1 |
root |
1.1 |
NAME |
2 |
root |
1.2 |
JSON::XS - JSON serialising/deserialising, done correctly and fast |
3 |
root |
1.1 |
|
4 |
root |
1.23 |
JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ |
5 |
root |
1.19 |
(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
6 |
|
|
|
7 |
root |
1.1 |
SYNOPSIS |
8 |
root |
1.2 |
use JSON::XS; |
9 |
root |
1.1 |
|
10 |
root |
1.8 |
# exported functions, they croak on error |
11 |
|
|
# and expect/generate UTF-8 |
12 |
root |
1.4 |
|
13 |
root |
1.22 |
$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref; |
14 |
|
|
$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text; |
15 |
root |
1.4 |
|
16 |
root |
1.8 |
# OO-interface |
17 |
root |
1.4 |
|
18 |
|
|
$coder = JSON::XS->new->ascii->pretty->allow_nonref; |
19 |
|
|
$pretty_printed_unencoded = $coder->encode ($perl_scalar); |
20 |
|
|
$perl_scalar = $coder->decode ($unicode_json_text); |
21 |
|
|
|
22 |
root |
1.21 |
# Note that JSON version 2.0 and above will automatically use JSON::XS |
23 |
|
|
# if available, at virtually no speed overhead either, so you should |
24 |
|
|
# be able to just: |
25 |
root |
1.30 |
|
26 |
|
|
use JSON; |
27 |
root |
1.21 |
|
28 |
|
|
# and do the same things, except that you have a pure-perl fallback now. |
29 |
|
|
|
30 |
root |
1.1 |
DESCRIPTION |
31 |
root |
1.2 |
This module converts Perl data structures to JSON and vice versa. Its |
32 |
|
|
primary goal is to be *correct* and its secondary goal is to be *fast*. |
33 |
|
|
To reach the latter goal it was written in C. |
34 |
|
|
|
35 |
root |
1.21 |
Beginning with version 2.0 of the JSON module, when both JSON and |
36 |
|
|
JSON::XS are installed, then JSON will fall back on JSON::XS (this can |
37 |
root |
1.26 |
be overridden) with no overhead due to emulation (by inheriting |
38 |
root |
1.21 |
constructor and methods). If JSON::XS is not available, it will fall |
39 |
|
|
back to the compatible JSON::PP module as backend, so using JSON instead |
40 |
|
|
of JSON::XS gives you a portable JSON API that can be fast when you need |
41 |
|
|
and doesn't require a C compiler when that is a problem. |
42 |
|
|
|
43 |
root |
1.2 |
As this is the n-th-something JSON module on CPAN, what was the reason |
44 |
|
|
to write yet another JSON module? While it seems there are many JSON |
45 |
|
|
modules, none of them correctly handle all corner cases, and in most |
46 |
|
|
cases their maintainers are unresponsive, gone missing, or not listening |
47 |
|
|
to bug reports for other reasons. |
48 |
|
|
|
49 |
root |
1.4 |
See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
50 |
|
|
vice versa. |
51 |
|
|
|
52 |
root |
1.2 |
FEATURES |
53 |
root |
1.23 |
* correct Unicode handling |
54 |
|
|
|
55 |
|
|
This module knows how to handle Unicode, documents how and when it |
56 |
|
|
does so, and even documents what "correct" means. |
57 |
|
|
|
58 |
|
|
* round-trip integrity |
59 |
root |
1.2 |
|
60 |
root |
1.26 |
When you serialise a perl data structure using only data types |
61 |
root |
1.35 |
supported by JSON and Perl, the deserialised data structure is |
62 |
|
|
identical on the Perl level. (e.g. the string "2.0" doesn't suddenly |
63 |
|
|
become "2" just because it looks like a number). There *are* minor |
64 |
|
|
exceptions to this, read the MAPPING section below to learn about |
65 |
|
|
those. |
66 |
root |
1.23 |
|
67 |
|
|
* strict checking of JSON correctness |
68 |
root |
1.2 |
|
69 |
root |
1.6 |
There is no guessing, no generating of illegal JSON texts by |
70 |
root |
1.4 |
default, and only JSON is accepted as input by default (the latter |
71 |
|
|
is a security feature). |
72 |
root |
1.2 |
|
73 |
root |
1.23 |
* fast |
74 |
|
|
|
75 |
|
|
Compared to other JSON modules and other serialisers such as |
76 |
|
|
Storable, this module usually compares favourably in terms of speed, |
77 |
|
|
too. |
78 |
|
|
|
79 |
|
|
* simple to use |
80 |
root |
1.2 |
|
81 |
root |
1.23 |
This module has both a simple functional interface as well as an |
82 |
root |
1.26 |
object oriented interface interface. |
83 |
root |
1.23 |
|
84 |
|
|
* reasonably versatile output formats |
85 |
|
|
|
86 |
|
|
You can choose between the most compact guaranteed-single-line |
87 |
root |
1.26 |
format possible (nice for simple line-based protocols), a pure-ASCII |
88 |
root |
1.8 |
format (for when your transport is not 8-bit clean, still supports |
89 |
root |
1.20 |
the whole Unicode range), or a pretty-printed format (for when you |
90 |
root |
1.8 |
want to read that stuff). Or you can combine those features in |
91 |
|
|
whatever way you like. |
92 |
root |
1.2 |
|
93 |
|
|
FUNCTIONAL INTERFACE |
94 |
root |
1.20 |
The following convenience methods are provided by this module. They are |
95 |
root |
1.2 |
exported by default: |
96 |
|
|
|
97 |
root |
1.22 |
$json_text = encode_json $perl_scalar |
98 |
root |
1.19 |
Converts the given Perl data structure to a UTF-8 encoded, binary |
99 |
|
|
string (that is, the string contains octets only). Croaks on error. |
100 |
root |
1.2 |
|
101 |
root |
1.6 |
This function call is functionally identical to: |
102 |
root |
1.2 |
|
103 |
root |
1.6 |
$json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
104 |
|
|
|
105 |
root |
1.26 |
Except being faster. |
106 |
root |
1.6 |
|
107 |
root |
1.22 |
$perl_scalar = decode_json $json_text |
108 |
|
|
The opposite of "encode_json": expects an UTF-8 (binary) string and |
109 |
root |
1.6 |
tries to parse that as an UTF-8 encoded JSON text, returning the |
110 |
root |
1.19 |
resulting reference. Croaks on error. |
111 |
root |
1.2 |
|
112 |
root |
1.6 |
This function call is functionally identical to: |
113 |
|
|
|
114 |
|
|
$perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
115 |
|
|
|
116 |
root |
1.26 |
Except being faster. |
117 |
root |
1.2 |
|
118 |
root |
1.14 |
$is_boolean = JSON::XS::is_bool $scalar |
119 |
|
|
Returns true if the passed scalar represents either JSON::XS::true |
120 |
|
|
or JSON::XS::false, two constants that act like 1 and 0, |
121 |
|
|
respectively and are used to represent JSON "true" and "false" |
122 |
|
|
values in Perl. |
123 |
|
|
|
124 |
|
|
See MAPPING, below, for more information on how JSON values are |
125 |
|
|
mapped to Perl. |
126 |
|
|
|
127 |
root |
1.19 |
A FEW NOTES ON UNICODE AND PERL |
128 |
|
|
Since this often leads to confusion, here are a few very clear words on |
129 |
|
|
how Unicode works in Perl, modulo bugs. |
130 |
|
|
|
131 |
|
|
1. Perl strings can store characters with ordinal values > 255. |
132 |
root |
1.20 |
This enables you to store Unicode characters as single characters in |
133 |
root |
1.19 |
a Perl string - very natural. |
134 |
|
|
|
135 |
|
|
2. Perl does *not* associate an encoding with your strings. |
136 |
root |
1.23 |
... until you force it to, e.g. when matching it against a regex, or |
137 |
root |
1.19 |
printing the scalar to a file, in which case Perl either interprets |
138 |
|
|
your string as locale-encoded text, octets/binary, or as Unicode, |
139 |
|
|
depending on various settings. In no case is an encoding stored |
140 |
|
|
together with your data, it is *use* that decides encoding, not any |
141 |
root |
1.23 |
magical meta data. |
142 |
root |
1.19 |
|
143 |
|
|
3. The internal utf-8 flag has no meaning with regards to the encoding |
144 |
|
|
of your string. |
145 |
|
|
Just ignore that flag unless you debug a Perl bug, a module written |
146 |
|
|
in XS or want to dive into the internals of perl. Otherwise it will |
147 |
|
|
only confuse you, as, despite the name, it says nothing about how |
148 |
root |
1.20 |
your string is encoded. You can have Unicode strings with that flag |
149 |
root |
1.19 |
set, with that flag clear, and you can have binary data with that |
150 |
|
|
flag set and that flag clear. Other possibilities exist, too. |
151 |
|
|
|
152 |
|
|
If you didn't know about that flag, just the better, pretend it |
153 |
|
|
doesn't exist. |
154 |
|
|
|
155 |
|
|
4. A "Unicode String" is simply a string where each character can be |
156 |
root |
1.26 |
validly interpreted as a Unicode code point. |
157 |
root |
1.19 |
If you have UTF-8 encoded data, it is no longer a Unicode string, |
158 |
|
|
but a Unicode string encoded in UTF-8, giving you a binary string. |
159 |
|
|
|
160 |
|
|
5. A string containing "high" (> 255) character values is *not* a UTF-8 |
161 |
|
|
string. |
162 |
root |
1.20 |
It's a fact. Learn to live with it. |
163 |
root |
1.19 |
|
164 |
|
|
I hope this helps :) |
165 |
|
|
|
166 |
root |
1.2 |
OBJECT-ORIENTED INTERFACE |
167 |
|
|
The object oriented interface lets you configure your own encoding or |
168 |
|
|
decoding style, within the limits of supported formats. |
169 |
|
|
|
170 |
|
|
$json = new JSON::XS |
171 |
|
|
Creates a new JSON::XS object that can be used to de/encode JSON |
172 |
|
|
strings. All boolean flags described below are by default |
173 |
|
|
*disabled*. |
174 |
|
|
|
175 |
|
|
The mutators for flags all return the JSON object again and thus |
176 |
|
|
calls can be chained: |
