@VisibleForTesting
    static boolean isExpected(long errorCode, ByteBuf debugData) {
        // 'Error flushing' happens when a client closes the connection early.
        return errorCode == CODE_INTERNAL_ERROR &&
               ByteBufUtil.equals(debugData, debugData.readerIndex(),
                                  ERROR_FLUSHING, 0, ERROR_FLUSHING_LEN);
    }
Returns {@code true} if the connection has received a GOAWAY frame with non-zero error code.
core/src/main/java/com/linecorp/armeria/internal/common/Http2GoAwayHandler.java