[PATCH b4 2/2] Parse just headers when extracting message ID from stdin mbox

[Kyle Meyer <kyle@kyleam.com>]

When the pr, mbox, and am subcommands grab a message ID from the mbox
on stdin, they call message_from_bytes(), which in turn calls
BytesParser().parsebytes(s).

parsebytes() has a headersonly parameter that can be used to tell it
to stop parsing after reading the headers.  The headers are all that's
needed here, so use BytesParser directly and set headersonly.

Signed-off-by: Kyle Meyer <kyle@kyleam.com>
---

  Note: I've tested only `b4 am/mbox' with the reproducer message
  mentioned in upthread; I haven't tested `b4 pr'.

 b4/__init__.py | 4 +++-
 b4/pr.py       | 5 ++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/b4/__init__.py b/b4/__init__.py
index 5b32fb4..4722826 100644
--- a/b4/__init__.py
+++ b/b4/__init__.py
@@ -1948,7 +1948,9 @@ def get_requests_session():
 
 def get_msgid_from_stdin():
     if not sys.stdin.isatty():
-        message = email.message_from_bytes(sys.stdin.buffer.read())
+        from email.parser import BytesParser
+        message = BytesParser().parsebytes(
+            sys.stdin.buffer.read(), headersonly=True)
         return message.get('Message-ID', None)
     return None
 
diff --git a/b4/pr.py b/b4/pr.py
index fbb2a71..e52c2ab 100644
--- a/b4/pr.py
+++ b/b4/pr.py
@@ -433,7 +433,10 @@ def main(cmdargs):
 
     if not sys.stdin.isatty():
         logger.debug('Getting PR message from stdin')
-        msg = email.message_from_bytes(sys.stdin.buffer.read())
+        from email.parser import BytesHeaderParser
+        from email.parser import BytesHeaderParser
+        msg = BytesParser().parsebytes(
+            sys.stdin.buffer.read(), headersonly=True)
         msgid = b4.LoreMessage.get_clean_msgid(msg)
         lmsg = parse_pr_data(msg)
     else:
-- 
2.32.0