177 |
|
|
|
178 |
root |
1.6 |
my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
179 |
root |
1.2 |
=> {"a": [1, 2]} |
180 |
|
|
|
181 |
root |
1.4 |
$json = $json->ascii ([$enable]) |
182 |
root |
1.21 |
$enabled = $json->get_ascii |
183 |
root |
1.4 |
If $enable is true (or missing), then the "encode" method will not |
184 |
root |
1.6 |
generate characters outside the code range 0..127 (which is ASCII). |
185 |
root |
1.20 |
Any Unicode characters outside that range will be escaped using |
186 |
root |
1.6 |
either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
187 |
root |
1.11 |
escape sequence, as per RFC4627. The resulting encoded JSON text can |
188 |
root |
1.20 |
be treated as a native Unicode string, an ascii-encoded, |
189 |
root |
1.11 |
latin1-encoded or UTF-8 encoded string, or any other superset of |
190 |
|
|
ASCII. |
191 |
root |
1.2 |
|
192 |
|
|
If $enable is false, then the "encode" method will not escape |
193 |
root |
1.11 |
Unicode characters unless required by the JSON syntax or other |
194 |
|
|
flags. This results in a faster and more compact format. |
195 |
|
|
|
196 |
root |
1.23 |
See also the section *ENCODING/CODESET FLAG NOTES* later in this |
197 |
|
|
document. |
198 |
|
|
|
199 |
root |
1.11 |
The main use for this flag is to produce JSON texts that can be |
200 |
|
|
transmitted over a 7-bit channel, as the encoded JSON texts will not |
201 |
|
|
contain any 8 bit characters. |
202 |
root |
1.2 |
|
203 |
root |
1.6 |
JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
204 |
|
|
=> ["\ud801\udc01"] |
205 |
root |
1.2 |
|
206 |
root |
1.11 |
$json = $json->latin1 ([$enable]) |
207 |
root |
1.21 |
$enabled = $json->get_latin1 |
208 |
root |
1.11 |
If $enable is true (or missing), then the "encode" method will |
209 |
|
|
encode the resulting JSON text as latin1 (or iso-8859-1), escaping |
210 |
|
|
any characters outside the code range 0..255. The resulting string |
211 |
root |
1.20 |
can be treated as a latin1-encoded JSON text or a native Unicode |
212 |
root |
1.11 |
string. The "decode" method will not be affected in any way by this |
213 |
root |
1.20 |
flag, as "decode" by default expects Unicode, which is a strict |
214 |
root |
1.11 |
superset of latin1. |
215 |
|
|
|
216 |
|
|
If $enable is false, then the "encode" method will not escape |
217 |
|
|
Unicode characters unless required by the JSON syntax or other |
218 |
|
|
flags. |
219 |
|
|
|
220 |
root |
1.23 |
See also the section *ENCODING/CODESET FLAG NOTES* later in this |
221 |
|
|
document. |
222 |
|
|
|
223 |
root |
1.11 |
The main use for this flag is efficiently encoding binary data as |
224 |
|
|
JSON text, as most octets will not be escaped, resulting in a |
225 |
|
|
smaller encoded size. The disadvantage is that the resulting JSON |
226 |
|
|
text is encoded in latin1 (and must correctly be treated as such |
227 |
root |
1.20 |
when storing and transferring), a rare encoding for JSON. It is |
228 |
root |
1.11 |
therefore most useful when you want to store data structures known |
229 |
|
|
to contain binary data efficiently in files or databases, not when |
230 |
|
|
talking to other JSON encoders/decoders. |
231 |
|
|
|
232 |
|
|
JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
233 |
|
|
=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
234 |
|
|
|
235 |
root |
1.4 |
$json = $json->utf8 ([$enable]) |
236 |
root |
1.21 |
$enabled = $json->get_utf8 |
237 |
root |
1.4 |
If $enable is true (or missing), then the "encode" method will |
238 |
root |
1.6 |
encode the JSON result into UTF-8, as required by many protocols, |
239 |
root |
1.4 |
while the "decode" method expects to be handled an UTF-8-encoded |
240 |
|
|
string. Please note that UTF-8-encoded strings do not contain any |
241 |
|
|
characters outside the range 0..255, they are thus useful for |
242 |
root |
1.6 |
bytewise/binary I/O. In future versions, enabling this option might |
243 |
|
|
enable autodetection of the UTF-16 and UTF-32 encoding families, as |
244 |
|
|
described in RFC4627. |
245 |
root |
1.2 |
|
246 |
|
|
If $enable is false, then the "encode" method will return the JSON |
247 |
root |
1.20 |
string as a (non-encoded) Unicode string, while "decode" expects |
248 |
|
|
thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or |
249 |
root |
1.2 |
UTF-16) needs to be done yourself, e.g. using the Encode module. |
250 |
|
|
|
251 |
root |
1.23 |
See also the section *ENCODING/CODESET FLAG NOTES* later in this |
252 |
|
|
document. |
253 |
|
|
|
254 |
root |
1.6 |
Example, output UTF-16BE-encoded JSON: |
255 |
|
|
|
256 |
|
|
use Encode; |
257 |
|
|
$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
258 |
|
|
|
259 |
|
|
Example, decode UTF-32LE-encoded JSON: |
260 |
|
|
|
261 |
|
|
use Encode; |
262 |
|
|
$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); |
263 |
root |
1.4 |
|
264 |
|
|
$json = $json->pretty ([$enable]) |
265 |
root |
1.2 |
This enables (or disables) all of the "indent", "space_before" and |
266 |
|
|
"space_after" (and in the future possibly more) flags in one call to |
267 |
|
|
generate the most readable (or most compact) form possible. |
268 |
|
|
|
269 |
root |
1.4 |
Example, pretty-print some simple structure: |
270 |
|
|
|
271 |
root |
1.2 |
my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
272 |
|
|
=> |
273 |
|
|
{ |
274 |
|
|
"a" : [ |
275 |
|
|
1, |
276 |
|
|
2 |
277 |
|
|
] |
278 |
|
|
} |
279 |
|
|
|
280 |
root |
1.4 |
$json = $json->indent ([$enable]) |
281 |
root |
1.21 |
$enabled = $json->get_indent |
282 |
root |
1.4 |
If $enable is true (or missing), then the "encode" method will use a |
283 |
|
|
multiline format as output, putting every array member or |
284 |
root |
1.20 |
object/hash key-value pair into its own line, indenting them |
285 |
root |
1.4 |
properly. |
286 |
root |
1.2 |
|
287 |
|
|
If $enable is false, no newlines or indenting will be produced, and |
288 |
root |
1.20 |
the resulting JSON text is guaranteed not to contain any "newlines". |
289 |
root |
1.2 |
|
290 |
root |
1.6 |
This setting has no effect when decoding JSON texts. |
291 |
root |
1.2 |
|
292 |
root |
1.4 |
$json = $json->space_before ([$enable]) |
293 |
root |
1.21 |
$enabled = $json->get_space_before |
294 |
root |
1.4 |
If $enable is true (or missing), then the "encode" method will add |
295 |
|
|
an extra optional space before the ":" separating keys from values |
296 |
|
|
in JSON objects. |
297 |
root |
1.2 |
|
298 |
|
|
If $enable is false, then the "encode" method will not add any extra |
299 |
|
|
space at those places. |
300 |
|
|
|
301 |
root |
1.6 |
This setting has no effect when decoding JSON texts. You will also |
302 |
root |
1.2 |
most likely combine this setting with "space_after". |
303 |
|
|
|
304 |
root |
1.4 |
Example, space_before enabled, space_after and indent disabled: |
305 |
|
|
|
306 |
|
|
{"key" :"value"} |
307 |
|
|
|
308 |
|
|
$json = $json->space_after ([$enable]) |
309 |
root |
1.21 |
$enabled = $json->get_space_after |
310 |
root |
1.4 |
If $enable is true (or missing), then the "encode" method will add |
311 |
|
|
an extra optional space after the ":" separating keys from values in |
312 |
|
|
JSON objects and extra whitespace after the "," separating key-value |
313 |
root |
1.2 |
pairs and array members. |
314 |
|
|
|
315 |
|
|
If $enable is false, then the "encode" method will not add any extra |
316 |
|
|
space at those places. |
317 |
|
|
|
318 |
root |
1.6 |
This setting has no effect when decoding JSON texts. |
319 |
root |
1.2 |
|
320 |
root |
1.4 |
Example, space_before and indent disabled, space_after enabled: |
321 |
|
|
|
322 |
|
|
{"key": "value"} |
323 |
|
|
|
324 |
root |
1.17 |
$json = $json->relaxed ([$enable]) |
325 |
root |
1.21 |
$enabled = $json->get_relaxed |
326 |
root |
1.17 |
If $enable is true (or missing), then "decode" will accept some |
327 |
|
|
extensions to normal JSON syntax (see below). "encode" will not be |
328 |
|
|
affected in anyway. *Be aware that this option makes you accept |
329 |
|
|
invalid JSON texts as if they were valid!*. I suggest only to use |
330 |
|
|
this option to parse application-specific files written by humans |
331 |
|
|
(configuration files, resource files etc.) |
332 |
|
|
|
333 |
|
|
If $enable is false (the default), then "decode" will only accept |
334 |
|
|
valid JSON texts. |
335 |
|
|
|
336 |
|
|
Currently accepted extensions are: |
337 |
|
|
|
338 |
root |
1.23 |
* list items can have an end-comma |
339 |
|
|
|
340 |
root |
1.17 |
JSON *separates* array elements and key-value pairs with commas. |
341 |
|
|
This can be annoying if you write JSON texts manually and want |
342 |
|
|
to be able to quickly append elements, so this extension accepts |
343 |
|
|
comma at the end of such items not just between them: |
344 |
|
|
|
345 |
|
|
[ |
346 |
|
|
1, |
347 |
|
|
2, <- this comma not normally allowed |
348 |
|
|
] |
349 |
|
|
{ |
350 |
|
|
"k1": "v1", |
351 |
|
|
"k2": "v2", <- this comma not normally allowed |
352 |
|
|
} |
353 |
|
|
|
354 |
root |
