[ViewVC] Contents 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 texts 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_text = 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:

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

        except being faster.

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

        This function call is functionally identical to:

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

        except being faster.

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])
        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.

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

          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 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.

        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])
        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 text is guarenteed not to contain any "newlines".

        This setting has no effect when decoding JSON texts.

    $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 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])
        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 = $json->canonical ([$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 text (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 texts.

    $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 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 = $json->shrink ([$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 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.

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

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

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 (JSON does not preserver object key
        ordering itself).

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

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

    number
        A JSON number becomes either an integer 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 a 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 text.

        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 texts).

        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 texts (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 comes a comparison between various modules using a very short JSON
    string:

       {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}

    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). Higher is better:

       module     |     encode |     decode |
       -----------|------------|------------|
       JSON       |  11488.516 |   7823.035 |
       JSON::DWIW |  94708.054 | 129094.260 |
       JSON::PC   |  63884.157 | 128528.212 |
       JSON::Syck |  34898.677 |  42096.911 |
       JSON::XS   | 654027.064 | 396423.669 |
       JSON::XS/2 | 371564.190 | 371725.613 |
       -----------+------------+------------+

    That is, JSON::XS is more than six times faster than JSON::DWIW on
    encoding, more than three times faster on decoding, and about thirty
    times faster than JSON, even with pretty-printing and key sorting.

    Using a longer test string (roughly 18KB, generated from Yahoo! Locals
    search API (http://nanoref.com/yahooapis/mgPdGg):

       module     |     encode |     decode |
       -----------|------------|------------|
       JSON       |    273.023 |     44.674 |
       JSON::DWIW |   1089.383 |   1145.704 |
       JSON::PC   |   3097.419 |   2393.921 |
       JSON::Syck |    514.060 |    843.053 |
       JSON::XS   |   6479.668 |   3636.364 |
       JSON::XS/2 |   3774.221 |   3599.124 |
       -----------+------------+------------+

    Again, JSON::XS leads by far.

    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.

