NAME
    Cpanel::JSON::XS - cPanel fork of JSON::XS, fast and correct serializing

SYNOPSIS
     use Cpanel::JSON::XS;

     # exported functions, they croak on error
     # and expect/generate UTF-8

     $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
     $perl_hash_or_arrayref  = decode_json $utf8_encoded_json_text;

     # OO-interface

     $coder = Cpanel::JSON::XS->new->ascii->pretty->allow_nonref;
     $pretty_printed_unencoded = $coder->encode ($perl_scalar);
     $perl_scalar = $coder->decode ($unicode_json_text);

     # Note that 5.6 misses most smart utf8 and encoding functionalities
     # of newer releases.

     # Note that L<JSON::MaybeXS> will automatically use Cpanel::JSON::XS
     # if available, at virtually no speed overhead either, so you should
     # be able to just:

     use JSON::MaybeXS;

     # and do the same things, except that you have a pure-perl fallback now.

     Note that this module will be replaced by a new JSON::Safe module soon,
     with the same API just guaranteed safe defaults.

DESCRIPTION
    This module converts Perl data structures to JSON and vice versa. Its
    primary goal is to be *correct* and its secondary goal is to be *fast*.
    To reach the latter goal it was written in C.

    As this is the n-th-something JSON module on CPAN, what was the reason
    to write yet another JSON module? While it seems there are many JSON
    modules, none of them correctly handle all corner cases, and in most
    cases their maintainers are unresponsive, gone missing, or not listening
    to bug reports for other reasons.

    See below for the cPanel fork.

    See MAPPING, below, on how Cpanel::JSON::XS maps perl values to JSON
    values and vice versa.

  FEATURES
    *   correct Unicode handling

        This module knows how to handle Unicode with Perl version higher
        than 5.8.5, documents how and when it does so, and even documents
        what "correct" means.

    *   round-trip integrity

        When you serialize a perl data structure using only data types
        supported by JSON and Perl, the deserialized data structure is
        identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
        become "2" just because it looks like a number). There *are* minor
        exceptions to this, read the MAPPING section below to learn about
        those.

    *   strict checking of JSON correctness

        There is no guessing, no generating of illegal JSON texts by
        default, and only JSON is accepted as input by default. the latter
        is a security feature.

    *   fast

        Compared to other JSON modules and other serializers such as
        Storable, this module usually compares favourably in terms of speed,
        too.

    *   simple to use

        This module has both a simple functional interface as well as an
        object oriented interface.

    *   reasonably versatile output formats

        You can choose between the most compact guaranteed-single-line
        format possible (nice for simple line-based protocols), a pure-ASCII
        format (for when your transport is not 8-bit clean, still supports
        the whole Unicode range), or a pretty-printed format (for when you
        want to read that stuff). Or you can combine those features in
        whatever way you like.

  cPanel fork
    Since the original author MLEHMANN has no public bugtracker, this cPanel
    fork sits now on github.

    src repo: <https://github.com/rurban/Cpanel-JSON-XS> original:
    <http://cvs.schmorp.de/JSON-XS/>

    RT: <https://github.com/rurban/Cpanel-JSON-XS/issues> or
    <https://rt.cpan.org/Public/Dist/Display.html?Queue=Cpanel-JSON-XS>

    Changes to JSON::XS

    - stricter decode_json() as documented. non-refs are disallowed. added a
    2nd optional argument. decode() honors now allow_nonref.

    - fixed encode of numbers for dual-vars. Different string
    representations are preserved, but numbers with temporary strings which
    represent the same number are here treated as numbers, not strings.
    Cpanel::JSON::XS is a bit slower, but preserves numeric types better.

    - numbers ending with .0 stray numbers, are not converted to integers.
    [#63] dual-vars which are represented as number not integer (42+"bar" !=
    5.8.9) are now encoded as number (=> 42.0) because internally it's now a
    NOK type. However !!1 which is wrongly encoded in 5.8 as "1"/1.0 is
    still represented as integer.

    - different handling of inf/nan. Default now to null, optionally with
    stringify_infnan() to "inf"/"nan". [#28, #32]

    - added "binary" extension, non-JSON and non JSON parsable, allows
    "\xNN" and "\NNN" sequences.

    - 5.6.2 support; sacrificing some utf8 features (assuming bytes
    all-over), no multi-byte unicode characters with 5.6.

    - interop for true/false overloading. JSON::XS, JSON::PP and Mojo::JSON
    representations for booleans are accepted and JSON::XS accepts
    Cpanel::JSON::XS booleans [#13, #37] Fixed overloading of booleans.
    Cpanel::JSON::XS::true stringifies again to "1", not "true", analog to
    all other JSON modules.

    - native boolean mapping of yes and no to true and false, as in
    YAML::XS. In perl "!0" is yes, "!1" is no. The JSON value true maps to
    1, false maps to 0. [#39]

    - support arbitrary stringification with encode, with convert_blessed
    and allow_blessed.

    - ithread support. Cpanel::JSON::XS is thread-safe, JSON::XS not

    - is_bool can be called as method, JSON::XS::is_bool not.

    - performance optimizations for threaded Perls

    - relaxed mode, allowing many popular extensions

    - additional fixes for:

      - [cpan #88061] AIX atof without USE_LONG_DOUBLE

      - #10 unshare_hek crash

      - #7, #29 avoid re-blessing where possible. It fails in JSON::XS for
       READONLY values, i.e. restricted hashes.

      - #41 overloading of booleans, use the object not the reference.

      - #62 -Dusequadmath conversion and no SEGV.

      - #72 parsing of values followed \0, like 1\0 does fail.

      - #72 parsing of illegal unicode or non-unicode characters.

      - #96 locale-insensitive numeric conversion.

      - #154 numeric conversion fixed since 5.22, using the same strtold as perl5.

      - #167 sort tied hashes with canonical.

    - public maintenance and bugtracker

    - use ppport.h, sanify XS.xs comment styles, harness C coding style

    - common::sense is optional. When available it is not used in the
    published production module, just during development and testing.

    - extended testsuite, passes all http://seriot.ch/parsing_json.html
    tests. In fact it is the only know JSON decoder which does so, while
    also being the fastest.

    - support many more options and methods from JSON::PP: stringify_infnan,
    allow_unknown, allow_stringify, allow_barekey, encode_stringify,
    allow_bignum, allow_singlequote, sort_by (partially), escape_slash,
    convert_blessed, ... optional decode_json(, allow_nonref) arg. relaxed
    implements allow_dupkeys.

    - support all 5 unicode BOM's: UTF-8, UTF-16LE, UTF-16BE, UTF-32LE,
    UTF-32BE, encoding internally to UTF-8.

FUNCTIONAL INTERFACE
    The following convenience methods are provided by this module. They are
    exported by default:

    $json_text = encode_json $perl_scalar, [json_type]
        Converts the given Perl data structure to a UTF-8 encoded, binary
        string (that is, the string contains octets only). Croaks on error.

        This function call is functionally identical to:

           $json_text = Cpanel::JSON::XS->new->utf8->encode ($perl_scalar, $json_type)

        Except being faster.

        For the type argument see Cpanel::JSON::XS::Type.

    $perl_scalar = decode_json $json_text [, $allow_nonref [, my $json_type
    ] ]
        The opposite of "encode_json": expects an UTF-8 (binary) string of
        an json reference and tries to parse that as an UTF-8 encoded JSON
        text, returning the resulting reference. Croaks on error.

        This function call is functionally identical to:

           $perl_scalar = Cpanel::JSON::XS->new->utf8->decode ($json_text, $json_type)

        except being faster.

        Note that older decode_json versions in Cpanel::JSON::XS older than
        3.0116 and JSON::XS did not set allow_nonref but allowed them due to
        a bug in the decoder.

        If the new 2nd optional $allow_nonref argument is set and not false,
        the "allow_nonref" option will be set and the function will act is
        described as in the relaxed RFC 7159 allowing all values such as
        objects, arrays, strings, numbers, "null", "true", and "false". See
        ""OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)" below, why you don't
        want to do that.

        For the 3rd optional type argument see Cpanel::JSON::XS::Type.

    $is_boolean = Cpanel::JSON::XS::is_bool $scalar
        Returns true if the passed scalar represents either "JSON::PP::true"
        or "JSON::PP::false", two constants that act like 1 and 0,
        respectively and are used to represent JSON "true" and "false"
        values in Perl. (Also recognizes the booleans produced by JSON::XS.)

        See MAPPING, below, for more information on how JSON values are
        mapped to Perl.

DEPRECATED FUNCTIONS
    from_json
        from_json has been renamed to decode_json

    to_json
        to_json has been renamed to encode_json

A FEW NOTES ON UNICODE AND PERL
    Since this often leads to confusion, here are a few very clear words on
    how Unicode works in Perl, modulo bugs.

    1. Perl strings can store characters with ordinal values > 255.
        This enables you to store Unicode characters as single characters in
        a Perl string - very natural.

    2. Perl does *not* associate an encoding with your strings.
        ... until you force it to, e.g. when matching it against a regex, or
        printing the scalar to a file, in which case Perl either interprets
        your string as locale-encoded text, octets/binary, or as Unicode,
        depending on various settings. In no case is an encoding stored
        together with your data, it is *use* that decides encoding, not any
        magical meta data.

    3. The internal utf-8 flag has no meaning with regards to the encoding
    of your string.
    4. A "Unicode String" is simply a string where each character can be
    validly interpreted as a Unicode code point.
        If you have UTF-8 encoded data, it is no longer a Unicode string,
        but a Unicode string encoded in UTF-8, giving you a binary string.

    5. A string containing "high" (> 255) character values is *not* a UTF-8
    string.
    6. Unicode noncharacters only warn, as in core.
        The 66 Unicode noncharacters U+FDD0..U+FDEF, and U+*FFFE, U+*FFFF
        just warn, see <http://www.unicode.org/versions/corrigendum9.html>.
        But illegal surrogate pairs fail to parse.

