Provided by: libjson-perl_2.97001-1_all 
NAME
JSON - JSON (JavaScript Object Notation) encoder/decoder
SYNOPSIS
use JSON; # imports encode_json, decode_json, to_json and from_json.
# simple and fast interfaces (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
$json = JSON->new->allow_nonref;
$json_text = $json->encode( $perl_scalar );
$perl_scalar = $json->decode( $json_text );
$pretty_printed = $json->pretty->encode( $perl_scalar ); # pretty-printing
VERSION
2.97001
DESCRIPTION
This module is a thin wrapper for JSON::XS-compatible modules with a few additional features. All the
backend modules convert a Perl data structure to a JSON text as of RFC4627 (which we know is obsolete but
we still stick to; see below for an option to support part of RFC7159) and vice versa. This module uses
JSON::XS by default, and when JSON::XS is not available, this module falls back on JSON::PP, which is in
the Perl core since 5.14. If JSON::PP is not available either, this module then falls back on
JSON::backportPP (which is actually JSON::PP in a different .pm file) bundled in the same distribution as
this module. You can also explicitly specify to use Cpanel::JSON::XS, a fork of JSON::XS by Reini Urban.
All these backend modules have slight incompatibilities between them, including extra features that other
modules don't support, but as long as you use only common features (most important ones are described
below), migration from backend to backend should be reasonably easy. For details, see each backend module
you use.
CHOOSING BACKEND
This module respects an environmental variable called "PERL_JSON_BACKEND" when it decides a backend
module to use. If this environmental variable is not set, it tries to load JSON::XS, and if JSON::XS is
not available, it falls back on JSON::PP, and then JSON::backportPP if JSON::PP is not available either.
If you always don't want it to fall back on pure perl modules, set the variable like this ("export" may
be "setenv", "set" and the likes, depending on your environment):
> export PERL_JSON_BACKEND=JSON::XS
If you prefer Cpanel::JSON::XS to JSON::XS, then:
> export PERL_JSON_BACKEND=Cpanel::JSON::XS,JSON::XS,JSON::PP
You may also want to set this variable at the top of your test files, in order not to be bothered with
incompatibilities between backends (you need to wrap this in "BEGIN", and set before actually "use"-ing
JSON module, as it decides its backend as soon as it's loaded):
BEGIN { $ENV{PERL_JSON_BACKEND}='JSON::backportPP'; }
use JSON;
USING OPTIONAL FEATURES
There are a few options you can set when you "use" this module:
-support_by_pp
BEGIN { $ENV{PERL_JSON_BACKEND} = 'JSON::XS' }
use JSON -support_by_pp;
my $json = JSON->new;
# escape_slash is for JSON::PP only.
$json->allow_nonref->escape_slash->encode("/");
With this option, this module loads its pure perl backend along with its XS backend (if available),
and lets the XS backend to watch if you set a flag only JSON::PP supports. When you do, the internal
JSON::XS object is replaced with a newly created JSON::PP object with the setting copied from the XS
object, so that you can use JSON::PP flags (and its slower "decode"/"encode" methods) from then on.
In other words, this is not something that allows you to hook JSON::XS to change its behavior while
keeping its speed. JSON::XS and JSON::PP objects are quite different (JSON::XS object is a blessed
scalar reference, while JSON::PP object is a blessed hash reference), and can't share their
internals.
To avoid needless overhead (by copying settings), you are advised not to use this option and just to
use JSON::PP explicitly when you need JSON::PP features.
-convert_blessed_universally
use JSON -convert_blessed_universally;
my $json = JSON->new->allow_nonref->convert_blessed;
my $object = bless {foo => 'bar'}, 'Foo';
$json->encode($object); # => {"foo":"bar"}
JSON::XS-compatible backend modules don't encode blessed objects by default (except for their boolean
values, which are typically blessed JSON::PP::Boolean objects). If you need to encode a data
structure that may contain objects, you usually need to look into the structure and replace objects
with alternative non-blessed values, or enable "convert_blessed" and provide a "TO_JSON" method for
each object's (base) class that may be found in the structure, in order to let the methods replace
the objects with whatever scalar values the methods return.
