mojo/system/channel.cc

// Copyright 2013 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 "mojo/system/channel.h"

#include <algorithm>

#include "base/bind.h"
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/strings/stringprintf.h"
#include "mojo/embedder/platform_handle_vector.h"
#include "mojo/system/message_pipe_endpoint.h"
#include "mojo/system/transport_data.h"

namespace mojo {
namespace system {

static_assert(Channel::kBootstrapEndpointId !=
                  MessageInTransit::kInvalidEndpointId,
              "kBootstrapEndpointId is invalid");

STATIC_CONST_MEMBER_DEFINITION const MessageInTransit::EndpointId
    Channel::kBootstrapEndpointId;

Channel::Channel(embedder::PlatformSupport* platform_support)
    : platform_support_(platform_support),
      is_running_(false),
      is_shutting_down_(false),
      next_local_id_(kBootstrapEndpointId) {
}

bool Channel::Init(scoped_ptr<RawChannel> raw_channel) {
  DCHECK(creation_thread_checker_.CalledOnValidThread());
  DCHECK(raw_channel);

  // No need to take |lock_|, since this must be called before this object
  // becomes thread-safe.
  DCHECK(!is_running_);
  raw_channel_ = raw_channel.Pass();

  if (!raw_channel_->Init(this)) {
    raw_channel_.reset();
    return false;
  }

  is_running_ = true;
  return true;
}

void Channel::Shutdown() {
  DCHECK(creation_thread_checker_.CalledOnValidThread());

  IdToEndpointMap to_destroy;
  {
    base::AutoLock locker(lock_);
    if (!is_running_)
      return;

    // Note: Don't reset |raw_channel_|, in case we're being called from within
    // |OnReadMessage()| or |OnError()|.
    raw_channel_->Shutdown();
    is_running_ = false;

    // We need to deal with it outside the lock.
    std::swap(to_destroy, local_id_to_endpoint_map_);
  }

  size_t num_live = 0;
  size_t num_zombies = 0;
  for (IdToEndpointMap::iterator it = to_destroy.begin();
       it != to_destroy.end();
       ++it) {
    if (it->second->state_ == ChannelEndpoint::STATE_NORMAL) {
      it->second->message_pipe_->OnRemove(it->second->port_);
      num_live++;
    } else {
      DCHECK(!it->second->message_pipe_.get());
      num_zombies++;
    }
    it->second->DetachFromChannel();
  }
  DVLOG_IF(2, num_live || num_zombies) << "Shut down Channel with " << num_live
                                       << " live endpoints and " << num_zombies
                                       << " zombies";
}

void Channel::WillShutdownSoon() {
  base::AutoLock locker(lock_);
  is_shutting_down_ = true;
}

// Note: |endpoint| being a |scoped_refptr| makes this function safe, since it
// keeps the endpoint alive even after the lock is released. Otherwise, there's
// the temptation to simply pass the result of |new ChannelEndpoint(...)|
// directly to this function, which wouldn't be sufficient for safety.
MessageInTransit::EndpointId Channel::AttachEndpoint(
    scoped_refptr<ChannelEndpoint> endpoint) {
  DCHECK(endpoint.get());

  MessageInTransit::EndpointId local_id;
  {
    base::AutoLock locker(lock_);

    DLOG_IF(WARNING, is_shutting_down_)
        << "AttachEndpoint() while shutting down";

    while (next_local_id_ == MessageInTransit::kInvalidEndpointId ||
           local_id_to_endpoint_map_.find(next_local_id_) !=
               local_id_to_endpoint_map_.end())
      next_local_id_++;

    local_id = next_local_id_;
    next_local_id_++;
    local_id_to_endpoint_map_[local_id] = endpoint;
  }

  endpoint->AttachToChannel(this, local_id);
  return local_id;
}

bool Channel::RunMessagePipeEndpoint(MessageInTransit::EndpointId local_id,
                                     MessageInTransit::EndpointId remote_id) {
  scoped_refptr<ChannelEndpoint> endpoint;
  ChannelEndpoint::State state;
  {
    base::AutoLock locker(lock_);

