[ViewVC] Annotation of: cvs/JSON-XS/README

NAME
    JSON::XS - JSON serialising/deserialising, done correctly and fast

SYNOPSIS
     use JSON::XS;

     # exported functions, croak on error

     $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
     $perl_hash_or_arrayref  = from_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);

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 COMPARISON, below, for a comparison to some other JSON modules.

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

  FEATURES
    * correct handling of unicode issues
        This module knows how to handle Unicode, and even documents how and
        when it does so.

    * round-trip integrity
        When you serialise a perl data structure using only datatypes
        supported by JSON, the deserialised data structure is identical on
        the Perl level. (e.g. the string "2.0" doesn't suddenly become "2").

    * strict checking of JSON correctness
        There is no guessing, no generating of illegal JSON strings by
        default, and only JSON is accepted as input by default (the latter
        is a security feature).

    * fast
        Compared to other JSON modules, this module compares favourably in
        terms of speed, too.

    * simple to use
        This module has both a simple functional interface as well as an OO
        interface.

    * reasonably versatile output formats
        You can choose between the most compact guarenteed single-line
        format possible (nice for simple line-based protocols), a pure-ascii
        format (for when your transport is not 8-bit clean), 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 convinience methods are provided by this module. They are
    exported by default:

    $json_string = to_json $perl_scalar
        Converts the given Perl data structure (a simple scalar or a
        reference to a hash or array) 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::XS->new->utf8->encode ($perl_scalar)".

    $perl_scalar = from_json $json_string
        The opposite of "to_json": expects an UTF-8 (binary) string and
        tries to parse that as an UTF-8 encoded JSON string, returning the
        resulting simple scalar or reference. Croaks on error.

        This function call is functionally identical to
        "JSON::XS->new->utf8->decode ($json_string)".

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(1)->space_after(1)->encode ({a => [1,2]})
           => {"a": [1, 2]}

    $json = $json->ascii ([$enable])
        If $enable is true (or missing), then the "encode" method will not
        generate characters outside the code range 0..127. 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.

        If $enable is false, then the "encode" method will not escape
        Unicode characters unless necessary.

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

    $json = $json->utf8 ([$enable])
        If $enable is true (or missing), then the "encode" method will
        encode the JSON string 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.

        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.

        Example, output UTF-16-encoded JSON:

    $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])
        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, identing them
        properly.

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

        This setting has no effect when decoding JSON strings.

    $json = $json->space_before ([$enable])
        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 strings. 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])
        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 strings.

        Example, space_before and indent disabled, space_after enabled:

           {"key": "value"}

    $json = $json->canonical ([$enable])
        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).

        This option is useful if you want the same data structure to be
        encoded as the same JSON string (given the same overall settings).
        If it is disabled, the same hash migh 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 strings.

    $json = $json->allow_nonref ([$enable])
        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 strings 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 = $json->shrink ([$enable])
        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 strings 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.

        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_string = $json->encode ($perl_scalar)
        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.

    $perl_scalar = $json->decode ($json_string)
        The opposite of "encode": expects a JSON string 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".

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 uppcercase *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.

    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 or numeric (floating point)
        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.

    true, false
        These JSON atoms become 0, 1, respectively. Information is lost in
        this process. Future versions might represent those values
        differently, but they will be guarenteed to act like these integers
        would normally in Perl.

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

  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, 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 the single run of a program.
        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.

    array references
        Perl array references become JSON arrays.

    blessed objects
        Blessed objects are not allowed. JSON::XS currently tries to encode
        their underlying representation (hash- or arrayref), but this
        behaviour might change in future versions.

    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 value, scalars that have last been used in a
        string context before encoding as JSON strings and anything else as
        number value:

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

           # used as string, so dump as string
           print $value;
           to_json [$value]                 # yields ["5"]

           # undef becomes null
           to_json [undef]                  # yields [null]

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

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

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

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

        You can not currently output JSON booleans or force the type in
        other, less obscure, ways. Tell me if you need this capability.

    circular data structures
        Those will be encoded until memory or stackspace runs out.

