In-Process MCP Server Example

This example demonstrates running a fastmcpp MCP server and Copilot SDK client in the same process.

Architecture

┌─────────────────────────────────────────────────────────┐
│                    Single Process                        │
│                                                          │
│  ┌──────────────────┐      SSE       ┌───────────────┐  │
│  │  fastmcpp Server │◄──────────────►│  Copilot SDK  │  │
│  │  (background     │   localhost    │    Client     │  │
│  │   thread)        │                │               │  │
│  │                  │                │               │  │
│  │  Tools:          │                │  Connects as  │  │
│  │  - secret_vault  │                │  remote MCP   │  │
│  │  - calculator    │                │  server       │  │
│  │  - system_info   │                │               │  │
│  └──────────────────┘                └───────────────┘  │
└─────────────────────────────────────────────────────────┘

How It Works

• fastmcpp SSE server runs as a background thread on localhost:18080
• Copilot SDK connects to it as a remote MCP server
• Single process - no child processes spawned
• Communication uses localhost HTTP (SSE transport)

Building

This example requires the COPILOT_WITH_FASTMCPP CMake option:

cmake -B build -DCOPILOT_WITH_FASTMCPP=ON
cmake --build build

The build system will:

1. First try find_package(fastmcpp) for a local installation
2. If not found, automatically fetch fastmcpp from GitHub via FetchContent

Running

./build/examples/mcp/inprocess/mcp_inprocess

The example starts an interactive REPL. Try these prompts:

• Look up the INTEROP_TEST secret
• Calculate 42 * 17 using the calculator
• Get system info from the MCP server

Type quit to exit.

Tools Provided

Tool	Description
secret_vault_lookup	Look up secrets (API_TOKEN, DATABASE_URL, ENCRYPTION_KEY, INTEROP_TEST)
logged_calculator	Perform add/multiply operations with logging
get_system_info	Get MCP server information

Use Cases

This pattern is useful when you want to:

• Expose native C++ functionality to Copilot via MCP tools
• Run everything in a single process without external dependencies
• Single binary deployment with embedded MCP capabilities