如果 socketIO 生成的 id 是自动生成的，如何在两个用户之间建立通信？

Question

Hello I hope you are very well, I would like to ask you a question that I have not been able to deduce the answer to.

In a course I was seeing that to send a message to a specific user with socketIO.js the to () method is used and the id as a parameter, but I have a doubt, that id is auto generated by socketIO as far as I understand, so I would like to know How can the frontend know that id? The example that I saw in the course does it from the console and sends it directly to the method with the id that it already knows, then that example is not so real, what I would like to know in itself How is it that it performs a one-to-one chat if the id is autogenerated by the socket? I don't know if I understand.

For example, to start a conversation with another user, you can click on a button, trigger an event that makes emit, send the id of the user who writes, the event that should trigger the backend with socket, but my question is how does it taste like who send the message? How do you know the id of who is being sent to when establishing communication between 2 users for the first time? Obviously this must be sent by frontent as a parameter but also how does the frontend give this id of who will it be sent to? I don't know if you can store a fixed socket id for a user in a DB or Can you use your DB id to use with sockets? more than everything is what I can not deduce how it would be done?

I do not know if I understood with the question, more than everything is that, I do not know how it obtains or assigns the id for the target from where the message is sent and if this can be fixed and stored in db or is there any method to this.

I thank you in advance for your response, and any resources that you share with me about it or if you recommend a course with, I would greatly appreciate it.

as an example I have this method

io.on('connection', (client) => {    
client.on('privateMessage', (data)=>{
            const person = user.getPersona(client.id) //get this 
            client.broadcast.to(data.para).emit('privateMessage', createMsj( person.name, data.messages));
        
        });
}

But where does the front-end of the person to receive the message to pass it to the method?

Answer 1

The front-end will not know the socket.io id of any other clients. This is where your server needs to be involved.

Each of your users presumably has some username that is displayed in the client UI and this is the name that other clients would know them by.

So, your server needs to keep a mapping between username and socket.io clientID. So, a user can send a request to your server to connect to BobS. Your server then needs to be able to look up BobS, find out if that user is currently connected and, if they are, then what is their socket.id value. That way, your server can facilitate connecting the two users.

This mapping would not typically be kept in a permanent store (such as a database) because the socket.id is a transient value and is only good for the duration of that client's socket.io connection. As such, it is more typically just kept in some sort of Javascript data structure (such as a Map object).