Implementing better base64 evaluation + appropriate zip entry naming

src/modules/Elsa.IO.Compression/Activities/CreateZipArchive.cs

@@ -80,7 +80,7 @@ public class CreateZipArchive : CodeActivity<Stream>
 
         try
         {
-            using var zipArchive = new ZipArchive(zipStream, ZipArchiveMode.Create, leaveOpen: true);
+            using var zipArchive = new ZipArchive(zipStream, ZipArchiveMode.Update, leaveOpen: true);
             var entryIndex = 0;
 
             var compressionLevel = CompressionLevel.Get(context);
@@ -122,19 +122,73 @@ public class CreateZipArchive : CodeActivity<Stream>
         CompressionLevel compressionLevel)
     {
         var binaryContent = await resolver.ResolveAsync(entryContent, context.CancellationToken);
-        
-        var entryName = binaryContent.Name?.GetNameAndExtension() 
+    
+        var entryName = binaryContent.Name?.GetNameAndExtension()
                         ?? string.Format(DefaultEntryNameFormat, entryIndex + 1);
-        
+    
+        // Get a unique name following Windows convention
+        entryName = GetUniqueEntryName(zipArchive, entryName);
+    
         var archiveEntry = zipArchive.CreateEntry(entryName, compressionLevel);
         
         await using var entryStream = archiveEntry.Open();
         await binaryContent.Stream.CopyToAsync(entryStream, context.CancellationToken);
         await entryStream.FlushAsync(context.CancellationToken);
-        
+    
         if (entryContent is not Stream)
         {
             await binaryContent.Stream.DisposeAsync();
         }
     }
+    
+    private static string GetUniqueEntryName(ZipArchive zipArchive, string originalName)
+    {
+        // If no duplicate exists, use the original name
+        if (!zipArchive.Entries.Any(entry => entry.Name.Equals(originalName, StringComparison.OrdinalIgnoreCase)))
+        {
+            return originalName;
+        }
+    
+        // Split the name into filename and extension
+        string filenameWithoutExtension = Path.GetFileNameWithoutExtension(originalName);
+        string extension = Path.GetExtension(originalName);
+    
+        // Find the highest index used for this filename pattern
+        int highestIndex = 0;
+        
+        // Check for the original name and any name with pattern "name(n).ext"
+        foreach (var entry in zipArchive.Entries)
+        {
+            if (entry.Name.Equals(originalName, StringComparison.OrdinalIgnoreCase))
+                continue; // Skip the exact match as we already know it exists
+                
+            string entryNameWithoutExt = Path.GetFileNameWithoutExtension(entry.Name);
+            string entryExt = Path.GetExtension(entry.Name);
+            
+            if (!entryExt.Equals(extension, StringComparison.OrdinalIgnoreCase))
+                continue; // Different extension
+                
+            if (entryNameWithoutExt.StartsWith(filenameWithoutExtension, StringComparison.OrdinalIgnoreCase) &&
+                entryNameWithoutExt.Length > filenameWithoutExtension.Length &&
+                entryNameWithoutExt[filenameWithoutExtension.Length] == '(')
+            {
+                // Extract the number between parentheses
+                var closingParenIndex = entryNameWithoutExt.LastIndexOf(')');
+                if (closingParenIndex > filenameWithoutExtension.Length + 1)
+                {
+                    var indexStr = entryNameWithoutExt.Substring(
+                        filenameWithoutExtension.Length + 1, 
+                        closingParenIndex - filenameWithoutExtension.Length - 1);
+                    
+                    if (int.TryParse(indexStr, out int index))
+                    {
+                        highestIndex = Math.Max(highestIndex, index);
+                    }
+                }
+            }
+        }
+    
+        // Create a new name with the next available index
+        return $"{filenameWithoutExtension}({highestIndex + 1}){extension}";
+    }
 }

src/modules/Elsa.IO/Extensions/ContentTypeExtensions.cs

@@ -96,27 +96,43 @@ public static class ContentTypeExtensions
         if (s.Length % 4 != 0)
             return false;
 
-        // Check valid Base64 characters
-        for (var i = 0; i < s.Length; i++)
+        // Check padding position and count
+        var paddingIndex = s.IndexOf('=');
+        if (paddingIndex > 0)
+        {
+            // Padding must be at the end
+            if (paddingIndex < s.Length - 2)
+                return false;
+            
+            // All characters after first '=' must also be '='
+            if (s.Substring(paddingIndex).Any(c => c != '='))
+                return false;
+        }
+
+        // Check for valid Base64 characters
+        for (int i = 0; i < (paddingIndex > 0 ? paddingIndex : s.Length); i++)
         {
             var c = s[i];
-
-            var isValid =
+            var isValid = 
                 c is >= 'A' and <= 'Z' ||
                 c is >= 'a' and <= 'z' ||
                 c is >= '0' and <= '9' ||
-                c == '+' || c == '/' || c == '=';
+                c == '+' || c == '/';
 
             if (!isValid)
                 return false;
         }
 
-        // Try actual decoding and roundtrip
+        // Additional check for short strings that are just lowercase+numbers
+        // This catches "content2" and similar false positives
+        if (s.Length <= 10 && s.All(c => char.IsLower(c) || char.IsDigit(c)))
+            return false;
+
+        // Try actual decoding
         try
         {
-            var data = Convert.FromBase64String(s);
-            var reEncoded = Convert.ToBase64String(data);
-            return s == reEncoded;
+            _ = Convert.FromBase64String(s);
+            return true;
         }
         catch
         {