Receive Data ROS2

We are trying to connect a Linux based machine (using Ubuntu 18.04 with ROS2 Dashing) to Matlab running on a Windows 10 PC, using ROS2 DDS services. They both are connected on the same network and their subnets are the same (PC is 10.221.114.24 and the device is 10.221.114.161). I set the domain ID of both to 5. When I create a node in either of them, I can detect it in another (using ros2 node list). Likewise, I can do the same for topics (using ros2 topic list). I have a basic publisher and subscriber (std_msgs string), which work perfectly fine, when run in the Linux device. When I run the publisher on the Linux machine; although Matlab in my PC can detect both the publisher’s node and the topic, the Matlab "receive" function always timeout and does not receive any messages. I tried both “reliable” and “besteffort” reliability settings, in the Matlab “ros2subscriber” function, with no luck. I also have turned all firewalls off. Moreover, I have tried to follow all guidelines given in this page, with no luck.

I tested this on both Matlab 2020a and 2021b with no luck.

Here is the Matlab code:

clear all
clc

setenv("ROS_DOMAIN_ID","5");
ros2 topic list
topicList=ros2("topic","list");

if(sum(contains(topicList, "test_publisher_topic")))
    SubscriberNode=ros2node("/matlab_subscriber");
    pause(2);
    msgSub=ros2subscriber(SubscriberNode, "/test_publisher_topic" ,"Reliability", "besteffort");
    while(1)
        Message=receive(msgSub, 5);
        disp(Message)
    end
else
    disp('hossein_topic not present!')
end

ERROR Code:

Error using ros2subscriber/receive (line 458)
Subscriber did not receive any messages and timed out.

Any idea?

Best

Hossein

[Cam Salzberger]

Hello Hossein,

I'd like to suggest a couple of tweaks to the test code to make it a little more consistent.

• Could use a pause after the first topic list call to allow a newly-created introspection node time to get metacommunication on the network. I know that's not the issue here, but it's good practice.
• Minor improvement to the conditional on checking if the topic is listed
• Use reliable to avoid potentially dealing with dropped messages
• Use the subscriber callback rather than receive to avoid blocking and allow the script to work no matter if MATLAB subscriber or Ubuntu publisher was created first
• Specify the message type for the same reason

clear

topic = "/test_publisher_topic";
type = "std_msgs/String";
domain = 5;

setenv("ROS_DOMAIN_ID", num2str(domain));
ros2("topic", "list"); % Dummy call to initialize the introspection node
pause(3)
topicList = ros2("topic", "list");
if ~ismember(topic, topicList)
    error(sprintf("Topic %s not present on domain %d", topic, domain))
end

node = ros2node("/matlab_subscriber");
if node.ID ~= domain
    error(sprintf("Node is on domain %d while environment specifies %d", node.ID, domain))
end

 % Using default QoS settings, but being explicit
sub = ros2subscriber(node, topic, type, @disp, ...
    "Reliability", "reliable", "Durability", "volatile");
% Incoming messages should now display

Then in Ubuntu, we want to make sure that the QoS settings are compatible. So we can run something like this:

source /path/to/ros/setup.bash
export ROS_DOMAIN_ID=5
ros2 topic pub --rate 1 --qos-reliability reliable --qos-durability volatile /test_publisher_topic std_msgs/String "{data: hello}"

Can you give it a try with the Ubuntu and MATLAB commands, and see if the result is different?

-Cam

[Hossein Moghimi]

Hi @Cam Salzberger

Thanks a lot for the response. I tried this and extremely strangely it worked only once and keeps giving me the same error after stopping and rerunnng the code. I tried that on both Matlab 2020a and 2021b and got the same result. Also restarting Matlab did not help. I have to add that my firewall is off.

Any ideas?

Best

[Cam Salzberger]

What error? It shouldn't give you the "receive" error, since it's not calling that any more.

Is the error in MATLAB or on Ubuntu?

[Hossein Moghimi]

The error is in Matlab, and it is the still the receive error.

I am suspisios of the network if there is any hardware (router) firewall. I will move into a router, not connected the office network, and see what I get.

Thanks a lot for the response again.

[Cam Salzberger]

If you are getting this error:

Error using ros2subscriber/receive (line 458)

Then there is something wrong with how you are running the code. Nowhere in my code does it call "receive". So if the "receive" method is still being triggered, then some other code is running it.

Clear everything from your workspace, make sure to run my code in isolation (nothing else in the file), and if you still get that error we need to look at shadowed files and startup scripts.

[Hossein Moghimi]

Sorry my bad, I should have explained better. The "disp" callback does not get trrigered. So I removed that and implemented the following again:

while(1)
    Message=receive(msgSub, 5);
    disp(Message)
end

So the timeout comes from this.

