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 |
# exported functions, croak on error |
10 |
|
11 |
$utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
12 |
$perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
13 |
|
14 |
# oo-interface |
15 |
|
16 |
$coder = JSON::XS->new->ascii->pretty->allow_nonref; |
17 |
$pretty_printed_unencoded = $coder->encode ($perl_scalar); |
18 |
$perl_scalar = $coder->decode ($unicode_json_text); |
19 |
|
20 |
=head1 DESCRIPTION |
21 |
|
22 |
This module converts Perl data structures to JSON and vice versa. Its |
23 |
primary goal is to be I<correct> and its secondary goal is to be |
24 |
I<fast>. To reach the latter goal it was written in C. |
25 |
|
26 |
As this is the n-th-something JSON module on CPAN, what was the reason |
27 |
to write yet another JSON module? While it seems there are many JSON |
28 |
modules, none of them correctly handle all corner cases, and in most cases |
29 |
their maintainers are unresponsive, gone missing, or not listening to bug |
30 |
reports for other reasons. |
31 |
|
32 |
See COMPARISON, below, for a comparison to some other JSON modules. |
33 |
|
34 |
See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
35 |
vice versa. |
36 |
|
37 |
=head2 FEATURES |
38 |
|
39 |
=over 4 |
40 |
|
41 |
=item * correct handling of unicode issues |
42 |
|
43 |
This module knows how to handle Unicode, and even documents how and when |
44 |
it does so. |
45 |
|
46 |
=item * round-trip integrity |
47 |
|
48 |
When you serialise a perl data structure using only datatypes supported |
49 |
by JSON, the deserialised data structure is identical on the Perl level. |
50 |
(e.g. the string "2.0" doesn't suddenly become "2"). |
51 |
|
52 |
=item * strict checking of JSON correctness |
53 |
|
54 |
There is no guessing, no generating of illegal JSON strings by default, |
55 |
and only JSON is accepted as input by default (the latter is a security |
56 |
feature). |
57 |
|
58 |
=item * fast |
59 |
|
60 |
Compared to other JSON modules, this module compares favourably in terms |
61 |
of speed, too. |
62 |
|
63 |
=item * simple to use |
64 |
|
65 |
This module has both a simple functional interface as well as an OO |
66 |
interface. |
67 |
|
68 |
=item * reasonably versatile output formats |
69 |
|
70 |
You can choose between the most compact guarenteed single-line format |
71 |
possible (nice for simple line-based protocols), a pure-ascii format (for |
72 |
when your transport is not 8-bit clean), or a pretty-printed format (for |
73 |
when you want to read that stuff). Or you can combine those features in |
74 |
whatever way you like. |
75 |
|
76 |
=back |
77 |
|
78 |
=cut |
79 |
|
80 |
package JSON::XS; |
81 |
|
82 |
BEGIN { |
83 |
$VERSION = '0.3'; |
84 |
@ISA = qw(Exporter); |
85 |
|
86 |
@EXPORT = qw(to_json from_json); |
87 |
require Exporter; |
88 |
|
89 |
require XSLoader; |
90 |
XSLoader::load JSON::XS::, $VERSION; |
91 |
} |
92 |
|
93 |
=head1 FUNCTIONAL INTERFACE |
94 |
|
95 |
The following convinience methods are provided by this module. They are |
96 |
exported by default: |
97 |
|
98 |
=over 4 |
99 |
|
100 |
=item $json_string = to_json $perl_scalar |
101 |
|
102 |
Converts the given Perl data structure (a simple scalar or a reference to |
103 |
a hash or array) to a UTF-8 encoded, binary string (that is, the string contains |
104 |
octets only). Croaks on error. |
105 |
|
106 |
This function call is functionally identical to C<< JSON::XS->new->utf8->encode ($perl_scalar) >>. |
107 |
|
108 |
=item $perl_scalar = from_json $json_string |
109 |
|
110 |
The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to |
111 |
parse that as an UTF-8 encoded JSON string, returning the resulting simple |
112 |
scalar or reference. Croaks on error. |
