Your IP : 216.73.216.86
PK �.�\�� �`
`
eg/benchnu �[��� #!/usr/bin/perl
# Usage: bench json-file
# which modules to test (JSON::PP usually excluded because its so slow)
my %tst = (
# "JSON" => ['JSON::encode_json $perl' , 'JSON::decode_json $json'],
"JSON::PP" => ['$pp->encode ($perl)' , '$pp->decode ($json)'],
"JSON::DWIW/FJ" => ['$dwiw->to_json ($perl)' , '$dwiw->from_json ($json)'],
"JSON::DWIW/DS" => ['$dwiw->to_json ($perl)' , 'JSON::DWIW::deserialize $json'],
# "JSON::PC" => ['$pc->convert ($perl)' , '$pc->parse ($json)'],
"JSON::Syck" => ['JSON::Syck::Dump $perl' , 'JSON::Syck::Load $json'],
"JSON::XS" => ['encode_json $perl' , 'decode_json $json'],
"JSON::XS/2" => ['$xs2->encode ($perl)' , '$xs2->decode ($json)'],
"JSON::XS/3" => ['$xs3->encode ($perl)' , '$xs3->decode ($json)'],
"Storable" => ['Storable::nfreeze $perl' , 'Storable::thaw $pst'],
);
use JSON ();
use JSON::DWIW;
use JSON::PC;
use JSON::PP ();
use JSON::XS qw(encode_json decode_json);
use JSON::Syck;
use Storable ();
use Time::HiRes;
use List::Util;
use utf8;
my $dwiw = new JSON::DWIW;
my $pc = new JSON::PC;
my $pp = JSON::PP->new->max_depth (512);
my $xs2 = JSON::XS->new->utf8->pretty->canonical;
my $xs3 = JSON::XS->new->utf8->shrink;
my $json; # the test string
local $/;
$json = <>;
# fix syck-brokenised stuff
#$json = JSON::XS->new->ascii(1)->encode (JSON::Syck::Load $json);
#srand 0; $json = JSON::XS->new->utf8(1)->ascii(0)->encode ([join "", map +(chr rand 255), 0..2047]);
#if (1) {
# use Storable;
# open my $fh, "<:unix", "/opt/crossfire/share/cfserver/faces" or die "$!";
# my $faces = Storable::thaw do { <$fh> };
# $json = objToJson $faces;
# open my $fh2, ">:unix", "faces.json" or die "$!";
# print $fh2 $json;
# warn length $json;
#}
sub bench($) {
my ($code) = @_;
my $pst = Storable::nfreeze JSON::XS::decode_json $json; # seperately decode as storable stringifies :/
my $perl = JSON::XS::decode_json $json;
my $count = 5;
my $times = 200;
my $cent = eval "sub { my \$t = Time::HiRes::time; " . (join ";", ($code) x $count) . "; Time::HiRes::time - \$t }";
$cent->();
my $min = 1e99;
for (1..$times) {
my $t = $cent->();
$min = $t if $t < $min;
}
return $count / $min;
}
printf "%-13s | %10s | %10s |\n", "module", "encode", "decode";
printf "--------------|------------|------------|\n";
for my $module (sort keys %tst) {
my $enc = bench $tst{$module}[0];
my $dec = bench $tst{$module}[1];
printf "%-13s | %10.3f | %10.3f |\n", $module, $enc, $dec;
}
printf "--------------+------------+------------+\n";
PK �.�\�h�mgM gM Changesnu �[��� Revision history for Perl extension JSON::XS
TODO: maybe detetc and croak on more invalid inputs (e.g. +-inf/nan)
TODO: maybe avoid the reblessing and better support readonly objects.
TODO: http://stevehanov.ca/blog/index.php?id=104 compression
TODO: how to cope with tagged values and standard json decoders
TODO: investigate magic (Eric Brine)
TODO: rfc7464
TODO: Victor Efimov
TODO: move json_xs to types::serialiser
3.04 Thu Aug 17 04:30:47 CEST 2017
- change exponential realloc algorithm on encoding and string decoding to be
really exponential (this helps slow/debugging allocators such as libumem)
(reported by Matthew Horsfall).
- string encoding would needlessly overallocate output space
(testcase by Matthew Horsfall).
- be very paranoid about extending buffer lengths and croak if buffers get too large,
which might (or might not) improve security.
- add cbor-packed type to json_xs.
- switch from YAML to YAML::XS in json_xs, as YAML is way too buggy and outdated.
3.03 Wed Nov 16 20:20:59 CET 2016
- fix a bug introduced by a perl bug workaround that would cause
incremental parsing to fail with a sv_chop panic.
- json_xs: toformat failure error message fixed.
- json_xs: allow cyclic data structures in CBOR.
3.02 Fri Feb 26 22:45:20 CET 2016
- allow_nonref now affects booleans (\1, $Types::Serialiser::Boolean)
as well (reported by Alex Efros).
- allow literal tabs in strings in relaxed mode (patch by
lubo.rintel@gooddata.com).
- support "cbor" format in json_xs tool.
- support (and fix) calling encode and decode in list context
(reported by Вадим Власов).
- work around a bug in older perls crashing when presented
with shared hash keys (Reini Urban).
- use stability canary.
3.01 Tue Oct 29 16:55:15 CET 2013
- backport to perls < 5.18 (reported by Paul Howarth).
3.0 Tue Oct 29 01:35:37 CET 2013
- implemented an object tagging extension (using the
Types::Serialiser serialisation protocol).
- reworked the documentation regarding object serialisation,
add a new OBJECT SERIALISATION section that explains th
whole process.
- new setting: allow_tags.
- switch to Types::Serialiser booleans.
- remove to_json/from_json.
- other minor improvements to the documentation.
2.34 Thu May 23 11:30:34 CEST 2013
- work around bugs in perl 5.18 breaking more than 100
widely used modules, without a fix in sight because
p5pers don't care about CPAN anymore.
- when canonicalising, only allocate up to 64 hash key
pointers on the stack. for larger hashes, use the heap,
to avoid using too much stackspace.
- discuss the problem with setlocale (reported by a few victims).
2.33 Wed Aug 1 21:03:52 CEST 2012
- internal encode/decode XS wrappers did not expect stack
moves caused by callbacks (analyzed and testcase by Jesse Luehrs).
- add bencode as to/from option in bin/json_xs.
- add -e option to json_xs, and none and string in/out formats.
2.32 Thu Aug 11 19:06:38 CEST 2011
- fix a bug in the initial whitespace accumulation.
2.31 Wed Jul 27 17:53:05 CEST 2011
- don't accumulate initial whitespace in the incremental buffer
(this can be useful to allow whitespace-keepalive on a tcp
connection without triggering the max_size limit).
- properly croak on some invalid inputs that are not strings
(e.g. undef) when trying to decode a json text (reported
and analyzed by Goro Fuji).
2.3 Wed Aug 18 01:26:47 CEST 2010
- make sure decoder doesn't change the decoding in the incremental
parser (testcase provided by Hendrik Schumacher).
- applied patch by DaTa for Data::Dumper support in json_xs.
- added -t dump support to json_xs, using Data::Dump.
- added -f eval support to json_xs.
2.29 Wed Mar 17 02:39:12 CET 2010
- fix a memory leak when callbacks set using filter_json_object
or filter_json_single_key_object were called (great testcase
by Eric Wilhelm).
2.28 Thu Mar 11 20:30:46 CET 2010
- implement our own atof function - perl's can be orders of
magnitudes slower than even the system one. on the positive
side, ours seems to be more exact in general than perl's.
(testcase provided by Tim Meadowcroft).
- clarify floating point conversion issues a bit.
- update jpsykes csrf article url.
- updated benchmark section - JSON::PP became much faster!
2.27 Thu Jan 7 07:35:08 CET 2010
- support relaxed option inside the incremental parser
(testcase provided by IKEGAMI via Makamaka).
2.26 Sat Oct 10 03:26:19 CEST 2009
- big integers could become truncated (based on patch
by Strobl Anton).
- output format change: indent now adds a final newline, which is
more expected and more true to the documentation.
2.25 Sat Aug 8 12:04:41 CEST 2009
- the perl debugger completely breaks lvalue subs - try to work
around the issue.
- ignore RMAGICAL hashes w.r.t. CANONICAL.
- try to work around a possible char signedness issue on aix.
- require common sense.
2.24 Sat May 30 08:25:45 CEST 2009
- the incremental parser did not update its parse offset
pointer correctly when parsing utf8-strings (nicely
debugged by Martin Evans).
- appending a non-utf8-string to the incremental parser
in utf8 mode failed to upgrade the string.
- wording of parse error messages has been improved.
2.232 Sun Feb 22 11:12:25 CET 2009
- use an exponential algorithm to extend strings, to
help platforms with bad or abysmal==windows memory
allocater performance, at the expense of some memory
wastage (use shrink to recover this extra memory).
(nicely analysed by Dmitry Karasik).
2.2311 Thu Feb 19 02:12:54 CET 2009
- add a section "JSON and ECMAscript" to explain some
incompatibilities between the two (problem was noted by
various people).
- add t/20_faihu.t.
2.231 Thu Nov 20 04:59:08 CET 2008
- work around 5.10.0 magic bugs where manipulating magic values
(such as $1) would permanently damage them as perl would
ignore the magicalness, by making a full copy of the string,
reported by Dmitry Karasik.
