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node.js.netserverport

Error: listen EADDRINUSE: address already in use :::5000 BUT dotnet server does let me run API in port 5000

I know this error has been asked a million times but I believe that the answers are not the correct ones or are not the most efficient.

// import all libraries
const express = require('express');
const cors = require('cors');
const mongoose = require('mongoose');

const app = express();

require('dotenv').config();

// setup connections
mongoose.connect(process.env.MONGODB_URL)
    .then(() => console.log("Connected to DB 🔌"))
    .catch(() => console.log("Couldn't connect to db ❌"));

// setup middlewares
app.use(cors()); // CORS => Cross origin resource sharing; // share frontend <-> backend
app.use(express.json());

// setup routes
app.use("/api/auth", require("./routes/user"));
app.use("/api/books", require("./routes/book"));
app.use("/api/rentals", require("./routes/rental"));

// start listening on server
const port = process.env.PORT;
app.listen(port, () => {
    console.log("Server running...");
})

There is my code for reference. If I change the port from 5000 to 5500 in the .env it all works fine. If I deactivate the air play port, it all works fine.

My problem is that when I run a dotnet api server IN PORT 5000 there is NO error.

Why can I run a dotnet server in 5000 with no problem but in node it gives me an error?

I ran lsof -i tcp:5000 meanwhile running my dotnet api:

COMMAND     PID             USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
firefox     938 arturofiliovilla  137u  IPv4 0x23e78a2a111d8441      0t0  TCP localhost:59093->localhost:commplex-main (ESTABLISHED)
ControlCe 25701 arturofiliovilla   21u  IPv4 0x23e78a2a108e4ed1      0t0  TCP *:commplex-main (LISTEN)
ControlCe 25701 arturofiliovilla   22u  IPv6 0x23e78a1babf17ce9      0t0  TCP *:commplex-main (LISTEN)
API       26565 arturofiliovilla  238u  IPv4 0x23e78a2a12ba39b1      0t0  TCP localhost:commplex-main (LISTEN)
API       26565 arturofiliovilla  239u  IPv6 0x23e78a1babf09189      0t0  TCP localhost:commplex-main (LISTEN)
API       26565 arturofiliovilla  241u  IPv4 0x23e78a2a10910ed1      0t0  TCP localhost:commplex-main->localhost:59093 (ESTABLISHED)

Maybe there is a masking? I'm not sure but I have no errors with my dotnet server.

Any ideas why this is happening?

Solution
    1. Node.js/Express tries to bind to [::]:5000 and/or 0.0.0.0:5000 by default, when you only specify port 5000. That's why a conflict occurs.
    2. ASP.NET Core, however, by default binds to localhost:5000.

    If you read a little bit more about computer networking, you will see how huge the differences are between the two binding approaches.

    You can try to ask Express to bind to localhost:5000, aka

    app.listen(port, "localhost", () => {
    console.log("Server running...");
})

    References