[solved] Server - client communication over LAN

[catalin1122]

Hello guys,

I'm am trying to make a server and a client to communicate over LAN. I started to use Qt a few days ago and I need your help :).
I connect two laptops on same WiFi and I want one to be server and the other one to be client. But the client can not see the server.

This is a part of the server code:

int port = 1234;

if(!this->listen(QHostAddress::AnyIPv4, port))
{
    qDebug() << "Could not start server";
}
else
{
   qDebug()<"Server started!";
}

This is a part of the client in which I get (at least this is what i want to do) the IP address of all the connected devices and try to connect to one of them.

   foreach ( const QHostAddress &address,  QNetworkInterface :: allAddresses() )
   {
       if (address.protocol()  ==  QAbstractSocket::IPv4Protocol &&
               address != QHostAddress(QHostAddress::LocalHost))
       {
           qDebug() << address.toString();
           socketClient->connectToHost(address.toString(), 1234);
           if( socketClient->waitForConnected(500) )
           {
                qDebug()<<"Connected!";
                break;
           }
       }
   }

The problem is that I can not make it work on 2 laptops. If I run the server and the client on the same machine it works but if i try over the LAN in doesn't.

Can you suggest me something to make it work? Is it even possible?

Thank you!

[hskoglund]

Hi, alas QNetworkInterface :: allAddresses() gives you only the IP addresses for the PC you're running on :-(

If you want to know about IP addresses on other computers, you can either use IP addresses agreed on in advance or use some kind of broadcast to query for them.

[mcosta]

Hi and welcome to devnet,

QNetworkInterface::allAddresses() returns the IP addresses of your client laptop.
You must know the address of the your server laptop

[SGaist]

Hi,

in addition to @hskoglund, you could also use zeroconf to setup your server

[catalin1122]

@hskoglund @mcosta @SGaist
Thank you for replying!

@SGaist
Do you know a good tutorial or something like this to help me understanding zeroconf?
I'm using Windows.

[SGaist]

Qt Quarterly 23 is a bit old but AFAIK you can still use it

[catalin1122]

@SGaist
Thanks! I did not try it because i found a way to make it work. But I will save that page for later in case I need it.

For now I use a QUdpSocket to broadcast my IP over the network, the clients listens, receives the IP and connects. And it works.
I managed to connect 2 laptops and a PC to my server . I plan to encrypt the IP address.

Do you think it's a good approach?

[hskoglund]

Your approach sounds good :-)
I'm not a network expert, but If you mean you're broadcasting to your LAN segment (like 192.168.1.255) then that is the same approach used by many games when setting up the multiplayer lobby.

[catalin1122]

@hskoglund
This is exactly what I meant :-).

[SGaist]

Yes, that's a standard approach that has worked quiet well already for a long time :-)