XS(3) User Contributed Perl Documentation XS(3)
NAME
Cpanel::JSON::XS - cPanel fork of JSON::XS, fast and correct
serializing
SYNOPSIS
use Cpanel::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 = Cpanel::JSON::XS->new->ascii->pretty->allow_nonref;
$pretty_printed_unencoded = $coder->encode ($perl_scalar);
$perl_scalar = $coder->decode ($unicode_json_text);
# Note that 5.6 misses most smart utf8 and encoding functionalities
# of newer releases.
# Note that L<JSON::MaybeXS> will automatically use Cpanel::JSON::XS
# if available, at virtually no speed overhead either, so you should
# be able to just:
use JSON::MaybeXS;
# and do the same things, except that you have a pure-perl fallback now.
Note that this module will be replaced by a new JSON::Safe module soon,
with the same API just guaranteed safe defaults.
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.
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 below for the cPanel fork.
See MAPPING, below, on how Cpanel::JSON::XS maps perl values to JSON
values and vice versa.
FEATURES
o correct Unicode handling
This module knows how to handle Unicode with Perl version higher
than 5.8.5, documents how and when it does so, and even documents
what "correct" means.
o round-trip integrity
When you serialize a perl data structure using only data types
supported by JSON and Perl, the deserialized 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.
o 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.
o fast
Compared to other JSON modules and other serializers such as
Storable, this module usually compares favourably in terms of
speed, too.
o simple to use
This module has both a simple functional interface as well as an
object oriented interface.
o 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.
cPanel fork
Since the original author MLEHMANN has no public bugtracker, this
cPanel fork sits now on github.
src repo: <https://github.com/rurban/Cpanel-JSON-XS> original:
<http://cvs.schmorp.de/JSON-XS/>
RT: <https://github.com/rurban/Cpanel-JSON-XS/issues> or
<https://rt.cpan.org/Public/Dist/Display.html?Queue=Cpanel-JSON-XS>
Changes to JSON::XS
- bare hashkeys are now checked for utf8. (GH #209)
- stricter decode_json() as documented. non-refs are disallowed.
safe by default.
added a 2nd optional argument. decode() honors now allow_nonref.
- fixed encode of numbers for dual-vars. Different string
representations are preserved, but numbers with temporary strings
which represent the same number are here treated as numbers, not
strings. Cpanel::JSON::XS is a bit slower, but preserves numeric
types better.
- numbers ending with .0 stray numbers, are not converted to
integers. [#63] dual-vars which are represented as number not
integer (42+"bar" != 5.8.9) are now encoded as number (=> 42.0)
because internally it's now a NOK type. However !!1 which is
wrongly encoded in 5.8 as "1"/1.0 is still represented as integer.
- different handling of inf/nan. Default now to null, optionally with
stringify_infnan() to "inf"/"nan". [#28, #32]
- added "binary" extension, non-JSON and non JSON parsable, allows
"\xNN" and "\NNN" sequences.
- 5.6.2 support; sacrificing some utf8 features (assuming bytes
all-over), no multi-byte unicode characters with 5.6.
- interop for true/false overloading. JSON::XS, JSON::PP and Mojo::JSON
representations for booleans are accepted and JSON::XS accepts
Cpanel::JSON::XS booleans [#13, #37]
Fixed overloading of booleans. Cpanel::JSON::XS::true stringifies
again
to "1", not "true", analog to all other JSON modules.
- native boolean mapping of yes and no to true and false, as in
YAML::XS.
In perl "!0" is yes, "!1" is no.
The JSON value true maps to 1, false maps to 0. [#39]
- support arbitrary stringification with encode, with convert_blessed
and allow_blessed.
- ithread support. Cpanel::JSON::XS is thread-safe, JSON::XS not
- is_bool can be called as method, JSON::XS::is_bool not.
- performance optimizations for threaded Perls
- relaxed mode, allowing many popular extensions
- protect our magic object from corruption by wrong or missing external
methods, like FREEZE/THAW or serialization with other methods.
- additional fixes for:
- #208 - no security-relevant out-of-bounds reading of module memory
when decoding hash keys without ending ':'
- [cpan #88061] AIX atof without USE_LONG_DOUBLE
- #10 unshare_hek crash
- #7, #29 avoid re-blessing where possible. It fails in JSON::XS for
READONLY values, i.e. restricted hashes.
- #41 overloading of booleans, use the object not the reference.
- #62 -Dusequadmath conversion and no SEGV.
- #72 parsing of values followed \0, like 1\0 does fail.
- #72 parsing of illegal unicode or non-unicode characters.
- #96 locale-insensitive numeric conversion.
- #154 numeric conversion fixed since 5.22, using the same strtold as perl5.
- #167 sort tied hashes with canonical.
