Fix: use MIMEBase for email attachments (#8762)

src/documents/mail.py

@@ -0,0 +1,61 @@
+from email.encoders import encode_base64
+from email.mime.base import MIMEBase
+from pathlib import Path
+from urllib.parse import quote
+
+from django.conf import settings
+from django.core.mail import EmailMessage
+from filelock import FileLock
+
+
+def send_email(
+    subject: str,
+    body: str,
+    to: list[str],
+    attachment: Path | None = None,
+    attachment_mime_type: str | None = None,
+) -> int:
+    """
+    Send an email with an optional attachment.
+    TODO: re-evaluate this pending https://code.djangoproject.com/ticket/35581 / https://github.com/django/django/pull/18966
+    """
+    email = EmailMessage(
+        subject=subject,
+        body=body,
+        to=to,
+    )
+    if attachment:
+        # Something could be renaming the file concurrently so it can't be attached
+        with FileLock(settings.MEDIA_LOCK), attachment.open("rb") as f:
+            file_content = f.read()
+
+            main_type, sub_type = (
+                attachment_mime_type.split("/", 1)
+                if attachment_mime_type
+                else ("application", "octet-stream")
+            )
+            mime_part = MIMEBase(main_type, sub_type)
+            mime_part.set_payload(file_content)
+
+            encode_base64(mime_part)
+
+            # see https://github.com/stumpylog/tika-client/blob/f65a2b792fc3cf15b9b119501bba9bddfac15fcc/src/tika_client/_base.py#L46-L57
+            try:
+                attachment.name.encode("ascii")
+            except UnicodeEncodeError:
+                filename_safed = attachment.name.encode("ascii", "ignore").decode(
+                    "ascii",
+                )
+                filepath_quoted = quote(attachment.name, encoding="utf-8")
+                mime_part.add_header(
+                    "Content-Disposition",
+                    f"attachment; filename={filename_safed}; filename*=UTF-8''{filepath_quoted}",
+                )
+            else:
+                mime_part.add_header(
+                    "Content-Disposition",
+                    f"attachment; filename={attachment.name}",
+                )
+
+            email.attach(mime_part)
+    return email.send()