If you need to serialise data structures that may contain arbitrary objects, it's probably better to
use other serialisers (such as Sereal or Storable for example), but if you do want to use this module
for that purpose, "-convert_blessed_universally" option may help, which tweaks "encode" method of the
backend to install "UNIVERSAL::TO_JSON" method (locally) before encoding, so that all the objects
that don't have their own "TO_JSON" method can fall back on the method in the "UNIVERSAL" namespace.
Note that you still need to enable "convert_blessed" flag to actually encode objects in a data
structure, and "UNIVERSAL::TO_JSON" method installed by this option only converts blessed hash/array
references into their unblessed clone (including private keys/values that are not supposed to be
exposed). Other blessed references will be converted into null.
This feature is experimental and may be removed in the future.
-no_export
When you don't want to import functional interfaces from a module, you usually supply "()" to its
"use" statement.
use JSON (); # no functional interfaces
If you don't want to import functional interfaces, but you also want to use any of the above options,
add "-no_export" to the option list.
# no functional interfaces, while JSON::PP support is enabled.
use JSON -support_by_pp, -no_export;
FUNCTIONAL INTERFACE
This section is taken from JSON::XS. "encode_json" and "decode_json" are exported by default.
This module also exports "to_json" and "from_json" for backward compatibility. These are slower, and may
expect/generate different stuff from what "encode_json" and "decode_json" do, depending on their options.
It's better just to use Object-Oriented interfaces than using these two functions.
encode_json
$json_text = encode_json $perl_scalar
Converts the given Perl data structure to a UTF-8 encoded, binary string (that is, the string contains
octets only). Croaks on error.
This function call is functionally identical to:
$json_text = JSON->new->utf8->encode($perl_scalar)
Except being faster.
decode_json
$perl_scalar = decode_json $json_text
The opposite of "encode_json": expects an UTF-8 (binary) string and tries to parse that as an UTF-8
encoded JSON text, returning the resulting reference. Croaks on error.
This function call is functionally identical to:
$perl_scalar = JSON->new->utf8->decode($json_text)
Except being faster.
to_json
$json_text = to_json($perl_scalar[, $optional_hashref])
Converts the given Perl data structure to a Unicode string by default. Croaks on error.
Basically, this function call is functionally identical to:
$json_text = JSON->new->encode($perl_scalar)
Except being slower.
You can pass an optional hash reference to modify its behavior, but that may change what "to_json"
expects/generates (see "ENCODING/CODESET FLAG NOTES" for details).
$json_text = to_json($perl_scalar, {utf8 => 1, pretty => 1})
# => JSON->new->utf8(1)->pretty(1)->encode($perl_scalar)
from_json
$perl_scalar = from_json($json_text[, $optional_hashref])
The opposite of "to_json": expects a Unicode string and tries to parse it, returning the resulting
reference. Croaks on error.
Basically, this function call is functionally identical to:
$perl_scalar = JSON->new->decode($json_text)
You can pass an optional hash reference to modify its behavior, but that may change what "from_json"
expects/generates (see "ENCODING/CODESET FLAG NOTES" for details).
$perl_scalar = from_json($json_text, {utf8 => 1})
# => JSON->new->utf8(1)->decode($json_text)
JSON::is_bool
$is_boolean = JSON::is_bool($scalar)
Returns true if the passed scalar represents either JSON::true or JSON::false, two constants that act
like 1 and 0 respectively and are also used to represent JSON "true" and "false" in Perl strings.
See MAPPING, below, for more information on how JSON values are mapped to Perl.
COMMON OBJECT-ORIENTED INTERFACE
This section is also taken from JSON::XS.
