Can you give an example of what real world metadata would look like ?

Each vendor rosidl buffer backend can include a string that contains backend specific information/data (what we call as backend metadata) in the endpoint information that it wants to share with the same type of backends in other endpoints.

While the actual backend metadata really depends on each vendor's needs, a good example would be for a backend to share information like the GPU resources an endpoint has access to so the backends in other endpoints can determine if it's compatible or not.

I got one point here, is this supposed to be human readable or is it just binary data ?

My point would be, if it is binary, switch to

std::vector<std::byte>

instead of string.

The metadata exposed here is intended to be textual (human readable) that matches what a backend's BufferBackend::get_backend_metadata() returns as std::string, thus keeping it std::string can fulfill our needs here.

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