Read-Only mode when checking out snapshot or tag (#313)

* Read-Only mode when checking out snapshot or tag

Closes #237

* lint

* Try better docstring

.gitignore

@@ -4,4 +4,7 @@
 .DS_Store
 
 # Docs build
-.docs
+.docs
+
+# hypothesis
+.hypothesis

icechunk-python/python/icechunk/__init__.py

@@ -159,6 +159,24 @@ def create(
         store = pyicechunk_store_create(storage, config=config)
         return cls(store=store, mode=mode, args=args, kwargs=kwargs)
 
+    def set_mode(self, mode: AccessModeLiteral) -> None:
+        """
+        Set the mode on this Store.
+
+        Parameters
+        ----------
+        mode: AccessModeLiteral
+            The new mode to use.
+
+        Returns
+        -------
+        None
+
+        """
+        read_only = mode == "r"
+        self._store.set_mode(read_only)
+
+
     def with_mode(self, mode: AccessModeLiteral) -> Self:
         """
         Return a new store of the same type pointing to the same location with a new mode.

icechunk-python/python/icechunk/_icechunk_python.pyi

@@ -5,6 +5,7 @@ from typing import Any
 
 class PyIcechunkStore:
     def as_bytes(self) -> bytes: ...
+    def set_mode(self, read_only: bool) -> None: ...
     def with_mode(self, read_only: bool) -> PyIcechunkStore: ...
     @property
     def snapshot_id(self) -> str: ...

icechunk-python/src/lib.rs

@@ -329,6 +329,18 @@ impl PyIcechunkStore {
         Ok(Cow::Owned(serialized))
     }
 
+    fn set_mode(&self, read_only: bool) -> PyResult<()> {
+        let access_mode = if read_only {
+            icechunk::zarr::AccessMode::ReadOnly
+        } else {
+            icechunk::zarr::AccessMode::ReadWrite
+        };
+
+        let mut writeable_store = self.store.blocking_write();
+        writeable_store.set_mode(access_mode);
+        Ok(())
+    }
+
     fn with_mode(&self, read_only: bool) -> PyResult<PyIcechunkStore> {
         let access_mode = if read_only {
             icechunk::zarr::AccessMode::ReadOnly

icechunk-python/tests/test_timetravel.py

@@ -30,6 +30,7 @@ def test_timetravel():
     assert air_temp[200, 6] == 54
 
     store.checkout(branch="main")
+    store.set_mode("w-")
     air_temp[:, :] = 76
     assert store.has_uncommitted_changes
     assert store.branch == "main"

icechunk/src/zarr.rs

@@ -346,6 +346,10 @@ impl Store {
         }
     }
 
+    pub fn set_mode(&mut self, mode: AccessMode) {
+        self.mode = mode;
+    }
+
     /// Creates a new clone of the store with the given access mode.
     pub fn with_access_mode(&self, mode: AccessMode) -> Self {
         Store {
@@ -396,8 +400,12 @@ impl Store {
 
     /// Checkout a specific version of the repository. This can be a snapshot id, a tag, or a branch tip.
     ///
-    /// If the version is a branch tip, the branch will be set as the current branch. If the version
-    /// is a tag or snapshot id, the current branch will be unset and the store will be in detached state.
+    /// If the version is a branch tip, the branch will be set as the current branch.
+    /// The current [`AccessMode`] will be unchanged.
+    ///
+    /// If the version is a tag or snapshot id, the current branch will be unset and the store
+    /// will be in detached state. No commits are allowed in this state. Further the store will
+    /// be set to [`AccessMode::ReadOnly`] mode so that any attempts to modify the store will fail.
     ///
     /// If there are uncommitted changes, this method will return an error.
     pub async fn checkout(&mut self, version: VersionInfo) -> StoreResult<()> {
@@ -412,10 +420,12 @@ impl Store {
             VersionInfo::SnapshotId(sid) => {
                 self.current_branch = None;
                 repo.set_snapshot_id(sid);
+                self.mode = AccessMode::ReadOnly;
             }
             VersionInfo::TagRef(tag) => {
                 self.current_branch = None;
-                repo.set_snapshot_from_tag(tag.as_str()).await?
+                repo.set_snapshot_from_tag(tag.as_str()).await?;
+                self.mode = AccessMode::ReadOnly;
             }
             VersionInfo::BranchTipRef(branch) => {
                 self.current_branch = Some(branch.clone());
@@ -2332,11 +2342,18 @@ mod tests {
         let new_snapshot_id = store.commit("update").await.unwrap();
 
         store.checkout(VersionInfo::SnapshotId(snapshot_id.clone())).await.unwrap();
+        assert_eq!(store.mode, AccessMode::ReadOnly);
         assert_eq!(store.get("array/c/0/1/0", &ByteRange::ALL).await.unwrap(), data);
 
-        store.checkout(VersionInfo::SnapshotId(new_snapshot_id)).await.unwrap();
+        store.checkout(VersionInfo::SnapshotId(new_snapshot_id.clone())).await.unwrap();
         assert_eq!(store.get("array/c/0/1/0", &ByteRange::ALL).await.unwrap(), new_data);
 
+        store.tag("tag_0", &new_snapshot_id).await.unwrap();
+        store.checkout(VersionInfo::TagRef("tag_0".to_string())).await.unwrap();
+        assert_eq!(store.mode, AccessMode::ReadOnly);
+
+        store.checkout(VersionInfo::BranchTipRef("main".to_string())).await.unwrap();
+        store.set_mode(AccessMode::ReadWrite);
         let _newest_data = Bytes::copy_from_slice(b"earth");
         store.set("array/c/0/1/0", data.clone()).await.unwrap();
         assert_eq!(store.has_uncommitted_changes().await, true);