domain-web

Web Domain

Layer 3: Domain Constraints

Domain Constraints → Design Implications Domain Rule Design Constraint Rust Implication Stateless HTTP No request-local globals State in extractors Concurrency Handle many connections Async, Send + Sync Latency SLA Fast response Efficient ownership Security Input validation Type-safe extractors Observability Request tracing tracing + tower layers Critical Constraints Async by Default RULE: Web handlers must not block WHY: Block one task = block many requests RUST: async/await, spawn_blocking for CPU work

State Management RULE: Shared state must be thread-safe WHY: Handlers run on any thread RUST: Arc, Arc> for mutable

Request Lifecycle RULE: Resources live only for request duration WHY: Memory management, no leaks RUST: Extractors, proper ownership

Trace Down ↓

From constraints to design (Layer 2):

"Need shared application state" ↓ m07-concurrency: Use Arc for thread-safe sharing ↓ m02-resource: Arc> for mutable state

"Need request validation" ↓ m05-type-driven: Validated extractors ↓ m06-error-handling: IntoResponse for errors

"Need middleware stack" ↓ m12-lifecycle: Tower layers ↓ m04-zero-cost: Trait-based composition

Framework Comparison Framework Style Best For axum Functional, tower Modern APIs actix-web Actor-based High performance warp Filter composition Composable APIs rocket Macro-driven Rapid development Key Crates Purpose Crate HTTP server axum, actix-web HTTP client reqwest JSON serde_json Auth/JWT jsonwebtoken Session tower-sessions Database sqlx, diesel Middleware tower Design Patterns Pattern Purpose Implementation Extractors Request parsing State(db), Json(payload) Error response Unified errors impl IntoResponse Middleware Cross-cutting Tower layers Shared state App config Arc Code Pattern: Axum Handler async fn handler( State(db): State>, Json(payload): Json, ) -> Result, 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 Mistake Domain Violation Fix Blocking in handler Latency spike spawn_blocking Rc in state Not Send + Sync Use Arc No validation Security risk Type-safe extractors No error response Bad UX IntoResponse impl Trace to Layer 1 Constraint Layer 2 Pattern Layer 1 Implementation Async handlers Async/await tokio runtime Thread-safe state Shared state Arc, Arc Request lifecycle Extractors Ownership via From Middleware Tower layers Trait-based composition Related Skills When See Async patterns m07-concurrency State management m02-resource Error handling m06-error-handling Middleware design m12-lifecycle