[libvirt] Should we switch to a different JSON library?
Hi everyone, so we are using yajl for parsing JSON. However there are some reasons why we might consider switching to another one: 1) It is basically dead upstream 2) We're just using the lexer part of it 3) We only use it for parsing 4) The are workarounds for it in the code So I looked at some options and found few other libraries, I only took those that are widely available (read: I checked if some random downstream distro has them), however most of them were not very much usable. Except one. But here's the list of few others that didn't look that bad either. All are MIT-licensed, try to be thread-safe and support pkg-config: - libfastjson [1] - from rsyslog community, optimized for working with logs, used almost only by rsyslog, it's supposed to have doxygen docs, they switched to libfastjson from json-c due to some problems with it (performance, ref counting bug, ...) - json-c [2] - looked abandoned until I looked at the proper github page, "documentation" in doxygen - Jansson [3] - I really like this one. The API seems very intuitive, it has nice documentation [4] in readthedocs (and I'm not talking about the visual style, but how easy is to find information), it can be used for formatting JSON in a similar way we are doing it. It has json_auto_t (optional) type that uses the attribute cleanup for automatic scope dereference (just in case we want to use it), it has iterators... did I tell you I like this one a lot? What do you (others) think of switching the JSON library? Do you know about any other projects that could be used considering license, platform support, etc.? Also feel free to fix any mistakes I might have posted. I double-checked it, but you know, "trust, but verify". Have a nice day, Martin [1] https://github.com/rsyslog/libfastjson [2] https://github.com/json-c/json-c [3] http://www.digip.org/jansson/ [4] https://jansson.readthedocs.io/
On Tue, Nov 07, 2017 at 02:05:25PM +0100, Martin Kletzander wrote:
Hi everyone,
so we are using yajl for parsing JSON. However there are some reasons why we might consider switching to another one:
1) It is basically dead upstream
One could say that it is simply "feature complete" upstream so doesn't need more work, but none the less, I have a general bad feeling about relying on a library with no active maint work going on for best part of 4 years, and 68 open pull requests.
2) We're just using the lexer part of it 3) We only use it for parsing
Aren't 2 & 3 the same point repeated ? Regardless though, we use yajl for formatting JSON too (virJSONValueToString)
4) The are workarounds for it in the code
I don't recall what these are now ?
So I looked at some options and found few other libraries, I only took those that are widely available (read: I checked if some random downstream distro has them), however most of them were not very much usable. Except one. But here's the list of few others that didn't look that bad either. All are MIT-licensed, try to be thread-safe and support pkg-config:
- libfastjson [1] - from rsyslog community, optimized for working with logs, used almost only by rsyslog, it's supposed to have doxygen docs, they switched to libfastjson from json-c due to some problems with it (performance, ref counting bug, ...)
If its only used by 1 app, I would stay well clear of it, as that's just one step away from be unused and dead.
- json-c [2] - looked abandoned until I looked at the proper github page, "documentation" in doxygen
Yeah, this is the main one I know about and existed way back when I picked yajl originally. It has plenty of apps using it in Fedora, which is good. At first the header files look to have good namespacing, but then I see horrific things like this polluting the namespaces: #undef FALSE #define FALSE ((json_bool)0) #undef TRUE #define TRUE ((json_bool)1) #define hexdigit(x) (((x) <= '9') ? (x) - '0' : ((x) & 7) + 9) #define error_ptr(error) ((void*)error) #define error_description(error) (json_tokener_errors[error]) #define is_error(ptr) (ptr == NULL)
- Jansson [3] - I really like this one. The API seems very intuitive, it has nice documentation [4] in readthedocs (and I'm not talking about the visual style, but how easy is to find information), it can be used for formatting JSON in a similar way we are doing it. It has json_auto_t (optional) type that uses the attribute cleanup for automatic scope dereference (just in case we want to use it), it has iterators... did I tell you I like this one a lot?
