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62 lines
2.9 KiB
Markdown
62 lines
2.9 KiB
Markdown
# Follower Maze Code Challenge Instructions
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Follower-Maze is a **client-server application** built for social networking.
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Users follow other users, post messages, send private messages, unfollow users, and so on.
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* Each of these actions is an _event_, created by an _event-source_ and sent to the _server_.
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* Each event is processed by the _server_.
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* The processing of the event may have follow-on effects on other _user-clients_.
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The **server** listens for two kinds of **clients**:
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* **1 event source**, which emits events.
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* **N user-clients** that connect to the server.
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#### Client/Server Protocol
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* The protocol is line-based i.e. a LF control character terminates each message.
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All strings are encoded in UTF-8.
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* Data is transmitted over TCP sockets.
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* The _event source_ connects on port 9090 and will start sending events as soon as the connection is accepted.
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* The _user clients_ connect on port 9099 and identify themselves with their user ID.
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For example, once connected a _user client_ may send down `2932\r\n`,
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indicating that it is representing user 2932.
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* After the identification is sent,
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the user client starts waiting for events to be sent to them by the server.
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#### Events
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There are five possible events.
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The table below describes payloads sent by the event source and what each represents:
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```
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| Payload | Sequence # | Type | From User Id | To User Id |
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|---------------|------------|---------------|--------------|------------|
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| 666|F|60|50 | 666 | Follow | 60 | 50 |
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| 1|U|12|9 | 1 | Unfollow | 12 | 9 |
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| 542532|B | 542532 | Broadcast | - | - |
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| 43|P|32|56 | 43 | Private Msg | 32 | 56 |
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| 634|S|32 | 634 | Status Update | 32 | - |
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```
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#### Event Rules
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* Each message begins with a sequence number.
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* However, the event source _does not send events in any given order_.
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In particular, sequence number has no effect on the order in which events are sent.
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* Events _may_ generate notifications for _user clients_.
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If there is a respective target _user client_ connected,
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the notification is routed according to the following rules:
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* Follow: Only the `To User Id` is notified
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* A follow event from user A to user B means that user A now follows user B.
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* Unfollow: No clients are notified
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* An unfollow event from user A to user B means that user A stopped following user B.
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* Broadcast: All connected _user clients_ are notified
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* Private Message: Only the `To User Id` is notified
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* Status Update: All current followers of the `From User ID` are notified
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* If there are no _user clients_ connected for a user,
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any notifications for them are currently ignored.
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_User clients_ are notified of events _in the correct sequence-number order_,
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regardless of the order in which the _event source_ sent them.
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