mojo/edk/system/raw_channel_posix.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/edk/system/raw_channel.h"

#include <errno.h>
#include <sys/uio.h>
#include <unistd.h>

#include <algorithm>
#include <deque>

#include "base/bind.h"
#include "base/location.h"
#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/memory/weak_ptr.h"
#include "base/message_loop/message_loop.h"
#include "base/synchronization/lock.h"
#include "mojo/edk/embedder/platform_channel_utils_posix.h"
#include "mojo/edk/embedder/platform_handle.h"
#include "mojo/edk/embedder/platform_handle_vector.h"
#include "mojo/edk/system/transport_data.h"
#include "mojo/public/cpp/system/macros.h"

namespace mojo {
namespace system {

namespace {

class RawChannelPosix final : public RawChannel,
                              public base::MessageLoopForIO::Watcher {
 public:
  explicit RawChannelPosix(embedder::ScopedPlatformHandle handle);
  ~RawChannelPosix() override;

  // |RawChannel| public methods:
  size_t GetSerializedPlatformHandleSize() const override;

 private:
  // |RawChannel| protected methods:
  // Actually override this so that we can send multiple messages with (only)
  // FDs if necessary.
  void EnqueueMessageNoLock(scoped_ptr<MessageInTransit> message) override;
  // Override this to handle those extra FD-only messages.
  bool OnReadMessageForRawChannel(
      const MessageInTransit::View& message_view) override;
  IOResult Read(size_t* bytes_read) override;
  IOResult ScheduleRead() override;
  embedder::ScopedPlatformHandleVectorPtr GetReadPlatformHandles(
      size_t num_platform_handles,
      const void* platform_handle_table) override;
  IOResult WriteNoLock(size_t* platform_handles_written,
                       size_t* bytes_written) override;
  IOResult ScheduleWriteNoLock() override;
  void OnInit() override;
  void OnShutdownNoLock(scoped_ptr<ReadBuffer> read_buffer,
                        scoped_ptr<WriteBuffer> write_buffer) override;

  // |base::MessageLoopForIO::Watcher| implementation:
  void OnFileCanReadWithoutBlocking(int fd) override;
  void OnFileCanWriteWithoutBlocking(int fd) override;

  // Implements most of |Read()| (except for a bit of clean-up):
  IOResult ReadImpl(size_t* bytes_read);

  // Watches for |fd_| to become writable. Must be called on the I/O thread.
  void WaitToWrite();

  embedder::ScopedPlatformHandle fd_;

  // The following members are only used on the I/O thread:
  scoped_ptr<base::MessageLoopForIO::FileDescriptorWatcher> read_watcher_;
  scoped_ptr<base::MessageLoopForIO::FileDescriptorWatcher> write_watcher_;

  bool pending_read_;

  std::deque<embedder::PlatformHandle> read_platform_handles_;

  // The following members are used on multiple threads and protected by
  // |write_lock()|:
  bool pending_write_;

  // This is used for posting tasks from write threads to the I/O thread. It
  // must only be accessed under |write_lock_|. The weak pointers it produces
  // are only used/invalidated on the I/O thread.
  base::WeakPtrFactory<RawChannelPosix> weak_ptr_factory_;

  MOJO_DISALLOW_COPY_AND_ASSIGN(RawChannelPosix);
};

RawChannelPosix::RawChannelPosix(embedder::ScopedPlatformHandle handle)
    : fd_(handle.Pass()),
      pending_read_(false),
      pending_write_(false),
      weak_ptr_factory_(this) {
  DCHECK(fd_.is_valid());
}

RawChannelPosix::~RawChannelPosix() {
  DCHECK(!pending_read_);
  DCHECK(!pending_write_);

  // No need to take the |write_lock()| here -- if there are still weak pointers
  // outstanding, then we're hosed anyway (since we wouldn't be able to
  // invalidate them cleanly, since we might not be on the I/O thread).
  DCHECK(!weak_ptr_factory_.HasWeakPtrs());

