Revert 69694 - Add support for sockets that can listen and accept a connectio...

ipc/ipc_channel_posix.cc

Index: ipc/ipc_channel_posix.cc
===================================================================
--- ipc/ipc_channel_posix.cc	(revision 69694)
+++ ipc/ipc_channel_posix.cc	(working copy)
@@ -17,8 +17,6 @@
 
 #include "base/command_line.h"
 #include "base/eintr_wrapper.h"
-#include "base/file_path.h"
-#include "base/file_util.h"
 #include "base/global_descriptors_posix.h"
 #include "base/lock.h"
 #include "base/logging.h"
@@ -35,18 +33,15 @@
 namespace IPC {
 
 // IPC channels on Windows use named pipes (CreateNamedPipe()) with
-// channel ids as the pipe names.  Channels on POSIX use sockets as
-// pipes  These don't quite line up.
+// 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 we use a socket pair and the parent side of
-// the fork arranges it such that the initial control channel ends up on the
+// 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().
-//
-// A POSIX IPC channel can also be set up as a server for a bound UNIX domain
-// socket, and will handle multiple connect and disconnect sequences.  Currently
-// it is limited to one connection at a time.
 
 //------------------------------------------------------------------------------
 namespace {
@@ -133,15 +128,31 @@
   friend struct DefaultSingletonTraits<PipeMap>;
 };
 
+// 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 = PipeMap::GetInstance()->Lookup(channel_id);
+
+  if (fd != -1) {
+    int dup_fd = dup(fd);
+    if (dup_fd < 0)
+      PLOG(FATAL) << "dup(" << fd << ") " << channel_id;
+    return dup_fd;
+  }
+
+  return fd;
+}
+
 //------------------------------------------------------------------------------
-// Verify that kMaxPipeNameLength is a decent size.
+// The standard size on linux is 108, mac is 104. To maintain consistency
+// across platforms we standardize on the smaller value.
+const size_t kMaxPipeNameLength = 104;
 COMPILE_ASSERT(sizeof(((sockaddr_un*)0)->sun_path) >= kMaxPipeNameLength,
                BAD_SUN_PATH_LENGTH);
 
-// Creates a unix domain socket bound to the specified name that is listening
-// for connections.
-bool CreateServerUnixDomainSocket(const std::string& pipe_name,
-                                  int* server_listen_fd) {
+// 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);
@@ -158,7 +169,7 @@
 
   // Make socket non-blocking
   if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1) {
-    PLOG(ERROR) << "fcntl(O_NONBLOCK) " << pipe_name;
+    PLOG(ERROR) << "fcntl " << pipe_name;
     if (HANDLE_EINTR(close(fd)) < 0)
       PLOG(ERROR) << "close " << pipe_name;
     return false;
@@ -167,20 +178,11 @@
   // Delete any old FS instances.
   unlink(pipe_name.c_str());
 
-    // Make sure the path we need exists.
-  FilePath path(pipe_name);
-  FilePath dir_path = path.DirName();
-  if (!file_util::CreateDirectory(dir_path)) {
-    return false;
-  }
-
   // Create unix_addr structure
   struct sockaddr_un unix_addr;
   memset(&unix_addr, 0, sizeof(unix_addr));
   unix_addr.sun_family = AF_UNIX;
-  DCHECK_EQ(static_cast<int>(pipe_name.length()),
-            snprintf(unix_addr.sun_path, kMaxPipeNameLength, "%s",
-                     pipe_name.c_str()));
+  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;
 
@@ -206,15 +208,15 @@
   return true;
 }
 
-// Accept a connection on a socket we are listening to.
-bool ServerAcceptConnection(int server_listen_fd, int* server_socket) {
+// 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) {
-    PLOG(ERROR) << "fcntl(O_NONBLOCK) " << accept_fd;
+    PLOG(ERROR) << "fcntl " << accept_fd;
     if (HANDLE_EINTR(close(accept_fd)) < 0)
       PLOG(ERROR) << "close " << accept_fd;
     return false;
@@ -224,8 +226,7 @@
   return true;
 }
 