The object oriented interface lets you configure your own encoding or decoding style, within the limits
of supported formats.
new
$json = JSON->new
Creates a new JSON::XS-compatible backend 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 backend object again and thus calls can be chained:
my $json = JSON->new->utf8->space_after->encode({a => [1,2]})
=> {"a": [1, 2]}
ascii
$json = $json->ascii([$enable])
$enabled = $json->get_ascii
If $enable is true (or missing), then the "encode" method will not generate characters outside the code
range 0..127 (which is ASCII). Any Unicode characters outside that range will be escaped using either a
single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627. The resulting
encoded JSON text can be treated as a native Unicode string, an ascii-encoded, latin1-encoded or UTF-8
encoded string, or any other superset of ASCII.
If $enable is false, then the "encode" method will not escape Unicode characters unless required by the
JSON syntax or other flags. This results in a faster and more compact format.
See also the section ENCODING/CODESET FLAG NOTES later in this document.
The main use for this flag is to produce JSON texts that can be transmitted over a 7-bit channel, as the
encoded JSON texts will not contain any 8 bit characters.
JSON->new->ascii(1)->encode([chr 0x10401])
=> ["\ud801\udc01"]
latin1
$json = $json->latin1([$enable])
$enabled = $json->get_latin1
If $enable is true (or missing), then the "encode" method will encode the resulting JSON text as latin1
(or iso-8859-1), escaping any characters outside the code range 0..255. The resulting string can be
treated as a latin1-encoded JSON text or a native Unicode string. The "decode" method will not be
affected in any way by this flag, as "decode" by default expects Unicode, which is a strict superset of
latin1.
If $enable is false, then the "encode" method will not escape Unicode characters unless required by the
JSON syntax or other flags.
See also the section ENCODING/CODESET FLAG NOTES later in this document.
The main use for this flag is efficiently encoding binary data as JSON text, as most octets will not be
escaped, resulting in a smaller encoded size. The disadvantage is that the resulting JSON text is encoded
in latin1 (and must correctly be treated as such when storing and transferring), a rare encoding for
JSON. It is therefore most useful when you want to store data structures known to contain binary data
efficiently in files or databases, not when talking to other JSON encoders/decoders.
JSON->new->latin1->encode (["\x{89}\x{abc}"]
=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
utf8
$json = $json->utf8([$enable])
$enabled = $json->get_utf8
If $enable is true (or missing), then the "encode" method will encode the JSON result into UTF-8, as
required by many protocols, while the "decode" method expects to be handled an UTF-8-encoded string.
Please note that UTF-8-encoded strings do not contain any characters outside the range 0..255, they are
thus useful for bytewise/binary I/O. In future versions, enabling this option might enable autodetection
of the UTF-16 and UTF-32 encoding families, as described in RFC4627.
If $enable is false, then the "encode" method will return the JSON string as a (non-encoded) Unicode
string, while "decode" expects thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16)
needs to be done yourself, e.g. using the Encode module.
See also the section ENCODING/CODESET FLAG NOTES later in this document.
Example, output UTF-16BE-encoded JSON:
use Encode;
$jsontext = encode "UTF-16BE", JSON->new->encode ($object);
Example, decode UTF-32LE-encoded JSON:
use Encode;
$object = JSON->new->decode (decode "UTF-32LE", $jsontext);
pretty
$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.
indent
$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.
space_before
$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"}
space_after
$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"}
relaxed
$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...
]
canonical
$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.
allow_nonref
$json = $json->allow_nonref([$enable])
$enabled = $json->get_allow_nonref
If $enable is true (or missing), then the "encode" method can convert a non-reference into its
corresponding string, number or null JSON value, which is an extension to RFC4627. Likewise, "decode"
will accept those JSON values instead of croaking.
If $enable is false, then the "encode" method will croak if it isn't passed an arrayref or hashref, as
JSON texts must either be an object or array. Likewise, "decode" will croak if given something that is
not a JSON object or array.
Example, encode a Perl scalar as JSON value with enabled "allow_nonref", resulting in an invalid JSON
text:
JSON->new->allow_nonref->encode ("Hello, World!")
=> "Hello, World!"
allow_unknown
$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.
allow_blessed
$json = $json->allow_blessed([$enable])
$enabled = $json->get_allow_blessed
See "OBJECT SERIALISATION" for details.
