From 1dc298c5ea62dda936f9654b32527b72c48c5012 Mon Sep 17 00:00:00 2001
From: chuenchen309 <48723787+chuenchen309@users.noreply.github.com>
Date: Sun, 19 Jul 2026 14:15:00 +0800
Subject: [PATCH] Fix broken string literal that disabled the quoted-printable
 attachment branch

A line-continuation inside the string literal made the comparison target
"quoted-                       printable" (the continuation line's indentation
became part of the string), so it never equalled "quoted-printable". The
branch handling quoted-printable application/* attachments was therefore dead:
such attachments fell through to the text branch and were decoded as UTF-8 with
errors="ignore", silently dropping every non-UTF8 byte and mis-flagging
binary=False.

Join the literal so the comparison works. Added a test with a quoted-printable
application/octet-stream attachment that round-trips losslessly.
---
 src/mailparser/core.py    |  4 +---
 tests/test_mail_parser.py | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/src/mailparser/core.py b/src/mailparser/core.py
index 44c0d5f..dc16bb1 100644
--- a/src/mailparser/core.py
+++ b/src/mailparser/core.py
@@ -407,9 +407,7 @@ def parse(self):
                         binary = False
                         log.debug(f"Filename {filename!r} part {i!r} is multipart")
                     elif transfer_encoding == "base64" or (
-                        transfer_encoding
-                        == "quoted-\
-                       printable"
+                        transfer_encoding == "quoted-printable"
                         and "application" in mail_content_type
                     ):
                         payload = p.get_payload(decode=False)
diff --git a/tests/test_mail_parser.py b/tests/test_mail_parser.py
index c3ef1bc..e1f5836 100644
--- a/tests/test_mail_parser.py
+++ b/tests/test_mail_parser.py
@@ -399,6 +399,31 @@ def test_defects_bug(self):
         result = len(mail.attachments)
         self.assertEqual(1, result)
 
+    def test_quoted_printable_application_attachment(self):
+        # A quoted-printable application/* attachment must be kept as binary
+        # (raw QP text), not decoded as UTF-8, which drops the non-UTF8 bytes.
+        import quopri
+
+        original = b"\xff\xfe\x00\x01PDFdata\x80\x81\x82\xc0\xc1"
+        qp = quopri.encodestring(original).decode("ascii")
+        raw = (
+            "From: a@b.com\r\nTo: c@d.com\r\nSubject: t\r\n"
+            "MIME-Version: 1.0\r\n"
+            'Content-Type: multipart/mixed; boundary="B"\r\n\r\n'
+            "--B\r\nContent-Type: text/plain\r\n\r\nbody\r\n"
+            '--B\r\nContent-Type: application/octet-stream; name="f.bin"\r\n'
+            "Content-Transfer-Encoding: quoted-printable\r\n"
+            'Content-Disposition: attachment; filename="f.bin"\r\n\r\n'
+            + qp
+            + "\r\n--B--\r\n"
+        )
+        attachment = mailparser.parse_from_string(raw).attachments[0]
+        self.assertTrue(attachment["binary"])
+        self.assertEqual(attachment["content_transfer_encoding"], "quoted-printable")
+        self.assertEqual(
+            quopri.decodestring(attachment["payload"].encode("ascii")), original
+        )
+
     def test_add_content_type(self):
         mail = mailparser.parse_from_file(mail_test_3)