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multiformats/js-multiformats: Multiformats interface (multihash, multicodec, multibase and CID)

Interface for multihash, multicodec, multibase and CID

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

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

import { CID } from 'multiformats/cid'
import * as 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)

import * as Block from 'multiformats/block'
import * as codec from '@ipld/dag-cbor'
import { sha256 as hasher } from 'multiformats/hashes/sha2'

const value = { hello: 'world' }

// encode a block
let block = await Block.encode({ value, codec, hasher })

block.value // { hello: 'world' }
block.bytes // Uint8Array
block.cid   // CID() w/ sha2-256 hash address and dag-cbor codec

// you can also decode blocks from their binary state
block = await Block.decode({ bytes: block.bytes, codec, hasher })

// if you have the cid you can also verify the hash on decode
block = await Block.create({ bytes: block.bytes, cid: block.cid, codec, hasher })

CIDs can be serialized to string representation using multibase encoders that implement MultibaseEncoder interface. This 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. This 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, base36, 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'

This library defines BlockEncoder, BlockDecoder and BlockCodec interfaces. Codec implementations should conform to the BlockCodec interface which implements both BlockEncoder and BlockDecoder. Here is an example implementation of JSON BlockCodec.

export const { name, code, encode, decode } = {
  name: 'json',
  code: 0x0200,
  encode: json => new TextEncoder().encode(JSON.stringify(json)),
  decode: bytes => JSON.parse(new TextDecoder().decode(bytes))
}

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)

This library contains higher-order functions for traversing graphs of data easily.

walk() walks through the links in each block of a DAG calling a user-supplied loader function for each one, in depth-first order with no duplicate block visits. The loader should return a Block object and can be used to inspect and collect block ordering for a full DAG walk. The loader should throw on error, and return null if a block should be skipped by walk().

import { walk } from 'multiformats/traversal'
import * as Block from 'multiformats/block'
import * as codec from 'multiformats/codecs/json'
import { sha256 as hasher } from 'multiformats/hashes/sha2'

// build a DAG (a single block for this simple example)
const value = { hello: 'world' }
const block = await Block.encode({ value, codec, hasher })
const { cid } = block
console.log(cid)
//> CID(bagaaierasords4njcts6vs7qvdjfcvgnume4hqohf65zsfguprqphs3icwea)

// create a loader function that also collects CIDs of blocks in
// their traversal order
const load = (cid, blocks) => async (cid) => {
  // fetch a block using its cid
  // e.g.: const block = await fetchBlockByCID(cid)
  blocks.push(cid)
  return block
}

// collect blocks in this DAG starting from the root `cid`
const blocks = []
await walk({ cid, load: load(cid, blocks) })

console.log(blocks)
//> [CID(bagaaierasords4njcts6vs7qvdjfcvgnume4hqohf65zsfguprqphs3icwea)]

blockcodec-to-ipld-format converts a multiformats BlockCodec into an interface-ipld-format for use with the ipld package. This can help bridge IPLD codecs implemented using the structure and interfaces defined here to existing code that assumes, or requires interface-ipld-format. This bridge also includes the relevant TypeScript definitions.

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

Other (less useful) bases implemented in multiformats/js-multiformats include: base2, base8, base10, base36 and base256emoji.

Loading this module through a script tag will make its exports available as Multiformats in the global namespace.

<script src="https://unpkg.com/multiformats/dist/index.min.js"></script>

• https://multiformats.github.io/js-multiformats

Licensed under either of

• Apache 2.0, (LICENSE-APACHE / http://www.apache.org/licenses/LICENSE-2.0)
• MIT (LICENSE-MIT / http://opensource.org/licenses/MIT)

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

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