net/http/httputil: avoid ReverseProxy data race on 1xx response and error
ReverseProxy uses a httptrace.ClientTrace.Got1xxResponse trace hook
to capture 1xx response headers for proxying. This hook can be called
asynchrnously after RoundTrip returns. (This should only happen when
RoundTrip has failed for some reason.) Add synchronization so we don't
attempt to modifying the ResponseWriter headers map from the hook
after another goroutine has begun making use of it.
Fixes #65123
Change-Id: I8b7ecb1a140f7ba7e37b9d27b8a20bca41a118b1
Reviewed-on: https://go-review.googlesource.com/c/go/+/567216
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Jonathan Amsterdam <jba@google.com>
Auto-Submit: Damien Neil <dneil@google.com>