- #212 fix utf8 object stringification
- public maintenance and bugtracker
- use ppport.h, sanify XS.xs comment styles, harness C coding style
- common::sense is optional. When available it is not used in the
published production module, just during development and testing.
- extended testsuite, passes all
http://seriot.ch/projects/parsing_json.html
tests. In fact it is the only know JSON decoder which does so,
while also being the fastest.
- support many more options and methods from JSON::PP:
stringify_infnan, allow_unknown, allow_stringify, allow_barekey,
encode_stringify, allow_bignum, allow_singlequote,
dupkeys_as_arrayref,
sort_by (partially), escape_slash, convert_blessed, ...
optional decode_json(, allow_nonref) arg.
relaxed implements allow_dupkeys.
- support all 5 unicode BOM's: UTF-8, UTF-16LE, UTF-16BE, UTF-32LE,
UTF-32BE, encoding internally to UTF-8.
FUNCTIONAL INTERFACE
The following convenience methods are provided by this module. They are
exported by default:
$json_text = encode_json $perl_scalar, [json_type]
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:
$json_text = Cpanel::JSON::XS->new->utf8->encode ($perl_scalar, $json_type)
Except being faster.
For the type argument see Cpanel::JSON::XS::Type.
$perl_scalar = decode_json $json_text [, $allow_nonref [, my $json_type
] ] The opposite of "encode_json": expects an UTF-8 (binary) string of
an json reference 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:
$perl_scalar = Cpanel::JSON::XS->new->utf8->decode ($json_text, $json_type)
except being faster.
Note that older decode_json versions in Cpanel::JSON::XS older than
3.0116 and JSON::XS did not set allow_nonref but allowed them due
to a bug in the decoder.
If the new 2nd optional $allow_nonref argument is set and not
false, the "allow_nonref" option will be set and the function will
act is described as in the relaxed RFC 7159 allowing all values
such as objects, arrays, strings, numbers, "null", "true", and
"false". See ""OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)" below,
why you don't want to do that.
For the 3rd optional type argument see Cpanel::JSON::XS::Type.
$is_boolean = Cpanel::JSON::XS::is_bool $scalar
Returns true if the passed scalar represents either
"JSON::PP::true" or "JSON::PP::false", two constants that act like
1 and 0, respectively and are used to represent JSON "true" and
"false" values in Perl. (Also recognizes the booleans produced by
JSON::XS.)
See MAPPING, below, for more information on how JSON values are
mapped to Perl.
DEPRECATED FUNCTIONS
from_json
from_json has been renamed to decode_json
to_json
to_json has been renamed to encode_json
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.
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.
6. Raw non-Unicode characters below U+10FFFF are allowed.
The 66 Unicode noncharacters U+FDD0..U+FDEF, and U+*FFFE, U+*FFFF
are allowed without warning, as JSON::PP does, see
<http://www.unicode.org/versions/corrigendum9.html>. But illegal
surrogate pairs fail to parse.
7. Raw non-Unicode characters above U+10FFFF are disallowed.
Raw non-Unicode characters outside the valid unicode range fail to
parse, because "A string is a sequence of zero or more Unicode
characters" RFC 7159 section 1 and "JSON text SHALL be encoded in
Unicode RFC 7159 section 8.1. We use now the UTF8_DISALLOW_SUPER
flag when parsing unicode.
8. Lone surrogates or illegal surrogate pairs are disallowed.
Since RFC 3629, U+D800 through U+DFFF are not legal Unicode values
and their UTF-8 encodings must be treated as an invalid byte
sequence. RFC 8259 section 8.2 admits the spec allows string
values that contain bit sequences that cannot encode Unicode
characters and that the behavior of software that receives such
values is unpredictable. To avoid introducing non-Unicode strings
into Perl we use the UTF8_DISALLOW_SURROGATE flag when parsing
Unicode and verify escaped surrogates form valid pairs.
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 Cpanel::JSON::XS
Creates a new JSON 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 = Cpanel::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.
Cpanel::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.
Cpanel::JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
$json = $json->binary ([$enable])
$enabled = $json = $json->get_binary
If the $enable argument is true (or missing), then the "encode"
method will not try to detect an UTF-8 encoding in any JSON string,
it will strictly interpret it as byte sequence. The result might
contain new "\xNN" sequences, which is unparsable JSON. The
"decode" method forbids "\uNNNN" sequences and accepts "\xNN" and
octal "\NNN" sequences.
There is also a special logic for perl 5.6 and utf8. 5.6 encodes
any string to utf-8 automatically when seeing a codepoint >= 0x80
and < 0x100. With the binary flag enabled decode the perl utf8
encoded string to the original byte encoding and encode this with
"\xNN" escapes. This will result to the same encodings as with
newer perls. But note that binary multi-byte codepoints with 5.6
will result in "illegal unicode character in binary string" errors,
unlike with newer perls.
