Implement branch reset functionality

This is history editing functionality. It works by creating a new
version of the branch ref, pointing to the given Snapshot.

icechunk-python/python/icechunk/__init__.py

@@ -377,6 +377,34 @@ def new_branch(self, branch_name: str) -> str:
         """
         return self._store.new_branch(branch_name)
 
+    async def async_reset_branch(self, to_snapshot: str) -> None:
+        """Reset the currently checked out branch to point to a different snapshot.
+
+        This requires having no uncommitted changes.
+
+        The snapshot id can be obtained as the result of a commit operation, but, more probably,
+        as the id of one of the SnapshotMetadata objects returned by `ancestry()`
+
+        This operation edits the repository history, it must be executed carefully.
+        In particular, the current snapshot may end up being inaccessible from any
+        other branches or tags.
+        """
+        return await self._store.async_reset_branch(to_snapshot)
+
+    def reset_branch(self, to_snapshot: str) -> None:
+        """Reset the currently checked out branch to point to a different snapshot.
+
+        This requires having no uncommitted changes.
+
+        The snapshot id can be obtained as the result of a commit operation, but, more probably,
+        as the id of one of the SnapshotMetadata objects returned by `ancestry()`
+
+        This operation edits the repository history, it must be executed carefully.
+        In particular, the current snapshot may end up being inaccessible from any
+        other branches or tags.
+        """
+        return self._store.reset_branch(to_snapshot)
+
     def tag(self, tag_name: str, snapshot_id: str) -> None:
         """Create a tag pointing to the current checked out snapshot."""
         return self._store.tag(tag_name, snapshot_id=snapshot_id)

icechunk-python/python/icechunk/_icechunk_python.pyi

@@ -31,6 +31,8 @@ class PyIcechunkStore:
     async def async_reset(self) -> None: ...
     def new_branch(self, branch_name: str) -> str: ...
     async def async_new_branch(self, branch_name: str) -> str: ...
+    def reset_branch(self, snapshot_id: str) -> None: ...
+    async def async_reset_branch(self, snapshot_id: str) -> None: ...
     def tag(self, tag: str, snapshot_id: str) -> None: ...
     async def async_tag(self, tag: str, snapshot_id: str) -> None: ...
     def ancestry(self) -> list[SnapshotMetadata]: ...

icechunk-python/src/lib.rs

@@ -530,6 +530,29 @@ impl PyIcechunkStore {
         })
     }
 
+    fn async_reset_branch<'py>(
+        &'py self,
+        py: Python<'py>,
+        to_snapshot: String,
+    ) -> PyResult<Bound<'py, PyAny>> {
+        let store = Arc::clone(&self.store);
+        pyo3_asyncio_0_21::tokio::future_into_py(py, async move {
+            do_reset_branch(store, to_snapshot).await
+        })
+    }
+
+    fn reset_branch<'py>(
+        &'py self,
+        py: Python<'py>,
+        to_snapshot: String,
+    ) -> PyResult<Bound<'py, PyNone>> {
+        let store = Arc::clone(&self.store);
+        pyo3_asyncio_0_21::tokio::get_runtime().block_on(async move {
+            do_reset_branch(store, to_snapshot).await?;
+            Ok(PyNone::get_bound(py).to_owned())
+        })
+    }
+
     fn async_tag<'py>(
         &'py self,
         py: Python<'py>,
@@ -955,6 +978,20 @@ async fn do_new_branch<'py>(
     Ok(String::from(&oid))
 }
 
+async fn do_reset_branch<'py>(
+    store: Arc<RwLock<Store>>,
+    to_snapshot: String,
+) -> PyResult<()> {
+    let to_snapshot = ObjectId::try_from(to_snapshot.as_str())
+        .map_err(|e| PyIcechunkStoreError::UnkownError(e.to_string()))?;
+    let mut writeable_store = store.write().await;
+    writeable_store
+        .reset_branch(to_snapshot)
+        .await
+        .map_err(PyIcechunkStoreError::from)?;
+    Ok(())
+}
+
 async fn do_tag<'py>(
     store: Arc<RwLock<Store>>,
     tag: String,

icechunk-python/tests/test_timetravel.py

@@ -58,3 +58,27 @@ def test_timetravel():
     ]
     assert sorted(parents, key=lambda p: p.written_at) == list(reversed(parents))
     assert len(set([snap.id for snap in parents])) == 4
+
+
+async def test_branch_reset():
+    store = icechunk.IcechunkStore.create(
+        storage=icechunk.StorageConfig.memory("test"),
+        config=icechunk.StoreConfig(inline_chunk_threshold_bytes=1),
+    )
+
+    group = zarr.group(store=store, overwrite=True)
+    group.create_group("a")
+    prev_snapshot_id = store.commit("group a")
+    group.create_group("b")
+    store.commit("group b")
+
+    keys = {k async for k in store.list()}
+    assert "a/zarr.json" in keys
+    assert "b/zarr.json" in keys
+
+    store.reset_branch(prev_snapshot_id)
+
+    keys = {k async for k in store.list()}
+    assert "a/zarr.json" in keys
+    assert "b/zarr.json" not in keys
+

