Re: A brief look at deprecating our JSON extensions over RFC 8259
On Mon, Feb 22, 2021 at 15:57:22 +0100, Markus Armbruster wrote:
We use JSON in several external interfaces:
* QMP
* The guest agent's QMP
* QAPIfied command line options when the option argument starts with
'{'
* The block layer's pseudo-protocol "json:" (which can get embedded in
image headers)
I *think* that's all.
The JSON parser we use for these interfaces supports extensions over RFC
8259. Quoting json-lexer.c:
- Extra escape sequence in strings:
0x27 (apostrophe) is recognized after escape, too
- Single-quoted strings:
Like double-quoted strings, except they're delimited by %x27
(apostrophe) instead of %x22 (quotation mark), and can't contain
unescaped apostrophe, but can contain unescaped quotation mark.
[...]
We could certainly tidy up the tests to stick to standard JSON.
However, the prevalence of single-quoted strings in iotests makes me
suspect that they are being used in the field as well. Deprecating the
extension is likely more trouble than it's worth.
Opinions?
Any user of QEMU through libvirt will not use any of the extensions even
in cases such as QMP command pasthrough (virsh qemu-monitor-command) and
the 'json:' pseudo-protocol, as libvirt parses the provided JSON to add
sequencing for QMP passthrough, and for image chain detection in case of
'json:'. Since libvirt's JSON library (yajl) doesn't support any of
those extensions users are forced to not use them.
So on behalf of libvirt, we'd be fine with deprecation/removal of those.