If $enable is true (or missing), then the "encode" method will not barf when it encounters a blessed
reference that it cannot convert otherwise. Instead, a JSON "null" value is encoded instead of the
object.
If $enable is false (the default), then "encode" will throw an exception when it encounters a blessed
object that it cannot convert otherwise.
This setting has no effect on "decode".
convert_blessed
$json = $json->convert_blessed([$enable])
$enabled = $json->get_convert_blessed
See "OBJECT SERIALISATION" for details.
If $enable is true (or missing), then "encode", upon encountering a blessed object, will check for the
availability of the "TO_JSON" method on the object's class. If found, it will be called in scalar context
and the resulting scalar will be encoded instead of the object.
The "TO_JSON" method may safely call die if it wants. If "TO_JSON" returns other blessed objects, those
will be handled in the same way. "TO_JSON" must take care of not causing an endless recursion cycle (==
crash) in this case. The name of "TO_JSON" was chosen because other methods called by the Perl core (==
not by the user of the object) are usually in upper case letters and to avoid collisions with any
"to_json" function or method.
If $enable is false (the default), then "encode" will not consider this type of conversion.
This setting has no effect on "decode".
filter_json_object
$json = $json->filter_json_object([$coderef])
When $coderef is specified, it will be called from "decode" each time it decodes a JSON object. The only
argument is a reference to the newly-created hash. If the code references returns a single scalar (which
need not be a reference), this value (i.e. a copy of that scalar to avoid aliasing) is inserted into the
deserialised data structure. If it returns an empty list (NOTE: not "undef", which is a valid scalar),
the original deserialised hash will be inserted. This setting can slow down decoding considerably.
When $coderef is omitted or undefined, any existing callback will be removed and "decode" will not change
the deserialised hash in any way.
Example, convert all JSON objects into the integer 5:
my $js = JSON->new->filter_json_object (sub { 5 });
# returns [5]
$js->decode ('[{}]'); # the given subroutine takes a hash reference.
# throw an exception because allow_nonref is not enabled
# so a lone 5 is not allowed.
$js->decode ('{"a":1, "b":2}');
filter_json_single_key_object
$json = $json->filter_json_single_key_object($key [=> $coderef])
Works remotely similar to "filter_json_object", but is only called for JSON objects having a single key
named $key.
This $coderef is called before the one specified via "filter_json_object", if any. It gets passed the
single value in the JSON object. If it returns a single value, it will be inserted into the data
structure. If it returns nothing (not even "undef" but the empty list), the callback from
"filter_json_object" will be called next, as if no single-key callback were specified.
If $coderef is omitted or undefined, the corresponding callback will be disabled. There can only ever be
one callback for a given key.
As this callback gets called less often then the "filter_json_object" one, decoding speed will not
usually suffer as much. Therefore, single-key objects make excellent targets to serialise Perl objects
into, especially as single-key JSON objects are as close to the type-tagged value concept as JSON gets
(it's basically an ID/VALUE tuple). Of course, JSON does not support this in any way, so you need to make
sure your data never looks like a serialised Perl hash.
Typical names for the single object key are "__class_whatever__", or "$__dollars_are_rarely_used__$" or
"}ugly_brace_placement", or even things like "__class_md5sum(classname)__", to reduce the risk of
clashing with real hashes.
Example, decode JSON objects of the form "{ "__widget__" => <id> }" into the corresponding $WIDGET{<id>}
object:
# return whatever is in $WIDGET{5}:
JSON
->new
->filter_json_single_key_object (__widget__ => sub {
$WIDGET{ $_[0] }
})
->decode ('{"__widget__": 5')
# this can be used with a TO_JSON method in some "widget" class
# for serialisation to json:
sub WidgetBase::TO_JSON {
my ($self) = @_;
unless ($self->{id}) {
$self->{id} = ..get..some..id..;
$WIDGET{$self->{id}} = $self;
}
{ __widget__ => $self->{id} }
}
max_depth
$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.
max_size
$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).
encode
$json_text = $json->encode($perl_scalar)
Converts the given Perl value or data structure to its JSON representation. Croaks on error.
decode
$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.
decode_prefix
($perl_scalar, $characters) = $json->decode_prefix($json_text)
This works like the "decode" method, but instead of raising an exception when there is trailing garbage
after the first JSON object, it will silently stop parsing there and return the number of characters
consumed so far.