- work around spurious warnings under older perl 5.8's.
2.23 Mon Sep 29 05:08:29 CEST 2008
- fix a compilation problem when perl is not using char * as, well,
char *.
- use PL_hexdigit in favour of rolling our own.
2.2222 Sun Jul 20 18:49:00 CEST 2008
- same game again, broken 5.10 finds yet another assertion
failure, and the workaround causes additional runtime warnings.
Work around the next assertion AND the warning. 5.10 seriously
needs to adjust it's attitude against working code.
2.222 Sat Jul 19 06:15:34 CEST 2008
- you work around one -DDEBUGGING assertion bug in perl 5.10
just to hit the next one. work around this one, too.
2.22 Tue Jul 15 13:26:51 CEST 2008
- allow higher nesting levels in incremental parser.
- error out earlier in some cases in the incremental parser
(as suggested by Yuval Kogman).
- improve incr-parser test (Yuval Kogman).
2.21 Tue Jun 3 08:43:23 CEST 2008
- (hopefully) work around a perl 5.10 bug with -DDEBUGGING.
- remove the experimental status of the incremental parser interface.
- move =encoding around again, to avoid bugs with search.cpan.org.
when can we finally have utf-8 in pod???
- add ->incr_reset method.
2.2 Wed Apr 16 20:37:25 CEST 2008
- lifted the log2 rounding restriction of max_depth and max_size.
- make booleans mutable by creating a copy instead of handing out
the same scalar (reported by pasha sadri).
- added support for incremental json parsing (still EXPERIMENTAL).
- implemented and added a json_xs command line utility that can convert
from/to a number of serialisation formats - tell me if you need more.
- implement allow_unknown/get_allow_unknown methods.
- fixed documentation of max_depth w.r.t. higher and equal.
- moved down =encoding directive a bit, too much breaks if it's the first
pod directive :/.
- removed documentation section on other modules, it became somewhat
outdated and is nowadays mostly of historical interest.
2.1 Wed Mar 19 23:23:18 CET 2008
- update documentation here and there: add a large section
about utf8/latin1/ascii flags, add a security consideration
and extend and clarify the JSON and YAML section.
- medium speed enhancements when encoding/decoding non-ascii chars.
- minor speedup in number encoding case.
- extend and clarify the section on incompatibilities
between YAML and JSON.
- switch to static inline from just inline when using gcc.
- add =encoding utf-8 to the manpage, now that perl 5.10 supports it.
- fix some issues with UV to JSON conversion of unknown impact.
- published the yahoo locals search result used in benchmarks as the
original url changes so comparison is impossible.
2.01 Wed Dec 5 11:40:28 CET 2007
- INCOMPATIBLE API CHANGE: to_json and from_json have been
renamed to encode_json/decode_json for JSON.pm compatibility.
The old functions croak and might be replaced by JSON.pm
comaptible versions in some later release.
2.0 Tue Dec 4 11:30:46 CET 2007
- this is supposed to be the first version of JSON::XS
compatible with version 2.0+ of the JSON module.
Using the JSON module as frontend to JSON::XS should be
as fast as using JSON::XS directly, so consider using it
instead.
- added get_* methods for all "simple" options.
- make JSON::XS subclassable.
1.53 Tue Nov 13 23:58:33 CET 2007
- minor doc clarifications.
- fixed many doc typos (patch by Thomas L. Shinnick).
1.52 Mon Oct 15 03:22:06 CEST 2007
- remove =encoding pod directive again, it confuses too many pod
parsers :/.
1.51 Sat Oct 13 03:55:56 CEST 2007
- encode empty arrays/hashes in a compact way when pretty is enabled.
- apparently JSON::XS was used to find some bugs in the
JSON_checker testsuite, so add (the corrected) JSON_checker tests to
the testsuite.
- quite a bit of doc updates/extension.
- require 5.8.2, as this seems to be the first unicode-stable version.
1.5 Tue Aug 28 04:05:38 CEST 2007
- add support for tied hashes, based on ideas and testcase by
Marcus Holland-Moritz.
- implemented relaxed parsing mode where some extensions are being
accepted. generation is still JSON-only.
1.44 Wed Aug 22 01:02:44 CEST 2007
- very experimental process-emulation support, slowing everything down.
the horribly broken perl threads are still not supported - YMMV.
1.43 Thu Jul 26 13:26:37 CEST 2007
- convert big json numbers exclusively consisting of digits to NV
only when there is no loss of precision, otherwise to string.
1.42 Tue Jul 24 00:51:18 CEST 2007
- fix a crash caused by not handling missing array elements
(report and testcase by Jay Kuri).
1.41 Tue Jul 10 18:21:44 CEST 2007
- fix compilation with NDEBUG (assert side-effect),
affects convert_blessed only.
- fix a bug in decode filters calling ENTER; SAVETMPS;
one time too often.
- catch a typical error in TO_JSON methods.
- antique-ised XS.xs again to work with outdated
C compilers (windows...).
1.4 Mon Jul 2 10:06:30 CEST 2007
- add convert_blessed setting.
- encode did not catch all blessed objects, encoding their
contents in most cases. This has been fixed by introducing
the allow_blessed setting.
- added filter_json_object and filter_json_single_key_object
settings that specify a callback to be called when
all/specific json objects are encountered.
- assume that most object keys are simple ascii words and
optimise this case, penalising the general case. This can
speed up decoding by 30% in typical cases and gives
a smaller and faster perl hash.
- implemented simpleminded, optional resource size checking
in decode_json.
- remove objToJson/jsonToObj aliases, as the next version
of JSON will not have them either.
- bit the bullet and converted the very simple json object
into a more complex one.
- work around a bug where perl wrongly claims an integer
is not an integer.
- unbundle JSON::XS::Boolean into own pm file so Storable
and similar modules can resolve the overloading when thawing.
1.3 Sun Jun 24 01:55:02 CEST 2007
- make JSON::XS::true and false special overloaded objects
and return those instead of 1 and 0 for those json atoms
(JSON::PP compatibility is NOT achieved yet).
- add JSON::XS::is_bool predicate to test for those special
values.
- add a reference to
http://jpsykes.com/47/practical-csrf-and-json-security.
- removed require 5.8.8 again, it is just not very expert-friendly.
Also try to be more compatible with slightly older versions,
which are not recommended (because they are buggy).
1.24 Mon Jun 11 05:40:49 CEST 2007
- added informative section on JSON-as-YAML.
- get rid of some c99-isms again.
- localise dec->cur in decode_str, speeding up
string decoding considerably (>15% on my amd64 + gcc).
- increased SHORT_STRING_LEN to 16kb: stack space is
usually plenty, and this actually saves memory
when !shrinking as short strings will fit perfectly.
1.23 Wed Jun 6 20:13:06 CEST 2007
- greatly improved small integer encoding and decoding speed.
- implement a number of µ-optimisations.
- updated benchmarks.
1.22 Thu May 24 00:07:25 CEST 2007
- require 5.8.8 explicitly as older perls do not seem to offer
the required macros.
- possibly made it compile on so-called C compilers by microsoft.
1.21 Wed May 9 18:40:32 CEST 2007
- character offset reported for trailing garbage was random.
1.2 Wed May 9 18:35:01 CEST 2007
- decode did not work with magical scalars (doh!).
- added latin1 flag to produce JSON texts in the latin1 subset
of unicode.
- flag trailing garbage as error.
- new decode_prefix method that returns the number
of characters consumed by a decode.
- max octets/char in perls UTF-X is actually 13, not 11,
as pointed out by Glenn Linderman.
- fixed typoe reported by YAMASHINA Hio.
1.11 Mon Apr 9 07:05:49 CEST 2007
- properly 0-terminate sv's returned by encode to help
C libraries that expect that 0 to be there.
- partially "port" JSON from C to microsofts fucking broken
pseudo-C. They should be burned to the ground for pissing
on standards. And I should be stoned for even trying to
support this filthy excuse for a c compiler.
1.1 Wed Apr 4 01:45:00 CEST 2007
- clarify documentation (pointed out by Quinn Weaver).
- decode_utf8 sometimes did not correctly flag errors,
leading to segfaults.
- further reduced default nesting depth to 512 due to the test
failure by that anonymous "chris" whose e-mail address seems
to be impossible to get. Tests on other freebsd systems indicate
that this is likely a problem in his/her configuration and not this
module.
- renamed json => JSON in error messages.
- corrected the character offset in some error messages.
1.01 Sat Mar 31 16:15:40 CEST 2007
- do not segfault when from_json/decode gets passed
a non-string object (reported by Florian Ragwitz).
This has no effect on normal operation.
1.0 Thu Mar 29 04:43:34 CEST 2007
- the long awaited (by me) 1.0 version.
- add \0 (JSON::XS::false) and \1 (JSON::XS::true) mappings to JSON
true and false.
- add some more notes to shrink, as suggested by Alex Efros.
- improve testsuite.
- halve the default nesting depth limit, to hopefully make it
work on Freebsd (unfortunately, the cpan tester did not
send me his report, so I cannot ask about the stack limit on fbsd).
0.8 Mon Mar 26 00:10:48 CEST 2007
- fix a memleak when decoding hashes.