COMPARISON
    As already mentioned, this module was created because none of the
    existing JSON modules could be made to work correctly. First I will
    describe the problems (or pleasures) I encountered with various existing
    JSON modules, followed by some benchmark values. JSON::XS was designed
    not to suffer from any of these problems or limitations.

    JSON 1.07
        Slow (but very portable, as it is written in pure Perl).

        Undocumented/buggy Unicode handling (how JSON handles unicode values
        is undocumented. One can get far by feeding it unicode strings and
        doing en-/decoding oneself, but unicode escapes are not working
        properly).

        No roundtripping (strings get clobbered if they look like numbers,
        e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
        will decode into the number 2.

    JSON::PC 0.01
        Very fast.

        Undocumented/buggy Unicode handling.

        No roundtripping.

        Has problems handling many Perl values (e.g. regex results and other
        magic values will make it croak).

        Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
        which is not a valid JSON string.

        Unmaintained (maintainer unresponsive for many months, bugs are not
        getting fixed).

    JSON::Syck 0.21
        Very buggy (often crashes).

        Very inflexible (no human-readable format supported, format pretty
        much undocumented. I need at least a format for easy reading by
        humans and a single-line compact format for use in a protocol, and
        preferably a way to generate ASCII-only JSON strings).

        Completely broken (and confusingly documented) Unicode handling
        (unicode escapes are not working properly, you need to set
        ImplicitUnicode to *different* values on en- and decoding to get
        symmetric behaviour).

        No roundtripping (simple cases work, but this depends on wether the
        scalar value was used in a numeric context or not).

        Dumping hashes may skip hash values depending on iterator state.

        Unmaintained (maintainer unresponsive for many months, bugs are not
        getting fixed).

        Does not check input for validity (i.e. will accept non-JSON input
        and return "something" instead of raising an exception. This is a
        security issue: imagine two banks transfering money between each
        other using JSON. One bank might parse a given non-JSON request and
        deduct money, while the other might reject the transaction with a
        syntax error. While a good protocol will at least recover, that is
        extra unnecessary work and the transaction will still not succeed).

    JSON::DWIW 0.04
        Very fast. Very natural. Very nice.

        Undocumented unicode handling (but the best of the pack. Unicode
        escapes still don't get parsed properly).

        Very inflexible.

        No roundtripping.

        Does not generate valid JSON (key strings are often unquoted, empty
        keys result in nothing being output)

        Does not check input for validity.

  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 is a comparison between various modules using a very simple JSON
    string, showing the number of encodes/decodes per second (JSON::XS is
    the functional interface, while JSON::XS/2 is the OO interface with
    pretty-printing and hashkey sorting enabled).

       module     |     encode |     decode |
       -----------|------------|------------|
       JSON       |      14006 |       6820 |
       JSON::DWIW |     200937 |     120386 |
       JSON::PC   |      85065 |     129366 |
       JSON::Syck |      59898 |      44232 |
       JSON::XS   |    1171478 |     342435 |
       JSON::XS/2 |     730760 |     328714 |
       -----------+------------+------------+

    That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80
    times faster than JSON, even with pretty-printing and key sorting.

    Using a longer test string (roughly 8KB, generated from Yahoo! Locals
    search API (http://nanoref.com/yahooapis/mgPdGg):

       module     |     encode |     decode |
       -----------|------------|------------|
       JSON       |        673 |         38 |
       JSON::DWIW |       5271 |        770 |
       JSON::PC   |       9901 |       2491 |
       JSON::Syck |       2360 |        786 |
       JSON::XS   |      37398 |       3202 |
       JSON::XS/2 |      13765 |       3153 |
       -----------+------------+------------+

    Again, JSON::XS leads by far in the encoding case, while still beating
    every other module in the decoding case.

