An associative array Map-type data structure for very large, distributed data sets built on IPLD.
This JavaScript implementation conforms to the IPLD HashMap specification.
The HashMap in this implementation has an API similar to JavaScript's native Map object but uses asynchronous accessors rather than synchronous. When creating a new HashMap or loading one with existing data, a backing store must be provided. The backing store is provided via a loader interface which should have a get() method that returns binary IPLD block data when provided a CID (content identifier) and a put() method that takes both a CID and binary block data that will store the IPLD block. This interface may connect to a P2P network, a block storage database or even a ZIP file.
The algorithm for this HashMap is implemented in IAMap, you can read more about it there, or in the IPLD HashMap specification. IAMap is serialization and storage agnostic and therefore does not contain any IPLD dependencies. IAMap is also immutable, where each mutation operation returns a new instance.
This implementation wraps IAMap with IPLD primitives, including the use of CIDs and the standard IPLD block encoding formats and presents a mutable interface. Each HashMap object has its own root CID in the cid property. Whenever the HashMap is mutated (get() and delete()), the cid property will change to the new root block CID.
You can create a new, empty, HashMap with async HashMap.create(loader[, options]). Loading a HashMap from existing data can be done with async HashMap.create(loader[, root][, options]).
Be aware that each mutation operation will create at least one new block, stored via loader.put(). Large numbers of mutations will create many extraneous intermediate blocks which will need to be garbage collected from the backing store if the intermediate states are not required.
class HashMapasync HashMap#get(key)async HashMap#has(key)async HashMap#size()async HashMap#set(key, value)async HashMap#delete(key)async HashMap#values()async HashMap#keys()async HashMap#entries()async HashMap#cids()async HashMap.create(loader[, root][, options])
An IPLD HashMap object. Create a new HashMap or load an existing one with the asynchronous
HashMap.create factory method.
This class serves mostly as a IPLD usability wrapper for
IAMap which implements the majority of the logic behind the
IPLD HashMap specification, without being IPLD-specific. IAMap is immutable, in that each
mutation (delete or set) returns a new IAMap instance. HashMap, however, is mutable, and
mutation operations may be performed on the same object but its cid property will change
with mutations.
Properties:
cid(CID): The current CID of this HashMap. It is important to note that this CID will change when successfully performing mutation operationsHashMap#setorHashMap#delete. Where aHashMap#setdoes not change an existing value (because a key already exists with that value) orHashMap#deletedoes not delete an existing key/value pair (because it doesn't already exist in this HashMap), thecidwill not change.
Fetches the value of the provided key stored in this HashMap, if it exists.
Parameters:
key(String): The key of the key/value pair entry to look up in this HashMap.
Return value (*|CID|undefined): The value stored for the given key which may be any type serializable by IPLD, or a CID to
an existing IPLD object. This should match what was provided by HashMap#set as the
value for this key. If the key is not stored in this HashMap, undefined will be
returned.
Check whether the provided key exists in this HashMap. The equivalent of performing
map.get(key) !== undefined.
Parameters:
key(String): The key of the key/value pair entry to look up in this HashMap.
Return value (boolean): true if the key exists in this HashMap, false otherwise.
Count the number of key/value pairs stored in this HashMap.
Return value (number): An integer greater than or equal to zero indicating the number of key/value pairse stored
in this HashMap.
Add a key/value pair to this HashMap. The value may be any object that can be serialized by
IPLD, or a CID to a more complex (or larger) object. HashMap#get operations on the
same key will retreve the value as it was set as long as serialization and deserialization
results in the same object.
If the key already exists in this HashMap, the existing entry will have the value replaced
with the new one provided. If the value is the same, the HashMap will remain unchanged.
As a mutation operation, performing a successful set() where a new key/value pair or new
value for a given key is set, a new root node will be generated so map.cid will be a
different CID. This CID should be used to refer to this collection in the backing store where
persistence is required.
