// 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 "content/browser/loader/intercepting_resource_handler.h"

#include "base/auto_reset.h"
#include "base/location.h"
#include "base/logging.h"
#include "base/strings/string_util.h"
#include "base/threading/thread_task_runner_handle.h"
#include "content/browser/loader/null_resource_controller.h"
#include "content/browser/loader/resource_controller.h"
#include "net/base/io_buffer.h"
#include "net/url_request/url_request.h"
#include "services/network/public/cpp/resource_response.h"

namespace content {

class InterceptingResourceHandler::Controller : public ResourceController {
 public:
  explicit Controller(InterceptingResourceHandler* mime_handler)
      : intercepting_handler_(mime_handler) {
    DCHECK(intercepting_handler_->has_controller());
  }

  void Resume() override {
    MarkAsUsed();
    intercepting_handler_->ResumeInternal();
  }

  void ResumeForRedirect(
      const std::vector<std::string>& removed_headers,
      const net::HttpRequestHeaders& modified_headers) override {
    DCHECK(removed_headers.empty() && modified_headers.IsEmpty())
        << "Removing or modifying headers from the |new_handler| is not used "
           "and not supported. See https://crbug.com/845683.";
    Resume();
  }

  void Cancel() override {
    MarkAsUsed();
    intercepting_handler_->Cancel();
  }

  void CancelWithError(int error_code) override {
    MarkAsUsed();
    intercepting_handler_->CancelWithError(error_code);
  }

 private:
  void MarkAsUsed() {
#if DCHECK_IS_ON()
    DCHECK(!used_);
    used_ = true;
#endif
  }

#if DCHECK_IS_ON()
  bool used_ = false;
#endif
  InterceptingResourceHandler* intercepting_handler_;

  DISALLOW_COPY_AND_ASSIGN(Controller);
};

InterceptingResourceHandler::InterceptingResourceHandler(
    std::unique_ptr<ResourceHandler> next_handler,
    net::URLRequest* request)
    : LayeredResourceHandler(request, std::move(next_handler)),
      weak_ptr_factory_(this) {
}

InterceptingResourceHandler::~InterceptingResourceHandler() {}

void InterceptingResourceHandler::OnResponseStarted(
    network::ResourceResponse* response,
    std::unique_ptr<ResourceController> controller) {
  // If there's no need to switch handlers, just start acting as a blind
  // pass-through ResourceHandler.
  if (!new_handler_) {
    state_ = State::PASS_THROUGH;
    next_handler_->OnResponseStarted(response, std::move(controller));
    return;
  }

  DCHECK_EQ(state_, State::STARTING);

  // TODO(yhirano): Retaining ownership from a raw pointer is bad.
  response_ = response;

  // Otherwise, switch handlers. First, inform the original ResourceHandler
  // that this will be handled entirely by the new ResourceHandler.
  HoldController(std::move(controller));
  state_ = State::SWAPPING_HANDLERS;

  DoLoop();
}

void InterceptingResourceHandler::OnWillRead(
    scoped_refptr<net::IOBuffer>* buf,
    int* buf_size,
    std::unique_ptr<ResourceController> controller) {
  if (state_ == State::PASS_THROUGH) {
    next_handler_->OnWillRead(buf, buf_size, std::move(controller));
    return;
  }

  DCHECK_EQ(State::STARTING, state_);
  DCHECK(!first_read_buffer_);
  DCHECK_EQ(0, first_read_buffer_size_);
  DCHECK(!parent_read_buffer_);
  DCHECK(!parent_read_buffer_size_);

  parent_read_buffer_ = buf;
  parent_read_buffer_size_ = buf_size;

  state_ = State::SENDING_ON_WILL_READ_TO_OLD_HANDLER;
  HoldController(std::move(controller));
  DoLoop();
}

void InterceptingResourceHandler::OnReadCompleted(
    int bytes_read,
    std::unique_ptr<ResourceController> controller) {
  DCHECK(!has_controller());

