Add multiplexing of message pipes in the new EDK.

mojo/edk/system/broker_messages.h

Index: mojo/edk/system/broker_messages.h
diff --git a/mojo/edk/system/broker_messages.h b/mojo/edk/system/broker_messages.h
index 351cbe6d5539ec5e8a4b5d366fac7051820e4ba0..bcee36e2d09a3a424e573b18667411fa28f2e15d 100644
--- a/mojo/edk/system/broker_messages.h
+++ b/mojo/edk/system/broker_messages.h
@@ -8,6 +8,7 @@
 #include <stdint.h>
 
 #include "base/compiler_specific.h"
+#include "base/process/process_handle.h"
 
 namespace mojo {
 namespace edk {
@@ -15,7 +16,11 @@ namespace edk {
 // This header defines the message format between ChildBroker and
 // ChildBrokerHost.
 
-enum MessageId {
+#if defined(OS_WIN)
+// Windows only messages needed because sandboxed child processes need the
+// parent's help. They are sent synchronously from child to parent and each have
+// a response. They are sent over a raw pipe.
+enum WindowsSandboxMessages {
   // The reply is two HANDLEs.
   CREATE_PLATFORM_CHANNEL_PAIR = 0,
   // The reply is tokens of the same count of passed in handles.
@@ -28,17 +33,47 @@ enum MessageId {
 
 struct BrokerMessage {
   uint32_t size;
-  MessageId id;
+  WindowsSandboxMessages id;
   // Data, if any, follows.
   union {
-#if defined(OS_WIN)
     HANDLE handles[1];  // If HANDLE_TO_TOKEN.
     uint64_t tokens[1];  // If TOKEN_TO_HANDLE.
-#endif
   };
 };
 
-const int kBrokerMessageHeaderSize = sizeof(uint32_t) + sizeof(MessageId);
+const int kBrokerMessageHeaderSize =

[Tom Sepez, 2015/12/03 23:35:28]

Actually, this hasn't been 100% correct since it doesn't account for possible
padding between size and id or between id and the union.  I think you actually
want offsetof(BrokerMessage, handles) here.

[jam, 2015/12/04 00:43:47]

This is only used on Windows and there's no padding between the first two
members with VS. If this did change in future compilers, it will be very obvious
(i.e. ipc fails). (btw note this isn't changed code, I just renamed the enum).

+  sizeof(uint32_t) + sizeof(WindowsSandboxMessages);
+
+#endif
+
+// Multiplexing related messages. They are all asynchronous messages.
+// They are sent over RawChannel.
+enum MultiplexMessages {
+// Messages from child to parent.

[Tom Sepez, 2015/12/03 23:35:28]

nit: indent.

[jam, 2015/12/04 00:43:47]

i had meant to put it like this to separate out both types of messages. I'll
switch it to blank lines instead.

+  CONNECT_MESSAGE_PIPE = 0,
+  CANCEL_CONNECT_MESSAGE_PIPE,
+// Messages from parent to child.
+  CONNECT_TO_PROCESS,
+  PEER_PIPE_CONNECTED,
+};
+
+struct ConnectMessagePipeMessage {
+  // CONNECT_MESSAGE_PIPE or CANCEL_CONNECT_MESSAGE_PIPE
+  MultiplexMessages type;
+  uint64_t pipe_id;
+};
+
+struct ConnectToProcessMessage {
+  MultiplexMessages type;  // CONNECT_TO_PROCESS
+  base::ProcessId process_id;
+  // Also has an attached platform handle.
+};
+
+struct PeerPipeConnectedMessage {
+  MultiplexMessages type;  // PEER_PIPE_CONNECTED
+  uint64_t pipe_id;
+  base::ProcessId process_id;
+};
 
 }  // namespace edk
 }  // namespace mojo