fix: write to balanced layout at width

Fixes a bug that occurs when writing chunks to a balanced layout when the chunks to be written cause the number of leaves to fall on the width boundary.

I was seeing this file link come out when adding a 1GiB file:

{
  cid: CID(bafkreihdwdcefgh4dqkjv67uzcmw7ojee6xedzdetojuzjevtenxquvyku),
  contentByteLength: 0,
  dagByteLength: 0
}

When using settings:

const settings = UnixFS.configure({
  fileChunkEncoder: raw,
  smallFileEncoder: raw,
  chunker: withMaxChunkSize(1024 * 1024),
  fileLayout: withWidth(1024),
})

Note that widths that are multiples of the chunk size also exhibit the behaviour e.g. 512, 128 etc. NOT 2048 though as this does not trigger the layout to do any work to rebalance.

For completeness, this is what is expected:

{
  cid: CID(bafybeigpyaqbbvedzatazfw6jf5daalt4tcegmqsmi32nlhdvvrw72ybea),
  contentByteLength: 1073741824,
  dagByteLength: 1073793035
}

Test code:

import fs from 'node:fs'
import { Readable } from 'node:stream'
import * as UnixFS from '@ipld/unixfs'
import * as raw from 'multiformats/codecs/raw'
import { withMaxChunkSize } from '@ipld/unixfs/file/chunker/fixed'
import { withWidth } from '@ipld/unixfs/file/layout/balanced'

const settings = UnixFS.configure({
  fileChunkEncoder: raw,
  smallFileEncoder: raw,
  chunker: withMaxChunkSize(1024 * 1024),
  fileLayout: withWidth(1024),
})

const queuingStrategy = UnixFS.withCapacity()

async function main () {
  console.log('start')
  const stream = Readable.toWeb(fs.createReadStream('./1GiB.bin'))
  const { readable, writable } = new TransformStream(undefined, queuingStrategy)
  ;(async () => {
    await readable.pipeTo(new WritableStream())
  })()
  const writer = UnixFS.createWriter({ writable, settings })
  const file = UnixFS.createFileWriter(writer)
  await stream.pipeTo(new WritableStream({
    async write (chunk) {
      await file.write(chunk)
    }
  }))
  const link = await file.close()
  console.log('file', link)

  const dir = UnixFS.createDirectoryWriter(writer)
  dir.set('1GiB.bin', link)
  const dirLink = await dir.close()
  console.log('dir', dirLink)

  console.log('end')
}

main()

ipld / js-unixfs

fix: write to balanced layout at width #52