Rust Development Patterns

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Master Rust development with Cursor IDE and Claude Code. This guide covers ownership patterns, async programming with Tokio, web frameworks like Actix and Axum, error handling strategies, and building safe, concurrent systems with AI assistance.

Quick Setup

Initialize Rust Project

Cursor
Claude Code

# Create new Rust project
Ask: "Create a new Rust project with workspace structure for a web API"

# Or use Agent mode
Agent: "Set up a Rust web service with Axum, SQLx, and Tokio with proper error handling"

# Generate project structure
claude "Create a Rust workspace with:
- API server crate
- Core business logic crate
- Database migrations
- Docker support
- GitHub Actions CI"

# With specific framework
claude "Set up Rust API with Actix-web, diesel ORM, and structured logging"

Configure Development Environment

[workspace]
members = ["api", "core", "db"]

[workspace.dependencies]
tokio = { version = "1.35", features = ["full"] }
serde = { version = "1.0", features = ["derive"] }
thiserror = "1.0"
anyhow = "1.0"
tracing = "0.1"

Set Up AI Rules

# .cursorrules or CLAUDE.md
- Use Rust 2021 edition
- Prefer Result<T, E> over panics
- Use thiserror for error types
- Apply clippy lints
- Write idiomatic Rust code
- Add comprehensive documentation
- Use async/await for I/O operations

Core Rust Patterns

// AI Prompt
Ask: "Explain and fix the ownership issues in this code:
fn process_data(data: Vec<String>) -> Vec<String> {
    let filtered = data.into_iter()
        .filter(|s| s.len() > 5)
        .collect();
    // Want to use 'data' again here
    println!('Original: {:?}', data);
    filtered
}"

// AI will explain ownership transfer and suggest:
fn process_data(data: &[String]) -> Vec<String> {
    let filtered: Vec<String> = data.iter()
        .filter(|s| s.len() > 5)
        .cloned()
        .collect();
    println!("Original: {:?}", data);
    filtered
}

// Or with owned data:
fn process_data(data: Vec<String>) -> (Vec<String>, Vec<String>) {
    let filtered = data.iter()
        .filter(|s| s.len() > 5)
        .cloned()
        .collect();
    println!("Original: {:?}", data);
    (data, filtered)
}

# Generate ownership examples
claude "Create Rust examples demonstrating:
1. Move semantics
2. Borrowing rules
3. Lifetime annotations
4. Smart pointers (Box, Rc, Arc)
5. Interior mutability patterns"

Error Handling

// AI Prompt: "Implement comprehensive error handling with custom error types"
use thiserror::Error;

#[derive(Error, Debug)]
pub enum AppError {
    #[error("Database error: {0}")]
    Database(#[from] sqlx::Error),

    #[error("Validation error: {message}")]
    Validation { message: String },

    #[error("Not found: {resource}")]
    NotFound { resource: String },

    #[error("Unauthorized")]
    Unauthorized,

    #[error("Internal server error")]
    Internal(#[source] anyhow::Error),
}

// Result type alias
pub type Result<T> = std::result::Result<T, AppError>;

// Usage in functions
pub async fn get_user(id: i64, pool: &PgPool) -> Result<User> {
    let user = sqlx::query_as!(User,
        "SELECT * FROM users WHERE id = $1",
        id
    )
    .fetch_optional(pool)
    .await?
    .ok_or_else(|| AppError::NotFound {
        resource: format!("User {}", id),
    })?;

    Ok(user)
}

// Error conversion for web frameworks
impl From<AppError> for actix_web::Error {
    fn from(err: AppError) -> Self {
        match err {
            AppError::NotFound { .. } => {
                actix_web::error::ErrorNotFound(err)
            }
            AppError::Unauthorized => {
                actix_web::error::ErrorUnauthorized(err)
            }
            AppError::Validation { .. } => {
                actix_web::error::ErrorBadRequest(err)
            }
            _ => actix_web::error::ErrorInternalServerError(err),
        }
    }
}