If $enable is false, then the "encode" method will smartly try to
detect Unicode characters unless required by the JSON syntax or
other flags and hex and octal sequences are forbidden.
See also the section ENCODING/CODESET FLAG NOTES later in this
document.
The main use for this flag is to avoid the smart unicode detection
and possible double encoding. The disadvantage is that the
resulting JSON text is encoded in new "\xNN" and in latin1
characters and must correctly be treated as such when storing and
transferring, a rare encoding for JSON. It will produce
non-readable JSON strings in the browser. 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. The binary decoding method can also
be used when an encoder produced a non-JSON conformant hex or octal
encoding "\xNN" or "\NNN".
Cpanel::JSON::XS->new->binary->encode (["\x{89}\x{abc}"])
5.6: Error: malformed or illegal unicode character in binary string
>=5.8: ['\x89\xe0\xaa\xbc']
Cpanel::JSON::XS->new->binary->encode (["\x{89}\x{bc}"])
=> ["\x89\xbc"]
Cpanel::JSON::XS->new->binary->decode (["\x89\ua001"])
Error: malformed or illegal unicode character in binary string
Cpanel::JSON::XS->new->decode (["\x89"])
Error: illegal hex character in non-binary string
$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;
$jsontext = encode "UTF-16BE", Cpanel::JSON::XS->new->encode ($object);
Example, decode UTF-32LE-encoded JSON:
use Encode;
$object = Cpanel::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 = Cpanel::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 = $json->indent_length([$number_of_spaces])
$length = $json->get_indent_length()
Set the indent length (default 3). This option is only useful when
you also enable indent or pretty. The acceptable range is from 0
(no indentation) to 15
$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:
o 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
}
o 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...
]
o literal ASCII TAB characters in strings
Literal ASCII TAB characters are now allowed in strings (and
treated as "\t") in relaxed mode. Despite JSON mandates, that
TAB character is substituted for "\t" sequence.
[
"Hello\tWorld",
"Hello<TAB>World", # literal <TAB> would not normally be allowed
]
o allow_singlequote
Single quotes are accepted instead of double quotes. See the
"allow_singlequote" option.
{ "foo":'bar' }
{ 'foo':"bar" }
{ 'foo':'bar' }
o allow_barekey
Accept unquoted object keys instead of with mandatory double
quotes. See the "allow_barekey" option.
{ foo:"bar" }
o allow_dupkeys
Allow decoding of duplicate keys in hashes. By default
duplicate keys are forbidden. See
<http://seriot.ch/projects/parsing_json.php#24>: RFC 7159
section 4: "The names within an object should be unique." See
the "allow_dupkeys" option.
$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 is now also done with tied hashes, contrary to JSON::XS. But
note that with most large tied hashes stored as tree it is advised
to sort the iterator already and don't sort the hash output here.
Most such iterators are already sorted, as such e.g. DB_File with
"DB_BTREE".
$json = $json->sort_by (undef, 0, 1 or a block)
This currently only (un)sets the "canonical" option, and ignores
custom sort blocks.
This setting has no effect when decoding JSON texts.
This setting has currently no effect on tied hashes.
$json = $json->escape_slash ([$enable])
$enabled = $json->get_escape_slash
According to the JSON Grammar, the forward slash character (U+002F)
"/" need to be escaped. But by default strings are encoded without
escaping slashes in all perl JSON encoders.
If $enable is true (or missing), then "encode" will escape slashes,
"\/".
This setting has no effect when decoding JSON texts.
$json = $json->unblessed_bool ([$enable])
$enabled = $json->get_unblessed_bool
$json = $json->unblessed_bool([$enable])
If $enable is true (or missing), then "decode" will return Perl
non-object boolean variables (1 and 0 as numbers or "1" and "" as
strings) for JSON booleans ("true" and "false"). If $enable is
false, then "decode" will return "JSON::PP::Boolean" objects for
JSON booleans.
$json = $json->allow_singlequote ([$enable])
$enabled = $json->get_allow_singlequote
$json = $json->allow_singlequote([$enable])
If $enable is true (or missing), then "decode" will accept JSON
strings quoted by single quotations that are invalid JSON format.
$json->allow_singlequote->decode({"foo":'bar'});
$json->allow_singlequote->decode({'foo':"bar"});
$json->allow_singlequote->decode({'foo':'bar'});
This is also enabled with "relaxed". As same as the "relaxed"
option, this option may be used to parse application-specific files
written by humans.
$json = $json->allow_barekey ([$enable])
$enabled = $json->get_allow_barekey
$json = $json->allow_barekey([$enable])
If $enable is true (or missing), then "decode" will accept bare
keys of JSON object that are invalid JSON format.
Same as with the "relaxed" option, this option may be used to parse
application-specific files written by humans.
