request_state_->finished);

  client_binding_.Close();
  url_loader_.reset();

  request_state_->finished = true;
  request_state_->net_error = net_error;
  // If it's a partial download or an error was received, erase the body.
  bool destroy_results =
      request_state_->net_error != net::OK && !allow_partial_results_;
  body_handler_->NotifyConsumerOfCompletion(destroy_results);
}

void SimpleURLLoaderImpl::Start(
    network::mojom::URLLoaderFactory* url_loader_factory) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK(resource_request_);
  // It's illegal to use a single SimpleURLLoaderImpl to make multiple requests.
  DCHECK(!request_state_->finished);
  DCHECK(!url_loader_);
  DCHECK(!request_state_->body_started);

  // If retries are enabled, stash the information needed to retry a request.
  if (remaining_retries_ > 0) {
    // Clone the URLLoaderFactory, to avoid any dependencies on its lifetime.
    // Results in an easier to use API, with no shutdown ordering requirements,
    // at the cost of some resources.
    url_loader_factory->Clone(mojo::MakeRequest(&url_loader_factory_ptr_));
  }

  StartRequest(url_loader_factory);
}

void SimpleURLLoaderImpl::StartRequest(
    network::mojom::URLLoaderFactory* url_loader_factory) {
  DCHECK(resource_request_);
  DCHECK(url_loader_factory);

  network::mojom::URLLoaderClientPtr client_ptr;
  client_binding_.Bind(mojo::MakeRequest(&client_ptr));
  client_binding_.set_connection_error_handler(base::BindOnce(
      &SimpleURLLoaderImpl::OnConnectionError, base::Unretained(this)));
  // Data elements that use pipes aren't reuseable, currently (Since the IPC
  // code doesn't call the Clone() method), so need to create another one, if
  // uploading a string via a data pipe.
  if (string_upload_data_pipe_getter_) {
    resource_request_->request_body = new network::ResourceRequestBody();
    network::mojom::DataPipeGetterPtr data_pipe_getter;
    resource_request_->request_body->AppendDataPipe(
        string_upload_data_pipe_getter_->GetPtrForNewUpload());
  }
  url_loader_factory->CreateLoaderAndStart(
      mojo::MakeRequest(&url_loader_), 0 /* routing_id */, 0 /* request_id */,
      0 /* options */, *resource_request_, std::move(client_ptr),
      net::MutableNetworkTrafficAnnotationTag(annotation_tag_));

  // If no more retries left, can clean up a little.
  if (remaining_retries_ == 0) {
    resource_request_.reset();
    url_loader_factory_ptr_.reset();
  }
}

void SimpleURLLoaderImpl::Retry() {
  DCHECK(resource_request_);
  DCHECK(url_loader_factory_ptr_);
  DCHECK_GT(remaining_retries_, 0);
  --remaining_retries_;

  client_binding_.Close();
  url_loader_.reset();

  request_state_ = std::make_unique<RequestState>();

  body_handler_->PrepareToRetry(base::BindOnce(
      &SimpleURLLoaderImpl::StartRequest, weak_ptr_factory_.GetWeakPtr(),
      url_loader_factory_ptr_.get()));
}

void SimpleURLLoaderImpl::OnReceiveResponse(
    const network::ResourceResponseHead& response_head,
    const base::Optional<net::SSLInfo>& ssl_info,
    network::mojom::DownloadedTempFilePtr downloaded_file) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  if (request_state_->response_info) {
    // The final headers have already been received, so the URLLoader is
    // violating the API contract.
    FinishWithResult(net::ERR_UNEXPECTED);
    return;
  }

  // Assume a 200 response unless headers were received indicating otherwise.
  // No headers indicates this was not a real HTTP response (Could be a file
  // URL, FTP, response could have been provided by something else, etc).
  int response_code = 200;
  if (response_head.headers)
    response_code = response_head.headers->response_code();

  // If a 5xx response was received, and |this| should retry on 5xx errors,
  // retry the request.
  if (response_code / 100 == 5 && remaining_retries_ > 0 &&
      (retry_mode_ & RETRY_ON_5XX)) {
    Retry();
    return;
  }

  request_state_->response_info =
      std::make_unique<network::ResourceResponseHead>(response_head);
  if (!allow_http_error_results_ && response_code / 100 != 2)
    FinishWithResult(net::ERR_FAILED);
}

void SimpleURLLoaderImpl::OnReceiveRedirect(
    const net::RedirectInfo& redirect_info,
    const network::ResourceResponseHead& response_head) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  if (request_state_->response_info) {
    // If the headers have already been received, the URLLoader is violating the
    // API contract.
    FinishWithResult(net::ERR_UNEXPECTED);
    return;
  }

