= Architecture of uHub =

uHub is single-threaded and handles network and timer events using the
libevent library.
For each state there is a read event (and sometimes a write event) and timeout
event in case an expected read (or write) event does not occur.


== Protocol overview ==
uHub "speaks" the ADC protocol, which works in short as follows:
(C = client, S = server aka uHub).

C: HSUP ADBASE
Client connects to hub and supplies a list of supported features to the hub.

S: ISUP ADBASE { }
Server responds with a list of supported features.

S: ISID xxxx
Server assigns a session-ID to the client (4 bytes, BASE32 encoded).

C: BINF xxxx (...)
Client sends information about itself, such as nick name, etc.
The hub will relay this information to all users, including the client.

S: BINF xxx1 NInick1 (...)
S: BINF xxx2 NInick2
S: (...)
S: BINF xxxx (client's own nick)
Client gets list of other clients, which ends with the client's own user info.
At this point the client is successfully logged into the hub.


== The hub architecture ==

Accepting new users





    ---------------------              -----------------
    | Accept connection | <----------  | libevent loop |
    ---------------------              -----------------
              |
              V
    ---------------------           ------------
    | Setup login timer | --+---->  | Timeout? | <----+
    ---------------------   |       ------------      |
              |             |             |           |
              V             |             V           |
    ---------------------   |      ---------------    |
    |   Receive 'HSUP'  | --+----> | DISCONNECT! |    |
    ---------------------          ---------------    |
              |                           ^           |
              V                           |           |
    ---------------------                 |           |
    | Send 'ISUP', and  |                 |           |
    | assign Session ID |                 |           |
    ---------------------                 |           |
              |                           |           |
              V                           |           |
    ---------------------                 |           |
    |   Receive 'BINF'  |-----------------+------------
 +--| Validate message  |                 ^
 |  ---------------------                 |
 |            |                           |
 |            V                           |
 |  ---------------------         ---------------------
 |  |   Send password   | ------> | Receive and check |
 |  | request, if needed|         | password.         |
 |  ---------------------         ---------------------
 |                                         |
 |                                         |
 |  ------------------------               |
 +->| Send welcome message |<--------------+
    ------------------------
              |
              V
    ------------------------
    | Send user list to    |
    | newly accepted user. |
    ------------------------
              |
              V
    ------------------------
    |  User is logged in.  |
    |   Announce to all.   |
    ------------------------