This class implements a Zarr HTTP store. With this class Zarr stores on web servers can be read. For Zarr v.2 HTTP stores there exists a standard for publishing arrays on the store, using consolidated metadata. This class will look for such metadata in the root of the store. If no consolidated metadata is found then a regular group or array is searched for. Note that if a group is found that there is no standard process to determine what arrays are available in the store and where they are located relative to the root. Typically such information is found in the attributes of the group and you are advised to inspect those attributes and refer to the documentation of the store publisher.
This class performs no sanity checks on any of the arguments passed to the methods, for performance reasons. Since this class should be accessed through group and array objects, it is up to that code to ensure that arguments are valid, in particular keys and prefixes.
Super class
zarr_store -> zarr_httpstore
Active bindings
friendlyClassName(read-only) Name of the class for printing.
root(read-only) The root of the HTTP store, identical to its URL.
uri(read-only) The URI of the store location.
separator(read-only) The default chunk separator of the store, usually a slash '/'.
Methods
zarr_httpstore$new()
Create an instance of this class.
HTTP stores are read-only. Currently two types of Zarr store can be accessed. A Zarr v.2 consolidated metadata file at the root of the store (immediately below the URL) can identify a hierarchy of groups and arrays. Alternatively, a store with a group or a single array, either v.2 or v.3.
Usage
zarr_httpstore$new(url)zarr_httpstore$exists()
Check if a key exists in the store. The key can point to a group, an array, or a metadata file. This check is only relevant for HTTP stores with consolidated metadata. In other cases the single group or array will be at the root.
zarr_httpstore$list_dir()
Retrieve all keys and prefixes with a given prefix and which do not contain the character "/" after the given prefix. In other words, this retrieves all the nodes in the store below the node indicated by the prefix.
zarr_httpstore$get()
Retrieve the value associated with a given key.
Arguments
keyCharacter string. The key for which to get data.
prototypeIgnored. The only buffer type that is supported maps directly to an R raw vector.
byte_rangeIf
NULL, all data associated with the key is retrieved. If a single positive integer, all bytes starting from a given byte offset to the end of the object are returned. If a single negative integer, the final bytes are returned. If an integer vector of length 2, request a specific range of bytes where the end is exclusive. If the range ends after the end of the object, the entire remainder of the object will be returned. If the given range is zero-length or starts after the end of the object, an error will be returned.
zarr_httpstore$get_metadata()
Retrieve the metadata document of the node at the location
indicated by the prefix argument. The metadata will always be
presented to the caller in the Zarr v.3 format. Attributes, if present,
will be added.