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; |
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6 | |
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7 | # exported functions, croak on error |
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8 | |
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9 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
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10 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
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11 | |
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12 | # oo-interface |
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13 | |
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14 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
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15 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
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16 | $perl_scalar = $coder->decode ($unicode_json_text); |
6 | |
17 | |
7 | DESCRIPTION |
18 | DESCRIPTION |
8 | This module converts Perl data structures to JSON and vice versa. Its |
19 | 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*. |
20 | 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. |
21 | To reach the latter goal it was written in C. |
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15 | cases their maintainers are unresponsive, gone missing, or not listening |
26 | cases their maintainers are unresponsive, gone missing, or not listening |
16 | to bug reports for other reasons. |
27 | to bug reports for other reasons. |
17 | |
28 | |
18 | See COMPARISON, below, for a comparison to some other JSON modules. |
29 | See COMPARISON, below, for a comparison to some other JSON modules. |
19 | |
30 | |
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31 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
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32 | vice versa. |
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33 | |
20 | FEATURES |
34 | FEATURES |
21 | * correct handling of unicode issues |
35 | * correct handling of unicode issues |
22 | This module knows how to handle Unicode, and even documents how it |
36 | This module knows how to handle Unicode, and even documents how and |
23 | does so. |
37 | when it does so. |
24 | |
38 | |
25 | * round-trip integrity |
39 | * round-trip integrity |
26 | When you serialise a perl data structure using only datatypes |
40 | When you serialise a perl data structure using only datatypes |
27 | supported by JSON, the deserialised data structure is identical on |
41 | 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"). |
42 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"). |
29 | |
43 | |
30 | * strict checking of JSON correctness |
44 | * strict checking of JSON correctness |
31 | There is no guessing, no generating of illegal JSON strings by |
45 | There is no guessing, no generating of illegal JSON strings by |
32 | default, and only JSON is accepted as input (the latter is a |
46 | default, and only JSON is accepted as input by default (the latter |
33 | security feature). |
47 | is a security feature). |
34 | |
48 | |
35 | * fast |
49 | * fast |
36 | compared to other JSON modules, this module compares favourably. |
50 | Compared to other JSON modules, this module compares favourably in |
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51 | terms of speed, too. |
37 | |
52 | |
38 | * simple to use |
53 | * simple to use |
39 | This module has both a simple functional interface as well as an OO |
54 | This module has both a simple functional interface as well as an OO |
40 | interface. |
55 | interface. |
41 | |
56 | |
42 | * reasonably versatile output formats |
57 | * reasonably versatile output formats |
43 | You can choose between the most compact format possible, a |
58 | You can choose between the most compact guarenteed single-line |
44 | pure-ascii format, or a pretty-printed format. Or you can combine |
59 | format possible (nice for simple line-based protocols), a pure-ascii |
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60 | format (for when your transport is not 8-bit clean), or a |
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61 | pretty-printed format (for when you want to read that stuff). Or you |
45 | those features in whatever way you like. |
62 | can combine those features in whatever way you like. |
46 | |
63 | |
47 | FUNCTIONAL INTERFACE |
64 | FUNCTIONAL INTERFACE |
48 | The following convinience methods are provided by this module. They are |
65 | The following convinience methods are provided by this module. They are |
49 | exported by default: |
66 | exported by default: |
50 | |
67 | |
51 | $json_string = to_json $perl_scalar |
68 | $json_string = to_json $perl_scalar |
52 | Converts the given Perl data structure (a simple scalar or a |
69 | Converts the given Perl data structure (a simple scalar or a |
53 | reference to a hash or array) to a UTF-8 encoded, binary string |
70 | reference to a hash or array) to a UTF-8 encoded, binary string |
54 | (that is, the string contains octets only). Croaks on error. |
71 | (that is, the string contains octets only). Croaks on error. |
55 | |
72 | |
56 | This function call is functionally identical to "JSON::XS->new->utf8 |
73 | This function call is functionally identical to |
57 | (1)->encode ($perl_scalar)". |
74 | "JSON::XS->new->utf8->encode ($perl_scalar)". |
58 | |
75 | |
59 | $perl_scalar = from_json $json_string |
76 | $perl_scalar = from_json $json_string |
60 | The opposite of "to_json": expects an UTF-8 (binary) string and |
77 | The opposite of "to_json": expects an UTF-8 (binary) string and |
61 | tries to parse that as an UTF-8 encoded JSON string, returning the |
78 | tries to parse that as an UTF-8 encoded JSON string, returning the |
62 | resulting simple scalar or reference. Croaks on error. |
79 | resulting simple scalar or reference. Croaks on error. |
63 | |
80 | |
64 | This function call is functionally identical to "JSON::XS->new->utf8 |
81 | This function call is functionally identical to |
65 | (1)->decode ($json_string)". |
82 | "JSON::XS->new->utf8->decode ($json_string)". |
66 | |
83 | |
67 | OBJECT-ORIENTED INTERFACE |
84 | OBJECT-ORIENTED INTERFACE |
68 | The object oriented interface lets you configure your own encoding or |
