ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/JSON-XS/XS.pm
Revision: 1.5
Committed: Thu Mar 22 21:36:52 2007 UTC (17 years, 2 months ago) by root
Branch: MAIN
Changes since 1.4: +4 -4 lines
Log Message:
*** empty log message ***

File Contents

# User Rev Content
1 root 1.1 =head1 NAME
2    
3     JSON::XS - JSON serialising/deserialising, done correctly and fast
4    
5     =head1 SYNOPSIS
6    
7     use JSON::XS;
8    
9     =head1 DESCRIPTION
10    
11 root 1.2 This module converts Perl data structures to JSON and vice versa. Its
12     primary goal is to be I<correct> and its secondary goal is to be
13     I<fast>. To reach the latter goal it was written in C.
14    
15     As this is the n-th-something JSON module on CPAN, what was the reason
16     to write yet another JSON module? While it seems there are many JSON
17     modules, none of them correctly handle all corner cases, and in most cases
18     their maintainers are unresponsive, gone missing, or not listening to bug
19     reports for other reasons.
20    
21     See COMPARISON, below, for a comparison to some other JSON modules.
22    
23     =head2 FEATURES
24    
25 root 1.1 =over 4
26    
27 root 1.2 =item * correct handling of unicode issues
28    
29     This module knows how to handle Unicode, and even documents how it does so.
30    
31     =item * round-trip integrity
32    
33     When you serialise a perl data structure using only datatypes supported
34     by JSON, the deserialised data structure is identical on the Perl level.
35     (e.g. the string "2.0" doesn't suddenly become "2").
36    
37     =item * strict checking of JSON correctness
38    
39     There is no guessing, no generating of illegal JSON strings by default,
40     and only JSON is accepted as input (the latter is a security feature).
41    
42     =item * fast
43    
44     compared to other JSON modules, this module compares favourably.
45    
46     =item * simple to use
47    
48     This module has both a simple functional interface as well as an OO
49     interface.
50    
51     =item * reasonably versatile output formats
52    
53     You can choose between the most compact format possible, a pure-ascii
54     format, or a pretty-printed format. Or you can combine those features in
55     whatever way you like.
56    
57     =back
58    
59 root 1.1 =cut
60    
61     package JSON::XS;
62    
63     BEGIN {
64     $VERSION = '0.1';
65     @ISA = qw(Exporter);
66    
67 root 1.2 @EXPORT = qw(to_json from_json);
68 root 1.1 require Exporter;
69    
70     require XSLoader;
71     XSLoader::load JSON::XS::, $VERSION;
72     }
73    
74 root 1.2 =head1 FUNCTIONAL INTERFACE
75    
76     The following convinience methods are provided by this module. They are
77     exported by default:
78    
79     =over 4
80    
81     =item $json_string = to_json $perl_scalar
82    
83     Converts the given Perl data structure (a simple scalar or a reference to
84     a hash or array) to a UTF-8 encoded, binary string (that is, the string contains
85     octets only). Croaks on error.
86    
87     This function call is functionally identical to C<< JSON::XS->new->utf8
88     (1)->encode ($perl_scalar) >>.
89    
90     =item $perl_scalar = from_json $json_string
91    
92     The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to
93     parse that as an UTF-8 encoded JSON string, returning the resulting simple
94     scalar or reference. Croaks on error.
95    
96     This function call is functionally identical to C<< JSON::XS->new->utf8
97     (1)->decode ($json_string) >>.
98    
99     =back
100    
101     =head1 OBJECT-ORIENTED INTERFACE
102    
103     The object oriented interface lets you configure your own encoding or
104     decoding style, within the limits of supported formats.
105    
106     =over 4
107    
108     =item $json = new JSON::XS
109    
110     Creates a new JSON::XS object that can be used to de/encode JSON
111     strings. All boolean flags described below are by default I<disabled>.
112 root 1.1
113 root 1.2 The mutators for flags all return the JSON object again and thus calls can
114     be chained:
115    
116 root 1.3 my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})
117     => {"a": [1, 2]}
118 root 1.2
119     =item $json = $json->ascii ($enable)
120    
121     If C<$enable> is true, then the C<encode> method will not generate
122     characters outside the code range C<0..127>. Any unicode characters
123     outside that range will be escaped using either a single \uXXXX (BMP
124     characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627.
125    
126     If C<$enable> is false, then the C<encode> method will not escape Unicode
127     characters unless necessary.