-bool CreateClientUnixDomainSocket(const std::string& pipe_name,
-                                  int* client_socket) {
+bool ClientConnectToFifo(const std::string &pipe_name, int* client_socket) {
   DCHECK(client_socket);
   DCHECK_GT(pipe_name.length(), 0u);
   DCHECK_LT(pipe_name.length(), kMaxPipeNameLength);
@@ -243,7 +244,7 @@
 
   // Make socket non-blocking
   if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1) {
-    PLOG(ERROR) << "fcntl(O_NONBLOCK) " << pipe_name;
+    PLOG(ERROR) << "fcntl " << pipe_name;
     if (HANDLE_EINTR(close(fd)) < 0)
       PLOG(ERROR) << "close " << pipe_name;
     return false;
@@ -253,9 +254,8 @@
   struct sockaddr_un server_unix_addr;
   memset(&server_unix_addr, 0, sizeof(server_unix_addr));
   server_unix_addr.sun_family = AF_UNIX;
-  DCHECK_EQ(static_cast<int>(pipe_name.length()),
-            snprintf(server_unix_addr.sun_path, kMaxPipeNameLength, "%s",
-                     pipe_name.c_str()));
+  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;
 
@@ -287,7 +287,7 @@
   return errno == EAGAIN || errno == EMSGSIZE;
 #else
   return errno == EAGAIN;
-#endif  // OS_MACOSX
+#endif
 }
 
 }  // namespace
@@ -297,37 +297,24 @@
                                   Mode mode, Listener* listener)
     : mode_(mode),
       is_blocked_on_write_(false),
-      waiting_connect_(true),
       message_send_bytes_written_(0),
+      uses_fifo_(CommandLine::ForCurrentProcess()->HasSwitch(
+                     switches::kIPCUseFIFO)),
       server_listen_pipe_(-1),
       pipe_(-1),
       client_pipe_(-1),
 #if defined(IPC_USES_READWRITE)
       fd_pipe_(-1),
       remote_fd_pipe_(-1),
-#endif  // IPC_USES_READWRITE
-      pipe_name_(channel_handle.name),
+#endif
       listener_(listener),
-      must_unlink_(false),
+      waiting_connect_(true),
       factory_(this) {
-  // Check to see if we want to implement using domain sockets.
-  bool uses_domain_socket = false;
-  bool listening_socket = false;
-  if (mode_ == MODE_NAMED_SERVER) {
-    uses_domain_socket = true;
-    listening_socket = true;
-    mode_ = MODE_SERVER;
-  } else if (mode_ == MODE_NAMED_CLIENT) {
-    uses_domain_socket = true;
-    mode_ = MODE_CLIENT;
-  }
-  if (!CreatePipe(channel_handle, uses_domain_socket, listening_socket)) {
+  if (!CreatePipe(channel_handle, mode_)) {
     // The pipe may have been closed already.
-    const char *modestr = (mode_ == MODE_SERVER
-                           || mode_ == MODE_NAMED_SERVER) ? "server" : "client";
-    // The pipe may have been closed already.
     LOG(WARNING) << "Unable to create pipe named \"" << channel_handle.name
-                 << "\" in " << modestr << " mode";
+                  << "\" in " << (mode_ == MODE_SERVER ? "server" : "client")
+                  << " mode";
   }
 }
 
@@ -335,6 +322,22 @@
   Close();
 }
 
+// static
+void AddChannelSocket(const std::string& name, int socket) {
+  PipeMap::GetInstance()->Insert(name, socket);
+}
+
+// static
+void RemoveAndCloseChannelSocket(const std::string& name) {
+  PipeMap::GetInstance()->RemoveAndClose(name);
+}
+
+// static
+bool ChannelSocketExists(const std::string& name) {
+  return PipeMap::GetInstance()->Lookup(name) != -1;
+}
+
+// static
 bool SocketPair(int* fd1, int* fd2) {
   int pipe_fds[2];
   if (socketpair(AF_UNIX, SOCK_STREAM, 0, pipe_fds) != 0) {
@@ -359,58 +362,43 @@
   return true;
 }
 
