Protocols/OSCAR/FLAP
| OSCAR Protocol |
| Introduction • Terms • Clients |
| Basic |
| Datatypes • FLAP • SNAC • TLV |
| UUIDs • Errors • Tool IDs |
| Host Interaction |
| Rate Limits • Migration • Messages |
| Other Services |
| ADMIN • ADVERT • ALERT |
| BART • BOS • BUCP • CHAT |
| CHAT_NAV |
| Tutorials |
| Sign On • BART • Rendezvous |
| ICBM • Locate • Buddies |
| Foodgroups |
| OSERVICE (0x0001) |
| LOCATE (0x0002) |
| BUDDY (0x0003) |
| ICBM (0x0004) |
| ADVERT (0x0005) |
| INVITE (0x0006) |
| ADMIN (0x0007) |
| POPUP (0x0008) |
| PD (0x0009) |
| USER_LOOKUP (0x000A) |
| STATS (0x000B) |
| TRANSLATE (0x000C) |
| 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 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 |
| FLAP__LENGTH | uint16 (word) | Length of data, does not include the 6 byte header length |
Class: FLAP__FRAME
There are several different frame types, with the most common being the DATA frame.
| Name | Value | Notes |
|---|---|---|
| FLAP__FRAME_SIGNON | 0x01 | Initialize the FLAP connection |
| FLAP__FRAME_DATA | 0x02 | Messages using the FLAP connection, usually a SNAC message |
| FLAP__FRAME_ERROR | 0x03 | A FLAP error - rare |
| FLAP__FRAME_SIGNOFF | 0x04 | Close down the FLAP connection gracefully |
| FLAP__FRAME_KEEP_ALIVE | 0x05 | Send a heartbeat to server to help keep connection open |
FLAP__FRAME_SIGNON
On connection, the server and client each send a FLAP SIGNON frame to initialize the connection. The sequence number field should be initialized with a random value. The data portion of the frame contains a 4 byte version number, currently always 1, followed by any TLVs that are required.
| Name | Type | Notes |
|---|---|---|
| header | FLAP Header | FLAP header, type will be FLAP__FRAME_SIGNON |
| flapVersion | uint32 (dword) | Always 1 |
| tlvs | Array of TLV length payloadLength-4 | [Class: FLAP__SIGNON_TAGS] TLVs |
Example in hex: 2a011234000400000001
FLAP__FRAME_DATA
A data frame will always just contain a single SNAC.
| Name | Type | Notes |
|---|---|---|
| header | FLAP Header | FLAP header, type will be FLAP__FRAME_KEEP_DATA |
| snacHeader | SNAC Header | SNAC header |
| snac | blob | snac described by the SNAC header |
FLAP__FRAME_ERROR
| Name | Type | Notes |
|---|---|---|
| header | FLAP Header | FLAP header, type will be FLAP__FRAME_ERROR |
FLAP__FRAME_SIGNOFF
This FLAP frame type is sent both to the client and server.
- Sent to the client to tell it that it is getting bumped off gracefully. The client should NOT try to auto reconnect if it receives one of these messages.
- Sent to the server by the client to tell it that it is going away gracefully.
| Name | Type | Notes |
|---|---|---|
| header | FLAP Header | FLAP header, type will be FLAP__FRAME_SIGNOFF |
FLAP__FRAME_KEEP_ALIVE
Many modern operating systems and networks come with firewalls and packet inspectors to protect the user. Unfortunately, these services and devices have proven to be buggy with long lived connections. We recommend that a client sends a FLAP KEEP_ALIVE packet to the server every minute after the connection has gone idle to help keep the connection alive. Please do not send it more often then once a minute or when the connection is not idle. There is no response to this message and a client will never receive a KEEP_ALIVE packet from the server.
| Name | Type | Notes |
|---|---|---|
| header | FLAP Header | FLAP header, type will be FLAP__FRAME_KEEP_ALIVE |