Split the IPC code into ipc/

This splits the ipc code from the common project.  The 'common' project pulls in
all of webkit, the v8 bindings, skia, googleurl, and a number of other projects
which makes it very difficult to deal with especially for external projects
wanting just to use some of Chromium's infrastructure.  This puts the ipc code
into its top-level ipc/ directory with a dependency only on base.  The common
project depends on the new ipc/ipc.gyp:ipc target so that all projects currently
pulling common in to get the IPC code still have it available.  This mostly
follows agl's pre-gyp attempt to do this which was r13062.

Known issues:
- Currently a number of projects depend on chrome/chrome.gyp:common in order to
use the IPC infrastructure.  Rather than fixing all of these dependencies I have
made common depend on ipc/ipc.gyp:ipc and added "ipc" to the include_rules
section of DEPS so that checkdeps.py doesn't complain.  Over time projects that
need IPC should depend on the IPC project themselves and dependencies on common
removed, although I don't think many projects that need IPC will be able to get
away without common currently.
- ipc/ipc_message_macros.h still has #include "chrome/common/..." inside of a
ipc/ should not refer to files in chrome/... now.  I'm not sure how to resolve
this since it's really an IDE bug
- the named pipe name (windows+linux) and the logging event name (all) + env
variable (posix) refer explicitly to 'Chrome' which somewhat hurts the illusion
of ipc/ being an independent library.  I think this should be examined in a
subsequent, much smaller patch.
- I've eliminated the IPC.SendMsgCount counter since it was implemented in a way
to create a dependency from ipc/ to chrome/common/chrome_counters. This is the
same approach that r13062 took.

http://codereview.chromium.org/155905

(Patch from James Robinson)


git-svn-id: svn://svn.chromium.org/chrome/trunk/src@21342 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 837 insertions, 0 deletions

diff --git a/ipc/ipc_channel_posix.cc b/ipc/ipc_channel_posix.cc
new file mode 100644
index 0000000..22b9241
--- /dev/null
+++ b/ipc/ipc_channel_posix.cc
@@ -0,0 +1,837 @@
+// Copyright (c) 2008 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 "ipc/ipc_channel_posix.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stddef.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/un.h>
+
+#include <string>
+#include <map>
+
+#include "base/command_line.h"
+#include "base/eintr_wrapper.h"
+#include "base/global_descriptors_posix.h"
+#include "base/lock.h"
+#include "base/logging.h"
+#include "base/process_util.h"
+#include "base/scoped_ptr.h"
+#include "base/singleton.h"
+#include "base/stats_counters.h"
+#include "base/string_util.h"
+#include "ipc/ipc_descriptors.h"
+#include "ipc/ipc_switches.h"
+#include "ipc/file_descriptor_set_posix.h"
+#include "ipc/ipc_logging.h"
+#include "ipc/ipc_message_utils.h"
+
+namespace IPC {
+
+// IPC channels on Windows use named pipes (CreateNamedPipe()) with
+// channel ids as the pipe names.  Channels on POSIX use anonymous
+// Unix domain sockets created via socketpair() as pipes.  These don't
+// quite line up.
+//
+// When creating a child subprocess, the parent side of the fork
+// arranges it such that the initial control channel ends up on the
+// magic file descriptor kPrimaryIPCChannel in the child.  Future
+// connections (file descriptors) can then be passed via that
+// connection via sendmsg().
+
+//------------------------------------------------------------------------------
+namespace {
+
+// The PipeMap class works around this quirk related to unit tests:
+//
+// When running as a server, we install the client socket in a
+// specific file descriptor number (@kPrimaryIPCChannel). However, we
+// also have to support the case where we are running unittests in the
+// same process.  (We do not support forking without execing.)
+//
+// Case 1: normal running
+//   The IPC server object will install a mapping in PipeMap from the
+//   name which it was given to the client pipe. When forking the client, the
+//   GetClientFileDescriptorMapping will ensure that the socket is installed in
+//   the magic slot (@kPrimaryIPCChannel). The client will search for the
+//   mapping, but it won't find any since we are in a new process. Thus the
+//   magic fd number is returned. Once the client connects, the server will
+//   close its copy of the client socket and remove the mapping.
