@ipld/dag-pb

@ipld/dag-pb

JS implementation of DAG-PB

Table of contents

• Install
• Overview
• Example
• Usage
  • prepare()
• createNode() & createLink()
• License
• Contribute

Install

$ npm i @ipld/dag-pb

Overview

An implementation of the DAG-PB spec for JavaScript designed for use with multiformats or via the higher-level Block abstraction in @ipld/block.

Example

import { CID } from 'multiformats/cid'
import { sha256 } from 'multiformats/hashes/sha2'
import * as dagPB from '@ipld/dag-pb'

async function run () {
  const bytes = dagPB.encode({
    Data: new TextEncoder().encode('Some data as a string'),
    Links: []
  })

  // also possible if you `import dagPB, { prepare } from '@ipld/dag-pb'`
  // const bytes = dagPB.encode(prepare('Some data as a string'))
  // const bytes = dagPB.encode(prepare(new TextEncoder().encode('Some data as a string')))

  const hash = await sha256.digest(bytes)
  const cid = CID.create(1, dagPB.code, hash)

  console.log(cid, '=>', Buffer.from(bytes).toString('hex'))

  const decoded = dagPB.decode(bytes)

  console.log(decoded)
  console.log(`decoded "Data": ${new TextDecoder().decode(decoded.Data)}`)
}

run().catch((err) => {
  console.error(err)
  process.exit(1)
})

Usage

@ipld/dag-pb is designed to be used within multiformats but can be used separately. encode(), decode(), validate() and prepare() functions are available if you pass in a multiformats object to the default export function. Each of these can operate independently as required.

prepare()

The DAG-PB encoding is very strict about the Data Model forms that are passed in. The objects must exactly resemble what they would if they were to undergo a round-trip of encode & decode. Therefore, extraneous or mistyped properties are not acceptable and will be rejected. See the DAG-PB spec for full details of the acceptable schema and additional constraints.

Due to this strictness, a prepare() function is made available which simplifies construction and allows for more flexible input forms. Prior to encoding objects, call prepare() to receive a new object that strictly conforms to the schema.

import { CID } from 'multiformats/cid'
import { prepare } from '@ipld/dag-pb'

console.log(prepare({ Data: 'some data' }))
// ->{ Data: Uint8Array(9) [115, 111, 109, 101, 32, 100,  97, 116, 97] }
console.log(prepare({ Links: [CID.parse('bafkqabiaaebagba')] }))
// -> { Links: [ { Hash: CID(bafkqabiaaebagba) } ] }

Some features of prepare():

• Extraneous properties are omitted
• String values for Data are converted
• Strings are converted to { Data: bytes } (as are Uint8Arrays)
• Multiple ways of finding CIDs in the Links array are attempted, including interpreting the whole link element as a CID, reading a Uint8Array as a CID
• Ensuring that properties are of the correct type (link Name is a string and Tsize is a number)
• Links array is always present, even if empty
• Links array is properly sorted

createNode() & createLink()

These utility exports are available to make transition from the older ipld-dag-pb library which used DAGNode and DAGLink objects with constructors. createNode() mirrors the new DAGNode() API while createLink() mirrors new DAGLink() API.

• createNode(data: Uint8Array, links: PBLink[]|void): PBNode: create a correctly formed PBNode object from a Uint8Array and an optional array of correctly formed PBLink objects. The returned object will be suitable for passing to encode() and using prepare() on it should result in a noop.
• createLink(name: string, size: number, cid: CID): PBLink: create a correctly formed PBLink object from a name, size and CID. The returned object will be suitable for attaching to a PBNode's Links array, or in an array for the second argument to createNode().

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

const { createLink, createNode } = codec

async function run () {
  const cid1 = CID.parse('QmWDtUQj38YLW8v3q4A6LwPn4vYKEbuKWpgSm6bjKW6Xfe')
  const cid2 = CID.parse('bafyreifepiu23okq5zuyvyhsoiazv2icw2van3s7ko6d3ixl5jx2yj2yhu')

  const links = [createLink('link1', 100, cid1), createLink('link2', 200, cid2)]
  const value = createNode(Uint8Array.from([0, 1, 2, 3, 4]), links)
  console.log(value)

  const block = await Block.encode({ value, codec, hasher })
  console.log(block.cid)
  console.log(`Encoded: ${bytes.toHex(block.bytes).replace(/(.{80})/g, '$1\n         ')}`)
}

run().catch((err) => console.error(err))

Results in:

{
  Data: Uint8Array(5) [ 0, 1, 2, 3, 4 ],
  Links: [
    {
      Hash: CID(QmWDtUQj38YLW8v3q4A6LwPn4vYKEbuKWpgSm6bjKW6Xfe),
      Name: 'link1',
      Tsize: 100
    },
    {
      Hash: CID(bafyreifepiu23okq5zuyvyhsoiazv2icw2van3s7ko6d3ixl5jx2yj2yhu),
      Name: 'link2',
      Tsize: 200
    }
  ]
}
CID(bafybeihsp53wkzsaif76mjv564cawzqyjwianosamlvf6sht2m25ttyxiy)
Encoded: 122d0a2212207521fe19c374a97759226dc5c0c8e674e73950e81b211f7dd3b6b30883a08a511205
         6c696e6b31186412300a2401711220a47a29adb950ee698ae0f272019ae902b6aa06ee5f53bc3da2
         ebea6fac27583d12056c696e6b3218c8010a050001020304

License

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)

Contribute

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.