Add Fuel World Support

[JShep1]

This PR adds functionality for the user to specify a fuel world URL after ign gazebo, ie, ign gazebo https://staging-fuel.ignitionrobotics.org/1.0/gmas/worlds/ShapesClone

It will first check for a cached copy of the world, and then download the world if no cached copy is found. After this, it will search for an sdf file on the locally downloaded/cached path and load the first one found.

See also gazebosim/gz-launch#43

Closes #89

[chapulina]

The example given on the PR works for me.

Worlds with spaces

I added .sdf files to the test worlds on Fuel that only had .world until now:

• https://app.ignitionrobotics.org/OpenRobotics/fuel/worlds/Test%20world
• https://app.ignitionrobotics.org/OpenRobotics/fuel/worlds/Test%20world%202

But I'm not being able to load either of them. I tried:

ign gazebo -v 4 https://fuel.ignitionrobotics.org/1.0/OpenRobotics/fuel/worlds/Test%20world

and

ign gazebo -v 4 "https://fuel.ignitionrobotics.org/1.0/OpenRobotics/fuel/worlds/Test world"

I didn't dig in to find out what the problem is, I suspect it's about encoding the space

Tests

Do you mind adding a test to ign_TEST.cc?

In order to avoid relying on the live server for the test, you could just test the cached case, and point to a custom cache inside the test folder, using the IGN_FUEL_CACHE_PATH variable to point there.

Loading file programmatically

With the current implementation, it isn't possible to load a Fuel world if it's passed to ServerConfig::SetSdfFile. I see on the ign-launch PR that you're resolving the world file with Fuel before passing it to ServerConfig. I think it would be more general to just support that directly inside ServerConfig. Do you think you could move that logic here?

When you do, it would also be good to add a test to Server_TEST.cc

[JShep1]

But I'm not being able to load either of them. I tried:

ign gazebo -v 4 https://fuel.ignitionrobotics.org/1.0/OpenRobotics/fuel/worlds/Test%20world

and

ign gazebo -v 4 "https://fuel.ignitionrobotics.org/1.0/OpenRobotics/fuel/worlds/Test world"

I didn't dig in to find out what the problem is, I suspect it's about encoding the space

I think the fuel part of those URLs isn't needed. It finds and downloads successfully with the URL https://fuel.ignitionrobotics.org/1.0/OpenRobotics/worlds/Test world

I'll make all remaining updates and changes now.

[chapulina]

I think the fuel part of those URLs isn't needed

Ha, thanks! I copied that from the Bibtex on the world's page, which is wrong: https://app.ignitionrobotics.org/OpenRobotics/fuel/worlds/Test%20world

I opened a PR to fix it: https://gitlab.com/ignitionrobotics/web/app/-/merge_requests/62

[nkoenig]

Works great.

[chapulina]

The functionality works. I just have some final comments about the tests and other tweaks.

[chapulina]

LGTM, feel free to merge with happy CI.