multiformats

This library defines common interfaces and low level building blocks for varios inter-related multiformat technologies (multicodec, multihash, multibase, and CID). They can be used to implement custom custom base encoders / decoders / codecs, codec encoders /decoders and multihash hashers that comply to the interface that layers above assume.

Library provides implementations for most basics and many others can be found in linked repositories.

Interfaces

import CID from 'multiformats/cid'
import json from 'multiformats/codecs/json'
import { sha256 } from 'multiformats/hashes/sha2'

const bytes = json.encode({ hello: 'world' })

const hash = await sha256.digest(bytes)
const cid = CID.create(1, json.code, hash)
//> CID(bagaaierasords4njcts6vs7qvdjfcvgnume4hqohf65zsfguprqphs3icwea)

Multibase Encoders / Decoders / Codecs

CIDs can be serialized to string representation using multibase encoders that implement MultibaseEncoder interface. Library provides quite a few implementations that can be imported:

import { base64 } from "multiformats/bases/base64"
cid.toString(base64.encoder)
//> 'mAYAEEiCTojlxqRTl6svwqNJRVM2jCcPBxy+7mRTUfGDzy2gViA'

Parsing CID string serialized CIDs requires multibase decoder that implements MultibaseDecoder interface. Library provides a decoder for every encoder it provides:

CID.parse('mAYAEEiCTojlxqRTl6svwqNJRVM2jCcPBxy+7mRTUfGDzy2gViA', base64.decoder)
//> CID(bagaaierasords4njcts6vs7qvdjfcvgnume4hqohf65zsfguprqphs3icwea)

Dual of multibase encoder & decoder is defined as multibase codec and it exposes them as encoder and decoder properties. For added convenience codecs also implement MultibaseEncoder and MultibaseDecoder interfaces so they could be used as either or both:

cid.toString(base64)
CID.parse(cid.toString(base64), base64)

Note: CID implementation comes bundled with base32 and base58btc multibase codecs so that CIDs can be base serialized to (version specific) default base encoding and parsed without having to supply base encoders/decoders:

const v1 = CID.parse('bagaaierasords4njcts6vs7qvdjfcvgnume4hqohf65zsfguprqphs3icwea')
v1.toString()
//> 'bagaaierasords4njcts6vs7qvdjfcvgnume4hqohf65zsfguprqphs3icwea'

const v0 = CID.parse('QmdfTbBqBPQ7VNxZEYEj14VmRuZBkqFbiwReogJgS1zR1n')
v0.toString()
//> 'QmdfTbBqBPQ7VNxZEYEj14VmRuZBkqFbiwReogJgS1zR1n'
v0.toV1().toString()
//> 'bafybeihdwdcefgh4dqkjv67uzcmw7ojee6xedzdetojuzjevtenxquvyku'

Multicodec Encoders / Decoders / Codecs

Library defines BlockEncoder, BlockDecoder and BlockCodec interfaces and utility function to take care of the boilerplate when implementing them:

import { codec } from 'multiformats/codecs/codec'

const json = codec({
  name: 'json',
  // As per multiformats table
  // https://github.com/multiformats/multicodec/blob/master/table.csv#L113
  code: 0x0200,
  encode: json => new TextEncoder().encode(JSON.stringify(json)),
  decode: bytes => JSON.parse(new TextDecoder().decode(bytes))
})

Just like with multibase, here codecs are duals of encoder and decoder parts, but they also implement both interfaces for convenience:

const hello = json.encoder.encode({ hello: 'world' })
json.decode(b1)
//> { hello: 'world' }

Multihash Hashers

This library defines MultihashHasher and MultihashDigest interfaces and convinient function for implementing them:

import * as hasher from 'multiformats/hashes/hasher')

const sha256 = hasher.from({
  // As per multiformats table
  // https://github.com/multiformats/multicodec/blob/master/table.csv#L9
  name: 'sha2-256',
  code: 0x12,

  encode: (input) => new Uint8Array(crypto.createHash('sha256').update(input).digest())
})

const hash = await sha256.digest(json.encode({ hello: 'world' }))
CID.create(1, json.code, hash)

//> CID(bagaaierasords4njcts6vs7qvdjfcvgnume4hqohf65zsfguprqphs3icwea)

Implementations

By default, no base encodings (other than base32 & base58btc), hash functions, or codec implementations are included exposed by multiformats, you need to import the ones you need yourself.

Multibase codecs

bases	import	repo
`base16`	`multiformats/bases/base16`	multiformats/js-multiformats
`base32`, `base32pad`, `base32hex`, `base32hexpad`, `base32z`	`multiformats/bases/base32`	multiformats/js-multiformats
`base64`, `base64pad`, `base64url`, `base64urlpad`	`multiformats/bases/base64`	multiformats/js-multiformats
`base58btc`, `base58flick4`	`multiformats/bases/base58`	multiformats/js-multiformats

Multihash hashers

hashes	import	repo
`sha2-256`, `sha2-512`	`multiformats/hashes/sha2`	multiformats/js-multiformats
`sha3-224`, `sha3-256`, `sha3-384`,`sha3-512`, `shake-128`, `shake-256`, `keccak-224`, `keccak-256`, `keccak-384`, `keccak-512`	`@multiformats/sha3`	multiformats/js-sha3
`identity`	`multiformats/hashes/identity`	multiformats/js-multiformats
`murmur3-128`, `murmur3-32`	`@multiformats/murmur3`	multiformats/js-murmur3
`blake2b-`, `blake2s-`	`@multiformats/blake2`	multiformats/js-blake2

Codec Implementations (multicodec)

codec	import	repo
`raw`	`multiformats/codecs/raw`	multiformats/js-multiformats
`json`	`multiformats/codecs/json`	multiformats/js-multiformats
`dag-cbor`	`@ipld/dag-cbor`	ipld/js-dag-cbor
`dag-json`	`@ipld/dag-json`	ipld/js-dag-json
`dag-pb`	`@ipld/dag-pb`	ipld/js-dag-pb
`dag-jose`	`dag-jose`	ceramicnetwork/js-dag-jose

andymatuschak / js-multiformats