Sessions: decode flow of packets when sniffing

class scapy.sessions.DefaultSession(prn: Optional[Callable[[Packet], Any]] = None, store: bool = False, supersession: Optional[DefaultSession] = None, *args: Any, **karg: Any)[source]

Bases: object

Default session: no stream decoding

property count
on_packet_received(pkt: Optional[Packet]) None[source]

DEV: entry point. Will be called by sniff() for each received packet (that passes the filters).

property prn
property store
toPacketList() PacketList[source]
class scapy.sessions.IPSession(*args: Any, **kwargs: Any)[source]

Bases: DefaultSession

Defragment IP packets ‘on-the-flow’.

Usage: >>> sniff(session=IPSession)

on_packet_received(pkt: Optional[Packet]) None[source]
class scapy.sessions.StringBuffer[source]

Bases: object

StringBuffer is an object used to re-order data received during a TCP transmission.

Each TCP fragment contains a sequence number, which marks (relatively to the first sequence number) the index of the data contained in the fragment.

If a TCP fragment is missed, this class will fill the missing space with zeros.

append(data: bytes, seq: int) None[source]
clear() None[source]
full() bool[source]
class scapy.sessions.TCPSession(app: bool = False, *args: Any, **kwargs: Any)[source]

Bases: IPSession

A Session that matches seq/ack packets together to dissect special protocols, such as HTTP.

DEV: implement a class-function tcp_reassemble in your Packet class:

def tcp_reassemble(cls, data, metadata, session):
    # data = the reassembled data from the same request/flow
    # metadata = empty dictionary, that can be used to store data
    #            during TCP reassembly
    # session = a dictionary proper to the bidirectional TCP session,
    #           that can be used to store anything
    # If the packet is available, return it. Otherwise don't.
    # Whenever you return a packet, the buffer will be discarded.
    return pkt
    # Otherwise, maybe store stuff in metadata, and return None,
    # as you need additional data.
    return None

For more details and a real example, see:


app – Whether the socket is on application layer = has no TCP layer. This is used for instance if you are using a native TCP socket. Default to False

on_packet_received(pkt: Optional[Packet]) None[source]

Hook to the Sessions API: entry point of the dissection. This will defragment IP if necessary, then process to TCP reassembly.