Async Programming with Tokio

Async Runtime Patterns

Cursor
Claude Code

// AI Prompt
Agent: "Create an async service with:
- Tokio runtime configuration
- Concurrent task management
- Graceful shutdown
- Channel communication
- Error propagation"

use tokio::sync::{mpsc, oneshot};
use tokio::task::JoinSet;
use std::time::Duration;

pub struct Service {
    shutdown_tx: Option<oneshot::Sender<()>>,
    task_handle: Option<tokio::task::JoinHandle<()>>,
}

impl Service {
    pub fn new() -> Self {
        Self {
            shutdown_tx: None,
            task_handle: None,
        }
    }

    pub async fn start(&mut self) -> Result<()> {
        let (shutdown_tx, shutdown_rx) = oneshot::channel();
        let (task_tx, mut task_rx) = mpsc::channel::<Task>(100);

        self.shutdown_tx = Some(shutdown_tx);

        let handle = tokio::spawn(async move {
            let mut tasks = JoinSet::new();

            loop {
                tokio::select! {
                    Some(task) = task_rx.recv() => {
                        tasks.spawn(async move {
                            process_task(task).await
                        });
                    }
                    _ = &mut shutdown_rx => {
                        info!("Shutting down service");
                        break;
                    }
                }
            }

            // Wait for all tasks to complete
            while let Some(result) = tasks.join_next().await {
                if let Err(e) = result {
                    error!("Task failed: {}", e);
                }
            }
        });

        self.task_handle = Some(handle);
        Ok(())
    }

    pub async fn shutdown(mut self) -> Result<()> {
        if let Some(tx) = self.shutdown_tx.take() {
            let _ = tx.send(());
        }

        if let Some(handle) = self.task_handle.take() {
            handle.await?;
        }

        Ok(())
    }
}

# Generate async patterns
claude "Create Rust async examples:
1. Stream processing with tokio-stream
2. Parallel HTTP requests
3. Rate limiting with governor
4. Retry logic with backoff
5. Timeout handling"

Concurrent Data Access

// AI Prompt: "Implement thread-safe shared state with async RwLock"
use std::sync::Arc;
use tokio::sync::RwLock;
use dashmap::DashMap;

#[derive(Clone)]
pub struct Cache {
    data: Arc<DashMap<String, CachedItem>>,
    config: Arc<RwLock<CacheConfig>>,
}

#[derive(Clone)]
struct CachedItem {
    value: String,
    expires_at: Instant,
}

impl Cache {
    pub fn new(config: CacheConfig) -> Self {
        Self {
            data: Arc::new(DashMap::new()),
            config: Arc::new(RwLock::new(config)),
        }
    }

    pub async fn get(&self, key: &str) -> Option<String> {
        let item = self.data.get(key)?;

        if item.expires_at > Instant::now() {
            Some(item.value.clone())
        } else {
            // Remove expired item
            drop(item);
            self.data.remove(key);
            None
        }
    }

    pub async fn set(&self, key: String, value: String) -> Result<()> {
        let config = self.config.read().await;
        let expires_at = Instant::now() + config.ttl;

        self.data.insert(key, CachedItem {
            value,
            expires_at,
        });

        Ok(())
    }

    pub async fn update_config(&self, new_config: CacheConfig) -> Result<()> {
        let mut config = self.config.write().await;
        *config = new_config;
        Ok(())
    }
}

Web Development

Axum Web Framework

Cursor
Claude Code

// AI Prompt
Agent: "Create a production Axum API with:
- JWT authentication
- Request validation
- Database connection pool
- Middleware stack
- OpenAPI documentation"

use axum::{
    Router, Extension, Json,
    extract::{Path, Query, State},
    middleware,
    response::IntoResponse,
    http::StatusCode,
};
use tower::ServiceBuilder;
use tower_http::{
    trace::TraceLayer,
    cors::CorsLayer,
    compression::CompressionLayer,
};

pub struct AppState {
    db: PgPool,
    redis: RedisPool,
    config: Config,
}

pub fn create_app(state: AppState) -> Router {
    let api_routes = Router::new()
        .route("/users", get(list_users).post(create_user))
        .route("/users/:id", get(get_user).put(update_user).delete(delete_user))
        .route_layer(middleware::from_fn_with_state(state.clone(), auth_middleware));

