The UDP packet sent from the client to the server has the following general
layout:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes 02 00 VERSION Identifies the packet as an ICQ packet
2 bytes xx xx COMMAND Code for service the server should provide
2 bytes xx xx SEQ_NUM Sequence number
4 bytes xx xx xx xx UIN The senders UIN
variable PARAMETERS 0 or more parameters (depending on COMMAND)
The UDP packet sent from the server to the client has the following general
layout:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes 02 00 VERSION Identifies the packet as an ICQ packet
2 bytes xx xx COMMAND Code for service the server should provide
2 bytes xx xx SEQ_NUM Sequence number
variable PARAMETERS 0 or more parameters (depending on COMMAND)
The VERSION field is present on all ICQ packets, and identifies the packet
as a ICQ message. The SEQ_NUM contains a sequence number for the packet. All
packets must have a unique sequence number (unless it is a retransmission).
This is used to avoid confusion if a UDP packet is lost or duplicated (as
may happen). Normally, the SEQ_NUM of the current packet is + 1. Note that the server and the client has separate
numbering, so that SEQ_NUM = 3 of a packet sent from the server is different
from SEQ_NUM = 3 of a packet sent from the client. Note also that the server
start counting on 00 00, and the client start counting on 01 00.
The following commands are available for the client to send to the server:
Code Name Description
---- ---- -----------
0A 00 ACK Acknowledgement
0E 01 SEND_MESSAGE Send message through server (to offline user)
E8 03 LOGIN Login on server
06 04 CONTACT_LIST Inform the server of my contact list
1A 04 SEARCH_UIN Search for user using his/her UIN
24 04 SEARCH_USER Search for user using his/her name or e-mail
2E 04 KEEP_ALIVE Sent to indicate connection is still up
38 04 SEND_TEXT_CODE Send special message to server as text
4C 04 LOGIN_1 Sent during login
60 04 INFO_REQ Request basic information about a user
6A 04 EXT_INFO_REQ Request extended information about a user
9C 04 CHANGE_PASSWORD Change the user's password
D8 04 STATUS_CHANGE User has changed online status (Away etc)
28 05 LOGIN_2 Sent during login
Not yet described in detail (v0.1 of this document)
0A 05 UPDATE_INFO Update my basic information
B0 04 UPDATE_EXT_INFO Update my extended information
3C 05 ADD_TO_LIST Add user to my contact list
56 04 REQ_ADD_TO_LIST Request authorization to add to contact list
BA 04 QUERY_SERVERS Query the server about address to other servers
C4 04 QUERY_ADDONS Query the server about globally defined add-ons
EC 04 NEW_USER_1 Ask for permission to add a new user
FC 03 NEW_USER_REG Register a new user
A6 04 NEW_USER_INFO Send basic information about a new user
42 04 CMD_X1 *Unknown
56 04 MSG_TO_NEW_USER Send a message to a user not on my contact list
(this one is also used to request permission to add someone with 'authorize'
status to your contact list)
The following commands can be sent from the server to the client, either as
a response to a client command, or to notify the client of some event.
Code Name Description
---- ---- -----------
0A 00 ACK Acknowledgement
5A 00 LOGIN_REPLY Login reply
6E 00 USER_ONLINE User on contact list is online/has changed online status
78 00 USER_OFFLINE User on contact list has gone offline
8C 00 USER_FOUND User record found matching search criteria
DC 00 RECEIVE_MESSAGE Message sent while offline/through server
A0 00 END_OF_SEARCH No more USER_FOUND will be sent
18 01 INFO_REPLY Return basic information about a user
22 01 EXT_INFO_REPLY Return extended information about a user
A4 01 STATUS_UPDATE User on contact list has changed online status (Away etc)
Not yet described in detail (v0.1 of this document)
1C 02 REPLY_X1 *Unknown (returned during login)
E6 00 REPLY_X2 *Unknown (confirm my UIN?)
E0 01 UPDATE_REPLY Confirmation of basic information update
C8 00 UPDATE_EXT_REPLY Confirmation of extended information update
46 00 NEW_USER_UIN Confirmation of creation of new user and newly assigned UIN
B4 00 NEW_USER_REPLY Confirmation of new user basic information
82 00 QUERY_REPLY Response to QUERY_SEVERS or QUERY_ADDONS
C2 01 SYSTEM_MESSAGE System message with URL'ed button
The UDP messages will now be examined in closer detail.