85 | The object oriented interface lets you configure your own encoding or |
69 | decoding style, within the limits of supported formats. |
86 | decoding style, within the limits of supported formats. |
70 | |
87 | |
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77 | calls can be chained: |
94 | calls can be chained: |
78 | |
95 | |
79 | my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) |
96 | my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) |
80 | => {"a": [1, 2]} |
97 | => {"a": [1, 2]} |
81 | |
98 | |
82 | $json = $json->ascii ($enable) |
99 | $json = $json->ascii ([$enable]) |
83 | If $enable is true, then the "encode" method will not generate |
100 | If $enable is true (or missing), then the "encode" method will not |
84 | characters outside the code range 0..127. Any unicode characters |
101 | generate characters outside the code range 0..127. Any unicode |
85 | outside that range will be escaped using either a single \uXXXX (BMP |
102 | characters outside that range will be escaped using either a single |
86 | characters) or a double \uHHHH\uLLLLL escape sequence, as per |
103 | \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, |
87 | RFC4627. |
104 | as per RFC4627. |
88 | |
105 | |
89 | If $enable is false, then the "encode" method will not escape |
106 | If $enable is false, then the "encode" method will not escape |
90 | Unicode characters unless necessary. |
107 | Unicode characters unless necessary. |
91 | |
108 | |
92 | JSON::XS->new->ascii (1)->encode (chr 0x10401) |
109 | JSON::XS->new->ascii (1)->encode (chr 0x10401) |
93 | => \ud801\udc01 |
110 | => \ud801\udc01 |
94 | |
111 | |
95 | $json = $json->utf8 ($enable) |
112 | $json = $json->utf8 ([$enable]) |
96 | If $enable is true, then the "encode" method will encode the JSON |
113 | If $enable is true (or missing), then the "encode" method will |
97 | string into UTF-8, as required by many protocols, while the "decode" |
114 | encode the JSON string into UTF-8, as required by many protocols, |
98 | method expects to be handled an UTF-8-encoded string. Please note |
115 | 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 |
116 | 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. |
117 | characters outside the range 0..255, they are thus useful for |
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118 | bytewise/binary I/O. |
101 | |
119 | |
102 | If $enable is false, then the "encode" method will return the JSON |
120 | If $enable is false, then the "encode" method will return the JSON |
103 | string as a (non-encoded) unicode string, while "decode" expects |
121 | 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 |
122 | 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. |
123 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
106 | |
124 | |
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125 | Example, output UTF-16-encoded JSON: |
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126 | |
107 | $json = $json->pretty ($enable) |
127 | $json = $json->pretty ([$enable]) |
108 | This enables (or disables) all of the "indent", "space_before" and |
128 | 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 |
129 | "space_after" (and in the future possibly more) flags in one call to |
110 | generate the most readable (or most compact) form possible. |
130 | generate the most readable (or most compact) form possible. |
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131 | |
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132 | Example, pretty-print some simple structure: |
111 | |
133 | |
112 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
134 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
113 | => |
135 | => |
114 | { |
136 | { |
115 | "a" : [ |
137 | "a" : [ |
116 | 1, |
138 | 1, |
117 | 2 |
139 | 2 |
118 | ] |
140 | ] |
119 | } |
141 | } |
120 | |
142 | |
121 | $json = $json->indent ($enable) |
143 | $json = $json->indent ([$enable]) |
122 | If $enable is true, then the "encode" method will use a multiline |
144 | If $enable is true (or missing), then the "encode" method will use a |
123 | format as output, putting every array member or object/hash |
145 | multiline format as output, putting every array member or |
124 | key-value pair into its own line, identing them properly. |
146 | object/hash key-value pair into its own line, identing them |
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147 | properly. |
125 | |
148 | |
126 | If $enable is false, no newlines or indenting will be produced, and |
149 | If $enable is false, no newlines or indenting will be produced, and |
127 | the resulting JSON strings is guarenteed not to contain any |
150 | the resulting JSON strings is guarenteed not to contain any |
128 | "newlines". |
151 | "newlines". |
129 | |
152 | |
130 | This setting has no effect when decoding JSON strings. |
153 | This setting has no effect when decoding JSON strings. |
131 | |
154 | |
132 | $json = $json->space_before ($enable) |
155 | $json = $json->space_before ([$enable]) |
133 | If $enable is true, then the "encode" method will add an extra |
156 | If $enable is true (or missing), then the "encode" method will add |
134 | optional space before the ":" separating keys from values in JSON |
157 | an extra optional space before the ":" separating keys from values |
135 | objects. |
158 | in JSON objects. |
136 | |
159 | |
137 | If $enable is false, then the "encode" method will not add any extra |
160 | If $enable is false, then the "encode" method will not add any extra |
138 | space at those places. |
161 | space at those places. |
139 | |
162 | |
140 | This setting has no effect when decoding JSON strings. You will also |
163 | This setting has no effect when decoding JSON strings. You will also |
141 | most likely combine this setting with "space_after". |
164 | most likely combine this setting with "space_after". |
142 | |
165 | |
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166 | Example, space_before enabled, space_after and indent disabled: |
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167 | |
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168 | {"key" :"value"} |
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169 | |
143 | $json = $json->space_after ($enable) |
170 | $json = $json->space_after ([$enable]) |
