1 | NAME |
1 | NAME |
2 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
2 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
3 | |
3 | |
4 | SYNOPSIS |
4 | SYNOPSIS |
5 | use JSON::XS; |
5 | use JSON::XS; |
|
|
6 | |
|
|
7 | # exported functions, they croak on error |
|
|
8 | # and expect/generate UTF-8 |
|
|
9 | |
|
|
10 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
|
|
11 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
|
|
12 | |
|
|
13 | # objToJson and jsonToObj aliases to to_json and from_json |
|
|
14 | # are exported for compatibility to the JSON module, |
|
|
15 | # but should not be used in new code. |
|
|
16 | |
|
|
17 | # OO-interface |
|
|
18 | |
|
|
19 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
|
|
20 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
|
|
21 | $perl_scalar = $coder->decode ($unicode_json_text); |
6 | |
22 | |
7 | DESCRIPTION |
23 | DESCRIPTION |
8 | This module converts Perl data structures to JSON and vice versa. Its |
24 | 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*. |
25 | 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. |
26 | To reach the latter goal it was written in C. |
… | |
… | |
15 | cases their maintainers are unresponsive, gone missing, or not listening |
31 | cases their maintainers are unresponsive, gone missing, or not listening |
16 | to bug reports for other reasons. |
32 | to bug reports for other reasons. |
17 | |
33 | |
18 | See COMPARISON, below, for a comparison to some other JSON modules. |
34 | See COMPARISON, below, for a comparison to some other JSON modules. |
19 | |
35 | |
|
|
36 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
|
|
37 | vice versa. |
|
|
38 | |
20 | FEATURES |
39 | FEATURES |
21 | * correct handling of unicode issues |
40 | * correct unicode handling |
22 | This module knows how to handle Unicode, and even documents how it |
41 | This module knows how to handle Unicode, and even documents how and |
23 | does so. |
42 | when it does so. |
24 | |
43 | |
25 | * round-trip integrity |
44 | * round-trip integrity |
26 | When you serialise a perl data structure using only datatypes |
45 | When you serialise a perl data structure using only datatypes |
27 | supported by JSON, the deserialised data structure is identical on |
46 | 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"). |
47 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" |
|
|
48 | just because it looks like a number). |
29 | |
49 | |
30 | * strict checking of JSON correctness |
50 | * strict checking of JSON correctness |
31 | There is no guessing, no generating of illegal JSON strings by |
51 | There is no guessing, no generating of illegal JSON texts by |
32 | default, and only JSON is accepted as input (the latter is a |
52 | default, and only JSON is accepted as input by default (the latter |
33 | security feature). |
53 | is a security feature). |
34 | |
54 | |
35 | * fast |
55 | * fast |
36 | compared to other JSON modules, this module compares favourably. |
56 | Compared to other JSON modules, this module compares favourably in |
|
|
57 | terms of speed, too. |
37 | |
58 | |
38 | * simple to use |
59 | * simple to use |
39 | This module has both a simple functional interface as well as an OO |
60 | This module has both a simple functional interface as well as an OO |
40 | interface. |
61 | interface. |
41 | |
62 | |
42 | * reasonably versatile output formats |
63 | * reasonably versatile output formats |
43 | You can choose between the most compact format possible, a |
64 | You can choose between the most compact guarenteed single-line |
44 | pure-ascii format, or a pretty-printed format. Or you can combine |
65 | format possible (nice for simple line-based protocols), a pure-ascii |
|
|
66 | format (for when your transport is not 8-bit clean, still supports |
|
|
67 | the whole unicode range), or a pretty-printed format (for when you |
|
|
68 | want to read that stuff). Or you can combine those features in |
45 | those features in whatever way you like. |
69 | whatever way you like. |
46 | |
70 | |
47 | FUNCTIONAL INTERFACE |
71 | FUNCTIONAL INTERFACE |
48 | The following convinience methods are provided by this module. They are |
72 | The following convinience methods are provided by this module. They are |
49 | exported by default: |
73 | exported by default: |
50 | |
74 | |
51 | $json_string = to_json $perl_scalar |
75 | $json_text = to_json $perl_scalar |
52 | Converts the given Perl data structure (a simple scalar or a |
76 | Converts the given Perl data structure (a simple scalar or a |
53 | reference to a hash or array) to a UTF-8 encoded, binary string |
77 | reference to a hash or array) to a UTF-8 encoded, binary string |
54 | (that is, the string contains octets only). Croaks on error. |
78 | (that is, the string contains octets only). Croaks on error. |
55 | |
79 | |
56 | This function call is functionally identical to "JSON::XS->new->utf8 |
80 | This function call is functionally identical to: |
57 | (1)->encode ($perl_scalar)". |
|
|
58 | |
81 | |
|
|
82 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
|
|
83 | |
|
|
84 | except being faster. |
|
|
85 | |
59 | $perl_scalar = from_json $json_string |
86 | $perl_scalar = from_json $json_text |
60 | The opposite of "to_json": expects an UTF-8 (binary) string and |
87 | The opposite of "to_json": expects an UTF-8 (binary) string and |