  DCHECK_GE(bytes_read, 0);
  if (state_ == State::PASS_THROUGH) {
    if (first_read_buffer_double_) {
      // |first_read_buffer_double_| was allocated and the user wrote data to
      // the buffer, but switching has not been done after all.
      memcpy(first_read_buffer_->data(), first_read_buffer_double_->data(),
             bytes_read);
      first_read_buffer_ = nullptr;
      first_read_buffer_double_ = nullptr;
    }
    next_handler_->OnReadCompleted(bytes_read, std::move(controller));
    return;
  }

  DCHECK_EQ(State::WAITING_FOR_ON_READ_COMPLETED, state_);
  first_read_buffer_bytes_read_ = bytes_read;
  state_ = State::SENDING_BUFFER_TO_NEW_HANDLER;
  HoldController(std::move(controller));
  DoLoop();
}

void InterceptingResourceHandler::OnResponseCompleted(
    const net::URLRequestStatus& status,
    std::unique_ptr<ResourceController> controller) {
  if (state_ == State::PASS_THROUGH) {
    LayeredResourceHandler::OnResponseCompleted(status, std::move(controller));
    return;
  }
  if (!new_handler_) {
    // Therer is only one ResourceHandler in this InterceptingResourceHandler.
    state_ = State::PASS_THROUGH;
    first_read_buffer_double_ = nullptr;
    next_handler_->OnResponseCompleted(status, std::move(controller));
    return;
  }

  // There are two ResourceHandlers in this InterceptingResourceHandler.
  // |next_handler_| is the old handler and |new_handler_| is the new handler.
  // As written in the class comment, this class assumes that the old handler
  // will immediately call Resume() in OnResponseCompleted.
  bool was_resumed = false;
  // TODO(mmenke): Get rid of NullResourceController and do something more
  // reasonable.
  next_handler_->OnResponseCompleted(
      status, std::make_unique<NullResourceController>(&was_resumed));
  DCHECK(was_resumed);

  state_ = State::PASS_THROUGH;
  first_read_buffer_double_ = nullptr;
  next_handler_ = std::move(new_handler_);
  next_handler_->OnResponseCompleted(status, std::move(controller));
}

void InterceptingResourceHandler::UseNewHandler(
    std::unique_ptr<ResourceHandler> new_handler,
    const std::string& payload_for_old_handler) {
  new_handler_ = std::move(new_handler);
  new_handler_->SetDelegate(delegate());
  payload_for_old_handler_ = payload_for_old_handler;
}

void InterceptingResourceHandler::DoLoop() {
  DCHECK(!in_do_loop_);
  DCHECK(!advance_to_next_state_);

  base::AutoReset<bool> auto_in_do_loop(&in_do_loop_, true);
  advance_to_next_state_ = true;

  while (advance_to_next_state_) {
    advance_to_next_state_ = false;

    switch (state_) {
      case State::STARTING:
      case State::WAITING_FOR_ON_READ_COMPLETED:
      case State::PASS_THROUGH:
        NOTREACHED();
        break;
      case State::SENDING_ON_WILL_READ_TO_OLD_HANDLER:
        SendOnWillReadToOldHandler();
        break;
      case State::WAITING_FOR_OLD_HANDLERS_BUFFER:
        OnBufferReceived();
        break;
      case State::SENDING_ON_WILL_START_TO_NEW_HANDLER:
        SendOnResponseStartedToNewHandler();
        break;
      case State::SENDING_ON_RESPONSE_STARTED_TO_NEW_HANDLER:
        if (first_read_buffer_double_) {
          // OnWillRead has been called, so copying the data from
          // |first_read_buffer_double_| to |first_read_buffer_| will be needed
          // when OnReadCompleted is called.
          state_ = State::WAITING_FOR_ON_READ_COMPLETED;
        } else {
          // OnWillRead has not been called, so no special handling will be
          // needed from now on.
          state_ = State::PASS_THROUGH;
        }
        ResumeInternal();
        break;
      case State::SWAPPING_HANDLERS:
        SendOnResponseStartedToOldHandler();
        break;
      case State::SENDING_PAYLOAD_TO_OLD_HANDLER:
        SendPayloadToOldHandler();
        break;
      case State::RECEIVING_BUFFER_FROM_OLD_HANDLER:
        ReceivedBufferFromOldHandler();
        break;
      case State::SENDING_BUFFER_TO_NEW_HANDLER:
        SendFirstReadBufferToNewHandler();
        break;
      case State::SENDING_BUFFER_TO_NEW_HANDLER_WAITING_FOR_BUFFER:
        ReceivedBufferFromNewHandler();
        break;
    }
  }
}