- export jsonToBj and objToJson as aliases
to to_json and from_json, to reduce incompatibilities
between JSON/JSON::PC and JSON::XS. (experimental).
- implement a maximum nesting depth for both en- and de-coding.
- added a security considerations sections.
0.7 Sun Mar 25 01:46:30 CET 2007
- code cleanup.
- fix a memory overflow bug when indenting.
- pretty-printing now up to 15% faster.
- improve decoding speed of strings by
up to 50% by specialcasing short strings.
- further decoding speedups for strings using
lots of \u escapes.
- improve utf8 decoding speed for U+80 .. U+7FF.
0.5 Sat Mar 24 20:41:51 CET 2007
- added the UTF-16 encoding example hinted at in previous
versions.
- minor documentation fixes.
- fix a bug in and optimise canonicalising fastpath
(reported by Craig Manley).
- remove a subtest that breaks with bleadperl (reported
by Andreas König).
0.31 Sat Mar 24 02:14:34 CET 2007
- documentation updates.
- do some casting to hopefully fix Andreas' problem.
- nuke bogus json rpc stuff.
0.3 Fri Mar 23 19:33:21 CET 2007
- remove spurious PApp::Util reference (John McNamara).
- adapted lots of tests from other json modules
(idea by Chris Carline).
- documented mapping from json to perl and vice versa.
- improved the documentation by adding more examples.
- added short escaping forms, reducing the created
json texts a bit.
- added shrink flag.
- when flag methods are called without enable argument
they will by default enable their flag.
- considerably improved string encoding speed (at least
with gcc 4).
- added a test that covers lots of different characters.
- clarified some error messages.
- error messages now use correct character offset
with F_UTF8.
- improve the "no bytes" and "no warnings" hacks in
case the called functions do... stuff.
- croak when encoding to ascii and an out-of-range
(non-unicode) codepoint is encountered.
0.2 Fri Mar 23 00:23:34 CET 2007
- the "could not sleep without debugging release".
it should basically work now, with many bugs as
no production tests have been run yet.
- added more testcases.
- the expected shitload of bugfixes.
- handle utf8 flag correctly in decode.
- fix segfault in decoder.
- utf8n_to_uvuni sets retlen to -1, but retlen is an
unsigned types (argh).
- fix decoding of utf-8 strings.
- improved error diagnostics.
- fix decoding of 'null'.
- fix parsing of empty array/hashes
- silence warnings when we prepare the croak message.
0.1 Thu Mar 22 22:13:43 CET 2007
- first release, very untested, basically just to claim
the namespace.
0.01 Thu Mar 22 06:08:12 CET 2007
- original version; cloned from Convert-Scalar
PK �.�\ױ��� � READMEnu �[��� NAME
JSON::XS - JSON serialising/deserialising, done correctly and fast
JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
SYNOPSIS
use JSON::XS;
# exported functions, they croak on error
# and expect/generate UTF-8
$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
# OO-interface
$coder = JSON::XS->new->ascii->pretty->allow_nonref;
$pretty_printed_unencoded = $coder->encode ($perl_scalar);
$perl_scalar = $coder->decode ($unicode_json_text);
# Note that JSON version 2.0 and above will automatically use JSON::XS
# if available, at virtually no speed overhead either, so you should
# be able to just:
use JSON;
# and do the same things, except that you have a pure-perl fallback now.
DESCRIPTION
This module converts Perl data structures to JSON and vice versa. Its
primary goal is to be *correct* and its secondary goal is to be *fast*.
To reach the latter goal it was written in C.
Beginning with version 2.0 of the JSON module, when both JSON and
JSON::XS are installed, then JSON will fall back on JSON::XS (this can
be overridden) with no overhead due to emulation (by inheriting
constructor and methods). If JSON::XS is not available, it will fall
back to the compatible JSON::PP module as backend, so using JSON instead
of JSON::XS gives you a portable JSON API that can be fast when you need
it and doesn't require a C compiler when that is a problem.
As this is the n-th-something JSON module on CPAN, what was the reason
to write yet another JSON module? While it seems there are many JSON
modules, none of them correctly handle all corner cases, and in most
cases their maintainers are unresponsive, gone missing, or not listening
to bug reports for other reasons.
See MAPPING, below, on how JSON::XS maps perl values to JSON values and
vice versa.
FEATURES
* correct Unicode handling
This module knows how to handle Unicode, documents how and when it
does so, and even documents what "correct" means.
* round-trip integrity
When you serialise a perl data structure using only data types
supported by JSON and Perl, the deserialised data structure is
identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
become "2" just because it looks like a number). There *are* minor
exceptions to this, read the MAPPING section below to learn about
those.
* strict checking of JSON correctness
There is no guessing, no generating of illegal JSON texts by
default, and only JSON is accepted as input by default (the latter
is a security feature).
* fast
Compared to other JSON modules and other serialisers such as
Storable, this module usually compares favourably in terms of speed,
too.
* simple to use
This module has both a simple functional interface as well as an
object oriented interface.
* reasonably versatile output formats
You can choose between the most compact guaranteed-single-line
format possible (nice for simple line-based protocols), a pure-ASCII
format (for when your transport is not 8-bit clean, still supports
the whole Unicode range), or a pretty-printed format (for when you
want to read that stuff). Or you can combine those features in
whatever way you like.
FUNCTIONAL INTERFACE
The following convenience methods are provided by this module. They are
exported by default:
$json_text = encode_json $perl_scalar
Converts the given Perl data structure to a UTF-8 encoded, binary
string (that is, the string contains octets only). Croaks on error.
This function call is functionally identical to:
$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
Except being faster.
$perl_scalar = decode_json $json_text
The opposite of "encode_json": expects an UTF-8 (binary) string and
tries to parse that as an UTF-8 encoded JSON text, returning the
resulting reference. Croaks on error.
This function call is functionally identical to:
$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
Except being faster.
A FEW NOTES ON UNICODE AND PERL
Since this often leads to confusion, here are a few very clear words on
how Unicode works in Perl, modulo bugs.
1. Perl strings can store characters with ordinal values > 255.
This enables you to store Unicode characters as single characters in
a Perl string - very natural.
2. Perl does *not* associate an encoding with your strings.
... until you force it to, e.g. when matching it against a regex, or
printing the scalar to a file, in which case Perl either interprets
your string as locale-encoded text, octets/binary, or as Unicode,
depending on various settings. In no case is an encoding stored
together with your data, it is *use* that decides encoding, not any
magical meta data.
3. The internal utf-8 flag has no meaning with regards to the encoding
of your string.
Just ignore that flag unless you debug a Perl bug, a module written
in XS or want to dive into the internals of perl. Otherwise it will
only confuse you, as, despite the name, it says nothing about how
your string is encoded. You can have Unicode strings with that flag
set, with that flag clear, and you can have binary data with that
flag set and that flag clear. Other possibilities exist, too.
If you didn't know about that flag, just the better, pretend it
doesn't exist.
4. A "Unicode String" is simply a string where each character can be
validly interpreted as a Unicode code point.
If you have UTF-8 encoded data, it is no longer a Unicode string,
but a Unicode string encoded in UTF-8, giving you a binary string.
5. A string containing "high" (> 255) character values is *not* a UTF-8
string.
It's a fact. Learn to live with it.
I hope this helps :)
OBJECT-ORIENTED INTERFACE
The object oriented interface lets you configure your own encoding or
decoding style, within the limits of supported formats.
$json = new JSON::XS
Creates a new JSON::XS object that can be used to de/encode JSON
strings. All boolean flags described below are by default
*disabled*.
The mutators for flags all return the JSON object again and thus
calls can be chained:
my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
=> {"a": [1, 2]}
$json = $json->ascii ([$enable])
$enabled = $json->get_ascii
If $enable is true (or missing), then the "encode" method will not
generate characters outside the code range 0..127 (which is ASCII).
Any Unicode characters outside that range will be escaped using
either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
escape sequence, as per RFC4627. The resulting encoded JSON text can
be treated as a native Unicode string, an ascii-encoded,
latin1-encoded or UTF-8 encoded string, or any other superset of
ASCII.
If $enable is false, then the "encode" method will not escape
Unicode characters unless required by the JSON syntax or other
flags. This results in a faster and more compact format.
See also the section *ENCODING/CODESET FLAG NOTES* later in this
document.
The main use for this flag is to produce JSON texts that can be
transmitted over a 7-bit channel, as the encoded JSON texts will not
contain any 8 bit characters.
JSON::XS->new->ascii (1)->encode ([chr 0x10401])
=> ["\ud801\udc01"]
$json = $json->latin1 ([$enable])
$enabled = $json->get_latin1
If $enable is true (or missing), then the "encode" method will
encode the resulting JSON text as latin1 (or iso-8859-1), escaping
any characters outside the code range 0..255. The resulting string
can be treated as a latin1-encoded JSON text or a native Unicode
string. The "decode" method will not be affected in any way by this
flag, as "decode" by default expects Unicode, which is a strict
superset of latin1.
If $enable is false, then the "encode" method will not escape
Unicode characters unless required by the JSON syntax or other
flags.
See also the section *ENCODING/CODESET FLAG NOTES* later in this
document.
