Upload stream fires "data" after "end"

Hi again,

Node v10.14.1, graphql-upload v8.0.3.

An odd one here, possibly not a bug, might also be a mistake on my side. Either way, would appreciate your advice! : ]

First, simplified example code. I use this code to upload a file to my GraphQL server. The type of input.icon is Upload.

The call to setTimeout simulates certain asynchronous logic present in my code. I perform an asynchronous call somewhere in the program, wait for a response, and only then I pipe the upload stream to where I want it to go.

const create = input => 
  new Promise(resolve => {
    input.icon.then(file => {
      const stream = file.createReadStream();

      setTimeout(() => {
        stream.on("data", () => {
          console.log("Receiving data");
        });

        stream.on("end", () => {
          console.log("Stream ended");
          resolve();
        });
      }, 300);
    });
  });

This code works fine and prints Receiving data a number of times and finishes with Stream ended. However, there is a condition when this does not work:

• The uploaded file is really small - smaller than the readableHighWaterMark.
• The "end" event handler is literally attached before the data handler, like this:

setTimeout(() => {
  stream.on("end", () => {
    console.log("Stream ended");
    resolve();
  });

  stream.on("data", () => {
    console.log("Receiving data");
  });
}, 300);

In this case, the code will print Stream ended first, and then Receiving data.

Some more notes:

• The code works fine if I use a different type of stream, not the one from graphql-upload. E.g. if I write const stream = fs.createReadStream("/home/juona/ex.tar.bz2"); to read the same file from the local file system, instead of uploading it via const stream = file.createReadStream();, it works just fine.
• Using stream.pause() before setTimeout and then stream.resume() anywhere in the timeout callback fixes the problem.
• The code also works correctly if setTimeout is removed or if the timeout is very low (e.g. if I use process.nextTick() instead), regardless of the order of event handler attachment. I would assume that the timeout has to be longer than the time it takes to upload the file.
• It does not matter what kind of file is being used, only its size.

I am having trouble understanding what is happening here. In the actual application I use a bunch of other stream libraries to transform the upload and one of them fails because it expects stream.end to be called after at at least one stream.write, which I guess is a fair expectation. Also the problem is more complex in the real scenario since stream.pause() does not really help in that case, but I have to start the investigation somewhere…

Could perhaps be an issue in Node itself or a compatibility problem, but since it matters whether or not I use the upload stream or a different one, I am coming to you first.

Any thoughts?

[jaydenseric]

The fix is published in v8.0.4!

[jaydenseric]

I’m pretty sure the right event to listen for when handling file upload streams in resolvers is finish, not end:

https://github.com/jaydenseric/apollo-upload-examples/blob/d2bf708591ad276929976d3e4e26ae8005bf4b87/api/resolvers.mjs#L31