Re: [PATCH] schemas: Add vim modeline

[Daniel P . Berrangé]

On Mon, Aug 03, 2020 at 02:16:19PM +0200, Paolo Bonzini wrote:
> On 03/08/20 13:36, Daniel P. Berrangé wrote:
> >>> Given that QEMU needs to pass
> >>> uint64 values, JSON was simply the wrong choice of format for QMP.
> >
> > I wasn't refering to RFC7159. The problem of undefined integer precision
> > with JSON came up right at the very start when QMP was first designed and
> > implemented, and has come up again periodically ever since then. libvirt
> > needed to do workarounds right at the start in 2009, in order to fully
> > handle signed/unsigned 64-bit integers with QMP.
> 
> I assume the workaround you refer to is to store the number as a string
> and converting it lazily to either an integer or a floating-point type
> in whoever uses the JSON API.  It may not be pretty but probably it
> would have been the same for any text-based, schema-less protocol.  For
> example, it didn't require writing your own parser.

Yes, we get the raw values as a string, but not all parsers for C
allow you to do this.  We'd really love to move off YAJL for JSON
parsing, but the most viable alternatives don't have a way to let
you get the string before they parse it as an integer and report
errors.

> It could be avoided by using a schema in Libvirt, just like QEMU has no
> problem with it on the other side; it's just a different design choice
> with different trade-offs, I don't think it's enough of an issue to
> declare JSON "the wrong choice of format for QMP".

The schema doesn't help - the problem is many JSON parsers don't allow
use of full uint64 values when parsing - alot will simply report an
error for anything bigger than LLONG_MAX and offer no workaround.

Regards,
Daniel
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