    7. Raw non-Unicode characters above U+10FFFF are disallowed.
        Raw non-Unicode characters outside the valid unicode range fail to
        parse, because "A string is a sequence of zero or more Unicode
        characters" RFC 7159 section 1 and "JSON text SHALL be encoded in
        Unicode RFC 7159 section 8.1. We use now the UTF8_DISALLOW_SUPER
        flag when parsing unicode.

    I hope this helps :)

OBJECT-ORIENTED INTERFACE
    The object oriented interface lets you configure your own encoding or
    decoding style, within the limits of supported formats.

    $json = new Cpanel::JSON::XS
        Creates a new JSON object that can be used to de/encode JSON
        strings. All boolean flags described below are by default
        *disabled*.

        The mutators for flags all return the JSON object again and thus
        calls can be chained:

           my $json = Cpanel::JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
           => {"a": [1, 2]}

    $json = $json->ascii ([$enable])
    $enabled = $json->get_ascii
        If $enable is true (or missing), then the "encode" method will not
        generate characters outside the code range 0..127 (which is ASCII).
        Any Unicode characters outside that range will be escaped using
        either a single "\uXXXX" (BMP characters) or a double
        "\uHHHH\uLLLLL" escape sequence, as per RFC4627. The resulting
        encoded JSON text can be treated as a native Unicode string, an
        ascii-encoded, latin1-encoded or UTF-8 encoded string, or any other
        superset of ASCII.

        If $enable is false, then the "encode" method will not escape
        Unicode characters unless required by the JSON syntax or other
        flags. This results in a faster and more compact format.

        See also the section *ENCODING/CODESET FLAG NOTES* later in this
        document.

        The main use for this flag is to produce JSON texts that can be
        transmitted over a 7-bit channel, as the encoded JSON texts will not
        contain any 8 bit characters.

          Cpanel::JSON::XS->new->ascii (1)->encode ([chr 0x10401])
          => ["\ud801\udc01"]

    $json = $json->latin1 ([$enable])
    $enabled = $json->get_latin1
        If $enable is true (or missing), then the "encode" method will
        encode the resulting JSON text as latin1 (or ISO-8859-1), escaping
        any characters outside the code range 0..255. The resulting string
        can be treated as a latin1-encoded JSON text or a native Unicode
        string. The "decode" method will not be affected in any way by this
        flag, as "decode" by default expects Unicode, which is a strict
        superset of latin1.

        If $enable is false, then the "encode" method will not escape
        Unicode characters unless required by the JSON syntax or other
        flags.

        See also the section *ENCODING/CODESET FLAG NOTES* later in this
        document.

        The main use for this flag is efficiently encoding binary data as
        JSON text, as most octets will not be escaped, resulting in a
        smaller encoded size. The disadvantage is that the resulting JSON
        text is encoded in latin1 (and must correctly be treated as such
        when storing and transferring), a rare encoding for JSON. It is
        therefore most useful when you want to store data structures known
        to contain binary data efficiently in files or databases, not when
        talking to other JSON encoders/decoders.

          Cpanel::JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
          => ["\x{89}\\u0abc"]    # (perl syntax, U+abc escaped, U+89 not)

    $json = $json->binary ([$enable])
    $enabled = $json = $json->get_binary
        If the $enable argument is true (or missing), then the "encode"
        method will not try to detect an UTF-8 encoding in any JSON string,
        it will strictly interpret it as byte sequence. The result might
        contain new "\xNN" sequences, which is unparsable JSON. The "decode"
        method forbids "\uNNNN" sequences and accepts "\xNN" and octal
        "\NNN" sequences.

        There is also a special logic for perl 5.6 and utf8. 5.6 encodes any
        string to utf-8 automatically when seeing a codepoint >= 0x80 and <
        0x100. With the binary flag enabled decode the perl utf8 encoded
        string to the original byte encoding and encode this with "\xNN"
        escapes. This will result to the same encodings as with newer perls.
        But note that binary multi-byte codepoints with 5.6 will result in
        "illegal unicode character in binary string" errors, unlike with
        newer perls.

        If $enable is false, then the "encode" method will smartly try to
        detect Unicode characters unless required by the JSON syntax or
        other flags and hex and octal sequences are forbidden.

        See also the section *ENCODING/CODESET FLAG NOTES* later in this
        document.

        The main use for this flag is to avoid the smart unicode detection
        and possible double encoding. The disadvantage is that the resulting
        JSON text is encoded in new "\xNN" and in latin1 characters and must
        correctly be treated as such when storing and transferring, a rare
        encoding for JSON. It will produce non-readable JSON strings in the
        browser. It is therefore most useful when you want to store data
        structures known to contain binary data efficiently in files or
        databases, not when talking to other JSON encoders/decoders. The
        binary decoding method can also be used when an encoder produced a
        non-JSON conformant hex or octal encoding "\xNN" or "\NNN".

          Cpanel::JSON::XS->new->binary->encode (["\x{89}\x{abc}"])
          5.6:   Error: malformed or illegal unicode character in binary string
          >=5.8: ['\x89\xe0\xaa\xbc']

          Cpanel::JSON::XS->new->binary->encode (["\x{89}\x{bc}"])
          => ["\x89\xbc"]

          Cpanel::JSON::XS->new->binary->decode (["\x89\ua001"])
          Error: malformed or illegal unicode character in binary string

          Cpanel::JSON::XS->new->decode (["\x89"])
          Error: illegal hex character in non-binary string

    $json = $json->utf8 ([$enable])
    $enabled = $json->get_utf8
        If $enable is true (or missing), then the "encode" method will
        encode the JSON result into UTF-8, as required by many protocols,
        while the "decode" method expects to be handled an UTF-8-encoded
        string. Please note that UTF-8-encoded strings do not contain any
        characters outside the range 0..255, they are thus useful for
        bytewise/binary I/O. In future versions, enabling this option might
        enable autodetection of the UTF-16 and UTF-32 encoding families, as
        described in RFC4627.

        If $enable is false, then the "encode" method will return the JSON
        string as a (non-encoded) Unicode string, while "decode" expects
        thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
        UTF-16) needs to be done yourself, e.g. using the Encode module.

        See also the section *ENCODING/CODESET FLAG NOTES* later in this
        document.

        Example, output UTF-16BE-encoded JSON:

          use Encode;
          $jsontext = encode "UTF-16BE", Cpanel::JSON::XS->new->encode ($object);

        Example, decode UTF-32LE-encoded JSON:

          use Encode;
          $object = Cpanel::JSON::XS->new->decode (decode "UTF-32LE", $jsontext);

    $json = $json->pretty ([$enable])
        This enables (or disables) all of the "indent", "space_before" and
        "space_after" (and in the future possibly more) flags in one call to
        generate the most readable (or most compact) form possible.

        Example, pretty-print some simple structure:

           my $json = Cpanel::JSON::XS->new->pretty(1)->encode ({a => [1,2]})
           =>
           {
              "a" : [
                 1,
                 2
              ]
           }

    $json = $json->indent ([$enable])
    $enabled = $json->get_indent
        If $enable is true (or missing), then the "encode" method will use a
        multiline format as output, putting every array member or
        object/hash key-value pair into its own line, indenting them
        properly.

        If $enable is false, no newlines or indenting will be produced, and
        the resulting JSON text is guaranteed not to contain any "newlines".

        This setting has no effect when decoding JSON texts.

    $json = $json->indent_length([$number_of_spaces])
    $length = $json->get_indent_length()
        Set the indent length (default 3). This option is only useful when
        you also enable indent or pretty. The acceptable range is from 0 (no
        indentation) to 15

    $json = $json->space_before ([$enable])
    $enabled = $json->get_space_before
        If $enable is true (or missing), then the "encode" method will add
        an extra optional space before the ":" separating keys from values
        in JSON objects.

        If $enable is false, then the "encode" method will not add any extra
        space at those places.

        This setting has no effect when decoding JSON texts. You will also
        most likely combine this setting with "space_after".

        Example, space_before enabled, space_after and indent disabled:

           {"key" :"value"}

    $json = $json->space_after ([$enable])
    $enabled = $json->get_space_after
        If $enable is true (or missing), then the "encode" method will add
        an extra optional space after the ":" separating keys from values in
        JSON objects and extra whitespace after the "," separating key-value
        pairs and array members.

        If $enable is false, then the "encode" method will not add any extra
        space at those places.

        This setting has no effect when decoding JSON texts.

        Example, space_before and indent disabled, space_after enabled:

           {"key": "value"}

    $json = $json->relaxed ([$enable])
    $enabled = $json->get_relaxed
        If $enable is true (or missing), then "decode" will accept some
        extensions to normal JSON syntax (see below). "encode" will not be
        affected in anyway. *Be aware that this option makes you accept
        invalid JSON texts as if they were valid!*. I suggest only to use
        this option to parse application-specific files written by humans
        (configuration files, resource files etc.)

        If $enable is false (the default), then "decode" will only accept
        valid JSON texts.

        Currently accepted extensions are:

        *   list items can have an end-comma

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

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

        *   shell-style '#'-comments

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

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

        *   literal ASCII TAB characters in strings

            Literal ASCII TAB characters are now allowed in strings (and
            treated as "\t") in relaxed mode. Despite JSON mandates, that
            TAB character is substituted for "\t" sequence.

              [
                 "Hello\tWorld",
                 "Hello<TAB>World", # literal <TAB> would not normally be allowed
              ]

        *   allow_singlequote

            Single quotes are accepted instead of double quotes. See the
            "allow_singlequote" option.