Like yajl did, they seem to have had an explicit ABI break at their 2.0 version, which was released in 2011. Not a big deal if we only support their 2.x series, especially if we keep yajl as an optional fallback It has 15 open PRs and 32 open bugs, but unlike yajl it actually has active development taking place Its header namespace looks clean too.
What do you (others) think of switching the JSON library? Do you know about any other projects that could be used considering license, platform support, etc.? Also feel free to fix any mistakes I might have posted. I double-checked it, but you know, "trust, but verify".
I'd be broadly in favour of switching to something that is not dead :-) I agree that Jansson appears the most promising. I think we would have to keep yajl support in parallel, but that's not too hard, since this is all isolated in virjson.c Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
On Tue, Nov 07, 2017 at 01:28:00PM +0000, Daniel P. Berrange wrote:
On Tue, Nov 07, 2017 at 02:05:25PM +0100, Martin Kletzander wrote:
4) The are workarounds for it in the code
I don't recall what these are now ?
libguestfs needs to disable some warnings around yajl code: /* GCC can't work out that the YAJL_IS_<foo> test is sufficient to * ensure that YAJL_GET_<foo> later doesn't return NULL. */ #if defined(__GNUC__) && __GNUC__ >= 6 /* gcc >= 6 */ #pragma GCC diagnostic ignored "-Wnull-dereference" #endif However we don't need any other workarounds. As you say yajl "just works". It might however be a problem in future if JSON itself was changed, eg. new types, fix the trailing comma problem, etc. We'd want a more responsive upstream to handle that. - - - Martin, did you look at the dependencies of these other libraries? If they depend on other stuff, that could make them harder to use. Also are they all available in at least Fedora, Debian, OpenSUSE and Arch/AUR? Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/
On Tue, Nov 07, 2017 at 01:38:51PM +0000, Richard W.M. Jones wrote:
On Tue, Nov 07, 2017 at 01:28:00PM +0000, Daniel P. Berrange wrote:
On Tue, Nov 07, 2017 at 02:05:25PM +0100, Martin Kletzander wrote:
4) The are workarounds for it in the code
I don't recall what these are now ?
I shouldn't have said 'workarounds', I meant all the conditioning for differentiation between yajl 1 and 2 and supporting both version with pkg-config and without.
libguestfs needs to disable some warnings around yajl code:
/* GCC can't work out that the YAJL_IS_<foo> test is sufficient to * ensure that YAJL_GET_<foo> later doesn't return NULL. */ #if defined(__GNUC__) && __GNUC__ >= 6 /* gcc >= 6 */ #pragma GCC diagnostic ignored "-Wnull-dereference" #endif
However we don't need any other workarounds.
As you say yajl "just works".
It might however be a problem in future if JSON itself was changed, eg. new types, fix the trailing comma problem, etc. We'd want a more responsive upstream to handle that.
- - -
Martin, did you look at the dependencies of these other libraries? If they depend on other stuff, that could make them harder to use. Also are they all available in at least Fedora, Debian, OpenSUSE and Arch/AUR?
Just did, all of these were successful: docker run -it fedora dnf search jansson docker run -it opensuse zypper search jansson docker run -it base/archlinux pacman -Sys jansson docker run -it ubuntu sh -c "apt update; apt search jansson" docker run -it debian sh -c "apt update; apt search jansson" Even: docker run -it debian:stable sh -c "apt update; apt search jansson" found version 2.9 which is the second latest one, I believe.
Rich.
-- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/
On Tue, Nov 7, 2017 at 9:34 AM, Martin Kletzander <mkletzan@redhat.com> wrote:
On Tue, Nov 07, 2017 at 01:38:51PM +0000, Richard W.M. Jones wrote:
On Tue, Nov 07, 2017 at 01:28:00PM +0000, Daniel P. Berrange wrote:
On Tue, Nov 07, 2017 at 02:05:25PM +0100, Martin Kletzander wrote:
4) The are workarounds for it in the code
I don't recall what these are now ?
