The theory of websockets with API

Question

I have an API running on a server, which handle users connection and a messaging system.

Beside that, I launched a websocket on that same server, waiting for connections and stuff.

And let's say we can get access to this by an Android app.

I'm having troubles to figure out what I should do now, here are my thoughts:

1 - When a user connect to the app, the API connect to the websocket. We allow the Android app only to listen on this socket to get new messages. When the user want to answer, the Android app send a message to the API. The API writes itself the received message to the socket, which will be read back by the Android app used by another user. This way, the API can store the message in database before writing it in the socket.

2- The API does not connect to the websocket in any way. The Android app listen and write to the websocket when needed, and should, when writing to the websocket, also send a request to the API so it can store the message in DB.

May be none of the above is correct, please let me know

EDIT

I already understood why I should use a websocket, seems like it's the best way to have this "real time" system (when getting a new message for example) instead of forcing the client to make an HTTP request every x seconds to check if there are new messages.

What I still don't understand, is how it is suppose to communicate with my database. Sorry if my example is not clear, but I'll try to keep going with it :

My messaging system need to store all messages in my API database, to have some kind of historic of the conversation.

But it seems like a websocket must be running separately from the API, I mean it's another program right? Because it's not for HTTP requests

So should the API also listen to this websocket to catch new messages and store them?

Answer 1

You really have not described what the requirements are for your application so it's hard for us to directly advise what your app should do. You really shouldn't start out your analysis by saying that you have a webSocket and you're trying to figure out what to do with it. Instead, lay out the requirements of your app and figure out what technology will best meet those requirements.

Since your requirements are not clear, I'll talk about what a webSocket is best used for and what more traditional http requests are best used for.

Here are some characteristics of a webSocket:

1. It's designed to be continuously connected over some longer duration of time (much longer than the duration of one exchange between client and server).
2. The connection is typically made from a client to a server.
3. Once the connection is established, then data can be sent in either direction from client to server or from server to client at any time. This is a huge difference from a typical http request where data can only be requested by the client - with an http request the server can not initiate the sending of data to the client.
4. A webSocket is not a request/response architecture by default. In fact to make it work like request/response requires building a layer on top of the webSocket protocol so you can tell which response goes with which request. http is natively request/response.
5. Because a webSocket is designed to be continuously connected (or at least connected for some duration of time), it works very well (and with lower overhead) for situations where there is frequent communication between the two endpoints. The connection is already established and data can just be sent without any connection establishment overhead. In addition, the overhead per message is typically smaller with a webSocket than with http.

So, here are a couple typical reasons why you might choose one over the other.

1. If you need to be able to send data from server to client without having the client regular poll for new data, then a webSocket is very well designed for that and http cannot do that.
2. If you are frequently sending lots of small bits of data (for example, a temperature probe sending the current temperature every 10 seconds), then a webSocket will incur less network and server overhead than initiating a new http request for every new piece of data.
3. If you don't have either of the above situations, then you may not have any real need for a webSocket and an http request/response model may just be simpler.
4. If you really need request/response where a specific response is tied to a specific request, then that is built into http and is not a built-in feature of webSockets.

You may also find these other posts useful:

What are the pitfalls of using Websockets in place of RESTful HTTP?

What's the difference between WebSocket and plain socket communication?

Push notification | is websocket mandatory?

How does WebSockets server architecture work?

Response to Your Edit

But it seems like a websocket must be running separately from the API, I mean it's another program right? Because it's not for HTTP requests

The same process that supports your API can also be serving the webSocket connections. Thus, when you get incoming data on the webSocket, you can just write it directly to the database the same way the API would access the database. So, NO the webSocket server does not have to be a separate program or process.

So should the API also listen to this websocket to catch new messages and store them?

No, I don't think so. Only one process can be listening to a set of incoming webSocket connections.