如何使用 JSON 正文在 Qt 中发送 POST 请求

Question

我正在尝试从 Qt 发送一个 POST 请求，其中正文为 JSON 格式。首先，我断言请求在 curl 中有效：

curl -i -H "Content-Type: application/json" -d '{"key1": "value1", "key2": "value2"}' -X POST http://myserver.com/api

工作正常，我收到了来自服务器的预期响应。在 Python 中同样有效。现在我需要从 C++/Qt 发送这个请求：

QNetworkAccessManager *mgr = new QNetworkAccessManager(this);
QHttpMultiPart *httpMultiPart = new QHttpMultiPart(mgr);
QHttpPart *httpPart = new QHttpPart();
httpPart->setHeader(QNetworkRequest::ContentTypeHeader, QVariant("application/json"));
httpPart->setBody("{\"key1\":\"value1\", \"key2\":\"value2\"}");

httpMultiPart->append(*httpPart);

QNetworkReply *reply = mgr->post(QNetworkRequest(QUrl("http://myserver.com/api")), httpMultiPart);
QObject::connect(reply, &QNetworkReply::finished, [=]()
        {
            QString err = reply->errorString();
            QString contents = QString::fromUtf8(reply->readAll());
        });

现在我收到一个错误，其中 errorString 返回：`

"Error downloading http://myserver.com/api - server replied: Unsupported Media Type"`

原因是什么？我应该如何像使用 curl 发送的那样发送 POST 请求？

Answer 1

QHttpMultiPart 用于发送 MIME 多部分消息，但在这种情况下不需要发送该类型的信息。相反，您应该使用 QJsonDocument 创建 json 并将其转换为 QByteArray：

QNetworkAccessManager *mgr = new QNetworkAccessManager(this);
const QUrl url(QStringLiteral("http://myserver.com/api"));
QNetworkRequest request(url);
request.setHeader(QNetworkRequest::ContentTypeHeader, "application/json");

QJsonObject obj;
obj["key1"] = "value1";
obj["key2"] = "value2";
QJsonDocument doc(obj);
QByteArray data = doc.toJson();
// or
// QByteArray data("{\"key1\":\"value1\",\"key2\":\"value2\"}");
QNetworkReply *reply = mgr->post(request, data);

QObject::connect(reply, &QNetworkReply::finished, [=](){
    if(reply->error() == QNetworkReply::NoError){
        QString contents = QString::fromUtf8(reply->readAll());
        qDebug() << contents;
    }
    else{
        QString err = reply->errorString();
        qDebug() << err;
    }
    reply->deleteLater();
});