@ipld/dag-pb


> JS implementation of DAG-PB

Table of contents

- Install
- Browser
`

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

`js
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.

$3

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.

`js
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().

`js
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
``

API Docs

-

License

Licensed under either of

- Apache 2.0, (LICENSE-APACHE / )
- MIT (LICENSE-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.