createRequestObject.js

const Stream = require("stream");
const queryString = require("querystring");
const http = require("http");

// Mock a HTTP IncomingMessage object from the Netlify Function event parameters
// Based on API Gateway Lambda Compat
// Source: https://github.com/serverless-nextjs/serverless-next.js/blob/master/packages/compat-layers/apigw-lambda-compat/lib/compatLayer.js

const createRequestObject = ({ event }) => {
  const {
    requestContext = {},
    path = "",
    multiValueQueryStringParameters,
    pathParameters,
    httpMethod,
    multiValueHeaders = {},
    body,
    isBase64Encoded,
  } = event;

  const newStream = new Stream.Readable();
  const req = Object.assign(newStream, http.IncomingMessage.prototype);
  req.url =
    (requestContext.path || path || "").replace(
      new RegExp("^/" + requestContext.stage),
      ""
    ) || "/";

  let qs = "";

  if (multiValueQueryStringParameters) {
    qs += queryString.stringify(multiValueQueryStringParameters);
  }

  if (pathParameters) {
    const pathParametersQs = queryString.stringify(pathParameters);

    if (qs.length > 0) {
      qs += `&${pathParametersQs}`;
    } else {
      qs += pathParametersQs;
    }
  }

  const hasQueryString = qs.length > 0;

  if (hasQueryString) {
    req.url += `?${qs}`;
  }

  req.method = httpMethod;
  req.rawHeaders = [];
  req.headers = {};

  for (const key of Object.keys(multiValueHeaders)) {
    for (const value of multiValueHeaders[key]) {
      req.rawHeaders.push(key);
      req.rawHeaders.push(value);
    }
    req.headers[key.toLowerCase()] = multiValueHeaders[key].toString();
  }

  req.getHeader = (name) => {
    return req.headers[name.toLowerCase()];
  };
  req.getHeaders = () => {
    return req.headers;
  };

  req.connection = {};

  if (body) {
    req.push(body, isBase64Encoded ? "base64" : undefined);
  }

  req.push(null);

  return req;
};

module.exports = createRequestObject;