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 | |
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4 | JSON::XS - 正しくて高速な JSON |
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5 | シリアライザ/デシリアライザ |
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6 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
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7 | |
4 | SYNOPSIS |
8 | SYNOPSIS |
5 | use JSON::XS; |
9 | use JSON::XS; |
6 | |
10 | |
7 | # exported functions, they croak on error |
11 | # exported functions, they croak on error |
8 | # and expect/generate UTF-8 |
12 | # and expect/generate UTF-8 |
9 | |
13 | |
10 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
14 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
11 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
15 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
12 | |
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13 | # objToJson and jsonToObj aliases to to_json and from_json |
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14 | # are exported for compatibility to the JSON module, |
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15 | # but should not be used in new code. |
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16 | |
16 | |
17 | # OO-interface |
17 | # OO-interface |
18 | |
18 | |
19 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
19 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
20 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
20 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
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35 | |
35 | |
36 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
36 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
37 | vice versa. |
37 | vice versa. |
38 | |
38 | |
39 | FEATURES |
39 | FEATURES |
40 | * correct unicode handling |
40 | * correct Unicode handling |
41 | This module knows how to handle Unicode, and even documents how and |
41 | This module knows how to handle Unicode, and even documents how and |
42 | when it does so. |
42 | when it does so. |
43 | |
43 | |
44 | * round-trip integrity |
44 | * round-trip integrity |
45 | When you serialise a perl data structure using only datatypes |
45 | When you serialise a perl data structure using only datatypes |
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59 | * simple to use |
59 | * simple to use |
60 | 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 |
61 | interface. |
61 | interface. |
62 | |
62 | |
63 | * reasonably versatile output formats |
63 | * reasonably versatile output formats |
64 | You can choose between the most compact guarenteed single-line |
64 | You can choose between the most compact guaranteed single-line |
65 | format possible (nice for simple line-based protocols), a pure-ascii |
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 |
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 |
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 |
68 | want to read that stuff). Or you can combine those features in |
69 | whatever way you like. |
69 | whatever way you like. |
70 | |
70 | |
71 | FUNCTIONAL INTERFACE |
71 | FUNCTIONAL INTERFACE |
72 | The following convinience methods are provided by this module. They are |
72 | The following convenience methods are provided by this module. They are |
73 | exported by default: |
73 | exported by default: |
74 | |
74 | |
75 | $json_text = to_json $perl_scalar |
75 | $json_text = to_json $perl_scalar |
76 | Converts the given Perl data structure (a simple scalar or a |
76 | Converts the given Perl data structure to a UTF-8 encoded, binary |
77 | reference to a hash or array) to a UTF-8 encoded, binary string |
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78 | (that is, the string contains octets only). Croaks on error. |
77 | string (that is, the string contains octets only). Croaks on error. |
79 | |
78 | |
80 | This function call is functionally identical to: |
79 | This function call is functionally identical to: |
81 | |
80 | |
82 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
81 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
83 | |
82 | |
84 | except being faster. |
83 | except being faster. |
85 | |
84 | |
86 | $perl_scalar = from_json $json_text |
85 | $perl_scalar = from_json $json_text |
87 | The opposite of "to_json": expects an UTF-8 (binary) string and |
86 | The opposite of "to_json": expects an UTF-8 (binary) string and |
88 | tries to parse that as an UTF-8 encoded JSON text, returning the |
87 | tries to parse that as an UTF-8 encoded JSON text, returning the |
89 | resulting simple scalar or reference. Croaks on error. |
88 | resulting reference. Croaks on error. |
90 | |
89 | |
91 | This function call is functionally identical to: |
90 | This function call is functionally identical to: |
92 | |
91 | |
93 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
92 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
94 | |
93 | |
95 | except being faster. |
94 | except being faster. |
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95 | |
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96 | $is_boolean = JSON::XS::is_bool $scalar |
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97 | Returns true if the passed scalar represents either JSON::XS::true |
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98 | or JSON::XS::false, two constants that act like 1 and 0, |
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99 | respectively and are used to represent JSON "true" and "false" |
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100 | values in Perl. |
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101 | |
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102 | See MAPPING, below, for more information on how JSON values are |
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103 | mapped to Perl. |
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104 | |
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105 | A FEW NOTES ON UNICODE AND PERL |
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106 | Since this often leads to confusion, here are a few very clear words on |
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107 | how Unicode works in Perl, modulo bugs. |
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108 | |
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109 | 1. Perl strings can store characters with ordinal values > 255. |