$json->allow_barekey->decode('{foo:"bar"}');
$json = $json->allow_bignum ([$enable])
$enabled = $json->get_allow_bignum
$json = $json->allow_bignum([$enable])
If $enable is true (or missing), then "decode" will convert the big
integer Perl cannot handle as integer into a Math::BigInt object
and convert a floating number (any) into a Math::BigFloat.
$int = $json->allow_nonref->allow_bignum->decode(1); # => 1
$bigint = $json->allow_bignum->decode('100000000000000000000000000000000000000');
$bigfloat = $json->allow_bignum->decode(1.0);
On the contrary, "encode" converts "Math::BigInt" objects and
"Math::BigFloat" objects into JSON numbers with "allow_blessed"
enable.
$json->allow_nonref->allow_blessed->allow_bignum;
$bigfloat = $json->decode('2.000000000000000000000000001');
print $json->encode($bigfloat);
# => 2.000000000000000000000000001
See "MAPPING" about the normal conversion of JSON number.
$json = $json->allow_bigint ([$enable])
This option is obsolete and replaced by allow_bignum.
$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:
Cpanel::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 = $json->allow_stringify ([$enable])
$enabled = $json->get_allow_stringify
If $enable is true (or missing), then "encode" will stringify the
non-object perl value or reference. Note that blessed objects are
not included here and are handled separately by "allow_blessed" and
"convert_blessed". String references are stringified to the string
value, other references as in perl.
This option does not affect "decode" in any way.
This option is special to this module, it is not supported by other
encoders. So it is not recommended to use it.
$json = $json->require_types ([$enable])
$enable = $json->get_require_types
$json = $json->require_types([$enable])
If $enable is true (or missing), then "encode" will require either
enabled "type_all_string" or second argument with supplied JSON
types. See Cpanel::JSON::XS::Type. When "type_all_string" is not
enabled or second argument is not provided (or is undef), then
"encode" croaks. It also croaks when the type for provided
structure in "encode" is incomplete.
$json = $json->type_all_string ([$enable])
$enable = $json->get_type_all_string
$json = $json->type_all_string([$enable])
If $enable is true (or missing), then "encode" will always produce
stable deterministic JSON string types in resulted output.
When $enable is false, then result of encoded JSON output may be
different for different Perl versions and may depends on loaded
modules.
This is useful it you need deterministic JSON types, independently
of used Perl version and other modules, but do not want to write
complicated type definitions for Cpanel::JSON::XS::Type.
$json = $json->allow_dupkeys ([$enable])
$enabled = $json->get_allow_dupkeys
If $enable is true (or missing), then the "decode" method will not
die when it encounters duplicate keys in a hash. "allow_dupkeys"
is also enabled in the "relaxed" mode.
The JSON spec allows duplicate name in objects but recommends to
disable it, however with Perl hashes they are impossible, parsing
JSON in Perl silently ignores duplicate names, using the last value
found.
See <http://seriot.ch/projects/parsing_json.php#24>: RFC 7159
section 4: "The names within an object should be unique."
$json = $json->dupkeys_as_arrayref ([$enable])
$enabled = $json->get_dupkeys_as_arrayref
If enabled, allow decoding of duplicate keys in hashes and store
the values as arrayref in the hash instead. By default duplicate
keys are forbidden. Enabling this also enables the "allow_dupkeys"
option, but disabling this does not disable the "allow_dupkeys"
option.
Example:
$json->dupkeys_as_arrayref;
print encode_json ($json->decode ('{"a":"b","a":"c"}'));
=> {"a":["b","c"]}
This changes the result structure, thus cannot be enabled by
default. The client must be aware of it. The resulting arrayref is
not yet marked somehow (blessed or such).
$json = $json->allow_blessed ([$enable])
$enabled = $json->get_allow_blessed
If $enable is true (or missing), then the "encode" method will not
barf when it encounters a blessed reference. Instead, the value of
the convert_blessed option will decide whether "null"
("convert_blessed" disabled or no "TO_JSON" method found) or a
representation of the object ("convert_blessed" enabled and
"TO_JSON" method found) is being encoded. Has no effect on
"decode".
If $enable is false (the default), then "encode" will throw an
exception when it encounters a blessed object without
"convert_blessed" and a "TO_JSON" method.
This setting has no effect on "decode".
$json = $json->convert_blessed ([$enable])
$enabled = $json->get_convert_blessed
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. If no "TO_JSON" method is found, a stringification overload
method is tried next. If both are not found, the value of
"allow_blessed" will decide what to do.
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 same care must be taken with
calling encode in stringify overloads (even if this works by luck
in older perls) or other callbacks. 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->get_allow_tags
See "OBJECT SERIALIZATION" 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
serialize the object into a nonstandard tagged JSON value (that
JSON decoders cannot decode).