1.23 |
* shell-style '#'-comments |
355 |
|
|
|
356 |
root |
1.18 |
Whenever JSON allows whitespace, shell-style comments are |
357 |
|
|
additionally allowed. They are terminated by the first |
358 |
|
|
carriage-return or line-feed character, after which more |
359 |
|
|
white-space and comments are allowed. |
360 |
|
|
|
361 |
|
|
[ |
362 |
|
|
1, # this comment not allowed in JSON |
363 |
|
|
# neither this one... |
364 |
|
|
] |
365 |
|
|
|
366 |
root |
1.4 |
$json = $json->canonical ([$enable]) |
367 |
root |
1.21 |
$enabled = $json->get_canonical |
368 |
root |
1.4 |
If $enable is true (or missing), then the "encode" method will |
369 |
|
|
output JSON objects by sorting their keys. This is adding a |
370 |
|
|
comparatively high overhead. |
371 |
root |
1.2 |
|
372 |
|
|
If $enable is false, then the "encode" method will output key-value |
373 |
|
|
pairs in the order Perl stores them (which will likely change |
374 |
|
|
between runs of the same script). |
375 |
|
|
|
376 |
|
|
This option is useful if you want the same data structure to be |
377 |
root |
1.6 |
encoded as the same JSON text (given the same overall settings). If |
378 |
root |
1.20 |
it is disabled, the same hash might be encoded differently even if |
379 |
root |
1.2 |
contains the same data, as key-value pairs have no inherent ordering |
380 |
|
|
in Perl. |
381 |
|
|
|
382 |
root |
1.6 |
This setting has no effect when decoding JSON texts. |
383 |
root |
1.2 |
|
384 |
root |
1.31 |
This setting has currently no effect on tied hashes. |
385 |
|
|
|
386 |
root |
1.4 |
$json = $json->allow_nonref ([$enable]) |
387 |
root |
1.21 |
$enabled = $json->get_allow_nonref |
388 |
root |
1.4 |
If $enable is true (or missing), then the "encode" method can |
389 |
|
|
convert a non-reference into its corresponding string, number or |
390 |
|
|
null JSON value, which is an extension to RFC4627. Likewise, |
391 |
|
|
"decode" will accept those JSON values instead of croaking. |
392 |
root |
1.2 |
|
393 |
|
|
If $enable is false, then the "encode" method will croak if it isn't |
394 |
root |
1.6 |
passed an arrayref or hashref, as JSON texts must either be an |
395 |
root |
1.2 |
object or array. Likewise, "decode" will croak if given something |
396 |
|
|
that is not a JSON object or array. |
397 |
|
|
|
398 |
root |
1.4 |
Example, encode a Perl scalar as JSON value with enabled |
399 |
|
|
"allow_nonref", resulting in an invalid JSON text: |
400 |
|
|
|
401 |
|
|
JSON::XS->new->allow_nonref->encode ("Hello, World!") |
402 |
|
|
=> "Hello, World!" |
403 |
|
|
|
404 |
root |
1.25 |
$json = $json->allow_unknown ([$enable]) |
405 |
|
|
$enabled = $json->get_allow_unknown |
406 |
|
|
If $enable is true (or missing), then "encode" will *not* throw an |
407 |
|
|
exception when it encounters values it cannot represent in JSON (for |
408 |
|
|
example, filehandles) but instead will encode a JSON "null" value. |
409 |
|
|
Note that blessed objects are not included here and are handled |
410 |
|
|
separately by c<allow_nonref>. |
411 |
|
|
|
412 |
|
|
If $enable is false (the default), then "encode" will throw an |
413 |
|
|
exception when it encounters anything it cannot encode as JSON. |
414 |
|
|
|
415 |
|
|
This option does not affect "decode" in any way, and it is |
416 |
|
|
recommended to leave it off unless you know your communications |
417 |
|
|
partner. |
418 |
|
|
|
419 |
root |
1.15 |
$json = $json->allow_blessed ([$enable]) |
420 |
root |
1.21 |
$enabled = $json->get_allow_blessed |
421 |
root |
1.15 |
If $enable is true (or missing), then the "encode" method will not |
422 |
|
|
barf when it encounters a blessed reference. Instead, the value of |
423 |
root |
1.20 |
the convert_blessed option will decide whether "null" |
424 |
root |
1.21 |
("convert_blessed" disabled or no "TO_JSON" method found) or a |
425 |
root |
1.15 |
representation of the object ("convert_blessed" enabled and |
426 |
root |
1.21 |
"TO_JSON" method found) is being encoded. Has no effect on "decode". |
427 |
root |
1.15 |
|
428 |
|
|
If $enable is false (the default), then "encode" will throw an |
429 |
|
|
exception when it encounters a blessed object. |
430 |
|
|
|
431 |
|
|
$json = $json->convert_blessed ([$enable]) |
432 |
root |
1.21 |
$enabled = $json->get_convert_blessed |
433 |
root |
1.15 |
If $enable is true (or missing), then "encode", upon encountering a |
434 |
|
|
blessed object, will check for the availability of the "TO_JSON" |
435 |
|
|
method on the object's class. If found, it will be called in scalar |
436 |
|
|
context and the resulting scalar will be encoded instead of the |
437 |
|
|
object. If no "TO_JSON" method is found, the value of |
438 |
|
|
"allow_blessed" will decide what to do. |
439 |
|
|
|
440 |
|
|
The "TO_JSON" method may safely call die if it wants. If "TO_JSON" |
441 |
|
|
returns other blessed objects, those will be handled in the same |
442 |
|
|
way. "TO_JSON" must take care of not causing an endless recursion |
443 |
|
|
cycle (== crash) in this case. The name of "TO_JSON" was chosen |
444 |
|
|
because other methods called by the Perl core (== not by the user of |
445 |
|
|
the object) are usually in upper case letters and to avoid |
446 |
root |
1.22 |
collisions with any "to_json" function or method. |
447 |
root |
1.15 |
|
448 |
|
|
This setting does not yet influence "decode" in any way, but in the |
449 |
|
|
future, global hooks might get installed that influence "decode" and |
450 |
|
|
are enabled by this setting. |
451 |
|
|
|
452 |
|
|
If $enable is false, then the "allow_blessed" setting will decide |
453 |
|
|
what to do when a blessed object is found. |
454 |
|
|
|
455 |
|
|
$json = $json->filter_json_object ([$coderef->($hashref)]) |
456 |
|
|
When $coderef is specified, it will be called from "decode" each |
457 |
|
|
time it decodes a JSON object. The only argument is a reference to |
458 |
|
|
the newly-created hash. If the code references returns a single |
459 |
|
|
scalar (which need not be a reference), this value (i.e. a copy of |
460 |
|
|
that scalar to avoid aliasing) is inserted into the deserialised |
461 |
|
|
data structure. If it returns an empty list (NOTE: *not* "undef", |
462 |
|
|
which is a valid scalar), the original deserialised hash will be |
463 |
|
|
inserted. This setting can slow down decoding considerably. |
464 |
|
|
|
465 |
|
|
When $coderef is omitted or undefined, any existing callback will be |
466 |
|
|
removed and "decode" will not change the deserialised hash in any |
467 |
|
|
way. |
468 |
|
|
|
469 |
|
|
Example, convert all JSON objects into the integer 5: |
470 |
|
|
|
471 |
|
|
my $js = JSON::XS->new->filter_json_object (sub { 5 }); |
472 |
|
|
# returns [5] |
473 |
|
|
$js->decode ('[{}]') |
474 |
|
|
# throw an exception because allow_nonref is not enabled |
475 |
|
|
# so a lone 5 is not allowed. |
476 |
|
|
$js->decode ('{"a":1, "b":2}'); |
477 |
|
|
|
478 |
|
|
$json = $json->filter_json_single_key_object ($key [=> |
479 |
|
|
$coderef->($value)]) |
480 |
|
|
Works remotely similar to "filter_json_object", but is only called |
481 |
|
|
for JSON objects having a single key named $key. |
482 |
|
|
|
483 |
|
|
This $coderef is called before the one specified via |
484 |
|
|
"filter_json_object", if any. It gets passed the single value in the |
485 |
|
|
JSON object. If it returns a single value, it will be inserted into |
486 |
|
|
the data structure. If it returns nothing (not even "undef" but the |
487 |
|
|
empty list), the callback from "filter_json_object" will be called |
488 |
|
|
next, as if no single-key callback were specified. |
489 |
|
|
|
490 |
|
|
If $coderef is omitted or undefined, the corresponding callback will |
491 |
|
|
be disabled. There can only ever be one callback for a given key. |
492 |
|
|
|
493 |
|
|
As this callback gets called less often then the |
494 |
|
|
"filter_json_object" one, decoding speed will not usually suffer as |
495 |
|
|
much. Therefore, single-key objects make excellent targets to |
496 |
|
|
serialise Perl objects into, especially as single-key JSON objects |
497 |
root |
1.20 |
are as close to the type-tagged value concept as JSON gets (it's |
498 |
root |
1.15 |
basically an ID/VALUE tuple). Of course, JSON does not support this |
499 |
|
|
in any way, so you need to make sure your data never looks like a |
500 |
|
|
serialised Perl hash. |
501 |
|
|
|
502 |
|
|
Typical names for the single object key are "__class_whatever__", or |
503 |
|
|
"$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even |
504 |
|
|
things like "__class_md5sum(classname)__", to reduce the risk of |
505 |
|
|
clashing with real hashes. |
506 |
|
|
|
507 |
|
|
Example, decode JSON objects of the form "{ "__widget__" => <id> }" |
508 |
|
|
into the corresponding $WIDGET{<id>} object: |
509 |
|
|
|
510 |
|
|
# return whatever is in $WIDGET{5}: |
511 |
|
|
JSON::XS |
512 |
|
|
->new |
513 |
|
|
->filter_json_single_key_object (__widget__ => sub { |
514 |
|
|
$WIDGET{ $_[0] } |
515 |
|
|
}) |
516 |
|
|
->decode ('{"__widget__": 5') |
517 |
