MCPServer

A generic, reusable Model Context Protocol (MCP) Server.

Exposes a list of llm4s ToolFunctions via two transport protocols:

• MCP 2025-06-18 Streamable HTTP — POST / DELETE {path}
• MCP 2024-11-05 HTTP+SSE — GET {path}/sse + POST {path}/messages?sessionId=… (required by Claude Desktop and other legacy MCP clients)

=== Authentication === Set MCPServerOptions.apiKey to enable Bearer-token authentication. When set, every HTTP request must include Authorization: Bearer <key>; unauthenticated requests receive HTTP 401. Without an API key the server logs a development-only security warning, and start() refuses to bind to a non-loopback host (returning a Left) so an unauthenticated server is never exposed to the network.

=== Concurrency === Connections are served by an elastic, bounded thread pool capped at MCPServer.MaxServerThreads threads (shared across long-lived SSE streams and short Streamable HTTP requests). Beyond that ceiling new connections are rejected until capacity frees up, providing backpressure under load.

val tools   = Seq(myTool1, myTool2)
val options = MCPServerOptions(8080, "/mcp", "MyServer", "1.0", apiKey = Some("secret"))
val server  = new MCPServer(options, tools)
server.start()