It also causes "decode" to parse such tagged JSON values and
deserialize 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 deserialized
data structure. If it returns an empty list (NOTE: not "undef",
which is a valid scalar), the original deserialized 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 deserialized hash in
any way.
Example, convert all JSON objects into the integer 5:
my $js = Cpanel::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 $coderef is omitted or undefined, the corresponding callback
will be disabled. There can only ever be one callback for a given
key.
As this callback gets called less often then the
"filter_json_object" one, decoding speed will not usually suffer as
much. Therefore, single-key objects make excellent targets to
serialize Perl objects into, especially as single-key JSON objects
are as close to the type-tagged value concept as JSON gets (it's
basically an ID/VALUE tuple). Of course, JSON does not support this
in any way, so you need to make sure your data never looks like a
serialized Perl hash.
Typical names for the single object key are "__class_whatever__",
or "$__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}:
Cpanel::JSON::XS
->new
->filter_json_single_key_object (__widget__ => sub {
$WIDGET{ $_[0] }
})
->decode ('{"__widget__": 5')
# this can be used with a TO_JSON method in some "widget" class
# for serialization to json:
sub WidgetBase::TO_JSON {
my ($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.
$json->stringify_infnan ([$infnan_mode = 1])
$infnan_mode = $json->get_stringify_infnan
Get or set how Cpanel::JSON::XS encodes "inf", "-inf" or "nan" for
numeric values. Also qnan, snan or negative nan on some platforms.
"null": infnan_mode = 0. Similar to most JSON modules in other
languages. Always null.
stringified: infnan_mode = 1. As in Mojo::JSON. Platform specific
strings. Stringified via sprintf(%g), with double quotes.
inf/nan: infnan_mode = 2. As in JSON::XS, and older releases.
Passes through platform dependent values, invalid JSON. Stringified
via sprintf(%g), but without double quotes.
"inf/-inf/nan": infnan_mode = 3. Platform independent inf/nan/-inf
strings. No QNAN/SNAN/negative NAN support, unified to "nan". Much
easier to detect, but may conflict with valid strings.
$json_text = $json->encode ($perl_scalar, $json_type)
Converts the given Perl data structure (a simple scalar or a
reference to a hash or array) to its JSON representation. Simple
scalars will be converted into JSON string or number sequences,
while references to arrays become JSON arrays and references to
hashes become JSON objects. Undefined Perl values (e.g. "undef")
become JSON "null" values. Neither "true" nor "false" values will
be generated.
For the type argument see Cpanel::JSON::XS::Type.
$perl_scalar = $json->decode ($json_text, my $json_type)
The opposite of "encode": expects a JSON text and tries to parse
it, returning the resulting simple scalar or reference. Croaks on
error.
JSON numbers and strings become simple Perl scalars. JSON arrays
become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
becomes 1, "false" becomes 0 and "null" becomes "undef".
For the type argument see Cpanel::JSON::XS::Type.
($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.
Cpanel::JSON::XS->new->decode_prefix ("[1] the tail")
=> ([1], 3)
$json->to_json ($perl_hash_or_arrayref)
Deprecated method for perl 5.8 and newer. Use encode_json instead.
$json->from_json ($utf8_encoded_json_text)
Deprecated method for perl 5.8 and newer. Use decode_json instead.
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).
Cpanel::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 of 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
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 = Cpanel::JSON::XS->new->incr_parse ("[5][7][1,2]");
$lvalue_string = $json->incr_text (>5.8 only)
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, and 2. only with Perl >= 5.8
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.
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 Cpanel::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 Cpanel::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 Cpanel::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 Cpanel::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
Cpanel::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 Cpanel::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 :).
BOM
Detect all unicode Byte Order Marks on decode. Which are UTF-8,
UTF-16LE, UTF-16BE, UTF-32LE and UTF-32BE.
The BOM encoding is set only for one specific decode call, it does not
change the state of the JSON object.
Warning: With perls older than 5.20 you need load the Encode module
before loading a multibyte BOM, i.e. >= UTF-16. Otherwise an error is
thrown. This is an implementation limitation and might get fixed later.
See <https://tools.ietf.org/html/rfc7159#section-8.1> "JSON text SHALL
be encoded in UTF-8, UTF-16, or UTF-32."
"Implementations MUST NOT add a byte order mark to the beginning of a
JSON text", "implementations (...) MAY ignore the presence of a byte
order mark rather than treating it as an error".
See also <http://www.unicode.org/faq/utf_bom.html#BOM>.
Beware that Cpanel::JSON::XS is currently the only JSON module which
does accept and decode a BOM.
The latest JSON spec
<https://www.greenbytes.de/tech/webdav/rfc8259.html#character.encoding>
forbid the usage of UTF-16 or UTF-32, the character encoding is UTF-8.
Thus in subsequent updates BOM's of UTF-16 or UTF-32 will throw an
error.