61 | tries to parse that as an UTF-8 encoded JSON string, returning the |
88 | tries to parse that as an UTF-8 encoded JSON text, returning the |
62 | resulting simple scalar or reference. Croaks on error. |
89 | resulting simple scalar or reference. Croaks on error. |
63 | |
90 | |
64 | This function call is functionally identical to "JSON::XS->new->utf8 |
91 | This function call is functionally identical to: |
65 | (1)->decode ($json_string)". |
92 | |
|
|
93 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
|
|
94 | |
|
|
95 | except being faster. |
|
|
96 | |
|
|
97 | $is_boolean = JSON::XS::is_bool $scalar |
|
|
98 | Returns true if the passed scalar represents either JSON::XS::true |
|
|
99 | or JSON::XS::false, two constants that act like 1 and 0, |
|
|
100 | respectively and are used to represent JSON "true" and "false" |
|
|
101 | values in Perl. |
|
|
102 | |
|
|
103 | See MAPPING, below, for more information on how JSON values are |
|
|
104 | mapped to Perl. |
66 | |
105 | |
67 | OBJECT-ORIENTED INTERFACE |
106 | OBJECT-ORIENTED INTERFACE |
68 | The object oriented interface lets you configure your own encoding or |
107 | The object oriented interface lets you configure your own encoding or |
69 | decoding style, within the limits of supported formats. |
108 | decoding style, within the limits of supported formats. |
70 | |
109 | |
… | |
… | |
74 | *disabled*. |
113 | *disabled*. |
75 | |
114 | |
76 | The mutators for flags all return the JSON object again and thus |
115 | The mutators for flags all return the JSON object again and thus |
77 | calls can be chained: |
116 | calls can be chained: |
78 | |
117 | |
79 | my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) |
118 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
80 | => {"a": [1, 2]} |
119 | => {"a": [1, 2]} |
81 | |
120 | |
82 | $json = $json->ascii ($enable) |
121 | $json = $json->ascii ([$enable]) |
83 | If $enable is true, then the "encode" method will not generate |
122 | If $enable is true (or missing), then the "encode" method will not |
84 | characters outside the code range 0..127. Any unicode characters |
123 | generate characters outside the code range 0..127 (which is ASCII). |
85 | outside that range will be escaped using either a single \uXXXX (BMP |
124 | Any unicode characters outside that range will be escaped using |
86 | characters) or a double \uHHHH\uLLLLL escape sequence, as per |
125 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
87 | RFC4627. |
126 | escape sequence, as per RFC4627. The resulting encoded JSON text can |
|
|
127 | be treated as a native unicode string, an ascii-encoded, |
|
|
128 | latin1-encoded or UTF-8 encoded string, or any other superset of |
|
|
129 | ASCII. |
88 | |
130 | |
89 | If $enable is false, then the "encode" method will not escape |
131 | If $enable is false, then the "encode" method will not escape |
90 | Unicode characters unless necessary. |
132 | Unicode characters unless required by the JSON syntax or other |
|
|
133 | flags. This results in a faster and more compact format. |
91 | |
134 | |
|
|
135 | The main use for this flag is to produce JSON texts that can be |
|
|
136 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
|
|
137 | contain any 8 bit characters. |
|
|
138 | |
92 | JSON::XS->new->ascii (1)->encode (chr 0x10401) |
139 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
93 | => \ud801\udc01 |
140 | => ["\ud801\udc01"] |
94 | |
141 | |
|
|
142 | $json = $json->latin1 ([$enable]) |
|
|
143 | If $enable is true (or missing), then the "encode" method will |
|
|
144 | encode the resulting JSON text as latin1 (or iso-8859-1), escaping |
|
|
145 | any characters outside the code range 0..255. The resulting string |
|
|
146 | can be treated as a latin1-encoded JSON text or a native unicode |
|
|
147 | string. The "decode" method will not be affected in any way by this |
|
|
148 | flag, as "decode" by default expects unicode, which is a strict |
|
|
149 | superset of latin1. |
|
|
150 | |
|
|
151 | If $enable is false, then the "encode" method will not escape |
|
|
152 | Unicode characters unless required by the JSON syntax or other |
|
|
153 | flags. |
|
|
154 | |
|
|
155 | The main use for this flag is efficiently encoding binary data as |
|
|
156 | JSON text, as most octets will not be escaped, resulting in a |
|
|
157 | smaller encoded size. The disadvantage is that the resulting JSON |
|
|
158 | text is encoded in latin1 (and must correctly be treated as such |
|
|
159 | when storing and transfering), a rare encoding for JSON. It is |
|
|
160 | therefore most useful when you want to store data structures known |
|
|
161 | to contain binary data efficiently in files or databases, not when |
|
|
162 | talking to other JSON encoders/decoders. |
|
|
163 | |
|
|
164 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
|
|
165 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
|
|
166 | |
95 | $json = $json->utf8 ($enable) |
167 | $json = $json->utf8 ([$enable]) |
96 | If $enable is true, then the "encode" method will encode the JSON |
168 | If $enable is true (or missing), then the "encode" method will |
97 | string into UTF-8, as required by many protocols, while the "decode" |
169 | encode the JSON result into UTF-8, as required by many protocols, |
98 | method expects to be handled an UTF-8-encoded string. Please note |
170 | while the "decode" method expects to be handled an UTF-8-encoded |
99 | that UTF-8-encoded strings do not contain any characters outside the |
171 | string. Please note that UTF-8-encoded strings do not contain any |
100 | range 0..255, they are thus useful for bytewise/binary I/O. |
172 | characters outside the range 0..255, they are thus useful for |
|
|
173 | bytewise/binary I/O. In future versions, enabling this option might |
|
|
174 | enable autodetection of the UTF-16 and UTF-32 encoding families, as |
|
|
175 | described in RFC4627. |
101 | |
176 | |
102 | If $enable is false, then the "encode" method will return the JSON |
177 | If $enable is false, then the "encode" method will return the JSON |
103 | string as a (non-encoded) unicode string, while "decode" expects |
178 | 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 |
179 | 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. |
180 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
106 | |
181 | |
|
|
182 | Example, output UTF-16BE-encoded JSON: |
|
|
183 | |
|
|
184 | use Encode; |
|
|
185 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
|
|
186 | |
|
|
187 | Example, decode UTF-32LE-encoded JSON: |
|
|
188 | |
|
|
189 | use Encode; |
|
|
190 | $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); |
|
|
191 | |
107 | $json = $json->pretty ($enable) |
192 | $json = $json->pretty ([$enable]) |
108 | This enables (or disables) all of the "indent", "space_before" and |
193 | 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 |
194 | "space_after" (and in the future possibly more) flags in one call to |
110 | generate the most readable (or most compact) form possible. |
195 | generate the most readable (or most compact) form possible. |
|
|
196 | |
|
|
197 | Example, pretty-print some simple structure: |
111 | |
198 | |
112 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
199 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
113 | => |
200 | => |
114 | { |
201 | { |
115 | "a" : [ |
202 | "a" : [ |
116 | 1, |
203 | 1, |
117 | 2 |
204 | 2 |
118 | ] |
205 | ] |
119 | } |
206 | } |
120 | |
207 | |
121 | $json = $json->indent ($enable) |
208 | $json = $json->indent ([$enable]) |
122 | If $enable is true, then the "encode" method will use a multiline |
209 | If $enable is true (or missing), then the "encode" method will use a |
123 | format as output, putting every array member or object/hash |
210 | multiline format as output, putting every array member or |
124 | key-value pair into its own line, identing them properly. |
211 | object/hash key-value pair into its own line, identing them |
|
|
212 | properly. |
125 | |
213 | |
126 | If $enable is false, no newlines or indenting will be produced, and |
214 | If $enable is false, no newlines or indenting will be produced, and |
127 | the resulting JSON strings is guarenteed not to contain any |
215 | the resulting JSON text is guarenteed not to contain any "newlines". |
128 | "newlines". |
|
|
129 | |
216 | |
130 | This setting has no effect when decoding JSON strings. |
217 | This setting has no effect when decoding JSON texts. |
131 | |
218 | |
132 | $json = $json->space_before ($enable) |
219 | $json = $json->space_before ([$enable]) |
133 | If $enable is true, then the "encode" method will add an extra |
220 | If $enable is true (or missing), then the "encode" method will add |
134 | optional space before the ":" separating keys from values in JSON |
221 | an extra optional space before the ":" separating keys from values |
135 | objects. |
222 | in JSON objects. |
136 | |
223 | |
137 | If $enable is false, then the "encode" method will not add any extra |
224 | If $enable is false, then the "encode" method will not add any extra |
138 | space at those places. |
225 | space at those places. |
139 | |
226 | |
140 | This setting has no effect when decoding JSON strings. You will also |
227 | This setting has no effect when decoding JSON texts. You will also |
141 | most likely combine this setting with "space_after". |
228 | most likely combine this setting with "space_after". |
142 | |
229 | |
|
|
230 | Example, space_before enabled, space_after and indent disabled: |
|
|
231 | |
|
|
232 | {"key" :"value"} |
|
|
233 | |
143 | $json = $json->space_after ($enable) |
234 | $json = $json->space_after ([$enable]) |
144 | If $enable is true, then the "encode" method will add an extra |
235 | If $enable is true (or missing), then the "encode" method will add |
145 | optional space after the ":" separating keys from values in JSON |
236 | an extra optional space after the ":" separating keys from values in |
146 | objects and extra whitespace after the "," separating key-value |
237 | JSON objects and extra whitespace after the "," separating key-value |
147 | pairs and array members. |
238 | pairs and array members. |
148 | |
239 | |
149 | If $enable is false, then the "encode" method will not add any extra |
240 | If $enable is false, then the "encode" method will not add any extra |
150 | space at those places. |
241 | space at those places. |
151 | |
242 | |
152 | This setting has no effect when decoding JSON strings. |
243 | This setting has no effect when decoding JSON texts. |
153 | |
244 | |
|
|
245 | Example, space_before and indent disabled, space_after enabled: |
|
|
246 | |
|
|
247 | {"key": "value"} |
|
|
248 | |
154 | $json = $json->canonical ($enable) |
249 | $json = $json->canonical ([$enable]) |
155 | If $enable is true, then the "encode" method will output JSON |
250 | If $enable is true (or missing), then the "encode" method will |
156 | objects by sorting their keys. This is adding a comparatively high |
251 | output JSON objects by sorting their keys. This is adding a |
157 | overhead. |
252 | comparatively high overhead. |
158 | |
253 | |
159 | If $enable is false, then the "encode" method will output key-value |
254 | If $enable is false, then the "encode" method will output key-value |
160 | pairs in the order Perl stores them (which will likely change |
255 | pairs in the order Perl stores them (which will likely change |
161 | between runs of the same script). |
256 | between runs of the same script). |
162 | |
257 | |
163 | This option is useful if you want the same data structure to be |
258 | 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). |
259 | encoded as the same JSON text (given the same overall settings). If |
165 | If it is disabled, the same hash migh be encoded differently even if |
260 | 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 |
261 | contains the same data, as key-value pairs have no inherent ordering |
167 | in Perl. |
262 | in Perl. |
168 | |
263 | |
169 | This setting has no effect when decoding JSON strings. |
264 | This setting has no effect when decoding JSON texts. |
170 | |
265 | |
171 | $json = $json->allow_nonref ($enable) |
266 | $json = $json->allow_nonref ([$enable]) |
172 | If $enable is true, then the "encode" method can convert a |
267 | If $enable is true (or missing), then the "encode" method can |
173 | non-reference into its corresponding string, number or null JSON |
268 | convert a non-reference into its corresponding string, number or |
174 | value, which is an extension to RFC4627. Likewise, "decode" will |
269 | null JSON value, which is an extension to RFC4627. Likewise, |
175 | accept those JSON values instead of croaking. |
270 | "decode" will accept those JSON values instead of croaking. |
176 | |
271 | |
177 | If $enable is false, then the "encode" method will croak if it isn't |
272 | 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 |
273 | passed an arrayref or hashref, as JSON texts must either be an |
179 | object or array. Likewise, "decode" will croak if given something |
274 | object or array. Likewise, "decode" will croak if given something |
180 | that is not a JSON object or array. |
275 | that is not a JSON object or array. |
181 | |
276 | |
|
|
277 | Example, encode a Perl scalar as JSON value with enabled |
|
|
278 | "allow_nonref", resulting in an invalid JSON text: |
|
|
279 | |
|
|
280 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
|
|
281 | => "Hello, World!" |
|
|
282 | |
|
|
283 | $json = $json->shrink ([$enable]) |
|
|
284 | Perl usually over-allocates memory a bit when allocating space for |
|
|
285 | strings. This flag optionally resizes strings generated by either |
|
|
286 | "encode" or "decode" to their minimum size possible. This can save |
|
|
287 | memory when your JSON texts are either very very long or you have |
|
|
288 | many short strings. It will also try to downgrade any strings to |
|
|
289 | octet-form if possible: perl stores strings internally either in an |
|
|
290 | encoding called UTF-X or in octet-form. The latter cannot store |
|
|
291 | everything but uses less space in general (and some buggy Perl or C |
|
|
292 | code might even rely on that internal representation being used). |
|
|
293 | |
|
|
294 | The actual definition of what shrink does might change in future |
|
|
295 | versions, but it will always try to save space at the expense of |
|
|
296 | time. |
|
|
297 | |
|
|
298 | If $enable is true (or missing), the string returned by "encode" |
|
|
299 | will be shrunk-to-fit, while all strings generated by "decode" will |
|
|
300 | also be shrunk-to-fit. |
|
|
301 | |
|
|
302 | If $enable is false, then the normal perl allocation algorithms are |
|
|
303 | used. If you work with your data, then this is likely to be faster. |
|
|
304 | |
|
|
305 | In the future, this setting might control other things, such as |
|
|
306 | converting strings that look like integers or floats into integers |
|
|
307 | or floats internally (there is no difference on the Perl level), |
|
|
308 | saving space. |
|
|
309 | |
|
|
310 | $json = $json->max_depth ([$maximum_nesting_depth]) |
|
|
311 | Sets the maximum nesting level (default 512) accepted while encoding |
|
|
312 | or decoding. If the JSON text or Perl data structure has an equal or |
|
|
313 | higher nesting level then this limit, then the encoder and decoder |
|
|
314 | will stop and croak at that point. |
|
|
315 | |
|
|
316 | Nesting level is defined by number of hash- or arrayrefs that the |
|
|
317 | encoder needs to traverse to reach a given point or the number of |
|
|
318 | "{" or "[" characters without their matching closing parenthesis |
|
|
319 | crossed to reach a given character in a string. |
|
|
320 | |
|
|
321 | Setting the maximum depth to one disallows any nesting, so that |
|
|
322 | ensures that the object is only a single hash/object or array. |
|
|
323 | |
|
|
324 | The argument to "max_depth" will be rounded up to the next nearest |
|
|
325 | power of two. |
|
|
326 | |
|
|
327 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
|
|
328 | useful. |
|
|
329 | |