+//
+// Case 2: unittests - client and server in the same process
+//   The IPC server will install a mapping as before. The client will search
+//   for a mapping and find out. It duplicates the file descriptor and
+//   connects. Once the client connects, the server will close the original
+//   copy of the client socket and remove the mapping. Thus, when the client
+//   object closes, it will close the only remaining copy of the client socket
+//   in the fd table and the server will see EOF on its side.
+//
+// TODO(port): a client process cannot connect to multiple IPC channels with
+// this scheme.
+
+class PipeMap {
+ public:
+  // Lookup a given channel id. Return -1 if not found.
+  int Lookup(const std::string& channel_id) {
+    AutoLock locked(lock_);
+
+    ChannelToFDMap::const_iterator i = map_.find(channel_id);
+    if (i == map_.end())
+      return -1;
+    return i->second;
+  }
+
+  // Remove the mapping for the given channel id. No error is signaled if the
+  // channel_id doesn't exist
+  void RemoveAndClose(const std::string& channel_id) {
+    AutoLock locked(lock_);
+
+    ChannelToFDMap::iterator i = map_.find(channel_id);
+    if (i != map_.end()) {
+      HANDLE_EINTR(close(i->second));
+      map_.erase(i);
+    }
+  }
+
+  // Insert a mapping from @channel_id to @fd. It's a fatal error to insert a
+  // mapping if one already exists for the given channel_id
+  void Insert(const std::string& channel_id, int fd) {
+    AutoLock locked(lock_);
+    DCHECK(fd != -1);
+
+    ChannelToFDMap::const_iterator i = map_.find(channel_id);
+    CHECK(i == map_.end()) << "Creating second IPC server (fd " << fd << ") "
+                           << "for '" << channel_id << "' while first "
+                           << "(fd " << i->second << ") still exists";
+    map_[channel_id] = fd;
+  }
+
+ private:
+  Lock lock_;
+  typedef std::map<std::string, int> ChannelToFDMap;
+  ChannelToFDMap map_;
+};
+
+// Used to map a channel name to the equivalent FD # in the current process.
+// Returns -1 if the channel is unknown.
+int ChannelNameToFD(const std::string& channel_id) {
+  // See the large block comment above PipeMap for the reasoning here.
+  const int fd = Singleton<PipeMap>()->Lookup(channel_id);
+
+  if (fd != -1) {
+    int dup_fd = dup(fd);
+    if (dup_fd < 0)
+      LOG(FATAL) << "dup(" << fd << "): " << strerror(errno);
+    return dup_fd;
+  }
+
+  return fd;
+}
+
+//------------------------------------------------------------------------------
+sockaddr_un sizecheck;
+const size_t kMaxPipeNameLength = sizeof(sizecheck.sun_path);
+
+// Creates a Fifo with the specified name ready to listen on.
+bool CreateServerFifo(const std::string& pipe_name, int* server_listen_fd) {
+  DCHECK(server_listen_fd);
+  DCHECK_GT(pipe_name.length(), 0u);
+  DCHECK_LT(pipe_name.length(), kMaxPipeNameLength);
+
+  if (pipe_name.length() == 0 || pipe_name.length() >= kMaxPipeNameLength) {
+    return false;
+  }
+
+  // Create socket.
+  int fd = socket(AF_UNIX, SOCK_STREAM, 0);
+  if (fd < 0) {
+    return false;
+  }
+
+  // Make socket non-blocking
+  if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1) {
+    HANDLE_EINTR(close(fd));
+    return false;
+  }
+
+  // Delete any old FS instances.
+  unlink(pipe_name.c_str());
+
+  // Create unix_addr structure
+  struct sockaddr_un unix_addr;
+  memset(&unix_addr, 0, sizeof(unix_addr));
+  unix_addr.sun_family = AF_UNIX;
+  snprintf(unix_addr.sun_path, kMaxPipeNameLength, "%s", pipe_name.c_str());
+  size_t unix_addr_len = offsetof(struct sockaddr_un, sun_path) +
+      strlen(unix_addr.sun_path) + 1;
+
+  // Bind the socket.
