node.js - 在 NodeJS 中监听 createReadStream 上的 'data' 事件时，写入 createWriteStream 的文件被损坏

Question

我有一个 Electron 应用程序，并且我编写了一个使用 Node 的 fs 模块复制文件的服务。当不监听 fs.createReadStream 的 data 事件时，文件复制工作正常，但是当我添加 readStream.on('data', ... 事件时，输出文件会损坏(输出文件的大小始终小于原始文件)。这是我复制文件的功能代码:

copyFile(sourcePath: string, targetPath: string): Observable<FileCopyResponseModel> {
        const copyResponse = new Subject<FileCopyResponseModel>();
        const fileSize = this.node.fs.statSync(sourcePath).size;
        const readStream = this.node.fs.createReadStream(sourcePath);
        let bytesCopied = 0;

        readStream.once("error", (err) => {
            const response = new FileCopyResponseModel();
            response.is_error = true;
            response.error = err;
            copyResponse.next(response);
        });

        readStream.on('data', (buffer) => {
            bytesCopied+= buffer.length

            const response = new FileCopyResponseModel();
            response.is_error = false;
            response.is_done = false;
            response.size = fileSize;
            response.size_copied = bytesCopied;
            copyResponse.next(response);
        });

        this.node.mkdirp(this.node.path.dirname(targetPath), (err) => {
            if (err) {
                const response = new FileCopyResponseModel();
                response.is_error = true;
                response.error = err;
                copyResponse.next(response);
            } else {
                const writeStream = this.node.fs.createWriteStream(targetPath);
                writeStream.once("error", (err) => {
                    const response = new FileCopyResponseModel();
                    response.is_error = true;
                    response.error = err;
                    copyResponse.next(response);
                });

                writeStream.once("close", (ex) => {
                    const response = new FileCopyResponseModel();
                    response.is_error = false;
                    response.is_done = true;
                    response.size = fileSize;
                    copyResponse.next(response);
                });

                readStream.pipe(writeStream);
            }
        });

        return copyResponse;
    }

如果我只是注释掉这部分代码，文件就会被正确复制:

readStream.on('data', (buffer) => {
            bytesCopied+= buffer.length

            const response = new FileCopyResponseModel();
            response.is_error = false;
            response.is_done = false;
            response.size = fileSize;
            response.size_copied = bytesCopied;
            copyResponse.next(response);
        });

知道这里出了什么问题吗？

附注:在监听 data 事件时，可以正确报告复制进度。

Answer 1

我认为您正在尝试使用可读流两次。一旦进入 on('data', 处理程序，一次进入 readStream.pipe(writeStream);。on('data', 将在将可读流传输到写入流之前先使用它。

您可以尝试更换该行:

readStream.pipe(writeStream);

与

readStream.on('data', (buffer) => {
     bytesCopied+= buffer.length

     const response = new FileCopyResponseModel();
     response.is_error = false;
     response.is_done = false;
     response.size = fileSize;
     response.size_copied = bytesCopied;
     copyResponse.next(response);
     // new bit
     writeStream.write(buffer);
 });

并从上面的处理程序中删除on('data,。

您还可以在读取流结束时结束 writeStream。

readStream.on('end', function() {
    console.log('end');
    writeStream.end();
});