                { "foo":'bar' }
                { 'foo':"bar" }
                { 'foo':'bar' }

        *   allow_barekey

            Accept unquoted object keys instead of with mandatory double
            quotes. See the "allow_barekey" option.

                { foo:"bar" }

        *   allow_dupkeys

            Allow decoding of duplicate keys in hashes. By default duplicate
            keys are forbidden. See <http://seriot.ch/parsing_json.php#24>:
            RFC 7159 section 4: "The names within an object should be
            unique." See the "allow_dupkeys" option.

    $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 is now also done with tied hashes, contrary to JSON::XS. But
        note that with most large tied hashes stored as tree it is advised
        to sort the iterator already and don't sort the hash output here.
        Most such iterators are already sorted, as such e.g. DB_File with
        "DB_BTREE".

    $json = $json->sort_by (undef, 0, 1 or a block)
        This currently only (un)sets the "canonical" option, and ignores
        custom sort blocks.

        This setting has no effect when decoding JSON texts.

        This setting has currently no effect on tied hashes.

    $json = $json->escape_slash ([$enable])
    $enabled = $json->get_escape_slash
        According to the JSON Grammar, the *forward slash* character
        (U+002F) "/" need to be escaped. But by default strings are encoded
        without escaping slashes in all perl JSON encoders.

        If $enable is true (or missing), then "encode" will escape slashes,
        "\/".

        This setting has no effect when decoding JSON texts.

    $json = $json->unblessed_bool ([$enable])
    $enabled = $json->get_unblessed_bool
            $json = $json->unblessed_bool([$enable])

        If $enable is true (or missing), then "decode" will return Perl
        non-object boolean variables (1 and 0) for JSON booleans ("true" and
        "false"). If $enable is false, then "decode" will return
        "JSON::PP::Boolean" objects for JSON booleans.

    $json = $json->allow_singlequote ([$enable])
    $enabled = $json->get_allow_singlequote
            $json = $json->allow_singlequote([$enable])

        If $enable is true (or missing), then "decode" will accept JSON
        strings quoted by single quotations that are invalid JSON format.

            $json->allow_singlequote->decode({"foo":'bar'});
            $json->allow_singlequote->decode({'foo':"bar"});
            $json->allow_singlequote->decode({'foo':'bar'});

        This is also enabled with "relaxed". As same as the "relaxed"
        option, this option may be used to parse application-specific files
        written by humans.

    $json = $json->allow_barekey ([$enable])
    $enabled = $json->get_allow_barekey
            $json = $json->allow_barekey([$enable])

        If $enable is true (or missing), then "decode" will accept bare keys
        of JSON object that are invalid JSON format.

        Same as with the "relaxed" option, this option may be used to parse
        application-specific files written by humans.

            $json->allow_barekey->decode('{foo:"bar"}');

    $json = $json->allow_bignum ([$enable])
    $enabled = $json->get_allow_bignum
            $json = $json->allow_bignum([$enable])

        If $enable is true (or missing), then "decode" will convert the big
        integer Perl cannot handle as integer into a Math::BigInt object and
        convert a floating number (any) into a Math::BigFloat.

        On the contrary, "encode" converts "Math::BigInt" objects and
        "Math::BigFloat" objects into JSON numbers with "allow_blessed"
        enable.

           $json->allow_nonref->allow_blessed->allow_bignum;
           $bigfloat = $json->decode('2.000000000000000000000000001');
           print $json->encode($bigfloat);
           # => 2.000000000000000000000000001

        See "MAPPING" about the normal conversion of JSON number.

    $json = $json->allow_bigint ([$enable])
        This option is obsolete and replaced by allow_bignum.

    $json = $json->allow_nonref ([$enable])
    $enabled = $json->get_allow_nonref
        If $enable is true (or missing), then the "encode" method can
        convert a non-reference into its corresponding string, number or
        null JSON value, which is an extension to RFC4627. Likewise,
        "decode" will accept those JSON values instead of croaking.

        If $enable is false, then the "encode" method will croak if it isn't
        passed an arrayref or hashref, as JSON texts must either be an
        object or array. Likewise, "decode" will croak if given something
        that is not a JSON object or array.

        Example, encode a Perl scalar as JSON value with enabled
        "allow_nonref", resulting in an invalid JSON text:

           Cpanel::JSON::XS->new->allow_nonref->encode ("Hello, World!")
           => "Hello, World!"

    $json = $json->allow_unknown ([$enable])
    $enabled = $json->get_allow_unknown
        If $enable is true (or missing), then "encode" will *not* throw an
        exception when it encounters values it cannot represent in JSON (for
        example, filehandles) but instead will encode a JSON "null" value.
        Note that blessed objects are not included here and are handled
        separately by c<allow_nonref>.

        If $enable is false (the default), then "encode" will throw an
        exception when it encounters anything it cannot encode as JSON.

        This option does not affect "decode" in any way, and it is
        recommended to leave it off unless you know your communications
        partner.

    $json = $json->allow_stringify ([$enable])
    $enabled = $json->get_allow_stringify
        If $enable is true (or missing), then "encode" will stringify the
        non-object perl value or reference. Note that blessed objects are
        not included here and are handled separately by "allow_blessed" and
        "convert_blessed". String references are stringified to the string
        value, other references as in perl.

        This option does not affect "decode" in any way.

        This option is special to this module, it is not supported by other
        encoders. So it is not recommended to use it.

    $json = $json->require_types ([$enable])
    $enable = $json->get_require_types
             $json = $json->require_types([$enable])

        If $enable is true (or missing), then "encode" will require either
        enabled "type_all_string" or second argument with supplied JSON
        types. See Cpanel::JSON::XS::Type. When "type_all_string" is not
        enabled or second argument is not provided (or is undef), then
        "encode" croaks. It also croaks when the type for provided structure
        in "encode" is incomplete.

    $json = $json->type_all_string ([$enable])
    $enable = $json->get_type_all_string
             $json = $json->type_all_string([$enable])

        If $enable is true (or missing), then "encode" will always produce
        stable deterministic JSON string types in resulted output.

        When $enable is false, then result of encoded JSON output may be
        different for different Perl versions and may depends on loaded
        modules.

        This is useful it you need deterministic JSON types, independently
        of used Perl version and other modules, but do not want to write
        complicated type definitions for Cpanel::JSON::XS::Type.

    $json = $json->allow_dupkeys ([$enable])
    $enabled = $json->get_allow_dupkeys
        If $enable is true (or missing), then the "decode" method will not
        die when it encounters duplicate keys in a hash. "allow_dupkeys" is
        also enabled in the "relaxed" mode.

        The JSON spec allows duplicate name in objects but recommends to
        disable it, however with Perl hashes they are impossible, parsing
        JSON in Perl silently ignores duplicate names, using the last value
        found.

        See <http://seriot.ch/parsing_json.php#24>: RFC 7159 section 4: "The
        names within an object should be unique."

    $json = $json->allow_blessed ([$enable])
    $enabled = $json->get_allow_blessed
        If $enable is true (or missing), then the "encode" method will not
        barf when it encounters a blessed reference. Instead, the value of
        the convert_blessed option will decide whether "null"
        ("convert_blessed" disabled or no "TO_JSON" method found) or a
        representation of the object ("convert_blessed" enabled and
        "TO_JSON" method found) is being encoded. Has no effect on "decode".

        If $enable is false (the default), then "encode" will throw an
        exception when it encounters a blessed object without
        "convert_blessed" and a "TO_JSON" method.

        This setting has no effect on "decode".

    $json = $json->convert_blessed ([$enable])
    $enabled = $json->get_convert_blessed
        If $enable is true (or missing), then "encode", upon encountering a
        blessed object, will check for the availability of the "TO_JSON"
        method on the object's class. If found, it will be called in scalar
        context and the resulting scalar will be encoded instead of the
        object. If no "TO_JSON" method is found, a stringification overload
        method is tried next. If both are not found, the value of
        "allow_blessed" will decide what to do.

        The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
        returns other blessed objects, those will be handled in the same
        way. "TO_JSON" must take care of not causing an endless recursion
        cycle (== crash) in this case. The same care must be taken with
        calling encode in stringify overloads (even if this works by luck in
        older perls) or other callbacks. The name of "TO_JSON" was chosen
        because other methods called by the Perl core (== not by the user of
        the object) are usually in upper case letters and to avoid
        collisions with any "to_json" function or method.

        If $enable is false (the default), then "encode" will not consider
        this type of conversion.

        This setting has no effect on "decode".

    $json = $json->allow_tags ([$enable])
    $enabled = $json->get_allow_tags
        See "OBJECT SERIALIZATION" for details.

        If $enable is true (or missing), then "encode", upon encountering a
        blessed object, will check for the availability of the "FREEZE"
        method on the object's class. If found, it will be used to serialize
        the object into a nonstandard tagged JSON value (that JSON decoders
        cannot decode).

        It also causes "decode" to parse such tagged JSON values and
        deserialize them via a call to the "THAW" method.

        If $enable is false (the default), then "encode" will not consider
        this type of conversion, and tagged JSON values will cause a parse
        error in "decode", as if tags were not part of the grammar.

    $json = $json->filter_json_object ([$coderef->($hashref)])
        When $coderef is specified, it will be called from "decode" each
        time it decodes a JSON object. The only argument is a reference to
        the newly-created hash. If the code references returns a single
        scalar (which need not be a reference), this value (i.e. a copy of
        that scalar to avoid aliasing) is inserted into the deserialized
        data structure. If it returns an empty list (NOTE: *not* "undef",
        which is a valid scalar), the original deserialized hash will be
        inserted. This setting can slow down decoding considerably.

        When $coderef is omitted or undefined, any existing callback will be
        removed and "decode" will not change the deserialized hash in any
        way.