144 | If $enable is true, then the "encode" method will add an extra |
171 | If $enable is true (or missing), then the "encode" method will add |
145 | optional space after the ":" separating keys from values in JSON |
172 | an extra optional space after the ":" separating keys from values in |
146 | objects and extra whitespace after the "," separating key-value |
173 | JSON objects and extra whitespace after the "," separating key-value |
147 | pairs and array members. |
174 | pairs and array members. |
148 | |
175 | |
149 | If $enable is false, then the "encode" method will not add any extra |
176 | If $enable is false, then the "encode" method will not add any extra |
150 | space at those places. |
177 | space at those places. |
151 | |
178 | |
152 | This setting has no effect when decoding JSON strings. |
179 | This setting has no effect when decoding JSON strings. |
153 | |
180 | |
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181 | Example, space_before and indent disabled, space_after enabled: |
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182 | |
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183 | {"key": "value"} |
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184 | |
154 | $json = $json->canonical ($enable) |
185 | $json = $json->canonical ([$enable]) |
155 | If $enable is true, then the "encode" method will output JSON |
186 | If $enable is true (or missing), then the "encode" method will |
156 | objects by sorting their keys. This is adding a comparatively high |
187 | output JSON objects by sorting their keys. This is adding a |
157 | overhead. |
188 | comparatively high overhead. |
158 | |
189 | |
159 | If $enable is false, then the "encode" method will output key-value |
190 | If $enable is false, then the "encode" method will output key-value |
160 | pairs in the order Perl stores them (which will likely change |
191 | pairs in the order Perl stores them (which will likely change |
161 | between runs of the same script). |
192 | between runs of the same script). |
162 | |
193 | |
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166 | contains the same data, as key-value pairs have no inherent ordering |
197 | contains the same data, as key-value pairs have no inherent ordering |
167 | in Perl. |
198 | in Perl. |
168 | |
199 | |
169 | This setting has no effect when decoding JSON strings. |
200 | This setting has no effect when decoding JSON strings. |
170 | |
201 | |
171 | $json = $json->allow_nonref ($enable) |
202 | $json = $json->allow_nonref ([$enable]) |
172 | If $enable is true, then the "encode" method can convert a |
203 | If $enable is true (or missing), then the "encode" method can |
173 | non-reference into its corresponding string, number or null JSON |
204 | convert a non-reference into its corresponding string, number or |
174 | value, which is an extension to RFC4627. Likewise, "decode" will |
205 | null JSON value, which is an extension to RFC4627. Likewise, |
175 | accept those JSON values instead of croaking. |
206 | "decode" will accept those JSON values instead of croaking. |
176 | |
207 | |
177 | If $enable is false, then the "encode" method will croak if it isn't |
208 | 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 |
209 | passed an arrayref or hashref, as JSON strings must either be an |
179 | object or array. Likewise, "decode" will croak if given something |
210 | object or array. Likewise, "decode" will croak if given something |
180 | that is not a JSON object or array. |
211 | that is not a JSON object or array. |
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212 | |
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213 | Example, encode a Perl scalar as JSON value with enabled |
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214 | "allow_nonref", resulting in an invalid JSON text: |
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215 | |
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216 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
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217 | => "Hello, World!" |
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218 | |
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219 | $json = $json->shrink ([$enable]) |
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220 | Perl usually over-allocates memory a bit when allocating space for |
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221 | strings. This flag optionally resizes strings generated by either |
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222 | "encode" or "decode" to their minimum size possible. This can save |
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223 | memory when your JSON strings are either very very long or you have |
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224 | many short strings. It will also try to downgrade any strings to |
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225 | octet-form if possible: perl stores strings internally either in an |
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226 | encoding called UTF-X or in octet-form. The latter cannot store |
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227 | everything but uses less space in general. |
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228 | |
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229 | If $enable is true (or missing), the string returned by "encode" |
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230 | will be shrunk-to-fit, while all strings generated by "decode" will |
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231 | also be shrunk-to-fit. |
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232 | |
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233 | If $enable is false, then the normal perl allocation algorithms are |
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234 | used. If you work with your data, then this is likely to be faster. |
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235 | |
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236 | In the future, this setting might control other things, such as |
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237 | converting strings that look like integers or floats into integers |