The main use for this flag is efficiently encoding binary data as
JSON text, as most octets will not be escaped, resulting in a
smaller encoded size. The disadvantage is that the resulting JSON
text is encoded in latin1 (and must correctly be treated as such
when storing and transferring), a rare encoding for JSON. It is
therefore most useful when you want to store data structures known
to contain binary data efficiently in files or databases, not when
talking to other JSON encoders/decoders.
JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
$json = $json->utf8 ([$enable])
$enabled = $json->get_utf8
If $enable is true (or missing), then the "encode" method will
encode the JSON result into UTF-8, as required by many protocols,
while the "decode" method expects to be handled an UTF-8-encoded
string. Please note that UTF-8-encoded strings do not contain any
characters outside the range 0..255, they are thus useful for
bytewise/binary I/O. In future versions, enabling this option might
enable autodetection of the UTF-16 and UTF-32 encoding families, as
described in RFC4627.
If $enable is false, then the "encode" method will return the JSON
string as a (non-encoded) Unicode string, while "decode" expects
thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
UTF-16) needs to be done yourself, e.g. using the Encode module.
See also the section *ENCODING/CODESET FLAG NOTES* later in this
document.
Example, output UTF-16BE-encoded JSON:
use Encode;
$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
Example, decode UTF-32LE-encoded JSON:
use Encode;
$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
$json = $json->pretty ([$enable])
This enables (or disables) all of the "indent", "space_before" and
"space_after" (and in the future possibly more) flags in one call to
generate the most readable (or most compact) form possible.
Example, pretty-print some simple structure:
my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
=>
{
"a" : [
1,
2
]
}
$json = $json->indent ([$enable])
$enabled = $json->get_indent
If $enable is true (or missing), then the "encode" method will use a
multiline format as output, putting every array member or
object/hash key-value pair into its own line, indenting them
properly.
If $enable is false, no newlines or indenting will be produced, and
the resulting JSON text is guaranteed not to contain any "newlines".
This setting has no effect when decoding JSON texts.
$json = $json->space_before ([$enable])
$enabled = $json->get_space_before
If $enable is true (or missing), then the "encode" method will add
an extra optional space before the ":" separating keys from values
in JSON objects.
If $enable is false, then the "encode" method will not add any extra
space at those places.
This setting has no effect when decoding JSON texts. You will also
most likely combine this setting with "space_after".
Example, space_before enabled, space_after and indent disabled:
{"key" :"value"}
$json = $json->space_after ([$enable])
$enabled = $json->get_space_after
If $enable is true (or missing), then the "encode" method will add
an extra optional space after the ":" separating keys from values in
JSON objects and extra whitespace after the "," separating key-value
pairs and array members.
If $enable is false, then the "encode" method will not add any extra
space at those places.
This setting has no effect when decoding JSON texts.
Example, space_before and indent disabled, space_after enabled:
{"key": "value"}
$json = $json->relaxed ([$enable])
$enabled = $json->get_relaxed
If $enable is true (or missing), then "decode" will accept some
extensions to normal JSON syntax (see below). "encode" will not be
affected in anyway. *Be aware that this option makes you accept
invalid JSON texts as if they were valid!*. I suggest only to use
this option to parse application-specific files written by humans
(configuration files, resource files etc.)
If $enable is false (the default), then "decode" will only accept
valid JSON texts.
Currently accepted extensions are:
* list items can have an end-comma
JSON *separates* array elements and key-value pairs with commas.
This can be annoying if you write JSON texts manually and want
to be able to quickly append elements, so this extension accepts
comma at the end of such items not just between them:
[
1,
2, <- this comma not normally allowed
]
{
"k1": "v1",
"k2": "v2", <- this comma not normally allowed
}
* shell-style '#'-comments
Whenever JSON allows whitespace, shell-style comments are
additionally allowed. They are terminated by the first
carriage-return or line-feed character, after which more
white-space and comments are allowed.
[
1, # this comment not allowed in JSON
# neither this one...
]
* literal ASCII TAB characters in strings
Literal ASCII TAB characters are now allowed in strings (and
treated as "\t").
[
"Hello\tWorld",
"Hello<TAB>World", # literal <TAB> would not normally be allowed
]
$json = $json->canonical ([$enable])
$enabled = $json->get_canonical
If $enable is true (or missing), then the "encode" method will
output JSON objects by sorting their keys. This is adding a
comparatively high overhead.
If $enable is false, then the "encode" method will output key-value
pairs in the order Perl stores them (which will likely change
between runs of the same script, and can change even within the same
run from 5.18 onwards).
This option is useful if you want the same data structure to be
encoded as the same JSON text (given the same overall settings). If
it is disabled, the same hash might be encoded differently even if
contains the same data, as key-value pairs have no inherent ordering
in Perl.
This setting has no effect when decoding JSON texts.
This setting has currently no effect on tied hashes.
$json = $json->allow_nonref ([$enable])
$enabled = $json->get_allow_nonref
If $enable is true (or missing), then the "encode" method can
convert a non-reference into its corresponding string, number or
null JSON value, which is an extension to RFC4627. Likewise,
"decode" will accept those JSON values instead of croaking.
If $enable is false, then the "encode" method will croak if it isn't
passed an arrayref or hashref, as JSON texts must either be an
object or array. Likewise, "decode" will croak if given something
that is not a JSON object or array.
Example, encode a Perl scalar as JSON value with enabled
"allow_nonref", resulting in an invalid JSON text:
JSON::XS->new->allow_nonref->encode ("Hello, World!")
=> "Hello, World!"
$json = $json->allow_unknown ([$enable])
$enabled = $json->get_allow_unknown
If $enable is true (or missing), then "encode" will *not* throw an
exception when it encounters values it cannot represent in JSON (for
example, filehandles) but instead will encode a JSON "null" value.
Note that blessed objects are not included here and are handled
separately by c<allow_nonref>.
If $enable is false (the default), then "encode" will throw an
exception when it encounters anything it cannot encode as JSON.
This option does not affect "decode" in any way, and it is
recommended to leave it off unless you know your communications
partner.
$json = $json->allow_blessed ([$enable])
$enabled = $json->get_allow_blessed
See "OBJECT SERIALISATION" for details.
If $enable is true (or missing), then the "encode" method will not
barf when it encounters a blessed reference that it cannot convert
otherwise. Instead, a JSON "null" value is encoded instead of the
object.
If $enable is false (the default), then "encode" will throw an
exception when it encounters a blessed object that it cannot convert
otherwise.
This setting has no effect on "decode".
$json = $json->convert_blessed ([$enable])
$enabled = $json->get_convert_blessed
See "OBJECT SERIALISATION" for details.
If $enable is true (or missing), then "encode", upon encountering a
blessed object, will check for the availability of the "TO_JSON"
method on the object's class. If found, it will be called in scalar
context and the resulting scalar will be encoded instead of the
object.
The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
returns other blessed objects, those will be handled in the same
way. "TO_JSON" must take care of not causing an endless recursion
cycle (== crash) in this case. The name of "TO_JSON" was chosen
because other methods called by the Perl core (== not by the user of
the object) are usually in upper case letters and to avoid
collisions with any "to_json" function or method.
If $enable is false (the default), then "encode" will not consider
this type of conversion.
This setting has no effect on "decode".
$json = $json->allow_tags ([$enable])
$enabled = $json->allow_tags
See "OBJECT SERIALISATION" for details.
If $enable is true (or missing), then "encode", upon encountering a
blessed object, will check for the availability of the "FREEZE"
method on the object's class. If found, it will be used to serialise
the object into a nonstandard tagged JSON value (that JSON decoders
cannot decode).
It also causes "decode" to parse such tagged JSON values and
deserialise them via a call to the "THAW" method.
If $enable is false (the default), then "encode" will not consider
this type of conversion, and tagged JSON values will cause a parse
error in "decode", as if tags were not part of the grammar.
$json = $json->filter_json_object ([$coderef->($hashref)])
When $coderef is specified, it will be called from "decode" each
time it decodes a JSON object. The only argument is a reference to
the newly-created hash. If the code references returns a single
scalar (which need not be a reference), this value (i.e. a copy of
that scalar to avoid aliasing) is inserted into the deserialised
data structure. If it returns an empty list (NOTE: *not* "undef",
which is a valid scalar), the original deserialised hash will be
inserted. This setting can slow down decoding considerably.
When $coderef is omitted or undefined, any existing callback will be
removed and "decode" will not change the deserialised hash in any
way.
Example, convert all JSON objects into the integer 5:
my $js = JSON::XS->new->filter_json_object (sub { 5 });
# returns [5]
$js->decode ('[{}]')
# throw an exception because allow_nonref is not enabled
# so a lone 5 is not allowed.
$js->decode ('{"a":1, "b":2}');
$json = $json->filter_json_single_key_object ($key [=>
$coderef->($value)])
Works remotely similar to "filter_json_object", but is only called
for JSON objects having a single key named $key.
This $coderef is called before the one specified via
"filter_json_object", if any. It gets passed the single value in the
JSON object. If it returns a single value, it will be inserted into
the data structure. If it returns nothing (not even "undef" but the
empty list), the callback from "filter_json_object" will be called
next, as if no single-key callback were specified.
If $coderef is omitted or undefined, the corresponding callback will
be disabled. There can only ever be one callback for a given key.
