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// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
import { copy as copyBytes } from "../bytes/copy.ts";import { assert } from "../_util/asserts.ts";import type { Reader, ReaderSync } from "../types.d.ts";
const DEFAULT_BUFFER_SIZE = 32 * 1024;
export interface ByteRange {  /** The 0 based index of the start byte for a range. */  start: number;
  /** The 0 based index of the end byte for a range, which is inclusive. */  end: number;}
/** * Read a range of bytes from a file or other resource that is readable and * seekable.  The range start and end are inclusive of the bytes within that * range. * * ```ts * import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts"; * import { readRange } from "https://deno.land/std@$STD_VERSION/io/read_range.ts"; * * // Read the first 10 bytes of a file * const file = await Deno.open("example.txt", { read: true }); * const bytes = await readRange(file, { start: 0, end: 9 }); * assertEquals(bytes.length, 10); * ``` */export async function readRange(  r: Reader & Deno.Seeker,  range: ByteRange,): Promise<Uint8Array> {  // byte ranges are inclusive, so we have to add one to the end  let length = range.end - range.start + 1;  assert(length > 0, "Invalid byte range was passed.");  await r.seek(range.start, Deno.SeekMode.Start);  const result = new Uint8Array(length);  let off = 0;  while (length) {    const p = new Uint8Array(Math.min(length, DEFAULT_BUFFER_SIZE));    const nread = await r.read(p);    assert(nread !== null, "Unexpected EOF reach while reading a range.");    assert(nread > 0, "Unexpected read of 0 bytes while reading a range.");    copyBytes(p, result, off);    off += nread;    length -= nread;    assert(length >= 0, "Unexpected length remaining after reading range.");  }  return result;}
/** * Read a range of bytes synchronously from a file or other resource that is * readable and seekable.  The range start and end are inclusive of the bytes * within that range. * * ```ts * import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts"; * import { readRangeSync } from "https://deno.land/std@$STD_VERSION/io/read_range.ts"; * * // Read the first 10 bytes of a file * const file = Deno.openSync("example.txt", { read: true }); * const bytes = readRangeSync(file, { start: 0, end: 9 }); * assertEquals(bytes.length, 10); * ``` */export function readRangeSync(  r: ReaderSync & Deno.SeekerSync,  range: ByteRange,): Uint8Array {  // byte ranges are inclusive, so we have to add one to the end  let length = range.end - range.start + 1;  assert(length > 0, "Invalid byte range was passed.");  r.seekSync(range.start, Deno.SeekMode.Start);  const result = new Uint8Array(length);  let off = 0;  while (length) {    const p = new Uint8Array(Math.min(length, DEFAULT_BUFFER_SIZE));    const nread = r.readSync(p);    assert(nread !== null, "Unexpected EOF reach while reading a range.");    assert(nread > 0, "Unexpected read of 0 bytes while reading a range.");    copyBytes(p, result, off);    off += nread;    length -= nread;    assert(length >= 0, "Unexpected length remaining after reading range.");  }  return result;}