@ipld/dag-pb

@ipld/dag-pb

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

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)

Contribution

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.