verae-mcp-timestamping-server-go/internal/server/server.go

package server

import (
	"fmt"
	"net/http"
	"os"
	"strconv"
	"strings"

	"git.georgelambert.org/marchon/verae-mcp-timestamping-server-go/internal/ledger"
	"git.georgelambert.org/marchon/verae-mcp-timestamping-server-go/internal/tools"
	"git.georgelambert.org/marchon/verae-mcp-timestamping-server-go/internal/veraetime"
	"github.com/modelcontextprotocol/go-sdk/mcp"
)

// Options configures the MCP HTTP server.
type Options struct {
	Ledger        *ledger.FileLedger
	Global        *veraetime.Client
	Keeper        *veraetime.Keeper
	AuthPath      string
	GlobalURL     string
	RequireBearer bool
	JSONResponse  bool
	Stateless     bool
}

// Server wraps the MCP Streamable HTTP handler mounted at /mcp.
type Server struct {
	mcp     *mcp.Server
	handler http.Handler
	deps    *tools.Deps
}

// New builds an MCP server and Streamable HTTP handler.
func New(opts Options) (*Server, error) {
	globalURL := strings.TrimSpace(opts.GlobalURL)
	if globalURL == "" {
		globalURL = veraetime.DefaultBaseURL
	}
	authPath := strings.TrimSpace(opts.AuthPath)
	if authPath == "" {
		authPath = veraetime.DefaultAuthPath()
	}

	global := opts.Global
	if global == nil {
		global = veraetime.NewClient(globalURL, veraetime.WithAuthPath(authPath))
	}
	keeper := opts.Keeper
	if keeper == nil {
		keeper = veraetime.NewKeeper(global, authPath)
	}
	led := opts.Ledger
	if led == nil {
		var err error
		led, err = ledger.Open(ledger.DefaultPath())
		if err != nil {
			return nil, fmt.Errorf("open ledger: %w", err)
		}
	}

	deps := &tools.Deps{
		Ledger:        led,
		Global:        global,
		Keeper:        keeper,
		RequireBearer: opts.RequireBearer,
	}
	mcpServer := tools.NewServer(deps)
	stream := mcp.NewStreamableHTTPHandler(func(*http.Request) *mcp.Server {
		return mcpServer
	}, &mcp.StreamableHTTPOptions{
		JSONResponse: opts.JSONResponse,
		Stateless:    opts.Stateless,
	})

	mux := http.NewServeMux()
	mux.Handle("/mcp", stream)
	mux.Handle("/mcp/", stream)

	return &Server{mcp: mcpServer, handler: mux, deps: deps}, nil
}

// Handler returns the HTTP handler (routes /mcp).
func (s *Server) Handler() http.Handler {
	if s == nil {
		return http.NotFoundHandler()
	}
	return s.handler
}

// MCP returns the underlying MCP server.
func (s *Server) MCP() *mcp.Server {
	if s == nil {
		return nil
	}
	return s.mcp
}

// Config is runtime configuration from flags and env.
type Config struct {
	Transport     string
	Host          string
	Port          int
	RequireBearer bool
	GlobalURL     string
	AuthPath      string
	LedgerPath    string
	NATSListen    string
	CORS          bool
}

// LoadConfig merges flag defaults with environment overrides.
// Env wins when set: VERAE_MCP_TRANSPORT, VERAE_MCP_HOST, VERAE_MCP_PORT,
// VERAE_MCP_REQUIRE_BEARER, VERAE_GLOBAL_URL, VERAE_AUTH_PROPERTIES, VERAE_LEDGER_PATH,
// VERAE_NATS_LISTEN, VERAE_MCP_CORS.
// VERAE_NATS_LISTEN defaults to 127.0.0.1:4223; set empty to disable embedded NATS.
func LoadConfig(transport, host string, port int) Config {
	cfg := Config{
		Transport:  transport,
		Host:       host,
		Port:       port,
		GlobalURL:  veraetime.DefaultBaseURL,
		AuthPath:   veraetime.DefaultAuthPath(),
		LedgerPath: ledger.DefaultPath(),
		NATSListen: "127.0.0.1:4223",
	}
	if v := strings.TrimSpace(os.Getenv("VERAE_MCP_TRANSPORT")); v != "" {
		cfg.Transport = v
	}
	if v := strings.TrimSpace(os.Getenv("VERAE_MCP_HOST")); v != "" {
		cfg.Host = v
	}
	if v := strings.TrimSpace(os.Getenv("VERAE_MCP_PORT")); v != "" {
		if n, err := strconv.Atoi(v); err == nil && n > 0 {
			cfg.Port = n
		}
	}
	if v := strings.TrimSpace(os.Getenv("VERAE_GLOBAL_URL")); v != "" {
		cfg.GlobalURL = v
	}
	if v := strings.TrimSpace(os.Getenv("VERAE_AUTH_PROPERTIES")); v != "" {
		cfg.AuthPath = v
	}
	if v := strings.TrimSpace(os.Getenv("VERAE_LEDGER_PATH")); v != "" {
		cfg.LedgerPath = v
	}
	if _, set := os.LookupEnv("VERAE_NATS_LISTEN"); set {
		cfg.NATSListen = strings.TrimSpace(os.Getenv("VERAE_NATS_LISTEN"))
	}
	cfg.RequireBearer = envTruthy("VERAE_MCP_REQUIRE_BEARER")
	cfg.CORS = envTruthy("VERAE_MCP_CORS")
	if cfg.Transport == "" {
		cfg.Transport = "streamable-http"
	}
	if cfg.Host == "" {
		cfg.Host = "127.0.0.1"
	}
	if cfg.Port == 0 {
		cfg.Port = 8000
	}
	return cfg
}

func envTruthy(key string) bool {
	v := strings.TrimSpace(os.Getenv(key))
	switch strings.ToLower(v) {
	case "1", "true", "yes", "on":
		return true
	default:
		return false
	}
}

// Addr returns host:port.
func (c Config) Addr() string {
	return fmt.Sprintf("%s:%d", c.Host, c.Port)
}

// WithCORS wraps h with permissive CORS when enabled (Python VERAE_MCP_CORS=1).
func WithCORS(h http.Handler, enabled bool) http.Handler {
	if !enabled {
		return h
	}
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Access-Control-Allow-Origin", "*")
		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, DELETE, OPTIONS")
		w.Header().Set("Access-Control-Allow-Headers", "*")
		w.Header().Set("Access-Control-Expose-Headers", "mcp-session-id, Mcp-Session-Id")
		if r.Method == http.MethodOptions {
			w.WriteHeader(http.StatusNoContent)
			return
		}
		h.ServeHTTP(w, r)
	})
}