feat(mcp): add SSE transport support and related configuration options

internal/app/app.go

@@ -193,11 +193,15 @@ func routes(logger *slog.Logger, cfg *config.Config, info buildinfo.Info, db *st
 		Describe:      tools.NewDescribeTool(db, mcpserver.BuildToolCatalog()),
 	}
 
-	mcpHandler, err := mcpserver.New(cfg.MCP, logger, toolSet, activeProjects.Clear)
+	mcpHandlers, err := mcpserver.NewHandlers(cfg.MCP, logger, toolSet, activeProjects.Clear)
 	if err != nil {
 		return nil, fmt.Errorf("build mcp handler: %w", err)
 	}
-	mux.Handle(cfg.MCP.Path, authMiddleware(mcpHandler))
+	mux.Handle(cfg.MCP.Path, authMiddleware(mcpHandlers.StreamableHTTP))
+	if mcpHandlers.SSE != nil {
+		mux.Handle(cfg.MCP.SSEPath, authMiddleware(mcpHandlers.SSE))
+		logger.Info("SSE transport enabled", slog.String("sse_path", cfg.MCP.SSEPath))
+	}
 	mux.Handle("/files", authMiddleware(fileHandler(filesTool)))
 	mux.Handle("/files/{id}", authMiddleware(fileHandler(filesTool)))
 	if oauthEnabled {

internal/config/config.go

@@ -32,6 +32,7 @@ type ServerConfig struct {
 
 type MCPConfig struct {
 	Path           string        `yaml:"path"`
+	SSEPath        string        `yaml:"sse_path"`
 	ServerName     string        `yaml:"server_name"`
 	Version        string        `yaml:"version"`
 	Transport      string        `yaml:"transport"`

internal/config/loader.go

@@ -58,6 +58,7 @@ func defaultConfig() Config {
 		},
 		MCP: MCPConfig{
 			Path:           "/mcp",
+			SSEPath:        "/sse",
 			ServerName:     "amcs",
 			Version:        info.Version,
 			Transport:      "streamable_http",

internal/config/validate.go

@@ -33,6 +33,14 @@ func (c Config) Validate() error {
 	if strings.TrimSpace(c.MCP.Path) == "" {
 		return fmt.Errorf("invalid config: mcp.path is required")
 	}
+	if c.MCP.SSEPath != "" {
+		if strings.TrimSpace(c.MCP.SSEPath) == "" {
+			return fmt.Errorf("invalid config: mcp.sse_path must not be blank whitespace")
+		}
+		if c.MCP.SSEPath == c.MCP.Path {
+			return fmt.Errorf("invalid config: mcp.sse_path %q must differ from mcp.path", c.MCP.SSEPath)
+		}
+	}
 	if c.MCP.SessionTimeout <= 0 {
 		return fmt.Errorf("invalid config: mcp.session_timeout must be greater than zero")
 	}

internal/mcpserver/server.go

@@ -46,7 +46,28 @@ type ToolSet struct {
 	Describe      *tools.DescribeTool
 }
 
+// Handlers groups the HTTP handlers produced for an MCP server instance.
+type Handlers struct {
+	// StreamableHTTP is the primary MCP handler (always non-nil).
+	StreamableHTTP http.Handler
+	// SSE is the SSE transport handler; nil when SSEPath is empty.
+	// SSE is the de facto transport for MCP over the internet and is required by most hosted MCP clients.
+	SSE http.Handler
+}
+
+// New builds the StreamableHTTP MCP handler. It is a convenience wrapper
+// around NewHandlers for callers that only need the primary transport.
 func New(cfg config.MCPConfig, logger *slog.Logger, toolSet ToolSet, onSessionClosed func(string)) (http.Handler, error) {
+	h, err := NewHandlers(cfg, logger, toolSet, onSessionClosed)
+	if err != nil {
+		return nil, err
+	}
+	return h.StreamableHTTP, nil
+}
+
+// NewHandlers builds MCP HTTP handlers for both transports.
+// SSE is nil when cfg.SSEPath is empty.
+func NewHandlers(cfg config.MCPConfig, logger *slog.Logger, toolSet ToolSet, onSessionClosed func(string)) (Handlers, error) {
 	instructions := cfg.Instructions
 	if instructions == "" {
 		instructions = string(amcsllm.MemoryInstructions)
@@ -77,7 +98,7 @@ func New(cfg config.MCPConfig, logger *slog.Logger, toolSet ToolSet, onSessionCl
 		registerDescribeTools,
 	} {
 		if err := register(server, logger, toolSet); err != nil {
-			return nil, err
+			return Handlers{}, err
 		}
 	}
 
@@ -89,9 +110,19 @@ func New(cfg config.MCPConfig, logger *slog.Logger, toolSet ToolSet, onSessionCl
 		opts.EventStore = newCleanupEventStore(mcp.NewMemoryEventStore(nil), onSessionClosed)
 	}
 
-	return mcp.NewStreamableHTTPHandler(func(*http.Request) *mcp.Server {
-		return server
-	}, opts), nil
+	h := Handlers{
+		StreamableHTTP: mcp.NewStreamableHTTPHandler(func(*http.Request) *mcp.Server {
+			return server
+		}, opts),
+	}
+
+	if strings.TrimSpace(cfg.SSEPath) != "" {
+		h.SSE = mcp.NewSSEHandler(func(*http.Request) *mcp.Server {
+			return server
+		}, nil)
+	}
+
+	return h, nil
 }
 
 // buildServerIcons returns icon definitions referencing the server's own /images/icon.png endpoint.

internal/mcpserver/sse_test.go

@@ -0,0 +1,136 @@
+package mcpserver
+
+import (
+	"context"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/modelcontextprotocol/go-sdk/mcp"
+
+	"git.warky.dev/wdevs/amcs/internal/config"
+)
+
+func TestNewHandlers_SSEDisabledByDefault(t *testing.T) {
+	h, err := NewHandlers(config.MCPConfig{
+		ServerName:     "test",
+		Version:        "0.0.1",
+		SessionTimeout: time.Minute,
+	}, nil, streamableTestToolSet(), nil)
+	if err != nil {
+		t.Fatalf("NewHandlers() error = %v", err)
+	}
+	if h.StreamableHTTP == nil {
+		t.Fatal("StreamableHTTP handler is nil")
+	}
+	if h.SSE != nil {
+		t.Fatal("SSE handler should be nil when SSEPath is empty")
+	}
+}
+
+func TestNewHandlers_SSEEnabledWhenPathSet(t *testing.T) {
+	h, err := NewHandlers(config.MCPConfig{
+		ServerName:     "test",
+		Version:        "0.0.1",
+		SessionTimeout: time.Minute,
+		SSEPath:        "/sse",
+	}, nil, streamableTestToolSet(), nil)
+	if err != nil {
+		t.Fatalf("NewHandlers() error = %v", err)
+	}
+	if h.StreamableHTTP == nil {
+		t.Fatal("StreamableHTTP handler is nil")
+	}
+	if h.SSE == nil {
+		t.Fatal("SSE handler is nil when SSEPath is set")
+	}
+}
+
+func TestNew_BackwardCompatibility(t *testing.T) {
+	handler, err := New(config.MCPConfig{
+		ServerName:     "test",
+		Version:        "0.0.1",
+		SessionTimeout: time.Minute,
+	}, nil, streamableTestToolSet(), nil)
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+	if handler == nil {
+		t.Fatal("New() returned nil handler")
+	}
+}
+
+func TestSSEListTools(t *testing.T) {
+	h, err := NewHandlers(config.MCPConfig{
+		ServerName:     "test",
+		Version:        "0.0.1",
+		SessionTimeout: time.Minute,
+		SSEPath:        "/sse",
+	}, nil, streamableTestToolSet(), nil)
+	if err != nil {
+		t.Fatalf("NewHandlers() error = %v", err)
+	}
+
+	srv := httptest.NewServer(h.SSE)
+	t.Cleanup(srv.Close)
+
+	client := mcp.NewClient(&mcp.Implementation{Name: "client", Version: "0.0.1"}, nil)
+	cs, err := client.Connect(context.Background(), &mcp.SSEClientTransport{Endpoint: srv.URL}, nil)
+	if err != nil {
+		t.Fatalf("connect SSE client: %v", err)
+	}
+	t.Cleanup(func() { _ = cs.Close() })
+
+	result, err := cs.ListTools(context.Background(), nil)
+	if err != nil {
+		t.Fatalf("ListTools() error = %v", err)
+	}
+	if len(result.Tools) == 0 {
+		t.Fatal("ListTools() returned no tools")
+	}
+}
+
+func TestSSEAndStreamableShareTools(t *testing.T) {
+	h, err := NewHandlers(config.MCPConfig{
+		ServerName:     "test",
+		Version:        "0.0.1",
+		SessionTimeout: time.Minute,
+		SSEPath:        "/sse",
+	}, nil, streamableTestToolSet(), nil)
+	if err != nil {
+		t.Fatalf("NewHandlers() error = %v", err)
+	}
+
+	sseSrv := httptest.NewServer(h.SSE)
+	t.Cleanup(sseSrv.Close)
+
+	streamSrv := httptest.NewServer(h.StreamableHTTP)
+	t.Cleanup(streamSrv.Close)
+
+	sseClient := mcp.NewClient(&mcp.Implementation{Name: "sse-client", Version: "0.0.1"}, nil)
+	sseSession, err := sseClient.Connect(context.Background(), &mcp.SSEClientTransport{Endpoint: sseSrv.URL}, nil)
+	if err != nil {
+		t.Fatalf("connect SSE client: %v", err)
+	}
+	t.Cleanup(func() { _ = sseSession.Close() })
+
+	streamClient := mcp.NewClient(&mcp.Implementation{Name: "stream-client", Version: "0.0.1"}, nil)
+	streamSession, err := streamClient.Connect(context.Background(), &mcp.StreamableClientTransport{Endpoint: streamSrv.URL}, nil)
+	if err != nil {
+		t.Fatalf("connect StreamableHTTP client: %v", err)
+	}
+	t.Cleanup(func() { _ = streamSession.Close() })
+
+	sseTools, err := sseSession.ListTools(context.Background(), nil)
+	if err != nil {
+		t.Fatalf("SSE ListTools() error = %v", err)
+	}
+	streamTools, err := streamSession.ListTools(context.Background(), nil)
+	if err != nil {
+		t.Fatalf("StreamableHTTP ListTools() error = %v", err)
+	}
+
+	if len(sseTools.Tools) != len(streamTools.Tools) {
+		t.Fatalf("SSE tool count = %d, StreamableHTTP tool count = %d, want equal", len(sseTools.Tools), len(streamTools.Tools))
+	}
+}