Parameters:
key(String): The key of the new key/value pair entry to store in this HashMap.value(*|CID): The value to store, either an object that can be serialized inline via IPLD or a CID pointing to another object.
Remove a key/value pair to this HashMap.
If the key exists in this HashMap, its entry will be entirely removed. If the key does not
exist in this HashMap, no changes will occur.
As a mutation operation, performing a successful delete() where an existing key/value pair
is removed from the collection, a new root node will be generated so map.cid will be a
different CID. This CID should be used to refer to this collection in the backing store where
persistence is required.
Parameters:
key(String): The key of the key/value pair entry to remove from this HashMap.
Asynchronously emit all values that exist within this HashMap collection. This will cause a full traversal of all nodes that make up this collection so may result in many block loads from the backing store if the collection is large.
Return value (AsyncIterator.<(*|CID)>): An async iterator that yields values of the type stored in this collection, either inlined
objects or CIDs.
Asynchronously emit all keys that exist within this HashMap collection. This will cause a full traversal of all nodes that make up this collection so may result in many block loads from the backing store if the collection is large.
Return value (AsyncIterator.<string>): An async iterator that yields string keys stored in this collection.
Asynchronously emit all key/value pairs that exist within this HashMap collection. This will cause a full traversal of all nodes that make up this collection so may result in many block loads from the backing store if the collection is large.
Entries are returned in tuple form like
Map#entries(),
an array of key/value pairs where element 0 is the key and 1 is the value.
Return value (AsyncIterator.<Object>): An async iterator that yields key/value pair tuples.
Asynchronously emit all CIDs for blocks that make up this HashMap. This will cause a full traversal of all nodes that make up this collection so may result in many block loads from the backing store if the collection is large.
Return value (AsyncIterator.<CID>): An async iterator that yields CIDs for the blocks that comprise this HashMap.
Create a new HashMap instance, beginning empty, or loading from existing data in a
backing store.
A backing store must be provided to make use of a HashMap, an interface to the store is given
through the mandatory loader parameter. The backing store stores IPLD blocks, referenced by
CIDs. loader must have two functions: get(cid) which should return the raw bytes (Buffer
or Uint8Array) of a block matching the given CID, and put(cid, block) that will store the
provided raw bytes of a block (block) and store it with the associated CID.
Parameters:
loader(Object): A loader withget(cid):blockandput(cid, block)functions for loading an storing block data by CID.root(CID, optional): A root of an existing HashMap. Provide a CID if you want to load existing data, otherwise omit this option and a new, empty HashMap will be created.options(Object, optional): Options for the HashMap. Defaults are provided but you can tweak behavior according to your needs with these options.options.blockCodec(string, optional, default='dag-json'): The IPLD codec used to encode the blocks.options.blockAlg(string, optional, default='sha2-256'): The hash algorithm to use when creating CIDs for the blocks.options.hamtAlg(string, optional, default='murmur3-32'): The hash algorithm used for indexing this HashMap.'murmur3-32'is the x86 32-bit Murmur3 hash algorithm, used by default. If you want to change this default, you need to provide a new algorithm. For custom hash algorithms,hamtAlg,hamtHasherandhashBytesmust be provided together.options.hamtHasher(function, optional, default=murmur3.x86): A function that takes a byte array (Uint8Array) and should return a byte representing a hash of the input. Supply this option if you wish to override the default'murmur3-32'hasher.options.hashBytes(number, optional, default=32): The number of bytes to expect fromhasherfunction. Supply this option if you wish to override the default'murmur3-32'hasher.options.bitWidth(number, optional, default=8): The number of bits to take from the hash of the key at each level of the HashMap tree to form an index. Read more about this option in the IAMap documentation.options.bucketSize(number, optional, default=3): The maximum number of elements to store at each leaf of the HashMap tree structure before overflowing to a new node. Read more about this option in the IAMap documentation.
Return value (HashMap): - A HashMap instance, either loaded from an existing root block CID, or a new,
empty HashMap if no CID is provided.
Copyright 2019 Rod Vagg
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
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