As this callback gets called less often then the
"filter_json_object" one, decoding speed will not usually suffer as
much. Therefore, single-key objects make excellent targets to
serialise Perl objects into, especially as single-key JSON objects
are as close to the type-tagged value concept as JSON gets (it's
basically an ID/VALUE tuple). Of course, JSON does not support this
in any way, so you need to make sure your data never looks like a
serialised Perl hash.
Typical names for the single object key are "__class_whatever__", or
"$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
things like "__class_md5sum(classname)__", to reduce the risk of
clashing with real hashes.
Example, decode JSON objects of the form "{ "__widget__" => <id> }"
into the corresponding $WIDGET{<id>} object:
# return whatever is in $WIDGET{5}:
JSON::XS
->new
->filter_json_single_key_object (__widget__ => sub {
$WIDGET{ $_[0] }
})
->decode ('{"__widget__": 5')
# this can be used with a TO_JSON method in some "widget" class
# for serialisation to json:
sub WidgetBase::TO_JSON {
my ($self) = @_;
unless ($self->{id}) {
$self->{id} = ..get..some..id..;
$WIDGET{$self->{id}} = $self;
}
{ __widget__ => $self->{id} }
}
$json = $json->shrink ([$enable])
$enabled = $json->get_shrink
Perl usually over-allocates memory a bit when allocating space for
strings. This flag optionally resizes strings generated by either
"encode" or "decode" to their minimum size possible. This can save
memory when your JSON texts are either very very long or you have
many short strings. It will also try to downgrade any strings to
octet-form if possible: perl stores strings internally either in an
encoding called UTF-X or in octet-form. The latter cannot store
everything but uses less space in general (and some buggy Perl or C
code might even rely on that internal representation being used).
The actual definition of what shrink does might change in future
versions, but it will always try to save space at the expense of
time.
If $enable is true (or missing), the string returned by "encode"
will be shrunk-to-fit, while all strings generated by "decode" will
also be shrunk-to-fit.
If $enable is false, then the normal perl allocation algorithms are
used. If you work with your data, then this is likely to be faster.
In the future, this setting might control other things, such as
converting strings that look like integers or floats into integers
or floats internally (there is no difference on the Perl level),
saving space.
$json = $json->max_depth ([$maximum_nesting_depth])
$max_depth = $json->get_max_depth
Sets the maximum nesting level (default 512) accepted while encoding
or decoding. If a higher nesting level is detected in JSON text or a
Perl data structure, then the encoder and decoder will stop and
croak at that point.
Nesting level is defined by number of hash- or arrayrefs that the
encoder needs to traverse to reach a given point or the number of
"{" or "[" characters without their matching closing parenthesis
crossed to reach a given character in a string.
Setting the maximum depth to one disallows any nesting, so that
ensures that the object is only a single hash/object or array.
If no argument is given, the highest possible setting will be used,
which is rarely useful.
Note that nesting is implemented by recursion in C. The default
value has been chosen to be as large as typical operating systems
allow without crashing.
See SECURITY CONSIDERATIONS, below, for more info on why this is
useful.
$json = $json->max_size ([$maximum_string_size])
$max_size = $json->get_max_size
Set the maximum length a JSON text may have (in bytes) where
decoding is being attempted. The default is 0, meaning no limit.
When "decode" is called on a string that is longer then this many
bytes, it will not attempt to decode the string but throw an
exception. This setting has no effect on "encode" (yet).
If no argument is given, the limit check will be deactivated (same
as when 0 is specified).
See SECURITY CONSIDERATIONS, below, for more info on why this is
useful.
$json_text = $json->encode ($perl_scalar)
Converts the given Perl value or data structure to its JSON
representation. Croaks on error.
$perl_scalar = $json->decode ($json_text)
The opposite of "encode": expects a JSON text and tries to parse it,
returning the resulting simple scalar or reference. Croaks on error.
($perl_scalar, $characters) = $json->decode_prefix ($json_text)
This works like the "decode" method, but instead of raising an
exception when there is trailing garbage after the first JSON
object, it will silently stop parsing there and return the number of
characters consumed so far.
This is useful if your JSON texts are not delimited by an outer
protocol and you need to know where the JSON text ends.
JSON::XS->new->decode_prefix ("[1] the tail")
=> ([1], 3)
INCREMENTAL PARSING
In some cases, there is the need for incremental parsing of JSON texts.
While this module always has to keep both JSON text and resulting Perl
data structure in memory at one time, it does allow you to parse a JSON
stream incrementally. It does so by accumulating text until it has a
full JSON object, which it then can decode. This process is similar to
using "decode_prefix" to see if a full JSON object is available, but is
much more efficient (and can be implemented with a minimum of method
calls).
JSON::XS will only attempt to parse the JSON text once it is sure it has
enough text to get a decisive result, using a very simple but truly
incremental parser. This means that it sometimes won't stop as early as
the full parser, for example, it doesn't detect mismatched parentheses.
The only thing it guarantees is that it starts decoding as soon as a
syntactically valid JSON text has been seen. This means you need to set
resource limits (e.g. "max_size") to ensure the parser will stop parsing
in the presence if syntax errors.
The following methods implement this incremental parser.
[void, scalar or list context] = $json->incr_parse ([$string])
This is the central parsing function. It can both append new text
and extract objects from the stream accumulated so far (both of
these functions are optional).
If $string is given, then this string is appended to the already
existing JSON fragment stored in the $json object.
After that, if the function is called in void context, it will
simply return without doing anything further. This can be used to
add more text in as many chunks as you want.
If the method is called in scalar context, then it will try to
extract exactly *one* JSON object. If that is successful, it will
return this object, otherwise it will return "undef". If there is a
parse error, this method will croak just as "decode" would do (one
can then use "incr_skip" to skip the erroneous part). This is the
most common way of using the method.
And finally, in list context, it will try to extract as many objects
from the stream as it can find and return them, or the empty list
otherwise. For this to work, there must be no separators (other than
whitespace) between the JSON objects or arrays, instead they must be
concatenated back-to-back. If an error occurs, an exception will be
raised as in the scalar context case. Note that in this case, any
previously-parsed JSON texts will be lost.
Example: Parse some JSON arrays/objects in a given string and return
them.
my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
$lvalue_string = $json->incr_text
This method returns the currently stored JSON fragment as an lvalue,
that is, you can manipulate it. This *only* works when a preceding
call to "incr_parse" in *scalar context* successfully returned an
object. Under all other circumstances you must not call this
function (I mean it. although in simple tests it might actually
work, it *will* fail under real world conditions). As a special
exception, you can also call this method before having parsed
anything.
That means you can only use this function to look at or manipulate
text before or after complete JSON objects, not while the parser is
in the middle of parsing a JSON object.
This function is useful in two cases: a) finding the trailing text
after a JSON object or b) parsing multiple JSON objects separated by
non-JSON text (such as commas).
$json->incr_skip
This will reset the state of the incremental parser and will remove
the parsed text from the input buffer so far. This is useful after
"incr_parse" died, in which case the input buffer and incremental
parser state is left unchanged, to skip the text parsed so far and
to reset the parse state.
The difference to "incr_reset" is that only text until the parse
error occurred is removed.
$json->incr_reset
This completely resets the incremental parser, that is, after this
call, it will be as if the parser had never parsed anything.
This is useful if you want to repeatedly parse JSON objects and want
to ignore any trailing data, which means you have to reset the
parser after each successful decode.
LIMITATIONS
All options that affect decoding are supported, except "allow_nonref".
The reason for this is that it cannot be made to work sensibly: JSON
objects and arrays are self-delimited, i.e. you can concatenate them
back to back and still decode them perfectly. This does not hold true
for JSON numbers, however.
For example, is the string 1 a single JSON number, or is it simply the
start of 12? Or is 12 a single JSON number, or the concatenation of 1
and 2? In neither case you can tell, and this is why JSON::XS takes the
conservative route and disallows this case.
EXAMPLES
Some examples will make all this clearer. First, a simple example that
works similarly to "decode_prefix": We want to decode the JSON object at
the start of a string and identify the portion after the JSON object:
my $text = "[1,2,3] hello";
my $json = new JSON::XS;
my $obj = $json->incr_parse ($text)
or die "expected JSON object or array at beginning of string";
my $tail = $json->incr_text;
# $tail now contains " hello"
Easy, isn't it?
Now for a more complicated example: Imagine a hypothetical protocol
where you read some requests from a TCP stream, and each request is a
JSON array, without any separation between them (in fact, it is often
useful to use newlines as "separators", as these get interpreted as
whitespace at the start of the JSON text, which makes it possible to
test said protocol with "telnet"...).
Here is how you'd do it (it is trivial to write this in an event-based
manner):
my $json = new JSON::XS;
# read some data from the socket
while (sysread $socket, my $buf, 4096) {
# split and decode as many requests as possible
for my $request ($json->incr_parse ($buf)) {
# act on the $request
}
}
Another complicated example: Assume you have a string with JSON objects
or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
[3]"). To parse them, we have to skip the commas between the JSON texts,
and here is where the lvalue-ness of "incr_text" comes in useful:
my $text = "[1],[2], [3]";
my $json = new JSON::XS;
# void context, so no parsing done
$json->incr_parse ($text);
# now extract as many objects as possible. note the
# use of scalar context so incr_text can be called.
while (my $obj = $json->incr_parse) {
# do something with $obj
# now skip the optional comma
$json->incr_text =~ s/^ \s* , //x;
}
Now lets go for a very complex example: Assume that you have a gigantic
JSON array-of-objects, many gigabytes in size, and you want to parse it,
but you cannot load it into memory fully (this has actually happened in
the real world :).
