path: root/README

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
      2.93

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  data structure to a JSON text as of RFC4627 (which we know is
  obsolete but we still stick to; see below for an option to support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.