  // These must have been shut down/destroyed on the I/O thread.
  DCHECK(!read_watcher_);
  DCHECK(!write_watcher_);

  embedder::CloseAllPlatformHandles(&read_platform_handles_);
}

size_t RawChannelPosix::GetSerializedPlatformHandleSize() const {
  // We don't actually need any space on POSIX (since we just send FDs).
  return 0;
}

void RawChannelPosix::EnqueueMessageNoLock(
    scoped_ptr<MessageInTransit> message) {
  if (message->transport_data()) {
    embedder::PlatformHandleVector* const platform_handles =
        message->transport_data()->platform_handles();
    if (platform_handles &&
        platform_handles->size() > embedder::kPlatformChannelMaxNumHandles) {
      // We can't attach all the FDs to a single message, so we have to "split"
      // the message. Send as many control messages as needed first with FDs
      // attached (and no data).
      size_t i = 0;
      for (; platform_handles->size() - i >
                 embedder::kPlatformChannelMaxNumHandles;
           i += embedder::kPlatformChannelMaxNumHandles) {
        scoped_ptr<MessageInTransit> fd_message(new MessageInTransit(
            MessageInTransit::Type::RAW_CHANNEL,
            MessageInTransit::Subtype::RAW_CHANNEL_POSIX_EXTRA_PLATFORM_HANDLES,
            0, nullptr));
        embedder::ScopedPlatformHandleVectorPtr fds(
            new embedder::PlatformHandleVector(
                platform_handles->begin() + i,
                platform_handles->begin() + i +
                    embedder::kPlatformChannelMaxNumHandles));
        fd_message->SetTransportData(make_scoped_ptr(
            new TransportData(fds.Pass(), GetSerializedPlatformHandleSize())));
        RawChannel::EnqueueMessageNoLock(fd_message.Pass());
      }

      // Remove the handles that we "moved" into the other messages.
      platform_handles->erase(platform_handles->begin(),
                              platform_handles->begin() + i);
    }
  }

  RawChannel::EnqueueMessageNoLock(message.Pass());
}

bool RawChannelPosix::OnReadMessageForRawChannel(
    const MessageInTransit::View& message_view) {
  DCHECK_EQ(message_view.type(), MessageInTransit::Type::RAW_CHANNEL);

  if (message_view.subtype() ==
      MessageInTransit::Subtype::RAW_CHANNEL_POSIX_EXTRA_PLATFORM_HANDLES) {
    // We don't need to do anything. |RawChannel| won't extract the platform
    // handles, and they'll be accumulated in |Read()|.
    return true;
  }

  return RawChannel::OnReadMessageForRawChannel(message_view);
}

RawChannel::IOResult RawChannelPosix::Read(size_t* bytes_read) {
  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());
  DCHECK(!pending_read_);

  IOResult rv = ReadImpl(bytes_read);
  if (rv != IO_SUCCEEDED && rv != IO_PENDING) {
    // Make sure that |OnFileCanReadWithoutBlocking()| won't be called again.
    read_watcher_.reset();
  }
  return rv;
}

RawChannel::IOResult RawChannelPosix::ScheduleRead() {
  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());
  DCHECK(!pending_read_);

  pending_read_ = true;

  return IO_PENDING;
}

embedder::ScopedPlatformHandleVectorPtr RawChannelPosix::GetReadPlatformHandles(
    size_t num_platform_handles,
    const void* /*platform_handle_table*/) {
  DCHECK_GT(num_platform_handles, 0u);

  if (read_platform_handles_.size() < num_platform_handles) {
    embedder::CloseAllPlatformHandles(&read_platform_handles_);
    read_platform_handles_.clear();
    return embedder::ScopedPlatformHandleVectorPtr();
  }

  embedder::ScopedPlatformHandleVectorPtr rv(
      new embedder::PlatformHandleVector(num_platform_handles));
  rv->assign(read_platform_handles_.begin(),
             read_platform_handles_.begin() + num_platform_handles);
  read_platform_handles_.erase(
      read_platform_handles_.begin(),
      read_platform_handles_.begin() + num_platform_handles);
  return rv.Pass();
}

RawChannel::IOResult RawChannelPosix::WriteNoLock(
    size_t* platform_handles_written,
    size_t* bytes_written) {
  write_lock().AssertAcquired();

  DCHECK(!pending_write_);

  size_t num_platform_handles = 0;
  ssize_t write_result;
  if (write_buffer_no_lock()->HavePlatformHandlesToSend()) {
    embedder::PlatformHandle* platform_handles;
    void* serialization_data;  // Actually unused.
    write_buffer_no_lock()->GetPlatformHandlesToSend(
        &num_platform_handles, &platform_handles, &serialization_data);
    DCHECK_GT(num_platform_handles, 0u);
    DCHECK_LE(num_platform_handles, embedder::kPlatformChannelMaxNumHandles);
    DCHECK(platform_handles);

