Before this change the transport could still be reading the request
body when Call returned, in two ways:
- the goroutine writing a multipart upload form was never stopped or
waited for, so after a failed request it kept reading the file body
while the caller retried
- the transport itself is documented to close the request body,
possibly in a different goroutine after the request has finished,
and hiding the body's Close method removed any way to wait for that
Both of these raced with callers which seek to the start of a pooled
buffer and retry the request, corrupting the retried body, and the
abandoned multipart goroutine could read pooled pages after they had
been returned to the pool.
Call now waits for the transport to finish with the request body
before returning, and the multipart form writer is stopped and waited
for once the request has finished.
Nick Craig-Wood
a18d9a6886