  if (on_redirect_callback_) {
    base::WeakPtr<SimpleURLLoaderImpl> weak_this =
        weak_ptr_factory_.GetWeakPtr();
    on_redirect_callback_.Run(redirect_info, response_head);
    // If deleted by the callback, bail now.
    if (!weak_this)
      return;
  }

  url_loader_->FollowRedirect();
}

void SimpleURLLoaderImpl::OnDataDownloaded(int64_t data_length,
                                           int64_t encoded_length) {
  NOTIMPLEMENTED();
}

void SimpleURLLoaderImpl::OnReceiveCachedMetadata(
    const std::vector<uint8_t>& data) {
  NOTREACHED();
}

void SimpleURLLoaderImpl::OnTransferSizeUpdated(int32_t transfer_size_diff) {}

void SimpleURLLoaderImpl::OnUploadProgress(
    int64_t current_position,
    int64_t total_size,
    OnUploadProgressCallback ack_callback) {}

void SimpleURLLoaderImpl::OnStartLoadingResponseBody(
    mojo::ScopedDataPipeConsumerHandle body) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  if (request_state_->body_started || !request_state_->response_info) {
    // If this was already called, or the headers have not yet been received,
    // the URLLoader is violating the API contract.
    FinishWithResult(net::ERR_UNEXPECTED);
    return;
  }
  request_state_->body_started = true;
  body_handler_->OnStartLoadingResponseBody(std::move(body));
}

void SimpleURLLoaderImpl::OnComplete(
    const network::URLLoaderCompletionStatus& status) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  // Request should not have been completed yet.
  DCHECK(!request_state_->finished);
  DCHECK(!request_state_->request_completed);

  // Close pipes to ignore any subsequent close notification.
  client_binding_.Close();
  url_loader_.reset();

  request_state_->request_completed = true;
  request_state_->expected_body_size = status.decoded_body_length;
  request_state_->net_error = status.error_code;
  // If |status| indicates success, but the body pipe was never received, the
  // URLLoader is violating the API contract.
  if (request_state_->net_error == net::OK && !request_state_->body_started)
    request_state_->net_error = net::ERR_UNEXPECTED;

  MaybeComplete();
}

void SimpleURLLoaderImpl::OnConnectionError() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  // |this| closes the pipe to the URLLoader in OnComplete(), so this method
  // being called indicates the pipe was closed before completion, most likely
  // due to peer death, or peer not calling OnComplete() on cancellation.

  // Request should not have been completed yet.
  DCHECK(!request_state_->finished);
  DCHECK(!request_state_->request_completed);
  DCHECK_EQ(net::ERR_IO_PENDING, request_state_->net_error);

  request_state_->request_completed = true;
  request_state_->net_error = net::ERR_FAILED;
  // Wait to receive any pending data on the data pipe before reporting the
  // failure.
  MaybeComplete();
}

void SimpleURLLoaderImpl::MaybeComplete() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  // Request should not have completed yet.
  DCHECK(!request_state_->finished);

  // Make sure the URLLoader's pipe has been closed.
  if (!request_state_->request_completed)
    return;

  // Make sure the body pipe either was never opened or has been closed. Even if
  // the request failed, if allow_partial_results_ is true, may still be able to
  // read more data.
  if (request_state_->body_started && !request_state_->body_completed)
    return;

  // Retry on network change errors. Waiting for body complete isn't strictly
  // necessary, but it guarantees a consistent situation, with no reads pending
  // on the body pipe.
  if (request_state_->net_error == net::ERR_NETWORK_CHANGED &&
      remaining_retries_ > 0 && (retry_mode_ & RETRY_ON_NETWORK_CHANGE)) {
    Retry();
    return;
  }

  // When OnCompleted sees a success result, still need to report an error if
  // the size isn't what was expected.
  if (request_state_->net_error == net::OK &&
      request_state_->expected_body_size !=
          request_state_->received_body_size) {
    if (request_state_->expected_body_size >
        request_state_->received_body_size) {
      // The body pipe was closed before it received the entire body.
      request_state_->net_error = net::ERR_FAILED;
    } else {
      // The caller provided more data through the pipe than it reported in
      // network::URLLoaderCompletionStatus, so the URLLoader is violating the
      // API contract. Just fail the request.
      request_state_->net_error = net::ERR_UNEXPECTED;
    }
  }

  FinishWithResult(request_state_->net_error);
}

}  // namespace

std::unique_ptr<SimpleURLLoader> SimpleURLLoader::Create(
    std::unique_ptr<network::ResourceRequest> resource_request,
    const net::NetworkTrafficAnnotationTag& annotation_tag) {
  DCHECK(resource_request);
  return std::make_unique<SimpleURLLoaderImpl>(std::move(resource_request),
                                               annotation_tag);
}

SimpleURLLoader::~SimpleURLLoader() {}

SimpleURLLoader::SimpleURLLoader() {}

}  // namespace content