index.js

var http = require("http");
var _forEach = require("lodash.foreach");

/**
 * Flatten headers from an expanded CloudFront headers object into an Express-like simple `headers` object
 * @param {object} cfHeaders - an expanded CloudFront `headers` object
 * @returns {object} headers - an Express-like simple `headers` object
 */

function flattenHeaders(cfHeaders) {
  var headers = {};

  _forEach(cfHeaders, function(value, key) {
    headers[key.toLowerCase()] = value[0].value;
  });

  return headers;
}

/**
 * Expand a simple Express `headers` object into an expanded CloudFront `headers` object
 * @param {object} headers - an Express/Express-like `headers` object.
 * @returns {object} cfHeaders - an expanded CloudFront headers object
 */

function expandHeaders(headers) {
  let cfHeaders = {};

  _forEach(headers, function(value, key) {
    cfHeaders[key.toLowerCase()] = [
      {
        key: key,
        value: value
      }
    ];
  });

  return cfHeaders;
}

/**
 * Parse a CloudFront viewer request event into an Express-like `request` object.
 * @param {object} cfEvent - a CloudFront viewer request event.
 * @returns {object} req - an Express-like request object
 */

exports.parseCloudfrontEvent = function(cfEvent) {
  const cfRequest = cfEvent.Records[0].cf.request;

  const req = {
    headers: flattenHeaders(cfRequest.headers),
    method: cfRequest.method,
    url: cfRequest.uri,
    originalCfReq: cfRequest
  };

  return req;
};

/**
 * Generate a CloudFront viewer `cfResponse` response object from a generic response object.
 * @param {object} response - a  generic response object.
 * @returns {object} cfRes - a CloudFront viewer response object.
 */

exports.generateCloudfrontResponse = function(response) {
  
  // if the response still contains the `originalCfReq` property, just set the response to that
  // this allows the bypassing of the function, for instance, on a successful authenticate,
  // mostly mirroring the semantics used in the docs without fuss
  if (response.originalCfReq) {
    return response.originalCfReq;
  } else {
    var cfRes = {
      status: response.status.toString(),
      statusDescription: http.STATUS_CODES[response.status],
      headers: expandHeaders(response.headers)
    };

    if (response.body) {
      cfRes.body = response.body;
    }

    return cfRes;
  }
};

/**
 * Generate an Express response from a generic response object.
 * @param {object} response - a generic response object.
 * @param {object} req - Express req object
 * @param {object} res - Express res object
 * @param {object} next - Express next object
 * @returns {object} cfRes - a CloudFront viewer response object.
 */

exports.sendExpressResponse = function(response, req, res, next) {
  // passing the original request as the response  will cause the
  if (response === req) {
    return next();
  }

  _forEach(response.headers, function(value, key) {
    res.set(key, value);
  });

  res.status(response.status);

  if (response.body) {
    res.send(response.body);
  } else {
    res.send("");
  }
};

exports.fromCf = exports.parseCloudfrontEvent;
exports.toCf = exports.generateCloudfrontResponse;