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Comments (5)

brettstack avatar brettstack commented on June 12, 2024 1

@metaskills happy to receive PRs for this. Express does support streaming response https://stackoverflow.com/a/38789462/436540

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paya-cz avatar paya-cz commented on June 12, 2024 1

So I found a temporary workaround: just grab the entire payload from serverlessExpress, wrap it in a stream and send it out via the streaming API. This gives the ability to send bigger payloads out of the lambda but obviously it somewhat defeats the purpose of streaming when the entire response is buffered first. So make sure to give enough memory to the lambda to store these buffers.

const pipeline = require('util').promisify(require('stream').pipeline);
const { Readable } = require('stream');

let serverlessExpressInstance;

const getServerlessExpress = async () => {
  if (!serverlessExpressInstance) {
    serverlessExpressInstance = serverlessExpress({
      app,
      resolutionMode: 'PROMISE',
    });
  }

  return serverlessExpressInstance;
}

// @ts-ignore: https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/issues/74
exports.handler = awslambda.streamifyResponse(async (event, responseStream, context) => {
  const serverlessHandler = await getServerlessExpress();
  const result = await serverlessHandler(event, context, () => { });

  const metadata = {
    statusCode: result.statusCode,
    headers: result.headers,
    cookies: result.cookies,
  };

  let payload;
  if (result.body) {
    payload = Buffer.from(result.body, result.isBase64Encoded ? 'base64' : 'utf8');
  } else {
    payload = Buffer.alloc(0);
  }

  // Assign to the responseStream parameter to prevent accidental reuse of the non-wrapped stream.
  // @ts-ignore: https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/issues/74
  responseStream = awslambda.HttpResponseStream.from(responseStream, metadata);

  await pipeline(
    Readable.from(payload),
    responseStream,
  );
});

I have also encountered some issues when there is no payload to send, only headers. So if your expressjs server returns status code only without any response body, you might encounter a dangling connection. This might be a bug in AWS infrastructure. More info aws/aws-lambda-nodejs-runtime-interface-client#95

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metaskills avatar metaskills commented on June 12, 2024

For those curious on streaming support. https://aaronstuyvenberg.com/posts/introducing-response-streaming

Is anyone looking into this for express? I kind of assumed given the popularity this was done already. Totally willing to help if Express itself allows this?

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metaskills avatar metaskills commented on June 12, 2024

Maybe related.

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carontony avatar carontony commented on June 12, 2024

Hello, Anyone find a solution to stream content?

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