+  if (bind(fd, reinterpret_cast<const sockaddr*>(&unix_addr),
+           unix_addr_len) != 0) {
+    HANDLE_EINTR(close(fd));
+    return false;
+  }
+
+  // Start listening on the socket.
+  const int listen_queue_length = 1;
+  if (listen(fd, listen_queue_length) != 0) {
+    HANDLE_EINTR(close(fd));
+    return false;
+  }
+
+  *server_listen_fd = fd;
+  return true;
+}
+
+// Accept a connection on a fifo.
+bool ServerAcceptFifoConnection(int server_listen_fd, int* server_socket) {
+  DCHECK(server_socket);
+
+  int accept_fd = HANDLE_EINTR(accept(server_listen_fd, NULL, 0));
+  if (accept_fd < 0)
+    return false;
+  if (fcntl(accept_fd, F_SETFL, O_NONBLOCK) == -1) {
+    HANDLE_EINTR(close(accept_fd));
+    return false;
+  }
+
+  *server_socket = accept_fd;
+  return true;
+}
+
+bool ClientConnectToFifo(const std::string &pipe_name, int* client_socket) {
+  DCHECK(client_socket);
+  DCHECK_LT(pipe_name.length(), kMaxPipeNameLength);
+
+  // Create socket.
+  int fd = socket(AF_UNIX, SOCK_STREAM, 0);
+  if (fd < 0) {
+    LOG(ERROR) << "fd is invalid";
+    return false;
+  }
+
+  // Make socket non-blocking
+  if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1) {
+    LOG(ERROR) << "fcntl failed";
+    HANDLE_EINTR(close(fd));
+    return false;
+  }
+
+  // Create server side of socket.
+  struct sockaddr_un  server_unix_addr;
+  memset(&server_unix_addr, 0, sizeof(server_unix_addr));
+  server_unix_addr.sun_family = AF_UNIX;
+  snprintf(server_unix_addr.sun_path, kMaxPipeNameLength, "%s",
+           pipe_name.c_str());
+  size_t server_unix_addr_len = offsetof(struct sockaddr_un, sun_path) +
+      strlen(server_unix_addr.sun_path) + 1;
+
+  if (HANDLE_EINTR(connect(fd, reinterpret_cast<sockaddr*>(&server_unix_addr),
+                           server_unix_addr_len)) != 0) {
+    HANDLE_EINTR(close(fd));
+    return false;
+  }
+
+  *client_socket = fd;
+  return true;
+}
+
+}  // namespace
+//------------------------------------------------------------------------------
+
+Channel::ChannelImpl::ChannelImpl(const std::string& channel_id, Mode mode,
+                                  Listener* listener)
+    : mode_(mode),
+      is_blocked_on_write_(false),
+      message_send_bytes_written_(0),
+      uses_fifo_(CommandLine::ForCurrentProcess()->HasSwitch(
+                     switches::kIPCUseFIFO)),
+      server_listen_pipe_(-1),
+      pipe_(-1),
+      client_pipe_(-1),
+      listener_(listener),
+      waiting_connect_(true),
+      processing_incoming_(false),
+      factory_(this) {
+  if (!CreatePipe(channel_id, mode)) {
+    // The pipe may have been closed already.
+    LOG(WARNING) << "Unable to create pipe named \"" << channel_id <<
+                    "\" in " << (mode == MODE_SERVER ? "server" : "client") <<
+                    " mode error(" << strerror(errno) << ").";
+  }
+}
+
+// static
+void AddChannelSocket(const std::string& name, int socket) {
+  Singleton<PipeMap>()->Insert(name, socket);
+}
+
+// static
+void RemoveAndCloseChannelSocket(const std::string& name) {
+  Singleton<PipeMap>()->RemoveAndClose(name);
+}
+
+// static
+bool SocketPair(int* fd1, int* fd2) {
+  int pipe_fds[2];
+  if (socketpair(AF_UNIX, SOCK_STREAM, 0, pipe_fds) != 0) {
+    LOG(ERROR) << "socketpair(): " << strerror(errno);
+    return false;
+  }
+
+  // Set both ends to be non-blocking.