113 |
|
114 |
This function call is functionally identical to C<< JSON::XS->new->utf8->decode ($json_string) >>. |
115 |
|
116 |
=back |
117 |
|
118 |
=head1 OBJECT-ORIENTED INTERFACE |
119 |
|
120 |
The object oriented interface lets you configure your own encoding or |
121 |
decoding style, within the limits of supported formats. |
122 |
|
123 |
=over 4 |
124 |
|
125 |
=item $json = new JSON::XS |
126 |
|
127 |
Creates a new JSON::XS object that can be used to de/encode JSON |
128 |
strings. All boolean flags described below are by default I<disabled>. |
129 |
|
130 |
The mutators for flags all return the JSON object again and thus calls can |
131 |
be chained: |
132 |
|
133 |
my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) |
134 |
=> {"a": [1, 2]} |
135 |
|
136 |
=item $json = $json->ascii ([$enable]) |
137 |
|
138 |
If C<$enable> is true (or missing), then the C<encode> method will |
139 |
not generate characters outside the code range C<0..127>. Any unicode |
140 |
characters outside that range will be escaped using either a single |
141 |
\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per |
142 |
RFC4627. |
143 |
|
144 |
If C<$enable> is false, then the C<encode> method will not escape Unicode |
145 |
characters unless necessary. |
146 |
|
147 |
JSON::XS->new->ascii (1)->encode (chr 0x10401) |
148 |
=> \ud801\udc01 |
149 |
|
150 |
=item $json = $json->utf8 ([$enable]) |
151 |
|
152 |
If C<$enable> is true (or missing), then the C<encode> method will encode |
153 |
the JSON string into UTF-8, as required by many protocols, while the |
154 |
C<decode> method expects to be handled an UTF-8-encoded string. Please |
155 |
note that UTF-8-encoded strings do not contain any characters outside the |
156 |
range C<0..255>, they are thus useful for bytewise/binary I/O. |
157 |
|
158 |
If C<$enable> is false, then the C<encode> method will return the JSON |
159 |
string as a (non-encoded) unicode string, while C<decode> expects thus a |
160 |
unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
161 |
to be done yourself, e.g. using the Encode module. |
162 |
|
163 |
Example, output UTF-16-encoded JSON: |
164 |
|
165 |
=item $json = $json->pretty ([$enable]) |
166 |
|
167 |
This enables (or disables) all of the C<indent>, C<space_before> and |
168 |
C<space_after> (and in the future possibly more) flags in one call to |
169 |
generate the most readable (or most compact) form possible. |
170 |
|
171 |
Example, pretty-print some simple structure: |
172 |
|
173 |
my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
174 |
=> |
175 |
{ |
176 |
"a" : [ |
177 |
1, |
178 |
2 |
179 |
] |
180 |
} |
181 |
|
182 |
=item $json = $json->indent ([$enable]) |
183 |
|
184 |
If C<$enable> is true (or missing), then the C<encode> method will use a multiline |
185 |
format as output, putting every array member or object/hash key-value pair |
186 |
into its own line, identing them properly. |
187 |
|
188 |
If C<$enable> is false, no newlines or indenting will be produced, and the |
189 |
resulting JSON strings is guarenteed not to contain any C<newlines>. |
190 |
|
191 |
This setting has no effect when decoding JSON strings. |
192 |
|
193 |
=item $json = $json->space_before ([$enable]) |
194 |
|
195 |
If C<$enable> is true (or missing), then the C<encode> method will add an extra |
196 |
optional space before the C<:> separating keys from values in JSON objects. |
197 |
|
198 |
If C<$enable> is false, then the C<encode> method will not add any extra |
199 |
space at those places. |
200 |
|
201 |
This setting has no effect when decoding JSON strings. You will also most |
202 |
likely combine this setting with C<space_after>. |
203 |
|
204 |
Example, space_before enabled, space_after and indent disabled: |