RESOURCE LIMITS
    JSON::XS does not impose any limits on the size of JSON texts or Perl
    values they represent - if your machine can handle it, JSON::XS will
    encode or decode it. Future versions might optionally impose structure
    depth and memory use resource limits.

BUGS
    While the goal of this module is to be correct, that unfortunately does
    not mean its bug-free, only that I think its design is bug-free. It is
    still very young and not well-tested. If you keep reporting bugs they
    will be fixed swiftly, though.

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

Revision:	1.4
Committed:	Fri Mar 23 18:33:50 2007 UTC (17 years, 2 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_3
Changes since 1.3:	+211 -48 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	NAME
2	root	1.2	JSON::XS - JSON serialising/deserialising, done correctly and fast
3	root	1.1
4			SYNOPSIS
5	root	1.2	use JSON::XS;
6	root	1.1
7	root	1.4	# exported functions, croak on error
8
9			$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
10			$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
11
12			# oo-interface
13
14			$coder = JSON::XS->new->ascii->pretty->allow_nonref;
15			$pretty_printed_unencoded = $coder->encode ($perl_scalar);
16			$perl_scalar = $coder->decode ($unicode_json_text);
17
18	root	1.1	DESCRIPTION
19	root	1.2	This module converts Perl data structures to JSON and vice versa. Its
20			primary goal is to be correct and its secondary goal is to be fast.
21			To reach the latter goal it was written in C.
22
23			As this is the n-th-something JSON module on CPAN, what was the reason
24			to write yet another JSON module? While it seems there are many JSON
25			modules, none of them correctly handle all corner cases, and in most
26			cases their maintainers are unresponsive, gone missing, or not listening
27			to bug reports for other reasons.
28
29			See COMPARISON, below, for a comparison to some other JSON modules.
30
31	root	1.4	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
32			vice versa.
33
34	root	1.2	FEATURES
35			* correct handling of unicode issues
36	root	1.4	This module knows how to handle Unicode, and even documents how and
37			when it does so.
38	root	1.2
39			* round-trip integrity
40			When you serialise a perl data structure using only datatypes
41			supported by JSON, the deserialised data structure is identical on
42			the Perl level. (e.g. the string "2.0" doesn't suddenly become "2").
43
44			* strict checking of JSON correctness
45			There is no guessing, no generating of illegal JSON strings by
46	root	1.4	default, and only JSON is accepted as input by default (the latter
47			is a security feature).
48	root	1.2
49			* fast
50	root	1.4	Compared to other JSON modules, this module compares favourably in
51			terms of speed, too.
52	root	1.2
53			* simple to use
54			This module has both a simple functional interface as well as an OO
55			interface.
56
57			* reasonably versatile output formats
58	root	1.4	You can choose between the most compact guarenteed single-line
59			format possible (nice for simple line-based protocols), a pure-ascii
60			format (for when your transport is not 8-bit clean), or a
61			pretty-printed format (for when you want to read that stuff). Or you
62			can combine those features in whatever way you like.
63	root	1.2
64			FUNCTIONAL INTERFACE
65			The following convinience methods are provided by this module. They are
66			exported by default:
67
68			$json_string = to_json $perl_scalar
69			Converts the given Perl data structure (a simple scalar or a
70			reference to a hash or array) to a UTF-8 encoded, binary string
71			(that is, the string contains octets only). Croaks on error.
72
73	root	1.4	This function call is functionally identical to
74			"JSON::XS->new->utf8->encode ($perl_scalar)".
75	root	1.2
76			$perl_scalar = from_json $json_string
77			The opposite of "to_json": expects an UTF-8 (binary) string and
78			tries to parse that as an UTF-8 encoded JSON string, returning the
79			resulting simple scalar or reference. Croaks on error.
80
81	root	1.4	This function call is functionally identical to
82			"JSON::XS->new->utf8->decode ($json_string)".
83	root	1.2
84			OBJECT-ORIENTED INTERFACE
85			The object oriented interface lets you configure your own encoding or
