RequestOrResponse::body_source_pull_algorithm used to have an optimization for proxyTransformStreams, where it simply copied the body from source to dest rather than reading and writing a chunk at a time. Proxy streams are notably created when you donew Request(requestWithBody).

This optimization results in truncated bodies, as there is an issue with the implementation that I have not fully understood yet. As such, this optimization has been temporarily disabled. We should fix the underlying issue and re-enable the optimization.