Protocols/OSCAR/Rate Limits

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)

To protect the server and other users from abusive clients, the server implements SNAC rate limiting. Rate limiting is done with a simple formula that calculates the average time between SNACs over the last few SNACs sent from the client to the server.

A client can optionally subscribe to notifications about its rates so that it can warn the user ahead of time or show UI about the rates. Even if the client does not subscribe, it will receive notifications when the rate limit has been reached and the server has started dropping SNACs. If the client continues to send SNACs, it will eventually be disconnected.

All SNACs are assigned to a Rate Class which controls the parameters to the rate limit forumla. Most SNACs are in the most lenient rate class by default, with SNACs like IM sending being in more strict classes. The rate formula is currentAvg = ((currentAvg * (windowSize -1)) + delta)/windowSize.

The currentAvg falling below certain thresholds causes the server to warn the client that it is about to be rate limited or disconnected. Once a client is rate limited, its average has to fall above the clear threshold before it can start sending SNACs again.

The actual parameters for the formula are not published in this document since they can change from time to time and are different depending on the current warning level and other things. A client can average around one IM every two seconds without being rate limited.

Client sends OSERVICE__RATE_PARAMS_QUERY

Server responds OSERVICE__RATE_PARAMS_REPLY

Client can send OSERVICE__RATE_ADD_PARAM_SUB to subscribe to specific rate changes.

Client can send OSERVICE__RATE_DEL_PARAM_SUB to unsubscribe to specific rate changes.

Server sends OSERVICE__RATE_PARAM_CHANGE when changes occur to any subscribed rate classes.

Datatype: Rate Parameters

Describes the rate parameters for a single rate class.

Name	Type	Notes
classId	uint16 (word)	Rate class being described
windowSize	uint32 (dword)	Number of events to count
clearThreshold	uint32 (dword)	Once rate limited the average has to reach this value in order to clear
alertThreshold	uint32 (dword)	Server will tell the client it is getting close to the limit
limitThreshold	uint32 (dword)	SNACs will be dropped below this value
disconnectThreshold	uint32 (dword)	Server will disconnect below this value
currentAverage	uint32 (dword)	Current value for the class; higher is better
maxAverage	uint32 (dword)	The maximum rate value; if the current value rises about this value it should be reset
lastArrivalDelta	uint32 (dword)	Last message was received this long ago
droppingSNACs	uint8 (byte)	Is the server dropping SNACs for this rate class

Datatype: Rate Class Members

Describes all the SNACs in a single rate class.

Name	Type	Notes
id	uint16 (word)	Rate class being described
numMembers	uint16 (word)	Number of SNACs in this rate class
snacIds	Array of SNAC__ID length numMembers	SNACs in this rate class

Class: OSERVICE__RATE_CODE

These are the codes used in OSERVICE__RATE_PARAM_CHANGE to describe the state of the rate class.

Name	Value	Notes
OSERVICE__RATE_CODE_CHANGE	0x01	Rate parameters have changed
OSERVICE__RATE_CODE_WARNING	0x02	Rate limit warning reached; if client does not slow down LIMIT state will be hit
OSERVICE__RATE_CODE_LIMIT	0x03	Rate limit reached; if client does not slow down client will be disconnected
OSERVICE__RATE_CODE_CLEAR	0x04	Rate limit cleared; client can send SNACs normally now