MESSAGES SENT BY THE CLIENT
===========================
ACK (0A 00) Acknowledgement
---
Parameters: None
NOTE! Unlike all other commands, in ACK the field SEQ_NUM contains the
sequence number of the *server's* packet the client wishes to acknowledge.
Note further that an ACK should *not* be acknowledged!
SEND_MESSAGE (0E 01) Send message through server (to offline user)
------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
4 bytes xx xx xx xx RECEIVER_UIN UIN of the user the message is sent to
2 bytes (see below) MESSAGE_TYPE Type of message being sent
2 bytes xx xx LENGTH Length of MESSAGE including NULL
variable MESSAGE The message, ended by a NULL (00)
MESSAGE_TYPE can be one of the following:
01 00 - the message is a normal message
04 00 - the message is an URL, and actually consists of two parts,
separated by the code FE.
The first part is the description of the URL, and the second part is the
actual URL.
LOGIN (E8 03) Login on server
-----
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
4 bytes xx xx xx xx PORT The TCP port to use for incoming connections
2 bytes xx xx LENGTH Length of PASSWORD including NULL
variable PASSWORD The user's password + NULL (max 8 chars)
4 bytes 78 00 00 00 X1 *Unknown
4 bytes xx xx xx xx USER_IP The user's IP address
1 byte 04 X2 *Unknown
4 bytes xx xx xx xx STATUS Users online status (normally 00 00 00 00)
4 bytes 02 00 00 00 X3 *Unknown
2 bytes xx xx LOGIN_SEQ_NUM Login sequence number
4 bytes 00 00 00 00 X4 *Unknown
4 bytes 08 00 78 00 X5 *Unknown
CONTACT_LIST (06 04) Inform the server of my contact list
------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx NUM_CONTACTS Number of contacts following
{4 bytes xx xx xx xx UIN UIN of user on contact list }
The last field is repeated for as many users as NUM_CONTACTS indicate.
The server will send online/offline notification to client only of users
registered using CONTACT_LIST.
SEARCH_UIN (1A 04) Search for user using his/her UIN
----------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx SEARCH_SEQ_NUM Search sequence number
4 bytes xx xx xx xx SEARCHED_UIN The UIN to search for
The SEARCH_SEQ_NUM should be a unique number, to distinguish from other
searches. The reply from the server will contain the SEARCH_SEQ_NUM of the
search, to facitilate matching query and answer.
SEARCH_USER (24 04) Search for user using his/her name or e-mail
-----------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx SEARCH_SEQ_NUM Search sequence number
2 bytes xx xx LENGTH Length of NICK_NAME including NULL
variable NICK_NAME Nick name to search for, NULL terminated
2 bytes xx xx LENGTH Length of FIRST_NAME including NULL
variable FIRST_NAME First name to search for, NULL terminated
2 bytes xx xx LENGTH Length of LAST_NAME including NULL
variable LAST_NAME Nick name to search for, NULL terminated
2 bytes xx xx LENGTH Length of E_MAIL including NULL
variable E_MAIL E-mail to search for, NULL terminated
Note that search fields (NICK_NAME, FIRST_NAME, LAST_NAME, E_MAIL) may be
empty, but not all at the same time, i.e. at least one field must contain
data. Note also that you may only search either on E_MAIL (in which the
other fields must be empty), or on name (in which E_MAIL must be empty, and
one or more of the other fields must contain data).
KEEP_ALIVE (2E 04) Sent to indicate connection is still up
----------
Parameters: None
This command should be sent at regular intervals (normally every 2 minutes,
or 120 seconds) from the client to the server.
SEND_TEXT_CODE (38 04) Send special message to server as text
--------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx LENGTH Length of TEXT_CODE including NULL
variable TEXT_CODE Message to send to server, NULL terminated
2 bytes xx xx X1 *Unknown (code, usually 04 00 or 05 00)
The TEXT_CODE can contain for instance:
"B_USER_DISCONNECTED" (in which case the X1 field should containt 05 00) if
the user has disconnected.
"B_MESSAGE_ACK" (in which case the X1 field should containt 05 00) if the
client has problem connecting to the server. This is a request for the
server to answer immediately to the client.