+  if (fcntl(pipe_fds[0], F_SETFL, O_NONBLOCK) == -1 ||
+      fcntl(pipe_fds[1], F_SETFL, O_NONBLOCK) == -1) {
+    LOG(ERROR) << "fcntl(O_NONBLOCK): " << strerror(errno);
+    HANDLE_EINTR(close(pipe_fds[0]));
+    HANDLE_EINTR(close(pipe_fds[1]));
+    return false;
+  }
+
+  *fd1 = pipe_fds[0];
+  *fd2 = pipe_fds[1];
+
+  return true;
+}
+
+bool Channel::ChannelImpl::CreatePipe(const std::string& channel_id,
+                                      Mode mode) {
+  DCHECK(server_listen_pipe_ == -1 && pipe_ == -1);
+
+  if (uses_fifo_) {
+    // This only happens in unit tests; see the comment above PipeMap.
+    // TODO(playmobil): We shouldn't need to create fifos on disk.
+    // TODO(playmobil): If we do, they should be in the user data directory.
+    // TODO(playmobil): Cleanup any stale fifos.
+    pipe_name_ = "/var/tmp/chrome_" + channel_id;
+    if (mode == MODE_SERVER) {
+      if (!CreateServerFifo(pipe_name_, &server_listen_pipe_)) {
+        return false;
+      }
+    } else {
+      if (!ClientConnectToFifo(pipe_name_, &pipe_)) {
+        return false;
+      }
+      waiting_connect_ = false;
+    }
+  } else {
+    // This is the normal (non-unit-test) case, where we're using sockets.
+    // Three possible cases:
+    // 1) It's for a channel we already have a pipe for; reuse it.
+    // 2) It's the initial IPC channel:
+    //   2a) Server side: create the pipe.
+    //   2b) Client side: Pull the pipe out of the GlobalDescriptors set.
+    pipe_name_ = channel_id;
+    pipe_ = ChannelNameToFD(pipe_name_);
+    if (pipe_ < 0) {
+      // Initial IPC channel.
+      if (mode == MODE_SERVER) {
+        if (!SocketPair(&pipe_, &client_pipe_))
+          return false;
+        AddChannelSocket(pipe_name_, client_pipe_);
+      } else {
+        pipe_ = Singleton<base::GlobalDescriptors>()->Get(kPrimaryIPCChannel);
+      }
+    } else {
+      waiting_connect_ = false;
+    }
+  }
+
+  // Create the Hello message to be sent when Connect is called
+  scoped_ptr<Message> msg(new Message(MSG_ROUTING_NONE,
+                                      HELLO_MESSAGE_TYPE,
+                                      IPC::Message::PRIORITY_NORMAL));
+  if (!msg->WriteInt(base::GetCurrentProcId())) {
+    Close();
+    return false;
+  }
+
+  output_queue_.push(msg.release());
+  return true;
+}
+
+bool Channel::ChannelImpl::Connect() {
+  if (mode_ == MODE_SERVER && uses_fifo_) {
+    if (server_listen_pipe_ == -1) {
+      return false;
+    }
+    MessageLoopForIO::current()->WatchFileDescriptor(
+        server_listen_pipe_,
+        true,
+        MessageLoopForIO::WATCH_READ,
+        &server_listen_connection_watcher_,
+        this);
+  } else {
+    if (pipe_ == -1) {
+      return false;
+    }
+    MessageLoopForIO::current()->WatchFileDescriptor(
+        pipe_,
+        true,
+        MessageLoopForIO::WATCH_READ,
+        &read_watcher_,
+        this);
+    waiting_connect_ = false;
+  }
+
+  if (!waiting_connect_)
+    return ProcessOutgoingMessages();
+  return true;
+}
+
+bool Channel::ChannelImpl::ProcessIncomingMessages() {
+  ssize_t bytes_read = 0;
+
+  struct msghdr msg = {0};
+  struct iovec iov = {input_buf_, Channel::kReadBufferSize};
+
+  msg.msg_iov = &iov;
+  msg.msg_iovlen = 1;
+  msg.msg_control = input_cmsg_buf_;
+
+  for (;;) {
+    msg.msg_controllen = sizeof(input_cmsg_buf_);
+
+    if (bytes_read == 0) {
+      if (pipe_ == -1)
+        return false;
+
+      // Read from pipe.
