Yahoo Messenger Protocol v 9
----------------------------

The Yahoo Messenger Protocol is an application layer protocol running most
of the time over TCP, but in some cases over HTTP as well.  Throughout
this document, we will speak about the YMSG packets, after stripping out
any other protocol data, but will mention this other data if it is of
relevance.

This document is incomplete.  For anything not mentioned here, refer to the
source of libyahoo2.


1. The YMSG packet structure

The YMSG packet structure is as follows:

(each byte is represented by 5 spaces in the following diagram,
including the | at the end)
注：每个字节有5位
     <------- 4B -------><------- 4B -------><---2B--->
    +-------------------+-------------------+---------+
    |   Y   M   S   G   |      version      | pkt_len |
    +---------+---------+---------+---------+---------+
    | service |      status       |    session_id     |
    +---------+-------------------+-------------------+
    |                                                 |
    :                    D A T A                      :
    |                   0 - 65535*                    |
    +-------------------------------------------------+
    

* 65535 is the theoretical limit, since the length field is two bytes
long.  Practically though, the data section does not exceed about 1000
bytes.
注：65535是理论限制，因为长度域是2个字节长。（这个长度域应该是指pkt_len，2个字节，总共10位，不明白怎么得出65535。）
All numeric fields are stored in network byte order.  i.e. Most
significant byte first.

YMSG    - The first four bytes of all packets are always YMSG - the
          protocol name.

version - The next four bytes are for the protocol version number.
          For version 9, these are 0x09 0x00 0x00 0x00
          NOTE: The last three bytes of this may just be padding bytes.

pkt_len - A two byte value, in network byte order, stating how many bytes
          are in the _data_ section of the packet.  In practice, this
          value does not exceed about 1000.

service - This is an opcode that tells the client/server what kind of
          service is requested/being responded to.  There are 45 known
          services.  See the services section of this document for a
          full listing.

status  - In case of a response from the server, indicates the status
          of the request (success/failure/etc.).  For a request, it is 0
          in most cases, except for packets that set the user's status
          (set status, typing notify, etc.)

session - The session id is used primarily when connecting through a HTTP
id        proxy.  It is set in all cases, but has no effect in a direct
          connection.  When the client sends the first packet, it is 0,
          the server responds with a session id that is used by the client
          and the server in all further packets.  The server may change
          the session id, in which case the client must use the new
          session id henceforth.

DATA    - The data section is pkt_len bytes long and consists of a series
          of key/value pairs.  All keys are numeric strings.  The packet
          contains their numeric values in the ASCII character set.  e.g.
          1 == 0x31, 21 == 0x32 0x31

          The maximum number of digits in a key is unknown, although keys
          of up to three digits have been seen.

          Every key and value is terminated by a two byte sequence of
          0xc0 0x80.  Some keys may have empty values.

          The actual keys sent, and their meanings depend on the service
          in use.

          e.g. The packet data to send an instant message looks like this:

          0x30 0xc080 yahoo_id 0xc080 0x31 0xc080 active_id 0xc080 0x35
          0xc080 recipient_id 0xc080 0x3134 0xc080 message_text 0xc080

          The 0xc080 byte sequence is a separator.  The values 0x30, 0x31,
          0x35 and 0x3134 are the keys.  Convert them to their ASCII
          equivalents and you get 0, 1, 5, 14  (0x3134 == 0x31 0x34)


2. Services

There are 45 known services at the moment, although more may exist.  All
known services are listed below along with the hex values that they
correspond to.  Any service without a hex value is one more than the
previous value.  i.e. YAHOO_SERVICE_LOGOFF=0x02 and
YAHOO_SERVICE_ISBACK=0x04.

        YAHOO_SERVICE_LOGON            = 0x01
        YAHOO_SERVICE_LOGOFF
        YAHOO_SERVICE_ISAWAY
        YAHOO_SERVICE_ISBACK
        YAHOO_SERVICE_IDLE             = 0x05
        YAHOO_SERVICE_MESSAGE
        YAHOO_SERVICE_IDACT
        YAHOO_SERVICE_IDDEACT
        YAHOO_SERVICE_MAILSTAT
        YAHOO_SERVICE_USERSTAT         = 0x0a
        YAHOO_SERVICE_NEWMAIL
        YAHOO_SERVICE_CHATINVITE
        YAHOO_SERVICE_CALENDAR
        YAHOO_SERVICE_NEWPERSONALMAIL
        YAHOO_SERVICE_NEWCONTACT       = 0x0f
        YAHOO_SERVICE_ADDIDENT         = 0x10
        YAHOO_SERVICE_ADDIGNORE
        YAHOO_SERVICE_PING
        YAHOO_SERVICE_GROUPRENAME
        YAHOO_SERVICE_SYSMESSAGE       = 0x14
        YAHOO_SERVICE_PASSTHROUGH2     = 0x16
        YAHOO_SERVICE_CONFINVITE       = 0x18
        YAHOO_SERVICE_CONFLOGON
        YAHOO_SERVICE_CONFDECLINE      = 0x1a
        YAHOO_SERVICE_CONFLOGOFF
        YAHOO_SERVICE_CONFADDINVITE
        YAHOO_SERVICE_CONFMSG
        YAHOO_SERVICE_CHATLOGON
        YAHOO_SERVICE_CHATLOGOFF       = 0x1f
        YAHOO_SERVICE_CHATMSG          = 0x20
        YAHOO_SERVICE_GAMELOGON        = 0x28
        YAHOO_SERVICE_GAMELOGOFF
        YAHOO_SERVICE_GAMEMSG          = 0x2a
        YAHOO_SERVICE_FILETRANSFER     = 0x46
        YAHOO_SERVICE_VOICECHAT        = 0x4a
        YAHOO_SERVICE_NOTIFY           = 0x4b
        YAHOO_SERVICE_P2PFILEXFER      = 0x4d
        YAHOO_SERVICE_PEERTOPEER       = 0x4f
        YAHOO_SERVICE_AUTHRESP         = 0x54
        YAHOO_SERVICE_LIST             = 0x55
        YAHOO_SERVICE_AUTH             = 0x57
        YAHOO_SERVICE_ADDBUDDY         = 0x83
        YAHOO_SERVICE_REMBUDDY         = 0x84
        YAHOO_SERVICE_IGNORECONTACT    = 0x85
        YAHOO_SERVICE_REJECTCONTACT    = 0x86

