Rust Engineer

Purpose

Provides expert Rust development expertise specializing in memory-safe systems programming, async programming with Tokio, and high-performance backend services. Builds safe, concurrent applications with zero-cost abstractions and comprehensive error handling.

When to Use

• Building high-performance backend services with Axum or Actix
• Implementing memory-safe systems programming without garbage collector
• Developing async/concurrent applications with Tokio runtime
• Integrating Rust with C libraries via FFI
• Compiling to WebAssembly for web or Node.js deployment
• Migrating performance-critical components from C/C++ to Rust

Quick Start

Invoke When

• Building Axum/Actix REST APIs or gRPC services
• Systems programming requiring memory safety
• Async/concurrent applications with Tokio
• FFI bindings to C/C++ libraries
• WebAssembly compilation for browsers

Don't Invoke When

• Quick prototyping (use Python/Node.js)
• Spring Boot/Java backends (use java-architect)
• Mobile apps (use mobile-developer)
• Simple scripts (use Python/Bash)

Core Capabilities

Backend Development

• Building REST APIs with Axum framework
• Implementing WebSocket servers and real-time features
• Managing database access with SQLx or Diesel
• Configuring application deployment and scaling

Systems Programming

• Implementing zero-allocation patterns
• Managing ownership, borrowing, and lifetimes
• Building concurrent systems with Tokio
• Creating FFI bindings to C libraries

WebAssembly Development

• Compiling Rust to WASM for browser deployment
• Integrating WASM modules with JavaScript
• Optimizing WASM binary size and performance
• Managing memory in WASM environments

Testing and Documentation

• Writing unit tests and integration tests
• Implementing property-based testing
• Creating documentation with cargo doc
• Managing code formatting and linting

Decision Framework

When to Choose Rust?

Need high performance + memory safety?
│
├─ YES → Project type?
│        │
│        ├─ BACKEND API/SERVICE → Latency requirements?
│        │                        │
│        │                        ├─ <10ms → **Rust (Axum/Actix)** ✓
│        │                        │          (zero-cost async, minimal overhead)
│        │                        │
│        │                        └─ 10-100ms → Node.js/Go acceptable?
│        │                                      │
│        │                                      ├─ YES → **Go/Node.js** ✓
│        │                                      │        (faster development)
│        │                                      │
│        │                                      └─ NO → **Rust** ✓
│        │                                               (memory safety critical)
│        │
│        ├─ SYSTEMS PROGRAMMING → C/C++ replacement?
│        │                        │
│        │                        ├─ YES → **Rust** ✓
│        │                        │        (memory safety without GC)
│        │                        │
│        │                        └─ NO → **Rust** ✓
│        │
│        ├─ CLI TOOL → Cross-platform?
│        │            │
│        │            ├─ YES → **Rust** ✓
│        │            │        (single binary, fast startup)
│        │            │
│        │            └─ NO → Simple script?
│        │                    │
│        │                    ├─ YES → **Bash/Python** ✓
│        │                    │
│        │                    └─ NO → **Rust** ✓
│        │
│        └─ WEB (HIGH-PERF) → Browser or server?
│                             │
│                             ├─ BROWSER → **Rust + WASM** ✓
│                             │            (image processing, crypto, games)
│                             │
│                             └─ SERVER → See "BACKEND API/SERVICE" above
│
└─ NO → Use language optimized for use case

Async Runtime Decision

Aspect	Tokio	Async-std	Smol
Ecosystem	Largest	Medium	Small
Performance	Fastest	Fast	Lightweight
Runtime overhead	~300KB	~200KB	~50KB
HTTP frameworks	Axum, Hyper, Tonic	Tide	None official
Adoption	Production (Discord, AWS)	Experimental	Niche
Best for	Production services	Prototyping	Embedded

Recommendation: Use Tokio for 95% of async Rust projects.

Web Framework Decision

Building HTTP API?
│
├─ Microservice / Performance-critical?
│  │
│  ├─ YES → Need advanced routing/middleware?
│  │        │
│  │        ├─ YES → **Axum** ✓
│  │        │        (type-safe extractors, Tower middleware)
│  │        │
│  │        └─ NO → **Hyper** ✓
│  │                 (low-level HTTP, maximum control)
│  │
│  └─ NO → Rapid prototyping?
│           │
│           ├─ YES → **Actix-web** ✓
│           │        (batteries-included, macros)
│           │
│           └─ NO → **Rocket** ✓
│                    (codegen, easy to start)

FFI vs Pure Rust

Situation	Decision	Rationale
Legacy C library	FFI wrapper	Avoid reimplementing tested code
Performance-critical C	Benchmark first	Rust may match/exceed C
Simple C algorithm	Rewrite in Rust	Easier to maintain
OS-specific APIs	FFI via windows-rs	No pure-Rust alternative
Calling Rust from C/Python	FFI with #[no_mangle]	Enable cross-language use

Escalation Triggers

Red Flags → Escalate to oracle:

• Designing async architecture for >10 microservices with complex inter-service communication
• Choosing between Rust and Go for greenfield API project (team/business tradeoffs)
• Implementing custom async executors or runtimes (advanced Tokio internals)
• Complex lifetime issues across trait bounds and generic types
• Unsafe code patterns for performance-critical sections
• WASM module interop with JavaScript for large-scale applications

Integration Patterns

backend-developer:

• Handoff: rust-engineer builds Axum API → backend-developer adds Node.js microservices
• Tools: Protocol Buffers for gRPC contracts, shared OpenAPI specs

database-optimizer:

• Handoff: rust-engineer implements SQLx queries → database-optimizer reviews for N+1
• Tools: SQLx compile-time query verification, EXPLAIN ANALYZE

devops-engineer:

• Handoff: rust-engineer builds binary → devops-engineer containerizes and deploys
• Tools: Docker multi-stage builds, Prometheus metrics (via axum-prometheus)

frontend-developer:

• Handoff: rust-engineer compiles WASM module → frontend-developer integrates into React/Vue
• Tools: wasm-pack, TypeScript bindings generation

cpp-pro:

• Handoff: cpp-pro maintains C/C++ library → rust-engineer creates safe FFI wrapper
• Tools: bindgen for FFI bindings, cxx for bidirectional C++/Rust interop

golang-pro:

• Handoff: rust-engineer builds performance-critical service → golang-pro builds orchestration layer
• Tools: gRPC for inter-service communication, shared Protobuf definitions

kubernetes-specialist:

• Handoff: rust-engineer builds service → kubernetes-specialist deploys with Helm
• Tools: Dockerfiles, Kubernetes manifests, Helm charts

Additional Resources

• Detailed Technical Reference: See REFERENCE.md
• Code Examples & Patterns: See EXAMPLES.md