128    
129 root 1.3 JSON::XS->new->ascii (1)->encode (chr 0x10401)
130     => \ud801\udc01
131    
132 root 1.2 =item $json = $json->utf8 ($enable)
133    
134     If C<$enable> is true, then the C<encode> method will encode the JSON
135     string into UTF-8, as required by many protocols, while the C<decode>
136     method expects to be handled an UTF-8-encoded string. Please note that
137     UTF-8-encoded strings do not contain any characters outside the range
138     C<0..255>, they are thus useful for bytewise/binary I/O.
139    
140     If C<$enable> is false, then the C<encode> method will return the JSON
141     string as a (non-encoded) unicode string, while C<decode> expects thus a
142     unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
143     to be done yourself, e.g. using the Encode module.
144    
145 root 1.3 =item $json = $json->pretty ($enable)
146 root 1.2
147     This enables (or disables) all of the C<indent>, C<space_before> and
148 root 1.3 C<space_after> (and in the future possibly more) flags in one call to
149 root 1.2 generate the most readable (or most compact) form possible.
150    
151 root 1.3 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
152     =>
153     {
154     "a" : [
155     1,
156     2
157     ]
158     }
159    
160 root 1.2 =item $json = $json->indent ($enable)
161    
162     If C<$enable> is true, then the C<encode> method will use a multiline
163     format as output, putting every array member or object/hash key-value pair
164     into its own line, identing them properly.
165    
166     If C<$enable> is false, no newlines or indenting will be produced, and the
167     resulting JSON strings is guarenteed not to contain any C<newlines>.
168    
169     This setting has no effect when decoding JSON strings.
170    
171     =item $json = $json->space_before ($enable)
172    
173     If C<$enable> is true, then the C<encode> method will add an extra
174     optional space before the C<:> separating keys from values in JSON objects.
175    
176     If C<$enable> is false, then the C<encode> method will not add any extra
177     space at those places.
178    
179     This setting has no effect when decoding JSON strings. You will also most
180     likely combine this setting with C<space_after>.
181    
182     =item $json = $json->space_after ($enable)
183    
184     If C<$enable> is true, then the C<encode> method will add an extra
185     optional space after the C<:> separating keys from values in JSON objects
186     and extra whitespace after the C<,> separating key-value pairs and array
187     members.
188    
189     If C<$enable> is false, then the C<encode> method will not add any extra
190     space at those places.
191    
192     This setting has no effect when decoding JSON strings.
193    
194     =item $json = $json->canonical ($enable)
195    
196     If C<$enable> is true, then the C<encode> method will output JSON objects
197     by sorting their keys. This is adding a comparatively high overhead.
198    
199     If C<$enable> is false, then the C<encode> method will output key-value
200     pairs in the order Perl stores them (which will likely change between runs
201     of the same script).
202    
203     This option is useful if you want the same data structure to be encoded as
204     the same JSON string (given the same overall settings). If it is disabled,
205     the same hash migh be encoded differently even if contains the same data,
206     as key-value pairs have no inherent ordering in Perl.
207    
208     This setting has no effect when decoding JSON strings.
209    
210 root 1.3 =item $json = $json->allow_nonref ($enable)
211    
212     If C<$enable> is true, then the C<encode> method can convert a
213     non-reference into its corresponding string, number or null JSON value,
214     which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
215     values instead of croaking.
216    
217     If C<$enable> is false, then the C<encode> method will croak if it isn't
218     passed an arrayref or hashref, as JSON strings must either be an object
219     or array. Likewise, C<decode> will croak if given something that is not a
220     JSON object or array.
221    
222 root 1.2 =item $json_string = $json->encode ($perl_scalar)
223    
224     Converts the given Perl data structure (a simple scalar or a reference
225     to a hash or array) to its JSON representation. Simple scalars will be
226     converted into JSON string or number sequences, while references to arrays
227     become JSON arrays and references to hashes become JSON objects. Undefined
228     Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
229     nor C<false> values will be generated.
230 root 1.1
231 root 1.2 =item $perl_scalar = $json->decode ($json_string)
232 root 1.1
233 root 1.2 The opposite of C<encode>: expects a JSON string and tries to parse it,
234     returning the resulting simple scalar or reference. Croaks on error.
235 root 1.1
236 root 1.2 JSON numbers and strings become simple Perl scalars. JSON arrays become
237     Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
238     C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
239 root 1.1
240     =back
241    
242 root 1.3 =head1 COMPARISON
243    
244     As already mentioned, this module was created because none of the existing
245     JSON modules could be made to work correctly. First I will describe the
246     problems (or pleasures) I encountered with various existing JSON modules,
247 root 1.4 followed by some benchmark values. JSON::XS was designed not to suffer
248     from any of these problems or limitations.
249 root 1.3
250     =over 4
251    
252 root 1.5 =item JSON 1.07
253 root 1.3
254     Slow (but very portable, as it is written in pure Perl).
255    
256     Undocumented/buggy Unicode handling (how JSON handles unicode values is
257     undocumented. One can get far by feeding it unicode strings and doing
258     en-/decoding oneself, but unicode escapes are not working properly).
