Creating a SSL socket in Qt for Android

[diego-qt]

Hello,

I am creating a project that communicates a PC app and an Android app through SSL.
In the PC side, I don't have any problems yet. But in the Android implementation, I have a problem and it is that QSslSocket is not recognized.

#ifndef SSLCLIENT_H
#define SSLCLIENT_H

#include <QObject>
#include <QtNetwork>
#include <QSslSocket>

class SslClient : public QObject
{
    Q_OBJECT

public:
    SslClient(QObject *parent = 0);
    ~SslClient();

    QSslSocket client_socket;

private slots:
    void tcpReady();
    void sslError(QList<QSslError> errors);
    void TCPError(QAbstractSocket::SocketError error);
    void connectToServer();
};

#endif // SSLCLIENT_H

Output is:

/home/xxx/AndroidDisplay/sslclient.h:16: erreur : unknown type name 'QSslSocket'

I have followed the instructions in https://doc.qt.io/qt-5/android-openssl-support.html, downloaded the Github OpenSSL for Android repository and added these lines at the end of my CMakeLists as requested :

if (ANDROID)
    include(~/android_openssl/CMakeLists.txt)
endif()

But this didn't solve the problem.

I am using Qt 5.15.3, Ubuntu 22.04

[jsulm]

@diego-qt said in Creating a SSL socket in Qt for Android:

I have followed the instructions in https://doc.qt.io/qt-5/android-openssl-support.html, downloaded the Github OpenSSL for Android

This has nothing to do with the error you get. QSslSocket is part of Qt. Did you add

find_package(Qt6 REQUIRED COMPONENTS Network)
target_link_libraries(mytarget PRIVATE Qt6::Network)

to your CMakeLists.txt file?
How did you install Qt for Android?

[diego-qt]

@jsulm you're right, I didn't add the lines to my CMakeLists file.
But I just added them and the error persists.

I installed Qt for Android from source from this page https://doc.qt.io/qt-5/android-building.html
I have already compiled a test app (from Qt examples) and installed it in my phone, but I'm having trouble in this next step with the SSL connection.

[jsulm]

@diego-qt said in Creating a SSL socket in Qt for Android:

I installed Qt for Android from source

Including QtSerialPort module?

"But I just added them and the error persists" - did you run cmake in an empty build folder?

[diego-qt]

@jsulm yes I have found it in /opt/Qt5.15/include/QtSerialPort
And yes I went to Projects > Build > CMake > Build directory and entered a new directory.

[jsulm]

@diego-qt Strange thing is that compiler does not complain about QSslSocket include. Check the QSslSocket header file to see whether it declares the QSslSocket class.

[diego-qt]

@jsulm hi, I'm back after some time, still with the QSslSocket problem, any help is much appreciated

I looked into the QSslSocket header file and it contains only this:

#include "qsslsocket.h"

And the so called qsslsocket.h does exist

[jsulm]

@diego-qt said in Creating a SSL socket in Qt for Android:

And the so called qsslsocket.h does exist

And does it define the QSslSocket class?

[diego-qt]

@jsulm yes indeed, the class definition starts with

class Q_NETWORK_EXPORT QSslSocket : public QTcpSocket
{

[diego-qt]

I see that my problem is Android-related, because when I try to compile the same project with my Desktop kit, it works. QSslSocket is recognized.

[jsulm]

@diego-qt Could be that QSslSocket is not available on Android. Look for #ifdef/#ifndef in the header file.

[diego-qt]

@jsulm I see something interesting now that you mention it.

#ifndef QT_NO_SSL

When I activate the Android kit, the code under this #ifndef directive is grayed out (so most of the code, actually). I'm guessing I have to activate it, but putting

#ifndef QT_NO_SSL
#define QT_NO_SSL
#endif

in my header file before calling #include <QSslSocket> does not do the trick. How could it be done ?

By the way, I see that when I activate the Desktop kit, the definition of QSslSocket in qsslsocket.h is not grayed out.

