TCP

class os_ken.lib.packet.tcp.tcp(src_port=1, dst_port=1, seq=0, ack=0, offset=0, bits=0, window_size=0, csum=0, urgent=0, option=None)

TCP (RFC 793) header encoder/decoder class.

An instance has the following attributes at least. Most of them are same to the on-wire counterparts but in host byte order. __init__ takes the corresponding args in this order.

Attribute	Description
src_port	Source Port
dst_port	Destination Port
seq	Sequence Number
ack	Acknowledgement Number
offset	Data Offset (0 means automatically-calculate when encoding)
bits	Control Bits
window_size	Window
csum	Checksum (0 means automatically-calculate when encoding)
urgent	Urgent Pointer
option	List of TCPOption sub-classes or an bytearray containing options. None if no options.

has_flags(*flags)

Check if flags are set on this packet.

returns boolean if all passed flags is set

Example:

>>> pkt = tcp.tcp(bits=(tcp.TCP_SYN | tcp.TCP_ACK))
>>> pkt.has_flags(tcp.TCP_SYN, tcp.TCP_ACK)
True

classmethod parser(buf)

Decode a protocol header.

This method is used only when decoding a packet.

Decode a protocol header at offset 0 in bytearray buf. Returns the following three objects.

• An object to describe the decoded header.

• A packet_base.PacketBase subclass appropriate for the rest of the packet. None when the rest of the packet should be considered as raw payload.

• The rest of packet.

serialize(payload, prev)

Encode a protocol header.

This method is used only when encoding a packet.

Encode a protocol header. Returns a bytearray which contains the header.

payload is the rest of the packet which will immediately follow this header.

prev is a packet_base.PacketBase subclass for the outer protocol header. prev is None if the current header is the outer-most. For example, prev is ipv4 or ipv6 for tcp.serialize.