205 |
|
206 |
{"key" :"value"} |
207 |
|
208 |
=item $json = $json->space_after ([$enable]) |
209 |
|
210 |
If C<$enable> is true (or missing), then the C<encode> method will add an extra |
211 |
optional space after the C<:> separating keys from values in JSON objects |
212 |
and extra whitespace after the C<,> separating key-value pairs and array |
213 |
members. |
214 |
|
215 |
If C<$enable> is false, then the C<encode> method will not add any extra |
216 |
space at those places. |
217 |
|
218 |
This setting has no effect when decoding JSON strings. |
219 |
|
220 |
Example, space_before and indent disabled, space_after enabled: |
221 |
|
222 |
{"key": "value"} |
223 |
|
224 |
=item $json = $json->canonical ([$enable]) |
225 |
|
226 |
If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
227 |
by sorting their keys. This is adding a comparatively high overhead. |
228 |
|
229 |
If C<$enable> is false, then the C<encode> method will output key-value |
230 |
pairs in the order Perl stores them (which will likely change between runs |
231 |
of the same script). |
232 |
|
233 |
This option is useful if you want the same data structure to be encoded as |
234 |
the same JSON string (given the same overall settings). If it is disabled, |
235 |
the same hash migh be encoded differently even if contains the same data, |
236 |
as key-value pairs have no inherent ordering in Perl. |
237 |
|
238 |
This setting has no effect when decoding JSON strings. |
239 |
|
240 |
=item $json = $json->allow_nonref ([$enable]) |
241 |
|
242 |
If C<$enable> is true (or missing), then the C<encode> method can convert a |
243 |
non-reference into its corresponding string, number or null JSON value, |
244 |
which is an extension to RFC4627. Likewise, C<decode> will accept those JSON |
245 |
values instead of croaking. |
246 |
|
247 |
If C<$enable> is false, then the C<encode> method will croak if it isn't |
248 |
passed an arrayref or hashref, as JSON strings must either be an object |
249 |
or array. Likewise, C<decode> will croak if given something that is not a |
250 |
JSON object or array. |
251 |
|
252 |
Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, |
253 |
resulting in an invalid JSON text: |
254 |
|
255 |
JSON::XS->new->allow_nonref->encode ("Hello, World!") |
256 |
=> "Hello, World!" |
257 |
|
258 |
=item $json = $json->shrink ([$enable]) |
259 |
|
260 |
Perl usually over-allocates memory a bit when allocating space for |
261 |
strings. This flag optionally resizes strings generated by either |
262 |
C<encode> or C<decode> to their minimum size possible. This can save |
263 |
memory when your JSON strings are either very very long or you have many |
264 |
short strings. It will also try to downgrade any strings to octet-form |
265 |
if possible: perl stores strings internally either in an encoding called |
266 |
UTF-X or in octet-form. The latter cannot store everything but uses less |
267 |
space in general. |
268 |
|
269 |
If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit, |
270 |
while all strings generated by C<decode> will also be shrunk-to-fit. |
271 |
|
272 |
If C<$enable> is false, then the normal perl allocation algorithms are used. |
273 |
If you work with your data, then this is likely to be faster. |
274 |
|
275 |
In the future, this setting might control other things, such as converting |
276 |
strings that look like integers or floats into integers or floats |
277 |
internally (there is no difference on the Perl level), saving space. |
278 |
|
279 |
=item $json_string = $json->encode ($perl_scalar) |
280 |
|
281 |
Converts the given Perl data structure (a simple scalar or a reference |
282 |
to a hash or array) to its JSON representation. Simple scalars will be |
283 |
