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README

The TCP server

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.

The events

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 Id should be notified
  • Unfollow: No clients should be notified
  • Broadcast: All connected user clients should be notified
  • Private Message: Only the To User Id should be notified
  • Status Update: All current followers of the From User ID should 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.

Running the program

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.

Running the tests

From the command line, run

$ mix test