lambda-node-code-that-streams

lambda-node-code-that-streams.ts

import util from "util";
import stream from "stream";
const { Readable } = stream;
const pipeline = util.promisify(stream.pipeline);

import { S3Client, GetObjectCommand } from "@aws-sdk/client-s3";

export const handler = awslambda.streamifyResponse(
  async (event, responseStream, context) => {
    const s3 = new S3Client({ region: "us-east-1" });
    const input = {
      Bucket: "-------------------FIXME------------------",
      Key: "-------------FIXME--------------",
    };

    const command = new GetObjectCommand(input);
    // console.log("sending...");
    const item = await s3.send(command);
    // console.log(item.Body);
    console.log(Object.getOwnPropertyNames(item.Body));
    // [
    //   "_readableState",
    //   "_events",
    //   "_eventsCount",
    //   "_maxListeners",
    //   "socket",
    //   "httpVersionMajor",
    //   "httpVersionMinor",
    //   "httpVersion",
    //   "complete",
    //   "rawHeaders",
    //   "rawTrailers",
    //   "aborted",
    //   "upgrade",
    //   "url",
    //   "method",
    //   "statusCode",
    //   "statusMessage",
    //   "client",
    //   "_consuming",
    //   "_dumped",
    //   "req",
    //   "transformToByteArray",
    //   "transformToString",
    //   "transformToWebStream",
    // ];

    const requestStream = item.Body.transformToWebStream();
    // item.Body is a Readable stream
    // https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/clients/client-s3/interfaces/getobjectcommandoutput.html#body

    // https://stackoverflow.com/questions/67366381/aws-s3-v3-javascript-sdk-stream-file-from-bucket-getobjectcommand

    const metadata = {
      statusCode: 200,
      headers: {
        "Content-Type": "image/jpeg",
        "X-Custom-Header": "Example-Custom-Header",
      },
    };

    responseStream = awslambda.HttpResponseStream.from(
      responseStream,
      metadata
    );

    // const requestStream = Readable.from(
    //   Buffer.from(new Array(1024 * 1024).join("🚣"))
    // );

    await pipeline(requestStream, responseStream);
  }
);

awslambda is a special global var available on AWS Node Lambdas