A capability stays maintainable only when the team can explain every state, retry, and piece of residual data—not merely show one successful run. One Wi-Fi name does not guarantee layer-two reachability; guest networks often isolate clients. Browsers may also hide host IP behind mDNS names.
Network diagnostics separates observed facts from inference. Candidate type, selected route, and stage timing describe connectivity; complete IP addresses or one probe are unnecessary and insufficient evidence.
Questions the design must answer
Turn the important choices into durable contracts: validate inputs, assign state ownership, define cleanup, and specify fallback for older peers. Later optimization must not change those semantics.
- Inspect candidate type, protocol, and selected pair locally without uploading addresses, then check subnet, mDNS resolution, AP isolation, and host/srflx reachability.
- Bound every input by size, count, and time, returning a stable actionable error code when a budget is exceeded.
- Treat cleanup as protocol behavior: timers, handles, queues, and temporary data must be safely releasable in every terminal state.
The delivery standard for Why WebRTC Uses TURN Even on the Same Local Network is a usable normal path, convergent failures, bounded resources, and a state users can understand. The result is a production capability that can be explained, degraded safely, and rolled back—not a demo that works once.
Edge cases are part of the feature
Boundaries turn hidden assumptions into incidents. Weak networks, refresh, concurrency, and capacity need combined coverage because retries can hide each one in isolation.
- Equal public IP does not imply LAN under CGNAT or office NAT, while forcing host candidates exposes interfaces and still fails through firewalls.
- Refresh and network change start two recovery paths, and duplicate side effects look like two genuine user actions.
- An untested fallback receives all traffic during a primary failure and becomes the slower, more expensive bottleneck.
Prove that it works with evidence
Write the expected state trace before injecting faults. At every phase, reconcile user-visible outcome, both protocol endpoints, persistent records, and resource counts to prove the loop.
- Compare candidates and selected paths on home, guest AP, enterprise Wi-Fi, mixed wired/wireless, and IPv6-only LANs with actionable conclusions.
- Run one hundred start, fail, retry, and cancel cycles; handles, listeners, queues, and temporary data must return to baseline.
- Cover direct, relayed, weak-network, background-tab, and mobile paths; do not rely on averages or one successful screenshot.
Completion is not one passing path. Every terminal state reconciles, automation stays below user intent, and every operational cost has an explicit ceiling.