test(mcp): add regression test for nil ClientInfo panic (#848)

Add a test that sends a raw initialize request without clientInfo
to verify the server doesn't panic. The go-sdk client always sets
clientInfo, so we bypass it with raw HTTP to reproduce the scenario
from non-compliant clients.

Ref: #842, #844

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

Author: manusa

pkg/mcp/mcp_test.go

@@ -2,7 +2,9 @@ package mcp
 
 import (
 	"fmt"
+	"io"
 	"net/http"
+	"net/http/httptest"
 	"runtime"
 	"sync"
 	"testing"
@@ -262,6 +264,54 @@ func (s *UserAgentPropagationSuite) TestFallsBackToServerPrefixWhenNoClientInfo(
 	})
 }
 
+func (s *UserAgentPropagationSuite) TestDoesNotPanicWhenClientInfoIsNil() {
+	// Regression test for https://github.com/containers/kubernetes-mcp-server/issues/842
+	// Fixed in https://github.com/containers/kubernetes-mcp-server/pull/844
+	//
+	// The MCP spec mandates that clientInfo is sent during initialization:
+	// https://modelcontextprotocol.io/specification/2025-11-25/basic/lifecycle#initialization
+	// However, some non-compliant clients omit it, which caused a nil pointer panic
+	// in the user-agent middleware. This test verifies that the server handles
+	// non-compliant clients gracefully by sending a raw initialize request without clientInfo.
+	provider, err := internalk8s.NewProvider(s.Cfg)
+	s.Require().NoError(err)
+	s.mcpServer, err = NewServer(Configuration{StaticConfig: s.Cfg}, provider)
+	s.Require().NoError(err)
+	handler := s.mcpServer.ServeHTTP()
+	strippedHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		r.Header.Del("User-Agent")
+		handler.ServeHTTP(w, r)
+	})
+	httpServer := httptest.NewServer(strippedHandler)
+	defer httpServer.Close()
+
+	// Send raw initialize request without clientInfo (non-compliant client)
+	endpoint := httpServer.URL + "/mcp"
+	initResp := test.McpRawPost(s.T(), endpoint, "",
+		`{"jsonrpc":"2.0","id":0,"method":"initialize","params":{"protocolVersion":"2025-03-26"}}`)
+	defer func() { _ = initResp.Body.Close() }()
+	_, _ = io.ReadAll(initResp.Body)
+	sessionID := initResp.Header.Get("Mcp-Session-Id")
+	s.Require().NotEmpty(sessionID, "Expected session ID in response")
+
+	// Send tool call - this would panic before the fix when ClientInfo was nil
+	toolResp := test.McpRawPost(s.T(), endpoint, sessionID,
+		`{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"pods_list","arguments":{}}}`)
+	defer func() { _ = toolResp.Body.Close() }()
+
+	s.pathHeadersMux.Lock()
+	podsHeaders := s.pathHeaders["/api/v1/namespaces/default/pods"]
+	s.pathHeadersMux.Unlock()
+
+	s.Require().NotNil(podsHeaders, "No requests were made to /api/v1/namespaces/default/pods")
+	s.Run("User-Agent uses server prefix only when clientInfo is nil", func() {
+		s.Equal(
+			fmt.Sprintf("kubernetes-mcp-server/0.0.0 (%s/%s)", runtime.GOOS, runtime.GOARCH),
+			podsHeaders.Get("User-Agent"),
+		)
+	})
+}
+
 func TestUserAgentPropagation(t *testing.T) {
 	suite.Run(t, new(UserAgentPropagationSuite))
 }