        Example, convert all JSON objects into the integer 5:

           my $js = Cpanel::JSON::XS->new->filter_json_object (sub { 5 });
           # returns [5]
           $js->decode ('[{}]')
           # throw an exception because allow_nonref is not enabled
           # so a lone 5 is not allowed.
           $js->decode ('{"a":1, "b":2}');

    $json = $json->filter_json_single_key_object ($key [=>
    $coderef->($value)])
        Works remotely similar to "filter_json_object", but is only called
        for JSON objects having a single key named $key.

        This $coderef is called before the one specified via
        "filter_json_object", if any. It gets passed the single value in the
        JSON object. If it returns a single value, it will be inserted into
        the data structure. If it returns nothing (not even "undef" but the
        empty list), the callback from "filter_json_object" will be called
        next, as if no single-key callback were specified.

        If $coderef is omitted or undefined, the corresponding callback will
        be disabled. There can only ever be one callback for a given key.

        As this callback gets called less often then the
        "filter_json_object" one, decoding speed will not usually suffer as
        much. Therefore, single-key objects make excellent targets to
        serialize Perl objects into, especially as single-key JSON objects
        are as close to the type-tagged value concept as JSON gets (it's
        basically an ID/VALUE tuple). Of course, JSON does not support this
        in any way, so you need to make sure your data never looks like a
        serialized Perl hash.

        Typical names for the single object key are "__class_whatever__", or
        "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
        things like "__class_md5sum(classname)__", to reduce the risk of
        clashing with real hashes.

        Example, decode JSON objects of the form "{ "__widget__" => <id> }"
        into the corresponding $WIDGET{<id>} object:

           # return whatever is in $WIDGET{5}:
           Cpanel::JSON::XS
              ->new
              ->filter_json_single_key_object (__widget__ => sub {
                    $WIDGET{ $_[0] }
                 })
              ->decode ('{"__widget__": 5')

           # this can be used with a TO_JSON method in some "widget" class
           # for serialization to json:
           sub WidgetBase::TO_JSON {
              my ($self) = @_;

              unless ($self->{id}) {
                 $self->{id} = ..get..some..id..;
                 $WIDGET{$self->{id}} = $self;
              }

              { __widget__ => $self->{id} }
           }

    $json = $json->shrink ([$enable])
    $enabled = $json->get_shrink
        Perl usually over-allocates memory a bit when allocating space for
        strings. This flag optionally resizes strings generated by either
        "encode" or "decode" to their minimum size possible. This can save
        memory when your JSON texts are either very very long or you have
        many short strings. It will also try to downgrade any strings to
        octet-form if possible: perl stores strings internally either in an
        encoding called UTF-X or in octet-form. The latter cannot store
        everything but uses less space in general (and some buggy Perl or C
        code might even rely on that internal representation being used).

        The actual definition of what shrink does might change in future
        versions, but it will always try to save space at the expense of
        time.

        If $enable is true (or missing), the string returned by "encode"
        will be shrunk-to-fit, while all strings generated by "decode" will
        also be shrunk-to-fit.

        If $enable is false, then the normal perl allocation algorithms are
        used. If you work with your data, then this is likely to be faster.

        In the future, this setting might control other things, such as
        converting strings that look like integers or floats into integers
        or floats internally (there is no difference on the Perl level),
        saving space.

    $json = $json->max_depth ([$maximum_nesting_depth])
    $max_depth = $json->get_max_depth
        Sets the maximum nesting level (default 512) accepted while encoding
        or decoding. If a higher nesting level is detected in JSON text or a
        Perl data structure, then the encoder and decoder will stop and
        croak at that point.

        Nesting level is defined by number of hash- or arrayrefs that the
        encoder needs to traverse to reach a given point or the number of
        "{" or "[" characters without their matching closing parenthesis
        crossed to reach a given character in a string.

        Setting the maximum depth to one disallows any nesting, so that
        ensures that the object is only a single hash/object or array.

        If no argument is given, the highest possible setting will be used,
        which is rarely useful.

        Note that nesting is implemented by recursion in C. The default
        value has been chosen to be as large as typical operating systems
        allow without crashing.

        See "SECURITY CONSIDERATIONS", below, for more info on why this is
        useful.

    $json = $json->max_size ([$maximum_string_size])
    $max_size = $json->get_max_size
        Set the maximum length a JSON text may have (in bytes) where
        decoding is being attempted. The default is 0, meaning no limit.
        When "decode" is called on a string that is longer then this many
        bytes, it will not attempt to decode the string but throw an
        exception. This setting has no effect on "encode" (yet).

        If no argument is given, the limit check will be deactivated (same
        as when 0 is specified).

        See "SECURITY CONSIDERATIONS", below, for more info on why this is
        useful.

    $json->stringify_infnan ([$infnan_mode = 1])
    $infnan_mode = $json->get_stringify_infnan
        Get or set how Cpanel::JSON::XS encodes "inf", "-inf" or "nan" for
        numeric values. Also qnan, snan or negative nan on some platforms.

        "null": infnan_mode = 0. Similar to most JSON modules in other
        languages. Always null.

        stringified: infnan_mode = 1. As in Mojo::JSON. Platform specific
        strings. Stringified via sprintf(%g), with double quotes.

        inf/nan: infnan_mode = 2. As in JSON::XS, and older releases. Passes
        through platform dependent values, invalid JSON. Stringified via
        sprintf(%g), but without double quotes.

        "inf/-inf/nan": infnan_mode = 3. Platform independent inf/nan/-inf
        strings. No QNAN/SNAN/negative NAN support, unified to "nan". Much
        easier to detect, but may conflict with valid strings.

    $json_text = $json->encode ($perl_scalar, $json_type)
        Converts the given Perl data structure (a simple scalar or a
        reference to a hash or array) to its JSON representation. Simple
        scalars will be converted into JSON string or number sequences,
        while references to arrays become JSON arrays and references to
        hashes become JSON objects. Undefined Perl values (e.g. "undef")
        become JSON "null" values. Neither "true" nor "false" values will be
        generated.

        For the type argument see Cpanel::JSON::XS::Type.

    $perl_scalar = $json->decode ($json_text, my $json_type)
        The opposite of "encode": expects a JSON text and tries to parse it,
        returning the resulting simple scalar or reference. Croaks on error.

        JSON numbers and strings become simple Perl scalars. JSON arrays
        become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
        becomes 1, "false" becomes 0 and "null" becomes "undef".

        For the type argument see Cpanel::JSON::XS::Type.

    ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
        This works like the "decode" method, but instead of raising an
        exception when there is trailing garbage after the first JSON
        object, it will silently stop parsing there and return the number of
        characters consumed so far.

        This is useful if your JSON texts are not delimited by an outer
        protocol and you need to know where the JSON text ends.

           Cpanel::JSON::XS->new->decode_prefix ("[1] the tail")
           => ([1], 3)

    $json->to_json ($perl_hash_or_arrayref)
        Deprecated method for perl 5.8 and newer. Use encode_json instead.

    $json->from_json ($utf8_encoded_json_text)
        Deprecated method for perl 5.8 and newer. Use decode_json instead.

INCREMENTAL PARSING
    In some cases, there is the need for incremental parsing of JSON texts.
    While this module always has to keep both JSON text and resulting Perl
    data structure in memory at one time, it does allow you to parse a JSON
    stream incrementally. It does so by accumulating text until it has a
    full JSON object, which it then can decode. This process is similar to
    using "decode_prefix" to see if a full JSON object is available, but is
    much more efficient (and can be implemented with a minimum of method
    calls).

    Cpanel::JSON::XS will only attempt to parse the JSON text once it is
    sure it has enough text to get a decisive result, using a very simple
    but truly incremental parser. This means that it sometimes won't stop as
    early as the full parser, for example, it doesn't detect mismatched
    parentheses. The only thing it guarantees is that it starts decoding as
    soon as a syntactically valid JSON text has been seen. This means you
    need to set resource limits (e.g. "max_size") to ensure the parser will
    stop parsing in the presence if syntax errors.

    The following methods implement this incremental parser.

    [void, scalar or list context] = $json->incr_parse ([$string])
        This is the central parsing function. It can both append new text
        and extract objects from the stream accumulated so far (both of
        these functions are optional).

        If $string is given, then this string is appended to the already
        existing JSON fragment stored in the $json object.

        After that, if the function is called in void context, it will
        simply return without doing anything further. This can be used to
        add more text in as many chunks as you want.

        If the method is called in scalar context, then it will try to
        extract exactly *one* JSON object. If that is successful, it will
        return this object, otherwise it will return "undef". If there is a
        parse error, this method will croak just as "decode" would do (one
        can then use "incr_skip" to skip the erroneous part). This is the
        most common way of using the method.

        And finally, in list context, it will try to extract as many objects
        from the stream as it can find and return them, or the empty list
        otherwise. For this to work, there must be no separators between the
        JSON objects or arrays, instead they must be concatenated
        back-to-back. If an error occurs, an exception will be raised as in
        the scalar context case. Note that in this case, any
        previously-parsed JSON texts will be lost.

        Example: Parse some JSON arrays/objects in a given string and return
        them.

           my @objs = Cpanel::JSON::XS->new->incr_parse ("[5][7][1,2]");

    $lvalue_string = $json->incr_text (>5.8 only)
        This method returns the currently stored JSON fragment as an lvalue,
        that is, you can manipulate it. This *only* works when a preceding
        call to "incr_parse" in *scalar context* successfully returned an
        object, and 2. only with Perl >= 5.8

        Under all other circumstances you must not call this function (I
        mean it. although in simple tests it might actually work, it *will*
        fail under real world conditions). As a special exception, you can
        also call this method before having parsed anything.

        This function is useful in two cases: a) finding the trailing text
        after a JSON object or b) parsing multiple JSON objects separated by
        non-JSON text (such as commas).

