std/bytes/copy.ts

// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

/** Copy bytes from the `src` array to the `dst` array. Returns the number of
 * bytes copied.
 *
 * If the `src` array is larger than what the `dst` array can hold, only the
 * amount of bytes that fit in the `dst` array are copied.
 *
 * An offset can be specified as the third argument that begins the copy at
 * that given index in the `dst` array. The offset defaults to the beginning of
 * the array.
 *
 * ```ts
 * import { copy } from "@std/bytes/copy";
 * const src = new Uint8Array([9, 8, 7]);
 * const dst = new Uint8Array([0, 1, 2, 3, 4, 5]);
 * console.log(copy(src, dst)); // 3
 * console.log(dst); // [9, 8, 7, 3, 4, 5]
 * ```
 *
 * ```ts
 * import { copy } from "@std/bytes/copy";
 * const src = new Uint8Array([1, 1, 1, 1]);
 * const dst = new Uint8Array([0, 0, 0, 0]);
 * console.log(copy(src, dst, 1)); // 3
 * console.log(dst); // [0, 1, 1, 1]
 * ```
 */
export function copy(src: Uint8Array, dst: Uint8Array, off = 0): number {
  off = Math.max(0, Math.min(off, dst.byteLength));
  const dstBytesAvailable = dst.byteLength - off;
  if (src.byteLength > dstBytesAvailable) {
    src = src.subarray(0, dstBytesAvailable);
  }
  dst.set(src, off);
  return src.byteLength;
}