converted into JSON string or number sequences, while references to arrays |
284 |
become JSON arrays and references to hashes become JSON objects. Undefined |
285 |
Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
286 |
nor C<false> values will be generated. |
287 |
|
288 |
=item $perl_scalar = $json->decode ($json_string) |
289 |
|
290 |
The opposite of C<encode>: expects a JSON string and tries to parse it, |
291 |
returning the resulting simple scalar or reference. Croaks on error. |
292 |
|
293 |
JSON numbers and strings become simple Perl scalars. JSON arrays become |
294 |
Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
295 |
C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
296 |
|
297 |
=back |
298 |
|
299 |
=head1 MAPPING |
300 |
|
301 |
This section describes how JSON::XS maps Perl values to JSON values and |
302 |
vice versa. These mappings are designed to "do the right thing" in most |
303 |
circumstances automatically, preserving round-tripping characteristics |
304 |
(what you put in comes out as something equivalent). |
305 |
|
306 |
For the more enlightened: note that in the following descriptions, |
307 |
lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> |
308 |
refers to the abstract Perl language itself. |
309 |
|
310 |
=head2 JSON -> PERL |
311 |
|
312 |
=over 4 |
313 |
|
314 |
=item object |
315 |
|
316 |
A JSON object becomes a reference to a hash in Perl. No ordering of object |
317 |
keys is preserved. |
318 |
|
319 |
=item array |
320 |
|
321 |
A JSON array becomes a reference to an array in Perl. |
322 |
|
323 |
=item string |
324 |
|
325 |
A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON |
326 |
are represented by the same codepoints in the Perl string, so no manual |
327 |
decoding is necessary. |
328 |
|
329 |
=item number |
330 |
|
331 |
A JSON number becomes either an integer or numeric (floating point) |
332 |
scalar in perl, depending on its range and any fractional parts. On the |
333 |
Perl level, there is no difference between those as Perl handles all the |
334 |
conversion details, but an integer may take slightly less memory and might |
335 |
represent more values exactly than (floating point) numbers. |
336 |
|
337 |
=item true, false |
338 |
|
339 |
These JSON atoms become C<0>, C<1>, respectively. Information is lost in |
340 |
this process. Future versions might represent those values differently, |
341 |
but they will be guarenteed to act like these integers would normally in |
342 |
Perl. |
343 |
|
344 |
=item null |
345 |
|
346 |
A JSON null atom becomes C<undef> in Perl. |
347 |
|
348 |
=back |
349 |
|
350 |
=head2 PERL -> JSON |
351 |
|
352 |
The mapping from Perl to JSON is slightly more difficult, as Perl is a |
353 |
truly typeless language, so we can only guess which JSON type is meant by |
354 |
a Perl value. |
355 |
|
356 |
=over 4 |
357 |
|
358 |
=item hash references |
359 |
|
360 |
Perl hash references become JSON objects. As there is no inherent ordering |
361 |
in hash keys, they will usually be encoded in a pseudo-random order that |
362 |
can change between runs of the same program but stays generally the same |
363 |
within the single run of a program. JSON::XS can optionally sort the hash |
364 |
keys (determined by the I<canonical> flag), so the same datastructure |
365 |
will serialise to the same JSON text (given same settings and version of |
366 |
JSON::XS), but this incurs a runtime overhead. |
367 |
|
368 |
=item array references |
369 |
|
370 |
Perl array references become JSON arrays. |
371 |
|
372 |
=item blessed objects |
373 |
|
374 |
Blessed objects are not allowed. JSON::XS currently tries to encode their |
375 |
underlying representation (hash- or arrayref), but this behaviour might |
376 |
