From efc4e6df11155eee2a3368274bab31833c1bd6fd Mon Sep 17 00:00:00 2001
From: Sergey Lavrinenko <s.lavrinenko@gmail.com>
Date: Tue, 31 Mar 2026 20:18:48 +0300
Subject: [PATCH 1/2] Skip data URIs in transformer to prevent broken
 attachments

Closes #62
---
 .../testsuite/transformer/test_transformer.py | 20 +++++++++++++++++++
 emails/transformer.py                         |  3 +++
 2 files changed, 23 insertions(+)

diff --git a/emails/testsuite/transformer/test_transformer.py b/emails/testsuite/transformer/test_transformer.py
index 5e82202..eb93d0d 100644
--- a/emails/testsuite/transformer/test_transformer.py
+++ b/emails/testsuite/transformer/test_transformer.py
@@ -66,6 +66,26 @@ def test_tag_attribute():
     assert m3.attachments['1.jpg'].content_disposition == "inline"
 
 
+def test_data_uri_preserved():
+    DATA_URI = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg=="
+
+    # data URIs in img src should be left untouched
+    html = '<img src="%s"/>' % DATA_URI
+    m = emails.loader.from_string(html=html)
+    assert len(m.attachments.keys()) == 0
+    assert DATA_URI in m.html
+
+    # data URIs in css url() should be left untouched
+    html = '<div style="background: url(%s);">x</div>' % DATA_URI
+    m = emails.loader.from_string(html=html)
+    assert len(m.attachments.keys()) == 0
+
+    # data URIs in background attribute should be left untouched
+    html = '<table background="%s"/>' % DATA_URI
+    m = emails.loader.from_string(html=html)
+    assert len(m.attachments.keys()) == 0
+
+
 ROOT = os.path.dirname(__file__)
 
 def test_local_premailer():
diff --git a/emails/transformer.py b/emails/transformer.py
index 3e1c299..b844e9b 100644
--- a/emails/transformer.py
+++ b/emails/transformer.py
@@ -242,6 +242,9 @@ def _load_attachment_func(self, uri, element=None, callback=None, **kw):
         # Return local uri
         #
 
+        if uri.startswith('data:'):
+            return uri
+
         if callback is None:
             # Default callback: skip images with data-emails="ignore" attribute
             callback = lambda _, hints: hints['attrib'] != 'ignore'

From f71c0dc959c9ba841045274c67c59c5a88e79964 Mon Sep 17 00:00:00 2001
From: Sergey Lavrinenko <s.lavrinenko@gmail.com>
Date: Tue, 31 Mar 2026 20:24:45 +0300
Subject: [PATCH 2/2] Handle mixed-case data URI schemes

---
 emails/testsuite/transformer/test_transformer.py | 6 ++++++
 emails/transformer.py                            | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/emails/testsuite/transformer/test_transformer.py b/emails/testsuite/transformer/test_transformer.py
index eb93d0d..be3c4dd 100644
--- a/emails/testsuite/transformer/test_transformer.py
+++ b/emails/testsuite/transformer/test_transformer.py
@@ -85,6 +85,12 @@ def test_data_uri_preserved():
     m = emails.loader.from_string(html=html)
     assert len(m.attachments.keys()) == 0
 
+    # mixed-case scheme should also be preserved
+    mixed = DATA_URI.replace('data:', 'Data:')
+    html = '<img src="%s"/>' % mixed
+    m = emails.loader.from_string(html=html)
+    assert len(m.attachments.keys()) == 0
+
 
 ROOT = os.path.dirname(__file__)
 
diff --git a/emails/transformer.py b/emails/transformer.py
index b844e9b..21d6e20 100644
--- a/emails/transformer.py
+++ b/emails/transformer.py
@@ -242,7 +242,7 @@ def _load_attachment_func(self, uri, element=None, callback=None, **kw):
         # Return local uri
         #
 
-        if uri.startswith('data:'):
+        if uri[:5].lower() == 'data:':
             return uri
 
         if callback is None: