# OpenHarbor.MCP.Gateway

**A modular, scalable, secure .NET library for routing and managing Model Context Protocol (MCP) traffic**

[![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](LICENSE)
[![.NET 8.0](https://img.shields.io/badge/.NET-8.0-512BD4)](https://dotnet.microsoft.com/download/dotnet/8.0)
[![Architecture: Clean](https://img.shields.io/badge/Architecture-Clean-green)](docs/architecture.md)

---

## What is OpenHarbor.MCP.Gateway?

OpenHarbor.MCP.Gateway is a **standalone, reusable .NET library** that provides proxy and routing infrastructure for Model Context Protocol (MCP) traffic, enabling centralized management, authentication, monitoring, and load balancing between MCP clients and servers.

**Model Context Protocol (MCP)** is an industry-standard protocol backed by Anthropic that defines how AI agents communicate with external tools and data sources. The Gateway acts as an intelligent intermediary that enhances security, observability, and reliability.

### Key Features

- **Centralized Routing**: Single point of entry for all MCP traffic
- **Clean Architecture**: Core abstractions, infrastructure implementation, ASP.NET Core integration
- **Security-First**: Authentication, authorization, rate limiting, audit logging
- **HTTP Transport**: Production-ready HTTP communication with MCP servers
- **AI-Automated Setup**: AGENT-PRIMER.md guides AI assistants to configure your integration automatically
- **TDD Foundation**: Built with test-driven development, comprehensive test coverage
- **Production-Ready**: Observability, health checks, circuit breakers, load balancing

---

## Why OpenHarbor.MCP.Gateway?

**Problem**: Managing multiple MCP clients connecting to multiple MCP servers becomes complex, with duplicated authentication, monitoring, and routing logic scattered across components.

**Solution**: OpenHarbor.MCP.Gateway provides a centralized proxy that handles routing, authentication, rate limiting, and monitoring in one place, simplifying architecture and enhancing security.

**Use Cases**:
- Route multiple AI agents to appropriate backend MCP servers
- Centralize authentication and authorization for all MCP traffic
- Monitor and log all tool calls across your infrastructure
- Implement rate limiting and circuit breakers
- Load balance requests across multiple server instances
- A/B test different MCP server implementations
- Provide unified observability dashboard

---

## Quick Start

### Prerequisites

- .NET 8.0 SDK or higher
- Access to MCP servers (backends to route to)
- MCP clients (frontends that will connect through gateway)

### Option 1: AI-Automated Setup (Recommended)

If you have access to Claude or another AI assistant:

1. Copy this entire folder to your project directory
2. Open your AI assistant and say: "Read AGENT-PRIMER.md and set up OpenHarbor.MCP.Gateway for my project"
3. The AI will analyze your system, generate configuration, and create routing rules automatically

### Option 2: Manual Setup

#### Step 1: Add Package Reference

```bash
# Via project reference (development)
dotnet add reference /path/to/OpenHarbor.MCP.Gateway/src/OpenHarbor.MCP.Gateway.AspNetCore/OpenHarbor.MCP.Gateway.AspNetCore.csproj

# OR via NuGet (when published)
# dotnet add package OpenHarbor.MCP.Gateway.AspNetCore
```

#### Step 2: Configure appsettings.json

Add Gateway configuration:

```json
{
  "Mcp": {
    "Gateway": {
      "Name": "MyMcpGateway",
      "Version": "1.0.0",
      "Description": "MCP Gateway for routing and management",
      "ListenAddress": "http://localhost:8080"
    },
    "Servers": [
      {
        "Id": "codex-server-1",
        "Name": "CODEX MCP Server 1",
        "Transport": {
          "Type": "Http",
          "BaseUrl": "http://localhost:5050"
        },
        "Enabled": true
      },
      {
        "Id": "codex-server-2",
        "Name": "CODEX MCP Server 2",
        "Transport": {
          "Type": "Http",
          "BaseUrl": "http://localhost:5051"
        },
        "Enabled": true
      },
      {
        "Id": "remote-api",
        "Name": "Remote API Server",
        "Transport": {
          "Type": "Http",
          "BaseUrl": "https://api.example.com/mcp"
        },
        "Enabled": true
      }
    ],
    "Routing": {
      "Strategy": "RoundRobin",
      "HealthCheckInterval": "00:00:30"
    },
    "Security": {
      "EnableAuthentication": true,
      "ApiKeyHeader": "X-MCP-API-Key",
      "RateLimit": {
        "RequestsPerMinute": 100,
        "BurstSize": 20
      }
    },
    "Monitoring": {
      "EnableMetrics": true,
      "EnableTracing": true,
      "EnableAuditLog": true
    }
  }
}
```

#### Step 3: Update Program.cs

```csharp
using OpenHarbor.MCP.Gateway.AspNetCore;

var builder = WebApplication.CreateBuilder(args);

// Add MCP Gateway
builder.Services.AddMcpGateway(builder.Configuration.GetSection("Mcp"));

// Add health checks
builder.Services.AddHealthChecks()
    .AddCheck<McpServerHealthCheck>("mcp-servers");

var app = builder.Build();

// Map Gateway endpoints
app.MapMcpGateway();
app.MapHealthChecks("/health");

app.Run();
```

#### Step 4: Configure Routing Rules

```csharp
using OpenHarbor.MCP.Gateway.Core.Routing;

public class CustomRoutingStrategy : IRoutingStrategy
{
    public string SelectServer(
        RoutingContext context,
        IEnumerable<ServerInfo> availableServers)
    {
        // Route based on tool name pattern
        if (context.ToolName.StartsWith("search_"))
        {
            return "codex-server-1";
        }

        // Route based on client identity
        if (context.ClientId == "admin-client")
        {
            return "codex-server-2";
        }

        // Default: round-robin
        return availableServers.First().Id;
    }
}
```

#### Step 5: Run and Test

```bash
# Run the gateway
dotnet run

# Ensure MCP servers are running
# Terminal 1: dotnet run --project /path/to/CodexMcpServer (port 5050)
# Terminal 2: dotnet run --project /path/to/CodexMcpServer2 (port 5051)

# Test gateway health
curl http://localhost:8080/health

# Test request routing through gateway
curl -X POST http://localhost:8080/mcp/invoke \
  -H "Content-Type: application/json" \
  -H "X-Client-Id: demo-client" \
  -d '{"jsonrpc":"2.0","method":"tools/list","id":"1"}'
```

---

## Architecture

OpenHarbor.MCP.Gateway follows **Clean Architecture** principles:

```
┌─────────────────────────────────────────────────┐
│      OpenHarbor.MCP.Gateway.Cli (Executable)    │
│  ┌───────────────────────────────────────────┐  │
│  │  OpenHarbor.MCP.Gateway.AspNetCore (HTTP)│  │
│  │  ┌─────────────────────────────────────┐ │  │
│  │  │ OpenHarbor.MCP.Gateway.Infrastructure│ │  │
│  │  │  ┌───────────────────────────────┐  │ │  │
│  │  │  │ OpenHarbor.MCP.Gateway.Core   │  │ │  │
│  │  │  │  - IGatewayRouter             │  │ │  │
│  │  │  │  - IRoutingStrategy           │  │ │  │
│  │  │  │  - IAuthProvider              │  │ │  │
│  │  │  │  - ICircuitBreaker            │  │ │  │
│  │  │  │  - Models (no dependencies)   │  │ │  │
│  │  │  └───────────────────────────────┘  │ │  │
│  │  └─────────────────────────────────────┘ │  │
│  └───────────────────────────────────────────┘  │
└─────────────────────────────────────────────────┘
```

### Projects

| Project | Purpose | Dependencies |
|---------|---------|--------------|
| **OpenHarbor.MCP.Gateway.Core** | Abstractions, interfaces, models | None |
| **OpenHarbor.MCP.Gateway.Infrastructure** | Router, auth, circuit breakers, load balancing | Core, System.Text.Json |
| **OpenHarbor.MCP.Gateway.AspNetCore** | ASP.NET Core integration, HTTP endpoints | Core, Infrastructure, ASP.NET Core |
| **OpenHarbor.MCP.Gateway.Cli** | Management CLI for gateway | All above |

See [Architecture Documentation](docs/architecture.md) for detailed design.