86			decoding style, within the limits of supported formats.
87
88			$json = new JSON::XS
89			Creates a new JSON::XS object that can be used to de/encode JSON
90			strings. All boolean flags described below are by default
91			disabled.
92
93			The mutators for flags all return the JSON object again and thus
94			calls can be chained:
95
96			my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})
97			=> {"a": [1, 2]}
98
99	root	1.4	$json = $json->ascii ([$enable])
100			If $enable is true (or missing), then the "encode" method will not
101			generate characters outside the code range 0..127. Any unicode
102			characters outside that range will be escaped using either a single
103			\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
104			as per RFC4627.
105	root	1.2
106			If $enable is false, then the "encode" method will not escape
107			Unicode characters unless necessary.
108
109			JSON::XS->new->ascii (1)->encode (chr 0x10401)
110			=> \ud801\udc01
111
112	root	1.4	$json = $json->utf8 ([$enable])
113			If $enable is true (or missing), then the "encode" method will
114			encode the JSON string into UTF-8, as required by many protocols,
115			while the "decode" method expects to be handled an UTF-8-encoded
116			string. Please note that UTF-8-encoded strings do not contain any
117			characters outside the range 0..255, they are thus useful for
118			bytewise/binary I/O.
119	root	1.2
120			If $enable is false, then the "encode" method will return the JSON
121			string as a (non-encoded) unicode string, while "decode" expects
122			thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or
123			UTF-16) needs to be done yourself, e.g. using the Encode module.
124
125	root	1.4	Example, output UTF-16-encoded JSON:
126
127			$json = $json->pretty ([$enable])
128	root	1.2	This enables (or disables) all of the "indent", "space_before" and
129			"space_after" (and in the future possibly more) flags in one call to
130			generate the most readable (or most compact) form possible.
131
132	root	1.4	Example, pretty-print some simple structure:
133
134	root	1.2	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
135			=>
136			{
137			"a" : [
138			1,
139			2
140			]
141			}
142
143	root	1.4	$json = $json->indent ([$enable])
144			If $enable is true (or missing), then the "encode" method will use a
145			multiline format as output, putting every array member or
146			object/hash key-value pair into its own line, identing them
147			properly.
148	root	1.2
149			If $enable is false, no newlines or indenting will be produced, and
150			the resulting JSON strings is guarenteed not to contain any
151			"newlines".
152
153			This setting has no effect when decoding JSON strings.
154
155	root	1.4	$json = $json->space_before ([$enable])
156			If $enable is true (or missing), then the "encode" method will add
157			an extra optional space before the ":" separating keys from values
158			in JSON objects.
159	root	1.2
160			If $enable is false, then the "encode" method will not add any extra
161			space at those places.
162
163			This setting has no effect when decoding JSON strings. You will also
164			most likely combine this setting with "space_after".
165
166	root	1.4	Example, space_before enabled, space_after and indent disabled:
167
168			{"key" :"value"}
169
170			$json = $json->space_after ([$enable])
171			If $enable is true (or missing), then the "encode" method will add
172			an extra optional space after the ":" separating keys from values in
173			JSON objects and extra whitespace after the "," separating key-value
174	root	1.2	pairs and array members.
175
176			If $enable is false, then the "encode" method will not add any extra
177			space at those places.
178
179			This setting has no effect when decoding JSON strings.
180
181	root	1.4	Example, space_before and indent disabled, space_after enabled:
182
183			{"key": "value"}
184
185			$json = $json->canonical ([$enable])
186			If $enable is true (or missing), then the "encode" method will
187			output JSON objects by sorting their keys. This is adding a
188			comparatively high overhead.
189	root	1.2
190			If $enable is false, then the "encode" method will output key-value
191			pairs in the order Perl stores them (which will likely change
192			between runs of the same script).