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:	1.7
Committed:	Sun Mar 25 00:47:42 2007 UTC (17 years, 1 month ago) by root
Branch:	MAIN
CVS Tags:	rel-0_7
Changes since 1.6:	+27 -24 lines
Log Message:	* empty log message *
#	Content
1	NAME
2	JSON::XS - JSON serialising/deserialising, done correctly and fast
3
4	SYNOPSIS
5	use JSON::XS;
6
7	# 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	DESCRIPTION
19	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	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
32	vice versa.
33
34	FEATURES
35	* correct handling of unicode issues
36	This module knows how to handle Unicode, and even documents how and
37	when it does so.
38
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 texts by
46	default, and only JSON is accepted as input by default (the latter
47	is a security feature).
48
49	* fast
50	Compared to other JSON modules, this module compares favourably in
51	terms of speed, too.
52
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	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
64	FUNCTIONAL INTERFACE
65	The following convinience methods are provided by this module. They are
66	exported by default:
67
68	$json_text = 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	This function call is functionally identical to:
74
75	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
76
77	except being faster.
78
79	$perl_scalar = from_json $json_text
80	The opposite of "to_json": expects an UTF-8 (binary) string and
81	tries to parse that as an UTF-8 encoded JSON text, returning the
82	resulting simple scalar or reference. Croaks on error.
83
84	This function call is functionally identical to:
85
86	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
87
88	except being faster.
89
90	OBJECT-ORIENTED INTERFACE
91	The object oriented interface lets you configure your own encoding or
92	decoding style, within the limits of supported formats.
93
94	$json = new JSON::XS
95	Creates a new JSON::XS object that can be used to de/encode JSON
96	strings. All boolean flags described below are by default
97	disabled.
98
99	The mutators for flags all return the JSON object again and thus
100	calls can be chained:
101
102	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
103	=> {"a": [1, 2]}
104
105	$json = $json->ascii ([$enable])
106	If $enable is true (or missing), then the "encode" method will not
107	generate characters outside the code range 0..127 (which is ASCII).
108	Any unicode characters outside that range will be escaped using
109	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
110	escape sequence, as per RFC4627.
111
112	If $enable is false, then the "encode" method will not escape
113	Unicode characters unless required by the JSON syntax. This results
114	in a faster and more compact format.
115
116	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
117	=> ["\ud801\udc01"]
118
119	$json = $json->utf8 ([$enable])
120	If $enable is true (or missing), then the "encode" method will
121	encode the JSON result into UTF-8, as required by many protocols,
122	while the "decode" method expects to be handled an UTF-8-encoded
123	string. Please note that UTF-8-encoded strings do not contain any
124	characters outside the range 0..255, they are thus useful for
125	bytewise/binary I/O. In future versions, enabling this option might
126	enable autodetection of the UTF-16 and UTF-32 encoding families, as
127	described in RFC4627.
128
129	If $enable is false, then the "encode" method will return the JSON
130	string as a (non-encoded) unicode string, while "decode" expects
131	thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or
132	UTF-16) needs to be done yourself, e.g. using the Encode module.
133
134	Example, output UTF-16BE-encoded JSON:
135
136	use Encode;
137	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
138
139	Example, decode UTF-32LE-encoded JSON:
140
141	use Encode;
142	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
143
144	$json = $json->pretty ([$enable])
145	This enables (or disables) all of the "indent", "space_before" and
146	"space_after" (and in the future possibly more) flags in one call to
147	generate the most readable (or most compact) form possible.
148
149	Example, pretty-print some simple structure:
150
151	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
152	=>
153	{
154	"a" : [
155	1,
156	2
157	]
158	}
159
160	$json = $json->indent ([$enable])
161	If $enable is true (or missing), then the "encode" method will use a
162	multiline format as output, putting every array member or
163	object/hash key-value pair into its own line, identing them
164	properly.
165
166	If $enable is false, no newlines or indenting will be produced, and
167	the resulting JSON text is guarenteed not to contain any "newlines".
168
169	This setting has no effect when decoding JSON texts.
170
171	$json = $json->space_before ([$enable])
172	If $enable is true (or missing), then the "encode" method will add
173	an extra optional space before the ":" separating keys from values
174	in JSON objects.
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 texts. You will also
180	most likely combine this setting with "space_after".
181
182	Example, space_before enabled, space_after and indent disabled:
183
184	{"key" :"value"}
185
186	$json = $json->space_after ([$enable])
187	If $enable is true (or missing), then the "encode" method will add
188	an extra optional space after the ":" separating keys from values in
189	JSON objects and extra whitespace after the "," separating key-value
190	pairs and array members.
191
192	If $enable is false, then the "encode" method will not add any extra
193	space at those places.
194
195	This setting has no effect when decoding JSON texts.
196
197	Example, space_before and indent disabled, space_after enabled:
198
199	{"key": "value"}
200
201	$json = $json->canonical ([$enable])
202	If $enable is true (or missing), then the "encode" method will
203	output JSON objects by sorting their keys. This is adding a
204	comparatively high overhead.
205
206	If $enable is false, then the "encode" method will output key-value
207	pairs in the order Perl stores them (which will likely change
208	between runs of the same script).
209
210	This option is useful if you want the same data structure to be
211	encoded as the same JSON text (given the same overall settings). If