MAPPING
This section describes how Cpanel::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, Cpanel::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, "Cpanel::JSON::XS" only
guarantees precision up to but not including the least significant
bit.
true, false
When "unblessed_bool" is set to true, then JSON "true" becomes 1
and JSON "false" becomes 0.
Otherwise these JSON atoms become "JSON::PP::true" and
"JSON::PP::false", respectively. They are "JSON::PP::Boolean"
objects and 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 "Cpanel::JSON::XS::is_bool" function.
The other round, from perl to JSON, "!0" which is represented as
"yes" becomes "true", and "!1" which is represented as "no" becomes
"false".
Via Cpanel::JSON::XS::Type you can now even force negation in
"encode", without overloading of "!":
my $false = Cpanel::JSON::XS::false;
print($json->encode([!$false], [JSON_TYPE_BOOL]));
=> [true]
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 SERIALIZATION", 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 that can change between runs of
the same program but stays generally the same within a single run
of a program. Cpanel::JSON::XS can optionally sort the hash keys
(determined by the canonical flag), so the same datastructure will
serialize to the same JSON text (given same settings and version of
Cpanel::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.
With the option "allow_stringify", you can ignore the exception and
return the stringification of the perl value.
With the option "allow_unknown", you can ignore the exception and
return "null" instead.
encode_json [\"x"] # => cannot encode reference to scalar 'SCALAR(0x..)'
# unless the scalar is 0 or 1
encode_json [\0, \1] # yields [false,true]
allow_stringify->encode_json [\"x"] # yields "x" unlike JSON::PP
allow_unknown->encode_json [\"x"] # yields null as in JSON::PP
Cpanel::JSON::XS::true, Cpanel::JSON::XS::false
These special values become JSON true and JSON false values,
respectively. You can also use "\1" and "\0" or "!0" and "!1"
directly if you want.
encode_json [Cpanel::JSON::XS::false, Cpanel::JSON::XS::true] # yields [false,true]
encode_json [!1, !0], [JSON_TYPE_BOOL, JSON_TYPE_BOOL] # yields [false,true]
eq/ne comparisons with true, false:
false is eq to the empty string or the string 'false' or the
special empty string "!!0" or "!1", i.e. "SV_NO", or the numbers 0
or 0.0.
true is eq to the string 'true' or to the special string "!0" (i.e.
"SV_YES") or to the numbers 1 or 1.0.
blessed objects
Blessed objects are not directly representable in JSON, but
"Cpanel::JSON::XS" allows various optional ways of handling
objects. See "OBJECT SERIALIZATION", below, for details.
See the "allow_blessed" and "convert_blessed" methods on various
options on how to deal with this: basically, you can choose between
throwing an exception, encoding the reference as if it weren't
blessed, use the objects overloaded stringification method or
provide your own serializer method.
simple scalars
Simple Perl scalars (any scalar that is not a reference) are the
most difficult objects to encode: Cpanel::JSON::XS will encode
undefined scalars or inf/nan as JSON "null" values and other
scalars to either number or string in non-deterministic way which
may be affected or changed by Perl version or any other loaded Perl
module.
If you want to have stable and deterministic types in JSON encoder
then use Cpanel::JSON::XS::Type.
Alternative way for deterministic types is to use "type_all_string"
method when all perl scalars are encoded to JSON strings.
Non-deterministic behavior is following: 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, but the two representations are for the same number
print $value;
encode_json [$value] # yields [5]
# used as different string (non-matching dual-var)
my $str = '0 but true';
my $num = 1 + $str;
encode_json [$num, $str] # yields [1,"0 but true"]
# undef becomes null
encode_json [undef] # yields [null]
# inf or nan becomes null, unless you answered
# "Do you want to handle inf/nan as strings" with yes
encode_json [9**9**9] # 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
$x *= 1; # same thing, the choice is yours.
Note that numerical precision has the same meaning as under Perl
(so binary to decimal conversion follows the same rules as in Perl,
which can differ to other languages). Also, your perl interpreter
might expose extensions to the floating point numbers of your
platform, such as infinities or NaN's - these cannot be represented
in JSON, and thus null is returned instead. Optionally you can
configure it to stringify inf and nan values.
OBJECT SERIALIZATION
As JSON cannot directly represent Perl objects, you have to choose
between a pure JSON representation (without the ability to deserialize
the object automatically again), and a nonstandard extension to the
JSON syntax, tagged values.
SERIALIZATION
What happens when "Cpanel::JSON::XS" encounters a Perl object depends
on the "allow_blessed", "convert_blessed" and "allow_tags" settings,
which are used in this order:
1. "allow_tags" is enabled and the object has a "FREEZE" method.
In this case, "Cpanel::JSON::XS" uses the Types::Serialiser object
serialization protocol to create a tagged JSON value, using a
nonstandard extension to the JSON syntax.
