Fails to resolve model paths on case-insensitive filesystems like in macOS

[azeey]

The recent change of owner name from openrobotics to OpenRobotics has caused a regression in homebrew builds of ign-gazebo (https://build.osrfoundation.org/job/ignition_gazebo-ci-ign-gazebo2-homebrew-amd64/129/testReport/). I think the issue stems from the fact that the filesystem in macOS can be case-insensitive, and if there's already a directory called openrobotics, it will not create a new one called OpenRobotics. However, when checking if a model is already downloaded, ign-fuel-tools compares the owner name from the URI and the owner name derived from the file path. Since that comparison fails, models are always downloaded. It also looks like ign-fuel-tools uses this comparison when determining the version number as it creates the final path to the downloaded model.sdf file. But due to the name mismatch, the version is set to tip instead of a numeric value. This causes failures downstream, for example, in sdformat as it tries to open a file with the pattern <cache path>/openrobotics/models/<model name>/tip, which doesn't actually exist in the filesystem.

[chapulina]

if there's already a directory called openrobotics, it will not create a new one called OpenRobotics

This specifically sounds like a one-time issue since we don't expect user names to be changing.

For downstream users: maybe we should officially communicate this issue and tell them to clear previously existing folders?

For the tests: I'd hope they wouldn't be affected by this. We've tried to use a custom cache location for tests and clear it between tests. If a previously existing directory is messing with the tests I think we could improve the tests.

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More generally, this could be an issue if Fuel allows different users to be created with the same letters but different cases, like someuser and SomeUser. Maybe this is something we need to disallow on the server side. CC @nkoenig