json::xs - phpMan

XS(3)                 User Contributed Perl Documentation                XS(3)

NAME
       JSON::XS - JSON serialising/deserialising, done correctly and fast
       JSON::XS - XXXXXXX JSON XXXXXX/XXXXXXX
                  (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
SYNOPSIS
        use 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 = JSON::XS->new->ascii->pretty->allow_nonref;
        $pretty_printed_unencoded = $coder->encode ($perl_scalar);
        $perl_scalar = $coder->decode ($unicode_json_text);
        # Note that JSON version 2.0 and above will automatically use JSON::XS
        # if available, at virtually no speed overhead either, so you should
        # be able to just:
        use JSON;
        # and do the same things, except that you have a pure-perl fallback now.
DESCRIPTION
       This module converts Perl data structures to JSON and vice versa. Its
       primary goal is to be correct and its secondary goal is to be fast. To
       reach the latter goal it was written in C.
       Beginning with version 2.0 of the JSON module, when both JSON and
       JSON::XS are installed, then JSON will fall back on JSON::XS (this can
       be overridden) with no overhead due to emulation (by inheriting
       constructor and methods). If JSON::XS is not available, it will fall
       back to the compatible JSON::PP module as backend, so using JSON
       instead of JSON::XS gives you a portable JSON API that can be fast when
       you need and doesn't require a C compiler when that is a problem.
       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 MAPPING, below, on how JSON::XS maps perl values to JSON values and
       vice versa.
   FEATURES
       o   correct Unicode handling
           This module knows how to handle Unicode, documents how and when it
           does so, and even documents what "correct" means.
       o   round-trip integrity
           When you serialise a perl data structure using only data types
           supported by JSON and Perl, the deserialised 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.
       o   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).
       o   fast
           Compared to other JSON modules and other serialisers such as
           Storable, this module usually compares favourably in terms of
           speed, too.
       o   simple to use
           This module has both a simple functional interface as well as an
           object oriented interface.
       o   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.
FUNCTIONAL INTERFACE
       The following convenience methods are provided by this module. They are
       exported by default:
       $json_text = encode_json $perl_scalar
           Converts the given Perl data structure to a UTF-8 encoded, binary
           string (that is, the string contains octets only). Croaks on error.
           This function call is functionally identical to:
              $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
           Except being faster.
       $perl_scalar = decode_json $json_text
           The opposite of "encode_json": expects an UTF-8 (binary) string and
           tries to parse that as an UTF-8 encoded JSON text, returning the
           resulting reference. Croaks on error.
           This function call is functionally identical to:
              $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
           Except being faster.
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.
           Just ignore that flag unless you debug a Perl bug, a module written
           in XS or want to dive into the internals of perl. Otherwise it will
           only confuse you, as, despite the name, it says nothing about how
           your string is encoded. You can have Unicode strings with that flag
           set, with that flag clear, and you can have binary data with that
           flag set and that flag clear. Other possibilities exist, too.
           If you didn't know about that flag, just the better, pretend it
           doesn't exist.
       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.
           It's a fact. Learn to live with it.
       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 JSON::XS
           Creates a new JSON::XS 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 = 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.
             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.
             JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
             => ["\x{89}\\u0abc"]    # (perl syntax, U+abc escaped, U+89 not)
       $json = $json->utf8 ([$enable])
       $enabled = $json->get_utf8
           If $enable is true (or missing), then the "encode" method will
           encode the JSON result into UTF-8, as required by many protocols,
           while the "decode" method expects to be handled an UTF-8-encoded
           string.  Please note that UTF-8-encoded strings do not contain any
           characters outside the range 0..255, they are thus useful for
           bytewise/binary I/O. In future versions, enabling this option might
           enable autodetection of the UTF-16 and UTF-32 encoding families, as
           described in RFC4627.
           If $enable is false, then the "encode" method will return the JSON
           string as a (non-encoded) Unicode string, while "decode" expects
           thus a Unicode string.  Any decoding or encoding (e.g. to UTF-8 or
           UTF-16) needs to be done yourself, e.g. using the Encode module.
           See also the section ENCODING/CODESET FLAG NOTES later in this
           document.
           Example, output UTF-16BE-encoded JSON:
             use Encode;
             $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
           Example, decode UTF-32LE-encoded JSON:
             use Encode;
             $object = 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 = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
              =>
              {
                 "a" : [
                    1,
                    2
                 ]
              }
       $json = $json->indent ([$enable])
       $enabled = $json->get_indent
           If $enable is true (or missing), then the "encode" method will use
           a multiline format as output, putting every array member or
           object/hash key-value pair into its own line, indenting them
           properly.
           If $enable is false, no newlines or indenting will be produced, and
           the resulting JSON text is guaranteed not to contain any
           "newlines".
           This setting has no effect when decoding JSON texts.
       $json = $json->space_before ([$enable])
       $enabled = $json->get_space_before
           If $enable is true (or missing), then the "encode" method will add
           an extra optional space before the ":" separating keys from values
           in JSON objects.
           If $enable is false, then the "encode" method will not add any
           extra space at those places.
           This setting has no effect when decoding JSON texts. You will also
           most likely combine this setting with "space_after".
           Example, space_before enabled, space_after and indent disabled:
              {"key" :"value"}
       $json = $json->space_after ([$enable])
       $enabled = $json->get_space_after
           If $enable is true (or missing), then the "encode" method will add
           an extra optional space after the ":" separating keys from values
           in JSON objects and extra whitespace after the "," separating key-
           value pairs and array members.
           If $enable is false, then the "encode" method will not add any
           extra space at those places.
           This setting has no effect when decoding JSON texts.
           Example, space_before and indent disabled, space_after enabled:
              {"key": "value"}
       $json = $json->relaxed ([$enable])
       $enabled = $json->get_relaxed
           If $enable is true (or missing), then "decode" will accept some
           extensions to normal JSON syntax (see below). "encode" will not be
           affected in anyway. Be aware that this option makes you accept
           invalid JSON texts as if they were valid!. I suggest only to use
           this option to parse application-specific files written by humans
           (configuration files, resource files etc.)
           If $enable is false (the default), then "decode" will only accept
           valid JSON texts.
           Currently accepted extensions are:
           o   list items can have an end-comma
               JSON separates array elements and key-value pairs with commas.
               This can be annoying if you write JSON texts manually and want
               to be able to quickly append elements, so this extension
               accepts comma at the end of such items not just between them:
                  [
                     1,
                     2, <- this comma not normally allowed
                  ]
                  {
                     "k1": "v1",
                     "k2": "v2", <- this comma not normally allowed
                  }
           o   shell-style '#'-comments
               Whenever JSON allows whitespace, shell-style comments are
               additionally allowed. They are terminated by the first
               carriage-return or line-feed character, after which more white-
               space and comments are allowed.
                 [
                    1, # this comment not allowed in JSON
                       # neither this one...
                 ]
       $json = $json->canonical ([$enable])
       $enabled = $json->get_canonical
           If $enable is true (or missing), then the "encode" method will
           output JSON objects by sorting their keys. This is adding a
           comparatively high overhead.
           If $enable is false, then the "encode" method will output key-value
           pairs in the order Perl stores them (which will likely change
           between runs of the same script, and can change even within the
           same run from 5.18 onwards).
           This option is useful if you want the same data structure to be
           encoded as the same JSON text (given the same overall settings). If
           it is disabled, the same hash might be encoded differently even if
           contains the same data, as key-value pairs have no inherent
           ordering in Perl.
           This setting has no effect when decoding JSON texts.
           This setting has currently no effect on tied hashes.
       $json = $json->allow_nonref ([$enable])
       $enabled = $json->get_allow_nonref
           If $enable is true (or missing), then the "encode" method can
           convert a non-reference into its corresponding string, number or
           null JSON value, which is an extension to RFC4627. Likewise,
           "decode" will accept those JSON values instead of croaking.
           If $enable is false, then the "encode" method will croak if it
           isn't passed an arrayref or hashref, as JSON texts must either be
           an object or array. Likewise, "decode" will croak if given
           something that is not a JSON object or array.
