undici-thread-interceptor

An Undici agent that routes requests to a worker thread.

Supports:

• load balancing (round robin)
• mesh networking between the worker threads

Installation

npm install undici undici-thread-interceptor

Usage

Main (main.js)

import { Worker } from "node:worker_threads";
import { join } from "node:path";
import { createThreadInterceptor } from "undici-thread-interceptor";
import { Agent, request } from "undici";

const worker = new Worker(join(import.meta.dirname, "worker.js"));

const interceptor = createThreadInterceptor({
  domain: ".local", // The prefix for all local domains
});
interceptor.route("myserver", worker);

const agent = new Agent().compose(interceptor);

const { statusCode, body } = await request("http://myserver.local", {
  dispatcher: agent,
});

console.log(statusCode, await body.json());

// worker.terminate()

Worker (worker.js)

Generic node HTTP application

import { wire } from "undici-thread-interceptor";
import { parentPort } from "node:worker_threads";

function app(req, res) {
  res.writeHead(200, { "Content-Type": "application/json" });
  res.end(JSON.stringify({ hello: "world" }));
}

// App can optionally be a string in the form `http://HOST:PORT`. In that case the interceptor
// will use the network to perform the request.
wire({ server: app, port: parentPort });

Fastify

import { wire } from "undici-thread-interceptor";
import { parentPort } from "node:worker_threads";
import fastify from "fastify";

const app = fastify();

app.get("/", (req, reply) => {
  reply.send({ hello: "world" });
});

wire({ server: app, port: parentPort });

Express

import { wire } from "undici-thread-interceptor";
import { parentPort } from "node:worker_threads";
import express from "express";

const app = express();

app.get("/", (req, res) => {
  res.send({ hello: "world" });
});

wire({ server: app, port: parentPort });

Koa

import { wire } from "undici-thread-interceptor";
import { parentPort } from "node:worker_threads";
import Koa from "koa";

const app = new Koa();

app.use((ctx) => {
  ctx.body = { hello: workerData?.message || "world" };
});

wire({ server: app.callback(), port: parentPort });

Replace the server at runtime

import { wire } from "undici-thread-interceptor";
import { parentPort } from "node:worker_threads";
import fastify from "fastify";

const app1 = fastify();

app1.get("/", (req, reply) => {
  reply.send({ hello: "this is app 1" });
});

const app2 = fastify();

app2.get("/", (req, reply) => {
  reply.send({ hello: "this is app 2" });
});

const { replaceServer } = wire({ server: app1, port: parentPort });

setTimeout(() => {
  replaceServer(app2);
}, 5000);

Gracefully close the worker thread

If you want to gracefully close the worker thread, remember to call the close function of the interceptor.

import { wire } from "undici-thread-interceptor";

// ...

const { interceptor } = wire({ server: app, port: parentPort });

// ...

await interceptor.close();

Gracefully close all the threads

If you call the close method from the main thread, it will call the close function on each routed thread.

After calling the close method, each call to route will throw an error, unless you call the restart method first.

API

Hooks

It's possible to set some simple synchronous functions as hooks:

• onServerRequest(req, cb)
• onServerResponse(req, res)
• onServerError(req, res, error)
• onClientRequest(req, clientCtx)
• onClientResponse(req, res, clientCtx)
• onClientResponseEnd(req, res, clientCtx)
• onClientError(req, res, clientCtx, error)

The clientCtx is used to pass through hooks calls objects which cannot be set on request (which is then sent through postMessage, so it might be not serializable).

Client hooks

These are set on the agent dispatcher.

const interceptor = createThreadInterceptor({
  domain: ".local",
  onClientRequest: (req) => console.log("onClientRequest called", req),
});
interceptor.route("myserver", worker);

const agent = new Agent().compose(interceptor);

const { statusCode } = await request("http://myserver.local", {
  dispatcher: agent,
});

Server hooks

These can be passed to the wire function in workers. e.g. with Fastify:

import { wire } from "undici-thread-interceptor";
import { parentPort } from "node:worker_threads";
import fastify from "fastify";

const app = fastify();

app.get("/", (req, reply) => {
  reply.send({ hello: "world" });
});

wire({
  server: app,
  port: parentPort,
  onServerRequest: (req, cb) => {
    console.log("onServerRequest called", req);
    cb();
  },
});

License

MIT