Fluture Express

Create Express middleware using Futures from Fluture.

Usage

npm install --save fluture fluture-express

Allows for the definition of pure functions to be used as Express middleware. This has benefits for testing and developer sanity. Another benefit of this particular approach, where every middleware is wrapped individually, is that it plays nicely with existing Express middleware, and they can be used interchangably.

// index.js

const {dispatcher} = require ('fluture-express');
const app = require ('express') ();
const dispatch = dispatcher ('./actions');

app.use (dispatch ('welcome'));
app.listen (3000);

// actions/welcome.js

const {Json} = require ('fluture-express');
const Future = require ('fluture');

module.exports = (req, locals) => Future.do (function* () {
  const user = yield locals.database.find ('sessions', locals.session.id);
  return Json (200, {welcome: user.name});
});

For a more in-depth example, see the example directory.

Documentation

Pseudo types

Req

The Express Request object.

Res a

The Express Response object with a locals property of type a.

The Response type

Fluture-Express mutates the response object for you, based on a specification of what the response should be. This specification is captured by the Response sum-type. It has these constructors:

Stream :: (Number, String, NodeReadableStream) -⁠> Response a

Indicates a streamed response. The first argument will be the response status code, the second will be used as a mime type, and the third will be piped into the response to form the response data.

Json :: (Number, Object) -⁠> Response a

Indicates a JSON response. The first argument will be the response status code, and the second will be converted to JSON and sent as-is.

Redirect :: (Number, String) -⁠> Response a

Indicates a redirection. The first argument will be the response status code, and the second will be the value of the Location header.

Empty :: Response a

Indicates an empty response. The response status will be set to 204, and no response body or Content-Type header will be sent.

Next :: a -⁠> Response a

Indicates that this middleware does not form a response. The supplied value will be assigned to res.locals and the next middleware will be called.

Middleware creation utilities

middleware :: ((Req, a) -⁠> Future b (Response a)) -⁠> (Req, Res a, (b -⁠> Undefined)) -⁠> Undefined

Converts an action to an Express middleware.

Takes a function that returns a Future of a Response, and returns an Express middleware that uses the returned structure to make the appropriate mutations to the res.

If the Future rejects, the rejection reason is passed into next for further error handling with Express.

dispatcher :: String -⁠> String -⁠> (Req, Res a, (Any -⁠> Undefined)) -⁠> Undefined

Creates middleware that uses the export from the given file in the given directory as an "action".

It takes the file in two steps for convenience. You are encouraged to use the first parameter to set up a sub-directory where all your actions live.

The exported value should be a function of the same signature as given to middleware.