           Example, encode a Perl scalar as JSON value with enabled
           "allow_nonref", resulting in an invalid JSON text:
              JSON::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 = $json->allow_blessed ([$enable])
       $enabled = $json->get_allow_blessed
           See "OBJECT SERIALISATION" for details.
           If $enable is true (or missing), then the "encode" method will not
           barf when it encounters a blessed reference that it cannot convert
           otherwise. Instead, a JSON "null" value is encoded instead of the
           object.
           If $enable is false (the default), then "encode" will throw an
           exception when it encounters a blessed object that it cannot
           convert otherwise.
           This setting has no effect on "decode".
       $json = $json->convert_blessed ([$enable])
       $enabled = $json->get_convert_blessed
           See "OBJECT SERIALISATION" for details.
           If $enable is true (or missing), then "encode", upon encountering a
           blessed object, will check for the availability of the "TO_JSON"
           method on the object's class. If found, it will be called in scalar
           context and the resulting scalar will be encoded instead of the
           object.
           The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
           returns other blessed objects, those will be handled in the same
           way. "TO_JSON" must take care of not causing an endless recursion
           cycle (== crash) in this case. The name of "TO_JSON" was chosen
           because other methods called by the Perl core (== not by the user
           of the object) are usually in upper case letters and to avoid
           collisions with any "to_json" function or method.
           If $enable is false (the default), then "encode" will not consider
           this type of conversion.
           This setting has no effect on "decode".
       $json = $json->allow_tags ([$enable])
       $enabled = $json->allow_tags
           See "OBJECT SERIALISATION" for details.
           If $enable is true (or missing), then "encode", upon encountering a
           blessed object, will check for the availability of the "FREEZE"
           method on the object's class. If found, it will be used to
           serialise the object into a nonstandard tagged JSON value (that
           JSON decoders cannot decode).
           It also causes "decode" to parse such tagged JSON values and
           deserialise 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 deserialised
           data structure. If it returns an empty list (NOTE: not "undef",
           which is a valid scalar), the original deserialised hash will be
           inserted. This setting can slow down decoding considerably.
           When $coderef is omitted or undefined, any existing callback will
           be removed and "decode" will not change the deserialised hash in
           any way.
           Example, convert all JSON objects into the integer 5:
              my $js = JSON::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 $coderef is omitted or undefined, the corresponding callback
           will be disabled. There can only ever be one callback for a given
           key.
           As this callback gets called less often then the
           "filter_json_object" one, decoding speed will not usually suffer as
           much. Therefore, single-key objects make excellent targets to
           serialise Perl objects into, especially as single-key JSON objects
           are as close to the type-tagged value concept as JSON gets (it's
           basically an ID/VALUE tuple). Of course, JSON does not support this
           in any way, so you need to make sure your data never looks like a
           serialised Perl hash.
           Typical names for the single object key are "__class_whatever__",
           or "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or
           even things like "__class_md5sum(classname)__", to reduce the risk
           of clashing with real hashes.
           Example, decode JSON objects of the form "{ "__widget__" => <id> }"
           into the corresponding $WIDGET{<id>} object:
              # return whatever is in $WIDGET{5}:
              JSON::XS
                 ->new
                 ->filter_json_single_key_object (__widget__ => sub {
                       $WIDGET{ $_[0] }
                    })
                 ->decode ('{"__widget__": 5')
              # this can be used with a TO_JSON method in some "widget" class
              # for serialisation to json:
              sub WidgetBase::TO_JSON {
                 my ($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_text = $json->encode ($perl_scalar)
           Converts the given Perl value or data structure to its JSON
           representation. Croaks on error.
       $perl_scalar = $json->decode ($json_text)
           The opposite of "encode": expects a JSON text and tries to parse
           it, returning the resulting simple scalar or reference. Croaks on
           error.
       ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
           This works like the "decode" method, but instead of raising an
           exception when there is trailing garbage after the first JSON
           object, it will silently stop parsing there and return the number
           of characters consumed so far.
           This is useful if your JSON texts are not delimited by an outer
           protocol and you need to know where the JSON text ends.
              JSON::XS->new->decode_prefix ("[1] the tail")
              => ([], 3)
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).