|
|
|
518 |
|
|
# this can be used with a TO_JSON method in some "widget" class |
519 |
|
|
# for serialisation to json: |
520 |
|
|
sub WidgetBase::TO_JSON { |
521 |
|
|
my ($self) = @_; |
522 |
|
|
|
523 |
|
|
unless ($self->{id}) { |
524 |
|
|
$self->{id} = ..get..some..id..; |
525 |
|
|
$WIDGET{$self->{id}} = $self; |
526 |
|
|
} |
527 |
|
|
|
528 |
|
|
{ __widget__ => $self->{id} } |
529 |
|
|
} |
530 |
|
|
|
531 |
root |
1.4 |
$json = $json->shrink ([$enable]) |
532 |
root |
1.21 |
$enabled = $json->get_shrink |
533 |
root |
1.4 |
Perl usually over-allocates memory a bit when allocating space for |
534 |
|
|
strings. This flag optionally resizes strings generated by either |
535 |
|
|
"encode" or "decode" to their minimum size possible. This can save |
536 |
root |
1.6 |
memory when your JSON texts are either very very long or you have |
537 |
root |
1.4 |
many short strings. It will also try to downgrade any strings to |
538 |
|
|
octet-form if possible: perl stores strings internally either in an |
539 |
|
|
encoding called UTF-X or in octet-form. The latter cannot store |
540 |
root |
1.9 |
everything but uses less space in general (and some buggy Perl or C |
541 |
|
|
code might even rely on that internal representation being used). |
542 |
|
|
|
543 |
|
|
The actual definition of what shrink does might change in future |
544 |
|
|
versions, but it will always try to save space at the expense of |
545 |
|
|
time. |
546 |
root |
1.4 |
|
547 |
|
|
If $enable is true (or missing), the string returned by "encode" |
548 |
|
|
will be shrunk-to-fit, while all strings generated by "decode" will |
549 |
|
|
also be shrunk-to-fit. |
550 |
|
|
|
551 |
|
|
If $enable is false, then the normal perl allocation algorithms are |
552 |
|
|
used. If you work with your data, then this is likely to be faster. |
553 |
|
|
|
554 |
|
|
In the future, this setting might control other things, such as |
555 |
|
|
converting strings that look like integers or floats into integers |
556 |
|
|
or floats internally (there is no difference on the Perl level), |
557 |
|
|
saving space. |
558 |
|
|
|
559 |
root |
1.8 |
$json = $json->max_depth ([$maximum_nesting_depth]) |
560 |
root |
1.21 |
$max_depth = $json->get_max_depth |
561 |
root |
1.10 |
Sets the maximum nesting level (default 512) accepted while encoding |
562 |
root |
1.25 |
or decoding. If a higher nesting level is detected in JSON text or a |
563 |
|
|
Perl data structure, then the encoder and decoder will stop and |
564 |
|
|
croak at that point. |
565 |
root |
1.8 |
|
566 |
|
|
Nesting level is defined by number of hash- or arrayrefs that the |
567 |
|
|
encoder needs to traverse to reach a given point or the number of |
568 |
|
|
"{" or "[" characters without their matching closing parenthesis |
569 |
|
|
crossed to reach a given character in a string. |
570 |
|
|
|
571 |
|
|
Setting the maximum depth to one disallows any nesting, so that |
572 |
|
|
ensures that the object is only a single hash/object or array. |
573 |
|
|
|
574 |
root |
1.25 |
If no argument is given, the highest possible setting will be used, |
575 |
|
|
which is rarely useful. |
576 |
|
|
|
577 |
|
|
Note that nesting is implemented by recursion in C. The default |
578 |
|
|
value has been chosen to be as large as typical operating systems |
579 |
|
|
allow without crashing. |
580 |
root |
1.15 |
|
581 |
|
|
See SECURITY CONSIDERATIONS, below, for more info on why this is |
582 |
|
|
useful. |
583 |
|
|
|
584 |
|
|
$json = $json->max_size ([$maximum_string_size]) |
585 |
root |
1.21 |
$max_size = $json->get_max_size |
586 |
root |
1.15 |
Set the maximum length a JSON text may have (in bytes) where |
587 |
|
|
decoding is being attempted. The default is 0, meaning no limit. |
588 |
root |
1.25 |
When "decode" is called on a string that is longer then this many |
589 |
|
|
bytes, it will not attempt to decode the string but throw an |
590 |
root |
1.15 |
exception. This setting has no effect on "encode" (yet). |
591 |
|
|
|
592 |
root |
1.25 |
If no argument is given, the limit check will be deactivated (same |
593 |
|
|
as when 0 is specified). |
594 |
root |
1.8 |
|
595 |
|
|
See SECURITY CONSIDERATIONS, below, for more info on why this is |
596 |
|
|
useful. |
597 |
|
|
|
598 |
root |
1.6 |
$json_text = $json->encode ($perl_scalar) |
599 |
root |
1.2 |
Converts the given Perl data structure (a simple scalar or a |
600 |
|
|
reference to a hash or array) to its JSON representation. Simple |
601 |
|
|
scalars will be converted into JSON string or number sequences, |
602 |
|
|
while references to arrays become JSON arrays and references to |
603 |
|
|
hashes become JSON objects. Undefined Perl values (e.g. "undef") |
604 |
|
|
become JSON "null" values. Neither "true" nor "false" values will be |
605 |
|
|
generated. |
606 |
|
|
|
607 |
root |
1.6 |
$perl_scalar = $json->decode ($json_text) |
608 |
|
|
The opposite of "encode": expects a JSON text and tries to parse it, |
609 |
|
|
returning the resulting simple scalar or reference. Croaks on error. |
610 |
root |
1.2 |
|
611 |
|
|
JSON numbers and strings become simple Perl scalars. JSON arrays |
612 |
|
|
become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
613 |
|
|
becomes 1, "false" becomes 0 and "null" becomes "undef". |
614 |
|
|
|
615 |
root |
1.11 |
($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
616 |
|
|
This works like the "decode" method, but instead of raising an |
617 |
|
|
exception when there is trailing garbage after the first JSON |
618 |
|
|
object, it will silently stop parsing there and return the number of |
619 |
|
|
characters consumed so far. |
620 |
|
|
|
621 |
|
|
This is useful if your JSON texts are not delimited by an outer |
622 |
|
|
protocol (which is not the brightest thing to do in the first place) |
623 |
|
|
and you need to know where the JSON text ends. |
624 |
|
|
|
625 |
|
|
JSON::XS->new->decode_prefix ("[1] the tail") |
626 |
|
|
=> ([], 3) |
627 |
|
|
|
628 |
root |
1.24 |
INCREMENTAL PARSING |
629 |
|
|
In some cases, there is the need for incremental parsing of JSON texts. |
630 |
|
|
While this module always has to keep both JSON text and resulting Perl |
631 |
|
|
data structure in memory at one time, it does allow you to parse a JSON |
632 |
|
|
stream incrementally. It does so by accumulating text until it has a |
633 |
|
|
full JSON object, which it then can decode. This process is similar to |
634 |
|
|
using "decode_prefix" to see if a full JSON object is available, but is |
635 |
root |
1.27 |
much more efficient (and can be implemented with a minimum of method |
636 |
|
|
calls). |
637 |
root |
1.24 |
|
638 |
root |
1.27 |
JSON::XS will only attempt to parse the JSON text once it is sure it has |
639 |
|
|
enough text to get a decisive result, using a very simple but truly |
640 |
|
|
incremental parser. This means that it sometimes won't stop as early as |
641 |
|
|
the full parser, for example, it doesn't detect parenthese mismatches. |
642 |
|
|
The only thing it guarantees is that it starts decoding as soon as a |
643 |
|
|
syntactically valid JSON text has been seen. This means you need to set |
644 |
|
|
resource limits (e.g. "max_size") to ensure the parser will stop parsing |
645 |
|
|
in the presence if syntax errors. |
646 |
|
|
|
647 |
|
|
The following methods implement this incremental parser. |
648 |
root |
1.24 |
|
649 |
|
|
[void, scalar or list context] = $json->incr_parse ([$string]) |
650 |
|
|
This is the central parsing function. It can both append new text |
651 |
|
|
and extract objects from the stream accumulated so far (both of |
652 |
|
|
these functions are optional). |
653 |
|
|
|
654 |
|
|
If $string is given, then this string is appended to the already |
655 |
|
|
existing JSON fragment stored in the $json object. |
656 |
|
|
|
657 |
|
|
After that, if the function is called in void context, it will |
658 |
|
|
simply return without doing anything further. This can be used to |
659 |
|
|
add more text in as many chunks as you want. |
660 |
|
|
|
661 |
|
|
If the method is called in scalar context, then it will try to |
662 |
|
|
extract exactly *one* JSON object. If that is successful, it will |
663 |
|
|
return this object, otherwise it will return "undef". If there is a |
664 |
|
|
parse error, this method will croak just as "decode" would do (one |
665 |
|
|
can then use "incr_skip" to skip the errornous part). This is the |
666 |
|
|
most common way of using the method. |
667 |
|
|
|
668 |
|
|
And finally, in list context, it will try to extract as many objects |
669 |
|
|
from the stream as it can find and return them, or the empty list |
670 |
|
|
otherwise. For this to work, there must be no separators between the |
671 |
|
|
JSON objects or arrays, instead they must be concatenated |
672 |
|
|
back-to-back. If an error occurs, an exception will be raised as in |
673 |
|
|
the scalar context case. Note that in this case, any |
674 |
|
|
previously-parsed JSON texts will be lost. |
675 |
|
|
|
676 |
root |
1.35 |
