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OSCAR Protocol
UUIDsErrorsTool IDs
Host Interaction
Rate LimitsMigrationMessages
Other Services
Sign OnBARTRendezvous
OSERVICE (0x0001)
LOCATE (0x0002)
BUDDY (0x0003)
ICBM (0x0004)
ADVERT (0x0005)
INVITE (0x0006)
ADMIN (0x0007)
POPUP (0x0008)
PD (0x0009)
STATS (0x000B)
CHAT_NAV (0x000D)
CHAT (0x000E)
ODIR (0x000F)
BART (0x0010)
FEEDBAG (0x0013)
ICQ (0x0015)
BUCP (0x0017)
ALERT (0x0018)
PLUGIN (0x0022)
UNNAMED_FG_24 (0x0024)
MDIR (0x0025)
ARS (0x044A)

FLAP (Frame Layer Protocol) provides the packet framing on top of TCP or TLS layer for the OSCAR protocol. Each message sent to and from the AIM backend is encapsulated in a FLAP frame that is easily identified using a 6 byte header followed by a variable length data segment. The payload of a FLAP frame is in most cases a [Protocols/OSCAR/SNAC|SNAC].

FLAP Header

The header contains the frame type, a sequence number, and the length of the following data segment. The sequence number is independently sequential in each direction. Packets from the server to client have one sequence number, while the packets from the client to server have a different independently increasing number.

If the server receives a sequence number out of order it will terminate the connection. A common mistake is to use a uint8 (byte) to represent the sequence number, which will roll over at 255 and cause the server to disconnect the client.

Name Type Notes
FLAP_MARKER uint8 (byte) ASTERISK (literal ASCII "*")
FLAP__FRAME uint8 (byte) Class: FLAP__FRAME_TYPE]
FLAP_SEQUENCE uint16 (word) Initialized to a random value, increments for each send
payloadLength uint16 (word) Length of data, does not include the 6 byte header length