Local UDP broadcast with FSocket

Development Programming & Scripting C++
1

Hi,

I’d like to allow my Android application to automatically connect to my game on a local network.
In order to do this I am trying to broadcast the host ip address on the local network using an udp FSocket.

I’m testing it between two computers on the same network. I can see the packets coming with Wireshark but I fail to catch them in unreal engine.
I tried several things:

  1. Creating an UDPReceiver with a callback. With this solution the callback is never called.

bool AUdpDataReceiver::StartUDPReceiver(const FString& YourChosenSocketName, const int32 ThePort)
{
	int32 BufferSize = 2 * 1024 * 1024;

	ListenSocket = FUdpSocketBuilder(*YourChosenSocketName)
		.AsNonBlocking()
		.AsReusable()
		.BoundToAddress(FIPv4Address::Any)
		.BoundToPort(ThePort)
		.WithReceiveBufferSize(BufferSize)
		.Build();

	FTimespan ThreadWaitTime = FTimespan::FromMilliseconds(100);
	UDPReceiver = new FUdpSocketReceiver(ListenSocket, ThreadWaitTime, TEXT("UDP RECEIVER"));
	UDPReceiver->OnDataReceived().BindUObject(this, &AUdpDataReceiver::Recv);
	UDPReceiver->Start();
	return true;
}

void AUdpDataReceiver::Recv(const FArrayReaderPtr& ArrayReaderPtr, const FIPv4Endpoint& EndPt)
{
	FString data;
	ScreenMsg("Recv data");
	*ArrayReaderPtr << data;		//Now de-serializing
	ScreenMsg(data);
	UE_LOG(LogTemp, Warning, TEXT("DATADATADATA %s"), *data);
}

I tried this solution without BoundToAddress(FIPv4Address::Any) and with WithBroadcast().

  1. Calling Recv or RecvFrom in Tick to catch the data.

void AUdpDataReceiver::Tick( float DeltaTime )
{
	Super::Tick( DeltaTime );

	int bytesRead;
	int32 BufferSize = 2 * 1024 * 1024;
	uint8* data = nullptr;
	TSharedRef < FInternetAddr > addr = ISocketSubsystem::Get(PLATFORM_SOCKETSUBSYSTEM)->CreateInternetAddr();
	addr->SetAnyAddress();
	ListenSocket->RecvFrom(data, BufferSize, bytesRead, *addr);
	ScreenMsg("DATADATADATA",(float) bytesRead);
	UE_LOG(LogTemp, Warning, TEXT("DATADATADATA %f"), (float)bytesRead);
}

bool AUdpDataReceiver::StartUDPReceiver(const FString& YourChosenSocketName, const int32 ThePort)
{
	int32 BufferSize = 2 * 1024 * 1024;

	ListenSocket = FUdpSocketBuilder(*YourChosenSocketName)
		.AsNonBlocking()
		.AsReusable()
		.BoundToAddress(FIPv4Address::Any)
		.BoundToPort(ThePort)
		.WithReceiveBufferSize(BufferSize)
		.Build();

return true;

}

I tried this solution with the alternative ways of creating the sockets I explained before.

I tried everything I could think of but never seem to receive anything, did I miss something?

2

HI ,
It’s not mandatory use 2 computers for debugging, you can test with your own, by connecting sockets with self connection 127.0.0.1
I made that example some time ago, I connect my little toy car with arduino and my cel phone and yeah!!, I use UDP sockets.

take a look:

I create a simple class inheriting from UActorComponent with few methods inside, I share you:

my header:



#pragma once
#include "Networking.h"
#include "Engine.h"
#include "SocketPower.Generated.h"

USTRUCT(BlueprintType)
struct FAnyCustomData
{
	GENERATED_USTRUCT_BODY()

		UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "DATA")
		float motor = 0;

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "DATA")
		float servo = 0;

	FAnyCustomData()
	{}
};

FORCEINLINE FArchive& operator<<(FArchive &Ar, FAnyCustomData& TheStruct)
{
	Ar << TheStruct.motor;
	Ar << TheStruct.servo;
	return Ar;
}

DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam(FGetReceivedData, const FAnyCustomData&, receivedData);

UCLASS(meta = (BlueprintSpawnableComponent), ClassGroup = (Hardware))
class USocketPower : public UActorComponent
{
	GENERATED_BODY()

private:
	bool isServer = false;
	FSocket* socket;
	FUdpSocketReceiver* UDPReceiver = nullptr;
	FAnyCustomData dataRev;

public:

	TSharedPtr<FInternetAddr>	RemoteAddr;

	UPROPERTY(BlueprintAssignable)
		FGetReceivedData OnSuccess;

	UFUNCTION(BlueprintPure, Category = "Internet")
		FAnyCustomData getDataRev();

	UFUNCTION(BlueprintCallable, Category = "Internet")
		bool sendData(FAnyCustomData data);