LOGIN_1 (4C 04) Sent during login
-------
Parameters: None
This is sent during login. The exact purpose of this command is *Unknown.
INFO_REQ (60 04) Request basic information about a user
--------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx INFO_SEQ_NUM Information sequential number
4 bytes xx xx xx xx QUERY_UIN UIN of user to request information about
The server will respond with a INFO_REPLY, with the same INFO_SEQ_NUM.
EXT_INFO_REQ (6A 04) Request extended information about a user
------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx INFO_SEQ_NUM Information sequential number
4 bytes xx xx xx xx QUERY_UIN UIN of user to request information about
The server will respond with a EXT_INFO_REPLY, with the same INFO_SEQ_NUM.
CHANGE_PASSWORD (9C 04) Change the user's password
---------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx PASSWORD_SEQ_NUM Password changing sequential number
2 bytes xx xx LENGTH Length of NEW_PASSWORD including NULL
variable NEW_PASSWORD The new password, NULL terminated (max 8 chars)
STATUS_CHANGE (D8 04) User has changed online status (Away etc)
-------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
4 bytes (see below) STATUS User's online status (Away etc)
The STATUS may take four different values:
00 00 00 00 = Online/connected
01 00 00 00 = Away
11 00 00 00 = Do Not Disturb (DND)
00 01 00 00 = Invisible
LOGIN_2 (28 05) Sent during login
-------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
1 byte 00 X1 *Unknown
MESSAGES SENT BY THE SERVER
===========================
ACK (0A 00) Acknowledgement
---
Parameters: None
NOTE! Unlike all other commands, in ACK the field SEQ_NUM contains the
sequence number of the *client's* packet the server acknowledges. Note
further that an ACK should *not* be acknowledged!
LOGIN_REPLY (5A 00) Login reply
-----------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
4 bytes xx xx xx xx USER_UIN The user's UIN
4 bytes xx xx xx xx USER_IP The user's IP address
2 bytes xx xx LOGIN_SEQ_NUM Login sequence number
4 bytes 01 00 01 00 X1 *Unknown
4 bytes xx 00 16 00 X2 *Unknown (xx=19 or 18)
4 bytes 8C 00 00 00 X3 *Unknown
4 bytes 78 00 05 00 X4 *Unknown
6 bytes 0A 00 05 00 01 00 X5 *Unknown
This is sent from the server upon receipt of a LOGIN. The LOGIN_SEQ_NUM is
the same as in the corresponding LOGIN.
USER_ONLINE (6E 00) User on contact list is online/has changed online status
-----------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
4 bytes xx xx xx xx REMOTE_UIN The UIN of the user who has logged in
4 bytes xx xx xx xx REMOTE_IP The IP address of the user
4 bytes xx xx xx xx REMOTE_PORT The TCP port of the user
4 bytes xx xx xx xx REMOTE_REAL_IP The actual IP address of the user
1 byte 04 X1 *Unknown
4 bytes xx xx xx xx STATUS New status of the user
4 bytes 02 00 00 00 X2 *Unkown
The REMOTE_IP is the "outer" IP address of the remote user, the
REMOTE_REAL_IP is the "inner" IP address. These two will be identical unless
the remote user is behind a firewall. The REMOTE_IP is the "official" IP
address, as shown e.g. by the Info box in the client. The REMOTE_PORT is the
TCP port number to use when the client wishes to open a direct connection
to the remote user.
USER_OFFLINE (78 00) User on contact list has gone offline
------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
4 bytes xx xx xx xx REMOTE_UIN The UIN of the user who has logged out
USER_FOUND (8C 00) User record found matching search criteria
----------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx SEARCH_SEQ_NUM Search sequence number
4 bytes xx xx xx xx FOUND_UIN Found user's UIN
2 bytes xx xx LENGTH Length of NICK_NAME including NULL
variable NICK_NAME Found user's nick name, NULL terminated
2 bytes xx xx LENGTH Length of FIRST_NAME including NULL
variable FIRST_NAME Found user's first name, NULL terminated
2 bytes xx xx LENGTH Length of LAST_NAME including NULL
variable LAST_NAME Found user's last name, NULL terminated
2 bytes xx xx LENGTH Length of E_MAIL including NULL
variable E_MAIL Found user's e-mail, NULL terminated
1 byte xx AUTHORIZE User's authorization status
For each user found matching the criterion, a USER_FOUND will be returned.