182 | $json_string = $json->encode ($perl_scalar) |
330 | $json_text = $json->encode ($perl_scalar) |
183 | Converts the given Perl data structure (a simple scalar or a |
331 | Converts the given Perl data structure (a simple scalar or a |
184 | reference to a hash or array) to its JSON representation. Simple |
332 | reference to a hash or array) to its JSON representation. Simple |
185 | scalars will be converted into JSON string or number sequences, |
333 | scalars will be converted into JSON string or number sequences, |
186 | while references to arrays become JSON arrays and references to |
334 | while references to arrays become JSON arrays and references to |
187 | hashes become JSON objects. Undefined Perl values (e.g. "undef") |
335 | hashes become JSON objects. Undefined Perl values (e.g. "undef") |
188 | become JSON "null" values. Neither "true" nor "false" values will be |
336 | become JSON "null" values. Neither "true" nor "false" values will be |
189 | generated. |
337 | generated. |
190 | |
338 | |
191 | $perl_scalar = $json->decode ($json_string) |
339 | $perl_scalar = $json->decode ($json_text) |
192 | The opposite of "encode": expects a JSON string and tries to parse |
340 | The opposite of "encode": expects a JSON text and tries to parse it, |
193 | it, returning the resulting simple scalar or reference. Croaks on |
341 | returning the resulting simple scalar or reference. Croaks on error. |
194 | error. |
|
|
195 | |
342 | |
196 | JSON numbers and strings become simple Perl scalars. JSON arrays |
343 | JSON numbers and strings become simple Perl scalars. JSON arrays |
197 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
344 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
198 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
345 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
|
|
346 | |
|
|
347 | ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
|
|
348 | This works like the "decode" method, but instead of raising an |
|
|
349 | exception when there is trailing garbage after the first JSON |
|
|
350 | object, it will silently stop parsing there and return the number of |
|
|
351 | characters consumed so far. |
|
|
352 | |
|
|
353 | This is useful if your JSON texts are not delimited by an outer |
|
|
354 | protocol (which is not the brightest thing to do in the first place) |
|
|
355 | and you need to know where the JSON text ends. |
|
|
356 | |
|
|
357 | JSON::XS->new->decode_prefix ("[1] the tail") |
|
|
358 | => ([], 3) |
|
|
359 | |
|
|
360 | MAPPING |
|
|
361 | This section describes how JSON::XS maps Perl values to JSON values and |
|
|
362 | vice versa. These mappings are designed to "do the right thing" in most |
|
|
363 | circumstances automatically, preserving round-tripping characteristics |
|
|
364 | (what you put in comes out as something equivalent). |
|
|
365 | |
|
|
366 | For the more enlightened: note that in the following descriptions, |
|
|
367 | lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* |
|
|
368 | refers to the abstract Perl language itself. |
|
|
369 | |
|
|
370 | JSON -> PERL |
|
|
371 | object |
|
|
372 | A JSON object becomes a reference to a hash in Perl. No ordering of |
|
|
373 | object keys is preserved (JSON does not preserver object key |
|
|
374 | ordering itself). |
|
|
375 | |
|
|
376 | array |
|
|
377 | A JSON array becomes a reference to an array in Perl. |
|
|
378 | |
|
|
379 | string |
|
|
380 | A JSON string becomes a string scalar in Perl - Unicode codepoints |
|
|
381 | in JSON are represented by the same codepoints in the Perl string, |
|
|
382 | so no manual decoding is necessary. |
|
|
383 | |
|
|
384 | number |
|
|
385 | A JSON number becomes either an integer or numeric (floating point) |
|
|
386 | scalar in perl, depending on its range and any fractional parts. On |
|
|
387 | the Perl level, there is no difference between those as Perl handles |
|
|
388 | all the conversion details, but an integer may take slightly less |
|
|
389 | memory and might represent more values exactly than (floating point) |
|
|
390 | numbers. |
|
|
391 | |
|
|
392 | true, false |
|
|
393 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
|
|
394 | respectively. They are overloaded to act almost exactly like the |
|
|
395 | numbers 1 and 0. You can check wether a scalar is a JSON boolean by |
|
|
396 | using the "JSON::XS::is_bool" function. |
|
|
397 | |
|
|
398 | null |
|
|
399 | A JSON null atom becomes "undef" in Perl. |
|
|
400 | |
|
|
401 | PERL -> JSON |
|
|
402 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
|
|
403 | truly typeless language, so we can only guess which JSON type is meant |
|
|
404 | by a Perl value. |
|
|
405 | |
|
|
406 | hash references |
|
|
407 | Perl hash references become JSON objects. As there is no inherent |
|
|
408 | ordering in hash keys (or JSON objects), they will usually be |
|
|
409 | encoded in a pseudo-random order that can change between runs of the |
|
|
410 | same program but stays generally the same within a single run of a |
|
|
411 | program. JSON::XS can optionally sort the hash keys (determined by |
|
|
412 | the *canonical* flag), so the same datastructure will serialise to |
|
|
413 | the same JSON text (given same settings and version of JSON::XS), |
|
|
414 | but this incurs a runtime overhead and is only rarely useful, e.g. |
|
|
415 | when you want to compare some JSON text against another for |
