Provided by: libcpanel-json-xs-perl_3.0239-1_amd64 
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.
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 stay 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
- 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
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)
Except being faster.
$perl_scalar = decode_json $json_text [, $allow_nonref ]
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)
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 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".
$is_boolean = Cpanel::JSON::XS::is_bool $scalar
Returns true if the passed scalar represents either "JSON::XS::true" or "JSON::XS::false", two
constants that act like 1 and 0, respectively and are used to represent JSON "true" and "false"
values in Perl.
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. 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.
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.
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 = $json->space_before ([$enable])
$enabled = $json->get_space_before
If $enable is true (or missing), then the "encode" method will add an extra optional space before the
":" separating keys from values in JSON objects.
If $enable is false, then the "encode" method will not add any extra space at those places.
This setting has no effect when decoding JSON texts. You will also most likely combine this setting
with "space_after".
Example, space_before enabled, space_after and indent disabled:
{"key" :"value"}
$json = $json->space_after ([$enable])
$enabled = $json->get_space_after
If $enable is true (or missing), then the "encode" method will add an extra optional space after the
":" separating keys from values in JSON objects and extra whitespace after the "," separating key-
value pairs and array members.
If $enable is false, then the "encode" method will not add any extra space at those places.
This setting has no effect when decoding JSON texts.
Example, space_before and indent disabled, space_after enabled:
{"key": "value"}
$json = $json->relaxed ([$enable])
$enabled = $json->get_relaxed
If $enable is true (or missing), then "decode" will accept some extensions to normal JSON syntax (see
below). "encode" will not be affected in anyway. Be aware that this option makes you accept invalid
JSON texts as if they were valid!. I suggest only to use this option to parse application-specific
files written by humans (configuration files, resource files etc.)
If $enable is false (the default), then "decode" will only accept valid JSON texts.
Currently accepted extensions are:
• list items can have an end-comma
JSON separates array elements and key-value pairs with commas. This can be annoying if you write
JSON texts manually and want to be able to quickly append elements, so this extension accepts
comma at the end of such items not just between them:
[
1,
2, <- this comma not normally allowed
]
{
"k1": "v1",
"k2": "v2", <- this comma not normally allowed
}
• shell-style '#'-comments
Whenever JSON allows whitespace, shell-style comments are additionally allowed. They are
terminated by the first carriage-return or line-feed character, after which more white-space and
comments are allowed.
[
1, # this comment not allowed in JSON
# neither this one...
]
• literal ASCII TAB characters in strings
Literal ASCII TAB characters are now allowed in strings (and treated as "\t") 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
]
• allow_singlequote
Single quotes are accepted instead of double quotes. See the "allow_singlequote" option.
{ "foo":'bar' }
{ 'foo':"bar" }
{ 'foo':'bar' }
• allow_barekey
Accept unquoted object keys instead of with mandatory double quotes. See the "allow_barekey"
option.
{ foo:"bar" }
• duplicate keys
With relaxed decoding of duplicate keys does not error and are silently accepted. See
<http://seriot.ch/parsing_json.php#24>: RFC 7159 section 4: "The names within an object should be
unique."
$json = $json->canonical ([$enable])
$enabled = $json->get_canonical
If $enable is true (or missing), then the "encode" method will output JSON objects by sorting their
keys. This is adding a comparatively high overhead.
If $enable is false, then the "encode" method will output key-value pairs in the order Perl stores
them (which will likely change between runs of the same script, and can change even within the same
run from 5.18 onwards).
This option is useful if you want the same data structure to be encoded as the same JSON text (given
the same overall settings). If it is disabled, the same hash might be encoded differently even if
contains the same data, as key-value pairs have no inherent ordering in Perl.
This setting has no effect when decoding JSON texts.
This setting has currently no effect on tied hashes.
$json = $json->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 = $json->allow_singlequote ([$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.
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 = $json->allow_blessed ([$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.
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 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)
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.
$perl_scalar = $json->decode ($json_text)
The opposite of "encode": expects a JSON text and tries to parse it, returning the resulting simple
scalar or reference. Croaks on error.
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".
($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 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, "<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.
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.
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
These JSON atoms become "Cpanel::JSON::XS::true" and "Cpanel::JSON::XS::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".
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::true, Cpanel::JSON::XS::true] # yields [false,true]
encode_json [!1, !0] # yields [false,true]
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, 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
}
2. "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 };
3. "allow_blessed" is enabled.
The object will be serialized as a JSON null value.
4. 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.
Unicode non-characters between U+FFFD and U+10FFFF are decoded either to the recommended U+FFFD
REPLACEMENT CHARACTER (see Unicode PR #121: Recommended Practice for Replacement Characters), or in the
binary or relaxed mode left as is, keeping the illegal non-characters as before.
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.
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/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.
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've setup a
tracker at RT, 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://rt.cpan.org/Public/Dist/Display.html?Queue=Cpanel-JSON-XS>
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, JSON::XS, JSON::MaybeXS, Mojo::JSON, Mojo::JSON::MaybeXS, JSON::SL, JSON::DWIW, JSON::YAJL,
JSON::Any, Test::JSON, Locale::Wolowitz, <https://metacpan.org/search?q=JSON>
<https://tools.ietf.org/html/rfc7159>
<https://tools.ietf.org/html/rfc4627>
AUTHOR
Marc Lehmann <schmorp@schmorp.de>, http://home.schmorp.de/
Reini Urban <rurban@cpan.org>
MAINTAINER
Reini Urban <rurban@cpan.org>