193
194			This option is useful if you want the same data structure to be
195			encoded as the same JSON string (given the same overall settings).
196			If it is disabled, the same hash migh be encoded differently even if
197			contains the same data, as key-value pairs have no inherent ordering
198			in Perl.
199
200			This setting has no effect when decoding JSON strings.
201
202	root	1.4	$json = $json->allow_nonref ([$enable])
203			If $enable is true (or missing), then the "encode" method can
204			convert a non-reference into its corresponding string, number or
205			null JSON value, which is an extension to RFC4627. Likewise,
206			"decode" will accept those JSON values instead of croaking.
207	root	1.2
208			If $enable is false, then the "encode" method will croak if it isn't
209			passed an arrayref or hashref, as JSON strings must either be an
210			object or array. Likewise, "decode" will croak if given something
211			that is not a JSON object or array.
212
213	root	1.4	Example, encode a Perl scalar as JSON value with enabled
214			"allow_nonref", resulting in an invalid JSON text:
215
216			JSON::XS->new->allow_nonref->encode ("Hello, World!")
217			=> "Hello, World!"
218
219			$json = $json->shrink ([$enable])
220			Perl usually over-allocates memory a bit when allocating space for
221			strings. This flag optionally resizes strings generated by either
222			"encode" or "decode" to their minimum size possible. This can save
223			memory when your JSON strings are either very very long or you have
224			many short strings. It will also try to downgrade any strings to
225			octet-form if possible: perl stores strings internally either in an
226			encoding called UTF-X or in octet-form. The latter cannot store
227			everything but uses less space in general.
228
229			If $enable is true (or missing), the string returned by "encode"
230			will be shrunk-to-fit, while all strings generated by "decode" will
231			also be shrunk-to-fit.
232
233			If $enable is false, then the normal perl allocation algorithms are
234			used. If you work with your data, then this is likely to be faster.
235
236			In the future, this setting might control other things, such as
237			converting strings that look like integers or floats into integers
238			or floats internally (there is no difference on the Perl level),
239			saving space.
240
241	root	1.2	$json_string = $json->encode ($perl_scalar)
242			Converts the given Perl data structure (a simple scalar or a
243			reference to a hash or array) to its JSON representation. Simple
244			scalars will be converted into JSON string or number sequences,
245			while references to arrays become JSON arrays and references to
246			hashes become JSON objects. Undefined Perl values (e.g. "undef")
247			become JSON "null" values. Neither "true" nor "false" values will be
248			generated.
249
250			$perl_scalar = $json->decode ($json_string)
251			The opposite of "encode": expects a JSON string and tries to parse
252			it, returning the resulting simple scalar or reference. Croaks on
253			error.
254
255			JSON numbers and strings become simple Perl scalars. JSON arrays
256			become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
257			becomes 1, "false" becomes 0 and "null" becomes "undef".
258
259	root	1.4	MAPPING
260			This section describes how JSON::XS maps Perl values to JSON values and
261			vice versa. These mappings are designed to "do the right thing" in most
262			circumstances automatically, preserving round-tripping characteristics
263			(what you put in comes out as something equivalent).
264
265			For the more enlightened: note that in the following descriptions,
266			lowercase perl refers to the Perl interpreter, while uppcercase Perl
267			refers to the abstract Perl language itself.
268
269			JSON -> PERL
270			object
271			A JSON object becomes a reference to a hash in Perl. No ordering of
272			object keys is preserved.
273
274			array
275			A JSON array becomes a reference to an array in Perl.
276
277			string
278			A JSON string becomes a string scalar in Perl - Unicode codepoints
279			in JSON are represented by the same codepoints in the Perl string,
280			so no manual decoding is necessary.
281
282			number
283			A JSON number becomes either an integer or numeric (floating point)