    DLOG_IF(WARNING, is_shutting_down_)
        << "RunMessagePipeEndpoint() while shutting down";

    IdToEndpointMap::const_iterator it =
        local_id_to_endpoint_map_.find(local_id);
    if (it == local_id_to_endpoint_map_.end())
      return false;
    endpoint = it->second;
    state = it->second->state_;
  }

  // Assume that this was in response to |kSubtypeChannelRunMessagePipeEndpoint|
  // and ignore it.
  if (state != ChannelEndpoint::STATE_NORMAL) {
    DVLOG(2) << "Ignoring run message pipe endpoint for zombie endpoint "
                "(local ID " << local_id << ", remote ID " << remote_id << ")";
    return true;
  }

  // TODO(vtl): FIXME -- We need to handle the case that message pipe is already
  // running when we're here due to |kSubtypeChannelRunMessagePipeEndpoint|).
  endpoint->Run(remote_id);
  return true;
}

void Channel::RunRemoteMessagePipeEndpoint(
    MessageInTransit::EndpointId local_id,
    MessageInTransit::EndpointId remote_id) {
#if DCHECK_IS_ON
  {
    base::AutoLock locker(lock_);
    DCHECK(local_id_to_endpoint_map_.find(local_id) !=
           local_id_to_endpoint_map_.end());
  }
#endif

  if (!SendControlMessage(
          MessageInTransit::kSubtypeChannelRunMessagePipeEndpoint,
          local_id,
          remote_id)) {
    HandleLocalError(base::StringPrintf(
        "Failed to send message to run remote message pipe endpoint (local ID "
        "%u, remote ID %u)",
        static_cast<unsigned>(local_id),
        static_cast<unsigned>(remote_id)));
  }
}

bool Channel::WriteMessage(scoped_ptr<MessageInTransit> message) {
  base::AutoLock locker(lock_);
  if (!is_running_) {
    // TODO(vtl): I think this is probably not an error condition, but I should
    // think about it (and the shutdown sequence) more carefully.
    LOG(WARNING) << "WriteMessage() after shutdown";
    return false;
  }

  DLOG_IF(WARNING, is_shutting_down_) << "WriteMessage() while shutting down";
  return raw_channel_->WriteMessage(message.Pass());
}

bool Channel::IsWriteBufferEmpty() {
  base::AutoLock locker(lock_);
  if (!is_running_)
    return true;
  return raw_channel_->IsWriteBufferEmpty();
}

void Channel::DetachMessagePipeEndpoint(
    MessageInTransit::EndpointId local_id,
    MessageInTransit::EndpointId remote_id) {
  DCHECK_NE(local_id, MessageInTransit::kInvalidEndpointId);

  // If this is non-null after the locked block, the endpoint should be detached
  // (and no remove message sent).
  scoped_refptr<ChannelEndpoint> endpoint_to_detach;
  {
    base::AutoLock locker_(lock_);
    if (!is_running_)
      return;

    IdToEndpointMap::iterator it = local_id_to_endpoint_map_.find(local_id);
    DCHECK(it != local_id_to_endpoint_map_.end());

    switch (it->second->state_) {
      case ChannelEndpoint::STATE_NORMAL:
        it->second->state_ = ChannelEndpoint::STATE_WAIT_REMOTE_REMOVE_ACK;
        it->second->message_pipe_ = nullptr;
        if (remote_id == MessageInTransit::kInvalidEndpointId)
          return;
        // We have to send a remove message (outside the lock).
        break;
      case ChannelEndpoint::STATE_WAIT_LOCAL_DETACH:
        endpoint_to_detach = it->second;
        local_id_to_endpoint_map_.erase(it);
        // We have to detach (outside the lock).
        break;
      case ChannelEndpoint::STATE_WAIT_REMOTE_REMOVE_ACK:
        NOTREACHED();
        return;
    }
  }
  if (endpoint_to_detach.get()) {
    endpoint_to_detach->DetachFromChannel();
    return;
  }

