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Nodeビギナーズブックでつまったところ(formidableのインタフェースが変わっている)

Last updated at Posted at 2024-08-16

要点

Nodeビギナーズブックの最後の方は当時とformidableのバージョンが違うため、そのままでは動かない。

筆者はJavaScript/TypeScript/Node.jsは全くの初心者ですので、
本記事の内容は正確ではない可能性があります。

開発環境

  • Ubuntu 24.04 LTS
  • node v20.16.0
  • formidable@3.5.1

目次

エラー内容

requestHandlers.js
function upload(response, request) {
  console.log("Request handler 'upload' was called.");

  var form = new formidable.IncomingForm();
  console.log("about to parse");
  form.parse(request, function(error, fields, files) {
    console.log("parsing done");

    /* Possible error on Windows systems:
       tried to rename to an already existing file */
    fs.rename(files.upload.path, "/tmp/test.png", function(err) {
      if (err) {
        fs.unlink("/tmp/test.png");
        fs.rename(files.upload.path, "/tmp/test.png");
      }
    });
    response.writeHead(200, {"Content-Type": "text/html"});
    response.write("received image:<br/>");
    response.write("<img src='/show' />");
    response.end();
  });
}
実行結果
node:internal/errors:541
      throw error;
      ^

TypeError [ERR_INVALID_ARG_TYPE]: The "oldPath" argument must be of type string or an instance of Buffer or URL. Received undefined
}

files.upload.pathがundefinedになってしまうため、エラーが発生している模様。

原因

筆者が使用したのformidableのバージョン(formidable@3.5.1)では、
form.parse()に渡しているコールバックの第3引数filesの要素はFileの配列になっているため、
配列の要素を指定してアクセスする必要がある。

~/.cache/typescript/5.5/node_modules/@types/formidable/index.d.ts
    type Files<U extends string = string> = {
        readonly [Prop in U]?: File[];
    };

解決方法

requestHandlers.js
function upload(response, request) {
	console.log("Request handler 'upload' was called.");

	let form = new formidable.IncomingForm();
	form.encoding = "utf-8";
	console.log("about to parse");
	form.parse(request, (error, fields, files) => {
		console.log("parsing done");
		// ↓↓↓ forEachで配列の要素にアクセス
		files.upload.forEach((file) => {
			let filePath = file.filepath;

			fs.rename(filePath, "./test.png", (err) => {
				if (err) {
					fs.unlink("./test.png");
					fs.rename(filePath, "./test.png");
				}
			});
		});

		// ↓でも動くには動いたがあまりにも汚い
		//let filePath = files.upload[0].filepath;

		response.writeHead(200, { "Content-Type": "text/html" });
		response.encoding = "UTF-8";
		response.write("received image:<br>");
		response.write("<img src='/show' />");
		response.end();
	});
}

参考

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