94 lines
2.5 KiB
JavaScript
94 lines
2.5 KiB
JavaScript
import Check from "./Check.js";
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import RuntimeError from "./RuntimeError.js";
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const compressedMagic = 0x7468dead;
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const compressedMagicSwap = 0xadde6874;
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/**
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* Decodes data that is received from the Google Earth Enterprise server.
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*
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* @param {ArrayBuffer} key The key used during decoding.
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* @param {ArrayBuffer} data The data to be decoded.
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*
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* @private
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*/
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function decodeGoogleEarthEnterpriseData(key, data) {
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if (decodeGoogleEarthEnterpriseData.passThroughDataForTesting) {
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return data;
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}
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//>>includeStart('debug', pragmas.debug);
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Check.typeOf.object("key", key);
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Check.typeOf.object("data", data);
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//>>includeEnd('debug');
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const keyLength = key.byteLength;
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if (keyLength === 0 || keyLength % 4 !== 0) {
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throw new RuntimeError(
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"The length of key must be greater than 0 and a multiple of 4.",
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);
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}
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const dataView = new DataView(data);
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const magic = dataView.getUint32(0, true);
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if (magic === compressedMagic || magic === compressedMagicSwap) {
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// Occasionally packets don't come back encoded, so just return
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return data;
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}
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const keyView = new DataView(key);
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let dp = 0;
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const dpend = data.byteLength;
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const dpend64 = dpend - (dpend % 8);
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const kpend = keyLength;
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let kp;
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let off = 8;
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// This algorithm is intentionally asymmetric to make it more difficult to
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// guess. Security through obscurity. :-(
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// while we have a full uint64 (8 bytes) left to do
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// assumes buffer is 64bit aligned (or processor doesn't care)
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while (dp < dpend64) {
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// rotate the key each time through by using the offsets 16,0,8,16,0,8,...
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off = (off + 8) % 24;
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kp = off;
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// run through one key length xor'ing one uint64 at a time
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// then drop out to rotate the key for the next bit
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while (dp < dpend64 && kp < kpend) {
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dataView.setUint32(
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dp,
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dataView.getUint32(dp, true) ^ keyView.getUint32(kp, true),
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true,
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);
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dataView.setUint32(
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dp + 4,
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dataView.getUint32(dp + 4, true) ^ keyView.getUint32(kp + 4, true),
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true,
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);
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dp += 8;
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kp += 24;
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}
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}
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// now the remaining 1 to 7 bytes
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if (dp < dpend) {
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if (kp >= kpend) {
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// rotate the key one last time (if necessary)
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off = (off + 8) % 24;
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kp = off;
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}
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while (dp < dpend) {
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dataView.setUint8(dp, dataView.getUint8(dp) ^ keyView.getUint8(kp));
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dp++;
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kp++;
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}
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}
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}
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decodeGoogleEarthEnterpriseData.passThroughDataForTesting = false;
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export default decodeGoogleEarthEnterpriseData;
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