Example: Parse some JSON arrays/objects in a given string and return |
677 |
|
|
them. |
678 |
|
|
|
679 |
|
|
my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]"); |
680 |
|
|
|
681 |
root |
1.24 |
$lvalue_string = $json->incr_text |
682 |
|
|
This method returns the currently stored JSON fragment as an lvalue, |
683 |
|
|
that is, you can manipulate it. This *only* works when a preceding |
684 |
|
|
call to "incr_parse" in *scalar context* successfully returned an |
685 |
|
|
object. Under all other circumstances you must not call this |
686 |
|
|
function (I mean it. although in simple tests it might actually |
687 |
|
|
work, it *will* fail under real world conditions). As a special |
688 |
|
|
exception, you can also call this method before having parsed |
689 |
|
|
anything. |
690 |
|
|
|
691 |
|
|
This function is useful in two cases: a) finding the trailing text |
692 |
|
|
after a JSON object or b) parsing multiple JSON objects separated by |
693 |
|
|
non-JSON text (such as commas). |
694 |
|
|
|
695 |
|
|
$json->incr_skip |
696 |
|
|
This will reset the state of the incremental parser and will remove |
697 |
root |
1.29 |
the parsed text from the input buffer so far. This is useful after |
698 |
root |
1.24 |
"incr_parse" died, in which case the input buffer and incremental |
699 |
|
|
parser state is left unchanged, to skip the text parsed so far and |
700 |
|
|
to reset the parse state. |
701 |
|
|
|
702 |
root |
1.29 |
The difference to "incr_reset" is that only text until the parse |
703 |
|
|
error occured is removed. |
704 |
|
|
|
705 |
root |
1.26 |
$json->incr_reset |
706 |
|
|
This completely resets the incremental parser, that is, after this |
707 |
|
|
call, it will be as if the parser had never parsed anything. |
708 |
|
|
|
709 |
root |
1.29 |
This is useful if you want to repeatedly parse JSON objects and want |
710 |
root |
1.26 |
to ignore any trailing data, which means you have to reset the |
711 |
|
|
parser after each successful decode. |
712 |
|
|
|
713 |
root |
1.24 |
LIMITATIONS |
714 |
|
|
All options that affect decoding are supported, except "allow_nonref". |
715 |
|
|
The reason for this is that it cannot be made to work sensibly: JSON |
716 |
|
|
objects and arrays are self-delimited, i.e. you can concatenate them |
717 |
|
|
back to back and still decode them perfectly. This does not hold true |
718 |
|
|
for JSON numbers, however. |
719 |
|
|
|
720 |
|
|
For example, is the string 1 a single JSON number, or is it simply the |
721 |
|
|
start of 12? Or is 12 a single JSON number, or the concatenation of 1 |
722 |
|
|
and 2? In neither case you can tell, and this is why JSON::XS takes the |
723 |
|
|
conservative route and disallows this case. |
724 |
|
|
|
725 |
|
|
EXAMPLES |
726 |
|
|
Some examples will make all this clearer. First, a simple example that |
727 |
|
|
works similarly to "decode_prefix": We want to decode the JSON object at |
728 |
|
|
the start of a string and identify the portion after the JSON object: |
729 |
|
|
|
730 |
|
|
my $text = "[1,2,3] hello"; |
731 |
|
|
|
732 |
|
|
my $json = new JSON::XS; |
733 |
|
|
|
734 |
|
|
my $obj = $json->incr_parse ($text) |
735 |
|
|
or die "expected JSON object or array at beginning of string"; |
736 |
|
|
|
737 |
|
|
my $tail = $json->incr_text; |
738 |
|
|
# $tail now contains " hello" |
739 |
|
|
|
740 |
|
|
Easy, isn't it? |
741 |
|
|
|
742 |
|
|
Now for a more complicated example: Imagine a hypothetical protocol |
743 |
|
|
where you read some requests from a TCP stream, and each request is a |
744 |
|
|
JSON array, without any separation between them (in fact, it is often |
745 |
|
|
useful to use newlines as "separators", as these get interpreted as |
746 |
|
|
whitespace at the start of the JSON text, which makes it possible to |
747 |
|
|
test said protocol with "telnet"...). |
748 |
|
|
|
749 |
|
|
Here is how you'd do it (it is trivial to write this in an event-based |
750 |
|
|
manner): |
751 |
|
|
|
752 |
|
|
my $json = new JSON::XS; |
753 |
|
|
|
754 |
|
|
# read some data from the socket |
755 |
|
|
while (sysread $socket, my $buf, 4096) { |
756 |
|
|
|
757 |
|
|
# split and decode as many requests as possible |
758 |
|
|
for my $request ($json->incr_parse ($buf)) { |
759 |
|
|
# act on the $request |
760 |
|
|
} |
761 |
|
|
} |
762 |
|
|
|
763 |
|
|
Another complicated example: Assume you have a string with JSON objects |
764 |
|
|
or arrays, all separated by (optional) comma characters (e.g. "[1],[2], |
765 |
|
|
[3]"). To parse them, we have to skip the commas between the JSON texts, |
766 |
|
|
and here is where the lvalue-ness of "incr_text" comes in useful: |
767 |
|
|
|
768 |
|
|
my $text = "[1],[2], [3]"; |
769 |
|
|
my $json = new JSON::XS; |
770 |
|
|
|
771 |
|
|
# void context, so no parsing done |
772 |
|
|
$json->incr_parse ($text); |
773 |
|
|
|
774 |
|
|
# now extract as many objects as possible. note the |
775 |
|
|
# use of scalar context so incr_text can be called. |
776 |
|
|
while (my $obj = $json->incr_parse) { |
777 |
|
|
# do something with $obj |
778 |
|
|
|
779 |
|
|
# now skip the optional comma |
780 |
|
|
$json->incr_text =~ s/^ \s* , //x; |
781 |
|
|
} |
782 |
|
|
|
783 |
|
|
Now lets go for a very complex example: Assume that you have a gigantic |
784 |
|
|
JSON array-of-objects, many gigabytes in size, and you want to parse it, |
785 |
|
|
but you cannot load it into memory fully (this has actually happened in |
786 |
|
|
the real world :). |
787 |
|
|
|
788 |
|
|
Well, you lost, you have to implement your own JSON parser. But JSON::XS |
789 |
|
|
can still help you: You implement a (very simple) array parser and let |
790 |
|
|
JSON decode the array elements, which are all full JSON objects on their |
791 |
|
|
own (this wouldn't work if the array elements could be JSON numbers, for |
792 |
|
|
example): |
793 |
|
|
|
794 |
|
|
my $json = new JSON::XS; |
795 |
|
|
|
796 |
|
|
# open the monster |
797 |
|
|
open my $fh, "<bigfile.json" |
798 |
|
|
or die "bigfile: $!"; |
799 |
|
|
|
800 |
|
|
# first parse the initial "[" |
801 |
|
|
for (;;) { |
802 |
|
|
sysread $fh, my $buf, 65536 |
803 |
|
|
or die "read error: $!"; |
804 |
|
|
$json->incr_parse ($buf); # void context, so no parsing |
805 |
|
|
|
806 |
|
|
# Exit the loop once we found and removed(!) the initial "[". |
807 |
|
|
# In essence, we are (ab-)using the $json object as a simple scalar |
808 |
|
|
# we append data to. |
809 |
|
|
last if $json->incr_text =~ s/^ \s* \[ //x; |
810 |
|
|
} |
811 |
|
|
|
812 |
|
|
# now we have the skipped the initial "[", so continue |
813 |
|
|
# parsing all the elements. |
814 |
|
|
for (;;) { |
815 |
|
|
# in this loop we read data until we got a single JSON object |
816 |
|
|
for (;;) { |
817 |
|
|
if (my $obj = $json->incr_parse) { |
818 |
|
|
# do something with $obj |
819 |
|
|
last; |
820 |
|
|
} |
821 |
|
|
|
822 |
|
|
# add more data |
823 |
|
|
sysread $fh, my $buf, 65536 |
824 |
|
|
or die "read error: $!"; |
825 |
|
|
$json->incr_parse ($buf); # void context, so no parsing |
826 |
|
|
} |
827 |
|
|
|
828 |
|
|
# in this loop we read data until we either found and parsed the |
829 |
|
|
# separating "," between elements, or the final "]" |
830 |
|
|
for (;;) { |
831 |
|
|
# first skip whitespace |
832 |
|
|
$json->incr_text =~ s/^\s*//; |
833 |
|
|
|
834 |
|
|
# if we find "]", we are done |
835 |
|
|
if ($json->incr_text =~ s/^\]//) { |
836 |
|
|
print "finished.\n"; |
837 |
|
|
exit; |
838 |
|
|
} |
839 |
|
|
|
840 |
|
|
# if we find ",", we can continue with the next element |
841 |
|
|
if ($json->incr_text =~ s/^,//) { |
842 |
|
|
last; |
843 |
|
|
} |
844 |
|
|
|
845 |
|
|
# if we find anything else, we have a parse error! |
846 |
|
|
if (length $json->incr_text) { |
847 |
|
|
die "parse error near ", $json->incr_text; |
848 |
|
|
} |
849 |
|
|
|
850 |
|
|
# else add more data |
851 |
|
|
sysread $fh, my $buf, 65536 |
852 |
|
|
or die "read error: $!"; |
853 |
|
|
$json->incr_parse ($buf); # void context, so no parsing |
854 |
|
|
} |
855 |
|
|
|
856 |
|
|
This is a complex example, but most of the complexity comes from the |
857 |
|
|
fact that we are trying to be correct (bear with me if I am wrong, I |
858 |
|
|
never ran the above example :). |
859 |
|
|
|
860 |
root |
1.4 |
MAPPING |
861 |
|
|
This section describes how JSON::XS maps Perl values to JSON values and |
862 |
|
|
vice versa. These mappings are designed to "do the right thing" in most |
863 |
|
|
circumstances automatically, preserving round-tripping characteristics |
864 |
|
|
(what you put in comes out as something equivalent). |
865 |
|
|
|
866 |
|
|
For the more enlightened: note that in the following descriptions, |
867 |
root |
1.20 |
lowercase *perl* refers to the Perl interpreter, while uppercase *Perl* |
868 |
root |
1.4 |
refers to the abstract Perl language itself. |
869 |
|
|
|
870 |
|
|
JSON -> PERL |
871 |
|
|
object |
872 |
|
|
A JSON object becomes a reference to a hash in Perl. No ordering of |
873 |
root |
1.20 |
object keys is preserved (JSON does not preserve object key ordering |
