node.js - Streaming file from S3 with Express including information on length and filetype

Question

Using the aws-sdk module and Express 4.13, it's possible to proxy a file from S3 a number of ways.

This callback version will return the file body as a buffer, plus other relevant headers like Content-Length:

function(req,res){

  var s3 = new AWS.S3();

  s3.getObject({Bucket: myBucket, Key: myFile},function(err,data){

    if (err) {
      return res.status(500).send("Error!");
    }

    // Headers
    res.set("Content-Length",data.ContentLength)
       .set("Content-Type",data.ContentType);

    res.send(data.Body); // data.Body is a buffer

  });

}

The problem with this version is that you have to get the entire file before sending it, which is not great, especially if it's something large like a video.

This version will directly stream the file:

function(req,res){

  var s3 = new AWS.S3();

  s3.getObject({Bucket: myBucket, Key: myFile})
    .createReadStream()
    .pipe(res);

}

But unlike the first one, it won't do anything about the headers, which a browser might need to properly handle the file.

Is there a way to get the best of both worlds, passing through the correct headers from S3 but sending the file as a stream? It could be done by first making a HEAD request to S3 to get the metadata, but can it be done with one API call?

Answer 1

One approach is listening the httpHeaders event and creating a stream within it.

s3.getObject(params)
    .on('httpHeaders', function (statusCode, headers) {
        res.set('Content-Length', headers['content-length']);
        res.set('Content-Type', headers['content-type']);
        this.response.httpResponse.createUnbufferedStream()
            .pipe(res);
    })
    .send();