ensureData = n => {
		if (contentPosition === contentItemLength) {
			nextContent();
		}
		while (contentItemLength - contentPosition < n) {
			const remaining = contentItem.slice(contentPosition);
			let lengthFromNext = n - remaining.length;
			const buffers = [remaining];
			for (let i = contentsIndex + 1; i < contents.length; i++) {
				const l = contents[i].length;
				if (l > lengthFromNext) {
					buffers.push(contents[i].slice(0, lengthFromNext));
					contents[i] = contents[i].slice(lengthFromNext);
					lengthFromNext = 0;
					break;
				} else {
					buffers.push(contents[i]);
					contentsIndex = i;
					lengthFromNext -= l;
				}
			}
			if (lengthFromNext > 0) throw new Error("Unexpected end of data");
			contentItem = Buffer.concat(buffers, n);
			contentItemLength = n;
			contentPosition = 0;
		}
	}
@param {number} n number of bytes to ensure