void InterceptingResourceHandler::ResumeInternal() {
  DCHECK(has_controller());
  if (state_ == State::STARTING ||
      state_ == State::WAITING_FOR_ON_READ_COMPLETED ||
      state_ == State::PASS_THROUGH) {
    // Uninteresting Resume: just delegate to the original resource controller.
    Resume();
    return;
  }

  // If called recusively from a DoLoop, advance state when returning to the
  // loop.
  if (in_do_loop_) {
    DCHECK(!advance_to_next_state_);
    advance_to_next_state_ = true;
    return;
  }

  // Can't call DoLoop synchronously, as it may call into |next_handler_|
  // synchronously, which is what called Resume().
  base::ThreadTaskRunnerHandle::Get()->PostTask(
      FROM_HERE, base::BindOnce(&InterceptingResourceHandler::DoLoop,
                                weak_ptr_factory_.GetWeakPtr()));
}

void InterceptingResourceHandler::SendOnWillReadToOldHandler() {
  DCHECK_EQ(State::SENDING_ON_WILL_READ_TO_OLD_HANDLER, state_);

  state_ = State::WAITING_FOR_OLD_HANDLERS_BUFFER;
  next_handler_->OnWillRead(&first_read_buffer_, &first_read_buffer_size_,
                            std::make_unique<Controller>(this));
}

void InterceptingResourceHandler::OnBufferReceived() {
  DCHECK_EQ(State::WAITING_FOR_OLD_HANDLERS_BUFFER, state_);

  // TODO(mmenke):  If this method is just going to allocate a double buffer
  // anyways, can the call to the old handler's OnWillRead be removed? That
  // would mean handling replaying data in the case that |next_handler_|'s
  // buffer is smaller than the double buffer, but SendPayloadToOldHandler
  // already handles that case, anyways, so could share that code with the
  // no-swap path as well. Or better, just have MimeSniffingResourceHandler
  // create and manage the buffer itself.
  first_read_buffer_double_ = base::MakeRefCounted<net::IOBuffer>(
      static_cast<size_t>(first_read_buffer_size_));
  *parent_read_buffer_ = first_read_buffer_double_;
  *parent_read_buffer_size_ = first_read_buffer_size_;

  parent_read_buffer_ = nullptr;
  parent_read_buffer_size_ = nullptr;

  state_ = State::STARTING;
  Resume();
}

void InterceptingResourceHandler::SendOnResponseStartedToOldHandler() {
  state_ = State::SENDING_PAYLOAD_TO_OLD_HANDLER;
  next_handler_->OnResponseStarted(response_.get(),
                                   std::make_unique<Controller>(this));
}

void InterceptingResourceHandler::SendPayloadToOldHandler() {
  DCHECK_EQ(State::SENDING_PAYLOAD_TO_OLD_HANDLER, state_);
  DCHECK(has_controller());

  if (static_cast<size_t>(payload_bytes_written_) ==
      payload_for_old_handler_.size()) {
    net::URLRequestStatus status(net::URLRequestStatus::SUCCESS, 0);
    if (payload_for_old_handler_.empty()) {
      // If there is no payload, just finalize the request on the old handler.
      status = net::URLRequestStatus::FromError(net::ERR_ABORTED);
    }
    bool was_resumed = false;
    // TODO(mmenke): Get rid of NullResourceController and do something more
    // reasonable.
    next_handler_->OnResponseCompleted(
        status, std::make_unique<NullResourceController>(&was_resumed));
    DCHECK(was_resumed);

