How To Send/Receive UDP Broadcasts

If you have a cool piece of software to share, but you are not hosting it officially yet, please dump it in here. If you have code snippets that are useful, please donate!
Post Reply
felipe2028
In need of some credit
In need of some credit
Posts: 1
Joined: Thu Aug 01, 2019 1:58 pm

How To Send/Receive UDP Broadcasts

Post by felipe2028 »

Hello. New member here. I've seen a lot of posts by people who have implemented wxDatagramSocket for UDP broadcasts, but are having trouble receiving the broadcast responses. Was working on this myself and found a solution. Turns out trying to read incoming data on a socket flagged with wxSOCKET_BROADCAST was what was causing my problem (and probably what was causing issues for everyone else). The solution is to have two wxDatagramSockets.

Outgoing Setup

Code: Select all

wxIPV4address ipLocalAddressOut;
ipLocalAddressOut.AnyAddress();    // sets this to "0.0.0.0"

wxDatagramSocket socketOut = new wxDatagramSocket(ipLocalAddressOut, wxSOCKET_BROADCAST | wxSOCKET_NOBIND);

wxIPV4address ipBroadcastAddress;    // we will use this later to send traffic out
ipBroadcastAddress.BroadcastAddress();    // sets this to "255.255.255.255"
ipBroadcastAddress.Service(INT_UDP_PORT);
Incoming Setup

Code: Select all

wxIPV4address ipLocalAddressIn;
ipLocalAddressIn.AnyAddress();    // sets this to "0.0.0.0"
ipLocalAddressIn.Service(INT_UDP_PORT);

wxWindowID idSocket = wxIdManager::ReserveId();

wxDatagramSocket socketIn = new wxDatagramSocket(ipLocalAddressIn, wxSOCKET_NONE);
socketIn->SetEventHandler(*this, idSocket);
socketIn->SetNotify(wxSOCKET_INPUT_FLAG);
socketIn->Notify(true);

wxEvtHandler::Bind(wxEVT_SOCKET, &OnSocketInput, this, idSocket);
Send Broadcast

Code: Select all

void BroadcastDatagram(const char* data, size_t length) {
    socketOut->SendTo(ipBroadcastAddress, data, length)    // use outgoing address set up earlier
}
Handle Input

Code: Select all

void OnSocketInput(const wxSocketEvent& event) {
    // we are only notifying the event handler of wxSOCKET_INPUT events, so assume we have data to read
    char data[INT_MAX_PACKET_SIZE];
    memset(data, 0, INT_MAX_PACKET_SIZE);
    socketIn->Read(data, INT_MAX_PACKET_SIZE);
    // use socketIn->LastReadCount() to determine how much data actually came in when processing
}
This was done in Windows 10, using wxWidgets 3.1.2, compiled in Visual Studio 2019.
Post Reply