I shouldn't have said 'workarounds', I meant all the conditioning for differentiation between yajl 1 and 2 and supporting both version with pkg-config and without.
libguestfs needs to disable some warnings around yajl code:
/* GCC can't work out that the YAJL_IS_<foo> test is sufficient to * ensure that YAJL_GET_<foo> later doesn't return NULL. */ #if defined(__GNUC__) && __GNUC__ >= 6 /* gcc >= 6 */ #pragma GCC diagnostic ignored "-Wnull-dereference" #endif
However we don't need any other workarounds.
As you say yajl "just works".
It might however be a problem in future if JSON itself was changed, eg. new types, fix the trailing comma problem, etc. We'd want a more responsive upstream to handle that.
- - -
Martin, did you look at the dependencies of these other libraries? If they depend on other stuff, that could make them harder to use. Also are they all available in at least Fedora, Debian, OpenSUSE and Arch/AUR?
Just did, all of these were successful:
docker run -it fedora dnf search jansson docker run -it opensuse zypper search jansson docker run -it base/archlinux pacman -Sys jansson docker run -it ubuntu sh -c "apt update; apt search jansson" docker run -it debian sh -c "apt update; apt search jansson"
Even:
docker run -it debian:stable sh -c "apt update; apt search jansson"
found version 2.9 which is the second latest one, I believe.
I used Repology to check jansson: https://repology.org/metapackage/jansson/versions It looks like the range of supported versions is v2.7 to v2.10. I see no reason it can't be used. -- 真実はいつも一つ！/ Always, there's only one truth!
On Tue, Nov 07, 2017 at 01:28:00PM +0000, Daniel P. Berrange wrote:
On Tue, Nov 07, 2017 at 02:05:25PM +0100, Martin Kletzander wrote:
Hi everyone,
so we are using yajl for parsing JSON. However there are some reasons why we might consider switching to another one:
1) It is basically dead upstream
One could say that it is simply "feature complete" upstream so doesn't need more work, but none the less, I have a general bad feeling about relying on a library with no active maint work going on for best part of 4 years, and 68 open pull requests.
2) We're just using the lexer part of it 3) We only use it for parsing
Aren't 2 & 3 the same point repeated ? Regardless though, we use yajl for formatting JSON too (virJSONValueToString)
I meant 2 different things. By only using the parser I meant that for some reason (I guess the first implementation wasn't good enough, but you'll be the one to know the proper one) we store it in our own object for which we need to parse the data similarly to how SAX works, right? We register callbacks and we do lot of stuff for each value found. It looks like jansson has enough APIs so that virJSON* could be just trivial wrappers around json_* functions/structures and for example for parsing we could just call json_load(). I haven't studied it thoroughly, but that's the feeling I got. The second thing was a bit of a misunderstanding on my part, we clearly use it for formatting as well, yes.
4) The are workarounds for it in the code
I don't recall what these are now ?
So I looked at some options and found few other libraries, I only took those that are widely available (read: I checked if some random downstream distro has them), however most of them were not very much usable. Except one. But here's the list of few others that didn't look that bad either. All are MIT-licensed, try to be thread-safe and support pkg-config:
- libfastjson [1] - from rsyslog community, optimized for working with logs, used almost only by rsyslog, it's supposed to have doxygen docs, they switched to libfastjson from json-c due to some problems with it (performance, ref counting bug, ...)
If its only used by 1 app, I would stay well clear of it, as that's just one step away from be unused and dead.
- json-c [2] - looked abandoned until I looked at the proper github page, "documentation" in doxygen
Yeah, this is the main one I know about and existed way back when I picked yajl originally.
It has plenty of apps using it in Fedora, which is good.