       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 = JSON::XS->new->incr_parse ("[5][7][1,2]");
       $lvalue_string = $json->incr_text
           This method returns the currently stored JSON fragment as an
           lvalue, that is, you can manipulate it. This only works when a
           preceding call to "incr_parse" in scalar context successfully
           returned an object. Under all other circumstances you must not call
           this function (I mean it.  although in simple tests it might
           actually work, it will fail under real world conditions). As a
           special exception, you can also call this method before having
           parsed anything.
           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 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 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 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 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
       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 JSON::XS;
          # open the monster
          open my $fh, "<bigfile.json"
             or die "bigfile: $!";
          # first parse the initial "["
          for (;;) {
             sysread $fh, my $buf, 65536
                or die "read error: $!";
             $json->incr_parse ($buf); # void context, so no parsing
             # Exit the loop once we found and removed(!) the initial "[".
             # In essence, we are (ab-)using the $json object as a simple scalar
             # we append data to.
             last if $json->incr_text =~ s/^ \s* \[ //x;
          }
          # now we have the skipped the initial "[", so continue
          # parsing all the elements.
          for (;;) {
             # in this loop we read data until we got a single JSON object
             for (;;) {
                if (my $obj = $json->incr_parse) {
                   # do something with $obj
                   last;
                }
                # add more data
                sysread $fh, my $buf, 65536
                   or die "read error: $!";
                $json->incr_parse ($buf); # void context, so no parsing
             }
             # in this loop we read data until we either found and parsed the
             # separating "," between elements, or the final "]"
             for (;;) {
                # first skip whitespace
                $json->incr_text =~ s/^\s*//;
                # if we find "]", we are done
                if ($json->incr_text =~ s/^\]//) {
                   print "finished.\n";
                   exit;
                }
                # if we find ",", we can continue with the next element
                if ($json->incr_text =~ s/^,//) {
                   last;
                }
                # if we find anything else, we have a parse error!
                if (length $json->incr_text) {
                   die "parse error near ", $json->incr_text;
                }
                # else add more data
                sysread $fh, my $buf, 65536
                   or die "read error: $!";
                $json->incr_parse ($buf); # void context, so no parsing
             }
       This is a complex example, but most of the complexity comes from the
       fact that we are trying to be correct (bear with me if I am wrong, I
       never ran the above example :).
MAPPING
       This section describes how 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, 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, JSON::XS only guarantees
           precision up to but not including the least significant bit.
       true, false
           These JSON atoms become "Types::Serialiser::true" and
           "Types::Serialiser::false", respectively. They are overloaded to
           act almost exactly like the numbers 1 and 0. You can check whether
           a scalar is a JSON boolean by using the
           "Types::Serialiser::is_bool" function (after "use
           Types::Serialier", of course).
       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 SERIALISATION", 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. JSON::XS can optionally sort the
           hash keys (determined by the canonical flag), so the same
           datastructure will serialise to the same JSON text (given same
           settings and version of 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.
           Since "JSON::XS" uses the boolean model from Types::Serialiser, you
           can also "use Types::Serialiser" and then use
           "Types::Serialiser::false" and "Types::Serialiser::true" to improve
           readability.
              use Types::Serialiser;
              encode_json [\0, Types::Serialiser::true]      # yields [false,true]
       Types::Serialiser::true, Types::Serialiser::false
           These special values from the Types::Serialiser module become JSON
           true and JSON false values, respectively. You can also use "\1" and
           "\0" directly if you want.
       blessed objects
           Blessed objects are not directly representable in JSON, but
           "JSON::XS" allows various ways of handling objects. See "OBJECT
           SERIALISATION", below, for details.
       simple scalars
           Simple Perl scalars (any scalar that is not a reference) are the
           most difficult objects to encode: JSON::XS will encode undefined
           scalars as JSON "null" values, scalars that have last been used in
           a string context before encoding as JSON strings, and anything else
           as number value:
              # dump as number
              encode_json [2]                      # yields [2]
              encode_json [-3.0e17]                # yields [-3e+17]
              my $value = 5; encode_json [$value]  # yields [5]
              # used as string, so dump as string
              print $value;
              encode_json [$value]                 # yields ["5"]
              # undef becomes null
              encode_json [undef]                  # yields [null]
           You can force the type to be a 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.
