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Filename : array-buffer.js
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import {getStreamContents} from './contents.js';
import {noop, throwObjectStream, getLengthProp} from './utils.js';

export async function getStreamAsArrayBuffer(stream, options) {
	return getStreamContents(stream, arrayBufferMethods, options);
}

const initArrayBuffer = () => ({contents: new ArrayBuffer(0)});

const useTextEncoder = chunk => textEncoder.encode(chunk);
const textEncoder = new TextEncoder();

const useUint8Array = chunk => new Uint8Array(chunk);

const useUint8ArrayWithOffset = chunk => new Uint8Array(chunk.buffer, chunk.byteOffset, chunk.byteLength);

const truncateArrayBufferChunk = (convertedChunk, chunkSize) => convertedChunk.slice(0, chunkSize);

// `contents` is an increasingly growing `Uint8Array`.
const addArrayBufferChunk = (convertedChunk, {contents, length: previousLength}, length) => {
	const newContents = hasArrayBufferResize() ? resizeArrayBuffer(contents, length) : resizeArrayBufferSlow(contents, length);
	new Uint8Array(newContents).set(convertedChunk, previousLength);
	return newContents;
};

// Without `ArrayBuffer.resize()`, `contents` size is always a power of 2.
// This means its last bytes are zeroes (not stream data), which need to be
// trimmed at the end with `ArrayBuffer.slice()`.
const resizeArrayBufferSlow = (contents, length) => {
	if (length <= contents.byteLength) {
		return contents;
	}

	const arrayBuffer = new ArrayBuffer(getNewContentsLength(length));
	new Uint8Array(arrayBuffer).set(new Uint8Array(contents), 0);
	return arrayBuffer;
};

// With `ArrayBuffer.resize()`, `contents` size matches exactly the size of
// the stream data. It does not include extraneous zeroes to trim at the end.
// The underlying `ArrayBuffer` does allocate a number of bytes that is a power
// of 2, but those bytes are only visible after calling `ArrayBuffer.resize()`.
const resizeArrayBuffer = (contents, length) => {
	if (length <= contents.maxByteLength) {
		contents.resize(length);
		return contents;
	}

	const arrayBuffer = new ArrayBuffer(length, {maxByteLength: getNewContentsLength(length)});
	new Uint8Array(arrayBuffer).set(new Uint8Array(contents), 0);
	return arrayBuffer;
};

// Retrieve the closest `length` that is both >= and a power of 2
const getNewContentsLength = length => SCALE_FACTOR ** Math.ceil(Math.log(length) / Math.log(SCALE_FACTOR));

const SCALE_FACTOR = 2;

const finalizeArrayBuffer = ({contents, length}) => hasArrayBufferResize() ? contents : contents.slice(0, length);

// `ArrayBuffer.slice()` is slow. When `ArrayBuffer.resize()` is available
// (Node >=20.0.0, Safari >=16.4 and Chrome), we can use it instead.
// eslint-disable-next-line no-warning-comments
// TODO: remove after dropping support for Node 20.
// eslint-disable-next-line no-warning-comments
// TODO: use `ArrayBuffer.transferToFixedLength()` instead once it is available
const hasArrayBufferResize = () => 'resize' in ArrayBuffer.prototype;

const arrayBufferMethods = {
	init: initArrayBuffer,
	convertChunk: {
		string: useTextEncoder,
		buffer: useUint8Array,
		arrayBuffer: useUint8Array,
		dataView: useUint8ArrayWithOffset,
		typedArray: useUint8ArrayWithOffset,
		others: throwObjectStream,
	},
	getSize: getLengthProp,
	truncateChunk: truncateArrayBufferChunk,
	addChunk: addArrayBufferChunk,
	getFinalChunk: noop,
	finalize: finalizeArrayBuffer,
};