GraphQL Server in Rust 🦀

A comprehensive GraphQL server implementation in Rust, built from scratch to understand the core concepts and architecture of GraphQL. This project follows Domain-Driven Design (DDD) principles and implements all major GraphQL features step by step.

🎯 Learning Objectives

This project aims to provide a deep understanding of:

• GraphQL specification and core concepts
• Server-side GraphQL implementation
• Rust programming for web services
• Domain-Driven Design principles
• Test-driven development

🏗️ Architecture Overview

The project is structured using Domain-Driven Design (DDD) principles:

src/
├── domain/          # Core business logic and entities
├── application/     # Use cases and application services
├── infrastructure/  # External concerns (HTTP, persistence)
└── presentation/    # API layer and request handling

📋 Major GraphQL Features

Core Features

• Schema Definition Language (SDL) - Define GraphQL schemas (✅ Implemented)
• Type System - Scalars, Objects, Interfaces, Unions, Enums (✅ Core complete, 4 test failures)
• Query Execution - Field resolution and data fetching (✅ Implemented)
• Mutation Support - Data modifications (🚧 In Progress - This PR)
• Subscription Support - Real-time updates (🚧 Planned)
• Introspection - Schema exploration at runtime (✅ Structure implemented)

Advanced Features

• Validation - Query validation against schema (🚧 Basic validation working)
• Error Handling - Comprehensive error reporting (✅ Domain errors implemented)
• DataLoader Pattern - Efficient data loading and N+1 prevention (🚧 Planned)
• Middleware/Directives - Cross-cutting concerns (🚧 Planned)
• Custom Scalars - Extended type system (🚧 Planned)
• Field Arguments - Parameterized field resolution (🚧 Planned)

Performance & Production Features

• Query Complexity Analysis - Prevent expensive queries (🚧 Planned)
• Rate Limiting - Request throttling (🚧 Planned)
• Caching - Response and field-level caching (🚧 Planned)
• Metrics & Monitoring - Observability (🚧 Planned)
• Security - Authentication, authorization, and input sanitization (🚧 Planned)

🚀 Implementation Roadmap

Current implementation status and PR tracking:

✅ Completed Features

1. [PR #1] Project Setup & Core Domain - ✅ Merged - Basic project structure and domain models
2. [PR #2] Schema Parser - ✅ Merged - SDL parsing and AST generation
3. [PR #11] Core Infrastructure & Bug Fixes - ✅ Merged - Lexer improvements, compilation fixes, schema service enhancements

🚧 Partially Implemented (59/59 tests passing)

• Query Execution - Complete implementation with comprehensive testing ✅
• Type System - Core implementation complete ✅
• Schema Validation - Basic validation working ✅
• Error Handling - Comprehensive error types implemented ✅
• Introspection - Schema introspection structure complete ✅

📋 Next Implementation Phase

1. [CURRENT PR] Mutation Support - Data modification capabilities (🚧 In Progress)
2. [PR #4] Field Resolution - Advanced resolver pattern implementation
3. [PR #5] Advanced Validation - Complete query validation against schema
4. [PR #6] Subscription Engine - Real-time subscription support
5. [PR #7] DataLoader Pattern - Efficient data loading and N+1 prevention
6. [PR #8] Middleware System - Directives and middleware
7. [PR #9] Custom Scalars - Extended scalar types
8. [PR #10] Query Complexity - Analysis and prevention
9. [PR #11] Security Layer - Auth and input sanitization
10. [PR #12] Performance Optimizations - Caching and monitoring

📊 Current Status

• Tests: 59 passing, 0 failing ✅
• Coverage: Core lexer, parser, schema service, type system, query execution ✅
• CI/CD: ✅ Multi-platform testing (Ubuntu, Windows, macOS)
• Documentation: ✅ Comprehensive inline docs and architectural guides

🔧 Technology Stack

• Language: Rust (Edition 2021)
• Web Framework: Axum (async/await)
• Parsing: Custom parser for GraphQL SDL
• Testing: Built-in Rust testing + integration tests
• Documentation: Extensive inline docs and examples

📚 Documentation

Detailed documentation for each feature can be found in the docs/ directory:

• GraphQL Fundamentals
• Domain Model Design
• Schema Definition
• Query Execution
• Mutation Support
• Advanced Validation (Coming Next)
• Error Handling (Coming Next)
• Advanced Features (Coming Next)
• Performance & Security (Coming Next)

🧪 Testing Strategy

• Unit Tests: Each domain component has comprehensive unit tests
• Integration Tests: End-to-end GraphQL query testing
• Property Tests: Using proptest for edge case discovery
• Benchmark Tests: Performance regression prevention

🤝 Contributing

This is a learning project following these principles:

• Each PR focuses on a single feature
• Comprehensive tests for all functionality
• Detailed documentation with examples
• Code reviews focusing on learning and best practices

📖 Learning Resources

• GraphQL Specification
• GraphQL Best Practices
• Domain-Driven Design
• Rust Book

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.