handoff fixes

backend/app/services/mail_sender.py

@@ -1,16 +1,33 @@
 import email.policy
 import email.utils
-from email.message import EmailMessage
+from email.message import EmailMessage, Message
+from email.mime.base import MIMEBase
+from email.mime.multipart import MIMEMultipart
+from email.mime.text import MIMEText
 
 import aiosmtplib
 import dkim
 
 from app.config import get_settings
 from app.models import MailDomain
+from app.services.mime_body_extractor import ExtractedMimePart
 
 SMTP_POLICY = email.policy.SMTP.clone(max_line_length=998)
 
 
+def _mime_attachment(part: ExtractedMimePart) -> MIMEBase:
+    maintype, _, subtype = part.content_type.partition("/")
+    if not subtype:
+        maintype, subtype = "application", "octet-stream"
+    mime = MIMEBase(maintype, subtype, policy=SMTP_POLICY)
+    mime.set_payload(part.payload)
+    email.utils.encode_base64(mime)
+    mime.add_header("Content-Disposition", part.disposition, filename=part.filename)
+    if part.content_id:
+        mime.add_header("Content-ID", f"<{part.content_id}>")
+    return mime
+
+
 def build_message(
     *,
     sender: str,
@@ -23,7 +40,47 @@ def build_message(
     in_reply_to: str | None = None,
     references: list[str] | None = None,
     message_id: str | None = None,
-) -> EmailMessage:
+    inline_parts: list[ExtractedMimePart] | None = None,
+    file_attachments: list[ExtractedMimePart] | None = None,
+) -> Message:
+    inline_parts = inline_parts or []
+    file_attachments = file_attachments or []
+
+    if inline_parts or file_attachments:
+        root = MIMEMultipart("mixed", policy=SMTP_POLICY)
+        root["From"] = sender
+        root["To"] = ", ".join(recipients)
+        if cc:
+            root["Cc"] = ", ".join(cc)
+        if reply_to:
+            root["Reply-To"] = reply_to
+        root["Subject"] = subject
+        root["Date"] = email.utils.formatdate(localtime=True)
+        generated_id = message_id or email.utils.make_msgid(domain=sender.split("@")[-1])
+        root["Message-ID"] = generated_id
+        if in_reply_to:
+            root["In-Reply-To"] = in_reply_to
+        if references:
+            root["References"] = " ".join(references)
+
+        alternative = MIMEMultipart("alternative", policy=SMTP_POLICY)
+        alternative.attach(MIMEText(body_text, "plain", "utf-8", policy=SMTP_POLICY))
+
+        if body_html:
+            if inline_parts:
+                related = MIMEMultipart("related", policy=SMTP_POLICY)
+                related.attach(MIMEText(body_html, "html", "utf-8", policy=SMTP_POLICY))
+                for part in inline_parts:
+                    related.attach(_mime_attachment(part))
+                alternative.attach(related)
+            else:
+                alternative.attach(MIMEText(body_html, "html", "utf-8", policy=SMTP_POLICY))
+
+        root.attach(alternative)
+        for attachment in file_attachments:
+            root.attach(_mime_attachment(attachment))
+        return root
+
     message = EmailMessage(policy=SMTP_POLICY)
     message["From"] = sender
     message["To"] = ", ".join(recipients)
@@ -45,7 +102,7 @@ def build_message(
     return message
 
 
-def sign_message(message: EmailMessage, domain: MailDomain) -> bytes:
+def sign_message(message: Message, domain: MailDomain) -> bytes:
     raw_message = message.as_bytes(policy=SMTP_POLICY)
     signed_headers = [
         b"from",
@@ -106,6 +163,8 @@ async def deliver_email(
     in_reply_to: str | None = None,
     references: list[str] | None = None,
     message_id: str | None = None,
+    inline_parts: list[ExtractedMimePart] | None = None,
+    file_attachments: list[ExtractedMimePart] | None = None,
 ) -> str:
     message = build_message(
         sender=sender,
@@ -118,6 +177,8 @@ async def deliver_email(
         in_reply_to=in_reply_to,
         references=references,
         message_id=message_id,
+        inline_parts=inline_parts,
+        file_attachments=file_attachments,
     )
     signed = sign_message(message, domain)
     await send_via_smtp(