           You can not currently force the type in other, less obscure, ways.
           Tell me if you need this capability (but don't forget to explain
           why it's needed :).
           Note that numerical precision has the same meaning as under Perl
           (so binary to decimal conversion follows the same rules as in Perl,
           which can differ to other languages). Also, your perl interpreter
           might expose extensions to the floating point numbers of your
           platform, such as infinities or NaN's - these cannot be represented
           in JSON, and it is an error to pass those in.
   OBJECT SERIALISATION
       As JSON cannot directly represent Perl objects, you have to choose
       between a pure JSON representation (without the ability to deserialise
       the object automatically again), and a nonstandard extension to the
       JSON syntax, tagged values.
       SERIALISATION
       What happens when "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, "JSON::XS" uses the Types::Serialiser object
           serialisation 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 serialise, and the second
           argument being the constant string "JSON" to distinguish it from
           other serialisers.
           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, $serialiser) = @_;
                 ($self->{type}, $self->{id})
              }
       2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
           In this case, the "TO_JSON" method of the object is invoked in
           scalar context. It must return a single scalar that can be directly
           encoded into JSON. This scalar replaces the object in the JSON
           text.
           For example, the following "TO_JSON" method will convert all URI
           objects to JSON strings when serialised. The fatc that these values
           originally were URI objects is lost.
              sub URI::TO_JSON {
                 my ($uri) = @_;
                 $uri->as_string
              }
       3. "allow_blessed" is enabled.
           The object will be serialised as a JSON null value.
       4. none of the above
           If none of the settings are enabled or the respective methods are
           missing, "JSON::XS" throws an exception.
       DESERIALISATION
       For deserialisation there are only two cases to consider: either
       nonstandard tagging was used, in which case "allow_tags" decides, or
       objects cannot be automatically be deserialised, in which case you can
       use postprocessing or the "filter_json_object" or
       "filter_json_single_key_object" callbacks to get some real objects our
       of your JSON.
       This section only considers the tagged value case: I a tagged JSON
       object is encountered during decoding and "allow_tags" is disabled, a
       parse error will result (as if tagged values were not part of the
       grammar).
       If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method
       of the package/classname used during serialisation (it will not attempt
       to load the package as a Perl module). If there is no such method, the
       decoding will fail with an error.
       Otherwise, the "THAW" method is invoked with the classname as first
       argument, the constant string "JSON" as second argument, and all the
       values from the JSON array (the values originally returned by the
       "FREEZE" method) as remaining arguments.
       The method must then return the object. While technically you can
       return any Perl scalar, you might have to enable the "enable_nonref"
       setting to make that work in all cases, so better return an actual
       blessed reference.
       As an example, let's implement a "THAW" function that regenerates the
       "My::Object" from the "FREEZE" example earlier:
          sub My::Object::THAW {
             my ($class, $serialiser, $type, $id) = @_;
             $class->new (type => $type, id => $id)
          }
ENCODING/CODESET FLAG NOTES
       The interested reader might have seen a number of flags that signify
       encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
       some confusion on what these do, so here is a short comparison:
       "utf8" controls whether the JSON text created by "encode" (and expected
       by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
       control whether "encode" escapes character values outside their
       respective codeset range. Neither of these flags conflict with each
       other, although some combinations make less sense than others.
       Care has been taken to make all flags symmetrical with respect to
       "encode" and "decode", that is, texts encoded with any combination of
       these flag values will be correctly decoded when the same flags are
       used - in general, if you use different flag settings while encoding
       vs. when decoding you likely have a bug somewhere.
       Below comes a verbose discussion of these flags. Note that a "codeset"
       is simply an abstract set of character-codepoint pairs, while an
       encoding takes those codepoint numbers and encodes them, in our case
       into octets. Unicode is (among other things) a codeset, UTF-8 is an
       encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
       encodings at the same time, which can be confusing.
