bodyDoneCh := make(chan struct{})
	doneCh := make(chan error)
	ctx := r.Context()
	go func() {
		canWrite := true
		write := func(b []byte) {
			if canWrite {
				n, err := w.Write(b)
				if err != nil || n != len(b) {
					canWrite = false
				}
			}
		}
		// Wait for body to be read.
		select {
		case <-ctx.Done():
		case <-bodyDoneCh: