Merge pull request #1 from thepwagner/accept-prefix

allow passing a prefix for exposing non-root commands

Author: thepwagner

command.go

@@ -16,9 +16,9 @@ import (
 	"github.com/urfave/cli/v3"
 )
 
-const toolDelimiter = "_"
+const ToolDelimiter = "_"
 
-func MCPCommand(root *cli.Command) *cli.Command {
+func MCPCommand(root *cli.Command, prefix ...string) *cli.Command {
 	// Calling root.Run will modify root.Action, so store if it is non-nil first
 	// We'll use this to decide to hide the root app if it's just a help command.
 	hasRootAction := root.Action != nil
@@ -30,7 +30,7 @@ func MCPCommand(root *cli.Command) *cli.Command {
 			slog.Debug("building MCP server", slog.Any("app", root.Name))
 
 			slog.Debug("serving MCP server")
-			srv, err := MPCServer(root, hasRootAction)
+			srv, err := MPCServer(root, hasRootAction, prefix...)
 			if err != nil {
 				return err
 			}
@@ -40,13 +40,18 @@ func MCPCommand(root *cli.Command) *cli.Command {
 	}
 }
 
-func MPCServer(root *cli.Command, hasRootAction bool) (*server.MCPServer, error) {
+func MPCServer(root *cli.Command, hasRootAction bool, prefix ...string) (*server.MCPServer, error) {
 	srv := server.NewMCPServer(root.Name, root.Version, server.WithToolCapabilities(true))
 
 	toolHandler := func(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-		args := strings.Split(request.Params.Name, toolDelimiter)
+		args := strings.Split(request.Params.Name, ToolDelimiter)
+
+		// Assume we were called with a root command - it should not be forwarded when we fork.
 		args = args[1:]
 
+		// If we were not called from the root command, add any prefix that was specified:
+		args = append(prefix, args...)
+
 		// We're about to execute some user input, how bad of an idea is that?
 		// Because we hardcode `os.Args[0]` and don't use a shell, we're safe from command injection.
 		// I _assume_ mcp-go has verified the arguments are actually what our tool said it can use.
@@ -68,8 +73,8 @@ func MPCServer(root *cli.Command, hasRootAction bool) (*server.MCPServer, error)
 			}
 		}
 		var logFields []any
-		for _, arg := range args {
-			logFields = append(logFields, slog.Any("arg", arg))
+		for i, arg := range args {
+			logFields = append(logFields, slog.Any(fmt.Sprintf("%d", i), arg))
 		}
 		slog.Info("forking", slog.Any("cmd", os.Args[0]), slog.Group("args", logFields...))
 

command_test.go

@@ -3,6 +3,7 @@ package urfaveclimcp_test
 import (
 	"context"
 	"os"
+	"strings"
 	"testing"
 
 	"github.com/mark3labs/mcp-go/client"
@@ -14,6 +15,12 @@ import (
 	"github.com/urfave/cli/v3"
 )
 
+func init() {
+	// The server is going to fork os.Args[0], because it thinks that is the CLI app.
+	// Right now it's actually some test harness value, let's spoof it to a known ~safe value
+	os.Args = []string{"/bin/echo"}
+}
+
 func TestMCPCommand(t *testing.T) {
 	t.Parallel()
 
@@ -89,10 +96,6 @@ func TestMCPCommandServer(t *testing.T) {
 func TestMCPCommandServer_CallTool(t *testing.T) {
 	t.Parallel()
 
-	// The server is going to fork os.Args[0], because it thinks that is the CLI app.
-	// Right now it's actually some test harness value, let's spoof it to a known ~safe value
-	os.Args = []string{"/bin/echo"}
-
 	root := &cli.Command{
 		Name: "test",
 		Flags: []cli.Flag{
@@ -108,7 +111,6 @@ func TestMCPCommandServer_CallTool(t *testing.T) {
 
 	transport := transport.NewInProcessTransport(srv)
 	c := client.NewClient(transport)
-
 	_, err = c.Initialize(t.Context(), mcp.InitializeRequest{})
 	require.NoError(t, err)
 
@@ -124,3 +126,35 @@ func TestMCPCommandServer_CallTool(t *testing.T) {
 	// The output of `echo --target 689` is returned, because that's how we would call the CLI app.
 	assert.Equal(t, "--target 689\n", content.Text)
 }
+
+func TestMCPCommandServer_CallTool_Subcommand(t *testing.T) {
+	t.Parallel()
+
+	root := &cli.Command{
+		Name: "test",
+		Commands: []*cli.Command{
+			{
+				Name:   "sub",
+				Action: func(context.Context, *cli.Command) error { return nil },
+			},
+		},
+	}
+	srv, err := urfaveclimcp.MPCServer(root, false, "foo", "bar")
+	assert.NoError(t, err)
+
+	transport := transport.NewInProcessTransport(srv)
+	c := client.NewClient(transport)
+	_, err = c.Initialize(t.Context(), mcp.InitializeRequest{})
+	require.NoError(t, err)
+
+	req := mcp.CallToolRequest{}
+	req.Params.Name = strings.Join([]string{"test", "sub"}, urfaveclimcp.ToolDelimiter)
+
+	callResult, err := c.CallTool(t.Context(), req)
+	require.NoError(t, err)
+	assert.Len(t, callResult.Content, 1)
+	content, ok := callResult.Content[0].(mcp.TextContent)
+	assert.True(t, ok)
+
+	assert.Equal(t, "foo bar sub\n", content.Text)
+}