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JSON(3)               User Contributed Perl Documentation              JSON(3)




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

           2.96


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       structure to a JSON text as of RFC4627 (which we know is obsolete but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:

       o   list items can have an end-comma

           JSON separates array elements and key-value pairs with commas. This
           can be annoying if you write JSON texts manually and want to be
           able to quickly append elements, so this extension accepts comma at
           the end of such items not just between them:

              [
                 1,
                 2, <- this comma not normally allowed
              ]
              {
                 "k1": "v1",
                 "k2": "v2", <- this comma not normally allowed
              }

       o   shell-style '#'-comments

           Whenever JSON allows whitespace, shell-style comments are
           additionally allowed. They are terminated by the first carriage-
           return or line-feed character, after which more white-space and
           comments are allowed.

             [
                1, # this comment not allowed in JSON
                   # neither this one...
             ]

   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(3), Cpanel::JSON::XS(3), JSON::PP(3) for backends.

       JSON::MaybeXS(3), an alternative that prefers Cpanel::JSON::XS(3).

       "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 v5.24.3                      2017-11-19                           JSON(3)

json 2.960.0 - Generated Tue Nov 21 07:57:28 CST 2017
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