[Cam Salzberger]

Well, there was a reason that I went for display callback rather than receive. It could take several seconds for the initial connection to be made, so a timeout on the very first messages isn't necessarily an indicator of an issue. But if the callback wasn't being triggered, then yeah, that's a problem.

Did the standalone router do the trick?

You can also run the Ubuntu and MATLAB code (remove the "receive" section so no error occurs and the subscriber stays active), then then run this in a separate window on Ubuntu:

ros2 topic info /test_publisher_topic
ros2 node list
ros2 node info /matlab_subscriber

I'm curious if Ubuntu is able to see the MATLAB node and subscriber.

[Hossein Moghimi]

Hi,

I went home yesterday, so sorry for the late reply. Well I tried the standalone router and no success. I ran a c++ subscriber on the ubuntu machine and have been able to get the messages. I did what you asked above (the coomands have been run on Ubuntu machine) and below is the result:

root@qrb5165-rb5:~# ros2 topic info /test_publisher_topic
Topic: /test_publisher_topic
Publisher count: 1
Subscriber count: 0
root@qrb5165-rb5:~# ros2 node list
/matlab_subscriber
root@qrb5165-rb5:~# ros2 node info /matlab_subscriber
/matlab_subscriber
Subscribers:

Publishers:

Services:

so both Matlab and Ubuntu machine can see the node and topic but the disp callback never happen. The recive with 10 second timeout also fails.

By the way I tested this on both Matlab 2020b and 2021b.

Just out of curocity, my ROS2 is Dashing, NOT Foxy. I assume it cannot be the issue?

[Hossein Moghimi]

Hi

@Cam Salzberger I tried turning all virus protection and firewalls off and still get the same error. As I mentioned above Matlab can see the nodes and topics on the ubuntu machine. The ubuntu machine, likewise, can see Matlab nodes. but I think the subscription simply does NOT happen. I am almost out of options and have no idea why it is happening.

Just one thing. To make sure that the office (possible) hardware firewalls do not interfier with the DDS, I did not connect the standalone router to the internet. the IP addresses assigned to the machines are 169.254.45.14 (PC) and 169.254.4.1 (ubuntu machine). I created the followowing "DEFAULT_FASTRTPS_PROFILES.xml" file and copied it in the matlab current directory.

<?xml version="1.0" encoding="UTF-8" ?>

<profiles>
<transport_descriptors>
<transport_descriptor>
<transport_id>veelpeers</transport_id> <!-- string -->
<type>UDPv4</type> <!-- string -->
<maxInitialPeersRange>1000</maxInitialPeersRange> <!-- uint32 -->
</transport_descriptor>
</transport_descriptors>
<participant profile_name="participant_somename" is_default_profile="true">
<rtps>
<builtin>
<metatrafficUnicastLocatorList> 
<locator/> 
</metatrafficUnicastLocatorList> 
<domainId>4</domainId>
<initialPeersList>
<locator>
<udpv4>
<address>169.254.45.14</address>
</udpv4>
</locator>
<locator>
<udpv4>
<address>169.254.4.1</address>
</udpv4>
</locator>
</initialPeersList>
</builtin>
<userTransports>
<transport_id>veelpeers</transport_id>
</userTransports>
<useBuiltinTransports>false</useBuiltinTransports>
</rtps>
</participant>
</profiles>

I followed this page and use the following commands after saving the .xml file in the ubuntu machine as well.

export FASTRTPS_DEFAULT_PROFILES_FILE=<path_to_xml_file>
export RMW_FASTRTPS_USE_QOS_FROM_XML=1

Still it does exactly the same as before. Can you think of any solutions?

Answer 1

[Cam Salzberger]

Sorry, this is a pretty new issue to me. I think I've seen one-directional communication, but not the inability to see the subscribers in MATLAB. And usually this issue is with ROS 1 not ROS 2.

Both R2020a and R2021b use Dashing on their back-end as well, so version incompatibility should not be the issue. If you upgrade to R2022a, it uses Foxy, so you may get an issue at that point fi your Ubuntu is still using Dashing.

If, after making your XML file, you are still able to see the MATLAB nodes in "ros2 node list" and are able to receive messages from MATLAB publishers on Ubuntu, then the XML file is working correctly. The environment variables you set, however, I believe only apply to Foxy (and maybe Eloquent), but not Dashing.

The one thing I think should be tried next is a bit intensive. If you are able to install ROS 2 Dashing on your Windows machine, we can isolate whether the issue is with MATLAB's ROS 2 implementation, or with the general ROS 2 communication between Windows and Ubuntu.

-Cam