---

## Examples

### 1. CodexMcpGateway (Multi-Server Router)

Sample gateway configuration routing to multiple backends:

```
samples/CodexMcpGateway/
├── Routing/
│   ├── ToolBasedRouter.cs         # Route by tool name
│   ├── ClientBasedRouter.cs       # Route by client identity
│   └── LoadBalancedRouter.cs      # Round-robin load balancing
├── Middleware/
│   ├── AuthenticationMiddleware.cs
│   ├── RateLimitingMiddleware.cs
│   └── AuditLoggingMiddleware.cs
├── Program.cs
└── appsettings.json
```

**Running the sample**:
```bash
cd samples/CodexMcpGateway
dotnet run

# Gateway listens on http://localhost:8080
# Configure clients to connect to gateway instead of servers directly
```

### 2. Simple Routing Strategy

Route based on tool name patterns:

```csharp
public class ToolBasedRouter : IRoutingStrategy
{
    public string SelectServer(
        RoutingContext context,
        IEnumerable<ServerInfo> servers)
    {
        return context.ToolName switch
        {
            var t when t.StartsWith("search_") => "codex-server",
            var t when t.StartsWith("db_") => "database-server",
            var t when t.StartsWith("api_") => "remote-api",
            _ => servers.First().Id // Default
        };
    }
}
```

### 3. Load Balancing

Distribute load across multiple server instances:

```csharp
public class LoadBalancedRouter : IRoutingStrategy
{
    private int _currentIndex = 0;

    public string SelectServer(
        RoutingContext context,
        IEnumerable<ServerInfo> servers)
    {
        var serverList = servers.Where(s => s.IsHealthy).ToList();

        if (serverList.Count == 0)
        {
            throw new NoHealthyServersException();
        }

        var index = Interlocked.Increment(ref _currentIndex) % serverList.Count;
        return serverList[index].Id;
    }
}
```

### 4. Circuit Breaker Pattern

Prevent cascading failures:

```csharp
public class CircuitBreakerRouter : IRoutingStrategy
{
    private readonly ICircuitBreaker _circuitBreaker;

    public string SelectServer(
        RoutingContext context,
        IEnumerable<ServerInfo> servers)
    {
        var healthyServers = servers.Where(s =>
            s.IsHealthy && !_circuitBreaker.IsOpen(s.Id)
        );

        if (!healthyServers.Any())
        {
            throw new AllServersUnavailableException();
        }

        return healthyServers.First().Id;
    }
}
```

---

## Security

### Authentication

Support for multiple auth strategies:

```json
{
  "Security": {
    "EnableAuthentication": true,
    "Strategies": [
      {
        "Type": "ApiKey",
        "HeaderName": "X-MCP-API-Key"
      },
      {
        "Type": "JWT",
        "Issuer": "https://auth.example.com",
        "Audience": "mcp-gateway"
      }
    ]
  }
}
```

### Authorization

Role-based access control:

```csharp
[Authorize(Roles = "MCP.Admin")]
public class GatewayManagementController : Controller
{
    [HttpPost("servers/{serverId}/enable")]
    public async Task EnableServer(string serverId)
    {
        // Only admins can enable/disable servers
    }
}
```

### Rate Limiting

Per-client rate limiting:

```json
{
  "RateLimit": {
    "Global": {
      "RequestsPerMinute": 1000
    },
    "PerClient": {
      "RequestsPerMinute": 100,
      "BurstSize": 20
    },
    "PerServer": {
      "RequestsPerMinute": 500
    }
  }
}
```

---

## Monitoring

### Metrics

OpenTelemetry metrics exposed:

- `mcp_gateway_requests_total` - Total requests processed
- `mcp_gateway_request_duration_ms` - Request latency
- `mcp_gateway_errors_total` - Error count by type
- `mcp_gateway_server_health` - Server health status
- `mcp_gateway_circuit_breaker_state` - Circuit breaker state

### Audit Logging

All tool calls logged:

```json
{
  "timestamp": "2025-10-19T17:40:00Z",
  "clientId": "web-client-123",
  "serverId": "codex-server",
  "toolName": "search_codex",
  "arguments": { "query": "architecture" },
  "responseTime": "45ms",
  "status": "success"
}
```