    next_handler_ = std::move(new_handler_);
    state_ = State::SENDING_ON_WILL_START_TO_NEW_HANDLER;
    next_handler_->OnWillStart(request()->url(),
                               std::make_unique<Controller>(this));
    return;
  }

  state_ = State::RECEIVING_BUFFER_FROM_OLD_HANDLER;

  scoped_refptr<net::IOBuffer> buffer;
  // If |first_read_buffer_| is non-NULL, it was already received from
  // |next_handler_| via OnWillRead.  Can just use the buffer.
  if (first_read_buffer_) {
    DCHECK_GT(first_read_buffer_size_, 0);

    ResumeInternal();
    return;
  }

  DCHECK(!first_read_buffer_size_);
  next_handler_->OnWillRead(&first_read_buffer_, &first_read_buffer_size_,
                            std::make_unique<Controller>(this));
}

void InterceptingResourceHandler::ReceivedBufferFromOldHandler() {
  DCHECK_EQ(State::RECEIVING_BUFFER_FROM_OLD_HANDLER, state_);
  DCHECK(first_read_buffer_);
  DCHECK_GT(first_read_buffer_size_, 0);

  int bytes_to_copy =
      std::min(first_read_buffer_size_,
               static_cast<int>(payload_for_old_handler_.size() -
                                payload_bytes_written_));
  memcpy(first_read_buffer_->data(),
         payload_for_old_handler_.data() + payload_bytes_written_,
         bytes_to_copy);
  payload_bytes_written_ += bytes_to_copy;

  first_read_buffer_ = nullptr;
  first_read_buffer_size_ = 0;

  state_ = State::SENDING_PAYLOAD_TO_OLD_HANDLER;
  next_handler_->OnReadCompleted(bytes_to_copy,
                                 std::make_unique<Controller>(this));
}

void InterceptingResourceHandler::SendOnResponseStartedToNewHandler() {
  state_ = State::SENDING_ON_RESPONSE_STARTED_TO_NEW_HANDLER;
  next_handler_->OnResponseStarted(response_.get(),
                                   std::make_unique<Controller>(this));
}

void InterceptingResourceHandler::SendFirstReadBufferToNewHandler() {
  DCHECK_EQ(state_, State::SENDING_BUFFER_TO_NEW_HANDLER);
  DCHECK(!new_handler_read_buffer_);
  DCHECK(!new_handler_read_buffer_size_);

  if (first_read_buffer_bytes_written_ == first_read_buffer_bytes_read_) {
    state_ = State::PASS_THROUGH;
    first_read_buffer_double_ = nullptr;
    ResumeInternal();
    return;
  }

  state_ = State::SENDING_BUFFER_TO_NEW_HANDLER_WAITING_FOR_BUFFER;
  next_handler_->OnWillRead(&new_handler_read_buffer_,
                            &new_handler_read_buffer_size_,
                            std::make_unique<Controller>(this));
}

void InterceptingResourceHandler::ReceivedBufferFromNewHandler() {
  DCHECK_EQ(state_, State::SENDING_BUFFER_TO_NEW_HANDLER_WAITING_FOR_BUFFER);
  DCHECK(new_handler_read_buffer_);
  DCHECK(new_handler_read_buffer_size_);

  int bytes_to_copy =
      std::min(new_handler_read_buffer_size_,
               static_cast<int>(first_read_buffer_bytes_read_ -
                                first_read_buffer_bytes_written_));
  memcpy(new_handler_read_buffer_->data(),
         first_read_buffer_double_->data() + first_read_buffer_bytes_written_,
         bytes_to_copy);
  first_read_buffer_bytes_written_ += bytes_to_copy;

  new_handler_read_buffer_ = nullptr;
  new_handler_read_buffer_size_ = 0;

  state_ = State::SENDING_BUFFER_TO_NEW_HANDLER;
  next_handler_->OnReadCompleted(bytes_to_copy,
                                 std::make_unique<Controller>(this));
}

}  // namespace content
