Provided by: libcpanel-json-xs-perl_3.0210-1ubuntu1_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.
- different handling of inf/nan. Default now to null, optionally with
-DSTRINGIFY_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.
- 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 now
to true, not 1.
- 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
- 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.
- 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
- support many more options and methods from JSON::PP
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.
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" }
$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" or "nan" for numeric values.
"null": infnan_mode = 0. Similar to most JSON modules in other languages.
stringified: infnan_mode = 1. As in Mojo::JSON.
inf/nan: infnan_mode = 2. As in JSON::XS, and older releases. Produces invalid
JSON.
$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")
=> ([], 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 :).
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.
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
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.
SECURITY CONSIDERATIONS
JSON::XS is 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.
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@cpanel.net>, http://cpanel.net/
MAINTAINER
Reini Urban <rurban@cpanel.net>