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238 | or floats internally (there is no difference on the Perl level), |
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239 | saving space. |
181 | |
240 | |
182 | $json_string = $json->encode ($perl_scalar) |
241 | $json_string = $json->encode ($perl_scalar) |
183 | Converts the given Perl data structure (a simple scalar or a |
242 | Converts the given Perl data structure (a simple scalar or a |
184 | reference to a hash or array) to its JSON representation. Simple |
243 | reference to a hash or array) to its JSON representation. Simple |
185 | scalars will be converted into JSON string or number sequences, |
244 | scalars will be converted into JSON string or number sequences, |
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194 | error. |
253 | error. |
195 | |
254 | |
196 | JSON numbers and strings become simple Perl scalars. JSON arrays |
255 | JSON numbers and strings become simple Perl scalars. JSON arrays |
197 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
256 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
198 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
257 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
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258 | |
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259 | MAPPING |
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260 | This section describes how JSON::XS maps Perl values to JSON values and |
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261 | vice versa. These mappings are designed to "do the right thing" in most |
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262 | circumstances automatically, preserving round-tripping characteristics |
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263 | (what you put in comes out as something equivalent). |
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264 | |
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265 | For the more enlightened: note that in the following descriptions, |
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266 | lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* |
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267 | refers to the abstract Perl language itself. |
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268 | |
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269 | JSON -> PERL |
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270 | object |
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271 | A JSON object becomes a reference to a hash in Perl. No ordering of |
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272 | object keys is preserved. |
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273 | |
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274 | array |
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275 | A JSON array becomes a reference to an array in Perl. |
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276 | |
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277 | string |
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278 | A JSON string becomes a string scalar in Perl - Unicode codepoints |
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279 | in JSON are represented by the same codepoints in the Perl string, |
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280 | so no manual decoding is necessary. |
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281 | |
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282 | number |
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283 | A JSON number becomes either an integer or numeric (floating point) |
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284 | scalar in perl, depending on its range and any fractional parts. On |
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285 | the Perl level, there is no difference between those as Perl handles |
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286 | all the conversion details, but an integer may take slightly less |
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287 | memory and might represent more values exactly than (floating point) |
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288 | numbers. |
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289 | |
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290 | true, false |
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291 | These JSON atoms become 0, 1, respectively. Information is lost in |
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292 | this process. Future versions might represent those values |
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293 | differently, but they will be guarenteed to act like these integers |
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294 | would normally in Perl. |
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295 | |
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296 | null |
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297 | A JSON null atom becomes "undef" in Perl. |
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298 | |
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299 | PERL -> JSON |
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300 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
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301 | truly typeless language, so we can only guess which JSON type is meant |
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302 | by a Perl value. |
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303 | |
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304 | hash references |
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305 | Perl hash references become JSON objects. As there is no inherent |
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306 | ordering in hash keys, they will usually be encoded in a |
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307 | pseudo-random order that can change between runs of the same program |
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308 | but stays generally the same within the single run of a program. |
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309 | JSON::XS can optionally sort the hash keys (determined by the |
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310 | *canonical* flag), so the same datastructure will serialise to the |
