Implement Application-Level TCP Keep-Alive - The Networker

                      TASK
                    

Implementation

Implement application-level TCP keep-alive detection. If a client goes silent for more than 30 seconds, detect it and close the connection. Use periodic ping messages instead of OS-level keep-alive.

Implement handlers:

Request:  {"type": "ka_register", "msg_id": 1, "client_id": "c1", "timeout_ms": 30000, "ping_interval_ms": 10000}
Response: {"type": "ka_register_ok", "in_reply_to": 1}

Request:  {"type": "ka_heartbeat", "msg_id": 2, "client_id": "c1"}
Response: {"type": "ka_heartbeat_ok", "in_reply_to": 2, "last_seen_ms_ago": 0}

Request:  {"type": "ka_check", "msg_id": 3, "current_time_ms": 45000}
Response: {"type": "ka_check_ok", "in_reply_to": 3, "expired": ["c1"], "active": ["c2"]}

Request:  {"type": "ka_status", "msg_id": 4}
Response: {"type": "ka_status_ok", "in_reply_to": 4, "connections": [
    {"client_id": "c2", "last_seen_ms_ago": 5000, "status": "active"}
]}

Sample Test Cases

Input

{"src":"c0","dest":"n1","body":{"type":"init","msg_id":1,"node_id":"n1","node_ids":["n1"]}}
{"src":"c1","dest":"n1","body":{"type":"ka_register","msg_id":2,"client_id":"c1","timeout_ms":30000,"ping_interval_ms":10000}}

Expected Output

{"src": "n1", "dest": "c0", "body": {"type": "init_ok", "in_reply_to": 1, "msg_id": 0}}
{"src": "n1", "dest": "c1", "body": {"type": "ka_register_ok", "in_reply_to": 2, "msg_id": 1}}

Heartbeat resets last_seenTimeout: 5000ms

Input

{"src":"c0","dest":"n1","body":{"type":"init","msg_id":1,"node_id":"n1","node_ids":["n1"]}}
{"src":"c1","dest":"n1","body":{"type":"ka_register","msg_id":2,"client_id":"c1","timeout_ms":30000,"ping_interval_ms":10000}}
{"src":"c1","dest":"n1","body":{"type":"ka_heartbeat","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": "ka_register_ok", "in_reply_to": 2, "msg_id": 1}}
{"src": "n1", "dest": "c1", "body": {"type": "ka_heartbeat_ok", "in_reply_to": 3, "last_seen_ms_ago": 0, "msg_id": 2}}

Hints

Hint 1▾

Send periodic ping messages to detect silent client failures

Hint 2▾

Track the last activity timestamp for each connection

Hint 3▾

If no activity for > 30s, send a ping. If no pong within 5s, close the connection

Hint 4▾

Do not rely on OS-level keep-alive; implement at the application layer

Hint 5▾

Maintain a connection state table with last_seen timestamps

Resources

TCP Keep-Alive in Detail

Understanding TCP keep-alive at both OS and application levels

                      OVERVIEW
                    

Theoretical Hub

Concept overview coming soon

Key Concepts

keep-aliveheartbeatconnection healthidle detection

main.py

python