# Svrnty.MCP.Gateway - Implementation Plan

**Document Type:** Implementation Roadmap
**Status:** Planned
**Version:** 1.0.0
**Last Updated:** 2025-10-19

---

## Overview

This document outlines the phased implementation plan for Svrnty.MCP.Gateway, following TDD principles and Clean Architecture.

### Goals

- Build production-ready MCP gateway library
- Follow Clean Architecture patterns
- Maintain >80% test coverage
- Enable centralized routing and management of MCP traffic

---

## Phase 1: Core Abstractions (2-3 days)

### Goal

Establish foundation with interfaces, models, and abstractions.

### Steps

#### Step 1.1: Core Models
- Create `ServerInfo` model (server metadata)
- Create `ServerConfig` model (server configuration)
- Create `RoutingContext` model (routing metadata)
- Create `McpRequest/Response` models
- Create `ServerHealthStatus` model
- **Tests**: Model validation, serialization

#### Step 1.2: Core Interfaces
- Define `IGatewayRouter` interface
- Define `IRoutingStrategy` interface
- Define `IAuthProvider` interface
- Define `ICircuitBreaker` interface
- Define `IServerConnection` interface
- **Tests**: Interface contracts (using mocks)

#### Step 1.3: Configuration Models
- Create `GatewayConfig`
- Create `RoutingConfig`
- Create `SecurityConfig`
- Create `RateLimitConfig`
- **Tests**: Configuration validation

### Exit Criteria

- [ ] All core models defined
- [ ] All core interfaces defined
- [ ] Unit tests passing (target: 25+ tests)
- [ ] Zero external dependencies in Core project

---

## Phase 2: Infrastructure - Server Connections (3-4 days)

### Goal

Implement connections to backend MCP servers.

### Steps

#### Step 2.1: Transport Layer
- Implement `StdioServerTransport`
- Implement `HttpServerTransport`
- Process lifecycle management
- HTTP client configuration
- **Tests**: Transport communication

#### Step 2.2: Server Connection
- Implement `ServerConnection` class
- Connection state management
- Request/response handling
- Timeout handling
- **Tests**: Connection lifecycle

#### Step 2.3: Connection Pool
- Implement `ServerConnectionPool`
- Connection pooling per server
- Idle connection eviction
- Max connections enforcement
- **Tests**: Pool behavior

### Exit Criteria

- [ ] Server connections functional
- [ ] Connection pooling working
- [ ] Unit tests passing (target: 40+ tests)
- [ ] Integration tests with mock servers (target: 10+ tests)

---

## Phase 3: Routing Implementation (3-4 days)

### Goal

Implement routing strategies and gateway router.

### Steps

#### Step 3.1: Routing Strategies
- Implement `RoundRobinStrategy`
- Implement `ToolBasedStrategy`
- Implement `ClientBasedStrategy`
- Implement `WeightedStrategy` (optional)
- **Tests**: Strategy selection logic

#### Step 3.2: Gateway Router
- Implement `GatewayRouter` class
- Server registration/discovery
- Route request to selected server
- Response handling
- **Tests**: Routing behavior

#### Step 3.3: Strategy Configuration
- Strategy factory
- Configuration-based strategy selection
- Custom strategy registration
- **Tests**: Strategy configuration

### Exit Criteria

- [ ] All routing strategies implemented
- [ ] Gateway router functional
- [ ] Unit tests passing (target: 50+ tests)
- [ ] Integration tests with real servers (target: 15+ tests)

---

## Phase 4: Health Monitoring (2-3 days)

### Goal

Implement health checks and monitoring.

### Steps

#### Step 4.1: Health Check Implementation
- Implement `ServerHealthChecker`
- Periodic health checks
- Health status tracking
- **Tests**: Health check behavior

#### Step 4.2: Circuit Breaker
- Implement `CircuitBreaker` class
- Failure tracking
- Circuit state management
- Half-open state handling
- **Tests**: Circuit breaker state transitions

#### Step 4.3: Health Dashboard
- ASP.NET Core health check integration
- Health status endpoints
- Metrics collection
- **Tests**: Health endpoint behavior

### Exit Criteria

- [ ] Health monitoring functional
- [ ] Circuit breaker working
- [ ] Unit tests passing (target: 30+ tests)
- [ ] Health endpoints operational

---

## Phase 5: Security Layer (2-3 days)

### Goal

Implement authentication, authorization, and rate limiting.

### Steps

#### Step 5.1: Authentication
- Implement `ApiKeyAuthProvider`
- API key validation
- Client identification
- **Tests**: Authentication flows

#### Step 5.2: Authorization
- Implement authorization rules
- Role-based access control
- Server-level permissions
- Tool-level permissions
- **Tests**: Authorization logic

#### Step 5.3: Rate Limiting
- Implement rate limiter
- Per-client rate limits
- Global rate limits
- Burst handling
- **Tests**: Rate limit enforcement

### Exit Criteria

- [ ] Authentication working
- [ ] Authorization functional
- [ ] Rate limiting operational
- [ ] Unit tests passing (target: 40+ tests)

---

## Phase 6: ASP.NET Core Integration (2 days)

### Goal

Provide HTTP endpoints and dependency injection support.

