Curveball

Curveball is a framework for building web services in Node.js. It fullfills a similar role to [Express][1] and it's heavily inspired by [Koa][2].

This web framework has the following goals:

A minimal foundation.
Completely written in and for [TypeScript][3].
Modern Ecmascript features.
Async/await-based middleware.
Support for Node, Bun, AWS Lambda, Azure functions.
Native support for HTTP/2, including easy access to HTTP/2 Push.
Native, deeply integrated Websocket.
Native support for modern HTTP features, such as [103 Early Hints][http-103].
The ability to easily do internal sub-requests without having to do a real HTTP request.

If you used Koa in the past, this is going to look pretty familiar. I'm a big fan of Koa myself and would recommend it over this project if you don't need any of the things this project offers.

Installation

npm install @curveball/core

Getting started

Curveball only provides a basic framework. Using it means implementing or using curveball middleware. For example, if you want a router, use or build a Router middleware.

All of the following examples are written in typescript, but it is also possible to use the framework with plain javascript.

import { Application, Context } from '@curveball/core';

const app = new Application();
app.use((ctx: Context) => {

  ctx.status = 200;
  ctx.response.body = 'Hello world!'

});

app.listen(4000);

Middlewares you might want

Router
Body Parser
[Controller][controller]
Access Logs
Sessions
Generating application/problem+json responses
CORS
Hypermedia Links
Server-rendered React support
Serving static files
JSON-Schema validation

Authentication

You might like a12n-server, a full OAuth2 authorization server, written in Curveball and works well with the OAuth2 middleware.

AWS Lambda support / 'Serverless'

Bun support

To use Curveball with Bun, use the kernel package:

import { Application } from '@curveball/kernel';

const app = new Application();

// Add all your middlewares here!
app.use( ctx => {
  ctx.response.body = {msg: 'hello world!'};
});

export default {
  port: 3000,
  fetch: app.fetch.bind(app)
};

Some more details can be found in this article.

Doing internal subrequests

Many Node.js HTTP frameworks don't easily allow doing internal sub-requests. Instead, they recommend doing a real HTTP request. These requests are more expensive though, as it has to go through the network stack.

Curveball allows you to do an internal request with 'mock' request and response objects.

Suggested use-cases:

Running cheaper integration tests.
Embedding resources in REST apis.

Example:

import { Application } from '@curveball/core';

const app = new Application();
const response = await app.subRequest('POST', '/foo/bar', { 'Content-Type': 'text/html' }, '<h1>Hi</h1>');

Only the first 2 arguments are required. It's also possible to pass a Request object instead.

import { Application, MemoryRequest } from '@curveball/core';

const app = new Application();
const request = new MemoryRequest('POST', '/foo/bar', { 'Content-Type': 'text/html' }, '<h1>Hi</h1>');
const response = await app.subRequest(request);

HTTP/2 push

HTTP/2 push can be used to anticipate GET requests client might want to do in the near future.

Example use-cases are:

Sending scripts and stylesheets earlier for HTML-based sites.
REST api's sending resources based on relationships clients might want to follow.

import { Application } from '@curveball/core';
import http2 from 'http2';

const app = new Application();
const server = http2.createSecureServer({
  key: fs.readFileSync('server-key.pem'),
  cert: fs.readFileSync('server-cert.pem')
}, app.callback());
server.listen(4443);

app.use( ctx => {

  ctx.response.status = 200;
  ctx.response.headers.set('Content-Type', 'text/html');
  ctx.response.body = '';

  await ctx.response.push( pushCtx => {

    pushCtx.path = '/script.js';
    return app.handle(pushCtx);

  });

});

HTTP/2 push works by sending HTTP responses to the client, but it also includes HTTP requests. This is because HTTP clients need to know which request the response belongs to.

The push function simply takes a middleware, similar to use on Application. The callback will only be triggered if the clients supports push and wants to receive pushes.

In the preceding example, we are using app.handle() to do a full HTTP request through all the regular middlewares.

It's not required to do this. You can also generate responses right in the callback or call an alternative middleware.

Lastly, pushCtx.request.method will be set to GET by default. GET is also the only supported method for pushes.

Sending 1xx Informational responses

Curveball has native support for sending informational responses. Examples are:

[100 Continue][http-100] to let a client know even before the request completed that it makes sense to continue, or that it should break off the request.
[102 Processing][http-102] to periodically indicate that the server is still working on the response. This might not be very useful anymore.
[103 Early Hints][http-103] a new standard to let a client or proxy know early in the process that some headers might be coming, allowing clients or proxies to for example pre-fetch certain resources even before the initial request completes.

Here's an example of a middleware using 103 Early Hints:

import { Application, Context, Middleware } from '@curveball/core';

const app = new Curveball();
app.use(async (ctx: Context, next: Middleware) => {

  await ctx.response.sendInformational(103, {
    'Link' : [
      '</style.css> rel="prefetch" as="style"',
      '</script.js> rel="prefetch" as="script"',
    ]
  });
  await next();

});

Websocket

To get Websocket up and running, just run:

app.listenWs(port);

This will start a websocket server on the specified port. Any incoming Websocket connections will now just work.

If a Websocket connection was started, the Context object will now have a webSocket property. This property is simply an instance of [Websocket][ws] from the [ws][ws] NPM package.

Example usage:

import { UpgradeRequired } from '@curveball/http-errors';

app.use( ctx => {
  if (!ctx.webSocket) {
    throw new UpgradeRequired('This endpoint only supports WebSocket');
  }

  ctx.webSocket.send('Hello');
  ctx.webSocket.on('message', (msg) => {
    console.log('Received %s', msg);
  });

});

If you use typescript, install the @types/ws package to get all the correct typings:

npm i -D @types/ws

The [Controller][controller] package also has built-in features to make this even easier.

API

The Application class

The application is main class for your project. It's mainly responsible for calling middlewares and hooking into the HTTP server.

It has the following methods

use(m: Middleware) - Add a middleware to your application.
handle(c: Context) - Take a Context object, and run all middlewares in order on it.
listen(port: number) - Run a HTTP server on the specified port.
listenWs(port: number) - Start a websocket server on the specified port.
callback() - The result of this function can be used as a requestListener for node.js http, https and http2 packages.
subRequest(method: string, path:string, headers: object, body: any) - Run an internal HTTP request and return the result.
subRequest(request: Request) - Run an internal HTTP request and return the result.
origin - Sets the 'origin' for the application. This is used to determine absolute URIs. You can set the origin directly on the application, but you can also set a CURVEBALL_ORIGIN environment variable. If nothing is set this value will default to http://localhost.

The Context class

The Context object has the following properties:

request - An instance of Request.
response - An instance of Response.
state - An object you can use to store request-specific state information. this object can be used to pass information between middlewares. A common example is that an authentication middlware might set 'currently logged in user' information here.
ip() - Get the ip address of the HTTP client that's trying to connect.
path - The path of the request, for example /foo.html.
method - For example, POST.
query - An object containing the query parametes.
status - The HTTP status code, for example 200 or 404.
sendInformational(status, headers?) - Sends a 100 Continue, 102 Processing or 103 Early Hints - response with optional headers.
push(callback: Middleware) - Do a HTTP/2 push.
redirect(status, location) - Send a redirect status code and set a Location header.
absoluteUrl - The absolute URL

Core

Install / Use

README