Is there any situation where archive.CompressStream should be closed? (mostly thinking if it should be returning a io.Nopcloser in that case)

If it's specific to this case, perhaps we should replace this line with a comment to outline "why".

Also wondering if something like a io.TeeReader would be something to involve 🤔

It is closed later down

Oh! Should've expanded the diff.

So do they have to be closed in a specific order? Because I also see that pr and pw are potentially closed multiple times ("with" or "without" error);

	defer pr.Close()
	defer pw.Close()


	// ... do things

	go func() {
		// ...
		pr.CloseWithError(err)
		// ...
	}()

	// ... do things

 	compressor.Close()
	pw.CloseWithError(err)

The reader and writer returned from io.Pipe are explicitly stated by the godoc to be fine when closed multiple times.
Compressor must be closed first because it produces input for the other streams.

In that case, would the reverse work? Keep this defer, and remove the other close further down? (would that be more readable?) The defers are executed in reverse order, so in this case,

defer pr.Close()
defer pw.Close()
defer compressor.Close()

Would be executed as;

pw.CloseWithError(err)
pr.CloseWithError(err)

# defers:
compressor.Close()
pw.Close()  // redundant, but ok
pr.Close()  // redundant, but ok

No, the compressor must be closed before compressedDigest := <-writeChan and before pr and pw are closed.

Closing pr or pw before compressor closes the writer the compressor writes to, so it doesn't have the chance to write all data.

DOH! Looking at that channel twice, and still not considering it for the order of events in my comment. 🙈 yup, makes sense.