Scope discovery to subtree of module that imports McpServer (#73)

This allows for multiple servers to run within a single Nest app,
each having its own separate set of tools.

This is a breaking change - previously all tools were discovered
regardless of where the McpModule was imported.

Author: david-sabata

src/mcp.module.ts

@@ -9,11 +9,18 @@ import { StdioService } from './transport/stdio.service';
 import { createStreamableHttpController } from './transport/streamable-http.controller.factory';
 import { normalizeEndpoint } from './utils/normalize-endpoint';
 
+let instanceIdCounter = 0;
+
 @Module({
   imports: [DiscoveryModule],
   providers: [McpRegistryService, McpExecutorService],
 })
 export class McpModule {
+  /**
+   * To avoid import circular dependency issues, we use a marker property.
+   */
+  readonly __isMcpModule = true;
+
   static forRoot(options: McpOptions): DynamicModule {
     const defaultOptions: Partial<McpOptions> = {
       transport: [
@@ -42,7 +49,9 @@ export class McpModule {
       mergedOptions.messagesEndpoint,
     );
     mergedOptions.mcpEndpoint = normalizeEndpoint(mergedOptions.mcpEndpoint);
-    const providers = this.createProvidersFromOptions(mergedOptions);
+
+    const moduleId = `mcp-module-${instanceIdCounter++}`;
+    const providers = this.createProvidersFromOptions(mergedOptions, moduleId);
     const controllers = this.createControllersFromOptions(mergedOptions);
 
     return {
@@ -92,12 +101,19 @@ export class McpModule {
     return controllers;
   }
 
-  private static createProvidersFromOptions(options: McpOptions): Provider[] {
+  private static createProvidersFromOptions(
+    options: McpOptions,
+    moduleId: string,
+  ): Provider[] {
     const providers: Provider[] = [
       {
         provide: 'MCP_OPTIONS',
         useValue: options,
       },
+      {
+        provide: 'MCP_MODULE_ID',
+        useValue: moduleId,
+      },
       McpRegistryService,
       McpExecutorService,
     ];

src/services/handlers/mcp-prompts.handler.ts

@@ -1,4 +1,4 @@
-import { Injectable, Scope } from '@nestjs/common';
+import { Inject, Injectable, Scope } from '@nestjs/common';
 import { ContextIdFactory, ModuleRef } from '@nestjs/core';
 import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
 import {
@@ -14,31 +14,37 @@ import { McpHandlerBase } from './mcp-handler.base';
 
 @Injectable({ scope: Scope.REQUEST })
 export class McpPromptsHandler extends McpHandlerBase {
-  constructor(moduleRef: ModuleRef, registry: McpRegistryService) {
+  constructor(
+    moduleRef: ModuleRef,
+    registry: McpRegistryService,
+    @Inject('MCP_MODULE_ID') private readonly mcpModuleId: string,
+  ) {
     super(moduleRef, registry, McpPromptsHandler.name);
   }
 
   registerHandlers(mcpServer: McpServer, httpRequest: Request) {
-    if (this.registry.getPrompts().length === 0) {
+    if (this.registry.getPrompts(this.mcpModuleId).length === 0) {
       this.logger.debug('No prompts registered, skipping prompt handlers');
       return;
     }
     mcpServer.server.setRequestHandler(ListPromptsRequestSchema, () => {
       this.logger.debug('ListPromptsRequestSchema is being called');
 
-      const prompts = this.registry.getPrompts().map((prompt) => ({
-        name: prompt.metadata.name,
-        description: prompt.metadata.description,
-        arguments: prompt.metadata.parameters
-          ? Object.entries(prompt.metadata.parameters.shape).map(
-              ([name, field]): PromptArgument => ({
-                name,
-                description: field.description,
-                required: !field.isOptional(),
-              }),
-            )
-          : [],
-      }));
+      const prompts = this.registry
+        .getPrompts(this.mcpModuleId)
+        .map((prompt) => ({
+          name: prompt.metadata.name,
+          description: prompt.metadata.description,
+          arguments: prompt.metadata.parameters
+            ? Object.entries(prompt.metadata.parameters.shape).map(
+                ([name, field]): PromptArgument => ({
+                  name,
+                  description: field.description,
+                  required: !field.isOptional(),
+                }),
+              )
+            : [],
+        }));
 
       return {
         prompts,
@@ -52,7 +58,7 @@ export class McpPromptsHandler extends McpHandlerBase {
 
         try {
           const name = request.params.name;
-          const promptInfo = this.registry.findPrompt(name);
+          const promptInfo = this.registry.findPrompt(this.mcpModuleId, name);
 
           if (!promptInfo) {
             throw new McpError(

src/services/handlers/mcp-resources.handler.ts

@@ -1,4 +1,4 @@
-import { Injectable, Scope } from '@nestjs/common';
+import { Inject, Injectable, Scope } from '@nestjs/common';
 import { ContextIdFactory, ModuleRef } from '@nestjs/core';
 import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
 import {
@@ -13,12 +13,16 @@ import { McpHandlerBase } from './mcp-handler.base';
 