    $json->incr_skip
        This will reset the state of the incremental parser and will remove
        the parsed text from the input buffer so far. This is useful after
        "incr_parse" died, in which case the input buffer and incremental
        parser state is left unchanged, to skip the text parsed so far and
        to reset the parse state.

        The difference to "incr_reset" is that only text until the parse
        error occurred is removed.

    $json->incr_reset
        This completely resets the incremental parser, that is, after this
        call, it will be as if the parser had never parsed anything.

        This is useful if you want to repeatedly parse JSON objects and want
        to ignore any trailing data, which means you have to reset the
        parser after each successful decode.

  LIMITATIONS
    All options that affect decoding are supported, except "allow_nonref".
    The reason for this is that it cannot be made to work sensibly: JSON
    objects and arrays are self-delimited, i.e. you can concatenate them
    back to back and still decode them perfectly. This does not hold true
    for JSON numbers, however.

    For example, is the string 1 a single JSON number, or is it simply the
    start of 12? Or is 12 a single JSON number, or the concatenation of 1
    and 2? In neither case you can tell, and this is why Cpanel::JSON::XS
    takes the conservative route and disallows this case.

  EXAMPLES
    Some examples will make all this clearer. First, a simple example that
    works similarly to "decode_prefix": We want to decode the JSON object at
    the start of a string and identify the portion after the JSON object:

       my $text = "[1,2,3] hello";

       my $json = new Cpanel::JSON::XS;

       my $obj = $json->incr_parse ($text)
          or die "expected JSON object or array at beginning of string";

       my $tail = $json->incr_text;
       # $tail now contains " hello"

    Easy, isn't it?

    Now for a more complicated example: Imagine a hypothetical protocol
    where you read some requests from a TCP stream, and each request is a
    JSON array, without any separation between them (in fact, it is often
    useful to use newlines as "separators", as these get interpreted as
    whitespace at the start of the JSON text, which makes it possible to
    test said protocol with "telnet"...).

    Here is how you'd do it (it is trivial to write this in an event-based
    manner):

       my $json = new Cpanel::JSON::XS;

       # read some data from the socket
       while (sysread $socket, my $buf, 4096) {

          # split and decode as many requests as possible
          for my $request ($json->incr_parse ($buf)) {
             # act on the $request
          }
       }

    Another complicated example: Assume you have a string with JSON objects
    or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
    [3]"). To parse them, we have to skip the commas between the JSON texts,
    and here is where the lvalue-ness of "incr_text" comes in useful:

       my $text = "[1],[2], [3]";
       my $json = new Cpanel::JSON::XS;

       # void context, so no parsing done
       $json->incr_parse ($text);

       # now extract as many objects as possible. note the
       # use of scalar context so incr_text can be called.
       while (my $obj = $json->incr_parse) {
          # do something with $obj

          # now skip the optional comma
          $json->incr_text =~ s/^ \s* , //x;
       }

    Now lets go for a very complex example: Assume that you have a gigantic
    JSON array-of-objects, many gigabytes in size, and you want to parse it,
    but you cannot load it into memory fully (this has actually happened in
    the real world :).

    Well, you lost, you have to implement your own JSON parser. But
    Cpanel::JSON::XS can still help you: You implement a (very simple) array
    parser and let JSON decode the array elements, which are all full JSON
    objects on their own (this wouldn't work if the array elements could be
    JSON numbers, for example):

       my $json = new Cpanel::JSON::XS;

       # open the monster
       open my $fh, "<bigfile.json"
          or die "bigfile: $!";

       # first parse the initial "["
       for (;;) {
          sysread $fh, my $buf, 65536
             or die "read error: $!";
          $json->incr_parse ($buf); # void context, so no parsing

          # Exit the loop once we found and removed(!) the initial "[".
          # In essence, we are (ab-)using the $json object as a simple scalar
          # we append data to.
          last if $json->incr_text =~ s/^ \s* \[ //x;
       }

       # now we have the skipped the initial "[", so continue
       # parsing all the elements.
       for (;;) {
          # in this loop we read data until we got a single JSON object
          for (;;) {
             if (my $obj = $json->incr_parse) {
                # do something with $obj
                last;
             }

             # add more data
             sysread $fh, my $buf, 65536
                or die "read error: $!";
             $json->incr_parse ($buf); # void context, so no parsing
          }

          # in this loop we read data until we either found and parsed the
          # separating "," between elements, or the final "]"
          for (;;) {
             # first skip whitespace
             $json->incr_text =~ s/^\s*//;

             # if we find "]", we are done
             if ($json->incr_text =~ s/^\]//) {
                print "finished.\n";
                exit;
             }

             # if we find ",", we can continue with the next element
             if ($json->incr_text =~ s/^,//) {
                last;
             }

             # if we find anything else, we have a parse error!
             if (length $json->incr_text) {
                die "parse error near ", $json->incr_text;
             }

             # else add more data
             sysread $fh, my $buf, 65536
                or die "read error: $!";
             $json->incr_parse ($buf); # void context, so no parsing
          }

    This is a complex example, but most of the complexity comes from the
    fact that we are trying to be correct (bear with me if I am wrong, I
    never ran the above example :).

BOM
    Detect all unicode Byte Order Marks on decode. Which are UTF-8,
    UTF-16LE, UTF-16BE, UTF-32LE and UTF-32BE.

    The BOM encoding is set only for one specific decode call, it does not
    change the state of the JSON object.

    Warning: With perls older than 5.20 you need load the Encode module
    before loading a multibyte BOM, i.e. >= UTF-16. Otherwise an error is
    thrown. This is an implementation limitation and might get fixed later.

    See <https://tools.ietf.org/html/rfc7159#section-8.1> *"JSON text SHALL
    be encoded in UTF-8, UTF-16, or UTF-32."*

    *"Implementations MUST NOT add a byte order mark to the beginning of a
    JSON text", "implementations (...) MAY ignore the presence of a byte
    order mark rather than treating it as an error".*

    See also <http://www.unicode.org/faq/utf_bom.html#BOM>.

    Beware that Cpanel::JSON::XS is currently the only JSON module which
    does accept and decode a BOM.

    The latest JSON spec
    <https://www.greenbytes.de/tech/webdav/rfc8259.html#character.encoding>
    forbid the usage of UTF-16 or UTF-32, the character encoding is UTF-8.
    Thus in subsequent updates BOM's of UTF-16 or UTF-32 will throw an
    error.

MAPPING
    This section describes how Cpanel::JSON::XS maps Perl values to JSON
    values and vice versa. These mappings are designed to "do the right
    thing" in most circumstances automatically, preserving round-tripping
    characteristics (what you put in comes out as something equivalent).

    For the more enlightened: note that in the following descriptions,
    lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
    refers to the abstract Perl language itself.

  JSON -> PERL
    object
        A JSON object becomes a reference to a hash in Perl. No ordering of
        object keys is preserved (JSON does not preserve object key ordering
        itself).

    array
        A JSON array becomes a reference to an array in Perl.

    string
        A JSON string becomes a string scalar in Perl - Unicode codepoints
        in JSON are represented by the same codepoints in the Perl string,
        so no manual decoding is necessary.

    number
        A JSON number becomes either an integer, numeric (floating point) or
        string scalar in perl, depending on its range and any fractional
        parts. On the Perl level, there is no difference between those as
        Perl handles all the conversion details, but an integer may take
        slightly less memory and might represent more values exactly than
        floating point numbers.

        If the number consists of digits only, Cpanel::JSON::XS will try to
        represent it as an integer value. If that fails, it will try to
        represent it as a numeric (floating point) value if that is possible
        without loss of precision. Otherwise it will preserve the number as
        a string value (in which case you lose roundtripping ability, as the
        JSON number will be re-encoded to a JSON string).

        Numbers containing a fractional or exponential part will always be
        represented as numeric (floating point) values, possibly at a loss
        of precision (in which case you might lose perfect roundtripping
        ability, but the JSON number will still be re-encoded as a JSON
        number).

        Note that precision is not accuracy - binary floating point values
        cannot represent most decimal fractions exactly, and when converting
        from and to floating point, "Cpanel::JSON::XS" only guarantees
        precision up to but not including the least significant bit.

    true, false
        When "unblessed_bool" is set to true, then JSON "true" becomes 1 and
        JSON "false" becomes 0.

        Otherwise these JSON atoms become "JSON::PP::true" and
        "JSON::PP::false", respectively. They are "JSON::PP::Boolean"
        objects and are overloaded to act almost exactly like the numbers 1
        and 0. You can check whether a scalar is a JSON boolean by using the
        "Cpanel::JSON::XS::is_bool" function.

        The other round, from perl to JSON, "!0" which is represented as
        "yes" becomes "true", and "!1" which is represented as "no" becomes
        "false".

        Via Cpanel::JSON::XS::Type you can now even force negation in
        "encode", without overloading of "!":

            my $false = Cpanel::JSON::XS::false;
            print($json->encode([!$false], [JSON_TYPE_BOOL]));
            => [true]

    null
        A JSON null atom becomes "undef" in Perl.

    shell-style comments ("# *text*")
        As a nonstandard extension to the JSON syntax that is enabled by the
        "relaxed" setting, shell-style comments are allowed. They can start
        anywhere outside strings and go till the end of the line.

    tagged values ("(*tag*)*value*").
        Another nonstandard extension to the JSON syntax, enabled with the
        "allow_tags" setting, are tagged values. In this implementation, the
        *tag* must be a perl package/class name encoded as a JSON string,
        and the *value* must be a JSON array encoding optional constructor
        arguments.

        See "OBJECT SERIALIZATION", below, for details.