When all USER_FOUND's have been sent, the server will send an END_OF_SEARCH.
If no users where found matching the criterion, an END_OF_SEARCH will be
sent immediately, and no USER_FOUND will be sent. The AUTHORIZE determine
wether the user allow anyone to include him/her on their contact list, or
wether the user must accept first. Possible values of AUTHORIZE:
00 = The user must authorize the client to include him/her on the client's
contact list
01 = The user allows anyone to include him/her on their contact list
RECEIVE_MESSAGE (DC 00) Message sent while offline/through server
---------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
4 bytes xx xx xx xx REMOTE_UIN The sending user's UIN
2 bytes xx xx YEAR The year the message was sent
1 byte xx MONTH The month the message was sent
1 byte xx DAY The day of the month the message was sent
1 byte xx HOUR The hour the message was sent in GMT
1 byte xx MINUTE The minute the message was sent
2 bytes xx xx TYPE The type of message (message, URL, etc)
2 bytes xx xx LENGTH Length of MESSAGE including NULL
variable MESSAGE The message sent, NULL terminated
Note that the HOUR contains the local time - 1 (unless GMT is involved
somehow?). The TYPE identifies the type of message this is:
01 00 = Normal message
04 00 = URL (MESSAGE contains first the description, then a FE, and then
the actual URL)
0C 00 = 'You were added' message. (MESSAGE contains: FE FE FE FE . The is '1' (31) if the user allows anyone to add him/her to their
contact list, and '0' (30) otherwise.)
END_OF_SEARCH (A0 00) No more USER_FOUND will be sent
-------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx SEARCH_SEQ_NUM Search sequence number
1 byte xx MORE_FOUND More users found but not displayed?
If MORE_FOUND is 00, then the returned USER_FOUND's contain information
about all matching users. If MORE_FOUND is 01 however, then the server has
found more users matching, but will not display more matches. The limit is
drawn by 40 users. If a search request results in more than 40 matches,
only the 40 first will be sent to the client, and MORE_FOUND will be set to
01.
INFO_REPLY (18 01) Return basic information about a user
----------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx INFO_SEQ_NUM Information sequence number
4 bytes xx xx xx xx REMOTE_UIN The remote user's UIN
2 bytes xx xx LENGTH Lenght of NICK_NAME including NULL
variable NICK_NAME The remote user's nick name
2 bytes xx xx LENGTH Lenght of FIRST_NAME including NULL
variable FIRST_NAME The remote user's first name
2 bytes xx xx LENGTH Lenght of LAST_NAME including NULL
variable LAST_NAME The remote user's last name
2 bytes xx xx LENGTH Lenght of E_MAIL including NULL
variable E_MAIL The remote user's e-mail
1 byte xx AUTHORIZE User's authorization status
Note that the parameters are identical to command USER_FOUND (8C 00). For
more information about the fields, see USER_FOUND.
EXT_INFO_REPLY (22 01) Return extended information about a user
--------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx INFO_SEQ_NUM Information sequence number
4 bytes xx xx xx xx REMOTE_UIN The remote user's UIN
2 bytes xx xx LENGTH Lenght of CITY including NULL
variable CITY The remote user's city
2 bytes xx xx COUNTRY_CODE The remote user's country code
1 byte xx COUNTRY_STATUS Indicates if COUNTRY_CODE is entered or not
2 bytes xx xx LENGTH Lenght of STATE including NULL
variable STATE The remote user's state (USA only)
2 bytes xx xx AGE The remote user's age
1 byte xx SEX The remote user's sex
2 bytes xx xx LENGTH Lenght of PHONE including NULL
variable PHONE The remote user's city
2 bytes xx xx LENGTH Lenght of HOME_PAGE including NULL
variable HOME_PAGE The remote user's city
2 bytes xx xx LENGTH Lenght of ABOUT including NULL
variable ABOUT The remote user's city
The code used in COUNTRY_CODE is the international telephone prefix, e.g.
01 00 (1) for the USA, 2C 00 (44) for the UK, 2E 00 (46) for Sweden, etc.