-bool Channel::ChannelImpl::CreatePipe(const IPC::ChannelHandle& channel_handle,
-                                      bool uses_domain_sockets,
-                                      bool listening_socket) {
+bool Channel::ChannelImpl::CreatePipe(const IPC::ChannelHandle &channel_handle,
+                                      Mode mode) {
   DCHECK(server_listen_pipe_ == -1 && pipe_ == -1);
-
-  // Four possible cases:
-  // 1) It's a channel wrapping a pipe that is given to us.
-  // 2) It's for a named channel, so we create it.
-  // 3) It's for a client that we implement ourself. This is used
-  //    in unittesting.
-  // 4) It's the initial IPC channel:
-  //   4a) Client side: Pull the pipe out of the GlobalDescriptors set.
-  //   4b) Server side: create the pipe.
-
-  if (channel_handle.socket.fd != -1) {
-    // Case 1 from comment above.
-    pipe_ = channel_handle.socket.fd;
-#if defined(IPC_USES_READWRITE)
-    // Test the socket passed into us to make sure it is nonblocking.
-    // We don't want to call read/write on a blocking socket.
-    int value = fcntl(pipe_, F_GETFL);
-    if (value == -1) {
-      PLOG(ERROR) << "fcntl(F_GETFL) " << pipe_name_;
-      return false;
-    }
-    if (!(value & O_NONBLOCK)) {
-      LOG(ERROR) << "Socket " << pipe_name_ << " must be O_NONBLOCK";
-      return false;
-    }
-#endif   // IPC_USES_READWRITE
-  } else if (uses_domain_sockets) {
-    // Case 2 from comment above.
-    must_unlink_ = true;
-    if (mode_ == MODE_SERVER) {
-      if (!CreateServerUnixDomainSocket(pipe_name_, &pipe_)) {
+  pipe_name_ = channel_handle.name;
+  pipe_ = channel_handle.socket.fd;
+  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.
+    if (mode == MODE_SERVER) {
+      if (!CreateServerFifo(pipe_name_, &server_listen_pipe_)) {
         return false;
       }
-    } else if (mode_ == MODE_CLIENT) {
-      if (!CreateClientUnixDomainSocket(pipe_name_, &pipe_)) {
+    } else {
+      if (!ClientConnectToFifo(pipe_name_, &pipe_)) {
         return false;
       }
+      waiting_connect_ = false;
     }
   } else {
-    pipe_ = PipeMap::GetInstance()->Lookup(pipe_name_);
-    if (mode_ == MODE_CLIENT) {
-      if (pipe_ != -1) {
-        // Case 3 from comment above.
-        // We only allow one connection.
-        pipe_ = HANDLE_EINTR(dup(pipe_));
-        PipeMap::GetInstance()->RemoveAndClose(pipe_name_);
+    // 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.
+    if (pipe_ < 0) {
+      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 {
-        // Case 4a from comment above.
         // Guard against inappropriate reuse of the initial IPC channel.  If
         // an IPC channel closes and someone attempts to reuse it by name, the
         // initial channel must not be recycled here.  http://crbug.com/26754.
@@ -424,51 +412,42 @@
 
         pipe_ = base::GlobalDescriptors::GetInstance()->Get(kPrimaryIPCChannel);
       }
-    } else if (mode_ == MODE_SERVER) {
-      // Case 4b from comment above.
-      if (pipe_ != -1) {
-        LOG(ERROR) << "Server already exists for " << pipe_name_;
-        return false;
-      }
-      if (!SocketPair(&pipe_, &client_pipe_))
-        return false;
-      PipeMap::GetInstance()->Insert(pipe_name_, client_pipe_);
     } else {
-      LOG(FATAL) << "Unknown mode " << mode_;
-      return false;
+      waiting_connect_ = mode == MODE_SERVER;
     }
   }
 