  PERL -> JSON
    The mapping from Perl to JSON is slightly more difficult, as Perl is a
    truly typeless language, so we can only guess which JSON type is meant
    by a Perl value.

    hash references
        Perl hash references become JSON objects. As there is no inherent
        ordering in hash keys (or JSON objects), they will usually be
        encoded in a pseudo-random order that can change between runs of the
        same program but stays generally the same within a single run of a
        program. Cpanel::JSON::XS can optionally sort the hash keys
        (determined by the *canonical* flag), so the same datastructure will
        serialize to the same JSON text (given same settings and version of
        Cpanel::JSON::XS), but this incurs a runtime overhead and is only
        rarely useful, e.g. when you want to compare some JSON text against
        another for equality.

    array references
        Perl array references become JSON arrays.

    other references
        Other unblessed references are generally not allowed and will cause
        an exception to be thrown, except for references to the integers 0
        and 1, which get turned into "false" and "true" atoms in JSON.

        With the option "allow_stringify", you can ignore the exception and
        return the stringification of the perl value.

        With the option "allow_unknown", you can ignore the exception and
        return "null" instead.

           encode_json [\"x"]        # => cannot encode reference to scalar 'SCALAR(0x..)'
                                     # unless the scalar is 0 or 1
           encode_json [\0, \1]      # yields [false,true]

           allow_stringify->encode_json [\"x"] # yields "x" unlike JSON::PP
           allow_unknown->encode_json [\"x"]   # yields null as in JSON::PP

    Cpanel::JSON::XS::true, Cpanel::JSON::XS::false
        These special values become JSON true and JSON false values,
        respectively. You can also use "\1" and "\0" or "!0" and "!1"
        directly if you want.

           encode_json [Cpanel::JSON::XS::false, Cpanel::JSON::XS::true] # yields [false,true]
           encode_json [!1, !0], [JSON_TYPE_BOOL, JSON_TYPE_BOOL] # yields [false,true]

        eq/ne comparisons with true, false:

        false is eq to the empty string or the string 'false' or the special
        empty string "!!0" or "!1", i.e. "SV_NO", or the numbers 0 or 0.0.

        true is eq to the string 'true' or to the special string "!0" (i.e.
        "SV_YES") or to the numbers 1 or 1.0.

    blessed objects
        Blessed objects are not directly representable in JSON, but
        "Cpanel::JSON::XS" allows various optional ways of handling objects.
        See "OBJECT SERIALIZATION", below, for details.

        See the "allow_blessed" and "convert_blessed" methods on various
        options on how to deal with this: basically, you can choose between
        throwing an exception, encoding the reference as if it weren't
        blessed, use the objects overloaded stringification method or
        provide your own serializer method.

    simple scalars
        Simple Perl scalars (any scalar that is not a reference) are the
        most difficult objects to encode: Cpanel::JSON::XS will encode
        undefined scalars or inf/nan as JSON "null" values and other scalars
        to either number or string in non-deterministic way which may be
        affected or changed by Perl version or any other loaded Perl module.

        If you want to have stable and deterministic types in JSON encoder
        then use Cpanel::JSON::XS::Type.

        Alternative way for deterministic types is to use "type_all_string"
        method when all perl scalars are encoded to JSON strings.

        Non-deterministic behavior is following: scalars that have last been
        used in a string context before encoding as JSON strings, and
        anything else as number value:

           # dump as number
           encode_json [2]                      # yields [2]
           encode_json [-3.0e17]                # yields [-3e+17]
           my $value = 5; encode_json [$value]  # yields [5]

           # used as string, but the two representations are for the same number
           print $value;
           encode_json [$value]                 # yields [5]

           # used as different string (non-matching dual-var)
           my $str = '0 but true';
           my $num = 1 + $str;
           encode_json [$num, $str]           # yields [1,"0 but true"]

           # undef becomes null
           encode_json [undef]                  # yields [null]

           # inf or nan becomes null, unless you answered
           # "Do you want to handle inf/nan as strings" with yes
           encode_json [9**9**9]                # yields [null]

        You can force the type to be a JSON string by stringifying it:

           my $x = 3.1; # some variable containing a number
           "$x";        # stringified
           $x .= "";    # another, more awkward way to stringify
           print $x;    # perl does it for you, too, quite often

        You can force the type to be a JSON number by numifying it:

           my $x = "3"; # some variable containing a string
           $x += 0;     # numify it, ensuring it will be dumped as a number
           $x *= 1;     # same thing, the choice is yours.

        Note that numerical precision has the same meaning as under Perl (so
        binary to decimal conversion follows the same rules as in Perl,
        which can differ to other languages). Also, your perl interpreter
        might expose extensions to the floating point numbers of your
        platform, such as infinities or NaN's - these cannot be represented
        in JSON, and thus null is returned instead. Optionally you can
        configure it to stringify inf and nan values.

  OBJECT SERIALIZATION
    As JSON cannot directly represent Perl objects, you have to choose
    between a pure JSON representation (without the ability to deserialize
    the object automatically again), and a nonstandard extension to the JSON
    syntax, tagged values.

   SERIALIZATION
    What happens when "Cpanel::JSON::XS" encounters a Perl object depends on
    the "allow_blessed", "convert_blessed" and "allow_tags" settings, which
    are used in this order:

    1. "allow_tags" is enabled and the object has a "FREEZE" method.
        In this case, "Cpanel::JSON::XS" uses the Types::Serialiser object
        serialization protocol to create a tagged JSON value, using a
        nonstandard extension to the JSON syntax.

        This works by invoking the "FREEZE" method on the object, with the
        first argument being the object to serialize, and the second
        argument being the constant string "JSON" to distinguish it from
        other serializers.

        The "FREEZE" method can return any number of values (i.e. zero or
        more). These values and the paclkage/classname of the object will
        then be encoded as a tagged JSON value in the following format:

           ("classname")[FREEZE return values...]

        e.g.:

           ("URI")["http://www.google.com/"]
           ("MyDate")[2013,10,29]
           ("ImageData::JPEG")["Z3...VlCg=="]

        For example, the hypothetical "My::Object" "FREEZE" method might use
        the objects "type" and "id" members to encode the object:

           sub My::Object::FREEZE {
              my ($self, $serializer) = @_;

              ($self->{type}, $self->{id})
           }

    2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
        In this case, the "TO_JSON" method of the object is invoked in
        scalar context. It must return a single scalar that can be directly
        encoded into JSON. This scalar replaces the object in the JSON text.

        For example, the following "TO_JSON" method will convert all URI
        objects to JSON strings when serialized. The fact that these values
        originally were URI objects is lost.

           sub URI::TO_JSON {
              my ($uri) = @_;
              $uri->as_string
           }

    3. "convert_blessed" is enabled and the object has a stringification
    overload.
        In this case, the overloaded "" method of the object is invoked in
        scalar context. It must return a single scalar that can be directly
        encoded into JSON. This scalar replaces the object in the JSON text.

        For example, the following "" method will convert all URI objects to
        JSON strings when serialized. The fact that these values originally
        were URI objects is lost.

            package URI;
            use overload '""' => sub { shift->as_string };

    4. "allow_blessed" is enabled.
        The object will be serialized as a JSON null value.

    5. none of the above
        If none of the settings are enabled or the respective methods are
        missing, "Cpanel::JSON::XS" throws an exception.

   DESERIALIZATION
    For deserialization there are only two cases to consider: either
    nonstandard tagging was used, in which case "allow_tags" decides, or
    objects cannot be automatically be deserialized, in which case you can
    use postprocessing or the "filter_json_object" or
    "filter_json_single_key_object" callbacks to get some real objects our
    of your JSON.

    This section only considers the tagged value case: I a tagged JSON
    object is encountered during decoding and "allow_tags" is disabled, a
    parse error will result (as if tagged values were not part of the
    grammar).

    If "allow_tags" is enabled, "Cpanel::JSON::XS" will look up the "THAW"
    method of the package/classname used during serialization (it will not
    attempt to load the package as a Perl module). If there is no such
    method, the decoding will fail with an error.

    Otherwise, the "THAW" method is invoked with the classname as first
    argument, the constant string "JSON" as second argument, and all the
    values from the JSON array (the values originally returned by the
    "FREEZE" method) as remaining arguments.

    The method must then return the object. While technically you can return
    any Perl scalar, you might have to enable the "enable_nonref" setting to
    make that work in all cases, so better return an actual blessed
    reference.

    As an example, let's implement a "THAW" function that regenerates the
    "My::Object" from the "FREEZE" example earlier:

       sub My::Object::THAW {
          my ($class, $serializer, $type, $id) = @_;

          $class->new (type => $type, id => $id)
       }

    See the "SECURITY CONSIDERATIONS" section below. Allowing external json
    objects being deserialized to perl objects is usually a very bad idea.

ENCODING/CODESET FLAG NOTES
    The interested reader might have seen a number of flags that signify
    encodings or codesets - "utf8", "latin1", "binary" and "ascii". There
    seems to be some confusion on what these do, so here is a short
    comparison:

    "utf8" controls whether the JSON text created by "encode" (and expected
    by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
    control whether "encode" escapes character values outside their
    respective codeset range. Neither of these flags conflict with each
    other, although some combinations make less sense than others.

    Care has been taken to make all flags symmetrical with respect to
    "encode" and "decode", that is, texts encoded with any combination of
    these flag values will be correctly decoded when the same flags are used
    - in general, if you use different flag settings while encoding vs. when
    decoding you likely have a bug somewhere.

    Below comes a verbose discussion of these flags. Note that a "codeset"
    is simply an abstract set of character-codepoint pairs, while an
    encoding takes those codepoint numbers and *encodes* them, in our case
    into octets. Unicode is (among other things) a codeset, UTF-8 is an
    encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
    encodings at the same time, which can be confusing.