874 |
|
|
itself). |
875 |
root |
1.4 |
|
876 |
|
|
array |
877 |
|
|
A JSON array becomes a reference to an array in Perl. |
878 |
|
|
|
879 |
|
|
string |
880 |
|
|
A JSON string becomes a string scalar in Perl - Unicode codepoints |
881 |
|
|
in JSON are represented by the same codepoints in the Perl string, |
882 |
|
|
so no manual decoding is necessary. |
883 |
|
|
|
884 |
|
|
number |
885 |
root |
1.16 |
A JSON number becomes either an integer, numeric (floating point) or |
886 |
|
|
string scalar in perl, depending on its range and any fractional |
887 |
|
|
parts. On the Perl level, there is no difference between those as |
888 |
|
|
Perl handles all the conversion details, but an integer may take |
889 |
|
|
slightly less memory and might represent more values exactly than |
890 |
root |
1.23 |
floating point numbers. |
891 |
root |
1.16 |
|
892 |
|
|
If the number consists of digits only, JSON::XS will try to |
893 |
|
|
represent it as an integer value. If that fails, it will try to |
894 |
|
|
represent it as a numeric (floating point) value if that is possible |
895 |
|
|
without loss of precision. Otherwise it will preserve the number as |
896 |
root |
1.23 |
a string value (in which case you lose roundtripping ability, as the |
897 |
|
|
JSON number will be re-encoded toa JSON string). |
898 |
root |
1.16 |
|
899 |
|
|
Numbers containing a fractional or exponential part will always be |
900 |
|
|
represented as numeric (floating point) values, possibly at a loss |
901 |
root |
1.23 |
of precision (in which case you might lose perfect roundtripping |
902 |
|
|
ability, but the JSON number will still be re-encoded as a JSON |
903 |
|
|
number). |
904 |
root |
1.4 |
|
905 |
root |
1.35 |
Note that precision is not accuracy - binary floating point values |
906 |
|
|
cannot represent most decimal fractions exactly, and when converting |
907 |
|
|
from and to floating point, JSON::XS only guarantees precision up to |
908 |
|
|
but not including the leats significant bit. |
909 |
|
|
|
910 |
root |
1.4 |
true, false |
911 |
root |
1.14 |
These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
912 |
|
|
respectively. They are overloaded to act almost exactly like the |
913 |
root |
1.20 |
numbers 1 and 0. You can check whether a scalar is a JSON boolean by |
914 |
root |
1.14 |
using the "JSON::XS::is_bool" function. |
915 |
root |
1.4 |
|
916 |
|
|
null |
917 |
|
|
A JSON null atom becomes "undef" in Perl. |
918 |
|
|
|
919 |
|
|
PERL -> JSON |
920 |
|
|
The mapping from Perl to JSON is slightly more difficult, as Perl is a |
921 |
|
|
truly typeless language, so we can only guess which JSON type is meant |
922 |
|
|
by a Perl value. |
923 |
|
|
|
924 |
|
|
hash references |
925 |
|
|
Perl hash references become JSON objects. As there is no inherent |
926 |
root |
1.9 |
ordering in hash keys (or JSON objects), they will usually be |
927 |
|
|
encoded in a pseudo-random order that can change between runs of the |
928 |
|
|
same program but stays generally the same within a single run of a |
929 |
|
|
program. JSON::XS can optionally sort the hash keys (determined by |
930 |
|
|
the *canonical* flag), so the same datastructure will serialise to |
931 |
|
|
the same JSON text (given same settings and version of JSON::XS), |
932 |
|
|
but this incurs a runtime overhead and is only rarely useful, e.g. |
933 |
|
|
when you want to compare some JSON text against another for |
934 |
|
|
equality. |
935 |
root |
1.4 |
|
936 |
|
|
array references |
937 |
|
|
Perl array references become JSON arrays. |
938 |
|
|
|
939 |
root |
1.9 |
other references |
940 |
|
|
Other unblessed references are generally not allowed and will cause |
941 |
|
|
an exception to be thrown, except for references to the integers 0 |
942 |
|
|
and 1, which get turned into "false" and "true" atoms in JSON. You |
943 |
|
|
can also use "JSON::XS::false" and "JSON::XS::true" to improve |
944 |
|
|
readability. |
945 |
|
|
|
946 |
root |
1.26 |
encode_json [\0, JSON::XS::true] # yields [false,true] |
947 |
root |
1.9 |
|
948 |
root |
1.14 |
JSON::XS::true, JSON::XS::false |
949 |
|
|
These special values become JSON true and JSON false values, |
950 |
root |
1.19 |
respectively. You can also use "\1" and "\0" directly if you want. |
951 |
root |
1.14 |
|
952 |
root |
1.4 |
blessed objects |
953 |
root |
1.23 |
Blessed objects are not directly representable in JSON. See the |
954 |
|
|
"allow_blessed" and "convert_blessed" methods on various options on |
955 |
|
|
how to deal with this: basically, you can choose between throwing an |
956 |
|
|
exception, encoding the reference as if it weren't blessed, or |
957 |
|
|
provide your own serialiser method. |
958 |
root |
1.4 |
|
959 |
|
|
simple scalars |
960 |
|
|
Simple Perl scalars (any scalar that is not a reference) are the |
961 |
|
|
most difficult objects to encode: JSON::XS will encode undefined |
962 |
root |
1.23 |
scalars as JSON "null" values, scalars that have last been used in a |
963 |
|
|
string context before encoding as JSON strings, and anything else as |
964 |
root |
1.4 |
number value: |
965 |
|
|
|
966 |
|
|
# dump as number |
967 |
root |
1.22 |
encode_json [2] # yields [2] |
968 |
|
|
encode_json [-3.0e17] # yields [-3e+17] |
969 |
|
|
my $value = 5; encode_json [$value] # yields [5] |
970 |
root |
1.4 |
|
971 |
|
|
# used as string, so dump as string |
972 |
|
|
print $value; |
973 |
root |
1.22 |
encode_json [$value] # yields ["5"] |
974 |
root |
1.4 |
|
975 |
|
|
# undef becomes null |
976 |
root |
1.22 |
encode_json [undef] # yields [null] |
977 |
root |
1.4 |
|
978 |
root |
1.20 |
You can force the type to be a JSON string by stringifying it: |
979 |
root |
1.4 |
|
980 |
|
|
my $x = 3.1; # some variable containing a number |
981 |
|
|
"$x"; # stringified |
982 |
|
|
$x .= ""; # another, more awkward way to stringify |
983 |
|
|
print $x; # perl does it for you, too, quite often |
984 |
|
|
|
985 |
root |
1.20 |
You can force the type to be a JSON number by numifying it: |
986 |
root |
1.4 |
|
987 |
|
|
my $x = "3"; # some variable containing a string |
988 |
|
|
$x += 0; # numify it, ensuring it will be dumped as a number |
989 |
root |
1.20 |
$x *= 1; # same thing, the choice is yours. |
990 |
root |
1.4 |
|
991 |
root |
1.20 |
You can not currently force the type in other, less obscure, ways. |
992 |
root |
1.23 |
Tell me if you need this capability (but don't forget to explain why |
993 |
root |
1.24 |
it's needed :). |
994 |
root |
1.23 |
|
995 |
root |
1.35 |
Note that numerical precision has the same meaning as under Perl (so |
996 |
|
|
binary to decimal conversion follows the same rules as in Perl, |
997 |
|
|
which can differ to other languages). Also, your perl interpreter |
998 |
|
|
might expose extensions to the floating point numbers of your |
999 |
|
|
platform, such as infinities or NaN's - these cannot be represented |
1000 |
|
|
in JSON, and it is an error to pass those in. |
1001 |
|
|
|
1002 |
root |
1.23 |
ENCODING/CODESET FLAG NOTES |
1003 |
|
|
The interested reader might have seen a number of flags that signify |
1004 |
|
|
encodings or codesets - "utf8", "latin1" and "ascii". There seems to be |
1005 |
|
|
some confusion on what these do, so here is a short comparison: |
1006 |
|
|
|
1007 |
root |
1.24 |
"utf8" controls whether the JSON text created by "encode" (and expected |
1008 |
root |
1.23 |
by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only |
1009 |
root |
1.24 |
control whether "encode" escapes character values outside their |
1010 |
root |
1.23 |
respective codeset range. Neither of these flags conflict with each |
1011 |
|
|
other, although some combinations make less sense than others. |
1012 |
|
|
|
1013 |
|
|
Care has been taken to make all flags symmetrical with respect to |
1014 |
|
|
"encode" and "decode", that is, texts encoded with any combination of |
1015 |
|
|
these flag values will be correctly decoded when the same flags are used |
1016 |
|
|
- in general, if you use different flag settings while encoding vs. when |
1017 |
|
|
decoding you likely have a bug somewhere. |
1018 |
|
|
|
1019 |
|
|
Below comes a verbose discussion of these flags. Note that a "codeset" |
1020 |
|
|
is simply an abstract set of character-codepoint pairs, while an |
1021 |
|
|
encoding takes those codepoint numbers and *encodes* them, in our case |
1022 |
|
|
into octets. Unicode is (among other things) a codeset, UTF-8 is an |
1023 |
|
|
encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and* |
1024 |
|
|
encodings at the same time, which can be confusing. |
1025 |
|
|
|
1026 |
|
|
"utf8" flag disabled |
1027 |
|
|
When "utf8" is disabled (the default), then "encode"/"decode" |
1028 |
|
|
generate and expect Unicode strings, that is, characters with high |
1029 |
|
|
ordinal Unicode values (> 255) will be encoded as such characters, |
1030 |
|
|
and likewise such characters are decoded as-is, no canges to them |
1031 |
|
|
will be done, except "(re-)interpreting" them as Unicode codepoints |
1032 |
|
|