Most of the service codes should be self explanatory.  Those that aren't
are listed here:

IDACT/IDDEACT - activate/deactivate an identity
NOTIFY        - typing/game notification
FILETRASNFER  - transfer a file using the yahoo filetransfer server as an
                intermediate
P2PFILEXFER   - transfer a file between two peers, yahoo server not used
PEERTOPEER    - check if peer to peer connections are possible
AUTH          - Send initial login packet (username), response contains
                challenge string
AUTHRESP      - Send response to challenge string, or, if received from
                server, contains reason for login failure
LOGON/LOGOFF  - a buddy logged in/out


3. Status codes

The status code is a four byte value.  Most status codes are two bytes
long.  The status codes (in decimal except for offline and typing) are:

        YAHOO_STATUS_AVAILABLE    = 0
        YAHOO_STATUS_BRB
        YAHOO_STATUS_BUSY
        YAHOO_STATUS_NOTATHOME
        YAHOO_STATUS_NOTATDESK
        YAHOO_STATUS_NOTINOFFICE  = 5
        YAHOO_STATUS_ONPHONE
        YAHOO_STATUS_ONVACATION
        YAHOO_STATUS_OUTTOLUNCH
        YAHOO_STATUS_STEPPEDOUT   = 9
        YAHOO_STATUS_INVISIBLE    = 12
        YAHOO_STATUS_CUSTOM       = 99
        YAHOO_STATUS_IDLE         = 999
        YAHOO_STATUS_OFFLINE      = 0x5a55aa56
        YAHOO_STATUS_TYPING       = 0x16

You may choose either AVAILABLE or INVISIBLE as your initial login status. 
TYPING is used only when sending a TYPING notification packet.


4. Session states

A Yahoo session has two states, Authentication and Messaging.

4.1. Authentication

The session starts in the authentication state.  The client sends the username
to the server.  The server responds with a challenge string.  The client
responds to this challenge with two response strings.  If authentication is
successful, the connection goes into the messaging state, else, an error
response is sent back.

4.2. Messaging state

After successful authentication, the session goes into the messaging state.
The server sends the buddy list, ignore list, identity list and a list of
cookies to the client.  These might all be sent in a single packet.  It then
sends the list of online buddies along with their status codes.  All this is
sent without the client requesting anything.

At this time, any offline messages are also delivered to the client.

In the messaging state, a client may send/receive messages, join conferences,
send/receive files, change state, etc.

Messaging state is terminated when the user goes offline by sending a LOGOFF
packet.


5. Requests

5.1. Authentication

The first packet sent from the client is the authentication request
packet.  This consists of the user's yahoo id, or any identity
corresponding to that yahoo id.  The AUTH packet has one key/value pair.

    service: YAHOO_SERVICE_AUTH
    status:  YAHOO_STATUS_AVAILABLE

    1: yahoo_id

The server responds with a Challenge string.  The client then hashes the
username and password with this challenge string, and sends it back as an
AUTH_RESP packet.

    service: YAHOO_SERVICE_AUTHRESP
    status:  initial login status

    0: yahoo_id
    6: response_string_1
    96: response_string_2
    1: active_id


5.2. Sending a message

    service: YAHOO_SERVICE_MESSAGE
    status:  0

    0: yahoo_id
    1: active_id
    5: recipient_id
    14: message to send

5.3. Send typing start/stop notification

    service: YAHOO_SERVICE_NOTIFY
    status:  YAHOO_STATUS_TYPING

    4: active_id
    5: recipient_id
    13: 1 or 0 depending on whether this is a typing start or stop
            packet
    14: <space>
    49: TYPING    /* The literal string */

5.4. Set status

    service: YAHOO_SERVICE_ISBACK or YAHOO_SERVICE_ISAWAY
    status:  the status to set to

    10: status_code
    if custom_status:
        19: custom away message
        47: 0 or 1 depending on whether it is away or not
   

5.5. Logoff

    service: YAHOO_SERVICE_LOGOFF
    status:  YAHOO_STATUS_AVAILABLE

    no key value pairs

5.6. Keep alive - sent every 20 minutes

    service: YAHOO_SERVICE_PING
    status:  YAHOO_STATUS_AVAILABLE

    no key value pairs

5.7. Add buddy

    service: YAHOO_SERVICE_ADDBUDDY
    status:  YAHOO_STATUS_AVAILABLE

    1: yahoo_id
    7: buddy_to_add
    65: group to add to

5.8. Remove buddy

    service: YAHOO_SERVICE_REMBUDDY
    status:  YAHOO_STATUS_AVAILABLE

    1: yahoo_id
    7: buddy_to_remove
    65: group to remove from
   

5.9. Reject buddy add

    service: YAHOO_SERVICE_REJECTCONTACT
    status:  YAHOO_STATUS_AVAILABLE

    1: yahoo_id
    7: buddy_to_reject
    14: reject message
   

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What?  Is that all?

   Use the source Luke!

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