-  if (mode_ == MODE_SERVER) {
-    if (listening_socket) {
-      server_listen_pipe_ = pipe_;
-      pipe_ = -1;
+  // 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 defined(IPC_USES_READWRITE)
+  if (!uses_fifo_) {
+    // Create a dedicated socketpair() for exchanging file descriptors.
+    // See comments for IPC_USES_READWRITE for details.
+    if (mode == MODE_SERVER) {
+      fd_pipe_ = -1;
+    } else if (remote_fd_pipe_ == -1) {
+      if (!SocketPair(&fd_pipe_, &remote_fd_pipe_)) {
+        return false;
+      }
     }
   }
-
-#if defined(IPC_USES_READWRITE)
-  // Create a dedicated socketpair() for exchanging file descriptors.
-  // See comments for IPC_USES_READWRITE for details.
-  if (mode_ == MODE_CLIENT) {
-    if (!SocketPair(&fd_pipe_, &remote_fd_pipe_)) {
-      return false;
-    }
+  #endif
+  if (!msg->WriteInt(base::GetCurrentProcId())) {
+    Close();
+    return false;
   }
-#endif  // IPC_USES_READWRITE
 
+  output_queue_.push(msg.release());
   return true;
 }
 
 bool Channel::ChannelImpl::Connect() {
-  if (server_listen_pipe_ == -1 && pipe_ == -1) {
-    NOTREACHED() << "Must call create on a channel before calling connect";
-    return false;
-  }
-
-  bool did_connect = true;
-  if (server_listen_pipe_ != -1) {
-    // Watch the pipe for connections, and turn any connections into
-    // active sockets.
+  if (mode_ == MODE_SERVER && uses_fifo_) {
+    if (server_listen_pipe_ == -1) {
+      return false;
+    }
     MessageLoopForIO::current()->WatchFileDescriptor(
         server_listen_pipe_,
         true,
@@ -476,9 +455,21 @@
         &server_listen_connection_watcher_,
         this);
   } else {
-    did_connect = AcceptConnection();
+    if (pipe_ == -1) {
+      return false;
+    }
+    MessageLoopForIO::current()->WatchFileDescriptor(
+        pipe_,
+        true,
+        MessageLoopForIO::WATCH_READ,
+        &read_watcher_,
+        this);
+    waiting_connect_ = mode_ == MODE_SERVER;
   }
-  return did_connect;
+
+  if (!waiting_connect_)
+    return ProcessOutgoingMessages();
+  return true;
 }
 
 bool Channel::ChannelImpl::ProcessIncomingMessages() {
@@ -506,7 +497,7 @@
                                        Channel::kReadBufferSize));
         msg.msg_controllen = 0;
       } else
-#endif  // IPC_USES_READWRITE
+#endif
       {
         msg.msg_controllen = sizeof(input_cmsg_buf_);
         bytes_read = HANDLE_EINTR(recvmsg(pipe_, &msg, MSG_DONTWAIT));
@@ -520,7 +511,7 @@
           // treat this as a special case to prevent spurious error messages
           // to the console.
           return false;
-#endif  // OS_MACOSX
+#endif  // defined(OS_MACOSX)
         } else if (errno == ECONNRESET || errno == EPIPE) {
           return false;
         } else {
@@ -575,7 +566,7 @@
                        << " fd:" << pipe_;
             for (unsigned i = 0; i < num_wire_fds; ++i)
               if (HANDLE_EINTR(close(wire_fds[i])) < 0)
-                PLOG(ERROR) << "close " << i;
+                PLOG(ERROR) << "close" << i;
             return false;
           }
           break;
@@ -634,49 +625,51 @@
             // the message has been completely received, but we didn't get
             // enough file descriptors.
 #if defined(IPC_USES_READWRITE)
-            char dummy;
-            struct iovec fd_pipe_iov = { &dummy, 1 };
-            msg.msg_iov = &fd_pipe_iov;
-            msg.msg_controllen = sizeof(input_cmsg_buf_);
-            ssize_t n = HANDLE_EINTR(recvmsg(fd_pipe_, &msg, MSG_DONTWAIT));
-            if (n == 1 && msg.msg_controllen > 0) {
-              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 (!uses_fifo_) {
+              char dummy;
+              struct iovec fd_pipe_iov = { &dummy, 1 };
+              msg.msg_iov = &fd_pipe_iov;
+              msg.msg_controllen = sizeof(input_cmsg_buf_);
+              ssize_t n = HANDLE_EINTR(recvmsg(fd_pipe_, &msg, MSG_DONTWAIT));
+              if (n == 1 && msg.msg_controllen > 0) {
+                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)
-                      if (HANDLE_EINTR(close(wire_fds[i])) < 0)
-                        PLOG(ERROR) << "close " << i;
-                    return false;
+                    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)
+                        if (HANDLE_EINTR(close(wire_fds[i])) < 0)
+                          PLOG(ERROR) << "close" << i;
+                      return false;
+                    }
+                    break;
                   }
-                  break;
                 }
-              }
-              if (input_overflow_fds_.empty()) {
-                fds = wire_fds;
-                num_fds = num_wire_fds;
-              } else {
-                if (num_wire_fds > 0) {
-                  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));
+                if (input_overflow_fds_.empty()) {
+                  fds = wire_fds;
+                  num_fds = num_wire_fds;
+                } else {
+                  if (num_wire_fds > 0) {
+                    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();
                 }
-                fds = &input_overflow_fds_[0];
-                num_fds = input_overflow_fds_.size();
               }
             }
             if (header_fds > num_fds - fds_i)
-#endif  // IPC_USES_READWRITE
+#endif
               error = "Message needs unreceived descriptors";
           }
 
