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When wrapping a body into a stream for compression, BodyIntoStream polls the underlying body to completion (None) to read data frames into the encoder. WrapBody then invokes poll_frame to collect any remaining trailers or non-data frames. Previously, poll_frame unconditionally re-polled the inner body if no trailers were buffered. When the underlying body is backed by a non-fused stream (such as futures::stream::unfold), this re-poll panics after EOF. Track when the inner body has yielded EOF (None), and return Ready(None) directly rather than re-polling the inner body. Fixes tower-rs#732.
cratelyn
reviewed
Sep 9, 2026
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if we want to avoid polling the underlying body after it yields Ready(None), i think that it would be more prudent to use http_body_util::combinators::Fuse<B>.
we can wrap B in that combinator, rather than reimplementing the logic for fusing a body here.
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| yielded_all_data: false, | ||
| non_data_frame: None, | ||
| body_eof: false, |
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it smells weird to me that this introduces a body_eof flag when there is already a yielded_all_data flag here. how do these differ?
De-ASI-INTERFACE
approved these changes
Sep 15, 2026
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Motivation
Closes #732
When compressing a streaming response body backed by a non-fused stream (e.g.
Body::from_stream(futures::stream::unfold(...))),Compressionpanics at the end of the stream with:Unfold must not be polled after it returned Poll::Ready(None).In
BodyIntoStream,poll_nextdrives the underlying body to read all data frames into the encoder. Oncethis.body.poll_frame(cx)returnsNone,yielded_all_datais set. After the encoder finishes writing all compressed output,WrapBody::poll_framecallsBodyIntoStream::poll_frameto forward any remaining frames (such as trailers).If no trailers were buffered,
BodyIntoStream::poll_frameunconditionally fell through tothis.body.poll_frame(cx). For bodies backed by non-fused streams, re-polling an already-exhausted body violates the stream contract and panics.Solution
Track whether the inner body has already returned
Nonevia a boolean field (body_eof). Whenbody_eofis true,BodyIntoStream::poll_frameimmediately returnsPoll::Ready(None)instead of re-polling the inner body.