feat: Support hot reloading of MCP operation files

router-tests/mcp_hot_reload_test.go

@@ -0,0 +1,191 @@
+package integration
+
+import (
+	"encoding/json"
+	"os"
+	"path"
+	"testing"
+	"time"
+
+	"github.com/mark3labs/mcp-go/mcp"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/wundergraph/cosmo/router-tests/testenv"
+	"github.com/wundergraph/cosmo/router/pkg/config"
+)
+
+func TestMCPOperationHotReload(t *testing.T) {
+	// create a temp graphql file into mcp_operations
+	mcpOperationsDirectory := "./testdata/mcp_operations"
+	fileName := "getEmployeeNotes.graphql"
+	filePath := path.Join(mcpOperationsDirectory, fileName)
+
+	t.Parallel()
+
+	t.Run("List Updated User Operations On Addition and Removal", func(t *testing.T) {
+		testenv.Run(t, &testenv.Config{
+			MCP: config.MCPConfiguration{
+				Enabled: true,
+				HotReloadConfig: config.MCPOperationsHotReloadConfig{
+					Enabled:  true,
+					Interval: 5 * time.Second,
+				},
+			},
+		}, func(t *testing.T, xEnv *testenv.Environment) {
+
+			os.Remove(filePath)
+
+			toolsRequest := mcp.ListToolsRequest{}
+			resp, err := xEnv.MCPClient.ListTools(xEnv.Context, toolsRequest)
+			require.NoError(t, err)
+			require.NotNil(t, resp)
+
+			// initial tools count
+			initialToolsCount := len(resp.Tools)
+
+			// create new mcp operation file
+			file, err := os.Create(filePath)
+			assert.NoError(t, err)
+			defer func() {
+				file.Close()
+				os.Remove(filePath)
+			}()
+
+			// write mcp operation content
+			_, err = file.WriteString(`
+			query getEmployeeNotes($id: Int!) {
+				employee(id: $id) {
+					id
+					notes
+				}
+			}
+			`)
+			assert.NoError(t, err)
+
+			require.EventuallyWithT(t, func(t *assert.CollectT) {
+				// List updated Tools
+				toolsRequest := mcp.ListToolsRequest{}
+				resp, err := xEnv.MCPClient.ListTools(xEnv.Context, toolsRequest)
+				assert.NoError(t, err)
+
+				// verify updated tools count
+				assert.Len(t, resp.Tools, initialToolsCount+1)
+
+				// verity getEmployeeNotes operation
+				require.Contains(t, resp.Tools, mcp.Tool{
+					Name:        "execute_operation_get_employee_notes",
+					Description: "Executes the GraphQL operation 'getEmployeeNotes' of type query.",
+					InputSchema: mcp.ToolInputSchema{
+						Type:       "object",
+						Properties: map[string]interface{}{"id": map[string]interface{}{"type": "integer"}},
+						Required:   []string{"id"},
+					},
+					RawInputSchema: json.RawMessage(nil),
+					Annotations: mcp.ToolAnnotation{
+						Title:          "Execute operation getEmployeeNotes",
+						ReadOnlyHint:   mcp.ToBoolPtr(true),
+						IdempotentHint: mcp.ToBoolPtr(true),
+						OpenWorldHint:  mcp.ToBoolPtr(true),
+					},
+				})
+			}, 15*time.Second, 250*time.Millisecond)
+
+		})
+	})
+
+	t.Run("List Updated User Operations On Content Update", func(t *testing.T) {
+		testenv.Run(t, &testenv.Config{
+			MCP: config.MCPConfiguration{
+				Enabled: true,
+				HotReloadConfig: config.MCPOperationsHotReloadConfig{
+					Enabled:  true,
+					Interval: 5 * time.Second,
+				},
+			},
+		}, func(t *testing.T, xEnv *testenv.Environment) {
+
+			os.Remove(filePath)
+
+			// create new mcp operation file
+			file, err := os.Create(filePath)
+			assert.NoError(t, err)
+			defer func() {
+				file.Close()
+				os.Remove(filePath)
+			}()
+
+			// write mcp operation content
+			_, err = file.WriteString(`
+			query getEmployeeNotes($id: Int!) {
+				employee(id: $id) {
+					id
+					notes
+				}
+			}
+			`)
+			assert.NoError(t, err)
+
+			require.EventuallyWithT(t, func(t *assert.CollectT) {
+				// List updated Tools
+				toolsRequest := mcp.ListToolsRequest{}
+				resp, err := xEnv.MCPClient.ListTools(xEnv.Context, toolsRequest)
+				assert.NoError(t, err)
+
+				// verity getEmployeeNotes operation
+				require.Contains(t, resp.Tools, mcp.Tool{
+					Name:        "execute_operation_get_employee_notes",
+					Description: "Executes the GraphQL operation 'getEmployeeNotes' of type query.",
+					InputSchema: mcp.ToolInputSchema{
+						Type:       "object",
+						Properties: map[string]interface{}{"id": map[string]interface{}{"type": "integer"}},
+						Required:   []string{"id"},
+					},
+					RawInputSchema: json.RawMessage(nil),
+					Annotations: mcp.ToolAnnotation{
+						Title:          "Execute operation getEmployeeNotes",
+						ReadOnlyHint:   mcp.ToBoolPtr(true),
+						IdempotentHint: mcp.ToBoolPtr(true),
+						OpenWorldHint:  mcp.ToBoolPtr(true),
+					},
+				})
+			}, 15*time.Second, 250*time.Millisecond)
+
+			// update mcp operation content
+			err = os.WriteFile(filePath, []byte(`
+			query getEmployeeNotesUpdatedTitle($id: Int!) {
+				employee(id: $id) {
+					id
+					notes
+				}
+			}
+			`), 0644)
+			assert.NoError(t, err)
+
+			require.EventuallyWithT(t, func(t *assert.CollectT) {
+				// fetch updated mcp tools list
+				toolsRequest := mcp.ListToolsRequest{}
+				resp, err := xEnv.MCPClient.ListTools(xEnv.Context, toolsRequest)
+				assert.NoError(t, err)
+
+				// verity getEmployeeNotesUpdatedTitle operation
+				require.Contains(t, resp.Tools, mcp.Tool{
+					Name:        "execute_operation_get_employee_notes_updated_title",
+					Description: "Executes the GraphQL operation 'getEmployeeNotesUpdatedTitle' of type query.",
+					InputSchema: mcp.ToolInputSchema{
+						Type:       "object",
+						Properties: map[string]interface{}{"id": map[string]interface{}{"type": "integer"}},
+						Required:   []string{"id"},
+					},
+					RawInputSchema: json.RawMessage(nil),
+					Annotations: mcp.ToolAnnotation{
+						Title:          "Execute operation getEmployeeNotesUpdatedTitle",
+						ReadOnlyHint:   mcp.ToBoolPtr(true),
+						IdempotentHint: mcp.ToBoolPtr(true),
+						OpenWorldHint:  mcp.ToBoolPtr(true),
+					},
+				})
+			}, 15*time.Second, 250*time.Millisecond)
+		})
+	})
+
+}

