The file cpp/thirdparty/versions.txt lists third-party dependencies, and the filename download_dependencies.sh should use to save them.
A couple of those files, for aws-checksums and aws-c-event-stream, are missing extensions.
When I try to use those files, e.g. with $ARROW_AWS_CHECKSUMS_URL, cmake has an error:
This error is fixed if I manually add .tar.gz to aws-checksums-v0.1.10 and aws-c-event-stream-v0.1.5.