experimental IPLD based (writable) storage for zarr

This repository should be considered as experimental.

examples

storing on IPFS

Store data on (local) IPFS node:

>>> import ipldstore
>>> import xarray as xr
>>> ds = xr.Dataset({"a": ("a", [1, 2, 3])})
>>> m = ipldstore.get_ipfs_mapper()
>>> ds.to_zarr(m, encoding={"a": {"compressor": None}}, consolidated=False)   # doctest: +SKIP
<xarray.backends.zarr.ZarrStore object at 0x...>
>>> print(m.freeze())   # doctest: +SKIP
bafyreidn66mk3fktszrfwayonvpq6y3agtnb5e5o22ivof5tgikbxt7k6u

(this example does only work if there's a local IPFS node running)

storing on a MutableMapping

Instead of storing the data directly on IPFS, it is also possible to store the data on a generic MutableMapping, which could be just a dictionary, but also some object store or a file system. MappingCAStore does the necessary API conversions, so we wrap our backend inside.

Let's try to store data in memory:

>>> backend = {}  # can be any MutableMapping[str, bytes]
>>> m = ipldstore.IPLDStore(ipldstore.MappingCAStore(backend))
>>> ds.to_zarr(m, encoding={"a": {"compressor": None}}, consolidated=False)
<xarray.backends.zarr.ZarrStore object at 0x...>
>>> print(m.freeze())
bafyreidn66mk3fktszrfwayonvpq6y3agtnb5e5o22ivof5tgikbxt7k6u

A look inside

Now that we've got full control over our backend, we can also have a look at what's stored inside:

>>> from pprint import pprint
>>> pprint(backend, width=120)
{'bafkreihc4ibtvz7btvualgou5mfbgwncwshmlovmoudgyml7x6crlhcu54': b'\x01\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00'
                                                                b'\x00\x00\x00\x00\x03\x00\x00\x00\x00\x00\x00\x00',
 'bafyreidn66mk3fktszrfwayonvpq6y3agtnb5e5o22ivof5tgikbxt7k6u': b'\xa3aa\xa3a0\xd8*X%\x00\x01U\x12 \xe2\xe2\x03:\xe7'
                                                                b'\xe1\x9dh\x05\x99\xd4\xeb\n\x13Y\xa2\xb4'
                                                                b'\x8e\xc5\xba\xacu\x06l1\x7f\xbf\x85\x15\x9cT\xefg.zar'
                                                                b'ray\xa8edtypec<i8eorderaCeshape\x81\x03fchunk'
                                                                b's\x81\x03gfilters\xf6jcompressor\xf6jfill_value\xf6'
                                                                b'kzarr_format\x02g.zattrs\xa1q_ARRAY_DIMENSIONS\x81aag'
                                                                b'.zattrs\xa0g.zgroup\xa1kzarr_format\x02'}

The store contains two objects which are keyed by their content identifier (CID). The first one are the raw bytes of our array data, the second is a combination of zarr metadata fields in DAG-CBOR encoding. Note that this is unconsolidated metadata, but the store is able to inline the metadata objects, which makes them traversable using common IPLD mechanisms.

In order to understand the parts better, we'll decode the objects a bit further:

First, let's just have a look at the raw array data:

>>> rawdata = backend['bafkreihc4ibtvz7btvualgou5mfbgwncwshmlovmoudgyml7x6crlhcu54']
>>> rawdata
b'\x01\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\x00\x00\x00\x00'
>>> import numpy as np
>>> np.frombuffer(rawdata, "int")
array([1, 2, 3])

Indeed, that's our original array-data.

For the second object, we'll use cbor2 to decode the object and cover the Link-type (CBOR tag 42) manually afterwards. Note that this object has the same content identifier as returned by m.freeze(), so we'll call it the root_object.

>>> import cbor2
>>> root_object = cbor2.loads(backend['bafyreidn66mk3fktszrfwayonvpq6y3agtnb5e5o22ivof5tgikbxt7k6u'])
>>> pprint(root_object, width=100)
{'.zattrs': {},
 '.zgroup': {'zarr_format': 2},
 'a': {'.zarray': {'chunks': [3],
                   'compressor': None,
                   'dtype': '<i8',
                   'fill_value': None,
                   'filters': None,
                   'order': 'C',
                   'shape': [3],
                   'zarr_format': 2},
       '.zattrs': {'_ARRAY_DIMENSIONS': ['a']},
       '0': CBORTag(42, b'\x00\x01U\x12 \xe2\xe2\x03:\xe7\xe1\x9dh\x05\x99\xd4\xeb\n\x13Y\xa2\xb4\x8e\xc5\xba\xacu\x06l1\x7f\xbf\x85\x15\x9cT\xef')}}

This structure represents the entire hierarchy of objects generated by zarr. In particular, it contains:

• .zattrs
• .zgroup
• a/.zarray
• a/.zattrs
• a/0

where all but a/0 have been inlined into the structure to make the contained metadata visible for IPLD. So far, this is just plain CBOR. In order to understand the link, we need to decode it using CID rules. In particular, we want to transform the link form its raw binary encoding within CBOR into the base32 string representation which is used by our backend. To do so, we'll use the multiformats package, which knows (among others) about baseN encodings, varints and CID encoding rules. As DAG-CBOR mandates a 0-byte as prefix before any CID, we'll have to remove that when passing it to the CID module.

>>> from multiformats import CID
>>> print(CID.decode(root_object["a"]["0"].value[1:]).set(base="base32"))
bafkreihc4ibtvz7btvualgou5mfbgwncwshmlovmoudgyml7x6crlhcu54

This is indeed the CID which links to our data block.

Transferring multiple blocks

It is also possible to transfer content via content archives (CAR):

>>> archive = m.to_car()
>>> type(archive), len(archive)
(<class 'bytes'>, 356)

The resulting archive is a valid CARv1 and can be imported to other IPLD speaking services (including IPFS). It can also be imported into another IPLDStore:

>>> new_backend = {}  # can be any MutableMapping[str, bytes]
>>> new_m = ipldstore.IPLDStore(ipldstore.MappingCAStore(new_backend))
>>> new_backend
{}
>>> new_m.import_car(archive)
>>> print(new_m.freeze())
bafyreidn66mk3fktszrfwayonvpq6y3agtnb5e5o22ivof5tgikbxt7k6u
>>> new_ds = xr.open_zarr(m, consolidated=False)
>>> new_ds.a.values
array([1, 2, 3])

We've correctly transferred values from one dataset to a different backend store.