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fix(cmd): disable klog in STDIO mode (#331)

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Prevents protocol issues with some clients.

Kubernetes tooling uses klog to log messages.
Some of these messages end up logged in the stderr or stdout which breaks some of the clients that expect jsonrpc messages.

Signed-off-by: Marc Nuri <marc@marcnuri.com>
This commit is contained in:
Marc Nuri
2025-09-17 17:03:40 +02:00
committed by GitHub
parent e16114dfc5
commit 94baad6570
3 changed files with 39 additions and 12 deletions
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6
pkg/kubernetes-mcp-server/cmd/root.go
View File

@@ -207,6 +207,12 @@ func (m *MCPServerOptions) loadFlags(cmd *cobra.Command) {
func (m *MCPServerOptions) initializeLogging() {
flagSet := flag.NewFlagSet("klog", flag.ContinueOnError)
klog.InitFlags(flagSet)
if m.StaticConfig.Port == "" {
// disable klog output for stdio mode
// this is needed to avoid klog writing to stderr and breaking the protocol
_ = flagSet.Parse([]string{"-logtostderr=false", "-alsologtostderr=false", "-stderrthreshold=FATAL"})
return
}
loggerOptions := []textlogger.ConfigOption{textlogger.Output(m.Out)}
if m.StaticConfig.LogLevel >= 0 {
loggerOptions = append(loggerOptions, textlogger.Verbosity(m.StaticConfig.LogLevel))

43
pkg/kubernetes-mcp-server/cmd/root_test.go
View File

@@ -10,6 +10,8 @@ import (
"strings"
"testing"
"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"
"k8s.io/cli-runtime/pkg/genericiooptions"
)
@@ -48,7 +50,7 @@ func TestConfig(t *testing.T) {
t.Run("defaults to none", func(t *testing.T) {
ioStreams, out := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1"})
rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1"})
expectedConfig := `" - Config: "`
if err := rootCmd.Execute(); !strings.Contains(out.String(), expectedConfig) {
t.Fatalf("Expected config to be %s, got %s %v", expectedConfig, out.String(), err)
@@ -59,7 +61,7 @@ func TestConfig(t *testing.T) {
rootCmd := NewMCPServer(ioStreams)
_, file, _, _ := runtime.Caller(0)
emptyConfigPath := filepath.Join(filepath.Dir(file), "testdata", "empty-config.toml")
rootCmd.SetArgs([]string{"--version", "--log-level=1", "--config", emptyConfigPath})
rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1", "--config", emptyConfigPath})
_ = rootCmd.Execute()
expected := `(?m)\" - Config\:[^\"]+empty-config\.toml\"`
if m, err := regexp.MatchString(expected, out.String()); !m || err != nil {
@@ -69,7 +71,7 @@ func TestConfig(t *testing.T) {
t.Run("invalid path throws error", func(t *testing.T) {
ioStreams, _ := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1", "--config", "invalid-path-to-config.toml"})
rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1", "--config", "invalid-path-to-config.toml"})
err := rootCmd.Execute()
if err == nil {
t.Fatal("Expected error for invalid config path, got nil")
@@ -142,7 +144,7 @@ func TestToolsets(t *testing.T) {
t.Run("default", func(t *testing.T) {
ioStreams, out := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1"})
rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1"})
if err := rootCmd.Execute(); !strings.Contains(out.String(), "- Toolsets: core, config, helm") {
t.Fatalf("Expected toolsets 'full', got %s %v", out, err)
}
@@ -150,7 +152,7 @@ func TestToolsets(t *testing.T) {
t.Run("set with --toolsets", func(t *testing.T) {
ioStreams, out := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1", "--toolsets", "helm,config"})
rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1", "--toolsets", "helm,config"})
_ = rootCmd.Execute()
expected := `(?m)\" - Toolsets\: helm, config\"`
if m, err := regexp.MatchString(expected, out.String()); !m || err != nil {
@@ -172,7 +174,7 @@ func TestListOutput(t *testing.T) {
t.Run("defaults to table", func(t *testing.T) {
ioStreams, out := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1"})
rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1"})
if err := rootCmd.Execute(); !strings.Contains(out.String(), "- ListOutput: table") {
t.Fatalf("Expected list-output 'table', got %s %v", out, err)
}
@@ -180,7 +182,7 @@ func TestListOutput(t *testing.T) {
t.Run("set with --list-output", func(t *testing.T) {
ioStreams, out := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1", "--list-output", "yaml"})
rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1", "--list-output", "yaml"})
_ = rootCmd.Execute()
expected := `(?m)\" - ListOutput\: yaml\"`
if m, err := regexp.MatchString(expected, out.String()); !m || err != nil {
@@ -193,7 +195,7 @@ func TestReadOnly(t *testing.T) {
t.Run("defaults to false", func(t *testing.T) {
ioStreams, out := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1"})
rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1"})
if err := rootCmd.Execute(); !strings.Contains(out.String(), " - Read-only mode: false") {
t.Fatalf("Expected read-only mode false, got %s %v", out, err)
}
@@ -201,7 +203,7 @@ func TestReadOnly(t *testing.T) {
t.Run("set with --read-only", func(t *testing.T) {
ioStreams, out := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1", "--read-only"})
rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1", "--read-only"})
_ = rootCmd.Execute()
expected := `(?m)\" - Read-only mode\: true\"`
if m, err := regexp.MatchString(expected, out.String()); !m || err != nil {
@@ -214,7 +216,7 @@ func TestDisableDestructive(t *testing.T) {
t.Run("defaults to false", func(t *testing.T) {
ioStreams, out := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1"})
rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1"})
if err := rootCmd.Execute(); !strings.Contains(out.String(), " - Disable destructive tools: false") {
t.Fatalf("Expected disable destructive false, got %s %v", out, err)
}
@@ -222,7 +224,7 @@ func TestDisableDestructive(t *testing.T) {
t.Run("set with --disable-destructive", func(t *testing.T) {
ioStreams, out := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1", "--disable-destructive"})
rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1", "--disable-destructive"})
_ = rootCmd.Execute()
expected := `(?m)\" - Disable destructive tools\: true\"`
if m, err := regexp.MatchString(expected, out.String()); !m || err != nil {
@@ -255,3 +257,22 @@ func TestAuthorizationURL(t *testing.T) {
}
})
}
func TestStdioLogging(t *testing.T) {
t.Run("stdio disables klog", func(t *testing.T) {
ioStreams, out := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1"})
err := rootCmd.Execute()
require.NoErrorf(t, err, "Expected no error executing command, got %v", err)
assert.Equalf(t, "0.0.0\n", out.String(), "Expected only version output, got %s", out.String())
})
t.Run("http mode enables klog", func(t *testing.T) {
ioStreams, out := testStream()
rootCmd := NewMCPServer(ioStreams)
rootCmd.SetArgs([]string{"--version", "--log-level=1", "--port=1337"})
err := rootCmd.Execute()
require.NoErrorf(t, err, "Expected no error executing command, got %v", err)
assert.Containsf(t, out.String(), "Starting kubernetes-mcp-server", "Expected klog output, got %s", out.String())
})
}