mcp/cmd/server/main.go

// Command server is the Einherjar MCP server: a streamable-HTTP service
// exposing framework knowledge tools to AI assistants.
//
// The framework index is embedded into the binary at build time by
// cmd/indexer. The server itself only reads it.
package main

import (
	"flag"
	"fmt"
	"log/slog"
	"net/http"
	"os"

	mcpmod "code.nochebuena.dev/einherjar/mcp"
	"code.nochebuena.dev/einherjar/mcp/internal/index"
	"code.nochebuena.dev/einherjar/mcp/internal/tools"

	"github.com/modelcontextprotocol/go-sdk/mcp"
)

const (
	serverName    = "einherjar-mcp"
	serverVersion = "v0.1.0"
)

func main() {
	addr := flag.String("addr", envOr("EINHERJAR_MCP_ADDR", ":8080"), "listen address")
	path := flag.String("path", envOr("EINHERJAR_MCP_PATH", "/mcp"), "HTTP path for the MCP streamable endpoint")
	flag.Parse()

	log := slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: slog.LevelInfo}))

	idx, err := index.Load(mcpmod.IndexJSON)
	if err != nil {
		log.Error("load index", "err", err)
		os.Exit(1)
	}
	log.Info("index loaded", "modules", len(idx.Modules), "builtAt", idx.BuiltAt)

	server := mcp.NewServer(&mcp.Implementation{
		Name:    serverName,
		Version: serverVersion,
	}, nil)
	tools.Register(server, idx)

	handler := mcp.NewStreamableHTTPHandler(func(*http.Request) *mcp.Server {
		return server
	}, nil)

	mux := http.NewServeMux()
	mux.Handle(*path, handler)
	mux.HandleFunc("/healthz", func(w http.ResponseWriter, _ *http.Request) {
		fmt.Fprintln(w, "ok")
	})

	log.Info("listening", "addr", *addr, "path", *path)
	if err := http.ListenAndServe(*addr, mux); err != nil {
		log.Error("server", "err", err)
		os.Exit(1)
	}
}

func envOr(key, def string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return def
}