Transports

An LspTransport sends and receives whole JSON-RPC messages: send(message), onMessage(listener), onClose(listener) and close(). The transport holds messages that arrive before the first listener and hands them to it. One transport carries one connection, and a session owns it from new LspSession(transport) on.

Transport	Over
createStreamTransport(stream, options?)	A ByteStream, such as the stdin and stdout of a server process, with Content-Length framing
connectWebSocket(url, options?)	A WebSocket, one JSON text frame per message; resolves once the socket is open
createMemoryTransportPair()	From @adecore/lsp/testing: two ends in memory, each message JSON-copied and delivered on a microtask

A server process

A ByteStream is the app's adapter over a process: write(chunk), onData, onClose and close. Wire stdout to onData and keep stderr apart, since a log line in stdout breaks the framing.

import { spawn } from 'node:child_process';
import { createStreamTransport, type ByteStream } from '@adecore/lsp';

const child = spawn(executable, ['--stdio'], { cwd: projectFolder });

const stream: ByteStream = {
    write: (chunk) => void child.stdin.write(chunk),
    onData: (listener) => {
        child.stdout.on('data', listener);
        return { dispose: () => child.stdout.off('data', listener) };
    },
    onClose: (listener) => {
        const exited = (): void => listener();
        child.once('exit', exited);
        return { dispose: () => child.off('exit', exited) };
    },
    close: () => void child.kill()
};

const transport = createStreamTransport(stream);
child.stderr.on('data', (chunk) => log(String(chunk)));

A frame over maxMessageBytes (32 MiB by default) or one it cannot read closes the stream. Pass another limit as createStreamTransport(stream, { maxMessageBytes }).

A WebSocket

connectWebSocket suits a server on another machine or behind a proxy that speaks one message per frame. Its WebSocketTransportOptions take protocols, a signal to cancel opening, timeoutMs (default 10 seconds) and a createWebSocket factory for runtimes without a global WebSocket.

import { connectWebSocket, LspSession } from '@adecore/lsp';

const transport = await connectWebSocket('wss://tools.example.com/lsp/php', { timeoutMs: 5_000 });
const session = new LspSession(transport, { rootUri });

A binary or non-JSON frame closes the socket. Reconnecting and authentication are the app's job.

In memory

createMemoryTransportPair() returns two connected ends, so a session and a fake server talk in a test without a process. See Testing.