Well, you lost, you have to implement your own JSON parser. But JSON::XS
can still help you: You implement a (very simple) array parser and let
JSON decode the array elements, which are all full JSON objects on their
own (this wouldn't work if the array elements could be JSON numbers, for
example):
my $json = new JSON::XS;
# open the monster
open my $fh, "<bigfile.json"
or die "bigfile: $!";
# first parse the initial "["
for (;;) {
sysread $fh, my $buf, 65536
or die "read error: $!";
$json->incr_parse ($buf); # void context, so no parsing
# Exit the loop once we found and removed(!) the initial "[".
# In essence, we are (ab-)using the $json object as a simple scalar
# we append data to.
last if $json->incr_text =~ s/^ \s* \[ //x;
}
# now we have the skipped the initial "[", so continue
# parsing all the elements.
for (;;) {
# in this loop we read data until we got a single JSON object
for (;;) {
if (my $obj = $json->incr_parse) {
# do something with $obj
last;
}
# add more data
sysread $fh, my $buf, 65536
or die "read error: $!";
$json->incr_parse ($buf); # void context, so no parsing
}
# in this loop we read data until we either found and parsed the
# separating "," between elements, or the final "]"
for (;;) {
# first skip whitespace
$json->incr_text =~ s/^\s*//;
# if we find "]", we are done
if ($json->incr_text =~ s/^\]//) {
print "finished.\n";
exit;
}
# if we find ",", we can continue with the next element
if ($json->incr_text =~ s/^,//) {
last;
}
# if we find anything else, we have a parse error!
if (length $json->incr_text) {
die "parse error near ", $json->incr_text;
}
# else add more data
sysread $fh, my $buf, 65536
or die "read error: $!";
$json->incr_parse ($buf); # void context, so no parsing
}
This is a complex example, but most of the complexity comes from the
fact that we are trying to be correct (bear with me if I am wrong, I
never ran the above example :).
MAPPING
This section describes how JSON::XS maps Perl values to JSON values and
vice versa. These mappings are designed to "do the right thing" in most
circumstances automatically, preserving round-tripping characteristics
(what you put in comes out as something equivalent).
For the more enlightened: note that in the following descriptions,
lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
refers to the abstract Perl language itself.
JSON -> PERL
object
A JSON object becomes a reference to a hash in Perl. No ordering of
object keys is preserved (JSON does not preserve object key ordering
itself).
array
A JSON array becomes a reference to an array in Perl.
string
A JSON string becomes a string scalar in Perl - Unicode codepoints
in JSON are represented by the same codepoints in the Perl string,
so no manual decoding is necessary.
number
A JSON number becomes either an integer, numeric (floating point) or
string scalar in perl, depending on its range and any fractional
parts. On the Perl level, there is no difference between those as
Perl handles all the conversion details, but an integer may take
slightly less memory and might represent more values exactly than
floating point numbers.
If the number consists of digits only, JSON::XS will try to
represent it as an integer value. If that fails, it will try to
represent it as a numeric (floating point) value if that is possible
without loss of precision. Otherwise it will preserve the number as
a string value (in which case you lose roundtripping ability, as the
JSON number will be re-encoded to a JSON string).
Numbers containing a fractional or exponential part will always be
represented as numeric (floating point) values, possibly at a loss
of precision (in which case you might lose perfect roundtripping
ability, but the JSON number will still be re-encoded as a JSON
number).
Note that precision is not accuracy - binary floating point values
cannot represent most decimal fractions exactly, and when converting
from and to floating point, JSON::XS only guarantees precision up to
but not including the least significant bit.
true, false
These JSON atoms become "Types::Serialiser::true" and
"Types::Serialiser::false", respectively. They are overloaded to act
almost exactly like the numbers 1 and 0. You can check whether a
scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
function (after "use Types::Serialier", of course).
null
A JSON null atom becomes "undef" in Perl.
shell-style comments ("# *text*")
As a nonstandard extension to the JSON syntax that is enabled by the
"relaxed" setting, shell-style comments are allowed. They can start
anywhere outside strings and go till the end of the line.
tagged values ("(*tag*)*value*").
Another nonstandard extension to the JSON syntax, enabled with the
"allow_tags" setting, are tagged values. In this implementation, the
*tag* must be a perl package/class name encoded as a JSON string,
and the *value* must be a JSON array encoding optional constructor
arguments.
See "OBJECT SERIALISATION", below, for details.
PERL -> JSON
The mapping from Perl to JSON is slightly more difficult, as Perl is a
truly typeless language, so we can only guess which JSON type is meant
by a Perl value.
hash references
Perl hash references become JSON objects. As there is no inherent
ordering in hash keys (or JSON objects), they will usually be
encoded in a pseudo-random order. JSON::XS can optionally sort the
hash keys (determined by the *canonical* flag), so the same
datastructure will serialise to the same JSON text (given same
settings and version of JSON::XS), but this incurs a runtime
overhead and is only rarely useful, e.g. when you want to compare
some JSON text against another for equality.
array references
Perl array references become JSON arrays.
other references
Other unblessed references are generally not allowed and will cause
an exception to be thrown, except for references to the integers 0
and 1, which get turned into "false" and "true" atoms in JSON.
Since "JSON::XS" uses the boolean model from Types::Serialiser, you
can also "use Types::Serialiser" and then use
"Types::Serialiser::false" and "Types::Serialiser::true" to improve
readability.
use Types::Serialiser;
encode_json [\0, Types::Serialiser::true] # yields [false,true]
Types::Serialiser::true, Types::Serialiser::false
These special values from the Types::Serialiser module become JSON
true and JSON false values, respectively. You can also use "\1" and
"\0" directly if you want.
blessed objects
Blessed objects are not directly representable in JSON, but
"JSON::XS" allows various ways of handling objects. See "OBJECT
SERIALISATION", below, for details.
simple scalars
Simple Perl scalars (any scalar that is not a reference) are the
most difficult objects to encode: JSON::XS will encode undefined
scalars as JSON "null" values, scalars that have last been used in a
string context before encoding as JSON strings, and anything else as
number value:
# dump as number
encode_json [2] # yields [2]
encode_json [-3.0e17] # yields [-3e+17]
my $value = 5; encode_json [$value] # yields [5]
# used as string, so dump as string
print $value;
encode_json [$value] # yields ["5"]
# undef becomes null
encode_json [undef] # yields [null]
You can force the type to be a JSON string by stringifying it:
my $x = 3.1; # some variable containing a number
"$x"; # stringified
$x .= ""; # another, more awkward way to stringify
print $x; # perl does it for you, too, quite often
You can force the type to be a JSON number by numifying it:
my $x = "3"; # some variable containing a string
$x += 0; # numify it, ensuring it will be dumped as a number
$x *= 1; # same thing, the choice is yours.
You can not currently force the type in other, less obscure, ways.
Tell me if you need this capability (but don't forget to explain why
it's needed :).
Note that numerical precision has the same meaning as under Perl (so
binary to decimal conversion follows the same rules as in Perl,
which can differ to other languages). Also, your perl interpreter
might expose extensions to the floating point numbers of your
platform, such as infinities or NaN's - these cannot be represented
in JSON, and it is an error to pass those in.
OBJECT SERIALISATION
As JSON cannot directly represent Perl objects, you have to choose
between a pure JSON representation (without the ability to deserialise
the object automatically again), and a nonstandard extension to the JSON
syntax, tagged values.
SERIALISATION
What happens when "JSON::XS" encounters a Perl object depends on the
"allow_blessed", "convert_blessed" and "allow_tags" settings, which are
used in this order:
1. "allow_tags" is enabled and the object has a "FREEZE" method.
In this case, "JSON::XS" uses the Types::Serialiser object
serialisation protocol to create a tagged JSON value, using a
nonstandard extension to the JSON syntax.
This works by invoking the "FREEZE" method on the object, with the
first argument being the object to serialise, and the second
argument being the constant string "JSON" to distinguish it from
other serialisers.
The "FREEZE" method can return any number of values (i.e. zero or
more). These values and the paclkage/classname of the object will
then be encoded as a tagged JSON value in the following format:
("classname")[FREEZE return values...]
e.g.:
("URI")["http://www.google.com/"]
("MyDate")[2013,10,29]
("ImageData::JPEG")["Z3...VlCg=="]
For example, the hypothetical "My::Object" "FREEZE" method might use
the objects "type" and "id" members to encode the object:
sub My::Object::FREEZE {
my ($self, $serialiser) = @_;
($self->{type}, $self->{id})
}
2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
In this case, the "TO_JSON" method of the object is invoked in
scalar context. It must return a single scalar that can be directly
encoded into JSON. This scalar replaces the object in the JSON text.
For example, the following "TO_JSON" method will convert all URI
objects to JSON strings when serialised. The fatc that these values
originally were URI objects is lost.
sub URI::TO_JSON {
my ($uri) = @_;
$uri->as_string
}
3. "allow_blessed" is enabled.
The object will be serialised as a JSON null value.
