Hopper CORS

A CORS extension for Hopper, an HTTP microframework for the Grain programming language.

Installation

This library is contained within a single Grain file, which should be installed into the same directory as your hopper.gr

curl https://raw.githubusercontent.com/alex-snezhko/hopper-cors/main/hopper-cors.gr -o hopper-cors.gr

Overview

The library exposes a single function, withCors, taking a list of options and returning a middleware that enables CORS support for the routes in its scope. Consult the API docs for all of the possible options and default behaviors.

withCors also automatically handles preflight requests for "non-simple" requests.

Example Usage

Basic - enable all CORS requests

import Hopper from "./hopper"
import Cors from "./hopper-cors"

Hopper.serveWithMiddleware(Cors.withCors([]), [
  Hopper.get("/hello", req => {
    // ...
  }),
  Hopper.put("/preflighted", req => {
    // ...
  }),
])

With dynamic origin checking and only on certain scope

import List from "list"
import Hopper from "./hopper"
import Cors from "./hopper-cors"

let withCorsDynamicOrigin = Cors.withCors([
  Cors.AllowOrigin(origin => {
    let allowedOrigins = // ...
    List.contains(origin, allowedOrigins)
  })
])

Hopper.serve([
  Hopper.scope("/with-cors", withCorsDynamicOrigin, [
    Hopper.get("/resource", req => {
      // ...
    })
  ])
])

API Docs

grain doc-generated API docs are available here

Acknowledgements

Aspects of the API and implementation of this library were adapted from Gin's Cors Library and Express' Cors Library.