MCP File System

Implementation Reference

• src/index.ts:111-122 (handler)

  The handler function for the 'list_directory' tool. It validates the input directory path, reads the directory contents using fs.readdir with file types, formats each entry indicating if it's a directory or file, joins them with newlines, and returns as text content in MCP format. Errors are caught and returned as text.

  async ({ path: dirPath }: { path: string }) => {
      try {
          const validPath = validatePath(dirPath);
          const entries = await fs.readdir(validPath, { withFileTypes: true });
          const listing = entries.map(entry => 
              `[${entry.isDirectory() ? 'DIR' : 'FILE'}] ${entry.name}`
          ).join('\n');
          return { content: [{ type: 'text', text: listing }] };
      } catch (error: any) {
          return { content: [{ type: 'text', text: `Error listing directory: ${error.message}` }] };
      }
  }

• src/index.ts:108-123 (registration)

  Registration of the 'list_directory' tool using McpServer.tool(), including the tool name, input schema (path: string), and inline handler function.

  server.tool(
      "list_directory",
      { path: z.string().describe("Directory path to list") },
      async ({ path: dirPath }: { path: string }) => {
          try {
              const validPath = validatePath(dirPath);
              const entries = await fs.readdir(validPath, { withFileTypes: true });
              const listing = entries.map(entry => 
                  `[${entry.isDirectory() ? 'DIR' : 'FILE'}] ${entry.name}`
              ).join('\n');
              return { content: [{ type: 'text', text: listing }] };
          } catch (error: any) {
              return { content: [{ type: 'text', text: `Error listing directory: ${error.message}` }] };
          }
      }
  );

• src/index.ts:14-20 (helper)

  Helper function used by the 'list_directory' handler (and other tools) to resolve and validate that the provided path is within one of the allowed directories specified via command-line arguments, preventing access outside sandbox.

  function validatePath(filePath: string): string {
      const absolutePath = path.resolve(filePath);
      if (!allowedDirs.some(dir => absolutePath.startsWith(path.resolve(dir)))) {
          throw new Error(`Access denied: ${filePath} is not within allowed directories`);
      }
      return absolutePath;
  }