212	it is disabled, the same hash migh be encoded differently even if
213	contains the same data, as key-value pairs have no inherent ordering
214	in Perl.
215
216	This setting has no effect when decoding JSON texts.
217
218	$json = $json->allow_nonref ([$enable])
219	If $enable is true (or missing), then the "encode" method can
220	convert a non-reference into its corresponding string, number or
221	null JSON value, which is an extension to RFC4627. Likewise,
222	"decode" will accept those JSON values instead of croaking.
223
224	If $enable is false, then the "encode" method will croak if it isn't
225	passed an arrayref or hashref, as JSON texts must either be an
226	object or array. Likewise, "decode" will croak if given something
227	that is not a JSON object or array.
228
229	Example, encode a Perl scalar as JSON value with enabled
230	"allow_nonref", resulting in an invalid JSON text:
231
232	JSON::XS->new->allow_nonref->encode ("Hello, World!")
233	=> "Hello, World!"
234
235	$json = $json->shrink ([$enable])
236	Perl usually over-allocates memory a bit when allocating space for
237	strings. This flag optionally resizes strings generated by either
238	"encode" or "decode" to their minimum size possible. This can save
239	memory when your JSON texts are either very very long or you have
240	many short strings. It will also try to downgrade any strings to
241	octet-form if possible: perl stores strings internally either in an
242	encoding called UTF-X or in octet-form. The latter cannot store
243	everything but uses less space in general.
244
245	If $enable is true (or missing), the string returned by "encode"
246	will be shrunk-to-fit, while all strings generated by "decode" will
247	also be shrunk-to-fit.
248
249	If $enable is false, then the normal perl allocation algorithms are
250	used. If you work with your data, then this is likely to be faster.
251
252	In the future, this setting might control other things, such as
253	converting strings that look like integers or floats into integers
254	or floats internally (there is no difference on the Perl level),
255	saving space.
256
257	$json_text = $json->encode ($perl_scalar)
258	Converts the given Perl data structure (a simple scalar or a
259	reference to a hash or array) to its JSON representation. Simple
260	scalars will be converted into JSON string or number sequences,
261	while references to arrays become JSON arrays and references to
262	hashes become JSON objects. Undefined Perl values (e.g. "undef")
263	become JSON "null" values. Neither "true" nor "false" values will be
264	generated.
265
266	$perl_scalar = $json->decode ($json_text)
267	The opposite of "encode": expects a JSON text and tries to parse it,
268	returning the resulting simple scalar or reference. Croaks on error.
269
270	JSON numbers and strings become simple Perl scalars. JSON arrays
271	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
272	becomes 1, "false" becomes 0 and "null" becomes "undef".
273
274	MAPPING
275	This section describes how JSON::XS maps Perl values to JSON values and
276	vice versa. These mappings are designed to "do the right thing" in most
277	circumstances automatically, preserving round-tripping characteristics
278	(what you put in comes out as something equivalent).
279
280	For the more enlightened: note that in the following descriptions,
281	lowercase perl refers to the Perl interpreter, while uppcercase Perl
282	refers to the abstract Perl language itself.
283
284	JSON -> PERL
285	object
286	A JSON object becomes a reference to a hash in Perl. No ordering of
287	object keys is preserved (JSON does not preserver object key
288	ordering itself).
289
290	array
291	A JSON array becomes a reference to an array in Perl.
292
293	string
294	A JSON string becomes a string scalar in Perl - Unicode codepoints
295	in JSON are represented by the same codepoints in the Perl string,
296	so no manual decoding is necessary.
297
298	number
299	A JSON number becomes either an integer or numeric (floating point)
300	scalar in perl, depending on its range and any fractional parts. On
301	the Perl level, there is no difference between those as Perl handles
302	all the conversion details, but an integer may take slightly less
303	memory and might represent more values exactly than (floating point)
304	numbers.
305
306	true, false
307	These JSON atoms become 0, 1, respectively. Information is lost in
308	this process. Future versions might represent those values
309	differently, but they will be guarenteed to act like these integers
310	would normally in Perl.
311
312	null
313	A JSON null atom becomes "undef" in Perl.
314
315	PERL -> JSON
316	The mapping from Perl to JSON is slightly more difficult, as Perl is a
317	truly typeless language, so we can only guess which JSON type is meant
318	by a Perl value.
319
320	hash references
321	Perl hash references become JSON objects. As there is no inherent
322	ordering in hash keys, they will usually be encoded in a
323	pseudo-random order that can change between runs of the same program
324	but stays generally the same within a single run of a program.
325	JSON::XS can optionally sort the hash keys (determined by the
326	canonical flag), so the same datastructure will serialise to the
327	same JSON text (given same settings and version of JSON::XS), but
328	this incurs a runtime overhead.
329
330	array references
331	Perl array references become JSON arrays.
332
333	blessed objects
334	Blessed objects are not allowed. JSON::XS currently tries to encode
335	their underlying representation (hash- or arrayref), but this
336	behaviour might change in future versions.
337
338	simple scalars
339	Simple Perl scalars (any scalar that is not a reference) are the
340	most difficult objects to encode: JSON::XS will encode undefined
341	scalars as JSON null value, scalars that have last been used in a
342	string context before encoding as JSON strings and anything else as
343	number value:
344
345	# dump as number
346	to_json [2] # yields [2]
347	to_json [-3.0e17] # yields [-3e+17]
348	my $value = 5; to_json [$value] # yields [5]
349
350	# used as string, so dump as string
351	print $value;
352	to_json [$value] # yields ["5"]
353
354	# undef becomes null
355	to_json [undef] # yields [null]
356
357	You can force the type to be a string by stringifying it:
358
