Merge pull request #351 from Hexer10/new-decipherer

[WIP] New signature decipherer

Author: Hexer10

lib/src/js/js_engine.dart

@@ -45,15 +45,16 @@ class JSEngine {
     return context['return'];
   }
 
-  void resolveNode(Node node) {
+  dynamic resolveNode(Node node) {
     return switch (node) {
       Statement() => resolveStatement(node),
       Expression() => resolveExpression(node),
+      Name() => node.value,
       Node() => throw UnimplementedError('Unknown node type: $node'),
     };
   }
 
-  void resolveStatement(Statement statement) {
+  dynamic resolveStatement(Statement statement) {
     return switch (statement) {
       VariableDeclaration() => resolveVariableDeclaration(statement),
       ExpressionStatement() => resolveExpression(statement.expression),
@@ -521,10 +522,21 @@ class JSEngine {
       IndexExpression() => resolveIndexExpression(expr),
       ConditionalExpression() => resolveConditionalExpression(expr),
       ThisExpression() => resolveThisExpression(),
+      ObjectExpression() => resolveObjectExpression(expr),
       Expression() =>
         throw UnimplementedError('Unknown expression type: $expr'),
     };
   }
+
+  dynamic resolveObjectExpression(ObjectExpression expr) {
+    final obj = <String, dynamic>{};
+    for (final prop in expr.properties) {
+      final key = resolveNode(prop.key);
+      final value = resolveNode(prop.value);
+      obj[key] = value;
+    }
+    return obj;
+  }
 }
 
 List<T> _splice<T>(List<T> array, int start,

lib/src/reverse_engineering/cipher/chiper_new.dart

@@ -0,0 +1,67 @@
+import 'package:freezed_annotation/freezed_annotation.dart';
+
+import '../../js/js_engine.dart';
+
+final _decFuncExp = RegExp(
+    r'\b([a-zA-Z0-9_$]+)&&\(\1=([a-zA-Z0-9_$]{2,})\(decodeURIComponent\(\1\)\)',
+    dotAll: true);
+
+RegExp _funcExp(String funcName) => RegExp(
+      '$funcName=(function.+?return.+?;)',
+      dotAll: true,
+    );
+
+final _varsExp = RegExp(r'(?<!\()\b([a-zA-Z][a-zA-Z0-9_$]*)\b');
+
+typedef DeciphererFunc = String Function(
+  String sig,
+);
+
+/// New implementation of the decipher due to the new YouTube cipher.
+@internal
+DeciphererFunc? getDecipherSignatureFunc(String? globalVar, String jscode) {
+  final globalVarName =
+      globalVar?.split('=')[0].trim().replaceFirst('var ', '');
+
+  final match = _decFuncExp.firstMatch(jscode);
+  final funcName = match?.group(2);
+  if (funcName == null) {
+    return null;
+  }
+
+  final decFunc = _funcExp(funcName)
+      .firstMatch(jscode)
+      ?.group(1)
+      ?.replaceFirst('function', 'function $funcName');
+
+  if (decFunc == null) {
+    return null;
+  }
+
+  // Find all the vars used
+  final vars = _varsExp.allMatches(decFunc).map((e) => e.group(1)).toSet();
+  final keywords = ['function', 'return'];
+  final varsList = vars
+      .where(
+          (e) => !keywords.contains(e) && e != funcName && e != globalVarName)
+      .skip(1)
+      .toList(); // Skip the first one, which is the function parameter
+
+  final varDecls = [];
+  for (final varName in varsList) {
+    final exp =
+        RegExp(r'(var ' + varName! + r'=\{(?:.|\n)+?)(;var)', dotAll: true);
+    final varMatch = exp.firstMatch(jscode);
+    if (varMatch == null) {
+      continue;
+    }
+    varDecls.add(varMatch.group(1)!);
+  }
+
+  // Construct the final code
+  var finalFunc = decFunc
+      .replaceFirst('{', '{\n${varDecls.join('\n;')}\n')
+      .replaceFirst('{', '{$globalVar');
+
+  return (String sig) => JSEngine.run(finalFunc, [sig]) as String;
+}

