Support trust gvfs idx files for scalar prefetch #766
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tyrielv
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GVFS protocol's prefetch operation (used to fetch pack files for commits and trees) includes idx files as well as pack files. Gvfs.exe (from VFSForGit) trusts the idx files it fetches, but scalar currently does not and always reindexes them locally. This has an observed performance impact where scalar clone takes up to 10x as long as gvfs clone for large repositories. This pull request adds support for trusting idx files to the prefetch operation in scalar, with the following behavior in priority order: 1. If --[no-]trust-idx is specified, use that 2. If global config `gvfs.trustidxfiles` is set, use that 3. If the url to clone/prefetch is Azure DevOps, trust it 4. Otherwise, do not trust it
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derrickstolee
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Jun 12, 2025
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I'm sorry that you spent time on this, but trusting the .idx files is a serious security issue. If we "trust" the .idx file, then we could have a rogue cache server deliver us a bad .idx file where it says "this Object Id has this content" but that content doesn't actually hash to that object ID.
There are similar checks when asking for a loose object by object ID: we used to trust the cache server for performance reasons, but this security boundary is really really important.
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GVFS protocol's prefetch operation (used to fetch pack files for commits and trees) includes idx files as well as pack files. Gvfs.exe (from VFSForGit) trusts the idx files it fetches, but scalar currently does not and always reindexes them locally.
This has an observed performance impact where scalar clone takes up to 10x as long as gvfs clone for large repositories.
This pull request adds support for trusting idx files to the prefetch operation in scalar, with the following behavior in priority order:
gvfs.trustidxfilesis set, use that