The challenge is to build a system which acts as a socket server, reading events from an event source and forwarding them when appropriate to user clients.
Clients will connect through TCP, using a string-based protocol (i.e. a CRLF control
character terminates each message). All strings are encoded in UTF-8.
The event source connects on port 9090 and will start sending events as soon as the connection is accepted.
The many user clients will connect on port 9099. As soon
as the connection is accepted, they will send to the server the ID of
the represented user, so that the server knows which events to
inform them of. For example, once connected a user client may send down:
2932\n, indicating that they are representing user 2932.
After the identification is sent, the user client starts waiting for events to be sent to them. Events coming from event source should be sent to relevant user clients exactly like read, no modification is required or allowed.
There are five possible events. The table below describe payloads sent by the event source and what they represent:
| Payload | Sequence # | Type | From User Id | To User Id |
|---|---|---|---|---|
| 666|F|60|50 | 666 | Follow | 60 | 50 |
| 1|U|12|9 | 1 | Unfollow | 12 | 9 |
| 542532|B | 542532 | Broadcast | - | - |
| 43|P|32|56 | 43 | Private Msg | 32 | 56 |
| 634|S|32 | 634 | Status Update | 32 | - |
Events may generate notifications for user clients, according to the following rules:
- Follow: Only the
To User Idshould be notified - Unfollow: No clients should be notified
- Broadcast: All connected user clients should be notified
- Private Message: Only the
To User Idshould be notified - Status Update: All current followers of the
From User IDshould be notified
If there are no user client connected for a user, any notifications for them must be silently ignored. user clients expect to be notified of events in the correct order, regardless of the order in which the event source sent them.
To run this program, you need an environment with Elixir (was developed using Elixir 1.9.1). From the command line, run
$ iex -S mix
to start the TCP server.
From the command line, run
$ mix test