+      // recvmsg() returns 0 if the connection has closed or EAGAIN if no data
+      // is waiting on the pipe.
+      bytes_read = HANDLE_EINTR(recvmsg(pipe_, &msg, MSG_DONTWAIT));
+
+      if (bytes_read < 0) {
+        if (errno == EAGAIN) {
+          return true;
+#if defined(OS_MACOSX)
+        } else if (errno == EPERM) {
+          // On OSX, reading from a pipe with no listener returns EPERM
+          // treat this as a special case to prevent spurious error messages
+          // to the console.
+          return false;
+#endif  // defined(OS_MACOSX)
+        } else {
+          LOG(ERROR) << "pipe error (" << pipe_ << "): " << strerror(errno);
+          return false;
+        }
+      } else if (bytes_read == 0) {
+        // The pipe has closed...
+        Close();
+        return false;
+      }
+    }
+    DCHECK(bytes_read);
+
+    if (client_pipe_ != -1) {
+      Singleton<PipeMap>()->RemoveAndClose(pipe_name_);
+      client_pipe_ = -1;
+    }
+
+    // a pointer to an array of |num_wire_fds| file descriptors from the read
+    const int* wire_fds = NULL;
+    unsigned num_wire_fds = 0;
+
+    // walk the list of control messages and, if we find an array of file
+    // descriptors, save a pointer to the array
+
+    // This next if statement is to work around an OSX issue where
+    // CMSG_FIRSTHDR will return non-NULL in the case that controllen == 0.
+    // Here's a test case:
+    //
+    // int main() {
+    // struct msghdr msg;
+    //   msg.msg_control = &msg;
+    //   msg.msg_controllen = 0;
+    //   if (CMSG_FIRSTHDR(&msg))
+    //     printf("Bug found!\n");
+    // }
+    if (msg.msg_controllen > 0) {
+      // On OSX, CMSG_FIRSTHDR doesn't handle the case where controllen is 0
+      // and will return a pointer into nowhere.
+      for (struct cmsghdr* cmsg = CMSG_FIRSTHDR(&msg); cmsg;
+           cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+        if (cmsg->cmsg_level == SOL_SOCKET &&
+            cmsg->cmsg_type == SCM_RIGHTS) {
+          const unsigned payload_len = cmsg->cmsg_len - CMSG_LEN(0);
+          DCHECK(payload_len % sizeof(int) == 0);
+          wire_fds = reinterpret_cast<int*>(CMSG_DATA(cmsg));
+          num_wire_fds = payload_len / 4;
+
+          if (msg.msg_flags & MSG_CTRUNC) {
+            LOG(ERROR) << "SCM_RIGHTS message was truncated"
+                       << " cmsg_len:" << cmsg->cmsg_len
+                       << " fd:" << pipe_;
+            for (unsigned i = 0; i < num_wire_fds; ++i)
+              HANDLE_EINTR(close(wire_fds[i]));
+            return false;
+          }
+          break;
+        }
+      }
+    }
+
+    // Process messages from input buffer.
+    const char *p;
+    const char *end;
+    if (input_overflow_buf_.empty()) {
+      p = input_buf_;
+      end = p + bytes_read;
+    } else {
+      if (input_overflow_buf_.size() >
+         static_cast<size_t>(kMaximumMessageSize - bytes_read)) {
+        input_overflow_buf_.clear();
+        LOG(ERROR) << "IPC message is too big";
+        return false;
+      }
+      input_overflow_buf_.append(input_buf_, bytes_read);
+      p = input_overflow_buf_.data();
+      end = p + input_overflow_buf_.size();
+    }
+
+    // A pointer to an array of |num_fds| file descriptors which includes any
+    // fds that have spilled over from a previous read.
