axum-core-state

Axum shared application state extraction returns 500 errors when resources are injected via Extension instead of Router::with_state. Using Router<S> with Router::with_state ensures only Router<()> is serveable, catching missing state wiring at compile time.

Use derive(FromRef) on your AppState struct to generate per-handler substate implementations. State<S> extractors then pull only the needed fields from the larger application state, keeping handlers decoupled from the full state tree.

Holding a std::sync::Mutex guard across .await makes Axum handler futures !Send, causing runtime panics. Use tokio::sync::Mutex for async scopes, or scope std::sync::Mutex guards to drop before any .await calls to maintain Send requirements.

Wrap heavy immutable data in Arc and ensure your Axum state is Clone. This allows Router::with_state to safely clone the state reference for each handler without deep copying the underlying data.

The Handler is not satisfied error occurs when Axum router state types mismatch handler extractors. Restructure your router to provide AppState via Router::with_state and use State<S> extractors to resolve the type mismatch.

Avoid Extension for sharing application state in Axum because it silently fails at runtime if missing. Use Router::with_state with State<S> extractors instead to guarantee state availability and catch wiring failures at compile time.