public void WriteRecordBatch(Message <TKey, TValue> message, IBufferWriter <byte> output)
{
// baseOffset: int64
// batchLength: int32
// partitionLeaderEpoch: int32
// magic: int8(current magic value is 2)
// crc: int32
// attributes: int16
// bit 0~2:
// 0: no compression
// 1: gzip
// 2: snappy
// 3: lz4
// 4: zstd
// bit 3: timestampType
// bit 4: isTransactional(0 means not transactional)
// bit 5: isControlBatch(0 means not a control batch)
// bit 6~15: unused
// lastOffsetDelta: int32
// firstTimestamp: int64
// maxTimestamp: int64
// producerId: int64
// producerEpoch: int16
// baseSequence: int32
// records: [Record]
// crc
using var buffer = new MemoryBufferWriter();
buffer.WriteUShort(0b0000_0000_0000_0000); // attributes: int16
buffer.WriteInt(0); // lastOffsetDelta: int32
var now = DateTime.UtcNow.DateTimeToUnixTimestampMs();
buffer.WriteLong(now); // firstTimestamp: int64
buffer.WriteLong(now); // maxTimestamp: int64
buffer.WriteLong(-1); // producerId: int64
buffer.WriteShort(-1); // producerEpoch: int16
buffer.WriteInt(-1); // baseSequence: int32
buffer.WriteInt(1); // one record in the batch
WriteRecord(message, buffer);
output.WriteInt(12 + 4 + 1 + 4 + buffer.Length); // size of records + "header" bytes (not documented)
output.WriteLong(0); // baseOffset: int64
output.WriteInt(4 + 1 + 4 + buffer.Length); // batchLength: int32
output.WriteInt(0); // partitionLeaderEpoch: int32
output.WriteByte(2); // magic: int8(current magic value is 2)
var crc = Hash.Crc32C.Compute(buffer);
output.WriteUInt(crc); // crc: int32
buffer.CopyTo(output);
}