Read/write a gzipped JSON lines file with Deno

deno-compressed-json-lines-reader.ts

const createInputReader = async (path: string) => {
  const file = await Deno.open(path, {
    read: true,
  })

  return file.readable
    .pipeThrough(new DecompressionStream('gzip'))
    .pipeThrough(new TextDecoderStream())
    .pipeThrough(new TextLineStream())
    .pipeThrough(
      new TransformStream({
        transform(chunk, controller) {
          controller.enqueue(JSON.parse(chunk))
        },
      })
    )
}

// const input = await createInputReader('example.jsonl.gz')
// for await (const item of input) {
//   // do something
// }

deno-compressed-json-lines-writer.ts

const createOutputWriter = async (path: string) => {
  const file = await Deno.open(path, {
    create: true,
    write: true,
    truncate: true,
  })

  const stream = new TransformStream()

  stream.readable
    .pipeThrough(
      new TransformStream({
        transform(chunk, controller) {
          controller.enqueue(JSON.stringify(chunk))
          controller.enqueue('\n')
        },
      })
    )
    .pipeThrough(new TextEncoderStream())
    .pipeThrough(new CompressionStream('gzip'))
    .pipeTo(file.writable)

  return stream.writable.getWriter()
}

// const writer = await createOutputWriter('example.jsonl.gz')
// await writer.write({ foo: 'bar' })