Can't publish string to ROS2 outside of Unreal

[samiamlabs]

Hi!

I'm having some trouble getting the topic I'm publishing on from inside Unreal to reach outside Unreal to a terminal on my main system.

Some info:
Ubuntu 22.04
Unreal 5.1 built from source
ROS2 humble

If I make a subscriber in Unreal it seems to receive what is published from the publisher in Unreal though.

The terminal just looks like this:

ros2 topic list
/parameter_events
/rosout

Any ideas as to what the problem could be?

Here is the code for the publisher (but I don't think the code is actually the issue):

TestPublisher.h

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"

#include "Msgs/ROS2Str.h"
#include <ROS2Publisher.h>

#include "TestPublisher.generated.h"



UCLASS()
class FIRSTUNREALPROJECT_API ATestPublisher : public AActor
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	ATestPublisher();

protected:
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;

public:	
	// Called every frame
	virtual void Tick(float DeltaTime) override;

	UPROPERTY(EditAnywhere, BlueprintReadWrite)
        UROS2NodeComponent* Node = nullptr;

        UPROPERTY(EditAnywhere, BlueprintReadWrite)
        UROS2Publisher* Publisher = nullptr;
	
	UPROPERTY(EditAnywhere, BlueprintReadWrite)
        FString TopicName = TEXT("test_topic");

	UPROPERTY(EditAnywhere, BlueprintReadWrite)
        FString Message = TEXT("Hello from C++");

private:

	void PublishMessage();

	FTimerHandle TimerHandle;
};

TestPublisher.cpp

#include "TestPublisher.h"


// Sets default values
ATestPublisher::ATestPublisher()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

	Node = CreateDefaultSubobject<UROS2NodeComponent>(TEXT("ROS2NodeComponent"));

	Node->Name = TEXT("subscriber_node");
}

// Called when the game starts or when spawned
void ATestPublisher::BeginPlay()
{
	Super::BeginPlay();
	Node->Init();

	Publisher = Node->CreatePublisher(TopicName, UROS2Publisher::StaticClass(), UROS2StrMsg::StaticClass(), UROS2QoS::KeepLast);
	
	FROSStr msg;
        msg.Data = FString::Printf(TEXT("%s from non loop publisher"), *Message);
        CastChecked<UROS2StrMsg>(Publisher->TopicMessage)->SetMsg(msg);

	GetWorld()->GetTimerManager().SetTimer(TimerHandle, this, &ATestPublisher::PublishMessage, 1.0, true);
}

// Called every frame
void ATestPublisher::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);

}

void ATestPublisher::PublishMessage()
{
	UE_LOG(LogTemp, Warning, TEXT("Publishing message"));
	Publisher->Publish();
}

[pabsan-0]

Hi, have you tried running a source run_discovery_service.sh in the receiving terminal?

[pabsan-0]

Hi, I just started using Ubuntu 22.04 with the turtlebot3 repo and I had the same problem. Ignoring the dds-wrapping scripts and just running the world with $UE5_DIR/Engine/Binaries/Linux/UnrealEditor turtlebot.uproject, then just sourcing ROS in the receiving terminal, made me able to see and echo all topics published by the simulation.