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

This web framework has the following goals:

• A minimal foundation.
• Completely written in and for TypeScript.
• 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.
• 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.

npm install @curveball/core

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);

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

• OAuth2
• OAuth2 add-on to let regular browsers log in

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

• aws-lambda.
• Azure functions

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.

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 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.

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

• 100 Continue 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 to periodically indicate that the server is still working on the response. This might not be very useful anymore.
• 103 Early Hints 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();

});

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 from the 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 package also has built-in features to make this even easier.

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 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 for the request.

The Request interface represents the HTTP request. It has the following properties and methods:

• headers - An instance of Headers.
• path - The path of the request, for example /foo.html.
• method - For example, POST.
• requestTarget - The full requestTarget from the first line of the HTTP request.
• body - This might represent the body, but is initially just empty. It's up to middlewares to do something with raw body and parse it.
• rawBody() - This function uses the raw-body function to parse the body from the request into a string or Buffer. You can only do this once, so a middleware should use this function to populate body.
• query - An object containing the query parametes.
• type - The Content-Type without additional parameters.
• accepts - Uses the accepts package to do content-negotiation.
• is(contentType) - Returns true or false if the Content-Type of the request matches the argument. If your Content-Type is application/hal+json it will return true for application/hal+json, hal+json and json.
• origin - The 'origin' for the request, for example: http://my-api:8008.
• absoluteUrl - The absolute URL for the request.
• ip() - Returns the ip address of the client. This may be ipv4 or ipv6. If CURVEBALL_TRUSTPROXY is set in the environment and truthy, this will use the information from the X-Forwarded-For header (if available).

The Response interface represents a HTTP response. It has the following properties and methods:

• headers - An instance of Headers.
• status - The HTTP status code, for example 200 or 404.
• body - The response body. Can be a string, a buffer or an Object. If it's an object, the server will serialize it as JSON.
• type - The Content-Type without additional parameters.
• 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.
• is(contentType) - Returns true or false if the Content-Type of the response matches the argument. If your Content-Type is application/hal+json it will return true for application/hal+json, hal+json and json.
• redirect(status, location) - Send a redirect status code and set a Location header.
• origin - The 'origin' for the request, for example: http://my-api:8008.

The Headers interface represents HTTP headers for both the Request and Response.

It has the following methods:

• set(name, value) - Sets a HTTP header.
• get(name) - Returns the value of a HTTP header, or null.
• has(name) - Returns true or false if the header exists.
• delete(name) - Deletes a HTTP header.
• append(name, value) - Adds a HTTP header, but doesn't erase an existing one with the same name.
• getAll() - Returns all HTTP headers as a key-value object.

Use the checkConditional function to verify the following headers:

• If-Match
• If-None-Match
• If-Modified-Since
• If-Unmodified-Since.

Signature:

checkConditionial(req: RequestInterface, lastModified: Date | null, etag: string | null): 200 | 304 : 412;

This function returns 200 if the conditional passed. If it didn't, it will return either 304 or 412. The former means you'll want to send a 304 Not Modified back, the latter 412 Precondition Failed.

200 does not mean you have to return a 200 OK status, it's just an easy way to indicate that all all conditions have passed.