@loaders.gl/zip/dist/parse-zip/search-from-the-end.js

Zip Archive Loader

// loaders.gl
// SPDX-License-Identifier: MIT
// Copyright (c) vis.gl contributors
import { getReadableFileSize, readRange } from "./readable-file-utils.js";
const buffLength = 1024;
/**
 * looking for the last occurrence of the provided
 * @param file
 * @param target
 * @returns
 */
export const searchFromTheEnd = async (file, target) => {
    const fileLength = await getReadableFileSize(file);
    const lastBytes = new Uint8Array(await readRange(file, fileLength - 3n, fileLength + 1n));
    const searchWindow = [lastBytes[3], lastBytes[2], lastBytes[1], undefined];
    let targetOffset = -1;
    // looking for the last record in the central directory
    let point = fileLength - 4n;
    do {
        const prevPoint = point;
        point -= BigInt(buffLength);
        point = point >= 0n ? point : 0n;
        const buff = new Uint8Array(await readRange(file, point, prevPoint));
        for (let i = buff.length - 1; i > -1; i--) {
            searchWindow[3] = searchWindow[2];
            searchWindow[2] = searchWindow[1];
            searchWindow[1] = searchWindow[0];
            searchWindow[0] = buff[i];
            if (searchWindow.every((val, index) => val === target[index])) {
                targetOffset = i;
                break;
            }
        }
    } while (targetOffset === -1 && point > 0n);
    return point + BigInt(targetOffset);
};
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