    Router::new()
        .route("/health", get(health_check))
        .nest("/api/v1", api_routes)
        .layer(
            ServiceBuilder::new()
                .layer(TraceLayer::new_for_http())
                .layer(CorsLayer::permissive())
                .layer(CompressionLayer::new())
                .layer(Extension(state))
        )
}

async fn create_user(
    State(state): State<AppState>,
    Json(payload): Json<CreateUserRequest>,
) -> Result<impl IntoResponse> {
    // Validate request
    payload.validate()?;

    // Create user in database
    let user = sqlx::query_as!(
        User,
        r#"
        INSERT INTO users (email, name, password_hash)
        VALUES ($1, $2, $3)
        RETURNING id, email, name, created_at
        "#,
        payload.email,
        payload.name,
        hash_password(&payload.password)?
    )
    .fetch_one(&state.db)
    .await?;

    Ok((StatusCode::CREATED, Json(user)))
}

# Generate complete web app
claude "Create an Axum web application with:
1. REST API endpoints
2. WebSocket support
3. Static file serving
4. Session management
5. Rate limiting
6. Request logging"

Database Integration with SQLx

// AI Prompt: "Implement database repository with SQLx and compile-time verification"
use sqlx::{PgPool, postgres::PgQueryResult};

pub struct UserRepository {
    pool: PgPool,
}

impl UserRepository {
    pub fn new(pool: PgPool) -> Self {
        Self { pool }
    }

    pub async fn find_by_email(&self, email: &str) -> Result<Option<User>> {
        let user = sqlx::query_as!(
            User,
            r#"
            SELECT id, email, name, password_hash,
                   created_at, updated_at
            FROM users
            WHERE email = $1
            "#,
            email
        )
        .fetch_optional(&self.pool)
        .await?;

        Ok(user)
    }

    pub async fn create(&self, user: &CreateUser) -> Result<User> {
        let rec = sqlx::query!(
            r#"
            INSERT INTO users (email, name, password_hash)
            VALUES ($1, $2, $3)
            RETURNING id, created_at, updated_at
            "#,
            user.email,
            user.name,
            user.password_hash
        )
        .fetch_one(&self.pool)
        .await?;

        Ok(User {
            id: rec.id,
            email: user.email.clone(),
            name: user.name.clone(),
            password_hash: user.password_hash.clone(),
            created_at: rec.created_at,
            updated_at: rec.updated_at,
        })
    }

    pub async fn update(&self, id: i64, update: &UpdateUser) -> Result<User> {
        let user = sqlx::query_as!(
            User,
            r#"
            UPDATE users
            SET name = COALESCE($1, name),
                email = COALESCE($2, email),
                updated_at = NOW()
            WHERE id = $3
            RETURNING id, email, name, password_hash,
                      created_at, updated_at
            "#,
            update.name,
            update.email,
            id
        )
        .fetch_one(&self.pool)
        .await?;

        Ok(user)
    }
}

Testing Strategies

Unit and Integration Tests

Cursor
Claude Code

// AI Prompt
Ask: "Generate comprehensive tests with:
- Unit tests with mocking
- Integration tests with test database
- Property-based tests
- Async test helpers
- Test fixtures"

#[cfg(test)]
mod tests {
    use super::*;
    use mockall::predicate::*;
    use proptest::prelude::*;
    use sqlx::postgres::PgPoolOptions;

    // Mock trait for testing
    #[mockall::automock]
    trait UserService {
        async fn get_user(&self, id: i64) -> Result<User>;
        async fn create_user(&self, user: CreateUser) -> Result<User>;
    }

    #[tokio::test]
    async fn test_create_user_success() {
        let mut mock = MockUserService::new();
        mock.expect_create_user()
            .with(eq(CreateUser {
                email: "test@example.com".to_string(),
                name: "Test User".to_string(),
            }))
            .times(1)
            .returning(|_| Ok(User {
                id: 1,
                email: "test@example.com".to_string(),
                name: "Test User".to_string(),
                created_at: Utc::now(),
            }));

        let result = mock.create_user(CreateUser {
            email: "test@example.com".to_string(),
            name: "Test User".to_string(),
        }).await;

        assert!(result.is_ok());
        let user = result.unwrap();
        assert_eq!(user.email, "test@example.com");
    }