change in future versions. |
377 |
|
378 |
=item simple scalars |
379 |
|
380 |
Simple Perl scalars (any scalar that is not a reference) are the most |
381 |
difficult objects to encode: JSON::XS will encode undefined scalars as |
382 |
JSON null value, scalars that have last been used in a string context |
383 |
before encoding as JSON strings and anything else as number value: |
384 |
|
385 |
# dump as number |
386 |
to_json [2] # yields [2] |
387 |
to_json [-3.0e17] # yields [-3e+17] |
388 |
my $value = 5; to_json [$value] # yields [5] |
389 |
|
390 |
# used as string, so dump as string |
391 |
print $value; |
392 |
to_json [$value] # yields ["5"] |
393 |
|
394 |
# undef becomes null |
395 |
to_json [undef] # yields [null] |
396 |
|
397 |
You can force the type to be a string by stringifying it: |
398 |
|
399 |
my $x = 3.1; # some variable containing a number |
400 |
"$x"; # stringified |
401 |
$x .= ""; # another, more awkward way to stringify |
402 |
print $x; # perl does it for you, too, quite often |
403 |
|
404 |
You can force the type to be a number by numifying it: |
405 |
|
406 |
my $x = "3"; # some variable containing a string |
407 |
$x += 0; # numify it, ensuring it will be dumped as a number |
408 |
$x *= 1; # same thing, the choise is yours. |
409 |
|
410 |
You can not currently output JSON booleans or force the type in other, |
411 |
less obscure, ways. Tell me if you need this capability. |
412 |
|
413 |
=item circular data structures |
414 |
|
415 |
Those will be encoded until memory or stackspace runs out. |
416 |
|
417 |
=back |
418 |
|
419 |
=head1 COMPARISON |
420 |
|
421 |
As already mentioned, this module was created because none of the existing |
422 |
JSON modules could be made to work correctly. First I will describe the |
423 |
problems (or pleasures) I encountered with various existing JSON modules, |
424 |
followed by some benchmark values. JSON::XS was designed not to suffer |
425 |
from any of these problems or limitations. |
426 |
|
427 |
=over 4 |
428 |
|
429 |
=item JSON 1.07 |
430 |
|
431 |
Slow (but very portable, as it is written in pure Perl). |
432 |
|
433 |
Undocumented/buggy Unicode handling (how JSON handles unicode values is |
434 |
undocumented. One can get far by feeding it unicode strings and doing |
435 |
en-/decoding oneself, but unicode escapes are not working properly). |
436 |
|
437 |
No roundtripping (strings get clobbered if they look like numbers, e.g. |
438 |
the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will |
439 |
decode into the number 2. |
440 |
|
441 |
=item JSON::PC 0.01 |
442 |
|
443 |
Very fast. |
444 |
|
445 |
Undocumented/buggy Unicode handling. |
446 |
|
447 |
No roundtripping. |
448 |
|
449 |
Has problems handling many Perl values (e.g. regex results and other magic |
450 |
values will make it croak). |
451 |
|
452 |
Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
453 |
which is not a valid JSON string. |
454 |
|
455 |
Unmaintained (maintainer unresponsive for many months, bugs are not |
456 |
getting fixed). |
457 |
|
458 |
=item JSON::Syck 0.21 |
459 |
|
460 |
Very buggy (often crashes). |
461 |
|
462 |
Very inflexible (no human-readable format supported, format pretty much |
463 |
undocumented. I need at least a format for easy reading by humans and a |
464 |
single-line compact format for use in a protocol, and preferably a way to |
465 |
generate ASCII-only JSON strings). |
466 |
|
467 |
Completely broken (and confusingly documented) Unicode handling (unicode |
468 |
escapes are not working properly, you need to set ImplicitUnicode to |
469 |
I<different> values on en- and decoding to get symmetric behaviour). |
470 |
|
471 |
No roundtripping (simple cases work, but this depends on wether the scalar |
472 |
