man > Cpanel::JSON::XS

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📖 NAME

Cpanel::JSON::XS – cPanel fork of JSON::XS, fast and correct serializing

🚀 Quick Reference

Use Case	Command	Description
🌐 Encode Perl to JSON (UTF-8)	`encode_json $perl_scalar`	Functional interface, returns UTF-8 binary string
🌐 Decode JSON to Perl	`decode_json $json_text`	Functional interface, expects UTF-8 binary string
🔧 OO Encoding with options	`$json = Cpanel::JSON::XS->new->utf8->pretty->encode($ref)`	Chainable, full control over encoding
🔧 OO Decoding	`$json->decode($unicode_json_text)`	Decode any Unicode string
📋 Pretty-print	`$json->pretty->encode($ref)`	Human-readable indented output
🔤 ASCII-only output	`$json->ascii->encode($ref)`	Escapes non-ASCII characters
🔓 Relaxed parsing	`$json->relaxed->decode($text)`	Accepts comments, trailing commas, single quotes
✅ Boolean check	`Cpanel::JSON::XS::is_bool($scalar)`	Returns true if scalar is JSON boolean
🛡️ Secure decoding	`$json->max_depth(512)->max_size(100000)`	Limit nesting and input size

📋 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

✅ 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.
🔄 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.
🔍 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 serializers 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.

🍴 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

stricter decode_json() as documented. non-refs are disallowed. 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
additional fixes for:
- [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.
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/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, 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 – has been renamed to decode_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.

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.
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.
The internal utf-8 flag has no meaning with regards to the encoding of your string.
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.
A string containing “high” (> 255) character values is not a UTF-8 string.
Unicode noncharacters only warn, as in core. The 66 Unicode noncharacters U+FDD0..U+FDEF, and U+*FFFE, U+*FFFF just warn, see http://www.unicode.org/versions/corrigendum9.html. But illegal surrogate pairs fail to parse.
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.

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. 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.

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. The main use for this flag is to avoid the smart unicode detection and possible double encoding. 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. 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. 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
💬 shell-style ‘#’-comments
📋 literal ASCII TAB characters in strings
📋 allow_singlequote
📋 allow_barekey
📋 allow_dupkeys

See the respective options for details. $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). 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. $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 ✅ If $enable is true (or missing), then “decode” will return Perl non-object boolean variables (1 and 0) 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 🔓 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 🔓 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 🔢 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. 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

$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 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 🔤 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 🔤 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/parsing_json.php#24: RFC 7159 section 4: “The names within an object should be unique.” $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. $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__” => }” into the corresponding $WIDGET{} 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. $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 can then 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 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 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, "