feat(mcp): log tool call (function name + arguments)

Signed-off-by: Marc Nuri <marc@marcnuri.com>

.gitignore

@@ -1,3 +1,4 @@
+_output/
 .idea/
 .vscode/
 .docusaurus/

pkg/mcp/common_test.go

@@ -1,13 +1,18 @@
 package mcp
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
+	"flag"
 	"fmt"
+	"k8s.io/klog/v2"
+	"k8s.io/klog/v2/textlogger"
 	"net/http/httptest"
 	"os"
 	"path/filepath"
 	"runtime"
+	"strconv"
 	"testing"
 	"time"
 
@@ -97,6 +102,7 @@ func TestMain(m *testing.M) {
 type mcpContext struct {
 	profile    Profile
 	listOutput output.Output
+	logLevel   int
 
 	staticConfig  *config.StaticConfig
 	clientOptions []transport.ClientOption
@@ -108,6 +114,8 @@ type mcpContext struct {
 	mcpServer     *Server
 	mcpHttpServer *httptest.Server
 	mcpClient     *client.Client
+	klogState     klog.State
+	logBuffer     bytes.Buffer
 }
 
 func (c *mcpContext) beforeEach(t *testing.T) {
@@ -130,6 +138,13 @@ func (c *mcpContext) beforeEach(t *testing.T) {
 	if c.before != nil {
 		c.before(c)
 	}
+	// Set up logging
+	c.klogState = klog.CaptureState()
+	flags := flag.NewFlagSet("test", flag.ContinueOnError)
+	klog.InitFlags(flags)
+	_ = flags.Set("v", strconv.Itoa(c.logLevel))
+	klog.SetLogger(textlogger.NewLogger(textlogger.NewConfig(textlogger.Verbosity(c.logLevel), textlogger.Output(&c.logBuffer))))
+	// MCP Server
 	if c.mcpServer, err = NewServer(Configuration{
 		Profile:      c.profile,
 		ListOutput:   c.listOutput,
@@ -143,6 +158,7 @@ func (c *mcpContext) beforeEach(t *testing.T) {
 		t.Fatal(err)
 		return
 	}
+	// MCP Client
 	if err = c.mcpClient.Start(c.ctx); err != nil {
 		t.Fatal(err)
 		return
@@ -165,6 +181,7 @@ func (c *mcpContext) afterEach() {
 	c.mcpServer.Close()
 	_ = c.mcpClient.Close()
 	c.mcpHttpServer.Close()
+	c.klogState.Restore()
 }
 
 func testCase(t *testing.T, test func(c *mcpContext)) {

pkg/mcp/mcp.go

@@ -3,6 +3,7 @@ package mcp
 import (
 	"context"
 	"fmt"
+	"k8s.io/klog/v2"
 	"net/http"
 	"slices"
 
@@ -56,6 +57,7 @@ func NewServer(configuration Configuration) (*Server, error) {
 			server.WithPromptCapabilities(true),
 			server.WithToolCapabilities(true),
 			server.WithLogging(),
+			server.WithToolHandlerMiddleware(toolCallLoggingMiddleware),
 		),
 	}
 	if err := s.reloadKubernetesClient(); err != nil {
@@ -165,3 +167,10 @@ func contextFunc(ctx context.Context, r *http.Request) context.Context {
 
 	return ctx
 }
+
+func toolCallLoggingMiddleware(next server.ToolHandlerFunc) server.ToolHandlerFunc {
+	return func(ctx context.Context, ctr mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+		klog.V(5).Infof("mcp tool call: %s(%v)", ctr.Params.Name, ctr.Params.Arguments)
+		return next(ctx, ctr)
+	}
+}

pkg/mcp/mcp_tools_test.go

@@ -1,10 +1,11 @@
 package mcp
 
 import (
-	"k8s.io/utils/ptr"
-	"testing"
-
 	"github.com/mark3labs/mcp-go/mcp"
+	"k8s.io/utils/ptr"
+	"regexp"
+	"strings"
+	"testing"
 
 	"github.com/manusa/kubernetes-mcp-server/pkg/config"
 )
@@ -116,3 +117,27 @@ func TestDisabledTools(t *testing.T) {
 		})
 	})
 }
+
+func TestToolCallLogging(t *testing.T) {
+	testCaseWithContext(t, &mcpContext{logLevel: 5}, func(c *mcpContext) {
+		_, _ = c.callTool("configuration_view", map[string]interface{}{
+			"minified": false,
+		})
+		t.Run("Logs tool name", func(t *testing.T) {
+			expectedLog := "mcp tool call: configuration_view("
+			if !strings.Contains(c.logBuffer.String(), expectedLog) {
+				t.Errorf("Expected log to contain '%s', got: %s", expectedLog, c.logBuffer.String())
+			}
+		})
+		t.Run("Logs tool call arguments", func(t *testing.T) {
+			expected := `"mcp tool call: configuration_view\((.+)\)"`
+			m := regexp.MustCompile(expected).FindStringSubmatch(c.logBuffer.String())
+			if len(m) != 2 {
+				t.Fatalf("Expected log entry to contain arguments, got %s", c.logBuffer.String())
+			}
+			if m[1] != "map[minified:false]" {
+				t.Errorf("Expected log arguments to be 'map[minified:false]', got %s", m[1])
+			}
+		})
+	})
+}