---name: domain-webdescription: Use when building web services. Keywords: web server, HTTP, REST API, GraphQL, WebSocket, axum, actix, warp, rocket, tower, hyper, reqwest, middleware, router, handler, extractor, state management, authentication, authorization, JWT, session, cookie, CORS, rate limiting, web 开发, HTTP 服务, API 设计, 中间件, 路由globs: ["**/Cargo.toml"]user-invocable: false---

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<T>, Arc<RwLock<T>> 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<RwLock<T>> 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<AppState>

Code Pattern: Axum Handler

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

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<RwLock>
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