denoland-deno/docs/examples/tcp_echo.md

TCP echo server

Concepts

• Listening for TCP port connections with Deno.listen.
• Use copy to take inbound data and redirect it to be outbound data.

Example

This is an example of a server which accepts connections on port 8080, and returns to the client anything it sends.

/**
 * echo_server.ts
 */
import { copy } from "https://deno.land/std@$STD_VERSION/io/util.ts";
const listener = Deno.listen({ port: 8080 });
console.log("listening on 0.0.0.0:8080");
for await (const conn of listener) {
  copy(conn, conn).finally(() => conn.close());
}

Run with:

deno run --allow-net echo_server.ts

To test it, try sending data to it with netcat (Linux/MacOS only). Below 'hello world' is sent over the connection, which is then echoed back to the user:

$ nc localhost 8080
hello world
hello world

Like the cat.ts example, the copy() function here also does not make unnecessary memory copies. It receives a packet from the kernel and sends back, without further complexity.