@@ -697,11 +690,11 @@
             LOG(WARNING) << "In the case of SELinux this can be caused when "
                             "using a --user-data-dir to which the default "
                             "policy doesn't give the renderer access to. ";
-#endif  // CHROMIUM_SELINUX
+#endif
             // close the existing file descriptors so that we don't leak them
             for (unsigned i = fds_i; i < num_fds; ++i)
               if (HANDLE_EINTR(close(fds[i])) < 0)
-                PLOG(ERROR) << "close " << i;
+                PLOG(ERROR) << "close" << i;
             input_overflow_fds_.clear();
             // abort the connection
             return false;
@@ -713,7 +706,8 @@
         }
         DVLOG(2) << "received message on channel @" << this
                  << " with type " << m.type() << " on fd " << pipe_;
-        if (IsHelloMessage(&m)) {
+        if (m.routing_id() == MSG_ROUTING_NONE &&
+            m.type() == HELLO_MESSAGE_TYPE) {
           // The Hello message contains only the process id.
           void *iter = NULL;
           int pid;
@@ -721,9 +715,9 @@
             NOTREACHED();
           }
 #if defined(IPC_USES_READWRITE)
-          if (mode_ == MODE_SERVER) {
-            // With IPC_USES_READWRITE, the Hello message from the client to the
-            // server also contains the fd_pipe_, which  will be used for all
+          if (mode_ == MODE_SERVER && !uses_fifo_) {
+            // On non-Mac, the Hello message from the client to the server
+            // also contains the fd_pipe_, which  will be used for all
             // subsequent file descriptor passing.
             DCHECK_EQ(m.file_descriptor_set()->size(), 1U);
             base::FileDescriptor descriptor;
@@ -733,7 +727,7 @@
             fd_pipe_ = descriptor.fd;
             CHECK(descriptor.auto_close);
           }
-#endif  // IPC_USES_READWRITE
+#endif
           listener_->OnChannelConnected(pid);
         } else {
           listener_->OnMessageReceived(m);
@@ -761,22 +755,52 @@
 
     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?
-  if (output_queue_.empty())
+  is_blocked_on_write_ = false;
+
+  if (output_queue_.empty()) {
     return true;
+  }
 
-  if (pipe_ == -1)
+  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();
 
+#if defined(IPC_USES_READWRITE)
+    scoped_ptr<Message> hello;
+    if (remote_fd_pipe_ != -1 &&
+        msg->routing_id() == MSG_ROUTING_NONE &&
+        msg->type() == HELLO_MESSAGE_TYPE) {
+      hello.reset(new Message(MSG_ROUTING_NONE,
+                              HELLO_MESSAGE_TYPE,
+                              IPC::Message::PRIORITY_NORMAL));
+      void* iter = NULL;
+      int pid;
+      if (!msg->ReadInt(&iter, &pid) ||
+          !hello->WriteInt(pid)) {
+        NOTREACHED();
+      }
+      DCHECK_EQ(hello->size(), msg->size());
+      if (!hello->WriteFileDescriptor(base::FileDescriptor(remote_fd_pipe_,
+                                                           false))) {
+        NOTREACHED();
+      }
+      msg = hello.get();
+      DCHECK_EQ(msg->file_descriptor_set()->size(), 1U);
+    }
+#endif
+
     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()) +
@@ -824,7 +848,9 @@
       msg->header()->num_fds = static_cast<uint16>(num_fds);
 
 #if defined(IPC_USES_READWRITE)
-      if (!IsHelloMessage(msg)) {
+      if (!uses_fifo_ &&
+          (msg->routing_id() != MSG_ROUTING_NONE ||
+           msg->type() != HELLO_MESSAGE_TYPE)) {
         // Only the Hello message sends the file descriptor with the message.
         // Subsequently, we can send file descriptors on the dedicated
         // fd_pipe_ which makes Seccomp sandbox operation more efficient.
@@ -838,19 +864,21 @@
           msg->file_descriptor_set()->CommitAll();
         }
       }
-#endif  // IPC_USES_READWRITE
+#endif
     }
 
     if (bytes_written == 1) {
       fd_written = pipe_;
 #if defined(IPC_USES_READWRITE)
-      if (mode_ != MODE_SERVER && IsHelloMessage(msg)) {
+      if (mode_ != MODE_SERVER && !uses_fifo_ &&
+          msg->routing_id() == MSG_ROUTING_NONE &&
+          msg->type() == HELLO_MESSAGE_TYPE) {
         DCHECK_EQ(msg->file_descriptor_set()->size(), 1U);
       }
-      if (!msgh.msg_controllen) {
+      if (!uses_fifo_ && !msgh.msg_controllen) {
         bytes_written = HANDLE_EINTR(write(pipe_, out_bytes, amt_to_write));
       } else
-#endif  // IPC_USES_READWRITE
+#endif
       {
         bytes_written = HANDLE_EINTR(sendmsg(pipe_, &msgh, MSG_DONTWAIT));
       }
@@ -912,11 +940,14 @@
 
 #ifdef IPC_MESSAGE_LOG_ENABLED
   Logging::GetInstance()->OnSendMessage(message, "");
-#endif  // IPC_MESSAGE_LOG_ENABLED
+#endif
 
   output_queue_.push(message);
-  if (!is_blocked_on_write_ && !waiting_connect_) {
-    return ProcessOutgoingMessages();
+  if (!waiting_connect_) {
+    if (!is_blocked_on_write_) {
+      if (!ProcessOutgoingMessages())
+        return false;
+    }
   }
 
   return true;
@@ -926,88 +957,43 @@
   return client_pipe_;
 }
 
-bool Channel::ChannelImpl::AcceptsConnections() const {
-  return server_listen_pipe_ != -1;
-}
+// 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) {
+    if (uses_fifo_) {
+      if (!ServerAcceptFifoConnection(server_listen_pipe_, &pipe_)) {
+        Close();
+      }
 
-bool Channel::ChannelImpl::HasAcceptedConnection() const {
-  return AcceptsConnections() && pipe_ != -1;
-}
+      // No need to watch the listening socket any longer since only one client
+      // can connect.  So unregister with libevent.
+      server_listen_connection_watcher_.StopWatchingFileDescriptor();
 
-void Channel::ChannelImpl::ResetToAcceptingConnectionState() {
-  // Unregister libevent for the unix domain socket and close it.
-  read_watcher_.StopWatchingFileDescriptor();
-  write_watcher_.StopWatchingFileDescriptor();
-  if (pipe_ != -1) {
-    if (HANDLE_EINTR(close(pipe_)) < 0)
-      PLOG(ERROR) << "close pipe_ " << pipe_name_;
-    pipe_ = -1;
-  }
-#if defined(IPC_USES_READWRITE)
-  if (fd_pipe_ != -1) {
-    if (HANDLE_EINTR(close(fd_pipe_)) < 0)
-      PLOG(ERROR) << "close fd_pipe_ " << pipe_name_;
-    fd_pipe_ = -1;
-  }
-  if (remote_fd_pipe_ != -1) {
-    if (HANDLE_EINTR(close(remote_fd_pipe_)) < 0)
-      PLOG(ERROR) << "close remote_fd_pipe_ " << pipe_name_;
-    remote_fd_pipe_ = -1;
-  }
-#endif  // IPC_USES_READWRITE
+      // Start watching our end of the socket.
+      MessageLoopForIO::current()->WatchFileDescriptor(
+          pipe_,
+          true,
+          MessageLoopForIO::WATCH_READ,
+          &read_watcher_,
+          this);
 
