Yahoo! Messenger Protocol Tutorial - Part 7

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Yahoo! Protocol: Part 7 - Yahoo! Packet Structure

 

All Yahoo! communications use TCP over IP communication and the Yahoo! data resides in the data field of the TCP packet as shown in Figure 13.

 

Figure 13 - Yahoo! Messenger Packet

 

Yahoo! extends the common TCP/IP convention of using headers by creating its own application level header format. A Yahoo! header is 20 bytes long and is identified by the first 4 bytes being âYMSG.â The Yahoo! header also includes the YMSG version, message length, service type, status, and session ID. Figure 14 shows a graphical representation of the Yahoo! header and data.

 

Figure 14 - Yahoo! Messenger Generic Header

 

The data portion of a Yahoo! packet also has a structure. Immediately following the session ID, the data starts in the form of FIELD ID, FIELD SEPERATOR, FIELD DATA, FIELD SEPERATOR, â¦, FIELD SEPERATOR. The field ID is represented as an ASCII integer that may consist of several characters. The Yahoo! field separator is the hexadecimal sequence of C0 80. Figure 15 shows a typical Yahoo! data field structure.

 

Figure 15 - Yahoo! Data Field Structure

 

Throughout this paper a short hand representation of a Yahoo! packet will be used as shown in Figure 16. The top of the figure contains the service type reference and the top right header shows the direction of communication. A quick reference for the field ID, service type, and status can be found in Appendix A.

 

Figure 16 - Yahoo! Packet Reference

 

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Edited February 6, 2009 by tansqrx (see edit history)