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