Functional HTTP server

A simple HTTP server inspired by Express and in tune with Functional Programming principles in JavaScript for Deno.

Simple HTTP server
Routing

Simple HTTP server

The fastest way to start a HTTP server is to use the startHTTPServer function. The function takes two arguments; the first argument is the options, and the second is a unary function that takes a Request and return a Task of a Response.

import Task from "https://deno.land/x/functional@v1.1.0/library/Task.js";
import Response from "https://deno.land/x/functional_io@v0.5.0/library/Response.js";
import startHTTPServer from "https://deno.land/x/functional_http_server@v0.1.0/library/server.js";

startHTTPServer({ port: 8080 }, request => Task.of(Response.OK({}, request.raw)));

You can test this simple server by executing it your file

$ deno run --allow-net server.js

$ curl localhost:8080 -d "Hello, Hoge!"
> Hello, Hoge!

Routing

The main routing tool that comes bundled with this library is conveniently called route. It takes a non-zero number of arguments which are defined by a pair of functions. The first function of the pair is used to assert whether or not to execute the second function. The assertion function takes a Request and return a Boolean, the handling function takes a Request and must return a Task of a Response.

import Task from "https://deno.land/x/functional@v1.1.0/library/Task.js";
import { encodeText } from "https://deno.land/x/functional@v1.1.0/library/utilities.js";
import Response from "https://deno.land/x/functional_io@v0.5.0/library/Response.js";
import { route } from "https://deno.land/x/functional_http_server@v0.1.0/library/route.js";

startHTTPServer(
  { port: 8080 },
  route(
    [
      request => request.headers.method === 'GET',
      _ => Task.of(Response.OK({ 'content-type': 'text/plain' }, encodeText("Hello, Hoge!")))
    ]
  );
);

Routing handlers

Because the pattern is common, this library also offers a collection of handler that automatically creates the assertion function. Each handler takes a String or a RegExp and a unary function.

import Task from "https://deno.land/x/functional@v1.1.0/library/Task.js";
import { encodeText } from "https://deno.land/x/functional@v1.1.0/library/utilities.js";
import Response from "https://deno.land/x/functional_io@v0.5.0/library/Response.js";
import { handlers, route } from "https://deno.land/x/functional_http_server@v0.1.0/library/route.js";

startHTTPServer(
  { port: 8080 },
  route(
    handlers.get('/', _ => Task.of(Response.OK({ 'content-type': 'text/plain' }, encodeText("Hello, Hoge!"))))
  )
);

Routing with the `explodeRequest` utility

The function explodeRequest is a utility that will parse the headers and serialize the body of a Request, for convenience. The function takes two arguments; a binary function that returns a Task of Response and a Request.

The binary function handler will be called with an object containing the original headers, the parsed query string and other parameters; the second argument is the body of request serialized based on the content type.

import { explodeRequest } from "https://deno.land/x/functional_http_server@v0.1.0/library/utilities.js";

startHTTPServer(
  { port: 8080 },
  route(
    handlers.get('/users', explodeRequest(({ status }) => retrieveUsers({ filters: { status } }))),
    handlers.post(/\/users\/(?<userID>.+)$/, explodeRequest(({ userID }, { data: user }) => updateUser(userID, user)))
  )
);

For this sample, a GET request made with a query string will be parsed as an object.

$ curl localhost:8080/users?status=active

And, a POST request with a body as JSON will be parsed as well.

$ curl localhost:8080/users/hoge -X POST -H "Content-Type: application/json" -d "{\"data\":{\"fullName\":\"Hoge\"}}"

The function explodeRequest should cover most use-cases but if you need to create your own parser, check out the parseRequest function.

Composing routes

Finally, you can compose your routes for increased readability.

const userRoutes = [ handlers.get('/', handleRetrieveUsers), ... ];
const sensorRoutes = [ handlers.get('/', handleRetrieveSensors), ... ];

startHTTPServer({ port: 8080 }, route(...userRoutes, ...sensorRoutes));

Middleware

Before talking about middlewares, I think it is important to talk about the power of function composition and couple of things special about startHTTPServer and route:

The function startHTTPServer takes a unary function that must return a Task of Response.
The function route, will always return early if the argument is not a Request.

So for example, if you needed to discard any request with a content type that is not application/json, you could do the following.

import { compose } from "https://x.nest.land/ramda@0.27.0/source/index.js";

startHTTPServer(
  { port: 8080 },
  compose(
    route(...routes),
    request => request.headers.accept !== 'application/json'
      ? Task.of(Response.BadRequest({}, new Uint8Array([])))
      : request
  )
);

Deno

This codebase uses Deno.

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.