284			scalar in perl, depending on its range and any fractional parts. On
285			the Perl level, there is no difference between those as Perl handles
286			all the conversion details, but an integer may take slightly less
287			memory and might represent more values exactly than (floating point)
288			numbers.
289
290			true, false
291			These JSON atoms become 0, 1, respectively. Information is lost in
292			this process. Future versions might represent those values
293			differently, but they will be guarenteed to act like these integers
294			would normally in Perl.
295
296			null
297			A JSON null atom becomes "undef" in Perl.
298
299			PERL -> JSON
300			The mapping from Perl to JSON is slightly more difficult, as Perl is a
301			truly typeless language, so we can only guess which JSON type is meant
302			by a Perl value.
303
304			hash references
305			Perl hash references become JSON objects. As there is no inherent
306			ordering in hash keys, they will usually be encoded in a
307			pseudo-random order that can change between runs of the same program
308			but stays generally the same within the single run of a program.
309			JSON::XS can optionally sort the hash keys (determined by the
310			canonical flag), so the same datastructure will serialise to the
311			same JSON text (given same settings and version of JSON::XS), but
312			this incurs a runtime overhead.
313
314			array references
315			Perl array references become JSON arrays.
316
317			blessed objects
318			Blessed objects are not allowed. JSON::XS currently tries to encode
319			their underlying representation (hash- or arrayref), but this
320			behaviour might change in future versions.
321
322			simple scalars
323			Simple Perl scalars (any scalar that is not a reference) are the
324			most difficult objects to encode: JSON::XS will encode undefined
325			scalars as JSON null value, scalars that have last been used in a
326			string context before encoding as JSON strings and anything else as
327			number value:
328
329			# dump as number
330			to_json [2] # yields [2]
331			to_json [-3.0e17] # yields [-3e+17]
332			my $value = 5; to_json [$value] # yields [5]
333
334			# used as string, so dump as string
335			print $value;
336			to_json [$value] # yields ["5"]
337
338			# undef becomes null
339			to_json [undef] # yields [null]
340
341			You can force the type to be a string by stringifying it:
342
343			my $x = 3.1; # some variable containing a number
344			"$x"; # stringified
345			$x .= ""; # another, more awkward way to stringify
346			print $x; # perl does it for you, too, quite often
347
348			You can force the type to be a number by numifying it:
349
350			my $x = "3"; # some variable containing a string
351			$x += 0; # numify it, ensuring it will be dumped as a number
352			$x *= 1; # same thing, the choise is yours.
353
354			You can not currently output JSON booleans or force the type in
355			other, less obscure, ways. Tell me if you need this capability.
356
357			circular data structures
358			Those will be encoded until memory or stackspace runs out.
359
360	root	1.2	COMPARISON
361			As already mentioned, this module was created because none of the
362			existing JSON modules could be made to work correctly. First I will
363			describe the problems (or pleasures) I encountered with various existing
364			JSON modules, followed by some benchmark values. JSON::XS was designed
365			not to suffer from any of these problems or limitations.
366
367	root	1.3	JSON 1.07
368	root	1.2	Slow (but very portable, as it is written in pure Perl).
369
370			Undocumented/buggy Unicode handling (how JSON handles unicode values
371			is undocumented. One can get far by feeding it unicode strings and
372			doing en-/decoding oneself, but unicode escapes are not working
373			properly).
374
375			No roundtripping (strings get clobbered if they look like numbers,
376			e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
377			will decode into the number 2.
378
379	root	1.3	JSON::PC 0.01
380	root	1.2	Very fast.
381
382			Undocumented/buggy Unicode handling.
383
384			No roundtripping.
385
386			Has problems handling many Perl values (e.g. regex results and other
387			magic values will make it croak).
388
389			Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
