[systemd-devel] sd-bus: get size of array container in D-Bus message

[Luca Boccassi]

On Wed, 2 Aug 2023 at 20:00, Giacinto Cifelli <gciofono at gmail.com> wrote:
>
> On Wed, Aug 2, 2023 at 6:44 PM Stephen Hemminger
> <stephen at networkplumber.org> wrote:
> >
> > On Wed, 02 Aug 2023 06:39:47 +0000
> > Stanislav Angelovič <stanislav.angelovic at protonmail.com> wrote:
> >
> > > Hi folks,
> > >
> > > I have a quick question: is there a way to get container size when deserializing an array from a D-Bus message (be it an array of trivial or non-trivial D-Bus types)? Say I enter a container with sd_bus_message_enter_container, and then, before reading individual elements, I'd like to get the number of elements in that array in that message (so I can reserve storage on my side, etc.).
> > >
> > > If not, could such an API function be added?
> > >
> > > Thanks in advance.
> > >
> > > Stanislav.
> >
> > The dbus messsage just an encoding of a byte stream. There is nothing in the byte stream
> > that indicates the length.
>
> yes, but the whole message is available locally, it could be parsed on
> request, discarding the data, and keeping only the number of elements
> in an array.

For basic types there's
https://www.freedesktop.org/software/systemd/man/sd_bus_message_read_array.html