Qt get external IP address using QNetworkReply

[CybeX]

Good day

Intro:

My application requires getting the external IP address and matching it with an internally acquired address, thus allowing the application to proceed.

For this, I am using a QNetworkAccessManager and QNetworkReply for this purpose.

My code was built using this example as a reference.

What I have tried:

Acquiring an external IP can be done by getting a JSon object from the ipify API.

I confirmed this by:

curl "https://api.ipify.org?format=json"

which in turn responds with my current IP address in the format:

{"ip":"255.255.255.255"}

which is a JSonObject. Using this, I created the code below.

Problem:

The problem is quite simple, I get no response. The post request is executed but simply no response (or finished) signal is ever triggered.

• POST -> GET request

I have changed the code for a get request as this solved this no response issue, found on this thread.

I did this by specifying the whole url with query parameters in the URL:

QNetworkRequest request(QUrl("https://api.ipify.org?format=json"));

including the header content type and size (as in the example below, finally calling the QNetworkAccessManager::get() with:

replyExternalAddress = networkManager->get(request);

but this too gave no response.

I figured that it is something small that I am missing, but I simply cannot see it.

Advice?

---

Code for querying external IP:

// public callable method, starting network request
void APICommunicator::requestExternalAddress(){
    qInfo(apicommunicator) << "Requesting external IP address from ipify.org";

    // creates network request
    // specifies "format=json"
    QUrlQuery postData;
    postData.addQueryItem("format", "json");
    QByteArray encodedQuery = postData.toString(QUrl::FullyEncoded).toUtf8();
    QNetworkRequest request(QUrl("https://api.ipify.org"));

    request.setHeader(QNetworkRequest::ContentTypeHeader, "application/x-www-form-urlencoded");
    request.setHeader(QNetworkRequest::ContentLengthHeader, QString::number(encodedQuery.size()));

    // creates merged URL from URL and query items and sends a post:
    //    https://api.ipify.org?format=json
    replyExternalAddress = networkManager->post(request, encodedQuery);
   
    // Creates QMetaObject::Connection connection for finished signal from QNetworkReply
    conExternalAddress = QObject::connect(replyExternalAddress, SIGNAL(finished()), this, SLOT(externalAddressResponse()));

    // attach error listener to reply
    addErrorListener(replyExternalAddress, conExternalAddress);


}

void APICommunicator::externalAddressResponse(){
    qDebug(apicommunicator) << "External Address response recieved";

    // disconnect signals
    QObject::disconnect(conExternalAddress);
    QObject::disconnect(conErrorListener);

    // read all output from JSon object
    QByteArray ba = replyExternalAddress->readAll();

    // delete QNetworkReply
    replyExternalAddress->deleteLater();

    LogMessageHandler::writeToApiLog(QString("\n\nCALL EXTERNAL [" + replyExternalAddress->request().url().toString() + "]\n" + QString(ba)));

    QJsonObject doc = QJsonDocument::fromJson(ba).object();
    QString ip = doc.value("ip").toString();    
    QHostAddress address = QHostAddress();

    if (ip.isEmpty()) {
        qWarning(apicommunicator) << "External Address: no data received";
    }
    else {
        address = QHostAddress(version);
    }

    // replies with address to external slot (in main application)
    emit ExternalAddressReply(address);
}

[hskoglund]

@CybeX Hi I made a small Qt test app, called TestExternalAddress which gave me my correct external address, you can try it:

TestExternalAddress.pro:

QT     += network
TARGET  = app
HEADERS = TestExternalAddress.h
SOURCES = main.cpp TestExternalAddress.cpp

main.cpp:

#include <QCoreApplication>
#include "TestExternalAddress.h"

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);
    TestExternalAddress test;
    return app.exec();
}

TestExternalAddress.h:

#include <QJsonDocument>
#include <QJsonObject>
#include <QHostAddress>
#include <QNetworkReply>

class TestExternalAddress : public QObject
{
    Q_OBJECT

public:
    TestExternalAddress();

private slots:
    void gotReply(QNetworkReply* networkReply);
};

TestExternalAddress.cpp:

#include "TestExternalAddress.h"
#include "qdebug.h"

TestExternalAddress::TestExternalAddress()
{
    QNetworkAccessManager* manager = new QNetworkAccessManager(this);
    connect(manager,SIGNAL(finished(QNetworkReply*)),SLOT(gotReply(QNetworkReply*)));
    manager->get(QNetworkRequest(QUrl("https://api.ipify.org?format=json")));
}

void TestExternalAddress::gotReply(QNetworkReply* networkReply)
{
    networkReply->deleteLater();
    qDebug() <<  QHostAddress(QJsonDocument::fromJson(networkReply->readAll()).object().value("ip").toString());
}

qDebug() printed out my external ip address :-)