This works by invoking the "FREEZE" method on the object, with the
first argument being the object to serialize, and the second
argument being the constant string "JSON" to distinguish it from
other serializers.
The "FREEZE" method can return any number of values (i.e. zero or
more). These values and the paclkage/classname of the object will
then be encoded as a tagged JSON value in the following format:
("classname")[FREEZE return values...]
e.g.:
("URI")["http://www.google.com/"]
("MyDate")[2013,10,29]
("ImageData::JPEG")["Z3...VlCg=="]
For example, the hypothetical "My::Object" "FREEZE" method might
use the objects "type" and "id" members to encode the object:
sub My::Object::FREEZE {
my ($self, $serializer) = @_;
($self->{type}, $self->{id})
}
2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
In this case, the "TO_JSON" method of the object is invoked in
scalar context. It must return a single scalar that can be directly
encoded into JSON. This scalar replaces the object in the JSON
text.
For example, the following "TO_JSON" method will convert all URI
objects to JSON strings when serialized. The fact that these values
originally were URI objects is lost.
sub URI::TO_JSON {
my ($uri) = @_;
$uri->as_string
}
3. "convert_blessed" is enabled and the object has a stringification
overload.
In this case, the overloaded "" 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 "" method will convert all URI objects
to JSON strings when serialized. The fact that these values
originally were URI objects is lost.
package URI;
use overload '""' => sub { shift->as_string };
4. "allow_blessed" is enabled.
The object will be serialized as a JSON null value.
5. none of the above
If none of the settings are enabled or the respective methods are
missing, "Cpanel::JSON::XS" throws an exception.
DESERIALIZATION
For deserialization there are only two cases to consider: either
nonstandard tagging was used, in which case "allow_tags" decides, or
objects cannot be automatically be deserialized, 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, "Cpanel::JSON::XS" will look up the "THAW"
method of the package/classname used during serialization (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, $serializer, $type, $id) = @_;
$class->new (type => $type, id => $id)
}
See the "SECURITY CONSIDERATIONS" section below. Allowing external json
objects being deserialized to perl objects is usually a very bad idea.
ENCODING/CODESET FLAG NOTES
The interested reader might have seen a number of flags that signify
encodings or codesets - "utf8", "latin1", "binary" 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", "binary" 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. With
"binary" enabled, ordinal values > 255 are illegal.
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", "binary" 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" or "binary" 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-standardized 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 Cpanel::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 Cpanel::JSON::XS;
print Cpanel::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 = Cpanel::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.
Raw non-Unicode characters outside the valid unicode range fail now to
parse, because "A string is a sequence of zero or more Unicode
characters" RFC 7159 section 1 and "JSON text SHALL be encoded in
Unicode RFC 7159 section 8.1. We use now the UTF8_DISALLOW_SUPER flag
when parsing unicode.
Since RFC 3629, U+D800 through U+DFFF are not legal Unicode values and
their UTF-8 encodings must be treated as an invalid byte sequence. RFC
8259 section 8.2 admits the spec allows string values that contain bit
sequences that cannot encode Unicode characters and that the behavior
of software that receives such values is unpredictable. To avoid
introducing non-Unicode strings into Perl we use the
UTF8_DISALLOW_SURROGATE flag when parsing Unicode and verify escaped
surrogates form valid pairs.
If you know of other incompatibilities, please let me know.
JSON and YAML
You often hear that JSON is a subset of YAML. 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 Cpanel::JSON::XS to
generate YAML, you should use this algorithm (subject to change in
future versions):
my $to_yaml = Cpanel::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.
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.
JSON::XS is with Data::MessagePack and Sereal one of the fastest
serializers, because JSON and JSON::XS do not support backrefs (no
graph structures), only trees. Storable supports backrefs, i.e. graphs.
Data::MessagePack encodes its data binary (as Storable) and supports
only very simple subset of JSON.
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 Cpanel::JSON::XS/2 uses the OO interface
with pretty-printing and hash key sorting enabled, Cpanel::JSON::XS/3
enables shrink. JSON::DWIW/DS uses the deserialize 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.
For updated graphs see
<https://github.com/Sereal/Sereal/wiki/Sereal-Comparison-Graphs>
INTEROP with JSON and JSON::XS and other JSON modules
As long as you only serialize data that can be directly expressed in
JSON, "Cpanel::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)). "Cpanel::JSON::XS" is currently the only known JSON decoder
which passes all <http://seriot.ch/projects/parsing_json.html> tests,
while being the fastest also.
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" or "allow_blessed" will allow you to
encode and decode Perl objects, at the cost of being totally insecure
and not outputting valid JSON anymore.
JSON-XS-3.01 broke interoperability with JSON-2.90 with booleans. See
JSON.
