OSCAR IM Protocols(Open System for CommunicAtion in Realtime)

In order to write an IM client, you have to learn a little about the protocol IM clients use to communicate. There areactually several protocols involved. The standard AIM client and other clients that AOL blesses (like Apple's iChat),use a protocol named OSCAR (Open System for CommunicAtion in Realtime). Unfortunately, OSCAR's name isinaccurate. There is nothing “open” about it! OSCAR is a proprietary protocol that AOL guards jealously. Those who write IM clients using OSCAR have to modify them regularly to cope with changes AOL introduces mainly so that non-standard clients stop working. After some complaining, AOL introduced a non-proprietary protocol that
can be used to write IM clients. This protocol is named TOC (Talk to OSCAR?). You will be using TOC.

TOC is a text-based protocol. All it requires is sending and processing text commands similar to those used in protocols like POP and SMTP. Much like POP and SMTP packets, each packet you send to a TOC server will begin with a code that indicates the type of the message being sent. We will begin by giving an overview of the types of packets your program will exchange with the TOC server. Then, we will discuss the details of the format of the contents of these packets.

Your program’s interaction with AOL’s TOC server will begin with the transmission of a “toc2_signon” packet that contains both the user’s screen name and password. If AOL accepts this packet, the TOC server will respond by sending a packet that starts with the prefix “SIGNON”. If the screen name or password are invalid, the TOC server will respond with a packet that starts with “ERROR”. One additional packet is required to complete the login process.
If your program receives a “SIGNON” message from the server it must send a “toc_init_done” message in response. Once your program has completed the login process, it can transmit messages to the user’s buddies by sending “toc2_send_im” packets. Each such packet will contain the body of a message and the screen name of the intended recipient. Unlike POP and SMTP servers, a TOC server will not respond to each such message with a packet indicating success or failure. If the message is rejected, the server may send an ERROR packet, but if it is accepted the server will not send any response.

When another user sends an IM message to the person using your program, the TOC server will send your program an “IM_IN2” packet containing the message and the sender’s screen name. While you are connected, the TOC server will also send you a variety of other messages. In particular, whenever someone included in the user’s buddy list goes offline, come online, puts up an away message, etc. your program will receive an “UPDATE_BUDDY2” message.

Finally, there is no special “QUIT” message that must be sent to terminate the connection. Instead, when the user of your program presses the logout button your program will simply close its connection to the server.

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Karpagarajan. R
Necessity is the mother of invention