  if (!SendControlMessage(
          MessageInTransit::kSubtypeChannelRemoveMessagePipeEndpoint,
          local_id,
          remote_id)) {
    HandleLocalError(base::StringPrintf(
        "Failed to send message to remove remote message pipe endpoint (local "
        "ID %u, remote ID %u)",
        static_cast<unsigned>(local_id),
        static_cast<unsigned>(remote_id)));
  }
}

size_t Channel::GetSerializedPlatformHandleSize() const {
  return raw_channel_->GetSerializedPlatformHandleSize();
}

Channel::~Channel() {
  // The channel should have been shut down first.
  DCHECK(!is_running_);
}

void Channel::OnReadMessage(
    const MessageInTransit::View& message_view,
    embedder::ScopedPlatformHandleVectorPtr platform_handles) {
  DCHECK(creation_thread_checker_.CalledOnValidThread());

  switch (message_view.type()) {
    case MessageInTransit::kTypeMessagePipeEndpoint:
    case MessageInTransit::kTypeMessagePipe:
      OnReadMessageForDownstream(message_view, platform_handles.Pass());
      break;
    case MessageInTransit::kTypeChannel:
      OnReadMessageForChannel(message_view, platform_handles.Pass());
      break;
    default:
      HandleRemoteError(
          base::StringPrintf("Received message of invalid type %u",
                             static_cast<unsigned>(message_view.type())));
      break;
  }
}

void Channel::OnError(Error error) {
  DCHECK(creation_thread_checker_.CalledOnValidThread());

  switch (error) {
    case ERROR_READ_SHUTDOWN:
      // The other side was cleanly closed, so this isn't actually an error.
      DVLOG(1) << "RawChannel read error (shutdown)";
      break;
    case ERROR_READ_BROKEN: {
      base::AutoLock locker(lock_);
      LOG_IF(ERROR, !is_shutting_down_)
          << "RawChannel read error (connection broken)";
      break;
    }
    case ERROR_READ_BAD_MESSAGE:
      // Receiving a bad message means either a bug, data corruption, or
      // malicious attack (probably due to some other bug).
      LOG(ERROR) << "RawChannel read error (received bad message)";
      break;
    case ERROR_READ_UNKNOWN:
      LOG(ERROR) << "RawChannel read error (unknown)";
      break;
    case ERROR_WRITE:
      // Write errors are slightly notable: they probably shouldn't happen under
      // normal operation (but maybe the other side crashed).
      LOG(WARNING) << "RawChannel write error";
      break;
  }
  Shutdown();
}

void Channel::OnReadMessageForDownstream(
    const MessageInTransit::View& message_view,
    embedder::ScopedPlatformHandleVectorPtr platform_handles) {
  DCHECK(creation_thread_checker_.CalledOnValidThread());
  DCHECK(message_view.type() == MessageInTransit::kTypeMessagePipeEndpoint ||
         message_view.type() == MessageInTransit::kTypeMessagePipe);

  MessageInTransit::EndpointId local_id = message_view.destination_id();
  if (local_id == MessageInTransit::kInvalidEndpointId) {
    HandleRemoteError("Received message with no destination ID");
    return;
  }

  ChannelEndpoint::State state = ChannelEndpoint::STATE_NORMAL;
  scoped_refptr<MessagePipe> message_pipe;
  unsigned port = ~0u;
  bool nonexistent_local_id_error = false;
  {
    base::AutoLock locker(lock_);

    // Since we own |raw_channel_|, and this method and |Shutdown()| should only
    // be called from the creation thread, |raw_channel_| should never be null
    // here.
    DCHECK(is_running_);

