MCP File System

Implementation Reference

• src/index.ts:78-90 (registration)

  Registration of the 'write_file' tool using server.tool, including schema and handler function.

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

• src/index.ts:81-89 (handler)

  The handler function for 'write_file' tool that validates the path and writes the content to the file using fs.writeFile.

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

• src/index.ts:80-80 (schema)

  Zod schema defining input parameters: path (string) and content (string) for the 'write_file' tool.

  { path: z.string().describe("File location"), content: z.string().describe("File content") },

• src/index.ts:14-20 (helper)

  Helper function validatePath used by the write_file handler to ensure the file path is within allowed directories.

  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;
  }