MCP Helper PoC

MCP Helper with Go Envoy external processor.

Run

docker-compose up --build

A streamable HTTP MCP server will now be available at: http://localhost:8080/

Test with MCP Inspector

# Start the inspector
DANGEROUSLY_OMIT_AUTH=true npx @modelcontextprotocol/inspector

1. Open http://localhost:6274/?transport=streamable-http&serverUrl=http://localhost:8080#resources
2. Click Connect
3. Click List Tools

You'll see federated tools from both backend MCP servers (server1 and server2), automatically prefixed to avoid conflicts:

Architecture Overview

Key Components:

• MCP Initialize/Tool List: main.go - handleInitialization() creates backend sessions, aggregateTools() fetches and prefixes tools from servers
• External Processor: ext-proc/ directory handles request/response processing:
  • request.go - extractMCPToolName() pulls tool name from JSON body, stripServerPrefix() removes prefixes, sets x-mcp-server routing header, maps session IDs
  • response.go - extractHelperSessionFromBackend() reverse-maps backend session IDs to helper sessions
• Routing Rules: envoy.yaml - routes based on x-mcp-server header (server1/server2 → backend clusters, default → helper)

Flow: Client → Envoy → Ext-Proc (extracts tool, strips prefix, sets routing headers) → Routes to backend or helper → Response (session reverse mapping) → Client