4. none of the above
If none of the settings are enabled or the respective methods are
missing, "JSON::XS" throws an exception.
DESERIALISATION
For deserialisation there are only two cases to consider: either
nonstandard tagging was used, in which case "allow_tags" decides, or
objects cannot be automatically be deserialised, in which case you can
use postprocessing or the "filter_json_object" or
"filter_json_single_key_object" callbacks to get some real objects our
of your JSON.
This section only considers the tagged value case: I a tagged JSON
object is encountered during decoding and "allow_tags" is disabled, a
parse error will result (as if tagged values were not part of the
grammar).
If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
the package/classname used during serialisation (it will not attempt to
load the package as a Perl module). If there is no such method, the
decoding will fail with an error.
Otherwise, the "THAW" method is invoked with the classname as first
argument, the constant string "JSON" as second argument, and all the
values from the JSON array (the values originally returned by the
"FREEZE" method) as remaining arguments.
The method must then return the object. While technically you can return
any Perl scalar, you might have to enable the "enable_nonref" setting to
make that work in all cases, so better return an actual blessed
reference.
As an example, let's implement a "THAW" function that regenerates the
"My::Object" from the "FREEZE" example earlier:
sub My::Object::THAW {
my ($class, $serialiser, $type, $id) = @_;
$class->new (type => $type, id => $id)
}
ENCODING/CODESET FLAG NOTES
The interested reader might have seen a number of flags that signify
encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
some confusion on what these do, so here is a short comparison:
"utf8" controls whether the JSON text created by "encode" (and expected
by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
control whether "encode" escapes character values outside their
respective codeset range. Neither of these flags conflict with each
other, although some combinations make less sense than others.
Care has been taken to make all flags symmetrical with respect to
"encode" and "decode", that is, texts encoded with any combination of
these flag values will be correctly decoded when the same flags are used
- in general, if you use different flag settings while encoding vs. when
decoding you likely have a bug somewhere.
Below comes a verbose discussion of these flags. Note that a "codeset"
is simply an abstract set of character-codepoint pairs, while an
encoding takes those codepoint numbers and *encodes* them, in our case
into octets. Unicode is (among other things) a codeset, UTF-8 is an
encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
encodings at the same time, which can be confusing.
"utf8" flag disabled
When "utf8" is disabled (the default), then "encode"/"decode"
generate and expect Unicode strings, that is, characters with high
ordinal Unicode values (> 255) will be encoded as such characters,
and likewise such characters are decoded as-is, no changes to them
will be done, except "(re-)interpreting" them as Unicode codepoints
or Unicode characters, respectively (to Perl, these are the same
thing in strings unless you do funny/weird/dumb stuff).
This is useful when you want to do the encoding yourself (e.g. when
you want to have UTF-16 encoded JSON texts) or when some other layer
does the encoding for you (for example, when printing to a terminal
using a filehandle that transparently encodes to UTF-8 you certainly
do NOT want to UTF-8 encode your data first and have Perl encode it
another time).
"utf8" flag enabled
If the "utf8"-flag is enabled, "encode"/"decode" will encode all
characters using the corresponding UTF-8 multi-byte sequence, and
will expect your input strings to be encoded as UTF-8, that is, no
"character" of the input string must have any value > 255, as UTF-8
does not allow that.
The "utf8" flag therefore switches between two modes: disabled means
you will get a Unicode string in Perl, enabled means you get an
UTF-8 encoded octet/binary string in Perl.
"latin1" or "ascii" flags enabled
With "latin1" (or "ascii") enabled, "encode" will escape characters
with ordinal values > 255 (> 127 with "ascii") and encode the
remaining characters as specified by the "utf8" flag.
If "utf8" is disabled, then the result is also correctly encoded in
those character sets (as both are proper subsets of Unicode, meaning
that a Unicode string with all character values < 256 is the same
thing as a ISO-8859-1 string, and a Unicode string with all
character values < 128 is the same thing as an ASCII string in
Perl).
If "utf8" is enabled, you still get a correct UTF-8-encoded string,
regardless of these flags, just some more characters will be escaped
using "\uXXXX" then before.
Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
encoding, while ASCII-encoded strings are. That is because the
ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
*codeset* being a subset of Unicode), while ASCII is.
Surprisingly, "decode" will ignore these flags and so treat all
input values as governed by the "utf8" flag. If it is disabled, this
allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
strict subsets of Unicode. If it is enabled, you can correctly
decode UTF-8 encoded strings.
So neither "latin1" nor "ascii" are incompatible with the "utf8"
flag - they only govern when the JSON output engine escapes a
character or not.
The main use for "latin1" is to relatively efficiently store binary
data as JSON, at the expense of breaking compatibility with most
JSON decoders.
The main use for "ascii" is to force the output to not contain
characters with values > 127, which means you can interpret the
resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
any character set and 8-bit-encoding, and still get the same data
structure back. This is useful when your channel for JSON transfer
is not 8-bit clean or the encoding might be mangled in between (e.g.
in mail), and works because ASCII is a proper subset of most 8-bit
and multibyte encodings in use in the world.
JSON and ECMAscript
JSON syntax is based on how literals are represented in javascript (the
not-standardised predecessor of ECMAscript) which is presumably why it
is called "JavaScript Object Notation".
However, JSON is not a subset (and also not a superset of course) of
ECMAscript (the standard) or javascript (whatever browsers actually
implement).
If you want to use javascript's "eval" function to "parse" JSON, you
might run into parse errors for valid JSON texts, or the resulting data
structure might not be queryable:
One of the problems is that U+2028 and U+2029 are valid characters
inside JSON strings, but are not allowed in ECMAscript string literals,
so the following Perl fragment will not output something that can be
guaranteed to be parsable by javascript's "eval":
use JSON::XS;
print encode_json [chr 0x2028];
The right fix for this is to use a proper JSON parser in your javascript
programs, and not rely on "eval" (see for example Douglas Crockford's
json2.js parser).
If this is not an option, you can, as a stop-gap measure, simply encode
to ASCII-only JSON:
use JSON::XS;
print JSON::XS->new->ascii->encode ([chr 0x2028]);
Note that this will enlarge the resulting JSON text quite a bit if you
have many non-ASCII characters. You might be tempted to run some regexes
to only escape U+2028 and U+2029, e.g.:
# DO NOT USE THIS!
my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
print $json;
Note that *this is a bad idea*: the above only works for U+2028 and
U+2029 and thus only for fully ECMAscript-compliant parsers. Many
existing javascript implementations, however, have issues with other
characters as well - using "eval" naively simply *will* cause problems.
Another problem is that some javascript implementations reserve some
property names for their own purposes (which probably makes them
non-ECMAscript-compliant). For example, Iceweasel reserves the
"__proto__" property name for its own purposes.
If that is a problem, you could parse try to filter the resulting JSON
output for these property strings, e.g.:
$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
This works because "__proto__" is not valid outside of strings, so every
occurrence of ""__proto__"\s*:" must be a string used as property name.
If you know of other incompatibilities, please let me know.
JSON and YAML
You often hear that JSON is a subset of YAML. This is, however, a mass
hysteria(*) and very far from the truth (as of the time of this
writing), so let me state it clearly: *in general, there is no way to
configure JSON::XS to output a data structure as valid YAML* that works
in all cases.
If you really must use JSON::XS to generate YAML, you should use this
algorithm (subject to change in future versions):
my $to_yaml = JSON::XS->new->utf8->space_after (1);
my $yaml = $to_yaml->encode ($ref) . "\n";
This will *usually* generate JSON texts that also parse as valid YAML.
Please note that YAML has hardcoded limits on (simple) object key
lengths that JSON doesn't have and also has different and incompatible
unicode character escape syntax, so you should make sure that your hash
keys are noticeably shorter than the 1024 "stream characters" YAML
allows and that you do not have characters with codepoint values outside
the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
sequences in strings (which JSON::XS does not *currently* generate, but
other JSON generators might).
There might be other incompatibilities that I am not aware of (or the
YAML specification has been changed yet again - it does so quite often).
In general you should not try to generate YAML with a JSON generator or
vice versa, or try to parse JSON with a YAML parser or vice versa:
chances are high that you will run into severe interoperability problems
when you least expect it.
(*) I have been pressured multiple times by Brian Ingerson (one of the
authors of the YAML specification) to remove this paragraph, despite
him acknowledging that the actual incompatibilities exist. As I was
personally bitten by this "JSON is YAML" lie, I refused and said I
will continue to educate people about these issues, so others do not
run into the same problem again and again. After this, Brian called
me a (quote)*complete and worthless idiot*(unquote).
In my opinion, instead of pressuring and insulting people who
actually clarify issues with YAML and the wrong statements of some
of its proponents, I would kindly suggest reading the JSON spec
(which is not that difficult or long) and finally make YAML
compatible to it, and educating users about the changes, instead of
spreading lies about the real compatibility for many *years* and
trying to silence people who point out that it isn't true.
Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
even though the incompatibilities have been documented (and are
known to Brian) for many years and the spec makes explicit claims
that YAML is a superset of JSON. It would be so easy to fix, but
apparently, bullying people and corrupting userdata is so much
easier.
SPEED
It seems that JSON::XS is surprisingly fast, as shown in the following
tables. They have been generated with the help of the "eg/bench" program
in the JSON::XS distribution, to make it easy to compare on your own
system.