This is useful if your JSON texts are not delimited by an outer protocol and you need to know where the
JSON text ends.
JSON->new->decode_prefix ("[1] the tail")
=> ([1], 3)
ADDITIONAL METHODS
The following methods are for this module only.
backend
$backend = $json->backend
Since 2.92, "backend" method returns an abstract backend module used currently, which should be
JSON::Backend::XS (which inherits JSON::XS or Cpanel::JSON::XS), or JSON::Backend::PP (which inherits
JSON::PP), not to monkey-patch the actual backend module globally.
If you need to know what is used actually, use "isa", instead of string comparison.
is_xs
$boolean = $json->is_xs
Returns true if the backend inherits JSON::XS or Cpanel::JSON::XS.
is_pp
$boolean = $json->is_pp
Returns true if the backend inherits JSON::PP.
property
$settings = $json->property()
Returns a reference to a hash that holds all the common flag settings.
$json = $json->property('utf8' => 1)
$value = $json->property('utf8') # 1
You can use this to get/set a value of a particular flag.
INCREMENTAL PARSING
This section is also taken from JSON::XS.
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).
This module 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.
incr_parse
$json->incr_parse( [$string] ) # void context
$obj_or_undef = $json->incr_parse( [$string] ) # scalar context
@obj_or_empty = $json->incr_parse( [$string] ) # list context
This is the central parsing function. It can both append new text and extract objects from the stream
accumulated so far (both of these functions are optional).
If $string is given, then this string is appended to the already existing JSON fragment stored in the
$json object.
After that, if the function is called in void context, it will simply return without doing anything
further. This can be used to add more text in as many chunks as you want.
If the method is called in scalar context, then it will try to extract exactly one JSON object. If that
is successful, it will return this object, otherwise it will return "undef". If there is a parse error,
this method will croak just as "decode" would do (one can then use "incr_skip" to skip the erroneous
part). This is the most common way of using the method.
And finally, in list context, it will try to extract as many objects from the stream as it can find and
return them, or the empty list otherwise. For this to work, there must be no separators (other than
whitespace) between the JSON objects or arrays, instead they must be concatenated back-to-back. If an
error occurs, an exception will be raised as in the scalar context case. Note that in this case, any
previously-parsed JSON texts will be lost.
Example: Parse some JSON arrays/objects in a given string and return them.
my @objs = JSON->new->incr_parse ("[5][7][1,2]");
incr_text
$lvalue_string = $json->incr_text
This method returns the currently stored JSON fragment as an lvalue, that is, you can manipulate it. This
only works when a preceding call to "incr_parse" in scalar context successfully returned an object. Under
all other circumstances you must not call this function (I mean it. although in simple tests it might
actually work, it will fail under real world conditions). As a special exception, you can also call this
method before having parsed anything.
That means you can only use this function to look at or manipulate text before or after complete JSON
objects, not while the parser is in the middle of parsing a JSON object.
This function is useful in two cases: a) finding the trailing text after a JSON object or b) parsing
multiple JSON objects separated by non-JSON text (such as commas).
incr_skip
$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.
incr_reset
$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.
MAPPING
Most of this section is also taken from JSON::XS.
This section describes how the backend modules map 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 preserver 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, this module 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, this module only guarantees
precision up to but not including the least significant bit.
true, false
These JSON atoms become "JSON::true" and "JSON::false", respectively. They are overloaded to act
almost exactly like the numbers 1 and 0. You can check whether a scalar is a JSON boolean by using
the "JSON::is_bool" function.
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.
