CarBufferWriter for synchronous in-memory CAR creation

ipfs-create-car-sync.js

import fs from 'fs'
import { CarBufferWriter } from '@ipld/car'
import { CID } from 'multiformats/cid'
import * as json from 'multiformats/codecs/json'
import * as raw from 'multiformats/codecs/raw'
import { sha256 } from 'multiformats/hashes/sha2'

/**
 * @param {CID} root
 * @param {Block[]} blocks
 * @returns {Uint8Array} car
 */
function createCARSync (root, blocks) {
  const headerSize = CarBufferWriter.headerLength({ roots: [root] })
  const bufferSize = blocks.reduce((size, block) => size + CarBufferWriter.blockLength(block), headerSize)
  const car = CarBufferWriter.createWriter(new ArrayBuffer(bufferSize), { roots: [root] })
  blocks.forEach(b => car.write(b))
  blocks.forEach(b => console.log(b.cid.toString()))
  return car.close()
}

function createRawBlock (str) {
  const bytes = new TextEncoder().encode(str)
  const hash = sha256.digest(raw.encode(bytes))
  const cid = CID.create(1, raw.code, hash)
  return { cid, bytes }
}

function createJsonBlock (obj) {
  const bytes = json.encode(obj)
  const hash = sha256.digest(bytes)
  const cid = CID.create(1, json.code, hash)
  return { cid, bytes }
}

function main () {
  const blocks = ['a', 'a', 'b', 'c'].map(createRawBlock)
  const root = blocks.at(-1).cid
  const car = createCARSync(root, blocks)
  fs.writeFileSync('dupe.car', car)
}

main()