-  while (!output_queue_.empty()) {
-    Message* m = output_queue_.front();
-    output_queue_.pop();
-    delete m;
+      waiting_connect_ = false;
+    } else {
+      // In the case of a socketpair() the server starts listening on its end
+      // of the pipe in Connect().
+      waiting_connect_ = false;
+    }
+    send_server_hello_msg = true;
   }
 
-  // Close any outstanding, received file descriptors.
-  for (std::vector<int>::iterator
-       i = input_overflow_fds_.begin(); i != input_overflow_fds_.end(); ++i) {
-    if (HANDLE_EINTR(close(*i)) < 0)
-      PLOG(ERROR) << "close";
-  }
-  input_overflow_fds_.clear();
-}
-
-// Called by libevent when we can read from the pipe without blocking.
-void Channel::ChannelImpl::OnFileCanReadWithoutBlocking(int fd) {
-  bool send_server_hello_msg = false;
-  if (fd == server_listen_pipe_) {
-    int new_pipe = 0;
-    if (!ServerAcceptConnection(server_listen_pipe_, &new_pipe)) {
+  if (!waiting_connect_ && fd == pipe_) {
+    if (!ProcessIncomingMessages()) {
       Close();
-      listener_->OnChannelListenError();
-    }
-
-    if (pipe_ != -1) {
-      // We already have a connection. We only handle one at a time.
-      // close our new descriptor.
-      if (HANDLE_EINTR(shutdown(new_pipe, SHUT_RDWR)) < 0)
-        PLOG(ERROR) << "shutdown " << pipe_name_;
-      if (HANDLE_EINTR(close(new_pipe)) < 0)
-        PLOG(ERROR) << "close " << pipe_name_;
-      listener_->OnChannelDenied();
+      listener_->OnChannelError();
+      // The OnChannelError() call may delete this, so we need to exit now.
       return;
     }
-    pipe_ = new_pipe;
-
-    if (!AcceptConnection()) {
-      NOTREACHED() << "AcceptConnection should not fail on server";
-    }
-    send_server_hello_msg = true;
-    waiting_connect_ = false;
-  } else if (fd == pipe_) {
-    if (waiting_connect_ && mode_ == MODE_SERVER) {
-      send_server_hello_msg = true;
-      waiting_connect_ = false;
-    }
-    if (!ProcessIncomingMessages()) {
-      ClosePipeOnError();
-    }
-  } else {
-    NOTREACHED() << "Unknown pipe " << fd;
   }
 
   // If we're a server and handshaking, then we want to make sure that we
@@ -1021,95 +1007,68 @@
 
 // Called by libevent when we can write to the pipe without blocking.
 void Channel::ChannelImpl::OnFileCanWriteWithoutBlocking(int fd) {
-  DCHECK(fd == pipe_);
-  is_blocked_on_write_ = false;
   if (!ProcessOutgoingMessages()) {
-    ClosePipeOnError();
-  }
-}
-
-bool Channel::ChannelImpl::AcceptConnection() {
-  MessageLoopForIO::current()->WatchFileDescriptor(pipe_,
-                                                   true,
-                                                   MessageLoopForIO::WATCH_READ,
-                                                   &read_watcher_,
-                                                   this);
-  QueueHelloMessage();
-
-  if (mode_ == MODE_CLIENT) {
-    // If we are a client we want to send a hello message out immediately.
-    // In server mode we will send a hello message when we receive one from a
-    // client.
-    waiting_connect_ = false;
-    return ProcessOutgoingMessages();
-  } else {
-    waiting_connect_ = true;
-    return true;
-  }
-}
-
-void Channel::ChannelImpl::ClosePipeOnError() {
-  if (HasAcceptedConnection()) {
-    ResetToAcceptingConnectionState();
-    listener_->OnChannelError();
-  } else {
     Close();
-    if (AcceptsConnections()) {
-      listener_->OnChannelListenError();
-    } else {
-      listener_->OnChannelError();
-    }
+    listener_->OnChannelError();
   }
 }
 