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. This module can optionally sort the
hash keys (determined by the canonical flag), so the same data structure will serialise to the same
JSON text (given same settings and version of the same backend), 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. You
can also use "JSON::false" and "JSON::true" to improve readability.
encode_json [\0,JSON::true] # yields [false,true]
JSON::true, JSON::false, JSON::null
These special values become JSON true and JSON false values, respectively. You can also use "\1" and
"\0" directly if you want.
blessed objects
Blessed objects are not directly representable in JSON, but "JSON::XS" allows various ways of
handling objects. See "OBJECT SERIALISATION", below, for details.
simple scalars
Simple Perl scalars (any scalar that is not a reference) are the most difficult objects to encode:
this module will encode undefined scalars as JSON "null" values, scalars that have last been used in
a string context before encoding as JSON strings, and anything else as number value:
# dump as number
encode_json [2] # yields [2]
encode_json [-3.0e17] # yields [-3e+17]
my $value = 5; encode_json [$value] # yields [5]
# used as string, so dump as string
print $value;
encode_json [$value] # yields ["5"]
# undef becomes null
encode_json [undef] # yields [null]
You can force the type to be a 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 number by numifying it:
my $x = "3"; # some variable containing a string
$x += 0; # numify it, ensuring it will be dumped as a number
$x *= 1; # same thing, the choice is yours.
You can not currently force the type in other, less obscure, ways. Tell me if you need this
capability (but don't forget to explain why it's needed :).
Note that numerical precision has the same meaning as under Perl (so binary to decimal conversion
follows the same rules as in Perl, which can differ to other languages). Also, your perl interpreter
might expose extensions to the floating point numbers of your platform, such as infinities or NaN's -
these cannot be represented in JSON, and it is an error to pass those in.
OBJECT SERIALISATION
As for Perl objects, this module only supports a pure JSON representation (without the ability to
deserialise the object automatically again).
SERIALISATION
What happens when this module encounters a Perl object depends on the "allow_blessed" and
"convert_blessed" settings, which are used in this order:
1. "convert_blessed" is enabled and the object has a "TO_JSON" method.
In this case, the "TO_JSON" method of the object is invoked in scalar context. It must return a
single scalar that can be directly encoded into JSON. This scalar replaces the object in the JSON
text.
For example, the following "TO_JSON" method will convert all URI objects to JSON strings when
serialised. The fact that these values originally were URI objects is lost.
sub URI::TO_JSON {
my ($uri) = @_;
$uri->as_string
}
2. "allow_blessed" is enabled.
The object will be serialised as a JSON null value.
3. none of the above
If none of the settings are enabled or the respective methods are missing, this module throws an
exception.
ENCODING/CODESET FLAG NOTES
This section is taken from JSON::XS.
The interested reader might have seen a number of flags that signify encodings or codesets - "utf8",
"latin1" and "ascii". There seems to be some confusion on what these do, so here is a short comparison:
"utf8" controls whether the JSON text created by "encode" (and expected by "decode") is UTF-8 encoded or
not, while "latin1" and "ascii" only control whether "encode" escapes character values outside their
respective codeset range. Neither of these flags conflict with each other, although some combinations
make less sense than others.
Care has been taken to make all flags symmetrical with respect to "encode" and "decode", that is, texts
encoded with any combination of these flag values will be correctly decoded when the same flags are used
- in general, if you use different flag settings while encoding vs. when decoding you likely have a bug
somewhere.
Below comes a verbose discussion of these flags. Note that a "codeset" is simply an abstract set of
character-codepoint pairs, while an encoding takes those codepoint numbers and encodes them, in our case
into octets. Unicode is (among other things) a codeset, UTF-8 is an encoding, and ISO-8859-1 (= latin 1)
and ASCII are both codesets and encodings at the same time, which can be confusing.
"utf8" flag disabled
When "utf8" is disabled (the default), then "encode"/"decode" generate and expect Unicode strings,
that is, characters with high ordinal Unicode values (> 255) will be encoded as such characters, and
likewise such characters are decoded as-is, no changes to them will be done, except
"(re-)interpreting" them as Unicode codepoints or Unicode characters, respectively (to Perl, these
are the same thing in strings unless you do funny/weird/dumb stuff).
