Handle gcs cloud storage file extensions with versioning.

[feuerste]

If a user uses its own IOSystem/IOStream for handling google cloud storage uris, with this PR the extension will still be correct. Together with #5157 the following will be supported without going over all possible importers and trying to detect the format:

Assimp::Importer importer;
importer.SetIOHandler(new GsIOSystem(...));
const aiScene* scene = importer.ReadFile("gs://bucket/model.glb#1234", ...);
...

[turol]

I'm not sure this is a good idea. # is technically a valid character in file names so this might break something for someone.

[feuerste]

I'm not sure this is a good idea. # is technically a valid character in file names so this might break something for someone.

Thanks @turol I agree that # is a valid file name character and we need to make sure that we don't strip too much. gcs tools (see e.g. gsutil: https://github.com/GoogleCloudPlatform/gsutil/blob/c80f329bc3c4011236c78ce8910988773b2606cb/gslib/storage_url.py#L39) can perfectly handle URLs with file versions behind the extension (marked with #), so it would be really useful for everyone extending IOSystem/IOStream with gcs support to already detect the corresponding files based on their extension (see also #5157 in combination with this PR) and not having to wait for the slow fallback where all possible importers try to open the file and read magic bytes or use other ways to detect the type.

[feuerste]

@kimkulling This PR depends on #5157. Once the other one is merged, I will update this one and let you know.

[turol]

I haven't used C++ regex but have heard many people (even on the committee) call it bad. We probably don't want to use it.

[feuerste]

I haven't used C++ regex but have heard many people (even on the committee) call it bad. We probably don't want to use it.

Fine with me, too.

[feuerste]

@kimkulling This one is ready for review now as well :)

[kimkulling]

Just working on it.

[kimkulling]

If I get it right hashes will only get filtered out when they re part of the extension. So for me this looks fine. Some unittests would be great to have.

[feuerste]

If I get it right hashes will only get filtered out when they re part of the extension. So for me this looks fine. Some unittests would be great to have.

Yes, this is correct. I added a few unit tests as well. PTAL!

[kimkulling]

Looks fine to me.

[kimkulling]

Merged, thanks a lot for your contribution.