Qt实现HTTP文件上传下载（Flask服务端）

太过爱你忘了你带给我的痛 2022-09-03 12:27 2554阅读 0赞

接上一篇 Qt HTTP 基本操作：[https://blog.csdn.net/gongjianbo1992/article/details/97568863][https_blog.csdn.net_gongjianbo1992_article_details_97568863]

# 1.准备服务端测试代码 #

只需要上传和下载两个接口，实际应用时可能还需要 token 验证之类的，而且也没有对文件传输结果进行校验。

#using flask 2.0.1
    import os,sys
    from flask import Flask,request,jsonify,send_file,send_from_directory
    
    app = Flask(__name__)
    filename_temp = ''
    BASE_PATH=os.path.join(os.path.dirname(os.path.abspath(__file__)),'upload')
    
    #测试
    @app.route('/',methods=['GET','POST'])
    def hello():
        return '<p>Hello!</p>'
    
    #上传
    @app.route('/upload',methods=['POST'])
    def upload_file():
        try:
            global filename_temp
            f = request.files['myfile']
            filename_temp = f.filename
            print('upload file:'+f.filename)
            f.save(os.path.join(BASE_PATH,f.filename))
            return jsonify({
                'filename':f.filename,
                'fileid':0 #假装对每个文件返回一个id，然后通过id再下载
            })
        except Exception as e:
            print('error:'+str(e))
            return jsonify({'error':0}),0
    
    #下载
    @app.route('/download/<fileid>',methods=['GET'])
    def download_file(fileid):
        try:
            global filename_temp
            print('download file:'+filename_temp) #假装是通过id从数据库拿到的文件
            return send_from_directory(BASE_PATH,filename_temp,as_attachment=True)
        except Exception as e:
            print('error:'+str(e))
            return jsonify({'error':0}),0 
    
    if __name__ == '__main__':
        print('server runing... ...')
        if not os.path.exists(BASE_PATH): 
            os.makedirs(BASE_PATH) 
        app.run(host='127.0.0.1',port=12345,debug=True)

# 2.文件上传 #

传文件主要是借助 QHttpMultiPart 类，并设置 Content-Type 为 multipart/form-data。我用 Flask 测试的时候，要给 QHttpPart 设置 multipart/form-data ，Flask 的 request.files 才能拿到 form-data 的 filename 等信息。

form-data 里的 name 设置为某个值如 "myfile" 后，Flask 里可以用 request.files\['myfile'\] 获取到这个 part，进而拿到设置的 filename。

注意 get/post 返回的 QNetworkReply 需要自己释放，Qt 5.14 可以设置 QNetworkAccessManager 的 setAutoDeleteReplies(true) 自动释放，Qt 5.15 又新增了 setTransferTimeout 设置超时时间。

有些情况还需要设置 QHttpMultiPart 的 boundary，不过我这个测试 demo 暂时用不到。

void HttpManager::upload(const QString &url, const QString &filepath)
    {
        qDebug()<<"[upload file]"<<url<<QFileInfo(filepath).fileName();
        QFile *file=new QFile(filepath);
        if(!file->open(QIODevice::ReadOnly)){
            file->deleteLater();
            qDebug()<<"open file error";
            return;
        }
    
        QNetworkRequest request;
        request.setUrl(QUrl(url));
        //request.setRawHeader("Content-Type","multipart/form-data");
    
        //QHttpMultiPart需要在请求完成后释放
        QHttpMultiPart *multi_part = new QHttpMultiPart(QHttpMultiPart::FormDataType);
        QHttpPart file_part;
        file_part.setHeader(QNetworkRequest::ContentDispositionHeader,
                            QVariant(QString("form-data; name=\"myfile\"; filename=\"%1\";")
                                     .arg(QFileInfo(filepath).fileName())));
        //part.header加上这句flask.request.files才能拿到form-data的信息
        //注意不是request的header
        file_part.setRawHeader("Content-Type", "multipart/form-data");
        file_part.setBodyDevice(file);
        file->setParent(multi_part);
        multi_part->append(file_part);
    
        QNetworkReply *reply = manager.post(request,multi_part);
        multi_part->setParent(reply); //在删除reply时一并释放
    
