cesiumDemo/Source/Core/decodeGoogleEarthEnterpriseData.js

import Check from './Check.js';
import RuntimeError from './RuntimeError.js';

    var compressedMagic = 0x7468dead;
    var compressedMagicSwap = 0xadde6874;

    /**
     * Decodes data that is received from the Google Earth Enterprise server.
     *
     * @param {ArrayBuffer} key The key used during decoding.
     * @param {ArrayBuffer} data The data to be decoded.
     *
     * @private
     */
    function decodeGoogleEarthEnterpriseData(key, data) {
        if (decodeGoogleEarthEnterpriseData.passThroughDataForTesting) {
            return data;
        }

        //>>includeStart('debug', pragmas.debug);
        Check.typeOf.object('key', key);
        Check.typeOf.object('data', data);
        //>>includeEnd('debug');

        var keyLength = key.byteLength;
        if (keyLength === 0 || (keyLength % 4) !== 0) {
            throw new RuntimeError('The length of key must be greater than 0 and a multiple of 4.');
        }

        var dataView = new DataView(data);
        var magic = dataView.getUint32(0, true);
        if (magic === compressedMagic || magic === compressedMagicSwap) {
            // Occasionally packets don't come back encoded, so just return
            return data;
        }

        var keyView = new DataView(key);

        var dp = 0;
        var dpend = data.byteLength;
        var dpend64 = dpend - (dpend % 8);
        var kpend = keyLength;
        var kp;
        var off = 8;

        // This algorithm is intentionally asymmetric to make it more difficult to
        // guess. Security through obscurity. :-(

        // while we have a full uint64 (8 bytes) left to do
        // assumes buffer is 64bit aligned (or processor doesn't care)
        while (dp < dpend64) {
            // rotate the key each time through by using the offets 16,0,8,16,0,8,...
            off = (off + 8) % 24;
            kp = off;

            // run through one key length xor'ing one uint64 at a time
            // then drop out to rotate the key for the next bit
            while ((dp < dpend64) && (kp < kpend)) {
                dataView.setUint32(dp, dataView.getUint32(dp, true) ^ keyView.getUint32(kp, true), true);
                dataView.setUint32(dp + 4, dataView.getUint32(dp + 4, true) ^ keyView.getUint32(kp + 4, true), true);
                dp += 8;
                kp += 24;
            }
        }

        // now the remaining 1 to 7 bytes
        if (dp < dpend) {
            if (kp >= kpend) {
                // rotate the key one last time (if necessary)
                off = (off + 8) % 24;
                kp = off;
            }

            while (dp < dpend) {
                dataView.setUint8(dp, dataView.getUint8(dp) ^ keyView.getUint8(kp));
                dp++;
                kp++;
            }
        }
    }

    decodeGoogleEarthEnterpriseData.passThroughDataForTesting = false;
export default decodeGoogleEarthEnterpriseData;