or Unicode characters, respectively (to Perl, these are the same |
1033 |
|
|
thing in strings unless you do funny/weird/dumb stuff). |
1034 |
|
|
|
1035 |
|
|
This is useful when you want to do the encoding yourself (e.g. when |
1036 |
|
|
you want to have UTF-16 encoded JSON texts) or when some other layer |
1037 |
|
|
does the encoding for you (for example, when printing to a terminal |
1038 |
|
|
using a filehandle that transparently encodes to UTF-8 you certainly |
1039 |
|
|
do NOT want to UTF-8 encode your data first and have Perl encode it |
1040 |
|
|
another time). |
1041 |
|
|
|
1042 |
|
|
"utf8" flag enabled |
1043 |
|
|
If the "utf8"-flag is enabled, "encode"/"decode" will encode all |
1044 |
|
|
characters using the corresponding UTF-8 multi-byte sequence, and |
1045 |
|
|
will expect your input strings to be encoded as UTF-8, that is, no |
1046 |
|
|
"character" of the input string must have any value > 255, as UTF-8 |
1047 |
|
|
does not allow that. |
1048 |
|
|
|
1049 |
|
|
The "utf8" flag therefore switches between two modes: disabled means |
1050 |
|
|
you will get a Unicode string in Perl, enabled means you get an |
1051 |
|
|
UTF-8 encoded octet/binary string in Perl. |
1052 |
|
|
|
1053 |
|
|
"latin1" or "ascii" flags enabled |
1054 |
|
|
With "latin1" (or "ascii") enabled, "encode" will escape characters |
1055 |
|
|
with ordinal values > 255 (> 127 with "ascii") and encode the |
1056 |
|
|
remaining characters as specified by the "utf8" flag. |
1057 |
|
|
|
1058 |
|
|
If "utf8" is disabled, then the result is also correctly encoded in |
1059 |
|
|
those character sets (as both are proper subsets of Unicode, meaning |
1060 |
|
|
that a Unicode string with all character values < 256 is the same |
1061 |
|
|
thing as a ISO-8859-1 string, and a Unicode string with all |
1062 |
|
|
character values < 128 is the same thing as an ASCII string in |
1063 |
|
|
Perl). |
1064 |
|
|
|
1065 |
|
|
If "utf8" is enabled, you still get a correct UTF-8-encoded string, |
1066 |
|
|
regardless of these flags, just some more characters will be escaped |
1067 |
|
|
using "\uXXXX" then before. |
1068 |
|
|
|
1069 |
|
|
Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8 |
1070 |
|
|
encoding, while ASCII-encoded strings are. That is because the |
1071 |
|
|
ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 |
1072 |
|
|
*codeset* being a subset of Unicode), while ASCII is. |
1073 |
|
|
|
1074 |
|
|
Surprisingly, "decode" will ignore these flags and so treat all |
1075 |
|
|
input values as governed by the "utf8" flag. If it is disabled, this |
1076 |
|
|
allows you to decode ISO-8859-1- and ASCII-encoded strings, as both |
1077 |
|
|
strict subsets of Unicode. If it is enabled, you can correctly |
1078 |
|
|
decode UTF-8 encoded strings. |
1079 |
|
|
|
1080 |
|
|
So neither "latin1" nor "ascii" are incompatible with the "utf8" |
1081 |
|
|
flag - they only govern when the JSON output engine escapes a |
1082 |
|
|
character or not. |
1083 |
|
|
|
1084 |
|
|
The main use for "latin1" is to relatively efficiently store binary |
1085 |
|
|
data as JSON, at the expense of breaking compatibility with most |
1086 |
|
|
JSON decoders. |
1087 |
|
|
|
1088 |
|
|
The main use for "ascii" is to force the output to not contain |
1089 |
|
|
characters with values > 127, which means you can interpret the |
1090 |
|
|
resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about |
1091 |
|
|
any character set and 8-bit-encoding, and still get the same data |
1092 |
|
|
structure back. This is useful when your channel for JSON transfer |
1093 |
|
|
is not 8-bit clean or the encoding might be mangled in between (e.g. |
1094 |
|
|
in mail), and works because ASCII is a proper subset of most 8-bit |
1095 |
|
|
and multibyte encodings in use in the world. |
1096 |
root |
1.4 |
|
1097 |
root |
1.29 |
JSON and ECMAscript |
1098 |
|
|
JSON syntax is based on how literals are represented in javascript (the |
1099 |
|
|
not-standardised predecessor of ECMAscript) which is presumably why it |
1100 |
|
|
is called "JavaScript Object Notation". |
1101 |
|
|
|
1102 |
|
|
However, JSON is not a subset (and also not a superset of course) of |
1103 |
|
|
ECMAscript (the standard) or javascript (whatever browsers actually |
1104 |
|
|
implement). |
1105 |
|
|
|
1106 |
|
|
If you want to use javascript's "eval" function to "parse" JSON, you |
1107 |
|
|
might run into parse errors for valid JSON texts, or the resulting data |
1108 |
|
|
structure might not be queryable: |
1109 |
|
|
|
1110 |
|
|
One of the problems is that U+2028 and U+2029 are valid characters |
1111 |
|
|
inside JSON strings, but are not allowed in ECMAscript string literals, |
1112 |
|
|
so the following Perl fragment will not output something that can be |
1113 |
|
|
guaranteed to be parsable by javascript's "eval": |
1114 |
|
|
|
1115 |
|
|
use JSON::XS; |
1116 |
|
|
|
1117 |
|
|
print encode_json [chr 0x2028]; |
1118 |
|
|
|
1119 |
|
|
The right fix for this is to use a proper JSON parser in your javascript |
1120 |
|
|
programs, and not rely on "eval" (see for example Douglas Crockford's |
1121 |
|
|
json2.js parser). |
1122 |
|
|
|
1123 |
|
|
If this is not an option, you can, as a stop-gap measure, simply encode |
1124 |
|
|
to ASCII-only JSON: |
1125 |
|
|
|
1126 |
|
|
use JSON::XS; |
1127 |
|
|
|
1128 |
|
|
print JSON::XS->new->ascii->encode ([chr 0x2028]); |
1129 |
|
|
|
1130 |
|
|
Note that this will enlarge the resulting JSON text quite a bit if you |
1131 |
|
|
have many non-ASCII characters. You might be tempted to run some regexes |
1132 |
|
|
to only escape U+2028 and U+2029, e.g.: |
1133 |
|
|
|
1134 |
|
|
# DO NOT USE THIS! |
1135 |
|
|
my $json = JSON::XS->new->utf8->encode ([chr 0x2028]); |
1136 |
|
|
$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028 |
1137 |
|
|
$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029 |
1138 |
|
|
print $json; |
1139 |
|
|
|
1140 |
|
|
Note that *this is a bad idea*: the above only works for U+2028 and |
1141 |
|
|
U+2029 and thus only for fully ECMAscript-compliant parsers. Many |
1142 |
|
|
existing javascript implementations, however, have issues with other |
1143 |
|
|
characters as well - using "eval" naively simply *will* cause problems. |
1144 |
|
|
|
1145 |
|
|
Another problem is that some javascript implementations reserve some |
1146 |
|
|
property names for their own purposes (which probably makes them |
1147 |
|
|
non-ECMAscript-compliant). For example, Iceweasel reserves the |
1148 |
|
|
"__proto__" property name for it's own purposes. |
1149 |
|
|
|
1150 |
|
|
If that is a problem, you could parse try to filter the resulting JSON |
1151 |
|
|
output for these property strings, e.g.: |
1152 |
|
|
|
1153 |
|
|
$json =~ s/"__proto__"\s*:/"__proto__renamed":/g; |
1154 |
|
|
|
1155 |
|
|
This works because "__proto__" is not valid outside of strings, so every |
1156 |
|
|
occurence of ""__proto__"\s*:" must be a string used as property name. |
1157 |
|
|
|
1158 |
|
|
If you know of other incompatibilities, please let me know. |
1159 |
|
|
|
1160 |
root |
1.13 |
JSON and YAML |
1161 |
root |
1.23 |
You often hear that JSON is a subset of YAML. This is, however, a mass |
1162 |
|
|
hysteria(*) and very far from the truth (as of the time of this |
1163 |
|
|
writing), so let me state it clearly: *in general, there is no way to |
1164 |
|
|
configure JSON::XS to output a data structure as valid YAML* that works |
1165 |
|
|
in all cases. |
1166 |
root |
1.13 |
|
1167 |
|
|
If you really must use JSON::XS to generate YAML, you should use this |
1168 |
|
|
algorithm (subject to change in future versions): |
1169 |
|
|
|
1170 |
|
|
my $to_yaml = JSON::XS->new->utf8->space_after (1); |
1171 |
|
|
my $yaml = $to_yaml->encode ($ref) . "\n"; |
1172 |
|
|
|
1173 |
root |
1.23 |
This will *usually* generate JSON texts that also parse as valid YAML. |
1174 |
root |
1.13 |
Please note that YAML has hardcoded limits on (simple) object key |
1175 |
root |
1.23 |
lengths that JSON doesn't have and also has different and incompatible |
1176 |
root |
1.32 |
unicode character escape syntax, so you should make sure that your hash |
1177 |
|
|
keys are noticeably shorter than the 1024 "stream characters" YAML |
1178 |
|
|
allows and that you do not have characters with codepoint values outside |
1179 |
|
|
the Unicode BMP (basic multilingual page). YAML also does not allow "\/" |
1180 |
root |
1.23 |
sequences in strings (which JSON::XS does not *currently* generate, but |
1181 |
|
|
other JSON generators might). |
1182 |
|
|
|
1183 |
|
|
There might be other incompatibilities that I am not aware of (or the |
1184 |
|
|
YAML specification has been changed yet again - it does so quite often). |
1185 |
|
|
In general you should not try to generate YAML with a JSON generator or |
1186 |
|
|
vice versa, or try to parse JSON with a YAML parser or vice versa: |
1187 |
|
|
chances are high that you will run into severe interoperability problems |
1188 |
|
|
when you least expect it. |
1189 |
root |
1.13 |
|
1190 |
root |
1.23 |
