Treatment restoreCache

work/cache::restoreCache

Inputs

⇥ filesystem: Block<FileSystem> (fs/filesystem::FileSystem)
⇥ name: Block<string>
⇥ path: Block<string>

Outputs

↦ finished: Block<void>
↦ missed: Block<void>
↦ restored: Block<void>

Restore a cache of api.melodium.tech.

The current version of the cache name of the run is restored at path of filesystem, such as a volume of the worker (work/resources::getFileSystem) or the local file system of the engine, replacing what is there. restored is emitted once it is in place.

The archive is downloaded, checked, decompressed and extracted all at once, into a directory next to path (<path>.melodium-restore), resuming the download after cuts. Only once the whole archive is extracted and its SHA-256 is the one api.melodium.tech recorded, path is removed and the directory renamed into its place: a damaged or tampered archive never reaches path.

When there is no cache of that name, or it cannot be restored (the API, the download or the extraction fails, the digest differs), missed is emitted with a warning giving the reason, and path is left as it was. A miss is never an error: a program falls back by restoring another name on missed, or by building what the cache would have held. finished is emitted in every case.

path cannot be the root of filesystem, the archive being extracted next to it. Caches are only restored by programs run by api.melodium.tech.