fix: refuse writes to a store zarr-python opened read-only - #190
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selmanozleyen wants to merge 1 commit into
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fix: refuse writes to a store zarr-python opened read-only#190selmanozleyen wants to merge 1 commit into
selmanozleyen wants to merge 1 commit into
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zarr-python enforces read-only in the store itself -- `Store._check_writable`, reached from the concrete store's `_set`. This pipeline never gets there: it is handed a `StoreConfig` and builds its own Rust store, writable whatever mode the array was opened in, so a write to a `mode="r"` array succeeds here and raises through the default pipeline. Silent divergence, and silent data loss for anyone relying on the mode. The flag has to be carried from Python because nothing on the Rust side can infer it: the mode is zarr-python's, not the store's. One guard, at the only entry point Python can write through. `store_chunk_bytes` and `store_chunk_subset_bytes` are reached only from it. The tests open STRICT. zarr's own refusal message is byte-identical to the guard's, so with a fallback available they would pass whether the guard fired or zarr-python served the write.
selmanozleyen
marked this pull request as ready for review
August 28, 2026 15:45
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Hi,
I'd like to propose some changes for the integer indexing case but because shard index caching depends on it and because it's also a nice thing to have in general I opened this PR. This enables us to be clear with the refusal of writing read only stores.
The flag has to be carried from Python because nothing on the Rust side can infer it: the mode is zarr-python's, not the store's. One guard, at the only entry point Python can write through.
store_chunk_bytesandstore_chunk_subset_bytesare reached only from it.