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311 | same JSON text (given same settings and version of JSON::XS), but |
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312 | this incurs a runtime overhead. |
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313 | |
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314 | array references |
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315 | Perl array references become JSON arrays. |
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316 | |
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317 | blessed objects |
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318 | Blessed objects are not allowed. JSON::XS currently tries to encode |
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319 | their underlying representation (hash- or arrayref), but this |
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320 | behaviour might change in future versions. |
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321 | |
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322 | simple scalars |
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323 | Simple Perl scalars (any scalar that is not a reference) are the |
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324 | most difficult objects to encode: JSON::XS will encode undefined |
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325 | scalars as JSON null value, scalars that have last been used in a |
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326 | string context before encoding as JSON strings and anything else as |
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327 | number value: |
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328 | |
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329 | # dump as number |
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330 | to_json [2] # yields [2] |
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331 | to_json [-3.0e17] # yields [-3e+17] |
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332 | my $value = 5; to_json [$value] # yields [5] |
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333 | |
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334 | # used as string, so dump as string |
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335 | print $value; |
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336 | to_json [$value] # yields ["5"] |
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337 | |
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338 | # undef becomes null |
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339 | to_json [undef] # yields [null] |
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340 | |
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341 | You can force the type to be a string by stringifying it: |
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342 | |
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343 | my $x = 3.1; # some variable containing a number |
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344 | "$x"; # stringified |
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345 | $x .= ""; # another, more awkward way to stringify |
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346 | print $x; # perl does it for you, too, quite often |
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347 | |
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348 | You can force the type to be a number by numifying it: |
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349 | |
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350 | my $x = "3"; # some variable containing a string |
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351 | $x += 0; # numify it, ensuring it will be dumped as a number |
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352 | $x *= 1; # same thing, the choise is yours. |
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353 | |
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354 | You can not currently output JSON booleans or force the type in |
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355 | other, less obscure, ways. Tell me if you need this capability. |
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356 | |
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357 | circular data structures |
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358 | Those will be encoded until memory or stackspace runs out. |
199 | |
359 | |
200 | COMPARISON |
360 | COMPARISON |
201 | As already mentioned, this module was created because none of the |
361 | As already mentioned, this module was created because none of the |
202 | existing JSON modules could be made to work correctly. First I will |
362 | existing JSON modules could be made to work correctly. First I will |
203 | describe the problems (or pleasures) I encountered with various existing |
363 | describe the problems (or pleasures) I encountered with various existing |
… | |
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314 | -----------+------------+------------+ |
474 | -----------+------------+------------+ |
315 | |
475 | |
316 | Again, JSON::XS leads by far in the encoding case, while still beating |
476 | Again, JSON::XS leads by far in the encoding case, while still beating |
317 | every other module in the decoding case. |
477 | every other module in the decoding case. |
318 | |
478 | |
319 | Last example is an almost 8MB large hash with many large binary values |
479 | RESOURCE LIMITS |
320 | (PNG files), resulting in a lot of escaping: |
480 | JSON::XS does not impose any limits on the size of JSON texts or Perl |
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481 | values they represent - if your machine can handle it, JSON::XS will |
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482 | encode or decode it. Future versions might optionally impose structure |
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483 | depth and memory use resource limits. |
321 | |
484 | |
322 | BUGS |
485 | BUGS |
323 | While the goal of this module is to be correct, that unfortunately does |
486 | 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 |
487 | 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 |
488 | still very young and not well-tested. If you keep reporting bugs they |