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110 | This enables you to store Unicode characters as single characters in |
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111 | a Perl string - very natural. |
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112 | |
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113 | 2. Perl does *not* associate an encoding with your strings. |
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114 | Unless you force it to, e.g. when matching it against a regex, or |
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115 | printing the scalar to a file, in which case Perl either interprets |
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116 | your string as locale-encoded text, octets/binary, or as Unicode, |
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117 | depending on various settings. In no case is an encoding stored |
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118 | together with your data, it is *use* that decides encoding, not any |
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119 | magical metadata. |
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120 | |
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121 | 3. The internal utf-8 flag has no meaning with regards to the encoding |
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122 | of your string. |
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123 | Just ignore that flag unless you debug a Perl bug, a module written |
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124 | in XS or want to dive into the internals of perl. Otherwise it will |
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125 | only confuse you, as, despite the name, it says nothing about how |
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126 | your string is encoded. You can have Unicode strings with that flag |
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127 | set, with that flag clear, and you can have binary data with that |
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128 | flag set and that flag clear. Other possibilities exist, too. |
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129 | |
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130 | If you didn't know about that flag, just the better, pretend it |
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131 | doesn't exist. |
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132 | |
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133 | 4. A "Unicode String" is simply a string where each character can be |
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134 | validly interpreted as a Unicode codepoint. |
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135 | If you have UTF-8 encoded data, it is no longer a Unicode string, |
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136 | but a Unicode string encoded in UTF-8, giving you a binary string. |
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137 | |
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138 | 5. A string containing "high" (> 255) character values is *not* a UTF-8 |
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139 | string. |
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140 | It's a fact. Learn to live with it. |
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141 | |
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142 | I hope this helps :) |
96 | |
143 | |
97 | OBJECT-ORIENTED INTERFACE |
144 | OBJECT-ORIENTED INTERFACE |
98 | The object oriented interface lets you configure your own encoding or |
145 | The object oriented interface lets you configure your own encoding or |
99 | decoding style, within the limits of supported formats. |
146 | decoding style, within the limits of supported formats. |
100 | |
147 | |
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110 | => {"a": [1, 2]} |
157 | => {"a": [1, 2]} |
111 | |
158 | |
112 | $json = $json->ascii ([$enable]) |
159 | $json = $json->ascii ([$enable]) |
113 | If $enable is true (or missing), then the "encode" method will not |
160 | If $enable is true (or missing), then the "encode" method will not |
114 | generate characters outside the code range 0..127 (which is ASCII). |
161 | generate characters outside the code range 0..127 (which is ASCII). |
115 | Any unicode characters outside that range will be escaped using |
162 | Any Unicode characters outside that range will be escaped using |
116 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
163 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
117 | escape sequence, as per RFC4627. |
164 | escape sequence, as per RFC4627. The resulting encoded JSON text can |
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165 | be treated as a native Unicode string, an ascii-encoded, |
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166 | latin1-encoded or UTF-8 encoded string, or any other superset of |
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167 | ASCII. |
118 | |
168 | |
119 | If $enable is false, then the "encode" method will not escape |
169 | If $enable is false, then the "encode" method will not escape |
120 | Unicode characters unless required by the JSON syntax. This results |
170 | Unicode characters unless required by the JSON syntax or other |
121 | in a faster and more compact format. |
171 | flags. This results in a faster and more compact format. |
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172 | |
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173 | The main use for this flag is to produce JSON texts that can be |
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174 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
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175 | contain any 8 bit characters. |
122 | |
176 | |
123 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
177 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
124 | => ["\ud801\udc01"] |
178 | => ["\ud801\udc01"] |
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179 | |
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180 | $json = $json->latin1 ([$enable]) |
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181 | If $enable is true (or missing), then the "encode" method will |
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182 | encode the resulting JSON text as latin1 (or iso-8859-1), escaping |
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183 | any characters outside the code range 0..255. The resulting string |