This is useful when you want to do the encoding yourself (e.g. when you want to have UTF-16 encoded
JSON texts) or when some other layer does the encoding for you (for example, when printing to a
terminal using a filehandle that transparently encodes to UTF-8 you certainly do NOT want to UTF-8
encode your data first and have Perl encode it another time).
"utf8" flag enabled
If the "utf8"-flag is enabled, "encode"/"decode" will encode all characters using the corresponding
UTF-8 multi-byte sequence, and will expect your input strings to be encoded as UTF-8, that is, no
"character" of the input string must have any value > 255, as UTF-8 does not allow that.
The "utf8" flag therefore switches between two modes: disabled means you will get a Unicode string in
Perl, enabled means you get an UTF-8 encoded octet/binary string in Perl.
"latin1" or "ascii" flags enabled
With "latin1" (or "ascii") enabled, "encode" will escape characters with ordinal values > 255 (> 127
with "ascii") and encode the remaining characters as specified by the "utf8" flag.
If "utf8" is disabled, then the result is also correctly encoded in those character sets (as both are
proper subsets of Unicode, meaning that a Unicode string with all character values < 256 is the same
thing as a ISO-8859-1 string, and a Unicode string with all character values < 128 is the same thing
as an ASCII string in Perl).
If "utf8" is enabled, you still get a correct UTF-8-encoded string, regardless of these flags, just
some more characters will be escaped using "\uXXXX" then before.
Note that ISO-8859-1-encoded strings are not compatible with UTF-8 encoding, while ASCII-encoded
strings are. That is because the ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
codeset being a subset of Unicode), while ASCII is.
Surprisingly, "decode" will ignore these flags and so treat all input values as governed by the
"utf8" flag. If it is disabled, this allows you to decode ISO-8859-1- and ASCII-encoded strings, as
both strict subsets of Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
So neither "latin1" nor "ascii" are incompatible with the "utf8" flag - they only govern when the
JSON output engine escapes a character or not.
The main use for "latin1" is to relatively efficiently store binary data as JSON, at the expense of
breaking compatibility with most JSON decoders.
The main use for "ascii" is to force the output to not contain characters with values > 127, which
means you can interpret the resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any
character set and 8-bit-encoding, and still get the same data structure back. This is useful when
your channel for JSON transfer is not 8-bit clean or the encoding might be mangled in between (e.g.
in mail), and works because ASCII is a proper subset of most 8-bit and multibyte encodings in use in
the world.
BACKWARD INCOMPATIBILITY
Since version 2.90, stringification (and string comparison) for "JSON::true" and "JSON::false" has not
been overloaded. It shouldn't matter as long as you treat them as boolean values, but a code that expects
they are stringified as "true" or "false" doesn't work as you have expected any more.
if (JSON::true eq 'true') { # now fails
print "The result is $JSON::true now."; # => The result is 1 now.
And now these boolean values don't inherit JSON::Boolean, either. When you need to test a value is a
JSON boolean value or not, use "JSON::is_bool" function, instead of testing the value inherits a
particular boolean class or not.
BUGS
Please report bugs on backend selection and additional features this module provides to RT or GitHub
issues for this module:
https://rt.cpan.org/Public/Dist/Display.html?Queue=JSON
https://github.com/makamaka/JSON/issues
Please report bugs and feature requests on decoding/encoding and boolean behaviors to the author of the
backend module you are using.
SEE ALSO
JSON::XS, Cpanel::JSON::XS, JSON::PP for backends.
JSON::MaybeXS, an alternative that prefers Cpanel::JSON::XS.
"RFC4627"(<http://www.ietf.org/rfc/rfc4627.txt>)
AUTHOR
Makamaka Hannyaharamitu, <makamaka[at]cpan.org>
JSON::XS was written by Marc Lehmann <schmorp[at]schmorp.de>
The release of this new version owes to the courtesy of Marc Lehmann.
COPYRIGHT AND LICENSE
Copyright 2005-2013 by Makamaka Hannyaharamitu
This library is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.
perl v5.26.1 2018-01-14 JSON(3pm)