@Override
    public int readEnum() throws IOException {
        checkIfPackedField();
        return readRawVarInt32();
    }
Read an enum field value from the internal buffer. Caller is responsible for converting the numeric value to an
actual enum.
jraft-rheakv/rheakv-core/src/main/java/com/alipay/sofa/jraft/rhea/serialization/impl/protostuff/io/NioBufInput.java