router/core/graph_server.go

@@ -1082,6 +1082,16 @@ func (s *graphServer) buildGraphMux(ctx context.Context,
 		if mErr := s.mcpServer.Reload(executor.ClientSchema); mErr != nil {
 			return nil, fmt.Errorf("failed to reload MCP server: %w", mErr)
 		}
+		go func() {
+			for {
+				if reloadOperations := <-s.mcpServer.ReloadOperationsChannel(); reloadOperations {
+					s.logger.Log(zap.InfoLevel, "Reloading mcp server!")
+					if mErr := s.mcpServer.Reload(executor.ClientSchema); mErr != nil {
+						return
+					}
+				}
+			}
+		}()
 	}
 
 	if s.Config.cacheWarmup != nil && s.Config.cacheWarmup.Enabled {

router/core/router.go

@@ -848,6 +848,8 @@ func (r *Router) bootstrap(ctx context.Context) error {
 			mcpserver.WithExcludeMutations(r.mcp.ExcludeMutations),
 			mcpserver.WithEnableArbitraryOperations(r.mcp.EnableArbitraryOperations),
 			mcpserver.WithExposeSchema(r.mcp.ExposeSchema),
+			mcpserver.WithHotReload(r.mcp.HotReloadConfig.Enabled),
+			mcpserver.WithHotReloadInterval(r.mcp.HotReloadConfig.Interval),
 		}
 
 		// Determine the router GraphQL endpoint

router/pkg/config/config.go

@@ -898,14 +898,15 @@ type CacheWarmupConfiguration struct {
 }
 
 type MCPConfiguration struct {
-	Enabled                   bool             `yaml:"enabled" envDefault:"false" env:"MCP_ENABLED"`
-	Server                    MCPServer        `yaml:"server,omitempty"`
-	Storage                   MCPStorageConfig `yaml:"storage,omitempty"`
-	GraphName                 string           `yaml:"graph_name" envDefault:"mygraph" env:"MCP_GRAPH_NAME"`
-	ExcludeMutations          bool             `yaml:"exclude_mutations" envDefault:"false" env:"MCP_EXCLUDE_MUTATIONS"`
-	EnableArbitraryOperations bool             `yaml:"enable_arbitrary_operations" envDefault:"false" env:"MCP_ENABLE_ARBITRARY_OPERATIONS"`
-	ExposeSchema              bool             `yaml:"expose_schema" envDefault:"false" env:"MCP_EXPOSE_SCHEMA"`
-	RouterURL                 string           `yaml:"router_url,omitempty" env:"MCP_ROUTER_URL"`
+	Enabled                   bool                         `yaml:"enabled" envDefault:"false" env:"MCP_ENABLED"`
+	Server                    MCPServer                    `yaml:"server,omitempty"`
+	Storage                   MCPStorageConfig             `yaml:"storage,omitempty"`
+	GraphName                 string                       `yaml:"graph_name" envDefault:"mygraph" env:"MCP_GRAPH_NAME"`
+	ExcludeMutations          bool                         `yaml:"exclude_mutations" envDefault:"false" env:"MCP_EXCLUDE_MUTATIONS"`
+	EnableArbitraryOperations bool                         `yaml:"enable_arbitrary_operations" envDefault:"false" env:"MCP_ENABLE_ARBITRARY_OPERATIONS"`
+	ExposeSchema              bool                         `yaml:"expose_schema" envDefault:"false" env:"MCP_EXPOSE_SCHEMA"`
+	RouterURL                 string                       `yaml:"router_url,omitempty" env:"MCP_ROUTER_URL"`
+	HotReloadConfig           MCPOperationsHotReloadConfig `yaml:"hot_reload_config,omitempty" envPrefix:"MCP_OPERATIONS_HOT_RELOAD_"`
 }
 
