t.Errorf("roundTrip = %#v, %v; want errServerClosedIdle, transportReadFromServerError, or nothingWrittenError", err, err)
	}

	<-pc.closech
	err = pc.closed
	if !isNothingWrittenError(err) && !isTransportReadFromServerError(err) && err != errServerClosedIdle {
		t.Errorf("pc.closed = %#v, %v; want errServerClosedIdle or transportReadFromServerError, or nothingWrittenError", err, err)
	}
}

func isNothingWrittenError(err error) bool {

		if b.br.Buffered() == 0 {
			b.br = nil
		}
		return n, err
	}
	return b.ReadWriteCloser.Read(p)
}

// nothingWrittenError wraps a write errors which ended up writing zero bytes.
type nothingWrittenError struct {
	error
}

func (nwe nothingWrittenError) Unwrap() error {
	return nwe.error
}

func (pc *persistConn) writeLoop() {
	defer close(pc.writeLoopDone)
	for {