Add support for sockets that can listen and accept a connection.

ipc/ipc_channel.h

Index: ipc/ipc_channel.h
diff --git a/ipc/ipc_channel.h b/ipc/ipc_channel.h
index 132b49432a52cfbd35948958badd852e8c2a6119..c257a8e9f9f753509f4e3b3d46cf1e59e14e5fd8 100644
--- a/ipc/ipc_channel.h
+++ b/ipc/ipc_channel.h
@@ -13,6 +13,21 @@
 namespace IPC {
 
 //------------------------------------------------------------------------------
+// See
+// http://www.chromium.org/developers/design-documents/inter-process-communication
+// for overview of IPC in Chromium.
+
+// Channels are implemented using named pipes on Windows, and
+// socket pairs (or in some special cases unix domain sockets) on POSIX.
+// On Windows we access pipes in various processes by name.
+// On POSIX we pass file descriptors to child processes and assign names to them
+// in a lookup table.
+// In general on POSIX we do not use unix domain sockets due to security
+// concerns and the fact that they can leave garbage around the file system
+// (MacOS does not support abstract named unix domain sockets).
+// You can use unix domain sockets if you like on POSIX by constructing the
+// the channel with the mode set to one of the NAMED modes. NAMED modes are
+// currently used by automation and service processes.
 
 class Channel : public Message::Sender {
   // Security tests need access to the pipe handle.
@@ -34,12 +49,29 @@ class Channel : public Message::Sender {
     // Called when an error is detected that causes the channel to close.
     // This method is not called when a channel is closed normally.
     virtual void OnChannelError() {}
+
+#if defined(OS_POSIX)
+    // Called on the server side when a channel that listens for connections
+    // denies an attempt to connect.
+    virtual void OnChannelDenied() {}
+
+    // Called on the server side when a channel that listens for connections
+    // has an error that causes the listening channel to close.
+    virtual void OnChannelListenError() {}
+#endif  // OS_POSIX
   };
 
   enum Mode {
     MODE_NONE,
     MODE_SERVER,
-    MODE_CLIENT
+    MODE_CLIENT,
+    // Channels on Windows are named by default and accessible from other
+    // processes. On POSIX channels are anonymous by default and not accessible
+    // from other processes. Named channels work via named unix domain sockets.
+    // On Windows MODE_NAMED_SERVER == MODE_SERVER and
+    // MODE_NAMED_CLIENT == MODE_CLIENT.
+    MODE_NAMED_SERVER,
+    MODE_NAMED_CLIENT,
   };
 
   enum {
@@ -77,6 +109,10 @@ class Channel : public Message::Sender {
   bool Connect() WARN_UNUSED_RESULT;
 
   // Close this Channel explicitly.  May be called multiple times.
+  // On POSIX calling close on an IPC channel that listens for connections will
+  // cause it to close any accepted connections, and it will stop listening for
+  // new connections. If you just want to close the currently accepted
+  // connection and listen for new ones, use ResetToAcceptingConnectionState.
   void Close();
 
   // Modify the Channel's listener.
@@ -92,11 +128,23 @@ class Channel : public Message::Sender {
   // On POSIX an IPC::Channel wraps a socketpair(), this method returns the
   // FD # for the client end of the socket.
   // This method may only be called on the server side of a channel.
-  //
-  // If the kTestingChannelID flag is specified on the command line then
-  // a named FIFO is used as the channel transport mechanism rather than a
-  // socketpair() in which case this method returns -1.
   int GetClientFileDescriptor() const;
+
+  // On POSIX an IPC::Channel can either wrap an established socket, or it
+  // can wrap a socket that is listening for connections. Currently an
+  // IPC::Channel that listens for connections can only accept one connection
+  // at a time.
+
+  // Returns true if the channel supports listening for connections.
+  bool AcceptsConnections() const;
+
+  // Returns true if the channel supports listening for connections and is
+  // currently connected.
+  bool HasAcceptedConnection() const;
+
+  // Closes any currently connected socket, and returns to a listening state
+  // for more connections.
+  void ResetToAcceptingConnectionState();
 #endif  // defined(OS_POSIX)
 
  protected: