/
copy_n.ts
41 lines (38 loc) · 1.02 KB
/
copy_n.ts
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// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
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;
}