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

[devin-ai-integration]

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

Issue

When using PreMailer.MoveCssInline with CSS containing base64 encoded images or SVG+XML data in URLs, the data gets truncated during processing. Additionally, quoted URLs get HTML escaped, resulting in " in the output.

Changes

1. Modified the regex pattern in CssParser.cs that handles data URLs to properly preserve base64 content:

   • Made the pattern less greedy to avoid accidentally matching content in base64 data
   • Added special handling for data URLs to ensure base64 content is preserved

2. Updated StyleClassApplier.cs to preserve original quotes in data URLs:

   • Added special case for data URLs to skip quote conversion
   • Only convert double quotes to single quotes for non-data URL values

3. Added comprehensive test cases in Base64UrlTests.cs to verify:

   • Unquoted base64 URLs
   • Quoted base64 URLs
   • SVG+XML encoded content
   • Base64 data with double equals (==) ending

Testing

All tests pass, including the new test cases that verify base64 data is preserved correctly.

Link to Devin run: https://app.devin.ai/sessions/fadfd33a7ae44b67a5c5d87c24a73045
Requested by: m@martinnormark.com

[devin-ai-integration]

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