COUNTRY_STATUS is normally FE, unless the remote user has not entered a
country, in which casse COUNTRY_CODE will be FF FF, and COUNTRY_STATUS will
be 9C. The field AGE has the value FF FF if the user has not entered his/her
age. The field SEX has three (!) possible values:
00 = Not specified
01 = Female
02 = Male
The ABOUT field is an optional free form field that allows the user to make
a personal presentation of himself/herself.
STATUS_UPDATE (A4 01) User on contact list has changed online status (Away etc)
-------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
4 bytes xx xx xx xx REMOTE_UIN UIN of the user whos status has changed
4 bytes xx xx xx xx STATUS The new online status of the user
The online status in STATUS is the same as used in STATUS_CHANGE (D8 04).
See STATUS_CHANGE for details.
COMMUNICATION BETWEEN TWO CLIENTS USING TCP (Peer to peer mode)
===============================================================
When a user wishes to send a message, an URL etc, to another user (called
the "remote" user as opposite to the "local" user), the local user first
checks to see if a TCP connection already is established to that user. If
so is the case, then that connection will be used. If not, the user checks
the remote users IP address and port number (information sent to the user
from the server when the remote user logged in), and makes a connection to
that address. Typical port numbers are in the range 1200-1300 (decimal).
When a new connection is formed, a CHANNEL_INIT message must be sent. From
there on, however, every time the user wishes to send a message, a
CHANNEL_MESSAGE is sent. All messages sent must be acknowledged by the other
side, using CHANNEL_ACK. Furthermore, all messages is replied to by another
message from the receiver - which most often is empty, unless the user has
posted a Away/DND message, in case this will be sent as a reply.
The TCP communication is similar to the UDP communication, in that all
communication is done trough separate packets (often, but now always
associated with individual TCP packets). Each packet must contain the
packet's length (excluding the length count) as the first two bytes. Most
messages contains the senders UIN as the next field.
CHANNEL_INIT Initiate inter-user communication using TCP
------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes 1A 00 LENGTH Length of this packet
1 byte FF INIT_IDENT Identifies this packet as an initiation
4 bytes 02 00 00 00 X1 *Unknown
4 bytes 00 00 00 00 X2 *Unknown
4 bytes xx xx xx xx MY_UIN The local user's UIN
4 bytes xx xx xx xx MY_IP The user's IP address
4 bytes xx xx xx xx MY_IP_REAL The user's actual IP address
1 byte 04 X3 *Unknown
4 bytes xx xx xx xx MY_PORT The user's TCP port for incoming messages
Note that the port used for the "outgoing" connection is different from
MY_PORT, the port other clients use to connect to this client. For the
difference between MY_IP and MY_IP_REAL, see USER_ONLINE.
CHANNEL_MESSAGE Send message to online user
------------
Parameters:
Length Content (if fixed) Name Description
------ ------------------ ---- -----------
2 bytes xx xx LENGTH Length of this packet
4 bytes xx xx xx xx UIN The local user's UIN
2 bytes 02 00 VERSION Identifies this as a ICQ packet
2 bytes EE 07 MSG_COMMAND The message type for CHANNEL_MESSAGE
2 bytes 00 00 X1 *Unknown
4 bytes xx xx xx xx UIN_2 The local user's UIN
2 bytes xx xx TYPE Message type
2 bytes xx xx LENGTH Length of MESSAGE including NULL
variable MESSAGE The message to be sent, NULL terminated
4 bytes xx xx xx xx MY_IP_REAL The user's actual IP address
4 bytes xx xx xx xx MY_IP The user's IP address
4 bytes xx xx xx xx PORT The user's TCP port for incoming messages
1 byte 04 X2 *Unknown
2 bytes 00 00 X3 *Unknown
2 bytes xx xx CMD_TYPE Identifies message as new message or reply
4 bytes xx xx xx xx X4 *Unknown (checksum? sequence number?)
The TYPE is the same as described in RECEIVE_MESSAGE. The difference between
MY_IP and MY_IP_REAL is described in USER_ONLINE. The CMD_TYPE can have two
possible values:
10 00 = This is a new ('real', user initiated) message
00 00 = This is an auto reply
The auto reply is sent as an acknowledgement to all 'real' messages. They
usually contains an empty message, but if the remote user is 'Away' or in
DND mode, the reply will contain the Away/DND message. The X4 field is a
bit tricky. It is always between 00 FF FF FF and FF FF FF FF, but the exact
function of the field is unknown.
.