    "utf8" flag disabled
        When "utf8" is disabled (the default), then "encode"/"decode"
        generate and expect Unicode strings, that is, characters with high
        ordinal Unicode values (> 255) will be encoded as such characters,
        and likewise such characters are decoded as-is, no changes to them
        will be done, except "(re-)interpreting" them as Unicode codepoints
        or Unicode characters, respectively (to Perl, these are the same
        thing in strings unless you do funny/weird/dumb stuff).

        This is useful when you want to do the encoding yourself (e.g. when
        you want to have UTF-16 encoded JSON texts) or when some other layer
        does the encoding for you (for example, when printing to a terminal
        using a filehandle that transparently encodes to UTF-8 you certainly
        do NOT want to UTF-8 encode your data first and have Perl encode it
        another time).

    "utf8" flag enabled
        If the "utf8"-flag is enabled, "encode"/"decode" will encode all
        characters using the corresponding UTF-8 multi-byte sequence, and
        will expect your input strings to be encoded as UTF-8, that is, no
        "character" of the input string must have any value > 255, as UTF-8
        does not allow that.

        The "utf8" flag therefore switches between two modes: disabled means
        you will get a Unicode string in Perl, enabled means you get an
        UTF-8 encoded octet/binary string in Perl.

    "latin1", "binary" or "ascii" flags enabled
        With "latin1" (or "ascii") enabled, "encode" will escape characters
        with ordinal values > 255 (> 127 with "ascii") and encode the
        remaining characters as specified by the "utf8" flag. With "binary"
        enabled, ordinal values > 255 are illegal.

        If "utf8" is disabled, then the result is also correctly encoded in
        those character sets (as both are proper subsets of Unicode, meaning
        that a Unicode string with all character values < 256 is the same
        thing as a ISO-8859-1 string, and a Unicode string with all
        character values < 128 is the same thing as an ASCII string in
        Perl).

        If "utf8" is enabled, you still get a correct UTF-8-encoded string,
        regardless of these flags, just some more characters will be escaped
        using "\uXXXX" then before.

        Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
        encoding, while ASCII-encoded strings are. That is because the
        ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
        *codeset* being a subset of Unicode), while ASCII is.

        Surprisingly, "decode" will ignore these flags and so treat all
        input values as governed by the "utf8" flag. If it is disabled, this
        allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
        strict subsets of Unicode. If it is enabled, you can correctly
        decode UTF-8 encoded strings.

        So neither "latin1", "binary" nor "ascii" are incompatible with the
        "utf8" flag - they only govern when the JSON output engine escapes a
        character or not.

        The main use for "latin1" or "binary" is to relatively efficiently
        store binary data as JSON, at the expense of breaking compatibility
        with most JSON decoders.

        The main use for "ascii" is to force the output to not contain
        characters with values > 127, which means you can interpret the
        resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
        any character set and 8-bit-encoding, and still get the same data
        structure back. This is useful when your channel for JSON transfer
        is not 8-bit clean or the encoding might be mangled in between (e.g.
        in mail), and works because ASCII is a proper subset of most 8-bit
        and multibyte encodings in use in the world.

  JSON and ECMAscript
    JSON syntax is based on how literals are represented in javascript (the
    not-standardized predecessor of ECMAscript) which is presumably why it
    is called "JavaScript Object Notation".

    However, JSON is not a subset (and also not a superset of course) of
    ECMAscript (the standard) or javascript (whatever browsers actually
    implement).

    If you want to use javascript's "eval" function to "parse" JSON, you
    might run into parse errors for valid JSON texts, or the resulting data
    structure might not be queryable:

    One of the problems is that U+2028 and U+2029 are valid characters
    inside JSON strings, but are not allowed in ECMAscript string literals,
    so the following Perl fragment will not output something that can be
    guaranteed to be parsable by javascript's "eval":

       use Cpanel::JSON::XS;

       print encode_json [chr 0x2028];

    The right fix for this is to use a proper JSON parser in your javascript
    programs, and not rely on "eval" (see for example Douglas Crockford's
    json2.js parser).

    If this is not an option, you can, as a stop-gap measure, simply encode
    to ASCII-only JSON:

       use Cpanel::JSON::XS;

       print Cpanel::JSON::XS->new->ascii->encode ([chr 0x2028]);

    Note that this will enlarge the resulting JSON text quite a bit if you
    have many non-ASCII characters. You might be tempted to run some regexes
    to only escape U+2028 and U+2029, e.g.:

       # DO NOT USE THIS!
       my $json = Cpanel::JSON::XS->new->utf8->encode ([chr 0x2028]);
       $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
       $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
       print $json;

    Note that *this is a bad idea*: the above only works for U+2028 and
    U+2029 and thus only for fully ECMAscript-compliant parsers. Many
    existing javascript implementations, however, have issues with other
    characters as well - using "eval" naively simply *will* cause problems.

    Another problem is that some javascript implementations reserve some
    property names for their own purposes (which probably makes them
    non-ECMAscript-compliant). For example, Iceweasel reserves the
    "__proto__" property name for its own purposes.

    If that is a problem, you could parse try to filter the resulting JSON
    output for these property strings, e.g.:

       $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;

    This works because "__proto__" is not valid outside of strings, so every
    occurrence of ""__proto__"\s*:" must be a string used as property name.

    Unicode non-characters between U+FFFD and U+10FFFF are decoded either to
    the recommended U+FFFD REPLACEMENT CHARACTER (see Unicode PR #121:
    Recommended Practice for Replacement Characters), or in the binary or
    relaxed mode left as is, keeping the illegal non-characters as before.

    Raw non-Unicode characters outside the valid unicode range fail now to
    parse, because "A string is a sequence of zero or more Unicode
    characters" RFC 7159 section 1 and "JSON text SHALL be encoded in
    Unicode RFC 7159 section 8.1. We use now the UTF8_DISALLOW_SUPER flag
    when parsing unicode.

    If you know of other incompatibilities, please let me know.

  JSON and YAML
    You often hear that JSON is a subset of YAML. *in general, there is no
    way to configure JSON::XS to output a data structure as valid YAML* that
    works in all cases. If you really must use Cpanel::JSON::XS to generate
    YAML, you should use this algorithm (subject to change in future
    versions):

       my $to_yaml = Cpanel::JSON::XS->new->utf8->space_after (1);
       my $yaml = $to_yaml->encode ($ref) . "\n";

    This will *usually* generate JSON texts that also parse as valid YAML.

  SPEED
    It seems that JSON::XS is surprisingly fast, as shown in the following
    tables. They have been generated with the help of the "eg/bench" program
    in the JSON::XS distribution, to make it easy to compare on your own
    system.

    JSON::XS is with Data::MessagePack and Sereal one of the fastest
    serializers, because JSON and JSON::XS do not support backrefs (no graph
    structures), only trees. Storable supports backrefs, i.e. graphs.
    Data::MessagePack encodes its data binary (as Storable) and supports
    only very simple subset of JSON.

    First comes a comparison between various modules using a very short
    single-line JSON string (also available at
    <http://dist.schmorp.de/misc/json/short.json>).

       {"method": "handleMessage", "params": ["user1",
       "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
       1,  0]}

    It shows the number of encodes/decodes per second (JSON::XS uses the
    functional interface, while Cpanel::JSON::XS/2 uses the OO interface
    with pretty-printing and hash key sorting enabled, Cpanel::JSON::XS/3
    enables shrink. JSON::DWIW/DS uses the deserialize function, while
    JSON::DWIW::FJ uses the from_json method). Higher is better:

       module        |     encode |     decode |
       --------------|------------|------------|
       JSON::DWIW/DS |  86302.551 | 102300.098 |
       JSON::DWIW/FJ |  86302.551 |  75983.768 |
       JSON::PP      |  15827.562 |   6638.658 |
       JSON::Syck    |  63358.066 |  47662.545 |
       JSON::XS      | 511500.488 | 511500.488 |
       JSON::XS/2    | 291271.111 | 388361.481 |
       JSON::XS/3    | 361577.931 | 361577.931 |
       Storable      |  66788.280 | 265462.278 |
       --------------+------------+------------+

    That is, JSON::XS is almost six times faster than JSON::DWIW on
    encoding, about five times faster on decoding, and over thirty to
    seventy times faster than JSON's pure perl implementation. It also
    compares favourably to Storable for small amounts of data.

    Using a longer test string (roughly 18KB, generated from Yahoo! Locals
    search API (<http://dist.schmorp.de/misc/json/long.json>).

       module        |     encode |     decode |
       --------------|------------|------------|
       JSON::DWIW/DS |   1647.927 |   2673.916 |
       JSON::DWIW/FJ |   1630.249 |   2596.128 |
       JSON::PP      |    400.640 |     62.311 |
       JSON::Syck    |   1481.040 |   1524.869 |
       JSON::XS      |  20661.596 |   9541.183 |
       JSON::XS/2    |  10683.403 |   9416.938 |
       JSON::XS/3    |  20661.596 |   9400.054 |
       Storable      |  19765.806 |  10000.725 |
       --------------+------------+------------+

    Again, JSON::XS leads by far (except for Storable which non-surprisingly
    decodes a bit faster).

    On large strings containing lots of high Unicode characters, some
    modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
    result will be broken due to missing (or wrong) Unicode handling. Others
    refuse to decode or encode properly, so it was impossible to prepare a
    fair comparison table for that case.

    For updated graphs see
    <https://github.com/Sereal/Sereal/wiki/Sereal-Comparison-Graphs>

INTEROP with JSON and JSON::XS and other JSON modules
    As long as you only serialize data that can be directly expressed in
    JSON, "Cpanel::JSON::XS" is incapable of generating invalid JSON output
    (modulo bugs, but "JSON::XS" has found more bugs in the official JSON
    testsuite (1) than the official JSON testsuite has found in "JSON::XS"
    (0)). "Cpanel::JSON::XS" is currently the only known JSON decoder which
    passes all <http://seriot.ch/parsing_json.html> tests, while being the
    fastest also.

