Add a Connection Pool with Configurable Backlog - The Networker

                      TASK
                    

Implementation

Extend your TCP server to accept up to N concurrent connections. When N is exceeded, queue new connections in a backlog. If the backlog is also full, reject the connection.

Implement handlers:

Request:  {"type": "pool_config", "msg_id": 1, "max_connections": 3, "backlog_size": 5}
Response: {"type": "pool_config_ok", "in_reply_to": 1}

Request:  {"type": "pool_connect", "msg_id": 2, "client_id": "c1"}
Response: {"type": "pool_connect_ok", "in_reply_to": 2, "status": "connected", "active": 1, "queued": 0}

Request:  {"type": "pool_connect", "msg_id": 5, "client_id": "c4"}
Response: {"type": "pool_connect_ok", "in_reply_to": 5, "status": "queued", "active": 3, "queued": 1}

Request:  {"type": "pool_disconnect", "msg_id": 6, "client_id": "c1"}
Response: {"type": "pool_disconnect_ok", "in_reply_to": 6, "promoted": "c4", "active": 3, "queued": 0}

Sample Test Cases

Configure pool and connectTimeout: 5000ms

Input

{"src":"c0","dest":"n1","body":{"type":"init","msg_id":1,"node_id":"n1","node_ids":["n1"]}}
{"src":"c1","dest":"n1","body":{"type":"pool_config","msg_id":2,"max_connections":2,"backlog_size":3}}
{"src":"c1","dest":"n1","body":{"type":"pool_connect","msg_id":3,"client_id":"c1"}}

Expected Output

{"src": "n1", "dest": "c0", "body": {"type": "init_ok", "in_reply_to": 1, "msg_id": 0}}
{"src": "n1", "dest": "c1", "body": {"type": "pool_config_ok", "in_reply_to": 2, "msg_id": 1}}
{"src": "n1", "dest": "c1", "body": {"type": "pool_connect_ok", "in_reply_to": 3, "status": "connected", "active": 1, "queued": 0, "msg_id": 2}}

Exceeding max connections queuesTimeout: 5000ms

Input

{"src":"c0","dest":"n1","body":{"type":"init","msg_id":1,"node_id":"n1","node_ids":["n1"]}}
{"src":"c1","dest":"n1","body":{"type":"pool_config","msg_id":2,"max_connections":2,"backlog_size":3}}
{"src":"c1","dest":"n1","body":{"type":"pool_connect","msg_id":3,"client_id":"c1"}}
{"src":"c1","dest":"n1","body":{"type":"pool_connect","msg_id":4,"client_id":"c2"}}
{"src":"c1","dest":"n1","body":{"type":"pool_connect","msg_id":5,"client_id":"c3"}}

Expected Output

{"src": "n1", "dest": "c0", "body": {"type": "init_ok", "in_reply_to": 1, "msg_id": 0}}

Hints

Hint 1▾

Track the number of active connections with a counter

Hint 2▾

When max connections is reached, either queue or reject new connections

Hint 3▾

Use a configurable backlog size for queued connections

Hint 4▾

Decrement the counter when a connection is closed

Hint 5▾

Consider what happens when the queue itself is full

Resources

TCP Backlog and Connection Queuing

Deep dive into how TCP backlog works in Linux

                      OVERVIEW
                    

Theoretical Hub

Concept overview coming soon

Key Concepts

connection poolbacklogconcurrencyresource management

main.py

python