/
byte_slice_stream.ts
44 lines (41 loc) · 1.34 KB
/
byte_slice_stream.ts
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// Copyright 2018-2023 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);
}
}
},
});
}
}