|
|
416 | equality. |
|
|
417 | |
|
|
418 | array references |
|
|
419 | Perl array references become JSON arrays. |
|
|
420 | |
|
|
421 | other references |
|
|
422 | Other unblessed references are generally not allowed and will cause |
|
|
423 | an exception to be thrown, except for references to the integers 0 |
|
|
424 | and 1, which get turned into "false" and "true" atoms in JSON. You |
|
|
425 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
|
|
426 | readability. |
|
|
427 | |
|
|
428 | to_json [\0,JSON::XS::true] # yields [false,true] |
|
|
429 | |
|
|
430 | JSON::XS::true, JSON::XS::false |
|
|
431 | These special values become JSON true and JSON false values, |
|
|
432 | respectively. You cna alos use "\1" and "\0" directly if you want. |
|
|
433 | |
|
|
434 | blessed objects |
|
|
435 | Blessed objects are not allowed. JSON::XS currently tries to encode |
|
|
436 | their underlying representation (hash- or arrayref), but this |
|
|
437 | behaviour might change in future versions. |
|
|
438 | |
|
|
439 | simple scalars |
|
|
440 | Simple Perl scalars (any scalar that is not a reference) are the |
|
|
441 | most difficult objects to encode: JSON::XS will encode undefined |
|
|
442 | scalars as JSON null value, scalars that have last been used in a |
|
|
443 | string context before encoding as JSON strings and anything else as |
|
|
444 | number value: |
|
|
445 | |
|
|
446 | # dump as number |
|
|
447 | to_json [2] # yields [2] |
|
|
448 | to_json [-3.0e17] # yields [-3e+17] |
|
|
449 | my $value = 5; to_json [$value] # yields [5] |
|
|
450 | |
|
|
451 | # used as string, so dump as string |
|
|
452 | print $value; |
|
|
453 | to_json [$value] # yields ["5"] |
|
|
454 | |
|
|
455 | # undef becomes null |
|
|
456 | to_json [undef] # yields [null] |
|
|
457 | |
|
|
458 | You can force the type to be a string by stringifying it: |
|
|
459 | |
|
|
460 | my $x = 3.1; # some variable containing a number |
|
|
461 | "$x"; # stringified |
|
|
462 | $x .= ""; # another, more awkward way to stringify |
|
|
463 | print $x; # perl does it for you, too, quite often |
|
|
464 | |
|
|
465 | You can force the type to be a number by numifying it: |
|
|
466 | |
|
|
467 | my $x = "3"; # some variable containing a string |
|
|
468 | $x += 0; # numify it, ensuring it will be dumped as a number |
|
|
469 | $x *= 1; # same thing, the choise is yours. |
|
|
470 | |
|
|
471 | You can not currently output JSON booleans or force the type in |
|
|
472 | other, less obscure, ways. Tell me if you need this capability. |
199 | |
473 | |
200 | COMPARISON |
474 | COMPARISON |
201 | As already mentioned, this module was created because none of the |
475 | As already mentioned, this module was created because none of the |
202 | existing JSON modules could be made to work correctly. First I will |
476 | existing JSON modules could be made to work correctly. First I will |
203 | describe the problems (or pleasures) I encountered with various existing |
477 | describe the problems (or pleasures) I encountered with various existing |
204 | JSON modules, followed by some benchmark values. JSON::XS was designed |
478 | JSON modules, followed by some benchmark values. JSON::XS was designed |
205 | not to suffer from any of these problems or limitations. |
479 | not to suffer from any of these problems or limitations. |
206 | |
480 | |
207 | JSON |
481 | JSON 1.07 |
208 | Slow (but very portable, as it is written in pure Perl). |
482 | Slow (but very portable, as it is written in pure Perl). |
209 | |
483 | |
210 | Undocumented/buggy Unicode handling (how JSON handles unicode values |
484 | Undocumented/buggy Unicode handling (how JSON handles unicode values |
211 | is undocumented. One can get far by feeding it unicode strings and |
485 | is undocumented. One can get far by feeding it unicode strings and |
212 | doing en-/decoding oneself, but unicode escapes are not working |
486 | doing en-/decoding oneself, but unicode escapes are not working |
… | |
… | |
214 | |
488 | |
215 | No roundtripping (strings get clobbered if they look like numbers, |
489 | 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 |
490 | e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that |
217 | will decode into the number 2. |
491 | will decode into the number 2. |
218 | |
492 | |
219 | JSON::PC |
493 | JSON::PC 0.01 |
220 | Very fast. |
494 | Very fast. |
221 | |
495 | |
222 | Undocumented/buggy Unicode handling. |
496 | Undocumented/buggy Unicode handling. |
223 | |
497 | |
224 | No roundtripping. |
498 | No roundtripping. |
225 | |
499 | |
226 | Has problems handling many Perl values (e.g. regex results and other |
500 | Has problems handling many Perl values (e.g. regex results and other |
227 | magic values will make it croak). |
501 | magic values will make it croak). |
228 | |
502 | |
229 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
503 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
230 | which is not a valid JSON string. |
504 | which is not a valid JSON text. |
231 | |
505 | |
232 | Unmaintained (maintainer unresponsive for many months, bugs are not |
506 | Unmaintained (maintainer unresponsive for many months, bugs are not |
233 | getting fixed). |
507 | getting fixed). |
234 | |
508 | |
235 | JSON::Syck |
509 | JSON::Syck 0.21 |
236 | Very buggy (often crashes). |
510 | Very buggy (often crashes). |
237 | |
