I'd take a patch to allow overriding the URL! I actually could use that for testing the S3 storage.
The S3 code went through a few revisions. I was originally using Rusoto (https://github.com/rusoto/rusoto), which is nice but just didn't quite meet my needs, so then I borrowed some code from the crates.io codebase and then rewrote most of it.
You can also run it using a local disk cache, similar to ccache, but it doesn't have any code to limit the size of the cache so it's not very good right now. (It's used in all the tests, though.) Fixing that specific issue is next on my plate.
The S3 code went through a few revisions. I was originally using Rusoto (https://github.com/rusoto/rusoto), which is nice but just didn't quite meet my needs, so then I borrowed some code from the crates.io codebase and then rewrote most of it.
You can also run it using a local disk cache, similar to ccache, but it doesn't have any code to limit the size of the cache so it's not very good right now. (It's used in all the tests, though.) Fixing that specific issue is next on my plate.