       "utf8" flag disabled
           When "utf8" is disabled (the default), then "encode"/"decode"
           generate and expect Unicode strings, that is, characters with high
           ordinal Unicode values (> 255) will be encoded as such characters,
           and likewise such characters are decoded as-is, no changes to them
           will be done, except "(re-)interpreting" them as Unicode codepoints
           or Unicode characters, respectively (to Perl, these are the same
           thing in strings unless you do funny/weird/dumb stuff).
           This is useful when you want to do the encoding yourself (e.g. when
           you want to have UTF-16 encoded JSON texts) or when some other
           layer does the encoding for you (for example, when printing to a
           terminal using a filehandle that transparently encodes to UTF-8 you
           certainly do NOT want to UTF-8 encode your data first and have Perl
           encode it another time).
       "utf8" flag enabled
           If the "utf8"-flag is enabled, "encode"/"decode" will encode all
           characters using the corresponding UTF-8 multi-byte sequence, and
           will expect your input strings to be encoded as UTF-8, that is, no
           "character" of the input string must have any value > 255, as UTF-8
           does not allow that.
           The "utf8" flag therefore switches between two modes: disabled
           means you will get a Unicode string in Perl, enabled means you get
           an UTF-8 encoded octet/binary string in Perl.
       "latin1" or "ascii" flags enabled
           With "latin1" (or "ascii") enabled, "encode" will escape characters
           with ordinal values > 255 (> 127 with "ascii") and encode the
           remaining characters as specified by the "utf8" flag.
           If "utf8" is disabled, then the result is also correctly encoded in
           those character sets (as both are proper subsets of Unicode,
           meaning that a Unicode string with all character values < 256 is
           the same thing as a ISO-8859-1 string, and a Unicode string with
           all character values < 128 is the same thing as an ASCII string in
           Perl).
           If "utf8" is enabled, you still get a correct UTF-8-encoded string,
           regardless of these flags, just some more characters will be
           escaped using "\uXXXX" then before.
           Note that ISO-8859-1-encoded strings are not compatible with UTF-8
           encoding, while ASCII-encoded strings are. That is because the
           ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the
           ISO-8859-1 codeset being a subset of Unicode), while ASCII is.
           Surprisingly, "decode" will ignore these flags and so treat all
           input values as governed by the "utf8" flag. If it is disabled,
           this allows you to decode ISO-8859-1- and ASCII-encoded strings, as
           both strict subsets of Unicode. If it is enabled, you can correctly
           decode UTF-8 encoded strings.
           So neither "latin1" nor "ascii" are incompatible with the "utf8"
           flag - they only govern when the JSON output engine escapes a
           character or not.
           The main use for "latin1" is to relatively efficiently store binary
           data as JSON, at the expense of breaking compatibility with most
           JSON decoders.
           The main use for "ascii" is to force the output to not contain
           characters with values > 127, which means you can interpret the
           resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
           any character set and 8-bit-encoding, and still get the same data
           structure back. This is useful when your channel for JSON transfer
           is not 8-bit clean or the encoding might be mangled in between
           (e.g. in mail), and works because ASCII is a proper subset of most
           8-bit and multibyte encodings in use in the world.
   JSON and ECMAscript
       JSON syntax is based on how literals are represented in javascript (the
       not-standardised 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 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 JSON::XS;
          print 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 = JSON::XS->new->utf8->encode ([chr 0x2028]);
          $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
          $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
          print $json;
       Note that this is a bad idea: the above only works for U+2028 and
       U+2029 and thus only for fully ECMAscript-compliant parsers. Many
       existing javascript implementations, however, have issues with other
       characters as well - using "eval" naively simply will cause problems.
       Another problem is that some javascript implementations reserve some
       property names for their own purposes (which probably makes them non-
       ECMAscript-compliant). For example, Iceweasel reserves the "__proto__"
       property name for its own purposes.
       If that is a problem, you could parse try to filter the resulting JSON
       output for these property strings, e.g.:
          $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
       This works because "__proto__" is not valid outside of strings, so
       every occurrence of ""__proto__"\s*:" must be a string used as property
       name.
       If you know of other incompatibilities, please let me know.
