code: func (b TCP) Encode(t *TCPFields) {
  	b.encodeSubset(t.SeqNum, t.AckNum, t.Flags, t.WindowSize)
  	binary.BigEndian.PutUint16(b[TCPSrcPortOffset:], t.SrcPort)
  	binary.BigEndian.PutUint16(b[TCPDstPortOffset:], t.DstPort)
  	b[TCPDataOffset] = (t.DataOffset / 4) << 4
  	binary.BigEndian.PutUint16(b[TCPChecksumOffset:], t.Checksum)
  	binary.BigEndian.PutUint16(b[TCPUrgentPtrOffset:], t.UrgentPointer)
  }
docs: // Encode encodes all the fields of the tcp header.