impl AsyncBufRead for Decoder

[DrewMcArthur]

Hi! So I've got a stream: impl AsyncBufRead, which may or may not be gzipped. I'm trying to return that stream in a function whose return type is Result<impl AsyncBufRead, Error>, but running into the issue where the GzipDecoder is AsyncRead, but not AsyncBufRead. Since the inner reader it pulls from is AsyncBufRead, is there any reason why the decoder itself can't be AsyncBufRead?

Or, am I misreading the docs, and I should just be calling into_inner()? the way I read it currently, this returns the original stream though, not the decoded version.

If it's easier, I just need this for the GzipDecoder, but I assume this level would be generic across all the Decoders.

[DrewMcArthur]

update: I was able to update my function to return a Box<dyn AsyncRead>, which covers both the GZipped case (returning a GzipDecoder: AsyncRead) and the plain filestream from S3 (returning an impl AsyncBufRead, which also is AsyncRead). Since my parsing function downstream just needs a Stream<Item=Bytes>, that's all I needed.

I'm still very curious what it would take to implement AsyncBufRead for the Decoder. I tried messing around with it a bit last night, but I'm too unfamiliar with Pins and all of that.

[link2xt]

Is this about bufread GzipDecoder? For write GzipDecoder #304 is going to pass through AsyncBufRead trait if underlying stream has it. For bufread GzipDecoder I think it makes sense that even though underlying stream may have a buffer, this is a buffer for gzipped data, so decoder implements AsyncRead which reads decompressed data into user-provided buffer and if you want the stream itself to have a buffer for decoded/decompressed data, you need to wrap it again into BufReader.

[robjtede]

#304 was implemented and released.

If there's more to do for this issue please say so and we'll get it re-opened.

[DrewMcArthur]

thank you @robjtede and @link2xt !! 😄