icechunk/src/repository.rs

@@ -265,6 +265,10 @@ impl Repository {
         }
     }
 
+    pub fn config(&self) -> &RepositoryConfig {
+        &self.config
+    }
+
     pub(crate) fn set_snapshot_id(&mut self, snapshot_id: SnapshotId) {
         self.snapshot_id = snapshot_id;
     }

icechunk/src/zarr.rs

@@ -27,7 +27,7 @@ use crate::{
         snapshot::{NodeData, UserAttributesSnapshot},
         ByteRange, ChunkOffset, IcechunkFormatError, SnapshotId,
     },
-    refs::{BranchVersion, Ref},
+    refs::{update_branch, BranchVersion, Ref, RefError},
     repository::{
         get_chunk, ArrayShape, ChunkIndices, ChunkKeyEncoding, ChunkPayload, ChunkShape,
         Codec, DataType, DimensionNames, FillValue, Path, RepositoryError,
@@ -275,6 +275,8 @@ pub enum StoreError {
     NotFound(#[from] KeyNotFoundError),
     #[error("unsuccessful repository operation: `{0}`")]
     RepositoryError(#[from] RepositoryError),
+    #[error("unsuccessful ref operation: `{0}`")]
+    RefError(#[from] RefError),
     #[error("cannot commit when no snapshot is present")]
     NoSnapshot,
     #[error("all commits must be made on a branch")]
@@ -443,6 +445,40 @@ impl Store {
         Ok((snapshot_id, version))
     }
 
+    /// Make the current branch point to the given snapshot.
+    /// This fails if there is uncommitted changes, or if the branch has been updated
+    /// since checkout.
+    /// After execution, history of the repo branch will be altered, and the current
+    /// store will point to a different base snapshot_id
+    pub async fn reset_branch(
+        &mut self,
+        to_snapshot: SnapshotId,
+    ) -> StoreResult<BranchVersion> {
+        // TODO: this should check the snapshot exists
+        let mut guard = self.repository.write().await;
+        if guard.has_uncommitted_changes() {
+            return Err(StoreError::UncommittedChanges);
+        }
+        match self.current_branch() {
+            None => Err(StoreError::NotOnBranch),
+            Some(branch) => {
+                let old_snapshot = guard.snapshot_id();
+                let storage = guard.storage();
+                let overwrite = guard.config().unsafe_overwrite_refs;
+                let version = update_branch(
+                    storage.as_ref(),
+                    branch.as_str(),
+                    to_snapshot.clone(),
+                    Some(old_snapshot),
+                    overwrite,
+                )
+                .await?;
+                guard.set_snapshot_id(to_snapshot);
+                Ok(version)
+            }
+        }
+    }
+
     /// Commit the current changes to the current branch. If the store is not currently
     /// on a branch, this will return an error.
     pub async fn commit(&mut self, message: &str) -> StoreResult<SnapshotId> {
@@ -2415,6 +2451,65 @@ mod tests {
         Ok(())
     }
 
+    #[tokio::test]
+    async fn test_branch_reset() -> Result<(), Box<dyn std::error::Error>> {
+        let storage: Arc<dyn Storage + Send + Sync> =
+            Arc::new(ObjectStorage::new_in_memory_store(Some("prefix".into())));
+
+        let mut store = Store::new_from_storage(Arc::clone(&storage)).await?;
+
+        store
+            .set(
+                "zarr.json",
+                Bytes::copy_from_slice(br#"{"zarr_format":3, "node_type":"group"}"#),
+            )
+            .await
+            .unwrap();
+
+        store.commit("root group").await.unwrap();
+
+        store
+            .set(
+                "a/zarr.json",
+                Bytes::copy_from_slice(br#"{"zarr_format":3, "node_type":"group"}"#),
+            )
+            .await
+            .unwrap();
+
+        let prev_snap = store.commit("group a").await?;
+
+        store
+            .set(
+                "b/zarr.json",
+                Bytes::copy_from_slice(br#"{"zarr_format":3, "node_type":"group"}"#),
+            )
+            .await
+            .unwrap();
+
+        store.commit("group b").await?;
+        assert!(store.exists("a/zarr.json").await?);
+        assert!(store.exists("b/zarr.json").await?);
+
+        store.reset_branch(prev_snap).await?;
+
+        assert!(!store.exists("b/zarr.json").await?);
+        assert!(store.exists("a/zarr.json").await?);
+
+        let (repo, _) =
+            RepositoryConfig::existing(VersionInfo::BranchTipRef("main".to_string()))
+                .make_repository(storage)
+                .await?;
+        let store = Store::from_repository(
+            repo,
+            AccessMode::ReadOnly,
+            Some("main".to_string()),
+            None,
+        );
+        assert!(!store.exists("b/zarr.json").await?);
+        assert!(store.exists("a/zarr.json").await?);
+        Ok(())
+    }
+
     #[tokio::test]
     async fn test_access_mode() {
         let storage: Arc<dyn Storage + Send + Sync> =