-void Channel::ChannelImpl::QueueHelloMessage() {
-  // Create the Hello message
-  scoped_ptr<Message> msg(new Message(MSG_ROUTING_NONE,
-                                      HELLO_MESSAGE_TYPE,
-                                      IPC::Message::PRIORITY_NORMAL));
-
-  if (!msg->WriteInt(base::GetCurrentProcId())) {
-    NOTREACHED() << "Unable to pickle hello message proc id";
-  }
-#if defined(IPC_USES_READWRITE)
-  scoped_ptr<Message> hello;
-  if (remote_fd_pipe_ != -1) {
-    if (!msg->WriteFileDescriptor(base::FileDescriptor(remote_fd_pipe_,
-                                                       false))) {
-      NOTREACHED() << "Unable to pickle hello message file descriptors";
-    }
-    DCHECK_EQ(msg->file_descriptor_set()->size(), 1U);
-  }
-#endif  // IPC_USES_READWRITE
-  output_queue_.push(msg.release());
-}
-
-bool Channel::ChannelImpl::IsHelloMessage(const Message* m) const {
-  return m->routing_id() == MSG_ROUTING_NONE && m->type() == HELLO_MESSAGE_TYPE;
-}
-
 void Channel::ChannelImpl::Close() {
   // Close can be called multiple time, so we need to make sure we're
   // idempotent.
 
-  ResetToAcceptingConnectionState();
+  // Unregister libevent for the listening socket and close it.
+  server_listen_connection_watcher_.StopWatchingFileDescriptor();
 
-  if (must_unlink_) {
-    unlink(pipe_name_.c_str());
-    must_unlink_ = false;
-  }
   if (server_listen_pipe_ != -1) {
     if (HANDLE_EINTR(close(server_listen_pipe_)) < 0)
       PLOG(ERROR) << "close " << server_listen_pipe_;
     server_listen_pipe_ = -1;
-    // Unregister libevent for the listening socket and close it.
-    server_listen_connection_watcher_.StopWatchingFileDescriptor();
   }
 
+  // Unregister libevent for the FIFO and close it.
+  read_watcher_.StopWatchingFileDescriptor();
+  write_watcher_.StopWatchingFileDescriptor();
+  if (pipe_ != -1) {
+    if (HANDLE_EINTR(close(pipe_)) < 0)
+      PLOG(ERROR) << "close " << pipe_;
+    pipe_ = -1;
+  }
   if (client_pipe_ != -1) {
     PipeMap::GetInstance()->RemoveAndClose(pipe_name_);
     client_pipe_ = -1;
   }
+#if defined(IPC_USES_READWRITE)
+  if (fd_pipe_ != -1) {
+    if (HANDLE_EINTR(close(fd_pipe_)) < 0)
+      PLOG(ERROR) << "close " << fd_pipe_;
+    fd_pipe_ = -1;
+  }
+  if (remote_fd_pipe_ != -1) {
+    if (HANDLE_EINTR(close(remote_fd_pipe_)) < 0)
+      PLOG(ERROR) << "close " << remote_fd_pipe_;
+    remote_fd_pipe_ = -1;
+  }
+#endif
+
+  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) {
+    if (HANDLE_EINTR(close(*i)) < 0)
+      PLOG(ERROR) << "close " << *i;
+  }
+  input_overflow_fds_.clear();
 }
 
 //------------------------------------------------------------------------------
@@ -1143,16 +1102,4 @@
   return channel_impl_->GetClientFileDescriptor();
 }
 
-bool Channel::AcceptsConnections() const {
-  return channel_impl_->AcceptsConnections();
-}
-
-bool Channel::HasAcceptedConnection() const {
-  return channel_impl_->HasAcceptedConnection();
-}
-
-void Channel::ResetToAcceptingConnectionState() {
-  channel_impl_->ResetToAcceptingConnectionState();
-}
-
 }  // namespace IPC