+    const int* fds;
+    unsigned num_fds;
+    unsigned fds_i = 0;  // the index of the first unused descriptor
+
+    if (input_overflow_fds_.empty()) {
+      fds = wire_fds;
+      num_fds = num_wire_fds;
+    } else {
+      const size_t prev_size = input_overflow_fds_.size();
+      input_overflow_fds_.resize(prev_size + num_wire_fds);
+      memcpy(&input_overflow_fds_[prev_size], wire_fds,
+             num_wire_fds * sizeof(int));
+      fds = &input_overflow_fds_[0];
+      num_fds = input_overflow_fds_.size();
+    }
+
+    while (p < end) {
+      const char* message_tail = Message::FindNext(p, end);
+      if (message_tail) {
+        int len = static_cast<int>(message_tail - p);
+        Message m(p, len);
+        if (m.header()->num_fds) {
+          // the message has file descriptors
+          const char* error = NULL;
+          if (m.header()->num_fds > num_fds - fds_i) {
+            // the message has been completely received, but we didn't get
+            // enough file descriptors.
+            error = "Message needs unreceived descriptors";
+          }
+
+          if (m.header()->num_fds >
+              FileDescriptorSet::MAX_DESCRIPTORS_PER_MESSAGE) {
+            // There are too many descriptors in this message
+            error = "Message requires an excessive number of descriptors";
+          }
+
+          if (error) {
+            LOG(WARNING) << error
+                         << " channel:" << this
+                         << " message-type:" << m.type()
+                         << " header()->num_fds:" << m.header()->num_fds
+                         << " num_fds:" << num_fds
+                         << " fds_i:" << fds_i;
+            // close the existing file descriptors so that we don't leak them
+            for (unsigned i = fds_i; i < num_fds; ++i)
+              HANDLE_EINTR(close(fds[i]));
+            input_overflow_fds_.clear();
+            // abort the connection
+            return false;
+          }
+
+          m.file_descriptor_set()->SetDescriptors(
+              &fds[fds_i], m.header()->num_fds);
+          fds_i += m.header()->num_fds;
+        }
+#ifdef IPC_MESSAGE_DEBUG_EXTRA
+        DLOG(INFO) << "received message on channel @" << this <<
+                      " with type " << m.type();
+#endif
+        if (m.routing_id() == MSG_ROUTING_NONE &&
+            m.type() == HELLO_MESSAGE_TYPE) {
+          // The Hello message contains only the process id.
+          listener_->OnChannelConnected(MessageIterator(m).NextInt());
+        } else {
+          listener_->OnMessageReceived(m);
+        }
+        p = message_tail;
+      } else {
+        // Last message is partial.
+        break;
+      }
+    }
+    input_overflow_buf_.assign(p, end - p);
+    input_overflow_fds_ = std::vector<int>(&fds[fds_i], &fds[num_fds]);
+
+    // When the input data buffer is empty, the overflow fds should be too. If
+    // this is not the case, we probably have a rogue renderer which is trying
+    // to fill our descriptor table.
+    if (input_overflow_buf_.empty() && !input_overflow_fds_.empty()) {
+      // We close these descriptors in Close()
+      return false;
+    }
+
+    bytes_read = 0;  // Get more data.
+  }
+
+  return true;
+}
+
+bool Channel::ChannelImpl::ProcessOutgoingMessages() {
+  DCHECK(!waiting_connect_);  // Why are we trying to send messages if there's
+                              // no connection?
+  is_blocked_on_write_ = false;
+
+  if (output_queue_.empty())
+    return true;
+
+  if (pipe_ == -1)
+    return false;
+
+  // Write out all the messages we can till the write blocks or there are no
+  // more outgoing messages.