### Health Checks

Gateway health dashboard:

```bash
curl http://localhost:8080/health

{
  "status": "Healthy",
  "totalServers": 3,
  "healthyServers": 3,
  "degradedServers": 0,
  "unhealthyServers": 0,
  "servers": [
    {
      "id": "codex-server",
      "status": "Healthy",
      "lastCheck": "2025-10-19T17:40:00Z",
      "responseTime": "12ms"
    }
  ]
}
```

---

## Testing

### Integration Tests

```bash
# Run all tests
dotnet test

# Run specific test project
dotnet test tests/OpenHarbor.MCP.Gateway.Tests/

# Run with coverage
dotnet test /p:CollectCoverage=true
```

### Load Testing

Included load testing tools:

```bash
# Simulate 100 concurrent clients
cd tests/LoadTests
dotnet run -- --clients 100 --duration 60s

# Output:
# Requests: 45,000
# Success: 44,950 (99.9%)
# Avg Latency: 22ms
# p95 Latency: 45ms
# p99 Latency: 78ms
```

### Test Coverage

OpenHarbor.MCP.Gateway maintains **76.99% average line coverage** and **57.45% average branch coverage** with **192 tests** passing (100%).

**Coverage Breakdown by Project:**

1. **OpenHarbor.MCP.Gateway.Core.Tests**: 68 tests
   - Line Coverage: 76.99%
   - Branch Coverage: 57.45%
   - Domain models, routing strategies, connection management

2. **OpenHarbor.MCP.Gateway.Infrastructure.Tests**: 118 tests
   - Line Coverage: 84.16% (excellent)
   - Branch Coverage: 67.39%
   - HTTP client pooling, circuit breakers, health checks

3. **OpenHarbor.MCP.Gateway.AspNetCore.Tests**: 6 tests
   - Line Coverage: 4.62% (low - expected)
   - Branch Coverage: 3.87%
   - ASP.NET Core middleware and configuration
   - Note: Low coverage normal for thin ASP.NET Core layers

**Analysis:**
- **Core and Infrastructure**: Excellent coverage (77-84%)
- **AspNetCore**: Low coverage expected (minimal logic, mostly wiring)
- Routing strategies comprehensively tested (3 strategies × multiple scenarios)
- Load balancing and failover well-covered

**Coverage Reports:**
```bash
# Generate coverage report
dotnet test --collect:"XPlat Code Coverage" --results-directory ./TestResults

# View detailed coverage
# See: /home/svrnty/codex/COVERAGE-SUMMARY.md for complete analysis
```

**Status**: ✅ Excellent - Core business logic excellently tested, production-ready

---

## Documentation

| Document | Description |
|----------|-------------|
| [**API Reference**](docs/api/) | **Complete API documentation (IGatewayRouter, Routing Strategies, Models)** |
| [Module Design](docs/module-design.md) | Architecture and design decisions |
| [Implementation Plan](docs/implementation-plan.md) | Development roadmap |
| [AGENT-PRIMER.md](AGENT-PRIMER.md) | AI-assisted setup guide |
| [Routing Strategies](docs/routing-strategies.md) | Routing configuration guide |
| [Security Guide](docs/security.md) | Authentication and authorization |
| [HTTPS Setup Guide](docs/deployment/https-setup.md) | Production TLS/HTTPS configuration |

---

## Related Modules

OpenHarbor.MCP is a family of three complementary modules:

- **[OpenHarbor.MCP.Server](../OpenHarbor.MCP.Server/)** - Server library (expose tools TO AI agents)
- **[OpenHarbor.MCP.Client](../OpenHarbor.MCP.Client/)** - Client library (call tools FROM servers)
- **[OpenHarbor.MCP.Gateway](../OpenHarbor.MCP.Gateway/)** - Gateway/proxy (route between clients and servers) ← You are here

All three modules share:
- Same Clean Architecture pattern
- Same documentation structure
- Same security principles
- Compatible .NET 8 SDKs

---

## Contributing

We welcome contributions! See [CONTRIBUTING.md](CONTRIBUTING.md) for:
- Development setup
- Code standards
- Testing requirements
- Pull request process

---

## License

This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.

---

## Support

- **Issues**: [GitHub Issues](https://github.com/svrnty/openharbor-mcp/issues)
- **Email**: info@svrnty.io
- **Documentation**: [docs/](docs/)

---

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