511 | |
238 | Very inflexible (no human-readable format supported, format pretty |
512 | Very inflexible (no human-readable format supported, format pretty |
239 | much undocumented. I need at least a format for easy reading by |
513 | 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 |
514 | humans and a single-line compact format for use in a protocol, and |
241 | preferably a way to generate ASCII-only JSON strings). |
515 | preferably a way to generate ASCII-only JSON texts). |
242 | |
516 | |
243 | Completely broken (and confusingly documented) Unicode handling |
517 | Completely broken (and confusingly documented) Unicode handling |
244 | (unicode escapes are not working properly, you need to set |
518 | (unicode escapes are not working properly, you need to set |
245 | ImplicitUnicode to *different* values on en- and decoding to get |
519 | ImplicitUnicode to *different* values on en- and decoding to get |
246 | symmetric behaviour). |
520 | symmetric behaviour). |
… | |
… | |
259 | other using JSON. One bank might parse a given non-JSON request and |
533 | 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 |
534 | deduct money, while the other might reject the transaction with a |
261 | syntax error. While a good protocol will at least recover, that is |
535 | syntax error. While a good protocol will at least recover, that is |
262 | extra unnecessary work and the transaction will still not succeed). |
536 | extra unnecessary work and the transaction will still not succeed). |
263 | |
537 | |
264 | JSON::DWIW |
538 | JSON::DWIW 0.04 |
265 | Very fast. Very natural. Very nice. |
539 | Very fast. Very natural. Very nice. |
266 | |
540 | |
267 | Undocumented unicode handling (but the best of the pack. Unicode |
541 | Undocumented unicode handling (but the best of the pack. Unicode |
268 | escapes still don't get parsed properly). |
542 | escapes still don't get parsed properly). |
269 | |
543 | |
270 | Very inflexible. |
544 | Very inflexible. |
271 | |
545 | |
272 | No roundtripping. |
546 | No roundtripping. |
273 | |
547 | |
274 | Does not generate valid JSON (key strings are often unquoted, empty |
548 | Does not generate valid JSON texts (key strings are often unquoted, |
275 | keys result in nothing being output) |
549 | empty keys result in nothing being output) |
276 | |
550 | |
277 | Does not check input for validity. |
551 | Does not check input for validity. |
|
|
552 | |
|
|
553 | JSON and YAML |
|
|
554 | You often hear that JSON is a subset (or a close subset) of YAML. This |
|
|
555 | is, however, a mass hysteria and very far from the truth. In general, |
|
|
556 | there is no way to configure JSON::XS to output a data structure as |
|
|
557 | valid YAML. |
|
|
558 | |
|
|
559 | If you really must use JSON::XS to generate YAML, you should use this |
|
|
560 | algorithm (subject to change in future versions): |
|
|
561 | |
|
|
562 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
|
|
563 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
|
|
564 | |
|
|
565 | This will usually generate JSON texts that also parse as valid YAML. |
|
|
566 | Please note that YAML has hardcoded limits on (simple) object key |
|
|
567 | lengths that JSON doesn't have, so you should make sure that your hash |
|
|
568 | keys are noticably shorter than the 1024 characters YAML allows. |
|
|
569 | |
|
|
570 | There might be other incompatibilities that I am not aware of. In |
|
|
571 | general you should not try to generate YAML with a JSON generator or |
|
|
572 | vice versa, or try to parse JSON with a YAML parser or vice versa: |
|
|
573 | chances are high that you will run into severe interoperability |
|
|
574 | problems. |
278 | |
575 | |
279 | SPEED |
576 | SPEED |
280 | It seems that JSON::XS is surprisingly fast, as shown in the following |
577 | 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 |
578 | 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 |
579 | in the JSON::XS distribution, to make it easy to compare on your own |
283 | system. |
580 | system. |
284 | |
581 | |
285 | First is a comparison between various modules using a very simple JSON |
582 | First comes a comparison between various modules using a very short |
|
|
583 | single-line JSON string: |
|
|
584 | |
|
|
585 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
|
|
586 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
|
|
587 | |
286 | string, showing the number of encodes/decodes per second (JSON::XS is |
588 | It shows the number of encodes/decodes per second (JSON::XS uses the |
287 | the functional interface, while JSON::XS/2 is the OO interface with |
589 | functional interface, while JSON::XS/2 uses the OO interface with |
288 | pretty-printing and hashkey sorting enabled). |
590 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
|
|
591 | Higher is better: |
289 | |
592 | |
290 | module | encode | decode | |
593 | module | encode | decode | |
291 | -----------|------------|------------| |
594 | -----------|------------|------------| |
292 | JSON | 14006 | 6820 | |
595 | JSON | 7645.468 | 4208.613 | |
293 | JSON::DWIW | 200937 | 120386 | |
596 | JSON::DWIW | 40721.398 | 77101.176 | |
294 | JSON::PC | 85065 | 129366 | |
597 | JSON::PC | 65948.176 | 78251.940 | |
295 | JSON::Syck | 59898 | 44232 | |
598 | JSON::Syck | 22844.793 | 26479.192 | |
296 | JSON::XS | 1171478 | 342435 | |