	UFUNCTION(BlueprintCallable, Category = "Internet")
		bool tryToConnect(FString socketname, FString IP, int32 port, bool UDP = false);

	UFUNCTION(BlueprintCallable, Category = "Internet")
		bool startServer(FString socketname, FString IP, int32 port);

	UFUNCTION(BlueprintCallable, Category = "Internet")
		void closeConnection();

	void Recv(const FArrayReaderPtr& ArrayReaderPtr, const FIPv4Endpoint& EndPt);

};

my cpp:



#include "SocketFuncPrivatePCH.h"
#include "SocketPower.h"

bool USocketPower::startServer(FString socketname, FString IP, int32 port)
{
	FIPv4Address Addr;
	FIPv4Address::Parse(IP, Addr);

	//Create Socket
	FIPv4Endpoint Endpoint(Addr, port);

	//BUFFER SIZE
	int32 BufferSize = 2 * 1024 * 1024;

	socket = FUdpSocketBuilder(*socketname)
		.AsNonBlocking()
		.AsReusable()
		.BoundToEndpoint(Endpoint)
		.WithReceiveBufferSize(BufferSize);
	;

	FTimespan ThreadWaitTime = FTimespan::FromMilliseconds(100);
	UDPReceiver = new FUdpSocketReceiver(socket, ThreadWaitTime, TEXT("UDP RECEIVER"));
	UDPReceiver->OnDataReceived().BindUObject(this, &USocketPower::Recv);

	if (socket)
	{
		isServer = true;
	}
	return isServer;
}

bool USocketPower::tryToConnect(FString socketname, FString IP, int32 port, bool UDP)
{
	RemoteAddr = ISocketSubsystem::Get(PLATFORM_SOCKETSUBSYSTEM)->CreateInternetAddr();
	bool bIsValid;
	RemoteAddr->SetIp(*IP, bIsValid);
	RemoteAddr->SetPort(port);

	if (!bIsValid)
	{
		GEngine->AddOnScreenDebugMessage(-1,3,FColor::Red,"IP address was not valid!");
		return false;
	}

	socket = FUdpSocketBuilder(*socketname).AsReusable().WithBroadcast();
	//Set Send Buffer Size
	int32 SendSize = 2 * 1024 * 1024;
	socket->SetSendBufferSize(SendSize, SendSize);
	socket->SetReceiveBufferSize(SendSize, SendSize);

	if (socket)
	{
		return true;
	}

	return false;
}

bool USocketPower::sendData(FAnyCustomData data)
{
	if (!socket || isServer)
	{
		GEngine->AddOnScreenDebugMessage(-1, 3, FColor::Red, "no sender socket");
		return false;
	}

	FArrayWriter Writer;
	Writer << data;
	int32 BytesSent = 0;
	socket->SendTo(Writer.GetData(), Writer.Num(), BytesSent, *RemoteAddr);
	if (BytesSent <= 0)
	{
		GEngine->AddOnScreenDebugMessage(-1, 3, FColor::Red, "invalid send");
		return false;
	}

	return true;
}

void USocketPower::closeConnection()
{
	if (UDPReceiver)
	{
		delete UDPReceiver;
		UDPReceiver = nullptr;
	}

	if (socket)
	{
		socket->Close();
		ISocketSubsystem::Get(PLATFORM_SOCKETSUBSYSTEM)->DestroySocket(socket);
	}
	
}

void USocketPower::Recv(const FArrayReaderPtr& ArrayReaderPtr, const FIPv4Endpoint& EndPt)
{
	FAnyCustomData Data;
	*ArrayReaderPtr << Data;
	FAnyCustomData copy;
	copy.motor = Data.motor;
	copy.servo = Data.servo;
	dataRev = copy;
}

FAnyCustomData USocketPower::getDataRev()
{
	return dataRev;
}

It’s super simple, I think is enough clear, but if you have some troubles, let me know

Cheers!

3

Hi ZkarmaKun

Thanks a lot for sharing your code, it really helps to have another example.
I do not see anything wrong comparing your code with mine. Can you tell which ip you give to your socket in your startServer function?

Also using two computers isn’t a problem and as I said I do receive the packets on the client, so I should be able to catch them. I can let the server run I don’t have to change anything on it :slight_smile:

4

Well in my example I hardcode my IP by setting in my modem, Really not matter at all, when you start a server just pass the IPv4 of the server, for example use 192.168.1.XX and all the clients need to connect to the same IP

5

Well my problem is that I want to broadcast on my local network, not just set an ip address and bind the sockets. I think the problem I have is when I try to receive any udp packet on a specific port, no matter where it comes from.

6

UDP packets are just targeted at an IP addr, not a port. In general when you want to send a packet to everyone in the local network you set the broadcast to true.

7

Yes I did that. I can see the packets coming on my computer with wireshark so the broadcast works. I just can’t get the data on the receiver part of the code. HasPendingData returns false everytime and the registered callback is never called.

8

can you share the blueprint of this code???