 @Injectable({ scope: Scope.REQUEST })
 export class McpResourcesHandler extends McpHandlerBase {
-  constructor(moduleRef: ModuleRef, registry: McpRegistryService) {
+  constructor(
+    moduleRef: ModuleRef,
+    registry: McpRegistryService,
+    @Inject('MCP_MODULE_ID') private readonly mcpModuleId: string,
+  ) {
     super(moduleRef, registry, McpResourcesHandler.name);
   }
 
   registerHandlers(mcpServer: McpServer, httpRequest: Request) {
-    if (this.registry.getResources().length === 0) {
+    if (this.registry.getResources(this.mcpModuleId).length === 0) {
       this.logger.debug('No resources registered, skipping resource handlers');
       return;
     }
@@ -27,7 +31,7 @@ export class McpResourcesHandler extends McpHandlerBase {
       this.logger.debug('ListResourcesRequestSchema is being called');
       return {
         resources: this.registry
-          .getResources()
+          .getResources(this.mcpModuleId)
           .map((resources) => resources.metadata),
       };
     });
@@ -38,7 +42,10 @@ export class McpResourcesHandler extends McpHandlerBase {
         this.logger.debug('ReadResourceRequestSchema is being called');
 
         const uri = request.params.uri;
-        const resourceInfo = this.registry.findResourceByUri(uri);
+        const resourceInfo = this.registry.findResourceByUri(
+          this.mcpModuleId,
+          uri,
+        );
 
         if (!resourceInfo) {
           throw new McpError(

src/services/handlers/mcp-tools.handler.ts

@@ -5,7 +5,7 @@ import {
   ListToolsRequestSchema,
   McpError,
 } from '@modelcontextprotocol/sdk/types.js';
-import { Injectable, Scope } from '@nestjs/common';
+import { Inject, Injectable, Scope } from '@nestjs/common';
 import { ContextIdFactory, ModuleRef } from '@nestjs/core';
 import { Request } from 'express';
 import { zodToJsonSchema } from 'zod-to-json-schema';
@@ -14,18 +14,22 @@ import { McpHandlerBase } from './mcp-handler.base';
 
 @Injectable({ scope: Scope.REQUEST })
 export class McpToolsHandler extends McpHandlerBase {
-  constructor(moduleRef: ModuleRef, registry: McpRegistryService) {
+  constructor(
+    moduleRef: ModuleRef,
+    registry: McpRegistryService,
+    @Inject('MCP_MODULE_ID') private readonly mcpModuleId: string,
+  ) {
     super(moduleRef, registry, McpToolsHandler.name);
   }
 
   registerHandlers(mcpServer: McpServer, httpRequest: Request) {
-    if (this.registry.getTools().length === 0) {
+    if (this.registry.getTools(this.mcpModuleId).length === 0) {
       this.logger.debug('No tools registered, skipping tool handlers');
       return;
     }
 
     mcpServer.server.setRequestHandler(ListToolsRequestSchema, () => {
-      const tools = this.registry.getTools().map((tool) => {
+      const tools = this.registry.getTools(this.mcpModuleId).map((tool) => {
         // Create base schema
         const toolSchema = {
           name: tool.metadata.name,
@@ -64,7 +68,10 @@ export class McpToolsHandler extends McpHandlerBase {
       async (request) => {
         this.logger.debug('CallToolRequestSchema is being called');
 
-        const toolInfo = this.registry.findTool(request.params.name);
+        const toolInfo = this.registry.findTool(
+          this.mcpModuleId,
+          request.params.name,
+        );
 
         if (!toolInfo) {
           throw new McpError(

src/services/mcp-executor.service.ts

@@ -1,5 +1,5 @@
 import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
-import { Injectable, Logger, Scope } from '@nestjs/common';
+import { Inject, Injectable, Logger, Scope } from '@nestjs/common';
 import { ModuleRef } from '@nestjs/core';
 import { Request } from 'express';
 import { McpRegistryService } from './mcp-registry.service';
@@ -17,10 +17,22 @@ export class McpExecutorService {
   private resourcesHandler: McpResourcesHandler;
   private promptsHandler: McpPromptsHandler;
 
-  constructor(moduleRef: ModuleRef, registry: McpRegistryService) {
-    this.toolsHandler = new McpToolsHandler(moduleRef, registry);
-    this.resourcesHandler = new McpResourcesHandler(moduleRef, registry);
-    this.promptsHandler = new McpPromptsHandler(moduleRef, registry);
+  constructor(
+    moduleRef: ModuleRef,
+    registry: McpRegistryService,
+    @Inject('MCP_MODULE_ID') mcpModuleId: string,
+  ) {
+    this.toolsHandler = new McpToolsHandler(moduleRef, registry, mcpModuleId);
+    this.resourcesHandler = new McpResourcesHandler(
+      moduleRef,
+      registry,
+      mcpModuleId,
+    );
+    this.promptsHandler = new McpPromptsHandler(
+      moduleRef,
+      registry,
+      mcpModuleId,
+    );
   }
 
   /**