CPP Chat: Quick Tips for Getting Started

CPP Chat Troubleshooting Guide — Common Issues and Fixes

1. Cannot connect / connection drops

• Likely causes: network instability, server down, incorrect server address/port, firewall/NAT blocking, TLS handshake failure.
• Quick fixes:
  1. Verify server hostname/IP and port.
  2. Test network with ping/traceroute and check other services.
  3. Temporarily disable firewall/antivirus or add allow rule for the app.
  4. Check TLS certificates and system time (expired certs or wrong clock cause failures).
  5. Inspect server logs for connection errors and increase client-side timeout/retry logic.

2. Authentication failing (login/keys rejected)

• Likely causes: wrong credentials, expired tokens, clock skew for time-limited tokens, misconfigured auth server.
• Quick fixes:
  1. Re-enter username/password or refresh tokens.
  2. Confirm token expiry/refresh flow and sync client/server clocks (NTP).
  3. Verify auth endpoint URL and client ID/secret.
  4. Check server auth logs and error codes for specific rejection reasons.

3. Messages delayed or out of order

• Likely causes: message buffering, retries, inconsistent sequence numbers, multiple concurrent servers without proper ordering, slow network.
• Quick fixes:
  1. Ensure the protocol includes sequence IDs or timestamps and enforce ordering on the client.
  2. Reduce aggressive retries that can duplicate messages; deduplicate using message IDs.
  3. Use a single authoritative message broker or enable consistent hashing/session affinity for load balancers.
  4. Monitor latency and increase heartbeat/keepalive frequency if needed.

4. Binary/text encoding issues (garbled messages)

• Likely causes: mismatched character encodings (UTF-8 vs ISO-8859-1), incorrect framing, endian mismatches for binary fields.
• Quick fixes:
  1. Standardize on UTF-8 for text; validate input/output encoding.
  2. Ensure message framing (length-prefix, delimiters) is implemented consistently.
  3. For binary payloads, define endianness and document field sizes; use base64 for safe transport over text channels.

5. File or attachment transfer fails

• Likely causes: size limits, timeouts, improper chunking, storage permission errors.
• Quick fixes:
  1. Implement chunked upload with resume support and confirm server max size.
  2. Increase upload timeout and provide progress/retry UI.
  3. Verify storage permissions and available disk/quota.
  4. Use checksums (MD5/SHA256) to validate integrity after transfer.

6. Presence/typing indicators incorrect

• Likely causes: missed presence events, race conditions, noisy heartbeats, stale state in caches.
• Quick fixes:
  1. Use reliable presence heartbeats with server-side expiring presence state.
  2. Debounce typing indicators and expire them after short interval.
  3. Reconcile client state on reconnect by fetching authoritative presence list.

7. High CPU / memory usage on client or server

• Likely causes: memory leaks, unbounded message queues, expensive serialization, too many concurrent connections per process.
• Quick fixes:
  1. Profile the app to find hotspots and fix leaks.
  2. Limit queue sizes and apply backpressure.
  3. Use binary serialization (protobuf) if JSON parsing is costly.
  4. Horizontally scale processes and tune connection limits.

8. Search or history not returning expected messages

• Likely causes: indexing lag, inconsistent data replication, wrong query parameters, access control filters.
• Quick fixes:
  1. Ensure the indexing pipeline is running and monitor lag.
  2. Check replication status and repair inconsistent shards.
  3. Review query syntax and user permissions; test with known message IDs.

9. Notifications not delivered to devices

• Likely causes: push credential issues (APNs/FCM), device token stale, background restrictions on mobile OS, user disabled notifications.
• Quick fixes:
  1. Validate push provider credentials and monitor error responses.
  2. Refresh device tokens on app start and handle token invalidation.
  3. Implement fallback (in-app badges) and educate users to enable background data/notifications.

10. Unexpected data loss

• Likely causes: improper acknowledgement logic, aggressive retention/cleanup, storage corruption, failed replication.
• Quick fixes:
  1. Verify ack/retry semantics and ensure messages are persisted before ack.
  2. Audit retention policies and backups; restore from backups if needed.
  3. Monitor storage health and enable replication with quorum writes.

Diagnostic checklist (quick)

1. Reproduce issue reliably and capture timestamps.
2. Collect client logs, server logs, network traces (tcpdump/wireshark).
3. Correlate logs by timestamps and request IDs.
4. Inspect metrics (CPU, memory, connections, queue depth, latency).
5. Test with minimal client/server setup to isolate components.

Preventive measures

• Monitoring: metrics, alerts, and distributed tracing.
• Resilience: retries with exponential backoff, circuit breakers, rate limiting.
• Testing: chaos testing for network faults and load testing for scale.
• Documentation: protocol spec, error codes, and runbook for common failures.

If you want, I can convert this into a one-page runbook, a checklist for on-call, or specific command examples for debugging (logs/wireshark/grep).