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From: David Bremner <david@tethera.net>
To: Floris Bruynooghe <flub@devork.be>, notmuch@notmuchmail.org
Subject: Re: [PATCH 2/4] lib: catch error from closed db in n_m_get_message_id
Date: Sat, 04 Jul 2020 14:17:09 -0300	[thread overview]
Message-ID: <87eeprkxnu.fsf@tethera.net> (raw)
In-Reply-To: <87h7unxp1j.fsf@powell.devork.be>

Floris Bruynooghe <flub@devork.be> writes:


>> - * This function will not return NULL since Notmuch ensures that every
>> - * message has a unique message ID, (Notmuch will generate an ID for a
>> - * message if the original file does not contain one).
>> + * This function will return NULL if triggers an unhandled Xapian
>> + * exception.

> How much of a departure from the existing API is this?  Will this be
> possible with all functions?  I had a quick look and tried some other
> functions that don't return notmuch_status_t:

It's upward compatible in that any code which crashes because it was not
expecting a NULL pointer, will already be crashing in the same
circumstances because of an uncaught exception / call to abort.

> notmuch_database_get_version currently returns and unsigned int and
> segfaults on use with a closed db.

Yes, the ones without a proper status value are going to be a bit work.

In the next series I just posted [1], I started providing status value
returning version (see notmuch_message_get_flag_st). We've been through
a few of these migrations and it has not been too painful.

> I wonder if a backwards-compatible errno-style API could work,
> notmuch_last_status(notmuch_database_t* database) or so.  This kind of
> thing is probably easy to adopt in bindings but harder for direct users
> of the API.  It's also an extra API call for everything that doesn't
> return notmuch_status_t.  But I'll leave the judgement to you, I'm not
> as experienced with the API.

I think my main objection to this is that there is no out-of-band value
to tell the caller they need to check errno. So basically every call to
to one of the relevant functions would need be followed by a call to
checking the error number. I don't think that's less work than switching
to a new API. Of course it's less work for me, and we already sort of
made that choice with notmuch_database_status_string. In that case it
was a matter of changing the entire API.  Here we're talking about 10
functions, and I'm not sure if they all need to be changed. For example
several of the notmuch_foo_valid functions just check pointers for being
NULL and can't generate I/O or exceptions.

d

[1]: id:20200704151805.3717715-1-david@tethera.net

  reply	other threads:[~2020-07-04 17:17 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-30  1:14 introduce exception handling at top level of libnotmuch David Bremner
2020-06-30  1:14 ` [PATCH 1/4] test: add known broken test for error handling on closed database David Bremner
2020-06-30  1:14 ` [PATCH 2/4] lib: catch error from closed db in n_m_get_message_id David Bremner
2020-07-04 15:44   ` Floris Bruynooghe
2020-07-04 17:17     ` David Bremner [this message]
2020-07-05 11:17       ` David Bremner
2020-07-08 19:55         ` Floris Bruynooghe
2020-07-08 19:52       ` Floris Bruynooghe
2020-06-30  1:14 ` [PATCH 3/4] test: add known broken test for n_m_get_thread_id on closed db David Bremner
2020-06-30  1:14 ` [PATCH 4/4] lib/message: catch exception in n_m_get_thread_id David Bremner
2020-07-02 19:16 ` introduce exception handling at top level of libnotmuch Daniel Kahn Gillmor
2020-07-04  0:15   ` David Bremner

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