QNetworkAccessManager 从不发出 finished() 信号

Question

我正在为一个项目开发一个模块，其中 HTTP GET 请求用于检索一些 XML 数据，然后将其转换为另一种格式并发送到子系统。

目前我写的代码如下：

CMakeLists.txt：

project(HttpDemo)
cmake_minimum_required(VERSION 2.8)
set(CMAKE_BUILD_TYPE Debug)

#find_package(Qt5Widgets)
find_package(Qt5Core)
find_package(Qt5Network)

set(CMAKE_AUTOMOC ON)
set(CMAKE_INCLUDE_CURRENT_DIR ON)

aux_source_directory(. SRC_LIST)
add_executable(${PROJECT_NAME} ${SRC_LIST})
qt5_use_modules(${PROJECT_NAME} Core Network) #Gui Widgets

ma​​in.cpp

#include <QtCore>
#include <QtNetwork>

class HttpHandler : public QObject
{
    Q_OBJECT
public:
    HttpHandler(QObject* parent=Q_NULLPTR) : QObject(parent)
    {
        QObject::connect(&nm, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyFinished(QNetworkReply*)));
        qDebug() << QSslSocket::sslLibraryBuildVersionString();
    }
private:
    QNetworkAccessManager nm;
public slots:
    void post(QString urlLink)
    {
        QUrl url(urlLink);
        QNetworkRequest request(url);
        QSslConfiguration sslConf;
        sslConf.setProtocol(QSsl::SslV3);
        request.setSslConfiguration(sslConf);
        request.setHeader(QNetworkRequest::ContentTypeHeader, "application/x-www-form-urlencded");

        QUrlQuery query;
        query.addQueryItem("client_id", "1234");
        query.addQueryItem("code", "abcd");

        QUrl params;
        params.setQuery(query);

        nm.post(request, params.toEncoded());
    }

    void get(QString urlLink)
    {
        QUrl url(urlLink);
        QNetworkRequest request(url);
        request.setHeader(QNetworkRequest::ContentTypeHeader, "application/x-www-form-urlencoded");

        nm.get(request);
    }

    void replyFinished(QNetworkReply* reply)
    {
        QVariant statusCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
        if(statusCode.isValid())
        {
            // Print or catch the status code
            QString status = statusCode.toString(); // or status_code.toInt();
            qDebug() << status;
            qDebug() << QString::fromStdString(reply->readAll().toStdString());
        }
    }
};

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    HttpHandler hh;
    hh.get("SOME_URL");

    return a.exec();
}

#include "main.moc"

对于SOME_URL，我尝试了很多链接，所有这些链接都可以正常工作，比如说Firefox 的Http Requester 插件。我明白了：

“OpenSSL 1.0.1j 2014 年 10 月 15 日”

qt.network.ssl：QSslSocket：无法解析 SSLv2_client_method

qt.network.ssl：QSslSocket：无法解析 SSLv2_server_method

根据互联网权威机构的说法，这应该不是问题。有一件事是肯定的 - 我的replyFinished(QNetworkReply*) 插槽没有被触发，尽管它连接到QNetworkAccessManager 的finished() 信号。这意味着无论出于何种原因都不会发出信号。将QSslConfiguration 更改为不同的QSsl::SslProtocol 不会对结果产生影响。

---

更新（根据 cmets 的要求）：

以下代码使用readyRead() 并动态分配回复。结果 - 与上面相同。

#include <QtCore>
#include <QtNetwork>

class HttpHandler : public QObject
{
    Q_OBJECT
public:
    HttpHandler(QObject* parent=Q_NULLPTR) : QObject(parent)
    {
        qDebug() << QSslSocket::sslLibraryBuildVersionString();
        this->manager = new QNetworkAccessManager(this);
        this->reply = Q_NULLPTR;
    }
private:
    QNetworkAccessManager* manager;
    QNetworkReply* reply;
signals:
    void finished();
public slots:
    void post(QString urlLink)
    {
        QUrl url(urlLink);
        QNetworkRequest request(url);
        QSslConfiguration sslConf;
        sslConf.setProtocol(QSsl::SslV2);
        request.setSslConfiguration(sslConf);
        request.setHeader(QNetworkRequest::ContentTypeHeader, "application/x-www-form-urlencoded");

        QUrlQuery query;
        query.addQueryItem("client_id", "1234");
        query.addQueryItem("code", "abcd");

        QUrl params;
        params.setQuery(query);

        manager->post(request, params.toEncoded());
    }

    void get(QString urlLink)
    {
        QUrl url(urlLink);
        QNetworkRequest request(url);
        request.setHeader(QNetworkRequest::ContentTypeHeader, "application/x-www-form-urlencoded");

        this->reply = manager->get(request);
        QObject::connect(reply, SIGNAL(readyRead()), this, SLOT(slotReadyRead()));
    }

    void slotReadyRead()
    {
        qDebug() << "Hello"; // I never land here
    }

    void replyFinished(QNetworkReply* reply)
    {
        QVariant statusCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
        if(statusCode.isValid())
        {
            QString status = statusCode.toString(); // or status_code.toInt();
            qDebug() << status;
            qDebug() << QString::fromStdString(reply->readAll().toStdString());
        }

        emit finished();
    }
};

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    HttpHandler *hh = new HttpHandler(&a);
    QObject::connect(hh, SIGNAL(finished()), &a, SLOT(quit()));

    hh->get("http://httpbin.org/ip"); // or any other httpbin.org endpoint

    return a.exec();
}

#include "main.moc"

更新 2：

我刚刚找到了一个example in the Qt documentation。下载、编译并运行了这个东西——同样的错误，但它可以工作。

Answer 1

问题已解决（请参阅here）。基本上问题出在公司的代理上。我的一位同事试了一下，用 HTTPS 替换了 HTTP（即使链接是 HTTP），它突然就工作了。然后它让我们震惊了——该公司的代理缓存 HTTP（并且还做其他事情），这会导致巨大的延迟，如果超时容限足够小，QNetworkAccessManager 将返回套接字超时。

使用QNetworkProxyFactory::setUseSystemConfiguration(true) 启用代理的方式不会使您的应用程序依赖于代码中的配置，而是依赖于系统的配置。