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184 | can be treated as a latin1-encoded JSON text or a native Unicode |
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185 | string. The "decode" method will not be affected in any way by this |
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186 | flag, as "decode" by default expects Unicode, which is a strict |
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187 | superset of latin1. |
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188 | |
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189 | If $enable is false, then the "encode" method will not escape |
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190 | Unicode characters unless required by the JSON syntax or other |
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191 | flags. |
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192 | |
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193 | The main use for this flag is efficiently encoding binary data as |
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194 | JSON text, as most octets will not be escaped, resulting in a |
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195 | smaller encoded size. The disadvantage is that the resulting JSON |
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196 | text is encoded in latin1 (and must correctly be treated as such |
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197 | when storing and transferring), a rare encoding for JSON. It is |
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198 | therefore most useful when you want to store data structures known |
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199 | to contain binary data efficiently in files or databases, not when |
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200 | talking to other JSON encoders/decoders. |
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201 | |
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202 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
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203 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
125 | |
204 | |
126 | $json = $json->utf8 ([$enable]) |
205 | $json = $json->utf8 ([$enable]) |
127 | If $enable is true (or missing), then the "encode" method will |
206 | If $enable is true (or missing), then the "encode" method will |
128 | encode the JSON result into UTF-8, as required by many protocols, |
207 | encode the JSON result into UTF-8, as required by many protocols, |
129 | while the "decode" method expects to be handled an UTF-8-encoded |
208 | while the "decode" method expects to be handled an UTF-8-encoded |
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132 | bytewise/binary I/O. In future versions, enabling this option might |
211 | bytewise/binary I/O. In future versions, enabling this option might |
133 | enable autodetection of the UTF-16 and UTF-32 encoding families, as |
212 | enable autodetection of the UTF-16 and UTF-32 encoding families, as |
134 | described in RFC4627. |
213 | described in RFC4627. |
135 | |
214 | |
136 | If $enable is false, then the "encode" method will return the JSON |
215 | If $enable is false, then the "encode" method will return the JSON |
137 | string as a (non-encoded) unicode string, while "decode" expects |
216 | string as a (non-encoded) Unicode string, while "decode" expects |
138 | thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or |
217 | thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or |
139 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
218 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
140 | |
219 | |
141 | Example, output UTF-16BE-encoded JSON: |
220 | Example, output UTF-16BE-encoded JSON: |
142 | |
221 | |
143 | use Encode; |
222 | use Encode; |
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165 | } |
244 | } |
166 | |
245 | |
167 | $json = $json->indent ([$enable]) |
246 | $json = $json->indent ([$enable]) |
168 | If $enable is true (or missing), then the "encode" method will use a |
247 | If $enable is true (or missing), then the "encode" method will use a |
169 | multiline format as output, putting every array member or |
248 | multiline format as output, putting every array member or |
170 | object/hash key-value pair into its own line, identing them |
249 | object/hash key-value pair into its own line, indenting them |
171 | properly. |
250 | properly. |
172 | |
251 | |
173 | If $enable is false, no newlines or indenting will be produced, and |
252 | If $enable is false, no newlines or indenting will be produced, and |
174 | the resulting JSON text is guarenteed not to contain any "newlines". |
253 | the resulting JSON text is guaranteed not to contain any "newlines". |
175 | |
254 | |
176 | This setting has no effect when decoding JSON texts. |
255 | This setting has no effect when decoding JSON texts. |
177 | |
256 | |
178 | $json = $json->space_before ([$enable]) |
257 | $json = $json->space_before ([$enable]) |
179 | If $enable is true (or missing), then the "encode" method will add |
258 | If $enable is true (or missing), then the "encode" method will add |
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203 | |
282 | |
204 | Example, space_before and indent disabled, space_after enabled: |
283 | Example, space_before and indent disabled, space_after enabled: |
205 | |
284 | |
206 | {"key": "value"} |
285 | {"key": "value"} |
207 | |
286 | |
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287 | $json = $json->relaxed ([$enable]) |
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288 | If $enable is true (or missing), then "decode" will accept some |
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289 | extensions to normal JSON syntax (see below). "encode" will not be |
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290 | affected in anyway. *Be aware that this option makes you accept |
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291 | invalid JSON texts as if they were valid!*. I suggest only to use |
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292 | this option to parse application-specific files written by humans |
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293 | (configuration files, resource files etc.) |
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294 | |
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295 | If $enable is false (the default), then "decode" will only accept |
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296 | valid JSON texts. |
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297 | |
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298 | Currently accepted extensions are: |
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299 | |
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300 | * list items can have an end-comma |
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301 | JSON *separates* array elements and key-value pairs with commas. |
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302 | This can be annoying if you write JSON texts manually and want |
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303 | to be able to quickly append elements, so this extension accepts |
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304 | comma at the end of such items not just between them: |
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305 | |
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306 | [ |
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307 | 1, |
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308 | 2, <- this comma not normally allowed |
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309 | ] |
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310 | { |
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311 | "k1": "v1", |
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312 | "k2": "v2", <- this comma not normally allowed |
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313 | } |
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314 | |
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315 | * shell-style '#'-comments |
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316 | Whenever JSON allows whitespace, shell-style comments are |
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317 | additionally allowed. They are terminated by the first |
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318 | carriage-return or line-feed character, after which more |
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319 | white-space and comments are allowed. |
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320 | |
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321 | [ |
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322 | 1, # this comment not allowed in JSON |
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323 | # neither this one... |
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324 | ] |
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325 | |
208 | $json = $json->canonical ([$enable]) |
326 | $json = $json->canonical ([$enable]) |
209 | If $enable is true (or missing), then the "encode" method will |
327 | If $enable is true (or missing), then the "encode" method will |
210 | output JSON objects by sorting their keys. This is adding a |
328 | output JSON objects by sorting their keys. This is adding a |
211 | comparatively high overhead. |
329 | comparatively high overhead. |
212 | |
330 | |
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214 | pairs in the order Perl stores them (which will likely change |
332 | pairs in the order Perl stores them (which will likely change |
215 | between runs of the same script). |
333 | between runs of the same script). |
216 | |
334 | |
217 | This option is useful if you want the same data structure to be |
335 | This option is useful if you want the same data structure to be |
218 | encoded as the same JSON text (given the same overall settings). If |
336 | encoded as the same JSON text (given the same overall settings). If |
219 | it is disabled, the same hash migh be encoded differently even if |
337 | it is disabled, the same hash might be encoded differently even if |
220 | contains the same data, as key-value pairs have no inherent ordering |
338 | contains the same data, as key-value pairs have no inherent ordering |
221 | in Perl. |
339 | in Perl. |
222 | |
340 | |
223 | This setting has no effect when decoding JSON texts. |
341 | This setting has no effect when decoding JSON texts. |
224 | |
342 | |
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236 | Example, encode a Perl scalar as JSON value with enabled |
354 | Example, encode a Perl scalar as JSON value with enabled |
237 | "allow_nonref", resulting in an invalid JSON text: |
355 | "allow_nonref", resulting in an invalid JSON text: |
238 | |
356 | |
239 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
357 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
240 | => "Hello, World!" |
358 | => "Hello, World!" |
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359 | |
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360 | $json = $json->allow_blessed ([$enable]) |
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361 | If $enable is true (or missing), then the "encode" method will not |
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362 | barf when it encounters a blessed reference. Instead, the value of |
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363 | the convert_blessed option will decide whether "null" |
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364 | ("convert_blessed" disabled or no "to_json" method found) or a |
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365 | representation of the object ("convert_blessed" enabled and |
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366 | "to_json" method found) is being encoded. Has no effect on "decode". |
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367 | |
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368 | If $enable is false (the default), then "encode" will throw an |
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369 | exception when it encounters a blessed object. |
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370 | |
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371 | $json = $json->convert_blessed ([$enable]) |
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372 | If $enable is true (or missing), then "encode", upon encountering a |
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373 | blessed object, will check for the availability of the "TO_JSON" |
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374 | method on the object's class. If found, it will be called in scalar |
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375 | context and the resulting scalar will be encoded instead of the |
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376 | object. If no "TO_JSON" method is found, the value of |