390			which is not a valid JSON string.
391
392			Unmaintained (maintainer unresponsive for many months, bugs are not
393			getting fixed).
394
395	root	1.3	JSON::Syck 0.21
396	root	1.2	Very buggy (often crashes).
397
398			Very inflexible (no human-readable format supported, format pretty
399			much undocumented. I need at least a format for easy reading by
400			humans and a single-line compact format for use in a protocol, and
401			preferably a way to generate ASCII-only JSON strings).
402
403			Completely broken (and confusingly documented) Unicode handling
404			(unicode escapes are not working properly, you need to set
405			ImplicitUnicode to different values on en- and decoding to get
406			symmetric behaviour).
407
408			No roundtripping (simple cases work, but this depends on wether the
409			scalar value was used in a numeric context or not).
410
411			Dumping hashes may skip hash values depending on iterator state.
412
413			Unmaintained (maintainer unresponsive for many months, bugs are not
414			getting fixed).
415
416			Does not check input for validity (i.e. will accept non-JSON input
417			and return "something" instead of raising an exception. This is a
418			security issue: imagine two banks transfering money between each
419			other using JSON. One bank might parse a given non-JSON request and
420			deduct money, while the other might reject the transaction with a
421			syntax error. While a good protocol will at least recover, that is
422			extra unnecessary work and the transaction will still not succeed).
423
424	root	1.3	JSON::DWIW 0.04
425	root	1.2	Very fast. Very natural. Very nice.
426
427			Undocumented unicode handling (but the best of the pack. Unicode
428			escapes still don't get parsed properly).
429
430			Very inflexible.
431
432			No roundtripping.
433
434			Does not generate valid JSON (key strings are often unquoted, empty
435			keys result in nothing being output)
436
437			Does not check input for validity.
438
439			SPEED
440			It seems that JSON::XS is surprisingly fast, as shown in the following
441			tables. They have been generated with the help of the "eg/bench" program
442			in the JSON::XS distribution, to make it easy to compare on your own
443			system.
444
445			First is a comparison between various modules using a very simple JSON
446			string, showing the number of encodes/decodes per second (JSON::XS is
447			the functional interface, while JSON::XS/2 is the OO interface with
448			pretty-printing and hashkey sorting enabled).
449
450			module \| encode \| decode \|
451			-----------\|------------\|------------\|
452			JSON \| 14006 \| 6820 \|
453			JSON::DWIW \| 200937 \| 120386 \|
454			JSON::PC \| 85065 \| 129366 \|
455			JSON::Syck \| 59898 \| 44232 \|
456			JSON::XS \| 1171478 \| 342435 \|
457			JSON::XS/2 \| 730760 \| 328714 \|
458			-----------+------------+------------+
459
460			That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80
461			times faster than JSON, even with pretty-printing and key sorting.
462
463			Using a longer test string (roughly 8KB, generated from Yahoo! Locals
464			search API (http://nanoref.com/yahooapis/mgPdGg):
465
466			module \| encode \| decode \|
467			-----------\|------------\|------------\|
468			JSON \| 673 \| 38 \|
469			JSON::DWIW \| 5271 \| 770 \|
470			JSON::PC \| 9901 \| 2491 \|
471			JSON::Syck \| 2360 \| 786 \|
472			JSON::XS \| 37398 \| 3202 \|
473			JSON::XS/2 \| 13765 \| 3153 \|
474			-----------+------------+------------+
475
476			Again, JSON::XS leads by far in the encoding case, while still beating
477			every other module in the decoding case.
478
479	root	1.4	RESOURCE LIMITS
480			JSON::XS does not impose any limits on the size of JSON texts or Perl
481			values they represent - if your machine can handle it, JSON::XS will
482			encode or decode it. Future versions might optionally impose structure
483			depth and memory use resource limits.
484	root	1.2
485			BUGS
486			While the goal of this module is to be correct, that unfortunately does
487			not mean its bug-free, only that I think its design is bug-free. It is
488			still very young and not well-tested. If you keep reporting bugs they
489			will be fixed swiftly, though.
490	root	1.1
491			AUTHOR
492			Marc Lehmann <schmorp@schmorp.de>
493			http://home.schmorp.de/
494