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// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
import { assert } from "../_util/asserts.ts";
/** * A transform stream that only transforms from the zero-indexed `start` and `end` bytes (both inclusive). * * @example * ```ts * import { ByteSliceStream } from "https://deno.land/std@$STD_VERSION/streams/byte_slice_stream.ts"; * const response = await fetch("https://example.com"); * const rangedStream = response.body! *   .pipeThrough(new ByteSliceStream(3, 8)); * ``` */export class ByteSliceStream extends TransformStream<Uint8Array, Uint8Array> {  #offsetStart = 0;  #offsetEnd = 0;
  constructor(start = 0, end = Infinity) {    super({      start: () => {        assert(start >= 0, "`start` must be greater than 0");        end += 1;      },      transform: (chunk, controller) => {        this.#offsetStart = this.#offsetEnd;        this.#offsetEnd += chunk.byteLength;        if (this.#offsetEnd > start) {          if (this.#offsetStart < start) {            chunk = chunk.slice(start - this.#offsetStart);          }          if (this.#offsetEnd >= end) {            chunk = chunk.slice(0, chunk.byteLength - this.#offsetEnd + end);            controller.enqueue(chunk);            controller.terminate();          } else {            controller.enqueue(chunk);          }        }      },    });  }}