Re: [PATCH 2/6] jsmn: Add convenience functions

[Patrick Steinhardt <ps@pks.im>]

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On Wed, Nov 06, 2019 at 12:44:58PM +0100, Daniel Kiper wrote:
> On Mon, Nov 04, 2019 at 07:56:48PM +0100, Patrick Steinhardt wrote:
> > On Mon, Nov 04, 2019 at 06:42:51PM +0100, Daniel Kiper wrote:
> > > On Mon, Nov 04, 2019 at 12:00:53PM +0100, Patrick Steinhardt wrote:
> > > > On Mon, Nov 04, 2019 at 10:26:21AM +0000, Max Tottenham wrote:
> > > > > On 11/02, Patrick Steinhardt wrote:
> > > > > > The newly added jsmn library is a really bare-bones library that
> > > > > > focusses on simplicity. Because of that, it is lacking some functions
> > > > > > for convenience to abstract away some of its inner workings and to make
> > > > > > code easier to read. As such, we're now adding some functions that are
> > > > > > going to be used by the LUKS2 implementation later on.
> > > > > >
> > > > > > Signed-off-by: Patrick Steinhardt <ps@pks.im>
> > > > > > ---
> > > > > >  include/grub/jsmn.h | 108 ++++++++++++++++++++++++++++++++++++++++++++
> > > > > >  1 file changed, 108 insertions(+)
> > > > > >
> > > > >
> > > > > Would it not make sense to keep the additions in a separate header from
> > > > > the vendored upstream library? That way it'll likely be easier to pull
> > > > > in any updates.
> > > >
> > > > Yeah, I thought about that, too. I wasn't sure about where
> > > > "jsmn.h" and our own extension should live, though, which is why
> > > > I just bailed for now and waited on some feedback. I could
> > > > imagine two things:
> > > >
> > > >     - We create "include/grub/json.h" with an API that uses
> > > >       GRUB's coding style. It would thus work as a wrapper around
> > > >       the jsmn API and contain functions like "grub_json_parse",
> > > >       "grub_json_get_object" and also a struct "grub_json_t" that
> > > >       contains all things required to work with the parsed JSON
> > > >       object. The implementation would be contained in
> > > >       "gurb-core/lib/json.c" and use "grub-core/lib/jsmn.h",
> > > >       which would be the unmodified upstream library. This would
> > > >       allow us to swap out the JSON parser in the future more
> > > >       easily without breaking any users and also make the API
> > > >       feel less foreign.
> > > >
> > > >     - Or there is both a "include/grub/jsmn.h" and
> > > >       "include/grub/json.h", where the former one is the
> > > >       unmodified JSMN dependency and the latter one provides our
> > > >       own extended functions.
> > >
> > > I would like to see JSON functionality in a module. Good example is
> > > in commit 461f1d8af (zstd: Import upstream zstd-1.3.6). So, please
> > > create grub-core/lib/json and put jsmn.h there in unmodified form.
> > > Then create json.c and put all required module and convenience
> > > functions there. If you need some globally available stuff please
> > > put it into include/grub/json.h. Last but not least, I want to ask
> > > you to describe jsmn.h import steps in docs/grub-dev.texi. Good example
> > > is in commit 35b909062 (gnulib: Upgrade Gnulib and switch to bootstrap
> > > tool).
> >
> > Thanks a lot for your advice.
> >
> > Just to make sure we're on the same page about the globally
> > available stuff. I take you'd like to have "json.h" in
> > "include/grub/json.h", but "json.h" will need to include "jsmn.h"
> > with `#define JSMN_HEADER` in order to make struct and function
> > declarations available. I guess it's kind of backwards to have
> > headers in "include/" include headers from "grub-core/lib", but I
> > can't really see a way around it without either re-declaring the
> > same things as in "jsmn.h" or by creating a wrapping API around
> > "jsmn.h".
> 
> Yeah, you are right that looks strange. So, let's go zstd way and
> put everything into grub-core/lib/json. Then add required CC/CPP
> flags to the Makefile as zstd module does.
> 
> Daniel

Well, since writing this I've posted v2, which implements a
complete wrapper around jsmn that looks and feels more like
GRUB-style functions (as proposed above in my first bullet
point). This actually does allow us to move "jsmn.h" into lib/
and the "json.h" lives in include/grub now. So while it does add
a few more lines compared to v1, it seems a lot cleaner to me.

Patrick

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