webdial

net.Conn over HTTP. Uses WebSocket when available, falls back to SSE+POST.

Both sides get a standard net.Conn (Go) or an equivalent read/write/close interface (JavaScript), so any stream-oriented protocol works over it.

Go

Install

go get github.com/jpillora/webdial

Server

*Server implements http.Handler, so mount it directly:

srv := webdial.NewServer()

mux := http.NewServeMux()
mux.Handle("/wd/", srv)

go http.ListenAndServe(":8080", mux)

for {
    conn, err := srv.Accept()
    if err != nil {
        break
    }
    go func() {
        defer conn.Close()
        io.Copy(conn, conn) // echo
    }()
}

srv.Accept() returns a net.Conn. Use it with any protocol that works over a byte stream.

Client

conn, err := webdial.Dial(ctx, "http://localhost:8080/wd")
if err != nil {
    log.Fatal(err)
}
defer conn.Close()

conn.Write([]byte("hello"))

buf := make([]byte, 1024)
n, err := conn.Read(buf)
fmt.Println(string(buf[:n])) // "hello"

Dial tries WebSocket first and falls back to SSE+POST automatically. The returned net.Conn works the same regardless of transport.

JavaScript

The ESM client (client.mjs) works in both browsers and Node.js 22+. Zero dependencies.

Install

npm install webdial

Or use it directly from a <script type="module">:

<script type="module">
import { dial } from "/path/to/client.mjs";
</script>

Usage

import { dial } from "webdial";

const conn = await dial("http://localhost:8080/wd");

// Send text
await conn.write("hello");

// Send binary
await conn.write(new Uint8Array([1, 2, 3]));

// Read (returns Uint8Array, or null on close)
const data = await conn.read();
console.log(new TextDecoder().decode(data));

// Close
await conn.close();

Options

Force a specific transport:

const conn = await dial(url, { transport: "ws" });  // WebSocket only
const conn = await dial(url, { transport: "sse" }); // SSE+POST only

By default, dial tries WebSocket first and falls back to SSE+POST.

Connection properties

• conn.transport — "ws" or "sse"
• conn.url — the base URL used to connect

Transports

Transport	Mechanism	Binary	Requirements
ws	WebSocket	native	WebSocket support
sse	Server-Sent Events (read) + POST (write)	base64	HTTP/1.1+

WebSocket is preferred. SSE+POST is the fallback for environments where WebSocket connections are blocked (e.g. some corporate proxies).

Protocol

The server is a single http.Handler that routes by content-negotiation:

• Upgrade: websocket header — WebSocket upgrade, binary frames carry data
• GET with Accept: text/event-stream — SSE stream; first event is sid (session ID), subsequent d events carry base64-encoded data, close event signals shutdown
• POST with ?s=<sid> — write body bytes to the session; append &close=1 to close