index.js

import express from "express";
import cors from "cors";
import axios from "axios";
import { typeCheck } from "type-check";
import build from "build-url";

const defaultOptions = {};

export default (options = defaultOptions) => {

  /* placeholder sanity for future functionality */
  if (!typeCheck("Object", options)) {
    throw new Error(`Expected Object options, encountered ${options}.`);
  } else if (Object.keys(options).length) {
    throw new Error(`Expected an empty Object, encountered ${Object.keys(options).join(",")}.`);
  }

  return express()
    .use(cors({ origin: (origin, callback) => callback(null, true) }))
    .use(
      async (req, res, next) => {
        try {
          const { path, method, headers, body, query: queryParams } = req;
          
          const url = build(
            path.substring(1),
            { queryParams },
          );

          const { host: ignored, ...extras } = headers;

          const { data, status, headers: responseHeaders } = await axios({
            url,
            method: method.toLowerCase(),
            headers: extras,
            ...(typeCheck("Object", body) && Object.keys(body).length > 0) ? { data: body } : {},
          });

          const { ["transfer-encoding"]: unused, ...response } = responseHeaders;

          return res
            .set(response)
            .status(status)
            .send(data);
        } catch (e) {
          const { response } = e;
          if (response) {
            const { status, data } = response;
            return res
              .status(status)
              .json(data);
          }
          return next(e);
        }
      },
    );
};