value was used in a numeric context or not). |
473 |
|
474 |
Dumping hashes may skip hash values depending on iterator state. |
475 |
|
476 |
Unmaintained (maintainer unresponsive for many months, bugs are not |
477 |
getting fixed). |
478 |
|
479 |
Does not check input for validity (i.e. will accept non-JSON input and |
480 |
return "something" instead of raising an exception. This is a security |
481 |
issue: imagine two banks transfering money between each other using |
482 |
JSON. One bank might parse a given non-JSON request and deduct money, |
483 |
while the other might reject the transaction with a syntax error. While a |
484 |
good protocol will at least recover, that is extra unnecessary work and |
485 |
the transaction will still not succeed). |
486 |
|
487 |
=item JSON::DWIW 0.04 |
488 |
|
489 |
Very fast. Very natural. Very nice. |
490 |
|
491 |
Undocumented unicode handling (but the best of the pack. Unicode escapes |
492 |
still don't get parsed properly). |
493 |
|
494 |
Very inflexible. |
495 |
|
496 |
No roundtripping. |
497 |
|
498 |
Does not generate valid JSON (key strings are often unquoted, empty keys |
499 |
result in nothing being output) |
500 |
|
501 |
Does not check input for validity. |
502 |
|
503 |
=back |
504 |
|
505 |
=head2 SPEED |
506 |
|
507 |
It seems that JSON::XS is surprisingly fast, as shown in the following |
508 |
tables. They have been generated with the help of the C<eg/bench> program |
509 |
in the JSON::XS distribution, to make it easy to compare on your own |
510 |
system. |
511 |
|
512 |
First is a comparison between various modules using a very simple JSON |
513 |
string, showing the number of encodes/decodes per second (JSON::XS is |
514 |
the functional interface, while JSON::XS/2 is the OO interface with |
515 |
pretty-printing and hashkey sorting enabled). |
516 |
|
517 |
module | encode | decode | |
518 |
-----------|------------|------------| |
519 |
JSON | 14006 | 6820 | |
520 |
JSON::DWIW | 200937 | 120386 | |
521 |
JSON::PC | 85065 | 129366 | |
522 |
JSON::Syck | 59898 | 44232 | |
523 |
JSON::XS | 1171478 | 342435 | |
524 |
JSON::XS/2 | 730760 | 328714 | |
525 |
-----------+------------+------------+ |
526 |
|
527 |
That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 |
528 |
times faster than JSON, even with pretty-printing and key sorting. |
529 |
|
530 |
Using a longer test string (roughly 8KB, generated from Yahoo! Locals |
531 |
search API (http://nanoref.com/yahooapis/mgPdGg): |
532 |
|
533 |
module | encode | decode | |
534 |
-----------|------------|------------| |
535 |
JSON | 673 | 38 | |
536 |
JSON::DWIW | 5271 | 770 | |
537 |
JSON::PC | 9901 | 2491 | |
538 |
JSON::Syck | 2360 | 786 | |
539 |
JSON::XS | 37398 | 3202 | |
540 |
JSON::XS/2 | 13765 | 3153 | |
541 |
-----------+------------+------------+ |
542 |
|
543 |
Again, JSON::XS leads by far in the encoding case, while still beating |
544 |
every other module in the decoding case. |
545 |
|
546 |
=head1 RESOURCE LIMITS |
547 |
|
548 |
JSON::XS does not impose any limits on the size of JSON texts or Perl |
549 |
values they represent - if your machine can handle it, JSON::XS will |
550 |
encode or decode it. Future versions might optionally impose structure |
551 |
depth and memory use resource limits. |
552 |
|
553 |
=head1 BUGS |
554 |
|
555 |
While the goal of this module is to be correct, that unfortunately does |
556 |
not mean its bug-free, only that I think its design is bug-free. It is |
557 |
still very young and not well-tested. If you keep reporting bugs they will |
558 |
be fixed swiftly, though. |
559 |
|
560 |
=cut |
561 |
|
562 |
1; |
563 |
|
564 |
=head1 AUTHOR |
565 |
|
566 |
Marc Lehmann <schmorp@schmorp.de> |
567 |
http://home.schmorp.de/ |
568 |
|
569 |
=cut |
570 |
|