Cpanel::JSON::XS needs to know the JSON and JSON::XS versions to be
able work with those objects, especially when encoding a booleans like
"{"is_true":true}". So you need to load these modules before.
true/false overloading and boolean representations are supported.
JSON::XS and JSON::PP representations are accepted and older JSON::XS
accepts Cpanel::JSON::XS booleans. All JSON modules JSON, JSON, PP,
JSON::XS, Cpanel::JSON::XS produce JSON::PP::Boolean objects, just Mojo
and JSON::YAJL not. Mojo produces Mojo::JSON::_Bool and
JSON::YAJL::Parser just an unblessed IV.
Cpanel::JSON::XS accepts JSON::PP::Boolean and Mojo::JSON::_Bool
objects as booleans.
I cannot think of any reason to still use JSON::XS 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 serialized objects, and you still want to
decode the generated serialize 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 serialized 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.
SECURITY CONSIDERATIONS
JSON::XS and Cpanel::JSON::XS are not only fast. JSON is generally the
most secure serializing format, because it is the only one besides
Data::MessagePack, which does not deserialize objects per default. For
all languages, not just perl. The binary variant BSON (MongoDB) does
more but is unsafe.
It is trivial for any attacker to create such serialized objects in
JSON and trick perl into expanding them, thereby triggering certain
methods. Watch <https://www.youtube.com/watch?v=Gzx6KlqiIZE> for an
exploit demo for "CVE-2015-1592 SixApart MovableType Storable Perl Code
Execution" for a deserializer which expands objects. Deserializing
even coderefs (methods, functions) or external data would be considered
the most dangerous.
Security relevant overview of serializers regarding deserializing
objects by default:
Objects Coderefs External Data
Data::Dumper YES YES YES
Storable YES NO (def) NO
Sereal YES NO NO
YAML YES NO NO
B::C YES YES YES
B::Bytecode YES YES YES
BSON YES YES NO
JSON::SL YES NO YES
JSON NO (def) NO NO
Data::MessagePack NO NO NO
XML NO NO YES
Pickle YES YES YES
PHP Deserialize YES NO NO
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.
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, Cpanel::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.
Also keep in mind that Cpanel::JSON::XS might leak contents of your
Perl data structures in its error messages, so when you serialize
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 Cpanel::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). You might also want to also look at
Mojo::JSON special escape rules to prevent from XSS attacks.
"OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)
TL;DR: Due to security concerns, Cpanel::JSON::XS will not allow scalar
data in JSON texts by default - you need to create your own
Cpanel::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 standardized it as RFC 4627 in 2006. Unfortunately the
inventor of JSON Douglas Crockford unilaterally changed the definition
of JSON in javascript. Rather than create a fork, the IETF decided to
standardize the new syntax (apparently, so I as told, without finding
it very amusing).
The biggest difference between the original JSON and the new JSON is
that the new JSON supports scalars (anything other than arrays and
objects) at the top-level 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,
the 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 neither 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.
THREADS
Cpanel::JSON::XS has proper ithreads support, unlike JSON::XS. If you
encounter any bugs with thread support please report them.
From Version 4.00 - 4.19 you couldn't encode true with threads::shared
magic.
BUGS
While the goal of the Cpanel::JSON::XS module is to be correct, that
unfortunately does not mean it's bug-free, only that the author thinks
its design is bug-free. If you keep reporting bugs and tests they will
be fixed swiftly, though.
Since the JSON::XS author refuses to use a public bugtracker and
prefers private emails, we use the tracker at github, so you might want
to report any issues twice. Once in private to MLEHMANN to be fixed in
JSON::XS and one to our the public tracker. Issues fixed by JSON::XS
with a new release will also be backported to Cpanel::JSON::XS and
5.6.2, as long as cPanel relies on 5.6.2 and Cpanel::JSON::XS as our
serializer of choice.
<https://github.com/rurban/Cpanel-JSON-XS/issues>
LICENSE
This module is available under the same licences as perl, the Artistic
license and the GPL.
SEE ALSO
The cpanel_json_xs command line utility for quick experiments.
JSON::PP(3), JSON(3), JSON::XS(3), JSON::MaybeXS(3), Mojo::JSON(3),
Mojo::JSON::MaybeXS(3), JSON::SL(3), JSON::DWIW(3), JSON::YAJL(3),
JSON::Any(3), Test::JSON(3), Locale::Wolowitz(3),
<https://metacpan.org/search?q=JSON>
<https://tools.ietf.org/html/rfc7159>
<https://tools.ietf.org/html/rfc4627>
AUTHOR
Reini Urban <rurban@cpan.org>
Marc Lehmann <schmorp@schmorp.de>, http://home.schmorp.de/
MAINTAINER
Reini Urban <rurban@cpan.org>
perl v5.34.3 2024-12-21 XS(3)
cpanel-json-xs 4.390.0 - Generated Sat Dec 21 10:37:45 CST 2024