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// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
import { assert } from "../_util/asserts.ts";import type { Reader, Writer } from "../types.d.ts";
const DEFAULT_BUFFER_SIZE = 32 * 1024;
/** * Copy N size at the most. If read size is lesser than N, then returns nread * @param r Reader * @param dest Writer * @param size Read size */export async function copyN(  r: Reader,  dest: Writer,  size: number,): Promise<number> {  let bytesRead = 0;  let buf = new Uint8Array(DEFAULT_BUFFER_SIZE);  while (bytesRead < size) {    if (size - bytesRead < DEFAULT_BUFFER_SIZE) {      buf = new Uint8Array(size - bytesRead);    }    const result = await r.read(buf);    const nread = result ?? 0;    bytesRead += nread;    if (nread > 0) {      let n = 0;      while (n < nread) {        n += await dest.write(buf.slice(n, nread));      }      assert(n === nread, "could not write");    }    if (result === null) {      break;    }  }  return bytesRead;}