Support embedding user-provided data in persisted snapshots #1839

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   added

   lifecycle/needs-reviewThe issue has not yet been reviewed.The issue has not yet been reviewed.

   on Sep 17, 2026
2. ludfjig commented on Sep 17, 2026

   

   ludfjig

   on Sep 17, 2026

   Last edited by ludfjig

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   Maybe extend Snapshot::save(path, tag) and Snapshot::load(path, reference) APIs, and add variants that accept and return user-provided data (changed is data parameter for save_with_data and returned Vec<u8> for load_with_data):

   pub fn save_with_data(
       &self,
       path: impl AsRef<Path>,
       tag: &OciTag,
       data: &[u8],
   ) -> Result<OciDigest>;
   
   pub fn load_with_data(
       path: impl AsRef<Path>,
       reference: impl Into<OciReference>,
   ) -> Result<(Self, Vec<u8>)>;
3. ludfjig

   closed this as completedon Sep 17, 2026
4. ludfjig

   reopened this on Sep 17, 2026
5. ludfjig commented on Sep 18, 2026

   

   ludfjig

   on Sep 18, 2026

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   Curious if you have any thoughts about this @jprendes
6. jprendes commented on Sep 21, 2026

   

   jprendes

   on Sep 21, 2026

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   I think I would hold the metadata in the snapshot, and then have the assignment and retrieval of the metadata as independent methods in the snapshot instead of doing it at load/save time:

   #[derive(Serialize, Deserialize)]
   struct Metadata { .. }
   
   // load the snapshot as normal
   let snapshot = snapshot.load(path)?;
   
   // get the metadata in "namespace"
   let metadata: Metadata = snapshot.metadata("namespace")?;
   
   // mutate metadata
   let metadata = mutate_metadata(metadata);
   
   // create a new snapshot, replacing the metadata in "namespace" with the new metadata
   let snapshot = snapshot.with_metadata("namespace", metadata)?;
   
   // save the snapshot as usual
   snapshot.save(path)?;

   what do you think?
7. ludfjig commented on Sep 22, 2026

   

   ludfjig

   on Sep 22, 2026

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   what do you think?

   This looks good! We'd need to be careful to make sure with_metadata can take in an Arc<Self> to make sure the api is ergonomic since snapshot() returns an Arc<snapshot>,. However this prevents the method from gettinga mut self, so we'd probably need to refactor the snapshots field slighly to make the inner state cheaply clonable via arc, and then create a new identical snapshot except for the metadata