lib/src/videos/streams/stream_client.dart

@@ -6,6 +6,7 @@ import '../../exceptions/exceptions.dart';
 import '../../extensions/helpers_extension.dart';
 import '../../js/js_engine.dart';
 import '../../retry.dart';
+import '../../reverse_engineering/cipher/chiper_new.dart';
 import '../../reverse_engineering/cipher/cipher_manifest.dart';
 import '../../reverse_engineering/heuristics.dart';
 import '../../reverse_engineering/models/stream_info_provider.dart';
@@ -212,6 +213,19 @@ class StreamClient {
   }
 
   String? _playerScript;
+  String? _globalVar;
+
+  String? _getGlobalVar(String playerScript) {
+    // Adapted from https://github.com/yt-dlp/yt-dlp/blob/7794374de8afb20499b023107e2abfd4e6b93ee4/yt_dlp/extractor/youtube/_video.py#L2295
+    return _globalVar ??= _matchPatterns(playerScript, [
+      (
+        r'''
+(["\'])use\s+strict\1;\s*(var\s+[a-zA-Z0-9_$]+\s*=\s*((["\'])(?:(?!(\4)).|\\.)+\4\.split\((["\'])(?:(?!(\6)).)+\6\)|\[\s*(?:(["\'])(?:(?!(\8)).|\\.)*\8\s*,?\s*)+\]))[;,]
+''',
+        2
+      ),
+    ]);
+  }
 
   Future<String> _getPlayerScript([WatchPage? page]) async {
     page ??= await WatchPage.get(_httpClient, '');
@@ -248,15 +262,7 @@ class StreamClient {
           'Could not find the decipher function in the player script.');
     }
 
-    // Adapted from https://github.com/yt-dlp/yt-dlp/blob/7794374de8afb20499b023107e2abfd4e6b93ee4/yt_dlp/extractor/youtube/_video.py#L2295
-    final globalVar = _matchPatterns(playerScript, [
-      (
-        r'''
-(["\'])use\s+strict\1;\s*(var\s+[a-zA-Z0-9_$]+\s*=\s*((["\'])(?:(?!(\4)).|\\.)+\4\.split\((["\'])(?:(?!(\6)).)+\6\)|\[\s*(?:(["\'])(?:(?!(\8)).|\\.)*\8\s*,?\s*)+\]))[;,]
-''',
-        2
-      ),
-    ]);
+    final globalVar = _getGlobalVar(playerScript);
 
     final func = funcMatch.replaceFirst('function', 'function main');
 
@@ -299,16 +305,28 @@ class StreamClient {
         url = url.setQueryParam('n', deciphered);
       }
       if (stream.signatureParameter != null) {
-        cipherManifest ??=
-            CipherManifest.decode(await _getPlayerScript(watchPage));
+        final playerScript = await _getPlayerScript(watchPage);
+        cipherManifest ??= CipherManifest.decode(playerScript);
         final sig = stream.signature!;
         final sigParam = stream.signatureParameter!;
         if (cipherManifest != null) {
           final sigDeciphered = cipherManifest.decipher(sig);
           url = url.setQueryParam(sigParam, sigDeciphered);
           _logger.fine('Deciphered signature: $sig -> $sigDeciphered');
         } else {
-          _logger.warning('Could not decipher signature: $sig');
+          final globalVar = _getGlobalVar(playerScript);
+
+          final deciphererFunc =
+              getDecipherSignatureFunc(globalVar, playerScript);
+          final deciphered = deciphererFunc?.call(sig);
+          if (deciphered != null) {
+            url = url.setQueryParam(sigParam, deciphered);
+            _logger.fine('[2] Deciphered signature: $sig -> $deciphered');
+          } else {
+            // If we cannot decipher the signature, we log a warning
+            // and continue with the original URL.
+            _logger.warning('Could not decipher signature: $sig');
+          }
         }
       }