    // TODO(vtl): Reduce code duplication. (This is duplicated from below.)
    std::vector<WriteBuffer::Buffer> buffers;
    write_buffer_no_lock()->GetBuffers(&buffers);
    DCHECK(!buffers.empty());
    const size_t kMaxBufferCount = 10;
    iovec iov[kMaxBufferCount];
    size_t buffer_count = std::min(buffers.size(), kMaxBufferCount);
    for (size_t i = 0; i < buffer_count; ++i) {
      iov[i].iov_base = const_cast<char*>(buffers[i].addr);
      iov[i].iov_len = buffers[i].size;
    }

    write_result = embedder::PlatformChannelSendmsgWithHandles(
        fd_.get(), iov, buffer_count, platform_handles, num_platform_handles);
    if (write_result >= 0) {
      for (size_t i = 0; i < num_platform_handles; i++)
        platform_handles[i].CloseIfNecessary();
    }
  } else {
    std::vector<WriteBuffer::Buffer> buffers;
    write_buffer_no_lock()->GetBuffers(&buffers);
    DCHECK(!buffers.empty());

    if (buffers.size() == 1) {
      write_result = embedder::PlatformChannelWrite(fd_.get(), buffers[0].addr,
                                                    buffers[0].size);
    } else {
      const size_t kMaxBufferCount = 10;
      iovec iov[kMaxBufferCount];
      size_t buffer_count = std::min(buffers.size(), kMaxBufferCount);
      for (size_t i = 0; i < buffer_count; ++i) {
        iov[i].iov_base = const_cast<char*>(buffers[i].addr);
        iov[i].iov_len = buffers[i].size;
      }

      write_result =
          embedder::PlatformChannelWritev(fd_.get(), iov, buffer_count);
    }
  }

  if (write_result >= 0) {
    *platform_handles_written = num_platform_handles;
    *bytes_written = static_cast<size_t>(write_result);
    return IO_SUCCEEDED;
  }

  if (errno == EPIPE)
    return IO_FAILED_SHUTDOWN;

  if (errno != EAGAIN && errno != EWOULDBLOCK) {
    PLOG(WARNING) << "sendmsg/write/writev";
    return IO_FAILED_UNKNOWN;
  }

  return ScheduleWriteNoLock();
}

RawChannel::IOResult RawChannelPosix::ScheduleWriteNoLock() {
  write_lock().AssertAcquired();

  DCHECK(!pending_write_);

  // Set up to wait for the FD to become writable.
  // If we're not on the I/O thread, we have to post a task to do this.
  if (base::MessageLoop::current() != message_loop_for_io()) {
    message_loop_for_io()->PostTask(FROM_HERE,
                                    base::Bind(&RawChannelPosix::WaitToWrite,
                                               weak_ptr_factory_.GetWeakPtr()));
    pending_write_ = true;
    return IO_PENDING;
  }

  if (message_loop_for_io()->WatchFileDescriptor(
          fd_.get().fd, false, base::MessageLoopForIO::WATCH_WRITE,
          write_watcher_.get(), this)) {
    pending_write_ = true;
    return IO_PENDING;
  }

  return IO_FAILED_UNKNOWN;
}

void RawChannelPosix::OnInit() {
  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());

  DCHECK(!read_watcher_);
  read_watcher_.reset(new base::MessageLoopForIO::FileDescriptorWatcher());
  DCHECK(!write_watcher_);
  write_watcher_.reset(new base::MessageLoopForIO::FileDescriptorWatcher());

  // I don't know how this can fail (unless |fd_| is bad, in which case it's a
  // bug in our code). I also don't know if |WatchFileDescriptor()| actually
  // fails cleanly.
  CHECK(message_loop_for_io()->WatchFileDescriptor(
      fd_.get().fd, true, base::MessageLoopForIO::WATCH_READ,
      read_watcher_.get(), this));
}

void RawChannelPosix::OnShutdownNoLock(
    scoped_ptr<ReadBuffer> /*read_buffer*/,
    scoped_ptr<WriteBuffer> /*write_buffer*/) {
  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());
  write_lock().AssertAcquired();

  read_watcher_.reset();   // This will stop watching (if necessary).
  write_watcher_.reset();  // This will stop watching (if necessary).

  pending_read_ = false;
  pending_write_ = false;