    IdToEndpointMap::const_iterator it =
        local_id_to_endpoint_map_.find(local_id);
    if (it == local_id_to_endpoint_map_.end()) {
      nonexistent_local_id_error = true;
    } else {
      state = it->second->state_;
      message_pipe = it->second->message_pipe_;
      port = it->second->port_;
    }
  }
  if (nonexistent_local_id_error) {
    HandleRemoteError(base::StringPrintf(
        "Received a message for nonexistent local destination ID %u",
        static_cast<unsigned>(local_id)));
    // This is strongly indicative of some problem. However, it's not a fatal
    // error, since it may indicate a buggy (or hostile) remote process. Don't
    // die even for Debug builds, since handling this properly needs to be
    // tested (TODO(vtl)).
    DLOG(ERROR) << "This should not happen under normal operation.";
    return;
  }

  // Ignore messages for zombie endpoints (not an error).
  if (state != ChannelEndpoint::STATE_NORMAL) {
    DVLOG(2) << "Ignoring downstream message for zombie endpoint (local ID = "
             << local_id << ", remote ID = " << message_view.source_id() << ")";
    return;
  }

  // We need to duplicate the message (data), because |EnqueueMessage()| will
  // take ownership of it.
  scoped_ptr<MessageInTransit> message(new MessageInTransit(message_view));
  if (message_view.transport_data_buffer_size() > 0) {
    DCHECK(message_view.transport_data_buffer());
    message->SetDispatchers(TransportData::DeserializeDispatchers(
        message_view.transport_data_buffer(),
        message_view.transport_data_buffer_size(),
        platform_handles.Pass(),
        this));
  }
  MojoResult result = message_pipe->EnqueueMessage(
      MessagePipe::GetPeerPort(port), message.Pass());
  if (result != MOJO_RESULT_OK) {
    // TODO(vtl): This might be a "non-error", e.g., if the destination endpoint
    // has been closed (in an unavoidable race). This might also be a "remote"
    // error, e.g., if the remote side is sending invalid control messages (to
    // the message pipe).
    HandleLocalError(base::StringPrintf(
        "Failed to enqueue message to local ID %u (result %d)",
        static_cast<unsigned>(local_id),
        static_cast<int>(result)));
    return;
  }
}

void Channel::OnReadMessageForChannel(
    const MessageInTransit::View& message_view,
    embedder::ScopedPlatformHandleVectorPtr platform_handles) {
  DCHECK(creation_thread_checker_.CalledOnValidThread());
  DCHECK_EQ(message_view.type(), MessageInTransit::kTypeChannel);

  // Currently, no channel messages take platform handles.
  if (platform_handles) {
    HandleRemoteError(
        "Received invalid channel message (has platform handles)");
    NOTREACHED();
    return;
  }

  switch (message_view.subtype()) {
    case MessageInTransit::kSubtypeChannelRunMessagePipeEndpoint:
      DVLOG(2) << "Handling channel message to run message pipe (local ID "
               << message_view.destination_id() << ", remote ID "
               << message_view.source_id() << ")";
      if (!RunMessagePipeEndpoint(message_view.destination_id(),
                                  message_view.source_id())) {
        HandleRemoteError(
            "Received invalid channel message to run message pipe");
      }
      break;
    case MessageInTransit::kSubtypeChannelRemoveMessagePipeEndpoint:
      DVLOG(2) << "Handling channel message to remove message pipe (local ID "
               << message_view.destination_id() << ", remote ID "
               << message_view.source_id() << ")";
      if (!RemoveMessagePipeEndpoint(message_view.destination_id(),
                                     message_view.source_id())) {
        HandleRemoteError(
            "Received invalid channel message to remove message pipe");
      }
      break;
    case MessageInTransit::kSubtypeChannelRemoveMessagePipeEndpointAck:
      DVLOG(2) << "Handling channel message to ack remove message pipe (local "
                  "ID " << message_view.destination_id() << ", remote ID "
               << message_view.source_id() << ")";
      if (!RemoveMessagePipeEndpoint(message_view.destination_id(),
                                     message_view.source_id())) {
        HandleRemoteError(
            "Received invalid channel message to ack remove message pipe");
      }
      break;
    default:
      HandleRemoteError("Received invalid channel message");
      NOTREACHED();
      break;
  }
}

