carbites/lib/rooted/joiner.js

Chunking for CAR files. Split a single CAR into multiple CARs.

import { CarWriter } from '@ipld/car'
import { decode, code } from '@ipld/dag-cbor'
import { Block } from 'multiformats/block'
import { isRootNode } from './root-node.js'
import { SimpleCarJoiner } from '../simple/joiner.js'

/**
 * @typedef {import('@ipld/car/api').BlockReader & import('@ipld/car/api').RootsReader} ICarReader
 */

export class RootedCarJoiner extends SimpleCarJoiner {
  async * car () {
    const reader = this._cars[0]
    const rblk = await getRootedBlock(reader)
    const roots = rblk.value[1]
    const { writer, out } = CarWriter.create(roots)
    const writeCar = async () => {
      try {
        for await (const b of filterBlock(rblk.cid, reader)) {
          await writer.put(b)
        }
        for (const reader of this._cars.slice(1)) {
          const rblk = await getRootedBlock(reader)
          for await (const b of filterBlock(rblk.cid, reader)) {
            await writer.put(b)
          }
        }
      } catch (err) {
        console.error(err) // TODO: how to forward this on?
      } finally {
        await writer.close()
      }
    }

    writeCar()
    yield * out
  }
}

/**
 * @param {ICarReader} reader
 * @returns {Promise<import('multiformats/block').Block<import('./root-node').RootNode>>}
 */
async function getRootedBlock (reader) {
  const roots = await reader.getRoots()
  if (roots.length !== 1) throw new Error(`invalid number of roots: ${roots.length}`)
  if (roots[0].code !== code) throw new Error(`invalid root block code: ${roots[0].code}`)
  const block = await reader.get(roots[0])
  if (!block) throw new Error(`missing root block: ${roots[0]}`)
  const node = decode(block.bytes)
  if (!isRootNode(node)) throw new Error(`invalid root node: ${block.cid}`)
  return new Block({ cid: block.cid, bytes: block.bytes, value: node })
}

/**
 * @param {import('multiformats').CID} cid
 * @param {ICarReader} reader
 */
async function * filterBlock (cid, reader) {
  for await (const b of reader.blocks()) {
    if (b.cid.equals(cid)) continue
    yield b
  }
}