  DCHECK(fd_.is_valid());
  fd_.reset();

  weak_ptr_factory_.InvalidateWeakPtrs();
}

void RawChannelPosix::OnFileCanReadWithoutBlocking(int fd) {
  DCHECK_EQ(fd, fd_.get().fd);
  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());

  if (!pending_read_) {
    NOTREACHED();
    return;
  }

  pending_read_ = false;
  size_t bytes_read = 0;
  IOResult io_result = Read(&bytes_read);
  if (io_result != IO_PENDING) {
    OnReadCompleted(io_result, bytes_read);
    // TODO(vtl): If we weren't destroyed, we'd like to do
    //
    //   DCHECK(!read_watcher_ || pending_read_);
    //
    // On failure, |read_watcher_| must have been reset; on success, we assume
    // that |OnReadCompleted()| always schedules another read. Otherwise, we
    // could end up spinning -- getting |OnFileCanReadWithoutBlocking()| again
    // and again but not doing any actual read.
    // TODO(yzshen): An alternative is to stop watching if RawChannel doesn't
    // schedule a new read. But that code won't be reached under the current
    // RawChannel implementation.
    return;  // |this| may have been destroyed in |OnReadCompleted()|.
  }

  DCHECK(pending_read_);
}

void RawChannelPosix::OnFileCanWriteWithoutBlocking(int fd) {
  DCHECK_EQ(fd, fd_.get().fd);
  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());

  IOResult io_result;
  size_t platform_handles_written = 0;
  size_t bytes_written = 0;
  {
    base::AutoLock locker(write_lock());

    DCHECK(pending_write_);

    pending_write_ = false;
    io_result = WriteNoLock(&platform_handles_written, &bytes_written);
  }

  if (io_result != IO_PENDING) {
    OnWriteCompleted(io_result, platform_handles_written, bytes_written);
    return;  // |this| may have been destroyed in |OnWriteCompleted()|.
  }
}

RawChannel::IOResult RawChannelPosix::ReadImpl(size_t* bytes_read) {
  char* buffer = nullptr;
  size_t bytes_to_read = 0;
  read_buffer()->GetBuffer(&buffer, &bytes_to_read);

  size_t old_num_platform_handles = read_platform_handles_.size();
  ssize_t read_result = embedder::PlatformChannelRecvmsg(
      fd_.get(), buffer, bytes_to_read, &read_platform_handles_);
  if (read_platform_handles_.size() > old_num_platform_handles) {
    DCHECK_LE(read_platform_handles_.size() - old_num_platform_handles,
              embedder::kPlatformChannelMaxNumHandles);

    // We should never accumulate more than |TransportData::kMaxPlatformHandles
    // + embedder::kPlatformChannelMaxNumHandles| handles. (The latter part is
    // possible because we could have accumulated all the handles for a message,
    // then received the message data plus the first set of handles for the next
    // message in the subsequent |recvmsg()|.)
    if (read_platform_handles_.size() >
        (TransportData::GetMaxPlatformHandles() +
         embedder::kPlatformChannelMaxNumHandles)) {
      LOG(ERROR) << "Received too many platform handles";
      embedder::CloseAllPlatformHandles(&read_platform_handles_);
      read_platform_handles_.clear();
      return IO_FAILED_UNKNOWN;
    }
  }

  if (read_result > 0) {
    *bytes_read = static_cast<size_t>(read_result);
    return IO_SUCCEEDED;
  }

  // |read_result == 0| means "end of file".
  if (read_result == 0)
    return IO_FAILED_SHUTDOWN;

  if (errno == EAGAIN || errno == EWOULDBLOCK)
    return ScheduleRead();

  if (errno == ECONNRESET)
    return IO_FAILED_BROKEN;

  PLOG(WARNING) << "recvmsg";
  return IO_FAILED_UNKNOWN;
}

void RawChannelPosix::WaitToWrite() {
  DCHECK_EQ(base::MessageLoop::current(), message_loop_for_io());

  DCHECK(write_watcher_);

  if (!message_loop_for_io()->WatchFileDescriptor(
          fd_.get().fd, false, base::MessageLoopForIO::WATCH_WRITE,
          write_watcher_.get(), this)) {
    {
      base::AutoLock locker(write_lock());

      DCHECK(pending_write_);
      pending_write_ = false;
    }
    OnWriteCompleted(IO_FAILED_UNKNOWN, 0, 0);
    return;  // |this| may have been destroyed in |OnWriteCompleted()|.
  }
}

}  // namespace

// -----------------------------------------------------------------------------

// Static factory method declared in raw_channel.h.
// static
scoped_ptr<RawChannel> RawChannel::Create(
    embedder::ScopedPlatformHandle handle) {
  return make_scoped_ptr(new RawChannelPosix(handle.Pass()));
}

}  // namespace system
}  // namespace mojo