    // Integration test with real database
    #[sqlx::test]
    async fn test_repository_create_user(pool: PgPool) {
        let repo = UserRepository::new(pool);

        let user = repo.create(&CreateUser {
            email: "integration@test.com".to_string(),
            name: "Integration Test".to_string(),
            password_hash: "hashed".to_string(),
        }).await.unwrap();

        assert_eq!(user.email, "integration@test.com");

        // Verify user exists
        let found = repo.find_by_email("integration@test.com")
            .await
            .unwrap()
            .expect("User should exist");

        assert_eq!(found.id, user.id);
    }

    // Property-based testing
    proptest! {
        #[test]
        fn test_password_hash_properties(password in "[a-zA-Z0-9]{8,32}") {
            let hash = hash_password(&password).unwrap();
            prop_assert!(verify_password(&password, &hash).unwrap());
            prop_assert_ne!(password, hash);
            prop_assert!(hash.len() > password.len());
        }
    }
}

# Generate test suite
claude "Create Rust test suite with:
1. Mocking with mockall
2. Test fixtures and factories
3. Snapshot testing
4. Benchmarks with criterion
5. Fuzz testing"

Test Helpers and Fixtures

// AI Prompt: "Create test helpers for database and HTTP testing"
pub mod test_helpers {
    use once_cell::sync::Lazy;
    use sqlx::PgPool;

    static TEST_DB: Lazy<String> = Lazy::new(|| {
        format!("test_db_{}", uuid::Uuid::new_v4())
    });

    pub async fn setup_test_db() -> PgPool {
        let db_url = std::env::var("DATABASE_URL")
            .unwrap_or_else(|_| "postgres://localhost/postgres".to_string());

        // Create test database
        let mut conn = PgConnection::connect(&db_url).await.unwrap();
        sqlx::query(&format!("CREATE DATABASE {}", *TEST_DB))
            .execute(&mut conn)
            .await
            .unwrap();

        // Run migrations
        let pool = PgPool::connect(&format!("{}/{}", db_url, *TEST_DB))
            .await
            .unwrap();

        sqlx::migrate!("./migrations")
            .run(&pool)
            .await
            .unwrap();

        pool
    }

    pub async fn teardown_test_db(pool: PgPool) {
        pool.close().await;

        let db_url = std::env::var("DATABASE_URL")
            .unwrap_or_else(|_| "postgres://localhost/postgres".to_string());

        let mut conn = PgConnection::connect(&db_url).await.unwrap();
        sqlx::query(&format!("DROP DATABASE IF EXISTS {}", *TEST_DB))
            .execute(&mut conn)
            .await
            .unwrap();
    }

    // Test data factory
    pub struct UserFactory;

    impl UserFactory {
        pub fn build() -> CreateUser {
            CreateUser {
                email: format!("user{}@test.com", rand::random::<u32>()),
                name: "Test User".to_string(),
                password: "password123".to_string(),
            }
        }

        pub async fn create(pool: &PgPool) -> User {
            let user_data = Self::build();
            let repo = UserRepository::new(pool.clone());
            repo.create(&user_data).await.unwrap()
        }
    }
}

Performance Optimization

Zero-Copy and Memory Efficiency

// AI Prompt: "Optimize this code for zero-copy operations and memory efficiency"
use bytes::Bytes;
use tokio::io::{AsyncRead, AsyncReadExt};

// Efficient buffer management
pub struct StreamProcessor {
    buffer: Vec<u8>,
    capacity: usize,
}

impl StreamProcessor {
    pub fn new(capacity: usize) -> Self {
        Self {
            buffer: Vec::with_capacity(capacity),
            capacity,
        }
    }

    pub async fn process_stream<R: AsyncRead + Unpin>(
        &mut self,
        mut reader: R,
    ) -> Result<ProcessedData> {
        // Reuse buffer
        self.buffer.clear();

        // Read efficiently
        let mut total_bytes = 0;
        loop {
            // Read directly into buffer
            let n = reader.read_buf(&mut self.buffer).await?;
            if n == 0 {
                break;
            }

