How does `agent.createConnection` handle WebSockets when `maxSockets=1`?

[mStirner]

Details

I try to understand the anatomy of a http request/live cycle better. I think for most of the developers this is not necessary, but i want to go down the rabbit hole.

When i have a custom http agent create, and set maxSockets=1 & keepAlive=true, how does the agent handle this situation? In my minimal reproducable example, for each Websocket connection a new tcp socket is created, event when maxSockets set to 1.

Where/how does the agent knew he has to create a new connection because the first one is still needed? I would expect that maxSockets tell the agent, "no matter what, you only create one tcp socket". In combination with WebSockets this seems dumb, and i wonder even more how this is handled by the agent.

Node.js version

v16.20.0

Example code

client.js

const { Agent } = require("http")
const { createConnection } = require("net");
const WebSocket = require("ws");

const agent = new Agent({
    maxSockets: 1,
    keepAlive: true
});

agent.createConnection = (options) => {

    let { host, port } = options;

    console.log("Create connection", host, port);

    let socket = createConnection(options);
    return socket;

};

const ws1 = new WebSocket("ws://127.0.0.1:8080", {
    agent
});

const ws2 = new WebSocket("ws://127.0.0.1:8080", {
    agent
});

[ws1, ws2].forEach((ws) => {

    ws.on("open", () => {
        console.log("WebSocket opend: %s", ws.url);
    });

    ws.on("close", () => {
        console.log("WebSocket closed: %s", ws.url);
    });

});

server.js

const { Server } = require("ws");

const wss = new Server({
    port: 8080
});

wss.on("connection", (ws) => {

    console.log("Client connected");

    ws.on("close", () => {
        console.log("Client disconnected");
    });

});

wss.on("listening", () => {
    console.log("Server listening")
});

Operating system

Ubuntu 18.04.6 LTS

Scope

no clue

Module and version

Not applicable.

[preveen-stack]

Guess max connection will be applicable only to http connections and once the connection is upgraded to websockets it will no longer be effective

[mStirner]

and once the connection is upgraded to websockets it will no longer be effective

And how does the underlaying http module signal/notify that to the agent?

[preveen-stack]

The spec details this quite extensively at https://datatracker.ietf.org/doc/html/rfc6455 As for implementation, folks at https://github.com/websockets/ws can probably better articulate

[github-actions[bot]]

It seems there has been no activity on this issue for a while, and it is being closed in 30 days. If you believe this issue should remain open, please leave a comment. If you need further assistance or have questions, you can also search for similar issues on Stack Overflow. Make sure to look at the README file for the most updated links.

[github-actions[bot]]

It seems there has been no activity on this issue for a while, and it is being closed. If you believe this issue should remain open, please leave a comment. If you need further assistance or have questions, you can also search for similar issues on Stack Overflow. Make sure to look at the README file for the most updated links.