Web Socket-Spring：确认收到的消息

Question

I am sending a message through WebSocket with Spring from Tomcat Server to a SockJSClient with the method:

WebSocketSession.sendMessage(WebSocketMessage<?> message)

and I would like to know when the message has been received (eventually with complementary information, for example whether the logic on client successfully processed), then go for next message.

This is an Activity diagram that explains the use case.

How can I receive confirmation of reception or result from client?

Answer 1

As Erwin pointed, you can adopt some higher protocol providing such feature like STOMP. However, if you are afraid to adopt it only for that feature, you can implement that feature by yourself.

• The first thing is to give each message id to identify each message, type to recognize the purpose of each message, data to transport a message's content and reply which is a flag to see whether or not ACK is required and to use a format like JSON to serialize/deserialize an object containing these data into/from WebSocket message.
• When sending a message, it creates an object by issuing a new id for that message, setting type to message and data to given message and reply to true if ACK is required or false if not. And it serializes it into JSON and sends it as a WebSocket message. - https://github.com/cettia/cettia-protocol/blob/1.0.0-Alpha1/lib/server.js#L88-L110
• When receiving a message, it deserializes JSON to the above object. If reply is true , it sends a special message whose type is reply setting data to id of that message. Then, the counterpart can confirm that its counterpart has received a message whose id is id . - https://github.com/cettia/cettia-protocol/blob/1.0.0-Alpha1/lib/server.js#L46-L76

The above links point similar implementation in Cettia which is a real-time web application framework I wrote. Though that implementation is a little bit complex as it is designed to allow for user to handle callbacks with result, you are likely to get the basic idea.

API implemented by that link looks like the following.

A server or client which requires a result of event processing.

// Using Java server with lambda
socket.send("foo", "bar", result -> /* resolved */, reason -> /* rejected */);

The corresponding client or server which has a responsibility to submit the result.

// Using JavaScript client with arrow functions
socket.on("foo", (data, reply) => {
    // data is 'bar'
    // 'reply.resolve(result)' if it successes
    // 'reply.reject(reason)' if it fails
});