Fix issue #235: Preserve base64 encoded images and URLs during CSS parsing and style application (#429)

* Fix issue #235: Preserve base64 encoded images and URLs during CSS parsing and style application

Co-Authored-By: [email protected] <[email protected]>

* Refactor StyleClassApplier to simplify data URL quote handling

Co-Authored-By: [email protected] <[email protected]>

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: [email protected] <[email protected]>

Author: devin-ai-integration[bot]

PreMailer.Net/PreMailer.Net.Tests/Base64UrlTests.cs

@@ -0,0 +1,50 @@
+using System;
+using Xunit;
+
+namespace PreMailer.Net.Tests
+{
+    public class Base64UrlTests
+    {
+        [Fact]
+        public void MoveCssInline_WithUnquotedBase64BackgroundImage_ShouldPreserveBase64Data()
+        {
+            string input = "<style>.pt-logo { background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA); background-repeat: no-repeat; }</style><span class=\"pt-logo\"></span>";
+            
+            var result = PreMailer.MoveCssInline(input);
+            
+            Assert.Contains("background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA)", result.Html);
+            Assert.Contains("background-repeat: no-repeat", result.Html);
+        }
+        
+        [Fact]
+        public void MoveCssInline_WithQuotedBase64BackgroundImage_ShouldPreserveBase64Data()
+        {
+            string input = "<style>.pt-logo { background-image: url(\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA\"); background-repeat: no-repeat; }</style><span class=\"pt-logo\"></span>";
+            
+            var result = PreMailer.MoveCssInline(input);
+            
+            Assert.Contains("background-image: url(\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA\")", result.Html);
+            Assert.Contains("background-repeat: no-repeat", result.Html);
+        }
+        
+        [Fact]
+        public void MoveCssInline_WithSvgXmlBackgroundImage_ShouldPreserveEncodedData()
+        {
+            string input = "<style>.my-icon { background-image: url(\"data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' fill='%23fff' width='8' height='8' viewBox='0 0 8 8'%3e%3cpath d='M5.25 0l-4 4 4 4 1.5-1.5L4.25 4l2.5-2.5L5.25 0z'/%3e%3c/svg%3e\"); }</style><span class=\"my-icon\"></span>";
+            
+            var result = PreMailer.MoveCssInline(input);
+            
+            Assert.Contains("background-image: url(\"data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' fill='%23fff' width='8' height='8' viewBox='0 0 8 8'%3e%3cpath d='M5.25 0l-4 4 4 4 1.5-1.5L4.25 4l2.5-2.5L5.25 0z'/%3e%3c/svg%3e\")", result.Html);
+        }
+        
+        [Fact]
+        public void MoveCssInline_WithBase64DataWithDoubleEquals_ShouldPreserveEnding()
+        {
+            string input = "<style>.pt-logo { background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA==); }</style><span class=\"pt-logo\"></span>";
+            
+            var result = PreMailer.MoveCssInline(input);
+            
+            Assert.Contains("background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA==)", result.Html);
+        }
+    }
+}

PreMailer.Net/PreMailer.Net/CssParser.cs

@@ -128,8 +128,8 @@ private static string CleanUp(string s)
 			temp = Regex.Replace(temp, "(['\"])([^'\"\\\\]*(?:\\\\.[^'\"\\\\]*)*?)http://([^'\"]*?)\\1", m => 
 				m.Groups[1].Value + m.Groups[2].Value + "http:" + httpProtocolMarker + m.Groups[3].Value + m.Groups[1].Value);
 
-			temp = Regex.Replace(temp, "(data:[^;]+;base64,[^)\"']*?)//([^)\"']*)", m => 
-				m.Groups[1].Value + dataUrlMarker + m.Groups[2].Value);
+			temp = Regex.Replace(temp, "(data:[^;]+;base64,)([^)\"']*?)//([^)\"']*)", m => 
+				m.Groups[1].Value + m.Groups[2].Value + dataUrlMarker + m.Groups[3].Value);
 
 			temp = _cssCommentRegex.Replace(temp, "");
 			temp = _unsupportedAtRuleRegex.Replace(temp, "");
@@ -141,6 +141,9 @@ private static string CleanUp(string s)
 			temp = temp.Replace(httpProtocolMarker, "//");
 			temp = temp.Replace(dataUrlMarker, "//");
 
+			temp = Regex.Replace(temp, @"url\s*\(\s*(['""]?)data:([^;]+);base64,([^)'""]*)(['""]?)\s*\)", m => 
+				"url(" + m.Groups[1].Value + "data:" + m.Groups[2].Value + ";base64," + m.Groups[3].Value + m.Groups[4].Value + ")");
+			
 			return temp;
 		}
 

PreMailer.Net/PreMailer.Net/StyleClassApplier.cs

@@ -47,8 +47,7 @@ private static void SetAttribute(IElement domElement, AttributeToCss attributeTo
 				value = value.Replace("px", string.Empty);
 			}
 
-			// Quotation marks in CSS is common, but when applied to the style attribute we will use single quotes instead.
-			if (value.Contains("\""))
+			if (value.Contains("\"") && !(value.Contains("data:") && value.Contains(";base64,")))
 			{
 				value = value.Replace("\"", "'");
 			}