First comes a comparison between various modules using a very short
single-line JSON string (also available at
<http://dist.schmorp.de/misc/json/short.json>).
{"method": "handleMessage", "params": ["user1",
"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1, 0]}
It shows the number of encodes/decodes per second (JSON::XS uses the
functional interface, while JSON::XS/2 uses the OO interface with
pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
the from_json method). Higher is better:
module | encode | decode |
--------------|------------|------------|
JSON::DWIW/DS | 86302.551 | 102300.098 |
JSON::DWIW/FJ | 86302.551 | 75983.768 |
JSON::PP | 15827.562 | 6638.658 |
JSON::Syck | 63358.066 | 47662.545 |
JSON::XS | 511500.488 | 511500.488 |
JSON::XS/2 | 291271.111 | 388361.481 |
JSON::XS/3 | 361577.931 | 361577.931 |
Storable | 66788.280 | 265462.278 |
--------------+------------+------------+
That is, JSON::XS is almost six times faster than JSON::DWIW on
encoding, about five times faster on decoding, and over thirty to
seventy times faster than JSON's pure perl implementation. It also
compares favourably to Storable for small amounts of data.
Using a longer test string (roughly 18KB, generated from Yahoo! Locals
search API (<http://dist.schmorp.de/misc/json/long.json>).
module | encode | decode |
--------------|------------|------------|
JSON::DWIW/DS | 1647.927 | 2673.916 |
JSON::DWIW/FJ | 1630.249 | 2596.128 |
JSON::PP | 400.640 | 62.311 |
JSON::Syck | 1481.040 | 1524.869 |
JSON::XS | 20661.596 | 9541.183 |
JSON::XS/2 | 10683.403 | 9416.938 |
JSON::XS/3 | 20661.596 | 9400.054 |
Storable | 19765.806 | 10000.725 |
--------------+------------+------------+
Again, JSON::XS leads by far (except for Storable which non-surprisingly
decodes a bit faster).
On large strings containing lots of high Unicode characters, some
modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
result will be broken due to missing (or wrong) Unicode handling. Others
refuse to decode or encode properly, so it was impossible to prepare a
fair comparison table for that case.
SECURITY CONSIDERATIONS
When you are using JSON in a protocol, talking to untrusted potentially
hostile creatures requires relatively few measures.
First of all, your JSON decoder should be secure, that is, should not
have any buffer overflows. Obviously, this module should ensure that and
I am trying hard on making that true, but you never know.
Second, you need to avoid resource-starving attacks. That means you
should limit the size of JSON texts you accept, or make sure then when
your resources run out, that's just fine (e.g. by using a separate
process that can crash safely). The size of a JSON text in octets or
characters is usually a good indication of the size of the resources
required to decode it into a Perl structure. While JSON::XS can check
the size of the JSON text, it might be too late when you already have it
in memory, so you might want to check the size before you accept the
string.
Third, JSON::XS recurses using the C stack when decoding objects and
arrays. The C stack is a limited resource: for instance, on my amd64
machine with 8MB of stack size I can decode around 180k nested arrays
but only 14k nested JSON objects (due to perl itself recursing deeply on
croak to free the temporary). If that is exceeded, the program crashes.
To be conservative, the default nesting limit is set to 512. If your
process has a smaller stack, you should adjust this setting accordingly
with the "max_depth" method.
Something else could bomb you, too, that I forgot to think of. In that
case, you get to keep the pieces. I am always open for hints, though...
Also keep in mind that JSON::XS might leak contents of your Perl data
structures in its error messages, so when you serialise sensitive
information you might want to make sure that exceptions thrown by
JSON::XS will not end up in front of untrusted eyes.
If you are using JSON::XS to return packets to consumption by JavaScript
scripts in a browser you should have a look at
<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
to see whether you are vulnerable to some common attack vectors (which
really are browser design bugs, but it is still you who will have to
deal with it, as major browser developers care only for features, not
about getting security right).
"OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)
TL;DR: Due to security concerns, JSON::XS will not allow scalar data in
JSON texts by default - you need to create your own JSON::XS object and
enable "allow_nonref":
my $json = JSON::XS->new->allow_nonref;
$text = $json->encode ($data);
$data = $json->decode ($text);
The long version: JSON being an important and supposedly stable format,
the IETF standardised it as RFC 4627 in 2006. Unfortunately, the
inventor of JSON, Dougles Crockford, unilaterally changed the definition
of JSON in javascript. Rather than create a fork, the IETF decided to
standardise the new syntax (apparently, so Iw as told, without finding
it very amusing).
The biggest difference between thed original JSON and the new JSON is
that the new JSON supports scalars (anything other than arrays and
objects) at the toplevel of a JSON text. While this is strictly
backwards compatible to older versions, it breaks a number of protocols
that relied on sending JSON back-to-back, and is a minor security
concern.
For example, imagine you have two banks communicating, and on one side,
trhe JSON coder gets upgraded. Two messages, such as 10 and 1000 might
then be confused to mean 101000, something that couldn't happen in the
original JSON, because niether of these messages would be valid JSON.
If one side accepts these messages, then an upgrade in the coder on
either side could result in this becoming exploitable.
This module has always allowed these messages as an optional extension,
by default disabled. The security concerns are the reason why the
default is still disabled, but future versions might/will likely upgrade
to the newer RFC as default format, so you are advised to check your
implementation and/or override the default with "->allow_nonref (0)" to
ensure that future versions are safe.
INTEROPERABILITY WITH OTHER MODULES
"JSON::XS" uses the Types::Serialiser module to provide boolean
constants. That means that the JSON true and false values will be
comaptible to true and false values of other modules that do the same,
such as JSON::PP and CBOR::XS.
INTEROPERABILITY WITH OTHER JSON DECODERS
As long as you only serialise data that can be directly expressed in
JSON, "JSON::XS" is incapable of generating invalid JSON output (modulo
bugs, but "JSON::XS" has found more bugs in the official JSON testsuite
(1) than the official JSON testsuite has found in "JSON::XS" (0)).
When you have trouble decoding JSON generated by this module using other
decoders, then it is very likely that you have an encoding mismatch or
the other decoder is broken.
When decoding, "JSON::XS" is strict by default and will likely catch all
errors. There are currently two settings that change this: "relaxed"
makes "JSON::XS" accept (but not generate) some non-standard extensions,
and "allow_tags" will allow you to encode and decode Perl objects, at
the cost of not outputting valid JSON anymore.
TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
When you use "allow_tags" to use the extended (and also nonstandard and
invalid) JSON syntax for serialised objects, and you still want to
decode the generated When you want to serialise objects, you can run a
regex to replace the tagged syntax by standard JSON arrays (it only
works for "normal" package names without comma, newlines or single
colons). First, the readable Perl version:
# if your FREEZE methods return no values, you need this replace first:
$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
# this works for non-empty constructor arg lists:
$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
And here is a less readable version that is easy to adapt to other
languages:
$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
Here is an ECMAScript version (same regex):
json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
Since this syntax converts to standard JSON arrays, it might be hard to
distinguish serialised objects from normal arrays. You can prepend a
"magic number" as first array element to reduce chances of a collision:
$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
And after decoding the JSON text, you could walk the data structure
looking for arrays with a first element of
"XU1peReLzT4ggEllLanBYq4G9VzliwKF".
The same approach can be used to create the tagged format with another
encoder. First, you create an array with the magic string as first
member, the classname as second, and constructor arguments last, encode
it as part of your JSON structure, and then:
$json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
Again, this has some limitations - the magic string must not be encoded
with character escapes, and the constructor arguments must be non-empty.
RFC7159
Since this module was written, Google has written a new JSON RFC, RFC
7159 (and RFC7158). Unfortunately, this RFC breaks compatibility with
both the original JSON specification on www.json.org and RFC4627.
As far as I can see, you can get partial compatibility when parsing by
using "->allow_nonref". However, consider the security implications of
doing so.
I haven't decided yet when to break compatibility with RFC4627 by
default (and potentially leave applications insecure) and change the
default to follow RFC7159, but application authors are well advised to
call "->allow_nonref(0)" even if this is the current default, if they
cannot handle non-reference values, in preparation for the day when the
default will change.
(I-)THREADS
This module is *not* guaranteed to be ithread (or MULTIPLICITY-) safe
and there are no plans to change this. Note that perl's builtin
so-called theeads/ithreads are officially deprecated and should not be
used.
THE PERILS OF SETLOCALE
Sometimes people avoid the Perl locale support and directly call the
system's setlocale function with "LC_ALL".
This breaks both perl and modules such as JSON::XS, as stringification
of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
on perl to stringify numbers).
The solution is simple: don't call "setlocale", or use it for only those
categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
If you need "LC_NUMERIC", you should enable it only around the code that
actually needs it (avoiding stringification of numbers), and restore it
afterwards.
BUGS
While the goal of this module is to be correct, that unfortunately does
not mean it's bug-free, only that I think its design is bug-free. If you
keep reporting bugs they will be fixed swiftly, though.
Please refrain from using rt.cpan.org or any other bug reporting
service. I put the contact address into my modules for a reason.
SEE ALSO
The json_xs command line utility for quick experiments.
AUTHOR
Marc Lehmann <schmorp@schmorp.de>
http://home.schmorp.de/
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