At first the header files look to have good namespacing, but then I see horrific things like this polluting the namespaces:
#undef FALSE #define FALSE ((json_bool)0)
#undef TRUE #define TRUE ((json_bool)1)
#define hexdigit(x) (((x) <= '9') ? (x) - '0' : ((x) & 7) + 9) #define error_ptr(error) ((void*)error) #define error_description(error) (json_tokener_errors[error]) #define is_error(ptr) (ptr == NULL)
- Jansson [3] - I really like this one. The API seems very intuitive, it has nice documentation [4] in readthedocs (and I'm not talking about the visual style, but how easy is to find information), it can be used for formatting JSON in a similar way we are doing it. It has json_auto_t (optional) type that uses the attribute cleanup for automatic scope dereference (just in case we want to use it), it has iterators... did I tell you I like this one a lot?
Like yajl did, they seem to have had an explicit ABI break at their 2.0 version, which was released in 2011. Not a big deal if we only support their 2.x series, especially if we keep yajl as an optional fallback
It has 15 open PRs and 32 open bugs, but unlike yajl it actually has active development taking place
Its header namespace looks clean too.
What do you (others) think of switching the JSON library? Do you know about any other projects that could be used considering license, platform support, etc.? Also feel free to fix any mistakes I might have posted. I double-checked it, but you know, "trust, but verify".
I'd be broadly in favour of switching to something that is not dead :-)
I agree that Jansson appears the most promising.
I think we would have to keep yajl support in parallel, but that's not too hard, since this is all isolated in virjson.c
Sure, I guess we would just have 2 implementations like we used to have with threads, selecting particular one at compile-time.
Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
On Tuesday, 7 November 2017 14:05:25 CET Martin Kletzander wrote:
- Jansson [3] - I really like this one. The API seems very intuitive, it has nice documentation [4] in readthedocs (and I'm not talking about the visual style, but how easy is to find information), it can be used for formatting JSON in a similar way we are doing it. It has json_auto_t (optional) type that uses the attribute cleanup for automatic scope dereference (just in case we want to use it), it has iterators... did I tell you I like this one a lot?
What do you (others) think of switching the JSON library? Do you know about any other projects that could be used considering license, platform support, etc.? Also feel free to fix any mistakes I might have posted. I double-checked it, but you know, "trust, but verify".
FYI: libguestfs just switched to Jansson [1], so any version starting from 1.39.1 will use it instead of Yajl. In case of libguestfs, yajl was used directly, without wrappers of any sort, and the switch was straightforward. [1] https://github.com/libguestfs/libguestfs/commit/bd1c5c9f4dcf38458099db8a0bf4... -- Pino Toscano
On Mon, Feb 12, 2018 at 02:38:02PM +0100, Pino Toscano wrote:
On Tuesday, 7 November 2017 14:05:25 CET Martin Kletzander wrote:
- Jansson [3] - I really like this one. The API seems very intuitive, it has nice documentation [4] in readthedocs (and I'm not talking about the visual style, but how easy is to find information), it can be used for formatting JSON in a similar way we are doing it. It has json_auto_t (optional) type that uses the attribute cleanup for automatic scope dereference (just in case we want to use it), it has iterators... did I tell you I like this one a lot?
What do you (others) think of switching the JSON library? Do you know about any other projects that could be used considering license, platform support, etc.? Also feel free to fix any mistakes I might have posted. I double-checked it, but you know, "trust, but verify".
FYI: libguestfs just switched to Jansson [1], so any version starting from 1.39.1 will use it instead of Yajl. In case of libguestfs, yajl was used directly, without wrappers of any sort, and the switch was straightforward.
[1] https://github.com/libguestfs/libguestfs/commit/bd1c5c9f4dcf38458099db8a0bf4...