+  while (!output_queue_.empty()) {
+    Message* msg = output_queue_.front();
+
+    size_t amt_to_write = msg->size() - message_send_bytes_written_;
+    DCHECK(amt_to_write != 0);
+    const char *out_bytes = reinterpret_cast<const char*>(msg->data()) +
+        message_send_bytes_written_;
+
+    struct msghdr msgh = {0};
+    struct iovec iov = {const_cast<char*>(out_bytes), amt_to_write};
+    msgh.msg_iov = &iov;
+    msgh.msg_iovlen = 1;
+    char buf[CMSG_SPACE(
+        sizeof(int[FileDescriptorSet::MAX_DESCRIPTORS_PER_MESSAGE]))];
+
+    if (message_send_bytes_written_ == 0 &&
+        !msg->file_descriptor_set()->empty()) {
+      // This is the first chunk of a message which has descriptors to send
+      struct cmsghdr *cmsg;
+      const unsigned num_fds = msg->file_descriptor_set()->size();
+
+      DCHECK_LE(num_fds, FileDescriptorSet::MAX_DESCRIPTORS_PER_MESSAGE);
+
+      msgh.msg_control = buf;
+      msgh.msg_controllen = CMSG_SPACE(sizeof(int) * num_fds);
+      cmsg = CMSG_FIRSTHDR(&msgh);
+      cmsg->cmsg_level = SOL_SOCKET;
+      cmsg->cmsg_type = SCM_RIGHTS;
+      cmsg->cmsg_len = CMSG_LEN(sizeof(int) * num_fds);
+      msg->file_descriptor_set()->GetDescriptors(
+          reinterpret_cast<int*>(CMSG_DATA(cmsg)));
+      msgh.msg_controllen = cmsg->cmsg_len;
+
+      msg->header()->num_fds = num_fds;
+    }
+
+    ssize_t bytes_written = HANDLE_EINTR(sendmsg(pipe_, &msgh, MSG_DONTWAIT));
+    if (bytes_written > 0)
+      msg->file_descriptor_set()->CommitAll();
+
+    if (bytes_written < 0 && errno != EAGAIN) {
+#if defined(OS_MACOSX)
+      // On OSX writing to a pipe with no listener returns EPERM.
+      if (errno == EPERM) {
+        Close();
+        return false;
+      }
+#endif  // OS_MACOSX
+      LOG(ERROR) << "pipe error on " << pipe_ << ": " << strerror(errno);
+      return false;
+    }
+
+    if (static_cast<size_t>(bytes_written) != amt_to_write) {
+      if (bytes_written > 0) {
+        // If write() fails with EAGAIN then bytes_written will be -1.
+        message_send_bytes_written_ += bytes_written;
+      }
+
+      // Tell libevent to call us back once things are unblocked.
+      is_blocked_on_write_ = true;
+      MessageLoopForIO::current()->WatchFileDescriptor(
+          pipe_,
+          false,  // One shot
+          MessageLoopForIO::WATCH_WRITE,
+          &write_watcher_,
+          this);
+      return true;
+    } else {
+      message_send_bytes_written_ = 0;
+
+      // Message sent OK!
+#ifdef IPC_MESSAGE_DEBUG_EXTRA
+      DLOG(INFO) << "sent message @" << msg << " on channel @" << this <<
+                    " with type " << msg->type();
+#endif
+      output_queue_.pop();
+      delete msg;
+    }
+  }
+  return true;
+}
+
+bool Channel::ChannelImpl::Send(Message* message) {
+#ifdef IPC_MESSAGE_DEBUG_EXTRA
+  DLOG(INFO) << "sending message @" << message << " on channel @" << this
+             << " with type " << message->type()
+             << " (" << output_queue_.size() << " in queue)";
+#endif
+
+#ifdef IPC_MESSAGE_LOG_ENABLED
+  Logging::current()->OnSendMessage(message, "");
+#endif
+
+  output_queue_.push(message);
+  if (!waiting_connect_) {
+    if (!is_blocked_on_write_) {
+      if (!ProcessOutgoingMessages())
+        return false;
+    }
+  }
+
+  return true;
+}
+
+int Channel::ChannelImpl::GetClientFileDescriptor() const {
+  return client_pipe_;
+}
+
+// Called by libevent when we can read from th pipe without blocking.