259    
260     No roundtripping (strings get clobbered if they look like numbers, e.g.
261     the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
262     decode into the number 2.
263    
264 root 1.5 =item JSON::PC 0.01
265 root 1.3
266     Very fast.
267    
268     Undocumented/buggy Unicode handling.
269    
270     No roundtripping.
271    
272 root 1.4 Has problems handling many Perl values (e.g. regex results and other magic
273     values will make it croak).
274 root 1.3
275     Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
276     which is not a valid JSON string.
277    
278     Unmaintained (maintainer unresponsive for many months, bugs are not
279     getting fixed).
280    
281 root 1.5 =item JSON::Syck 0.21
282 root 1.3
283     Very buggy (often crashes).
284    
285 root 1.4 Very inflexible (no human-readable format supported, format pretty much
286     undocumented. I need at least a format for easy reading by humans and a
287     single-line compact format for use in a protocol, and preferably a way to
288     generate ASCII-only JSON strings).
289 root 1.3
290     Completely broken (and confusingly documented) Unicode handling (unicode
291     escapes are not working properly, you need to set ImplicitUnicode to
292     I<different> values on en- and decoding to get symmetric behaviour).
293    
294     No roundtripping (simple cases work, but this depends on wether the scalar
295     value was used in a numeric context or not).
296    
297     Dumping hashes may skip hash values depending on iterator state.
298    
299     Unmaintained (maintainer unresponsive for many months, bugs are not
300     getting fixed).
301    
302     Does not check input for validity (i.e. will accept non-JSON input and
303     return "something" instead of raising an exception. This is a security
304     issue: imagine two banks transfering money between each other using
305     JSON. One bank might parse a given non-JSON request and deduct money,
306     while the other might reject the transaction with a syntax error. While a
307     good protocol will at least recover, that is extra unnecessary work and
308     the transaction will still not succeed).
309    
310 root 1.5 =item JSON::DWIW 0.04
311 root 1.3
312     Very fast. Very natural. Very nice.
313    
314     Undocumented unicode handling (but the best of the pack. Unicode escapes
315     still don't get parsed properly).
316    
317     Very inflexible.
318    
319     No roundtripping.
320    
321 root 1.4 Does not generate valid JSON (key strings are often unquoted, empty keys
322     result in nothing being output)
323    
324 root 1.3 Does not check input for validity.
325    
326     =back
327    
328     =head2 SPEED
329    
330 root 1.4 It seems that JSON::XS is surprisingly fast, as shown in the following
331     tables. They have been generated with the help of the C<eg/bench> program
332     in the JSON::XS distribution, to make it easy to compare on your own
333     system.
334    
335     First is a comparison between various modules using a very simple JSON
336     string, showing the number of encodes/decodes per second (JSON::XS is
337     the functional interface, while JSON::XS/2 is the OO interface with
338     pretty-printing and hashkey sorting enabled).
339    
340     module | encode | decode |
341     -----------|------------|------------|
342     JSON | 14006 | 6820 |
343     JSON::DWIW | 200937 | 120386 |
344     JSON::PC | 85065 | 129366 |
345     JSON::Syck | 59898 | 44232 |
346     JSON::XS | 1171478 | 342435 |
347     JSON::XS/2 | 730760 | 328714 |
348     -----------+------------+------------+
349    
350     That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80
351     times faster than JSON, even with pretty-printing and key sorting.
352    
353     Using a longer test string (roughly 8KB, generated from Yahoo! Locals
354     search API (http://nanoref.com/yahooapis/mgPdGg):
355    
356     module | encode | decode |
357     -----------|------------|------------|
358     JSON | 673 | 38 |
359     JSON::DWIW | 5271 | 770 |
360     JSON::PC | 9901 | 2491 |
361     JSON::Syck | 2360 | 786 |
362     JSON::XS | 37398 | 3202 |
363     JSON::XS/2 | 13765 | 3153 |
364     -----------+------------+------------+
365    
366     Again, JSON::XS leads by far in the encoding case, while still beating
367     every other module in the decoding case.
368    
369     Last example is an almost 8MB large hash with many large binary values
370     (PNG files), resulting in a lot of escaping:
371    
372     =head1 BUGS
373    
374     While the goal of this module is to be correct, that unfortunately does
375     not mean its bug-free, only that I think its design is bug-free. It is
376     still very young and not well-tested. If you keep reporting bugs they will
377     be fixed swiftly, though.
378    
379 root 1.2 =cut
380    
381     1;
382    
383 root 1.1 =head1 AUTHOR
384    
385     Marc Lehmann <schmorp@schmorp.de>
386     http://home.schmorp.de/
387    
388     =cut
389