MCP File System

Implementation Reference

• src/index.ts:37-45 (handler)

  Handler function for the 'read_file' tool. Validates the file path using validatePath and reads the file content using fs.readFile, returning it as MCP content block or error message.

  async ({ path: filePath }: { path: string }) => {
      try {
          const validPath = validatePath(filePath);
          const content = await fs.readFile(validPath, 'utf-8');
          return { content: [{ type: 'text', text: content }] };
      } catch (error: any) {
          return { content: [{ type: 'text', text: `Error reading file: ${error.message}` }] };
      }
  }

• src/index.ts:36-36 (schema)

  Input schema for the 'read_file' tool using Zod, defining 'path' as a string.

  { path: z.string().describe("File path to read") },

• src/index.ts:34-46 (registration)

  Registration of the 'read_file' tool on the MCP server using server.tool(name, schema, handler).

  server.tool(
      "read_file",
      { path: z.string().describe("File path to read") },
      async ({ path: filePath }: { path: string }) => {
          try {
              const validPath = validatePath(filePath);
              const content = await fs.readFile(validPath, 'utf-8');
              return { content: [{ type: 'text', text: content }] };
          } catch (error: any) {
              return { content: [{ type: 'text', text: `Error reading file: ${error.message}` }] };
          }
      }
  );

• src/index.ts:14-20 (helper)

  Helper function validatePath used by read_file (and other tools) to ensure the file path is within allowed directories for security.

  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;
  }