@Override
    public byte[] encode(final LogEntry log) {
        if (log.hasLearners()) {
            throw new IllegalArgumentException("V1 log entry encoder doesn't support learners");
        }
        EntryType type = log.getType();
        LogId id = log.getId();
        List<PeerId> peers = log.getPeers();
        List<PeerId> oldPeers = log.getOldPeers();
        ByteBuffer data = log.getData();

        // magic number 1 byte
        int totalLen = 1;
        final int iType = type.getNumber();
        final long index = id.getIndex();
        final long term = id.getTerm();
        // type(4) + index(8) + term(8)
        totalLen += 4 + 8 + 8;
        int peerCount = 0;
        // peer count
        totalLen += 4;
        final List<String> peerStrs = new ArrayList<>(peerCount);
        if (peers != null) {
            peerCount = peers.size();
            for (final PeerId peer : peers) {
                final String peerStr = peer.toString();
                // peer len (short in 2 bytes)
                // peer str
                totalLen += 2 + peerStr.length();
                peerStrs.add(peerStr);
            }
        }
        int oldPeerCount = 0;
        // old peer count
        totalLen += 4;
        final List<String> oldPeerStrs = new ArrayList<>(oldPeerCount);
        if (oldPeers != null) {
            oldPeerCount = oldPeers.size();
            for (final PeerId peer : oldPeers) {
                final String peerStr = peer.toString();
                // peer len (short in 2 bytes)
                // peer str
                totalLen += 2 + peerStr.length();
                oldPeerStrs.add(peerStr);
            }
        }

        final int bodyLen = data != null ? data.remaining() : 0;
        totalLen += bodyLen;

        final byte[] content = new byte[totalLen];
        // {0} magic
        content[0] = LogEntryV1CodecFactory.MAGIC;
        // 1-5 type
        Bits.putInt(content, 1, iType);
        // 5-13 index
        Bits.putLong(content, 5, index);
        // 13-21 term
        Bits.putLong(content, 13, term);
        // peers
        // 21-25 peer count
        Bits.putInt(content, 21, peerCount);
        int pos = 25;
        for (final String peerStr : peerStrs) {
            final byte[] ps = AsciiStringUtil.unsafeEncode(peerStr);
            Bits.putShort(content, pos, (short) peerStr.length());
            System.arraycopy(ps, 0, content, pos + 2, ps.length);
            pos += 2 + ps.length;
        }
        // old peers
        // old peers count
        Bits.putInt(content, pos, oldPeerCount);
        pos += 4;
        for (final String peerStr : oldPeerStrs) {
            final byte[] ps = AsciiStringUtil.unsafeEncode(peerStr);
            Bits.putShort(content, pos, (short) peerStr.length());
            System.arraycopy(ps, 0, content, pos + 2, ps.length);
            pos += 2 + ps.length;
        }
        // data
        if (data != null) {
            System.arraycopy(data.array(), data.position(), content, pos, data.remaining());
        }

        return content;
    }
V1 log entry encoder
@author boyan(boyan@antfin.com)
jraft-core/src/main/java/com/alipay/sofa/jraft/entity/codec/v1/V1Encoder.java