359	my $x = 3.1; # some variable containing a number
360	"$x"; # stringified
361	$x .= ""; # another, more awkward way to stringify
362	print $x; # perl does it for you, too, quite often
363
364	You can force the type to be a number by numifying it:
365
366	my $x = "3"; # some variable containing a string
367	$x += 0; # numify it, ensuring it will be dumped as a number
368	$x *= 1; # same thing, the choise is yours.
369
370	You can not currently output JSON booleans or force the type in
371	other, less obscure, ways. Tell me if you need this capability.
372
373	circular data structures
374	Those will be encoded until memory or stackspace runs out.
375
376	COMPARISON
377	As already mentioned, this module was created because none of the
378	existing JSON modules could be made to work correctly. First I will
379	describe the problems (or pleasures) I encountered with various existing
380	JSON modules, followed by some benchmark values. JSON::XS was designed
381	not to suffer from any of these problems or limitations.
382
383	JSON 1.07
384	Slow (but very portable, as it is written in pure Perl).
385
386	Undocumented/buggy Unicode handling (how JSON handles unicode values
387	is undocumented. One can get far by feeding it unicode strings and
388	doing en-/decoding oneself, but unicode escapes are not working
389	properly).
390
391	No roundtripping (strings get clobbered if they look like numbers,
392	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
393	will decode into the number 2.
394
395	JSON::PC 0.01
396	Very fast.
397
398	Undocumented/buggy Unicode handling.
399
400	No roundtripping.
401
402	Has problems handling many Perl values (e.g. regex results and other
403	magic values will make it croak).
404
405	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
406	which is not a valid JSON text.
407
408	Unmaintained (maintainer unresponsive for many months, bugs are not
409	getting fixed).
410
411	JSON::Syck 0.21
412	Very buggy (often crashes).
413
414	Very inflexible (no human-readable format supported, format pretty
415	much undocumented. I need at least a format for easy reading by
416	humans and a single-line compact format for use in a protocol, and
417	preferably a way to generate ASCII-only JSON texts).
418
419	Completely broken (and confusingly documented) Unicode handling
420	(unicode escapes are not working properly, you need to set
421	ImplicitUnicode to different values on en- and decoding to get
422	symmetric behaviour).
423
424	No roundtripping (simple cases work, but this depends on wether the
425	scalar value was used in a numeric context or not).
426
427	Dumping hashes may skip hash values depending on iterator state.
428
429	Unmaintained (maintainer unresponsive for many months, bugs are not
430	getting fixed).
431
432	Does not check input for validity (i.e. will accept non-JSON input
433	and return "something" instead of raising an exception. This is a
434	security issue: imagine two banks transfering money between each
435	other using JSON. One bank might parse a given non-JSON request and
436	deduct money, while the other might reject the transaction with a
437	syntax error. While a good protocol will at least recover, that is
438	extra unnecessary work and the transaction will still not succeed).
439
440	JSON::DWIW 0.04
441	Very fast. Very natural. Very nice.
442
443	Undocumented unicode handling (but the best of the pack. Unicode
444	escapes still don't get parsed properly).
445
446	Very inflexible.
447
448	No roundtripping.
449
450	Does not generate valid JSON texts (key strings are often unquoted,
451	empty keys result in nothing being output)
452
453	Does not check input for validity.
454
455	SPEED
456	It seems that JSON::XS is surprisingly fast, as shown in the following
457	tables. They have been generated with the help of the "eg/bench" program
458	in the JSON::XS distribution, to make it easy to compare on your own
459	system.
460
461	First comes a comparison between various modules using a very short JSON
462	string:
463
464	{"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}
465
466	It shows the number of encodes/decodes per second (JSON::XS uses the
467	functional interface, while JSON::XS/2 uses the OO interface with
468	pretty-printing and hashkey sorting enabled). Higher is better:
469
470	module \| encode \| decode \|
471	-----------\|------------\|------------\|
472	JSON \| 11488.516 \| 7823.035 \|
473	JSON::DWIW \| 94708.054 \| 129094.260 \|
474	JSON::PC \| 63884.157 \| 128528.212 \|
475	JSON::Syck \| 34898.677 \| 42096.911 \|
476	JSON::XS \| 654027.064 \| 396423.669 \|
477	JSON::XS/2 \| 371564.190 \| 371725.613 \|
478	-----------+------------+------------+
479
480	That is, JSON::XS is more than six times faster than JSON::DWIW on
481	encoding, more than three times faster on decoding, and about thirty
482	times faster than JSON, even with pretty-printing and key sorting.
483
484	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
485	search API (http://nanoref.com/yahooapis/mgPdGg):
486
487	module \| encode \| decode \|
488	-----------\|------------\|------------\|
489	JSON \| 273.023 \| 44.674 \|
490	JSON::DWIW \| 1089.383 \| 1145.704 \|
491	JSON::PC \| 3097.419 \| 2393.921 \|
492	JSON::Syck \| 514.060 \| 843.053 \|
493	JSON::XS \| 6479.668 \| 3636.364 \|
494	JSON::XS/2 \| 3774.221 \| 3599.124 \|
495	-----------+------------+------------+
496
497	Again, JSON::XS leads by far.
498
499	On large strings containing lots of high unicode characters, some
500	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
501	result will be broken due to missing (or wrong) unicode handling. Others
502	refuse to decode or encode properly, so it was impossible to prepare a
503	fair comparison table for that case.
504
505	RESOURCE LIMITS
506	JSON::XS does not impose any limits on the size of JSON texts or Perl
507	values they represent - if your machine can handle it, JSON::XS will
508	encode or decode it. Future versions might optionally impose structure
509	depth and memory use resource limits.
510
511	BUGS
512	While the goal of this module is to be correct, that unfortunately does
513	not mean its bug-free, only that I think its design is bug-free. It is
514	still very young and not well-tested. If you keep reporting bugs they
515	will be fixed swiftly, though.
516
517	AUTHOR
518	Marc Lehmann <schmorp@schmorp.de>
519	http://home.schmorp.de/
520