componentized/directory

wasmcloud:keyvalue

interface dependency

interface store wasmcloud:keyvalue/store@0.2.0

A keyvalue interface that provides eventually consistent key-value operations.

Each of these operations acts on a single key-value pair.

The value in the key-value pair is defined as a u8 byte array and the intention is that it is the common denominator for all data types defined by different key-value stores to handle data, ensuring compatibility between different key-value stores. Note: the clients will be expecting serialization/deserialization overhead to be handled by the key-value store. The value could be a serialized object from JSON, HTML or vendor-specific data types like AWS S3 objects.

Data consistency in a key value store refers to the guarantee that once a write operation completes, all subsequent read operations will return the value that was written.

Any implementation of this interface must have enough consistency to guarantee "reading your writes." In particular, this means that the client should never get a value that is older than the one it wrote, but it MAY get a newer value if one was written around the same time. These guarantees only apply to the same client (which will likely be provided by the host or an external capability of some kind). In this context a "client" is referring to the caller or guest that is consuming this interface. Once a write request is committed by a specific client, all subsequent read requests by the same client will reflect that write or any subsequent writes. Another client running in a different context may or may not immediately see the result due to the replication lag.

Unlike wasi:keyvalue@0.2.0-draft, every operation that touches a backend is an async func. This lets a single component issue many in-flight key-value operations concurrently without the wasi:io/poll ceremony required under wasip2.

Types

use resource bucket

from wasmcloud:keyvalue/types@0.2.0

A bucket is a collection of key-value pairs. Each key-value pair is stored as an entry in the bucket, and the bucket itself acts as a collection of all these entries.

It is worth noting that the exact terminology for bucket in key-value stores can vary depending on the specific implementation. For example:

  1. Amazon DynamoDB calls a collection of key-value pairs a table
  2. Redis has hashes, sets, and sorted sets as different types of collections
  3. Cassandra calls a collection of key-value pairs a column family
  4. MongoDB calls a collection of key-value pairs a collection
  5. Riak calls a collection of key-value pairs a bucket
  6. Memcached calls a collection of key-value pairs a slab
  7. Azure Cosmos DB calls a collection of key-value pairs a container

In this interface, we use the term bucket to refer to a collection of key-value pairs

  • get: async func(key: string) -> result<option<list<u8>>, error>

    Get the value associated with the specified key

    The value is returned as an option. If the key-value pair exists in the store, it returns ok(value). If the key does not exist in the store, it returns ok(none).

    If any other error occurs, it returns an err(error).

  • set: async func( key: string, value: list<u8>, options: option<set-options>, ) -> result<_, error>

    Set the value associated with the key in the store. If the key already exists in the store, it overwrites the value.

    If the key does not exist in the store, it creates a new key-value pair.

    options controls expiry (ttl-ms) and conditional writes (if-not-exists); pass none for the default overwrite-on-exists behavior with no expiry.

    If any other error occurs, it returns an err(error).

  • delete: async func(key: string) -> result<_, error>

    Delete the key-value pair associated with the key in the store.

    If the key does not exist in the store, it does nothing.

    If any other error occurs, it returns an err(error).

  • exists: async func(key: string) -> result<bool, error>

    Check if the key exists in the store.

    If the key exists in the store, it returns ok(true). If the key does not exist in the store, it returns ok(false).

    If any other error occurs, it returns an err(error).

  • list-keys: async func( prefix: option<string>, cursor: option<string>, ) -> result<key-response, error>

    Get the keys in the store, optionally restricted to those starting with prefix, with an optional cursor (for use in pagination). It returns a list of keys. Please note that for most KeyValue implementations, this can be a very expensive operation and so it should be used judiciously. Implementations can return any number of keys in a single response, but they should never attempt to send more data than is reasonable (i.e. on a small edge device, this may only be a few KB, while on a large machine this could be several MB). Any response should also return a cursor that can be used to fetch the next page of keys. See the key-response record for more information.

    prefix filters the result to keys that begin with the given string; pass none to list all keys. When paginating, the same prefix should be supplied alongside each cursor.

    Note that the keys are not guaranteed to be returned in any particular order.

    If the store is empty (or no keys match prefix), it returns an empty list.

    MAY show an out-of-date list of keys if there are concurrent writes to the store.

    If any error occurs, it returns an err(error).

use variant error

from wasmcloud:keyvalue/types@0.2.0

The set of errors which may be raised by functions in this package.

Following the wasip3 convention, this enumerates specific named cases rather than leaning on stringly-typed errors. It is intentionally non-exhaustive: future versions may add cases, and generated bindings are marked non-exhaustive accordingly, so consumers must always include a catch-all arm. Backend-specific failures that do not map to a named case are reported via other.

  • no-such-store

    The host does not recognize the store identifier requested.

  • access-denied

    The requesting component does not have access to the specified store (which may or may not exist).

  • invalid-argument

    The request was malformed or self-contradictory, e.g. a cas.swap whose cas-options sets no precondition.

  • precondition-failed

    A conditional operation did not meet its precondition, e.g. a set with if-not-exists against a key that already exists.

  • timeout

    The operation did not complete within the host- or backend-imposed time limit.

  • store-unavailable

    The store is currently unreachable or otherwise unavailable. The operation may succeed if retried later.

  • quota-exceeded

    The operation was rejected because a quota or rate limit was exceeded.

  • other: string

    Some other implementation-specific error has occurred (e.g. I/O). Used for backend-specific failures that do not map to a named case above.

Functions

open: async func(identifier: string) -> result<bucket, error>

Get the bucket with the specified identifier.

identifier must refer to a bucket provided by the host.

error::no-such-store will be raised if the identifier is not recognized.

WIT

/// A keyvalue interface that provides eventually consistent key-value operations.
///
/// Each of these operations acts on a single key-value pair.
///
/// The value in the key-value pair is defined as a `u8` byte array and the intention is that it is
/// the common denominator for all data types defined by different key-value stores to handle data,
/// ensuring compatibility between different key-value stores. Note: the clients will be expecting
/// serialization/deserialization overhead to be handled by the key-value store. The value could be
/// a serialized object from JSON, HTML or vendor-specific data types like AWS S3 objects.
///
/// Data consistency in a key value store refers to the guarantee that once a write operation
/// completes, all subsequent read operations will return the value that was written.
///
/// Any implementation of this interface must have enough consistency to guarantee "reading your
/// writes." In particular, this means that the client should never get a value that is older than
/// the one it wrote, but it MAY get a newer value if one was written around the same time. These
/// guarantees only apply to the same client (which will likely be provided by the host or an
/// external capability of some kind). In this context a "client" is referring to the caller or
/// guest that is consuming this interface. Once a write request is committed by a specific client,
/// all subsequent read requests by the same client will reflect that write or any subsequent
/// writes. Another client running in a different context may or may not immediately see the result
/// due to the replication lag.
///
/// Unlike `wasi:keyvalue@0.2.0-draft`, every operation that touches a backend is an `async func`.
/// This lets a single component issue many in-flight key-value operations concurrently without the
/// `wasi:io/poll` ceremony required under wasip2.
interface store {
  use types.{bucket, error};

  /// Get the bucket with the specified identifier.
  ///
  /// `identifier` must refer to a bucket provided by the host.
  ///
  /// `error::no-such-store` will be raised if the `identifier` is not recognized.
  open: async func(identifier: string) -> result<bucket, error>;
}