If we return regular Message objects, python will try to destroy them,
and the underlying notmuch object, causing e.g. the crash [1].
[1]: id:87sfu6utxg.fsf@tethera.net
This reverses the logic of StandaloneMessage to instead create a
OwnedMessage. Only the Thread class allows retrieving messages more
then once so it can explicitly create such messages.
The added test fails with SIGABRT without the fix for the message
re-use in threads being present.
Any messages retrieved from a query - either directly via
search_messages() or indirectly via thread objects - are owned by that
query. Retrieving the same message (i.e. corresponding to the same
message ID / database object) several times will always yield the same
C object.
The caller is allowed to destroy message objects owned by a query before
the query itself - which can save memory for long-lived queries.
However, that message must then never be retrieved again from that
query.
The python-notmuch2 bindings will currently destroy every message object
in Message._destroy(), which will lead to an invalid free if the same
message is then retrieved again. E.g. the following python program leads
to libtalloc abort()ing:
import notmuch2
db = notmuch2.Database(mode = notmuch2.Database.MODE.READ_ONLY)
t = next(db.threads('*'))
msgs = list(zip(t.toplevel(), t.toplevel()))
msgs = list(zip(t.toplevel(), t.toplevel()))
Fix this issue by creating a subclass of Message, which is used for
"standalone" message which have to be freed by the caller. Message class
is then used only for messages descended from a query, which do not need
to be freed by the caller.
Another fix to the docstrings, this time for the English part of the
docstrings, not the Python class name. No functional changes here.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
