feat(filesystem): add Resources and Prompts

src/filesystem/README.md

@@ -10,6 +10,8 @@ Node.js server implementing Model Context Protocol (MCP) for filesystem operatio
 - Search files
 - Get file metadata
 - Dynamic directory access control via [Roots](https://modelcontextprotocol.io/docs/learn/client-concepts#roots)
+- Expose allowed directories and files as MCP Resources
+- Built-in prompt for file review
 
 ## Directory Access Control
 
@@ -204,6 +206,28 @@ The mapping for filesystem tools is:
 
 > Note: `idempotentHint` and `destructiveHint` are meaningful only when `readOnlyHint` is `false`, as defined by the MCP spec.
 
+### Resources
+
+- **filesystem://allowed-directories**
+  - Returns the list of directories the server is currently allowed to access
+  - No arguments required
+  - Returns a plain text list with one directory per line
+  - Reflects the live state of allowed directories, whether set via command-line arguments or updated at runtime via MCP Roots
+
+- **file://{path}**
+  - Reads a file within the allowed directories and returns its contents as a resource
+  - URI format: `file:///absolute/path/to/file`
+  - Returns the file contents as plain text
+  - The path is validated against allowed directories before the file is read
+
+### Prompts
+
+- **read-file**
+  - Asks the model to read a file and summarize its contents
+  - Arguments:
+    - `path` (string): Absolute path to the file
+  - Returns a user message that instructs the model to read and summarize the file at the given path
+
 ## Usage with Claude Desktop
 Add this to your `claude_desktop_config.json`:
 

src/filesystem/__tests__/prompts.test.ts

@@ -0,0 +1,11 @@
+import { it, expect, vi } from 'vitest';
+import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
+import { registerPrompts } from '../prompts.js';
+
+it('registers read-file prompt with path in message', () => {
+  const s = { registerPrompt: vi.fn() } as unknown as McpServer;
+  registerPrompts(s);
+  const [name,, handler] = (s.registerPrompt as any).mock.calls[0];
+  expect(name).toBe('read-file');
+  expect(handler({ path: '/a/b.txt' }).messages[0].content.text).toContain('/a/b.txt');
+});

src/filesystem/__tests__/resources.test.ts

@@ -0,0 +1,20 @@
+import { it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { McpServer, ResourceTemplate } from '@modelcontextprotocol/sdk/server/mcp.js';
+import { mkdtempSync, rmSync, realpathSync } from 'fs';
+import { tmpdir } from 'os';
+import { join } from 'path';
+import { setAllowedDirectories } from '../lib.js';
+import { registerResources } from '../resources.js';
+
+let dir: string;
+beforeEach(() => { dir = realpathSync(mkdtempSync(join(tmpdir(), 'mcp-fs-'))); setAllowedDirectories([dir]); });
+afterEach(() => { rmSync(dir, { recursive: true, force: true }); setAllowedDirectories([]); });
+
+it('registers allowed-directories and file resources', () => {
+  const s = { registerResource: vi.fn() } as unknown as McpServer;
+  registerResources(s);
+  const calls = (s.registerResource as any).mock.calls;
+  expect(calls).toHaveLength(2);
+  expect(calls.map((c: any) => c[0])).toEqual(expect.arrayContaining(['allowed-directories', 'file']));
+  expect(calls.find((c: any) => c[0] === 'file')[1]).toBeInstanceOf(ResourceTemplate);
+});

src/filesystem/index.ts

@@ -27,6 +27,8 @@ import {
   headFile,
   setAllowedDirectories,
 } from './lib.js';
+import { registerResources } from './resources.js';
+import { registerPrompts } from './prompts.js';
 
 // Command line argument parsing
 const args = process.argv.slice(2);
@@ -702,6 +704,9 @@ server.registerTool(
   }
 );
 
+registerResources(server);
+registerPrompts(server);
+
 // Updates allowed directories based on MCP client roots
 async function updateAllowedDirectoriesFromRoots(requestedRoots: Root[]) {
   const validatedRootDirs = await getValidRootDirectories(requestedRoots);

src/filesystem/prompts.ts

@@ -0,0 +1,8 @@
+import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
+import { z } from "zod";
+
+export const registerPrompts = (server: McpServer): void => {
+  server.registerPrompt("read-file",
+    { title: "Read File", description: "Read a file for review.", argsSchema: { path: z.string().describe("Absolute file path") } },
+    ({ path }) => ({ messages: [{ role: "user", content: { type: "text", text: `Read ${path} and summarize.` } }] }));
+};

src/filesystem/resources.ts

@@ -0,0 +1,14 @@
+import { McpServer, ResourceTemplate } from "@modelcontextprotocol/sdk/server/mcp.js";
+import { validatePath, readFileContent, getAllowedDirectories } from "./lib.js";
+
+export const registerResources = (server: McpServer): void => {
+  server.registerResource("allowed-directories", "filesystem://allowed-directories",
+    { title: "Allowed Directories", description: "Allowed access directories.", mimeType: "text/plain" },
+    async (uri) => ({ contents: [{ uri: uri.toString(), mimeType: "text/plain", text: getAllowedDirectories().join("\n") || "None configured" }] }));
+  server.registerResource("file", new ResourceTemplate("file://{path}", { list: undefined }),
+    { title: "File", description: "Read a file. URI: file:///path/to/file", mimeType: "text/plain" },
+    async (uri, v) => {
+      const validPath = await validatePath(String(v.path ?? ""));
+      return { contents: [{ uri: uri.toString(), mimeType: "text/plain", text: await readFileContent(validPath) }] };
+    });
+};