 type MCPStorageConfig struct {
@@ -917,6 +918,11 @@ type MCPServer struct {
 	BaseURL    string `yaml:"base_url,omitempty" env:"MCP_SERVER_BASE_URL"`
 }
 
+type MCPOperationsHotReloadConfig struct {
+	Enabled  bool          `yaml:"enabled" envDefault:"false" env:"ENABLED"`
+	Interval time.Duration `yaml:"interval" envDefault:"10s" env:"INTERVAL"`
+}
+
 type PluginsConfiguration struct {
 	Enabled bool   `yaml:"enabled" envDefault:"false" env:"ENABLED"`
 	Path    string `yaml:"path" envDefault:"plugins" env:"PATH"`

router/pkg/config/config.schema.json

@@ -1903,6 +1903,27 @@
           "type": "boolean",
           "default": false,
           "description": "Expose the full GraphQL schema through MCP. When enabled, AI models can request the complete schema of your API."
+        },
+        "hot_reload_config": {
+          "type": "object",
+          "default": false,
+          "description": "Hot reloading configuration for MCP operations.",
+          "additionalProperties": false,
+          "properties": {
+            "enabled": {
+              "type": "boolean",
+              "description": "Enable hot reloading for MCP Operations.",
+              "default": false
+            },
+            "interval": {
+              "type": "string",
+              "description": "The interval at which the MCP Operations directory is checked for changes. The period is specified as a string with a number and a unit, e.g. 10ms, 1s, 1m, 1h. The supported units are 'ms', 's', 'm', 'h'.",
+              "default": "10s",
+              "duration": {
+                "minimum": "5s"
+              }
+            }
+          }
         }
       }
     },

router/pkg/config/fixtures/full.yaml

@@ -49,6 +49,9 @@ mcp:
     base_url: "http://localhost:5025"
   storage:
     provider_id: mcp
+  hot_reload_config:
+    enabled: false
+    interval: '10s'
 
 watch_config:
   enabled: true

router/pkg/config/testdata/config_defaults.json

@@ -122,7 +122,11 @@
     "ExcludeMutations": false,
     "EnableArbitraryOperations": false,
     "ExposeSchema": false,
-    "RouterURL": ""
+    "RouterURL": "",
+    "HotReloadConfig": {
+      "Enabled": false,
+      "Interval": 10000000000
+    }
   },
   "DemoMode": false,
   "Modules": null,

router/pkg/config/testdata/config_full.json

@@ -157,7 +157,11 @@
     "ExcludeMutations": false,
     "EnableArbitraryOperations": false,
     "ExposeSchema": false,
-    "RouterURL": "https://cosmo-router.wundergraph.com"
+    "RouterURL": "https://cosmo-router.wundergraph.com",
+    "HotReloadConfig": {
+      "Enabled": false,
+      "Interval": 10000000000
+    }
   },
   "DemoMode": true,
   "Modules": {

router/pkg/mcpserver/operation_manager.go

@@ -2,6 +2,7 @@ package mcpserver
 
 import (
 	"fmt"
+	"time"
 
 	"github.com/wundergraph/cosmo/router/pkg/schemaloader"
 	"github.com/wundergraph/graphql-go-tools/v2/pkg/ast"
@@ -30,10 +31,10 @@ func NewOperationsManager(schemaDoc *ast.Document, logger *zap.Logger, excludeMu
 }
 
 // LoadOperationsFromDirectory loads operations from a specified directory
-func (om *OperationsManager) LoadOperationsFromDirectory(operationsDir string) error {
+func (om *OperationsManager) LoadOperationsFromDirectory(operationsDir string, reloadOperationsChan chan bool, hotReload bool, hotReloadInterval time.Duration) error {
 	// Load operations
 	loader := schemaloader.NewOperationLoader(om.logger, om.schemaDoc)
-	operations, err := loader.LoadOperationsFromDirectory(operationsDir)
+	operations, err := loader.LoadOperationsFromDirectory(operationsDir, reloadOperationsChan, hotReload, hotReloadInterval)
 	if err != nil {
 		return fmt.Errorf("failed to load operations: %w", err)
 	}