bridge.js

const http = require("http");

function normalizeEvent(event) {
  let isApiGateway = true;

  if (event.Action === "Invoke") {
    isApiGateway = false;
    const invokeEvent = JSON.parse(event.body);

    const { method, path, headers, encoding } = invokeEvent;

    let { body } = invokeEvent;

    if (body) {
      if (encoding === "base64") {
        body = Buffer.from(body, encoding);
      } else if (encoding === undefined) {
        body = Buffer.from(body);
      } else {
        throw new Error(`Unsupported encoding: ${encoding}`);
      }
    }

    return {
      isApiGateway,
      method,
      path,
      headers,
      body
    };
  }

  const { httpMethod: method, path, headers, body } = event;

  return {
    isApiGateway,
    method,
    path,
    headers,
    body
  };
}

class Bridge {
  constructor() {
    this.launcher = this.launcher.bind(this);
  }

  launcher(event) {
    // eslint-disable-next-line consistent-return
    return new Promise((resolve, reject) => {
      if (this.userError) {
        console.error("Error while initializing entrypoint:", this.userError);
        return resolve({ statusCode: 500, body: "" });
      }

      if (!this.port) {
        return resolve({ statusCode: 504, body: "" });
      }

      const { isApiGateway, method, path, headers, body } = normalizeEvent(
        event
      );

      const opts = {
        hostname: "127.0.0.1",
        port: this.port,
        path,
        method,
        headers
      };

      const req = http.request(opts, res => {
        const response = res;
        const respBodyChunks = [];
        response.on("data", chunk => respBodyChunks.push(Buffer.from(chunk)));
        response.on("error", reject);
        response.on("end", () => {
          const bodyBuffer = Buffer.concat(respBodyChunks);
          delete response.headers.connection;

          if (isApiGateway) {
            delete response.headers["content-length"];
          } else if (response.headers["content-length"]) {
            response.headers["content-length"] = bodyBuffer.length;
          }

          resolve({
            statusCode: response.statusCode,
            headers: response.headers,
            body: bodyBuffer.toString("base64"),
            isBase64Encoded: true
          });
        });
      });

      req.on("error", error => {
        setTimeout(() => {
          // this lets express print the true error of why the connection was closed.
          // it is probably 'Cannot set headers after they are sent to the client'
          reject(error);
        }, 2);
      });

      if (body) req.write(body);
      req.end();
    });
  }
}

module.exports = {
  Bridge
};