foxglove websocket in C++ and JSON)

[GianlucaCerilli]

Good morning,

I was looking at these examples and was wondering if you also have a working example server in C++ that uses JSON messages.

In addition to this, I also wanted to ask you if it is possible to link foxglove-websocket from CMakeLists in C++, without using Python and Conan.

Thanks

[achim-k]

foxglove/ws-protocol#724 adds an example JSON C++ server

Yes, you can use foxglove-websocket directly with CMakelist, you probably have to use add_subdirectory() or something similar.

[achim-k]

Foxglove can only connect to one websocket server at a time. However, you can publish two different topics from the same server and visualize both topics in the 3D panel.

[GianlucaCerilli]

I see. Is it possible to establish a connection to one single server and publish topics from two different executables? They should both use the same server somehow.
So, for example:

• Executable 1 - It just creates a server for connecting to Foxglove
• Executable 2 - It uses that server to publish a cube (for example)
• Executable 3 - It uses that server to publish a sphere (for example)

Or a similar solution that could allow to publish different topics in parallel, from different executables though.

Thanks!

[jtbandes]

No, since Foxglove only connects to one server at a time, you would have to manage the inter-process communication yourself so the messages can be published from executable 1. (This is the role played by DDS, TCPROS, or other middlewares.)

[GianlucaCerilli]

Ok, thanks...is there a way to add the channels dynamically, instead?

For example, I have a run function that fills a std::vector<foxglove::ChannelWithoutId> channels iteratively, as soon as it discovers new topics.
Then, at each cycle the server->addChannels is called, taking the channels as parameter.

I can see the list of topics on Foxglove, but without content and with this error:

Multiple channels advertise on the same topic: topic_name (number1 and number2).

number2 seems to be the ChannelId, and I think number1 is the handler id.
I also notice number2 always increases, is there a way to reset it at each iteration? I guess calling server->removeChannels soon before the server->addChannels is not the solution.

Thanks a lot

[jtbandes]

It’s ok to add channels dynamically. Just call addChannels with only the new ones.