Socket.IO

Try it in 3 steps

1. 1

   Check Node.js and install fixed versions

   Socket.IO 4.8.4 itself supports Node.js 10.2.0 or later, but this sample requires Node.js 18 or later because it uses node:-prefixed built-in modules; then it installs matching server and client versions.

   node -e 'const M=Number(process.versions.node.split(".")[0]);if(M<18)throw new Error("This local sample requires Node.js >=18");console.log(process.version)' && mkdir socketio-roundtrip && cd socketio-roundtrip && npm init -y && npm install socket.io@4.8.4 socket.io-client@4.8.4Copy
2. 2

   Create a round-trip script

   Use only an ephemeral 127.0.0.1 port, then close the client, Socket.IO instance, and owned HTTP server after the acknowledgement.

   printf '%s\n' 'const fs=require("node:fs");const http=require("node:http");const {Server}=require("socket.io");const {io:client}=require("socket.io-client");const server=http.createServer();const io=new Server(server);io.on("connection",s=>s.on("ping",(v,ack)=>ack(`pong:${v}`)));server.listen(0,"127.0.0.1",()=>{const port=server.address().port;fs.writeFileSync(".port",String(port));const c=client(`http://127.0.0.1:${port}`,{transports:["websocket"]});const stop=(code)=>{c.close();io.close(()=>server.close(()=>process.exit(code)))};c.on("connect",()=>c.timeout(2000).emit("ping","local",(e,v)=>{if(e||v!=="pong:local"){console.error(e||v);stop(1)}else{console.log(v);stop(0)}}));c.on("connect_error",e=>{console.error(e.message);stop(1)})});' > roundtrip.cjsCopy
3. 3

   Run the event round trip

   Confirm that pong:local is printed and a follow-up connection to the owned server port fails specifically with ECONNREFUSED.

   node roundtrip.cjs && node -e 'const fs=require("node:fs"),net=require("node:net"),port=Number(fs.readFileSync(".port","utf8"));const s=net.connect({host:"127.0.0.1",port});const fail=e=>{console.error(e);process.exit(1)};s.setTimeout(2000,()=>fail(new Error("timeout")));s.on("connect",()=>fail(new Error("port still open")));s.on("error",e=>{if(e.code==="ECONNREFUSED"){console.log(`closed:${port}`);process.exit(0)}fail(e)})'Copy

Built with

• TypeScript
• JavaScript
• Node.js

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