+void Channel::ChannelImpl::OnFileCanReadWithoutBlocking(int fd) {
+  bool send_server_hello_msg = false;
+  if (waiting_connect_ && mode_ == MODE_SERVER) {
+    // In the case of a socketpair() the server starts listening on its end
+    // of the pipe in Connect().
+    DCHECK(uses_fifo_);
+
+    if (!ServerAcceptFifoConnection(server_listen_pipe_, &pipe_)) {
+      Close();
+    }
+
+    // No need to watch the listening socket any longer since only one client
+    // can connect.  So unregister with libevent.
+    server_listen_connection_watcher_.StopWatchingFileDescriptor();
+
+    // Start watching our end of the socket.
+    MessageLoopForIO::current()->WatchFileDescriptor(
+        pipe_,
+        true,
+        MessageLoopForIO::WATCH_READ,
+        &read_watcher_,
+        this);
+
+    waiting_connect_ = false;
+    send_server_hello_msg = true;
+  }
+
+  if (!waiting_connect_ && fd == pipe_) {
+    if (!ProcessIncomingMessages()) {
+      Close();
+      listener_->OnChannelError();
+    }
+  }
+
+  // If we're a server and handshaking, then we want to make sure that we
+  // only send our handshake message after we've processed the client's.
+  // This gives us a chance to kill the client if the incoming handshake
+  // is invalid.
+  if (send_server_hello_msg) {
+    // This should be our first write so there's no chance we can block here...
+    DCHECK(is_blocked_on_write_ == false);
+    ProcessOutgoingMessages();
+  }
+}
+
+// Called by libevent when we can write to the pipe without blocking.
+void Channel::ChannelImpl::OnFileCanWriteWithoutBlocking(int fd) {
+  if (!ProcessOutgoingMessages()) {
+    Close();
+    listener_->OnChannelError();
+  }
+}
+
+void Channel::ChannelImpl::Close() {
+  // Close can be called multiple time, so we need to make sure we're
+  // idempotent.
+
+  // Unregister libevent for the listening socket and close it.
+  server_listen_connection_watcher_.StopWatchingFileDescriptor();
+
+  if (server_listen_pipe_ != -1) {
+    HANDLE_EINTR(close(server_listen_pipe_));
+    server_listen_pipe_ = -1;
+  }
+
+  // Unregister libevent for the FIFO and close it.
+  read_watcher_.StopWatchingFileDescriptor();
+  write_watcher_.StopWatchingFileDescriptor();
+  if (pipe_ != -1) {
+    HANDLE_EINTR(close(pipe_));
+    pipe_ = -1;
+  }
+  if (client_pipe_ != -1) {
+    Singleton<PipeMap>()->RemoveAndClose(pipe_name_);
+    client_pipe_ = -1;
+  }
+
+  if (uses_fifo_) {
+    // Unlink the FIFO
+    unlink(pipe_name_.c_str());
+  }
+
+  while (!output_queue_.empty()) {
+    Message* m = output_queue_.front();
+    output_queue_.pop();
+    delete m;
+  }
+
+  // Close any outstanding, received file descriptors
+  for (std::vector<int>::iterator
+       i = input_overflow_fds_.begin(); i != input_overflow_fds_.end(); ++i) {
+    HANDLE_EINTR(close(*i));
+  }
+  input_overflow_fds_.clear();
+}
+
+//------------------------------------------------------------------------------
+// Channel's methods simply call through to ChannelImpl.
+Channel::Channel(const std::string& channel_id, Mode mode,
+                 Listener* listener)
+    : channel_impl_(new ChannelImpl(channel_id, mode, listener)) {
+}
+
+Channel::~Channel() {
+  delete channel_impl_;
+}
+
+bool Channel::Connect() {
+  return channel_impl_->Connect();
+}
+
+void Channel::Close() {
+  channel_impl_->Close();
+}
+
+void Channel::set_listener(Listener* listener) {
+  channel_impl_->set_listener(listener);
+}
+
+bool Channel::Send(Message* message) {
+  return channel_impl_->Send(message);
+}
+
+int Channel::GetClientFileDescriptor() const {
+  return channel_impl_->GetClientFileDescriptor();
+}
+
+}  // namespace IPC