599 | JSON::XS | 388361.481 | 199728.762 | |
297 | JSON::XS/2 | 730760 | 328714 | |
600 | JSON::XS/2 | 218453.333 | 192399.266 | |
|
|
601 | JSON::XS/3 | 338250.323 | 192399.266 | |
|
|
602 | Storable | 15779.925 | 14169.946 | |
298 | -----------+------------+------------+ |
603 | -----------+------------+------------+ |
299 | |
604 | |
300 | That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 |
605 | That is, JSON::XS is about five times faster than JSON::DWIW on |
|
|
606 | encoding, about three times faster on decoding, and over fourty times |
301 | times faster than JSON, even with pretty-printing and key sorting. |
607 | faster than JSON, even with pretty-printing and key sorting. It also |
|
|
608 | compares favourably to Storable for small amounts of data. |
302 | |
609 | |
303 | Using a longer test string (roughly 8KB, generated from Yahoo! Locals |
610 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
304 | search API (http://nanoref.com/yahooapis/mgPdGg): |
611 | search API (http://nanoref.com/yahooapis/mgPdGg): |
305 | |
612 | |
306 | module | encode | decode | |
613 | module | encode | decode | |
307 | -----------|------------|------------| |
614 | -----------|------------|------------| |
308 | JSON | 673 | 38 | |
615 | JSON | 254.685 | 37.665 | |
309 | JSON::DWIW | 5271 | 770 | |
616 | JSON::DWIW | 843.343 | 1049.731 | |
310 | JSON::PC | 9901 | 2491 | |
617 | JSON::PC | 3602.116 | 2307.352 | |
311 | JSON::Syck | 2360 | 786 | |
618 | JSON::Syck | 505.107 | 787.899 | |
312 | JSON::XS | 37398 | 3202 | |
619 | JSON::XS | 5747.196 | 3690.220 | |
313 | JSON::XS/2 | 13765 | 3153 | |
620 | JSON::XS/2 | 3968.121 | 3676.634 | |
|
|
621 | JSON::XS/3 | 6105.246 | 3662.508 | |
|
|
622 | Storable | 4417.337 | 5285.161 | |
314 | -----------+------------+------------+ |
623 | -----------+------------+------------+ |
315 | |
624 | |
316 | Again, JSON::XS leads by far in the encoding case, while still beating |
625 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
317 | every other module in the decoding case. |
626 | decodes faster). |
318 | |
627 | |
319 | Last example is an almost 8MB large hash with many large binary values |
628 | On large strings containing lots of high unicode characters, some |
320 | (PNG files), resulting in a lot of escaping: |
629 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
|
|
630 | result will be broken due to missing (or wrong) unicode handling. Others |
|
|
631 | refuse to decode or encode properly, so it was impossible to prepare a |
|
|
632 | fair comparison table for that case. |
|
|
633 | |
|
|
634 | SECURITY CONSIDERATIONS |
|
|
635 | When you are using JSON in a protocol, talking to untrusted potentially |
|
|
636 | hostile creatures requires relatively few measures. |
|
|
637 | |
|
|
638 | First of all, your JSON decoder should be secure, that is, should not |
|
|
639 | have any buffer overflows. Obviously, this module should ensure that and |
|
|
640 | I am trying hard on making that true, but you never know. |
|
|
641 | |
|
|
642 | Second, you need to avoid resource-starving attacks. That means you |
|
|
643 | should limit the size of JSON texts you accept, or make sure then when |
|
|
644 | your resources run out, thats just fine (e.g. by using a separate |
|
|
645 | process that can crash safely). The size of a JSON text in octets or |
|
|
646 | characters is usually a good indication of the size of the resources |
|
|
647 | required to decode it into a Perl structure. |
|
|
648 | |
|
|
649 | Third, JSON::XS recurses using the C stack when decoding objects and |
|
|
650 | arrays. The C stack is a limited resource: for instance, on my amd64 |
|
|
651 | machine with 8MB of stack size I can decode around 180k nested arrays |
|
|
652 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
|
|
653 | croak to free the temporary). If that is exceeded, the program crashes. |
|
|
654 | to be conservative, the default nesting limit is set to 512. If your |
|
|
655 | process has a smaller stack, you should adjust this setting accordingly |
|
|
656 | with the "max_depth" method. |
|
|
657 | |
|
|
658 | And last but least, something else could bomb you that I forgot to think |
|
|
659 | of. In that case, you get to keep the pieces. I am always open for |
|
|
660 | hints, though... |
|
|
661 | |
|
|
662 | If you are using JSON::XS to return packets to consumption by javascript |
|
|
663 | scripts in a browser you should have a look at |
|
|
664 | <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether |
|
|
665 | you are vulnerable to some common attack vectors (which really are |
|
|
666 | browser design bugs, but it is still you who will have to deal with it, |
|
|
667 | as major browser developers care only for features, not about doing |
|
|
668 | security right). |
321 | |
669 | |
322 | BUGS |
670 | BUGS |
323 | While the goal of this module is to be correct, that unfortunately does |
671 | 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 |
672 | 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 |
673 | still relatively early in its development. If you keep reporting bugs |
326 | will be fixed swiftly, though. |
674 | they will be fixed swiftly, though. |
327 | |
675 | |
328 | AUTHOR |
676 | AUTHOR |
329 | Marc Lehmann <schmorp@schmorp.de> |
677 | Marc Lehmann <schmorp@schmorp.de> |
330 | http://home.schmorp.de/ |
678 | http://home.schmorp.de/ |
331 | |
679 | |