(*) I have been pressured multiple times by Brian Ingerson (one of the |
1191 |
|
|
authors of the YAML specification) to remove this paragraph, despite |
1192 |
|
|
him acknowledging that the actual incompatibilities exist. As I was |
1193 |
|
|
personally bitten by this "JSON is YAML" lie, I refused and said I |
1194 |
|
|
will continue to educate people about these issues, so others do not |
1195 |
|
|
run into the same problem again and again. After this, Brian called |
1196 |
|
|
me a (quote)*complete and worthless idiot*(unquote). |
1197 |
|
|
|
1198 |
|
|
In my opinion, instead of pressuring and insulting people who |
1199 |
|
|
actually clarify issues with YAML and the wrong statements of some |
1200 |
|
|
of its proponents, I would kindly suggest reading the JSON spec |
1201 |
|
|
(which is not that difficult or long) and finally make YAML |
1202 |
|
|
compatible to it, and educating users about the changes, instead of |
1203 |
|
|
spreading lies about the real compatibility for many *years* and |
1204 |
|
|
trying to silence people who point out that it isn't true. |
1205 |
root |
1.13 |
|
1206 |
root |
1.32 |
Addendum/2009: the YAML 1.2 spec is still incomaptible with JSON, |
1207 |
|
|
even though the incompatibilities have been documented (and are |
1208 |
|
|
known to Brian) for many years and the spec makes explicit claims |
1209 |
|
|
that YAML is a superset of JSON. It would be so easy to fix, but |
1210 |
|
|
apparently, bullying and corrupting userdata is so much easier. |
1211 |
|
|
|
1212 |
root |
1.2 |
SPEED |
1213 |
|
|
It seems that JSON::XS is surprisingly fast, as shown in the following |
1214 |
|
|
tables. They have been generated with the help of the "eg/bench" program |
1215 |
|
|
in the JSON::XS distribution, to make it easy to compare on your own |
1216 |
|
|
system. |
1217 |
|
|
|
1218 |
root |
1.12 |
First comes a comparison between various modules using a very short |
1219 |
root |
1.23 |
single-line JSON string (also available at |
1220 |
|
|
<http://dist.schmorp.de/misc/json/short.json>). |
1221 |
root |
1.7 |
|
1222 |
root |
1.25 |
{"method": "handleMessage", "params": ["user1", |
1223 |
|
|
"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
1224 |
root |
1.34 |
1, 0]} |
1225 |
root |
1.7 |
|
1226 |
|
|
It shows the number of encodes/decodes per second (JSON::XS uses the |
1227 |
|
|
functional interface, while JSON::XS/2 uses the OO interface with |
1228 |
root |
1.34 |
pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink. |
1229 |
|
|
JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses |
1230 |
|
|
the from_json method). Higher is better: |
1231 |
|
|
|
1232 |
|
|
module | encode | decode | |
1233 |
|
|
--------------|------------|------------| |
1234 |
|
|
JSON::DWIW/DS | 86302.551 | 102300.098 | |
1235 |
|
|
JSON::DWIW/FJ | 86302.551 | 75983.768 | |
1236 |
|
|
JSON::PP | 15827.562 | 6638.658 | |
1237 |
|
|
JSON::Syck | 63358.066 | 47662.545 | |
1238 |
|
|
JSON::XS | 511500.488 | 511500.488 | |
1239 |
|
|
JSON::XS/2 | 291271.111 | 388361.481 | |
1240 |
|
|
JSON::XS/3 | 361577.931 | 361577.931 | |
1241 |
|
|
Storable | 66788.280 | 265462.278 | |
1242 |
|
|
--------------+------------+------------+ |
1243 |
|
|
|
1244 |
|
|
That is, JSON::XS is almost six times faster than JSON::DWIW on |
1245 |
|
|
encoding, about five times faster on decoding, and over thirty to |
1246 |
|
|
seventy times faster than JSON's pure perl implementation. It also |
1247 |
root |
1.12 |
compares favourably to Storable for small amounts of data. |
1248 |
root |
1.2 |
|
1249 |
root |
1.5 |
Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1250 |
root |
1.23 |
search API (<http://dist.schmorp.de/misc/json/long.json>). |
1251 |
root |
1.2 |
|
1252 |
root |
1.34 |
module | encode | decode | |
1253 |
|
|
--------------|------------|------------| |
1254 |
|
|
JSON::DWIW/DS | 1647.927 | 2673.916 | |
1255 |
|
|
JSON::DWIW/FJ | 1630.249 | 2596.128 | |
1256 |
|
|
JSON::PP | 400.640 | 62.311 | |
1257 |
|
|
JSON::Syck | 1481.040 | 1524.869 | |
1258 |
|
|
JSON::XS | 20661.596 | 9541.183 | |
1259 |
|
|
JSON::XS/2 | 10683.403 | 9416.938 | |
1260 |
|
|
JSON::XS/3 | 20661.596 | 9400.054 | |
1261 |
|
|
Storable | 19765.806 | 10000.725 | |
1262 |
|
|
--------------+------------+------------+ |
1263 |
root |
1.2 |
|
1264 |
root |
1.13 |
Again, JSON::XS leads by far (except for Storable which non-surprisingly |
1265 |
root |
1.34 |
decodes a bit faster). |
1266 |
root |
1.2 |
|
1267 |
root |
1.20 |
On large strings containing lots of high Unicode characters, some |
1268 |
root |
1.7 |
modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
1269 |
root |
1.20 |
result will be broken due to missing (or wrong) Unicode handling. Others |
1270 |
root |
1.7 |
refuse to decode or encode properly, so it was impossible to prepare a |
1271 |
|
|
fair comparison table for that case. |
1272 |
root |
1.5 |
|
1273 |
root |
1.8 |
SECURITY CONSIDERATIONS |
1274 |
|
|
When you are using JSON in a protocol, talking to untrusted potentially |
1275 |
|
|
hostile creatures requires relatively few measures. |
1276 |
|
|
|
1277 |
|
|
First of all, your JSON decoder should be secure, that is, should not |
1278 |
|
|
have any buffer overflows. Obviously, this module should ensure that and |
1279 |
|
|
I am trying hard on making that true, but you never know. |
1280 |
|
|
|
1281 |
|
|
Second, you need to avoid resource-starving attacks. That means you |
1282 |
|
|
should limit the size of JSON texts you accept, or make sure then when |
1283 |
root |
1.20 |
your resources run out, that's just fine (e.g. by using a separate |
1284 |
root |
1.8 |
process that can crash safely). The size of a JSON text in octets or |
1285 |
|
|
characters is usually a good indication of the size of the resources |
1286 |
root |
1.15 |
required to decode it into a Perl structure. While JSON::XS can check |
1287 |
|
|
the size of the JSON text, it might be too late when you already have it |
1288 |
|
|
in memory, so you might want to check the size before you accept the |
1289 |
|
|
string. |
1290 |
root |
1.8 |
|
1291 |
|
|
Third, JSON::XS recurses using the C stack when decoding objects and |
1292 |
|
|
arrays. The C stack is a limited resource: for instance, on my amd64 |
1293 |
|
|
machine with 8MB of stack size I can decode around 180k nested arrays |
1294 |
root |
1.10 |
but only 14k nested JSON objects (due to perl itself recursing deeply on |
1295 |
|
|
croak to free the temporary). If that is exceeded, the program crashes. |
1296 |
root |
1.23 |
To be conservative, the default nesting limit is set to 512. If your |
1297 |
root |
1.8 |
process has a smaller stack, you should adjust this setting accordingly |
1298 |
|
|
with the "max_depth" method. |
1299 |
|
|
|
1300 |
root |
1.23 |
Something else could bomb you, too, that I forgot to think of. In that |
1301 |
|
|
case, you get to keep the pieces. I am always open for hints, though... |
1302 |
|
|
|
1303 |
|
|
Also keep in mind that JSON::XS might leak contents of your Perl data |
1304 |
|
|
structures in its error messages, so when you serialise sensitive |
1305 |
|
|
information you might want to make sure that exceptions thrown by |
1306 |
|
|
JSON::XS will not end up in front of untrusted eyes. |
1307 |
root |
1.2 |
|
1308 |
root |
1.20 |
If you are using JSON::XS to return packets to consumption by JavaScript |
1309 |
root |
1.14 |
scripts in a browser you should have a look at |
1310 |
root |
1.33 |
<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> |
1311 |
|
|
to see whether you are vulnerable to some common attack vectors (which |
1312 |
|
|
really are browser design bugs, but it is still you who will have to |
1313 |
|
|
deal with it, as major browser developers care only for features, not |
1314 |
|
|
about getting security right). |
1315 |
root |
1.14 |
|
1316 |
root |
1.19 |
THREADS |
1317 |
root |
1.20 |
This module is *not* guaranteed to be thread safe and there are no plans |
1318 |
root |
1.19 |
to change this until Perl gets thread support (as opposed to the |
1319 |
|
|
horribly slow so-called "threads" which are simply slow and bloated |
1320 |
root |
1.24 |
process simulations - use fork, it's *much* faster, cheaper, better). |
1321 |
root |
1.19 |
|
1322 |
root |
1.20 |
(It might actually work, but you have been warned). |
1323 |
root |
1.19 |
|
1324 |
root |
1.2 |
BUGS |
1325 |
|
|
While the goal of this module is to be correct, that unfortunately does |
1326 |
root |
1.26 |
not mean it's bug-free, only that I think its design is bug-free. If you |
1327 |
|
|
keep reporting bugs they will be fixed swiftly, though. |
1328 |
root |
1.1 |
|
1329 |
root |
1.19 |
Please refrain from using rt.cpan.org or any other bug reporting |
1330 |
|
|
service. I put the contact address into my modules for a reason. |
1331 |
|
|
|
1332 |
root |
1.24 |
SEE ALSO |
1333 |
|
|
The json_xs command line utility for quick experiments. |
1334 |
|
|
|
1335 |
root |
1.1 |
AUTHOR |
1336 |
|
|
Marc Lehmann <schmorp@schmorp.de> |
1337 |
|
|
http://home.schmorp.de/ |
1338 |
|
|
|