   JSON and YAML
       You often hear that JSON is a subset of YAML. This is, however, a mass
       hysteria(*) and very far from the truth (as of the time of this
       writing), so let me state it clearly: 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 JSON::XS to generate YAML, you should use this
       algorithm (subject to change in future versions):
          my $to_yaml = 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.
       Please note that YAML has hardcoded limits on (simple) object key
       lengths that JSON doesn't have and also has different and incompatible
       unicode character escape syntax, so you should make sure that your hash
       keys are noticeably shorter than the 1024 "stream characters" YAML
       allows and that you do not have characters with codepoint values
       outside the Unicode BMP (basic multilingual page). YAML also does not
       allow "\/" sequences in strings (which JSON::XS does not currently
       generate, but other JSON generators might).
       There might be other incompatibilities that I am not aware of (or the
       YAML specification has been changed yet again - it does so quite
       often). In general you should not try to generate YAML with a JSON
       generator or vice versa, or try to parse JSON with a YAML parser or
       vice versa: chances are high that you will run into severe
       interoperability problems when you least expect it.
       (*) I have been pressured multiple times by Brian Ingerson (one of the
           authors of the YAML specification) to remove this paragraph,
           despite him acknowledging that the actual incompatibilities exist.
           As I was personally bitten by this "JSON is YAML" lie, I refused
           and said I will continue to educate people about these issues, so
           others do not run into the same problem again and again. After
           this, Brian called me a (quote)complete and worthless
           idiot(unquote).
           In my opinion, instead of pressuring and insulting people who
           actually clarify issues with YAML and the wrong statements of some
           of its proponents, I would kindly suggest reading the JSON spec
           (which is not that difficult or long) and finally make YAML
           compatible to it, and educating users about the changes, instead of
           spreading lies about the real compatibility for many years and
           trying to silence people who point out that it isn't true.
           Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
           even though the incompatibilities have been documented (and are
           known to Brian) for many years and the spec makes explicit claims
           that YAML is a superset of JSON. It would be so easy to fix, but
           apparently, bullying people and corrupting userdata is so much
           easier.
   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.
       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 JSON::XS/2 uses the OO interface with
       pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
       JSON::DWIW/DS uses the deserialise 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.
SECURITY CONSIDERATIONS
       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
       and I am trying hard on making that true, but you never know.
       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, 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.
       Something else could bomb you, too, that I forgot to think of. In that
       case, you get to keep the pieces. I am always open for hints, though...
       Also keep in mind that JSON::XS might leak contents of your Perl data
       structures in its error messages, so when you serialise 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 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).
INTEROPERABILITY WITH OTHER MODULES
       "JSON::XS" uses the Types::Serialiser module to provide boolean
       constants. That means that the JSON true and false values will be
       comaptible to true and false values of iother modules that do the same,
       such as JSON::PP and CBOR::XS.
THREADS
       This module is not guaranteed to be thread safe and there are no plans
       to change this until Perl gets thread support (as opposed to the
       horribly slow so-called "threads" which are simply slow and bloated
       process simulations - use fork, it's much faster, cheaper, better).
       (It might actually work, but you have been warned).
THE PERILS OF SETLOCALE
       Sometimes people avoid the Perl locale support and directly call the
       system's setlocale function with "LC_ALL".
       This breaks both perl and modules such as JSON::XS, as stringification
       of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
       might print 1, and JSON::XS might output illegal JSON as JSON::XS
       relies on perl to stringify numbers).
       The solution is simple: don't call "setlocale", or use it for only
       those categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
       If you need "LC_NUMERIC", you should enable it only around the code
       that actually needs it (avoiding stringification of numbers), and
       restore it afterwards.
BUGS
       While the goal of this module is to be correct, that unfortunately does
       not mean it's bug-free, only that I think its design is bug-free. If
       you keep reporting bugs they will be fixed swiftly, though.
       Please refrain from using rt.cpan.org or any other bug reporting
       service. I put the contact address into my modules for a reason.
SEE ALSO
       The json_xs command line utility for quick experiments.
AUTHOR
        Marc Lehmann <schmorp AT schmorp.de>
        http://home.schmorp.de/

perl v5.16.3                      2013-10-29                             XS(3)