        //因为是测试所以同步等待
        QEventLoop eventLoop;
        //上传进度
        connect(reply, &QNetworkReply::uploadProgress,
                this, [this](qint64 bytesSent, qint64 bytesTotal){
            qDebug()<<"[upload file] bytesSend"<<bytesSent<<"bytesTotal"<<bytesTotal;
        });
        //结束退出事件循环
        connect(reply, &QNetworkReply::finished, &eventLoop, &QEventLoop::quit);
        eventLoop.exec();
    
        int status_code = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
        qDebug()<<"reply"<<status_code<<QString(reply->readAll());
        qDebug()<<"[upload file] finished";
    }

# 3.文件下载 #

文件的下载相对就更简单的，只是要注意处理下载的异常情况。

void HttpManager::download(const QString &url, const QString &fileid, const QString &filepath)
    {
        qDebug()<<"[download file]"<<url<<fileid;
    
        QNetworkRequest request;
        request.setUrl(QUrl(url+QString("/%1").arg(fileid)));
        QNetworkReply *reply = manager.get(request);
    
        //先删除已有的
        QFile file(filepath);
        file.remove();
    
        //因为是测试所以同步等待
        QEventLoop eventLoop;
        //数据可读
        connect(reply, &QNetworkReply::readyRead, this, [this,reply,&file](){
               if(!reply->isOpen()){
                   if(!reply->open(QIODevice::ReadOnly)){
                       qDebug()<<"[download file] reply open failed";
                       return;
                   }
               }
               if(!file.isOpen()){
                   if(!file.open(QIODevice::WriteOnly | QIODevice::Append)){
                       qDebug()<<"[download file] file open failed";
                       return;
                   }
               }
               file.write(reply->readAll());
        });
        //下载进度
        connect(reply, &QNetworkReply::downloadProgress,
                this, [this](qint64 bytesReceived, qint64 bytesTotal){
            qDebug()<<"[download file] bytesReceived"<<bytesReceived<<"bytesTotal"<<bytesTotal;
        });
        //结束退出事件循环
        connect(reply, &QNetworkReply::finished, &eventLoop, &QEventLoop::quit);
        eventLoop.exec();
        file.close(); //关闭文件
    
        int status_code = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
        //如果是无效的响应吧数据清除
        if(status_code != 200)
            file.remove();
        qDebug()<<"reply"<<status_code<<QString(reply->readAll());
        qDebug()<<"[download file] finished";
    }

# 4.操作实例（代码链接） #

我的 demo 只是测试了两个功能的基本使用，很多异常场景需要自己根据需求处理。对于大文件，目前测试将近 4G 可以正常上传下载，但是下载时可能会阻塞当前线程（我的 demo 没多线程所以界面会假死）。下面两个是个上传后下载的文件，分别为 1G 和 3点8G：

![20210807231321180.png][]

我的示例链接：[https://github.com/gongjianbo/MyTestCode2021/tree/master/Qt/TestQt\_20210807\_HttpFile][https_github.com_gongjianbo_MyTestCode2021_tree_master_Qt_TestQt_20210807_HttpFile]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2dvbmdqaWFuYm8xOTky_size_16_color_FFFFFF_t_70][]

# 5.参考 #

文档：[https://doc.qt.io/qt-5/qnetworkaccessmanager.html][https_doc.qt.io_qt-5_qnetworkaccessmanager.html]

博客：[https://blog.csdn.net/u012321968/article/details/111636380][https_blog.csdn.net_u012321968_article_details_111636380]

[https_blog.csdn.net_gongjianbo1992_article_details_97568863]: https://blog.csdn.net/gongjianbo1992/article/details/97568863
[20210807231321180.png]: /images/20220829/ac1bffd39ef74670a7a633b5701a6f0c.png
[https_github.com_gongjianbo_MyTestCode2021_tree_master_Qt_TestQt_20210807_HttpFile]: https://github.com/gongjianbo/MyTestCode2021/tree/master/Qt/TestQt_20210807_HttpFile
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2dvbmdqaWFuYm8xOTky_size_16_color_FFFFFF_t_70]: /images/20220829/cd1ea4c811184e39bc14044e8652819f.png
[https_doc.qt.io_qt-5_qnetworkaccessmanager.html]: https://doc.qt.io/qt-5/qnetworkaccessmanager.html
[https_blog.csdn.net_u012321968_article_details_111636380]: https://blog.csdn.net/u012321968/article/details/111636380