Class BER

modules/crypt/etc/ber.js:38–480

 */

export default class BER {
	#a;
	#i = 0;

	constructor(buffer) {
		if (buffer instanceof ArrayBuffer)
			this.#a = new Uint8Array(buffer)
		else if (buffer instanceof Uint8Array)
			this.#a = buffer;
		else
			this.#a = new Uint8Array(new ArrayBuffer(0, {maxByteLength: 16896}));
	}
	get readable() {
		return this.#a.byteLength - this.#i;
	}
	getTag() {
		return this.#a[this.#i++];
	}
	getLength() {
		let length = this.#a[this.#i++];
		if (length < 128)
			return length;

		length &= 0x7F;
		if (!length)
			return -1;	// indefinite length

		let result = 0;
		while (length--)
			result = (result << 8) | this.#a[this.#i++];

		return result;
	}
	peek() {
		return this.#a[this.#i];
	}
	skip(length) {
		this.#i += length;
	}
	next() {
		const i = this.#i;
		this.skip(1);
		this.skip(this.getLength());
		return this.#a.subarray(i, this.#i)
	}
	getInteger() {
		if (this.getTag() !== 2)
			throw new Error("BER: not an integer");
		const length = this.getLength();
		const offset = this.#a.byteOffset + this.#i;
		if (this.peek() & 0x80) {
			const c = this.getChunk(length).slice();		// copy. cannot modify source data.
			for (let i = 0; i < length; i++)	// could use Logical.not
				c[i] = ~c[i];
			return -(BigInt.fromArrayBuffer(c.buffer) + 1n);
		}
		else {
			this.skip(length)