Web Development

Domain Constraints

Critical Rules

• Web handlers must not block — block one task = block many requests. Use spawn_blocking for CPU work.
• Shared state must be thread-safe — handlers run on any thread. Use Arc<T>, Arc<RwLock<T>> for mutable.
• Resources live only for request duration — use extractors for proper ownership.

Framework Comparison

Key Crates

Design Patterns

Axum Handler Pattern

async fn handler(
    State(db): State<Arc<DbPool>>,
    Json(payload): Json<CreateUser>,
) -> Result<Json<User>, AppError> {
    let user = db.create_user(&payload).await?;
    Ok(Json(user))
}

// Error handling
impl IntoResponse for AppError {
    fn into_response(self) -> Response {
        let (status, message) = match self {
            Self::NotFound => (StatusCode::NOT_FOUND, "Not found"),
            Self::Internal(_) => (StatusCode::INTERNAL_SERVER_ERROR, "Internal error"),
        };
        (status, Json(json!({"error": message}))).into_response()
    }
}

Common Mistakes