### Steps

#### Step 6.1: DI Extensions
- Create `AddMcpGateway` extension method
- Service registration
- Configuration binding
- **Tests**: DI registration

#### Step 6.2: HTTP Endpoints
- Implement gateway endpoint
- Implement health endpoints
- Implement management endpoints
- **Tests**: Endpoint behavior

#### Step 6.3: Middleware
- Authentication middleware
- Rate limiting middleware
- Audit logging middleware
- **Tests**: Middleware integration

### Exit Criteria

- [ ] DI integration complete
- [ ] HTTP endpoints working
- [ ] Unit tests passing (target: 25+ tests)
- [ ] Sample ASP.NET Core app working

---

## Phase 7: CLI Tool (1-2 days)

### Goal

Provide command-line interface for management.

### Steps

#### Step 7.1: CLI Commands
- `gateway list-servers` - List registered servers
- `gateway add-server <config>` - Register server
- `gateway remove-server <id>` - Unregister server
- `gateway health` - Check server health
- `gateway route-test <tool>` - Test routing
- **Tests**: CLI command execution

#### Step 7.2: Configuration
- Support for config file
- Environment variable support
- Interactive mode
- **Tests**: Configuration loading

### Exit Criteria

- [ ] CLI functional for all operations
- [ ] Integration tests passing (target: 10+ tests)
- [ ] Documentation complete

---

## Phase 8: Sample Application (1-2 days)

### Goal

Create CodexMcpGateway sample demonstrating usage.

### Steps

#### Step 8.1: Sample Project Setup
- Create ASP.NET Core project
- Configure to route to multiple servers
- **Validation**: Successful routing

#### Step 8.2: Sample Routing Strategies
- Implement custom routing strategy
- Demonstrate tool-based routing
- Demonstrate client-based routing
- **Validation**: All strategies functional

#### Step 8.3: Sample Documentation
- Usage examples
- Configuration guide
- Troubleshooting
- **Validation**: Clear and complete

### Exit Criteria

- [ ] Sample app compiles and runs
- [ ] All routing strategies demonstrated
- [ ] Documentation complete

---

## Phase 9: Documentation & Polish (1-2 days)

### Goal

Finalize documentation and prepare for release.

### Steps

#### Step 9.1: API Documentation
- XML documentation comments
- Generate API reference
- **Validation**: Complete coverage

#### Step 9.2: User Guides
- Getting Started guide
- Configuration reference
- Routing strategies guide
- Security guide
- Troubleshooting guide
- **Validation**: User-friendly

#### Step 9.3: Code Quality
- Run code analysis
- Apply code formatting
- **Validation**: Clean codebase

### Exit Criteria

- [ ] All documentation complete
- [ ] Code analysis passes
- [ ] Ready for use

---

## Test Strategy

### Unit Tests

- **Target**: >80% coverage
- **Framework**: xUnit + Moq
- **Pattern**: AAA (Arrange-Act-Assert)
- **Focus**: Core logic, edge cases, routing strategies

### Integration Tests

- **Target**: >70% coverage
- **Approach**: Real MCP server connections
- **Focus**: End-to-end routing, health checks, authentication

### Load Tests

- **Focus**: Gateway throughput and latency
- **Metrics**: Requests per second, p95/p99 latency
- **Goal**: <50ms average latency for routing decisions

---

## Milestones

| Phase | Duration | Test Target | Milestone |
|-------|----------|-------------|-----------|
| Phase 1 | 2-3 days | 25+ tests | Core abstractions complete |
| Phase 2 | 3-4 days | 40+ tests | Server connections functional |
| Phase 3 | 3-4 days | 50+ tests | Routing strategies working |
| Phase 4 | 2-3 days | 30+ tests | Health monitoring operational |
| Phase 5 | 2-3 days | 40+ tests | Security layer complete |
| Phase 6 | 2 days | 25+ tests | ASP.NET Core integration |
| Phase 7 | 1-2 days | 10+ tests | CLI tool complete |
| Phase 8 | 1-2 days | N/A | Sample app functional |
| Phase 9 | 1-2 days | N/A | Documentation complete |

**Total Estimated Time**: 17-26 days

---

## Risk Mitigation

### Risk: Server Failures

**Mitigation**:
- Circuit breaker pattern implementation
- Health monitoring with automatic failover
- Retry logic with exponential backoff

### Risk: Performance Bottlenecks

**Mitigation**:
- Connection pooling from start
- Performance testing in Phase 3
- Caching of health check results

### Risk: Security Vulnerabilities

**Mitigation**:
- Input validation throughout
- Rate limiting implementation
- Audit logging of all requests
- Regular security reviews

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## Dependencies

### Required

- .NET 8.0 SDK
- System.Text.Json (built-in)
- xUnit, Moq (testing)

### Optional

- Microsoft.Extensions.DependencyInjection
- Microsoft.Extensions.Http
- Microsoft.Extensions.Diagnostics.HealthChecks
- Microsoft.AspNetCore.RateLimiting

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## Success Criteria

- [ ] All phases complete
- [ ] >80% test coverage (Core, Infrastructure)
- [ ] >70% test coverage (AspNetCore)
- [ ] Sample application working
- [ ] Documentation complete
- [ ] Zero critical bugs
- [ ] Performance targets met (<50ms routing latency)
- [ ] Security audit passed

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**Document Version:** 1.0.0
**Status:** Planned
**Next Review:** Before Phase 1 start