Mojo UDP socket API definition review.

mojo/services/public/interfaces/network/udp_socket.mojom

Index: mojo/services/public/interfaces/network/udp_socket.mojom
diff --git a/mojo/services/public/interfaces/network/udp_socket.mojom b/mojo/services/public/interfaces/network/udp_socket.mojom
index 6f0cff3efe324a30aa8abca656222b3915c3b920..d7784cb77f09a2f31a18134e9decc3bccca45af3 100644
--- a/mojo/services/public/interfaces/network/udp_socket.mojom
+++ b/mojo/services/public/interfaces/network/udp_socket.mojom
@@ -15,6 +15,7 @@ module mojo {
 // - (optional) Set options which are allowed after Bind().
 // - Send / request to receive packets. Received packets will be delivered to
 //   UDPSocketClient.OnReceived().
+
 [Client=UDPSocketClient]
 interface UDPSocket {
   // Allows the socket to share the local address to which it will be bound with
@@ -28,20 +29,34 @@ interface UDPSocket {
   // returned in |bound_addr|.
   Bind(NetAddress addr) => (NetworkError result, NetAddress? bound_addr);
 
-  // Sets the send buffer size (in bytes) for the socket. The socket must be
+  // Sets the OS send buffer size (in bytes) for the socket. The socket must be
   // bound.
   //
   // Note: This is only treated as a hint. Even if it succeeds, the service
   // doesn't guarantee it will conform to the size.

[wtc, 2014/10/02 22:14:05]

I believe this note can be deleted. If this note is referring to the problem on
Windows, net::UDPSocketWin::SetSendBufferSize already detects this problem and
will return ERR_SOCKET_SEND_BUFFER_SIZE_UNCHANGEABLE.

If some other platform has a similar problem, then we can keep this note but
please try to find out what that platform is and add a reference to a detailed
description of the problem.

[yzshen1, 2014/10/02 22:40:31]

Done.

   SetSendBufferSize(uint32 size) => (NetworkError result);
 
-  // Sets the receive buffer size (in bytes) for the socket. The socket must be
-  // bound.
+  // Sets the OS receive buffer size (in bytes) for the socket. The socket must
+  // be bound.
   //
   // Note: This is only treated as a hint. Even if it succeeds, the service
   // doesn't guarantee it will conform to the size.
   SetReceiveBufferSize(uint32 size) => (NetworkError result);
 
+  // Negotiates the maximum number of pending SendTo() requests. If
+  // |requested_size| is set to 0, this method queries the current settings.
+  //
+  // The service stores SendTo() requests in a queue while they are waiting to
+  // be executed (i.e., while they are waiting to be placed in the OS send
+  // buffer and send out). This method negotiates how many requests (not bytes)
+  // this queue is able to store. If the queue is full, the service fails new
+  // requests directly with error code ERR_INSUFFICIENT_RESOURCES and discard
+  // those packets. If the client wants to avoid such failure, it needs to keep
+  // track of how many SendTo() calls are pending and make sure the number
+  // doesn't exceed the result of this method.
+  NegotiateMaxPendingSendRequests(uint32 requested_size)
+      => (uint32 actual_size);
+
   // Notifies that the client is ready to accept |number| of packets.

[wtc, 2014/10/02 22:14:05]

Nit: it would be good to explain why it is useful to pass a |number| > 1. The
reason was not obvious to me.

[yzshen1, 2014/10/02 22:40:31]

Done.

   // Correspondingly, OnReceived() of the UDPSocketClient interface will be
   // called |number| times (errors also count), unless the connection is closed
@@ -59,16 +74,19 @@ interface UDPSocket {
   ReceiveMorePackets(uint32 number);
 
   // Sends data to the specified destination. The socket must be bound.
-  // The method doesn't report the result of the operation.
-  SendToAndForget(NetAddress addr, uint8[] data);
-
-  // Sends data to the specified destination. The socket must be bound.
-  SendTo(NetAddress addr, uint8[] data) => (NetworkError result);
+  // On success, |result.code| is a non-negative number indicating how many
+  // bytes have been written. Otherwise, it is a network error code, including
+  // (but not limited to):
+  // - ERR_INSUFFICIENT_RESOURCES (-12): The service doesn't have sufficient
+  //   resource to complete the operation. One possible cause is that the client
+  //   tries to send too many packets in a short period of time.
+  SendTo(NetAddress dest_addr, uint8[] data) => (NetworkError result);
 };
 
 interface UDPSocketClient {
-  // |addr| and |data| are non-NULL on success.
-  OnReceived(NetworkError result, NetAddress? addr, uint8[]? data);
+  // On success, |src_addr| and |data| are non-NULL, |result.code| is a
+  // non-negative number indicating how many bytes have been received.
+  OnReceived(NetworkError result, NetAddress? src_addr, uint8[]? data);
 };
 
 }