I do have a working virjson.c implementation in my local git waiting to be polished and sent. The issues with libvirt were: * virjson.c storing numbers as a string * backwards compatibility (AFAIK we want to support building on RHEL/CentOS 6, which did not have recent enough jansson - for the _foreach macros, at least 2.5 is needed) If we really need to maintain two implementations side-by-side, one of them should have an expiration date. I don't see any version check in that libguestfs commit, what are the compatibility requirements there? Jan
On Mon, Feb 12, 2018 at 07:47:00PM +0100, Ján Tomko wrote:
On Mon, Feb 12, 2018 at 02:38:02PM +0100, Pino Toscano wrote:
On Tuesday, 7 November 2017 14:05:25 CET Martin Kletzander wrote:
- Jansson [3] - I really like this one. The API seems very intuitive, it has nice documentation [4] in readthedocs (and I'm not talking about the visual style, but how easy is to find information), it can be used for formatting JSON in a similar way we are doing it. It has json_auto_t (optional) type that uses the attribute cleanup for automatic scope dereference (just in case we want to use it), it has iterators... did I tell you I like this one a lot?
What do you (others) think of switching the JSON library? Do you know about any other projects that could be used considering license, platform support, etc.? Also feel free to fix any mistakes I might have posted. I double-checked it, but you know, "trust, but verify".
FYI: libguestfs just switched to Jansson [1], so any version starting from 1.39.1 will use it instead of Yajl. In case of libguestfs, yajl was used directly, without wrappers of any sort, and the switch was straightforward.
[1] https://github.com/libguestfs/libguestfs/commit/bd1c5c9f4dcf38458099db8a0bf4...
I do have a working virjson.c implementation in my local git waiting to be polished and sent. The issues with libvirt were: * virjson.c storing numbers as a string * backwards compatibility (AFAIK we want to support building on RHEL/CentOS 6, which did not have recent enough jansson - for the _foreach macros, at least 2.5 is needed) If we really need to maintain two implementations side-by-side, one of them should have an expiration date.
IMHO we only need to keepp yajl if RHEL6 doesn't have suitable jansson. So ideally we'd figure out how to get that working, so we can ditch yajl straightaway. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
On Monday, 12 February 2018 19:47:00 CET Ján Tomko wrote:
On Mon, Feb 12, 2018 at 02:38:02PM +0100, Pino Toscano wrote:
On Tuesday, 7 November 2017 14:05:25 CET Martin Kletzander wrote:
- Jansson [3] - I really like this one. The API seems very intuitive, it has nice documentation [4] in readthedocs (and I'm not talking about the visual style, but how easy is to find information), it can be used for formatting JSON in a similar way we are doing it. It has json_auto_t (optional) type that uses the attribute cleanup for automatic scope dereference (just in case we want to use it), it has iterators... did I tell you I like this one a lot?
What do you (others) think of switching the JSON library? Do you know about any other projects that could be used considering license, platform support, etc.? Also feel free to fix any mistakes I might have posted. I double-checked it, but you know, "trust, but verify".
FYI: libguestfs just switched to Jansson [1], so any version starting from 1.39.1 will use it instead of Yajl. In case of libguestfs, yajl was used directly, without wrappers of any sort, and the switch was straightforward.
[1] https://github.com/libguestfs/libguestfs/commit/bd1c5c9f4dcf38458099db8a0bf4...
I do have a working virjson.c implementation in my local git waiting to be polished and sent. The issues with libvirt were: * virjson.c storing numbers as a string * backwards compatibility (AFAIK we want to support building on RHEL/CentOS 6, which did not have recent enough jansson - for the _foreach macros, at least 2.5 is needed) If we really need to maintain two implementations side-by-side, one of them should have an expiration date.
RHEL/CentOS 6 do not seem to have jansson -- it's in EPEL, and its version there is 2.9. RHEL/CentOS 7 have jansson 2.10.
I don't see any version check in that libguestfs commit, what are the compatibility requirements there?
I though the APIs we used were old enough, but apparently not for an old distro I still had around (Mageia 5, EOL). I just bumped the minimum requirement in libguestfs to 2.7, which is old enough, and IMHO good enough as baseline; see https://repology.org/metapackage/jansson/versions -- Pino Toscano
participants (7)
-
Daniel P. Berrange -
Daniel P. Berrangé
-
Ján Tomko -
Martin Kletzander -
Neal Gompa -
Pino Toscano -
Richard W.M. Jones