Strangers Talk (Backend)

Overview

The project is a websocket based realtime user management application, that allows users to randomly join a chat-room where both of them can interact in realtime. The project uses socket.io library to achieve realtime communication between users.

Getting Started

To run the project, perform the following steps

git clone https://github.com/AkshayCHD/strangers-talk-backend.git
cd strangers-talk-backend
npm install
node index.js

To run project test cases,

node index.js

// Simulaneously use another terminal and run

npm test

Implementation Algorithms

The implementation of the project can be explained using the following algorithms

• Initialize the following empty data-structures.
  • allPairs
    • type: Hashmap
    • purpose: To map all active socket connections to their socker ids.
  • rooms
    • type: Hashmap
    • purpose: To map the room addresses to which socket is joined, to the socket ids.
  • queue
    • type: array
    • purpose: To store the connections that havn't been paired up with any other connection.
• Handle events like user login, logout and disconnect and perform the following actions on their emission
  • Login
    • Save/Update the socket connection in the allPairs hashmap referenceable by the socket id.
    • Check if the first element of the queue is the same as current socket id.
      • Remove queue front if that is the case
    • Check for other unpaired socket connections in the queue
      • If there is a connection then pair the current connection with the available one(access using allPairs).
        • Emit event roomCreated to both connections.
      • Else push the current connection in the unpaired queue.
        • Emit event addedToQueue to the current socket.
  • Logout
    • If the connection is in the waiting queue then remove the connection from there.
    • If the connection is in any room
      • Determine the room id using rooms hashmap
      • Make the socket leave the room
      • Determine the pair socket id using room id
      • Get the pair socket connection using allPairs
      • Make the pair also leave the room
      • Emit event roomDeleted to both current socket and its pair.
      • Add pair to the waiting queue so that it can be joined into some new room with some other connection.
      • Remove instances of the currenct socket from allPair and rooms hashmap.

Note: In the above implementation the array queue will always contain a single element as, as soon as there is another idle connection it would be paired with the available connection, but it has been kept an array to help reader get an intuitive idea of the waiting queue. Plus in the future if application supports multiple connections in a room, then the queue might contain multiple entries.

Project Testing

The test for the project have been written using the mocha testing framework, as of now the following test cases have been covered in the project.

• Connect single socket client: When a client logs into the system, he should be added to the waiting queue if no other connections are present, and the event addedToQueue should be emitted.
• Create room for 2 differenct socket IDs: When there is an existing connection in the waiting queue the current connection should be paired with him and the roomCreated event should be emitted.
• Add socket to queue if partner exits: When the partner of the current connection exits the, and no other idle connection is present, the partner should be added to waiting queue and addedToQueue event should be emitted.
• Delete room when connection logs out: When the connection logs out, if it is in a room then the room should be deleted and roomDeleted event should be emitted.
• Delete room when pair logs out: When connection's pair logs out then their room should be deleted and connection should be notified by roomDeleted event.
• Rejoin other random socket if current pair logs out: If pair of current connection logs out their is another waiting connection in the queue, then the current connection must be joined to idle one and roomCreated event must be emitted
• Connect idle sockets if their pairs logout: If there are 2 socket pairs and one out of both of them log out, then both the left connections must pair with each other and roomCreated event must be emitted.

Future Scope

The following features are in the scope of the project and can be implemented in the future,

• Chat Functionality: Since we are already create rooms, we can support a message event in the handlers to support real time messaging among the connected clients.
• Multiple Connections: We might allow one to many connections in the future and could allow users to connect to multiple random clients instead of just one.