http2: avoid spurious context cancelation error from Response.Body.Close

When a request has a deadline set, the net/http package can cancel
the request context after reading an error (including io.EOF) from
the response body. Avoid returning a spurious error from
transportResponseBody if the request context is canceled.

For golang/go#49366.

Change-Id: I645466a1d6e405bdf17b3cc087204e4622a140eb
Reviewed-on: https://go-review.googlesource.com/c/net/+/362354
Trust: Damien Neil <[email protected]>
Run-TryBot: Damien Neil <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: neild

http2/transport.go

@@ -2452,7 +2452,10 @@ func (b transportResponseBody) Close() error {
 	select {
 	case <-cs.donec:
 	case <-cs.ctx.Done():
-		return cs.ctx.Err()
+		// See golang/go#49366: The net/http package can cancel the
+		// request context after the response body is fully read.
+		// Don't treat this as an error.
+		return nil
 	case <-cs.reqCancel:
 		return errRequestCanceled
 	}