Create a Reader from an iterable of Uint8Arrays.

import { readerFromIterable } from "https://deno.land/std@0.212.0/streams/reader_from_iterable.ts";
import { copy } from "https://deno.land/std@0.212.0/streams/copy.ts";

const file = await Deno.open("metrics.txt", { write: true });
const reader = readerFromIterable((async function* () {
  while (true) {
    await new Promise((r) => setTimeout(r, 1000));
    const message = `data: ${JSON.stringify(Deno.metrics())}\n\n`;
    yield new TextEncoder().encode(message);
  }
})());
await copy(reader, file);