    When you have trouble decoding JSON generated by this module using other
    decoders, then it is very likely that you have an encoding mismatch or
    the other decoder is broken.

    When decoding, "JSON::XS" is strict by default and will likely catch all
    errors. There are currently two settings that change this: "relaxed"
    makes "JSON::XS" accept (but not generate) some non-standard extensions,
    and "allow_tags" or "allow_blessed" will allow you to encode and decode
    Perl objects, at the cost of being totally insecure and not outputting
    valid JSON anymore.

    JSON-XS-3.01 broke interoperability with JSON-2.90 with booleans. See
    JSON.

    Cpanel::JSON::XS needs to know the JSON and JSON::XS versions to be able
    work with those objects, especially when encoding a booleans like
    "{"is_true":true}". So you need to load these modules before.

    true/false overloading and boolean representations are supported.

    JSON::XS and JSON::PP representations are accepted and older JSON::XS
    accepts Cpanel::JSON::XS booleans. All JSON modules JSON, JSON, PP,
    JSON::XS, Cpanel::JSON::XS produce JSON::PP::Boolean objects, just Mojo
    and JSON::YAJL not. Mojo produces Mojo::JSON::_Bool and
    JSON::YAJL::Parser just an unblessed IV.

    Cpanel::JSON::XS accepts JSON::PP::Boolean and Mojo::JSON::_Bool objects
    as booleans.

    I cannot think of any reason to still use JSON::XS anymore.

  TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
    When you use "allow_tags" to use the extended (and also nonstandard and
    invalid) JSON syntax for serialized objects, and you still want to
    decode the generated serialize objects, you can run a regex to replace
    the tagged syntax by standard JSON arrays (it only works for "normal"
    package names without comma, newlines or single colons). First, the
    readable Perl version:

       # if your FREEZE methods return no values, you need this replace first:
       $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;

       # this works for non-empty constructor arg lists:
       $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;

    And here is a less readable version that is easy to adapt to other
    languages:

       $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;

    Here is an ECMAScript version (same regex):

       json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");

    Since this syntax converts to standard JSON arrays, it might be hard to
    distinguish serialized objects from normal arrays. You can prepend a
    "magic number" as first array element to reduce chances of a collision:

       $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;

    And after decoding the JSON text, you could walk the data structure
    looking for arrays with a first element of
    "XU1peReLzT4ggEllLanBYq4G9VzliwKF".

    The same approach can be used to create the tagged format with another
    encoder. First, you create an array with the magic string as first
    member, the classname as second, and constructor arguments last, encode
    it as part of your JSON structure, and then:

       $json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;

    Again, this has some limitations - the magic string must not be encoded
    with character escapes, and the constructor arguments must be non-empty.

RFC7159
    Since this module was written, Google has written a new JSON RFC, RFC
    7159 (and RFC7158). Unfortunately, this RFC breaks compatibility with
    both the original JSON specification on www.json.org and RFC4627.

    As far as I can see, you can get partial compatibility when parsing by
    using "->allow_nonref". However, consider the security implications of
    doing so.

    I haven't decided yet when to break compatibility with RFC4627 by
    default (and potentially leave applications insecure) and change the
    default to follow RFC7159, but application authors are well advised to
    call "->allow_nonref(0)" even if this is the current default, if they
    cannot handle non-reference values, in preparation for the day when the
    default will change.

SECURITY CONSIDERATIONS
    JSON::XS and Cpanel::JSON::XS are not only fast. JSON is generally the
    most secure serializing format, because it is the only one besides
    Data::MessagePack, which does not deserialize objects per default. For
    all languages, not just perl. The binary variant BSON (MongoDB) does
    more but is unsafe.

    It is trivial for any attacker to create such serialized objects in JSON
    and trick perl into expanding them, thereby triggering certain methods.
    Watch <https://www.youtube.com/watch?v=Gzx6KlqiIZE> for an exploit demo
    for "CVE-2015-1592 SixApart MovableType Storable Perl Code Execution"
    for a deserializer which expands objects. Deserializing even coderefs
    (methods, functions) or external data would be considered the most
    dangerous.

    Security relevant overview of serializers regarding deserializing
    objects by default:

                          Objects   Coderefs  External Data

        Data::Dumper      YES       YES       YES
        Storable          YES       NO (def)  NO
        Sereal            YES       NO        NO
        YAML              YES       NO        NO
        B::C              YES       YES       YES
        B::Bytecode       YES       YES       YES
        BSON              YES       YES       NO
        JSON::SL          YES       NO        YES
        JSON              NO (def)  NO        NO
        Data::MessagePack NO        NO        NO
        XML               NO        NO        YES

        Pickle            YES       YES       YES
        PHP Deserialize   YES       NO        NO

    When you are using JSON in a protocol, talking to untrusted potentially
    hostile creatures requires relatively few measures.

    First of all, your JSON decoder should be secure, that is, should not
    have any buffer overflows. Obviously, this module should ensure that.

    Second, you need to avoid resource-starving attacks. That means you
    should limit the size of JSON texts you accept, or make sure then when
    your resources run out, that's just fine (e.g. by using a separate
    process that can crash safely). The size of a JSON text in octets or
    characters is usually a good indication of the size of the resources
    required to decode it into a Perl structure. While JSON::XS can check
    the size of the JSON text, it might be too late when you already have it
    in memory, so you might want to check the size before you accept the
    string.

    Third, Cpanel::JSON::XS recurses using the C stack when decoding objects
    and arrays. The C stack is a limited resource: for instance, on my amd64
    machine with 8MB of stack size I can decode around 180k nested arrays
    but only 14k nested JSON objects (due to perl itself recursing deeply on
    croak to free the temporary). If that is exceeded, the program crashes.
    To be conservative, the default nesting limit is set to 512. If your
    process has a smaller stack, you should adjust this setting accordingly
    with the "max_depth" method.

    Also keep in mind that Cpanel::JSON::XS might leak contents of your Perl
    data structures in its error messages, so when you serialize sensitive
    information you might want to make sure that exceptions thrown by
    JSON::XS will not end up in front of untrusted eyes.

    If you are using Cpanel::JSON::XS to return packets to consumption by
    JavaScript scripts in a browser you should have a look at
    <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
    to see whether you are vulnerable to some common attack vectors (which
    really are browser design bugs, but it is still you who will have to
    deal with it, as major browser developers care only for features, not
    about getting security right). You might also want to also look at
    Mojo::JSON special escape rules to prevent from XSS attacks.

"OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)
    TL;DR: Due to security concerns, Cpanel::JSON::XS will not allow scalar
    data in JSON texts by default - you need to create your own
    Cpanel::JSON::XS object and enable "allow_nonref":

       my $json = JSON::XS->new->allow_nonref;

       $text = $json->encode ($data);
       $data = $json->decode ($text);

    The long version: JSON being an important and supposedly stable format,
    the IETF standardized it as RFC 4627 in 2006. Unfortunately the inventor
    of JSON Douglas Crockford unilaterally changed the definition of JSON in
    javascript. Rather than create a fork, the IETF decided to standardize
    the new syntax (apparently, so I as told, without finding it very
    amusing).

    The biggest difference between the original JSON and the new JSON is
    that the new JSON supports scalars (anything other than arrays and
    objects) at the top-level of a JSON text. While this is strictly
    backwards compatible to older versions, it breaks a number of protocols
    that relied on sending JSON back-to-back, and is a minor security
    concern.

    For example, imagine you have two banks communicating, and on one side,
    the JSON coder gets upgraded. Two messages, such as 10 and 1000 might
    then be confused to mean 101000, something that couldn't happen in the
    original JSON, because neither of these messages would be valid JSON.

    If one side accepts these messages, then an upgrade in the coder on
    either side could result in this becoming exploitable.

    This module has always allowed these messages as an optional extension,
    by default disabled. The security concerns are the reason why the
    default is still disabled, but future versions might/will likely upgrade
    to the newer RFC as default format, so you are advised to check your
    implementation and/or override the default with "->allow_nonref (0)" to
    ensure that future versions are safe.

THREADS
    Cpanel::JSON::XS has proper ithreads support, unlike JSON::XS. If you
    encounter any bugs with thread support please report them.

    From Version 4.00 - 4.19 you couldn't encode true with threads::shared
    magic.

BUGS
    While the goal of the Cpanel::JSON::XS module is to be correct, that
    unfortunately does not mean it's bug-free, only that the author thinks
    its design is bug-free. If you keep reporting bugs and tests they will
    be fixed swiftly, though.

    Since the JSON::XS author refuses to use a public bugtracker and prefers
    private emails, we use the tracker at github, so you might want to
    report any issues twice. Once in private to MLEHMANN to be fixed in
    JSON::XS and one to our the public tracker. Issues fixed by JSON::XS
    with a new release will also be backported to Cpanel::JSON::XS and
    5.6.2, as long as cPanel relies on 5.6.2 and Cpanel::JSON::XS as our
    serializer of choice.

    <https://github.com/rurban/Cpanel-JSON-XS/issues>

LICENSE
    This module is available under the same licences as perl, the Artistic
    license and the GPL.

SEE ALSO
    The cpanel_json_xs command line utility for quick experiments.

    JSON, JSON::XS, JSON::MaybeXS, Mojo::JSON, Mojo::JSON::MaybeXS,
    JSON::SL, JSON::DWIW, JSON::YAJL, JSON::Any, Test::JSON,
    Locale::Wolowitz, <https://metacpan.org/search?q=JSON>

    <https://tools.ietf.org/html/rfc7159>

    <https://tools.ietf.org/html/rfc4627>

AUTHOR
    Reini Urban <rurban@cpan.org>

    Marc Lehmann <schmorp@schmorp.de>, http://home.schmorp.de/

MAINTAINER
    Reini Urban <rurban@cpan.org>