import-bug-from-debian: handle multipart messages

With multipart messages, like #1073996, `import-bug-from-debian` would
produce bug description with this:
```
[<email.message.Message object at 0x7fbe14096fa0>, <email.message.Message object at 0x7fbe15143820>]
```
For that kind of bug, it now produces a correct description with the
plain text parts concatenated in the description, the attachments added
as attachments, and the inline images converted to attachments with an
inline message placeholder.

See #981577 for a particularly weird case now gracefully handled.
If something weirder happens, then the tool will now abort with a clear
message instead of producing garbage.

Closes: #969510

debian/changelog

@@ -1,11 +1,15 @@
 ubuntu-dev-tools (0.202ubuntu1) UNRELEASED; urgency=medium
 
+  [ Steve Langasek ]
   * ubuntu-build: handle TOCTOU issue with the "can be retried" value on
     builds.
   * Recommend sbuild over pbuilder.  sbuild is the tool recommended by
     Ubuntu developers whose behavior most closely approximates Launchpad
     builds.
 
+  [ Florent 'Skia' Jacquet ]
+  * import-bug-from-debian: handle multipart message (Closes: #969510)
+
  -- Steve Langasek <steve.langasek@ubuntu.com>  Sun, 26 May 2024 12:58:38 -0700
 
 ubuntu-dev-tools (0.202) unstable; urgency=medium

import-bug-from-debian

@@ -37,6 +37,7 @@ from ubuntutools import getLogger
 from ubuntutools.config import UDTConfig
 
 Logger = getLogger()
+ATTACHMENT_MAX_SIZE = 2000
 
 
 def main():
@@ -118,7 +119,48 @@ def main():
         bug_num = bug.bug_num
         subject = bug.subject
         log = debianbts.get_bug_log(bug_num)
-        summary = log[0]["message"].get_payload()
+        message = log[0]["message"]
+        attachments = []
+        if message.is_multipart():
+            summary = ""
+            i = 1
+            for part in message.walk():
+                content_type = part.get_content_type()
+                if content_type.startswith("multipart/"):
+                    # we're already iterating on multipart items
+                    # let's just skip the multipart extra metadata
+                    continue
+                if content_type == "application/pgp-signature":
+                    # we don't want to import pgp signature
+                    continue
+
+                if part.is_attachment():
+                    attachments.append((i, part))
+                elif content_type.startswith("image/"):
+                    # images here are not attachment, they are inline, but Launchpad can't handle
+                    # that, so let's add them as attachments
+                    summary += f"Message part #{i}\n"
+                    summary += f"[inline image '{part.get_filename()}']\n\n"
+                    attachments.append((i, part))
+                elif content_type.startswith("text/html"):
+                    summary += f"Message part #{i}\n"
+                    summary += "[inline html]\n\n"
+                    attachments.append((i, part))
+                elif content_type == "text/plain":
+                    summary += f"Message part #{i}\n"
+                    summary += part.get_content() + "\n"
+                else:
+                    raise RuntimeError(
+                        f"""Unknown message part
+Your Debian bug is too weird to be imported in Launchpad, sorry.
+You can fix that by patching this script in ubuntu-dev-tools.
+Faulty message part:
+{part}"""
+                    )
+                i += 1
+        else:
+            summary = log[0]["message"].get_payload()
+
         target = ubuntu.getSourcePackage(name=ubupackage)
         if target is None:
             Logger.error(
@@ -137,12 +179,36 @@ def main():
         Logger.debug("Subject: %s", subject)
         Logger.debug("Description: ")
         Logger.debug(description)
+        for i, attachment in attachments:
+            Logger.debug("Attachment #%s (%s)", i, attachment.get_filename() or "inline")
+            Logger.debug("Content:")
+            if attachment.get_content_type() == "text/plain":
+                content = attachment.get_content()
+                if len(content) > ATTACHMENT_MAX_SIZE:
+                    content = (
+                        content[:ATTACHMENT_MAX_SIZE]
+                        + f" [attachment cropped after {ATTACHMENT_MAX_SIZE} characters...]"
+                    )
+                Logger.debug(content)
+            else:
+                Logger.debug("[data]")
 
         if options.dry_run:
             Logger.info("Dry-Run: not creating Ubuntu bug.")
             continue
 
         u_bug = launchpad.bugs.createBug(target=target, title=subject, description=description)
+        for i, attachment in attachments:
+            name = f"#{i}-{attachment.get_filename() or "inline"}"
+            content = attachment.get_content()
+            if isinstance(content, str):
+                # Launchpad only wants bytes
+                content = content.encode()
+            u_bug.addAttachment(
+                filename=name,
+                data=content,
+                comment=f"Imported from Debian bug http://bugs.debian.org/{bug_num}",
+            )
         d_sp = debian.getSourcePackage(name=package)
         if d_sp is None and options.package:
             d_sp = debian.getSourcePackage(name=options.package)