bool Channel::RemoveMessagePipeEndpoint(
    MessageInTransit::EndpointId local_id,
    MessageInTransit::EndpointId remote_id) {
  DCHECK(creation_thread_checker_.CalledOnValidThread());

  // If this is non-null after the locked block, the endpoint should be detached
  // (and no remove ack message sent).
  scoped_refptr<ChannelEndpoint> endpoint_to_detach;
  scoped_refptr<MessagePipe> message_pipe;
  unsigned port = ~0u;
  {
    base::AutoLock locker(lock_);

    IdToEndpointMap::iterator it = local_id_to_endpoint_map_.find(local_id);
    if (it == local_id_to_endpoint_map_.end()) {
      DVLOG(2) << "Remove message pipe error: not found";
      return false;
    }

    switch (it->second->state_) {
      case ChannelEndpoint::STATE_NORMAL:
        it->second->state_ = ChannelEndpoint::STATE_WAIT_LOCAL_DETACH;
        message_pipe = it->second->message_pipe_;
        port = it->second->port_;
        it->second->message_pipe_ = nullptr;
        // We have to send a remove ack message (outside the lock).
        break;
      case ChannelEndpoint::STATE_WAIT_LOCAL_DETACH:
        DVLOG(2) << "Remove message pipe error: wrong state";
        return false;
      case ChannelEndpoint::STATE_WAIT_REMOTE_REMOVE_ACK:
        endpoint_to_detach = it->second;
        local_id_to_endpoint_map_.erase(it);
        // We have to detach (outside the lock).
        break;
    }
  }
  if (endpoint_to_detach.get()) {
    endpoint_to_detach->DetachFromChannel();
    return true;
  }

  if (!SendControlMessage(
          MessageInTransit::kSubtypeChannelRemoveMessagePipeEndpointAck,
          local_id,
          remote_id)) {
    HandleLocalError(base::StringPrintf(
        "Failed to send message to remove remote message pipe endpoint ack "
        "(local ID %u, remote ID %u)",
        static_cast<unsigned>(local_id),
        static_cast<unsigned>(remote_id)));
  }

  message_pipe->OnRemove(port);

  return true;
}

bool Channel::SendControlMessage(MessageInTransit::Subtype subtype,
                                 MessageInTransit::EndpointId local_id,
                                 MessageInTransit::EndpointId remote_id) {
  DVLOG(2) << "Sending channel control message: subtype " << subtype
           << ", local ID " << local_id << ", remote ID " << remote_id;
  scoped_ptr<MessageInTransit> message(new MessageInTransit(
      MessageInTransit::kTypeChannel, subtype, 0, nullptr));
  message->set_source_id(local_id);
  message->set_destination_id(remote_id);
  return WriteMessage(message.Pass());
}

void Channel::HandleRemoteError(const base::StringPiece& error_message) {
  // TODO(vtl): Is this how we really want to handle this? Probably we want to
  // terminate the connection, since it's spewing invalid stuff.
  LOG(WARNING) << error_message;
}

void Channel::HandleLocalError(const base::StringPiece& error_message) {
  // TODO(vtl): Is this how we really want to handle this?
  // Sometimes we'll want to propagate the error back to the message pipe
  // (endpoint), and notify it that the remote is (effectively) closed.
  // Sometimes we'll want to kill the channel (and notify all the endpoints that
  // their remotes are dead.
  LOG(WARNING) << error_message;
}

}  // namespace system
}  // namespace mojo