            // Process without copying
            self.process_chunk(&self.buffer[total_bytes..total_bytes + n])?;
            total_bytes += n;

            // Prevent unbounded growth
            if self.buffer.len() > self.capacity {
                self.buffer.truncate(self.capacity);
            }
        }

        Ok(ProcessedData {
            bytes_processed: total_bytes
        })
    }

    fn process_chunk(&self, chunk: &[u8]) -> Result<()> {
        // Process without allocation
        for window in chunk.windows(4) {
            // Process 4-byte windows without copying
            let value = u32::from_le_bytes(window.try_into()?);
            // ... process value
        }
        Ok(())
    }
}

// Zero-copy string handling
pub fn process_text(input: &str) -> Result<Vec<&str>> {
    // Return slices instead of owned strings
    Ok(input
        .lines()
        .filter(|line| !line.is_empty())
        .map(|line| line.trim())
        .collect())
}

Best Practices

Rust Development Guidelines

Safety First - Leverage Rust’s type system
Error Handling - Use Result everywhere, avoid unwrap in production
Documentation - Write comprehensive docs with examples
Testing - Aim for high test coverage
Performance - Profile before optimizing
Idioms - Follow Rust API guidelines

Common Patterns

Builder Pattern
Type State Pattern

// AI: "Implement builder pattern with validation"
#[derive(Default)]
pub struct ServerBuilder {
    host: Option<String>,
    port: Option<u16>,
    workers: Option<usize>,
}

impl ServerBuilder {
    pub fn new() -> Self {
        Self::default()
    }

    pub fn host(mut self, host: impl Into<String>) -> Self {
        self.host = Some(host.into());
        self
    }

    pub fn port(mut self, port: u16) -> Self {
        self.port = Some(port);
        self
    }

    pub fn workers(mut self, workers: usize) -> Self {
        self.workers = Some(workers);
        self
    }

    pub fn build(self) -> Result<Server> {
        Ok(Server {
            host: self.host.ok_or_else(|| anyhow!("host required"))?,
            port: self.port.unwrap_or(8080),
            workers: self.workers.unwrap_or_else(num_cpus::get),
        })
    }
}

// AI: "Implement type state pattern for compile-time guarantees"
pub struct Connection<State> {
    inner: TcpStream,
    _state: PhantomData<State>,
}

pub struct Disconnected;
pub struct Connected;
pub struct Authenticated;

impl Connection<Disconnected> {
    pub async fn connect(addr: &str) -> Result<Connection<Connected>> {
        let inner = TcpStream::connect(addr).await?;
        Ok(Connection {
            inner,
            _state: PhantomData,
        })
    }
}

impl Connection<Connected> {
    pub async fn authenticate(
        self,
        credentials: &Credentials
    ) -> Result<Connection<Authenticated>> {
        // ... perform authentication
        Ok(Connection {
            inner: self.inner,
            _state: PhantomData,
        })
    }
}

impl Connection<Authenticated> {
    pub async fn execute(&mut self, query: &str) -> Result<Response> {
        // Can only execute when authenticated
        // ...
    }
}

Deployment

Optimized Docker Build

# AI Prompt: "Create multi-stage Docker build for Rust with caching"
# Build stage
FROM rust:1.75 as builder

# Create app user
RUN useradd -m -u 1001 app

WORKDIR /usr/src/app

# Cache dependencies
COPY Cargo.toml Cargo.lock ./
RUN mkdir src && \
    echo "fn main() {}" > src/main.rs && \
    cargo build --release && \
    rm -rf src

# Build application
COPY . .
RUN cargo build --release

# Runtime stage
FROM debian:bookworm-slim

# Install runtime dependencies
RUN apt-get update && apt-get install -y \
    ca-certificates \
    && rm -rf /var/lib/apt/lists/*

# Copy user from builder
COPY --from=builder /etc/passwd /etc/passwd

# Copy binary
COPY --from=builder /usr/src/app/target/release/app /usr/local/bin/app

USER app
EXPOSE 8080

CMD ["app"]

Next Steps

Advanced Rust Patterns Explore unsafe Rust, FFI, and advanced type system features

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