87 lines
2.4 KiB
Dart
87 lines
2.4 KiB
Dart
/// Cloudreve obfuscated thumbnail URL decoder.
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/// Ported from the Go reference implementation in the API documentation.
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class TimeFlowDecoder {
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/// Decode an obfuscated time-flow string.
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/// Tries current time, then ±1000ms to account for clock drift.
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/// Returns null if all attempts fail.
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static String? decodeTimeFlowString(String str) {
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if (str.isEmpty) return null;
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final timeNow = DateTime.now().millisecondsSinceEpoch;
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for (final offset in [0, -1000, 1000]) {
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final result = _decodeTimeFlowStringTime(str, timeNow + offset);
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if (result != null) return result;
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}
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return null;
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}
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static String? _decodeTimeFlowStringTime(String str, int timeNowMillis) {
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if (str.isEmpty) return null;
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int timeNow = timeNowMillis ~/ 1000;
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final timeNowBackup = timeNow;
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final timeDigits = <int>[];
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if (timeNow == 0) {
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timeDigits.add(0);
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} else {
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int tempTime = timeNow;
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while (tempTime > 0) {
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timeDigits.add(tempTime % 10);
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tempTime = tempTime ~/ 10;
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}
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}
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final res = str.split('');
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var secret = str.split('');
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var add = secret.length % 2 == 0;
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var timeDigitIndex = (secret.length - 1) % timeDigits.length;
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final l = secret.length;
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for (int pos = 0; pos < l; pos++) {
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final targetIndex = l - 1 - pos;
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int newIndex = targetIndex;
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if (add) {
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newIndex += timeDigits[timeDigitIndex] * timeDigitIndex;
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} else {
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newIndex = 2 * timeDigitIndex * timeDigits[timeDigitIndex] - newIndex;
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}
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if (newIndex < 0) {
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newIndex = newIndex.abs();
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}
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newIndex = newIndex % secret.length;
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res[targetIndex] = secret[newIndex];
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// Swap secret[newIndex] with last element, then shrink
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final lastSecretIndex = secret.length - 1;
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final a = secret[lastSecretIndex];
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final b = secret[newIndex];
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secret[newIndex] = a;
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secret[lastSecretIndex] = b;
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secret = secret.sublist(0, lastSecretIndex);
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add = !add;
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timeDigitIndex--;
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if (timeDigitIndex < 0) {
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timeDigitIndex = timeDigits.length - 1;
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}
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}
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final resStr = res.join('');
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final pipeIndex = resStr.indexOf('|');
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if (pipeIndex < 0) return null;
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final timestampPart = resStr.substring(0, pipeIndex);
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if (timestampPart != timeNowBackup.toString()) return null;
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return resStr.substring(pipeIndex + 1);
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}
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}
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