[diego-qt]

These bug reports suggest that I'm not the only one with this problem:
https://bugreports.qt.io/browse/QTBUG-88238
https://bugreports.qt.io/browse/QTBUG-65531

But there haven't been answers on the issues.

[diego-qt]

@jsulm I found that the qsslsocket.h file starts with:

#include <QtNetwork/qtnetworkglobal.h>
#include <QtCore/qlist.h>
#include <QtCore/qregexp.h>
#include <QtCore/qvector.h>

And the QtNetwork/qtnetworkglobal.h file starts with:

#include <QtCore/qglobal.h>
#include <QtNetwork/qtnetwork-config.h>

And finally, in the QtNetwork/qtnetwork-config.h file I found (among other defines):

#define QT_NO_SSL

I have the impression then that QSslSocket can't be defined when in Android kit. However, when I activate the Desktop kit, the #define QT_NO_SSL is not found in the last file I mentioned, that's why my project compiles with this kit.
I don't understand why this happens. I might need to rerun a configuration file but I don't know what exactly to do.

[diego-qt]

Hello @jsulm I have looked deeper into my problem and found some things. Could you help me by confirming as far as you can? Or recommend someone that may know the answer?

I found a new documentation page I hadn't read: https://doc.qt.io/qt-5/ssl.html#enabling-and-disabling-ssl-support
When I launched the configure program with the openssl-linked option, I finally got a QtNetwork/qtnetwork-config.h file without the definition that caused trouble (see above). However, when I tried to save the new qmake version and its Android kit, I get an error saying that the Android Clang compiler "can't produce code for the Qt version "Qt 5.15.13 (Qt-5.15.13)" (x86-linux-generic-elf-64bit)."

What I understand is that I didn't activate the target for cross-compilation in the initial configuration step.
So I went back and launched this

OPENSSL_LIBS='-L~/android-sdk/android_openssl/ssl_1.1/arm64-v8a/include -lssl -lcrypto' \
~/qt5/configure -openssl-linked -prefix /opt/Qt5.15 -xplatform android-clang \
-disable-rpath -nomake tests -nomake examples -android-ndk ~/android-sdk/ndk/21.3.6528147 \
-android-sdk ~/android-sdk -no-warnings-are-errors -opensource -confirm-license

But I got the following error:

ERROR: Feature 'openssl-linked' was enabled, but the pre-condition '!features.securetransport && !features.schannel && libs.openssl' failed.

Check config.log for details.

Please note that when I launch the mentioned command without -xplatform android-clang, it seems to work and I am asked to launch gmake. So for the time being I have found myself in an incompatibility of installing an SSL-supported Qt and cross-compiling for Android.

Regarding the config log file that the error indicates me, I don't know what exactly to look at.
What I find interesting is that at some point there is this SSL-related error (with the -xplatform option):

+ cd /home/diego/qt-build/config.tests/openssl && MAKEFLAGS= /usr/bin/gmake clean && MAKEFLAGS= /usr/bin/gmake
> rm -rf /home/diego/qt-build/config.tests/openssl/android-build
> rm -f main.o
> rm -f *~ core *.core
> /home/diego/android-sdk/ndk/21.3.6528147/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ -c -target aarch64-linux-android21 -fno-limit-debug-info -fPIC -fstack-protector-strong -DANDROID -O2 -fPIC  -I. -I/home/diego/qt5/qtbase/mkspecs/android-clang -o main.o main.cpp
> main.cpp:2:10: fatal error: 'openssl/ssl.h' file not found
> #include <openssl/ssl.h>
>          ^~~~~~~~~~~~~~~
> 1 error generated.
> gmake: *** [Makefile:193 : main.o] Erreur 1

The weird thing is that without the -xplatform option, I don't see this error, and yet the two command lines are otherwise the same one.

Apart from that, there are many other errors, but as I said I don't know exactly what to look at.