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377 | "allow_blessed" will decide what to do. |
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378 | |
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379 | The "TO_JSON" method may safely call die if it wants. If "TO_JSON" |
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380 | returns other blessed objects, those will be handled in the same |
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381 | way. "TO_JSON" must take care of not causing an endless recursion |
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382 | cycle (== crash) in this case. The name of "TO_JSON" was chosen |
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383 | because other methods called by the Perl core (== not by the user of |
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384 | the object) are usually in upper case letters and to avoid |
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385 | collisions with the "to_json" function. |
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386 | |
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387 | This setting does not yet influence "decode" in any way, but in the |
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388 | future, global hooks might get installed that influence "decode" and |
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389 | are enabled by this setting. |
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390 | |
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391 | If $enable is false, then the "allow_blessed" setting will decide |
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392 | what to do when a blessed object is found. |
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393 | |
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394 | $json = $json->filter_json_object ([$coderef->($hashref)]) |
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395 | When $coderef is specified, it will be called from "decode" each |
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396 | time it decodes a JSON object. The only argument is a reference to |
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397 | the newly-created hash. If the code references returns a single |
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398 | scalar (which need not be a reference), this value (i.e. a copy of |
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399 | that scalar to avoid aliasing) is inserted into the deserialised |
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400 | data structure. If it returns an empty list (NOTE: *not* "undef", |
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401 | which is a valid scalar), the original deserialised hash will be |
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402 | inserted. This setting can slow down decoding considerably. |
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403 | |
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404 | When $coderef is omitted or undefined, any existing callback will be |
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405 | removed and "decode" will not change the deserialised hash in any |
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406 | way. |
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407 | |
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408 | Example, convert all JSON objects into the integer 5: |
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409 | |
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410 | my $js = JSON::XS->new->filter_json_object (sub { 5 }); |
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411 | # returns [5] |
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412 | $js->decode ('[{}]') |
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413 | # throw an exception because allow_nonref is not enabled |
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414 | # so a lone 5 is not allowed. |
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415 | $js->decode ('{"a":1, "b":2}'); |
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416 | |
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417 | $json = $json->filter_json_single_key_object ($key [=> |
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418 | $coderef->($value)]) |
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419 | Works remotely similar to "filter_json_object", but is only called |
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420 | for JSON objects having a single key named $key. |
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421 | |
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422 | This $coderef is called before the one specified via |
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423 | "filter_json_object", if any. It gets passed the single value in the |
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424 | JSON object. If it returns a single value, it will be inserted into |
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425 | the data structure. If it returns nothing (not even "undef" but the |
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426 | empty list), the callback from "filter_json_object" will be called |
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427 | next, as if no single-key callback were specified. |
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428 | |
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429 | If $coderef is omitted or undefined, the corresponding callback will |
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430 | be disabled. There can only ever be one callback for a given key. |
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431 | |
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432 | As this callback gets called less often then the |
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433 | "filter_json_object" one, decoding speed will not usually suffer as |
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434 | much. Therefore, single-key objects make excellent targets to |
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435 | serialise Perl objects into, especially as single-key JSON objects |
|
|
436 | are as close to the type-tagged value concept as JSON gets (it's |
|
|
437 | basically an ID/VALUE tuple). Of course, JSON does not support this |
|
|
438 | in any way, so you need to make sure your data never looks like a |
|
|
439 | serialised Perl hash. |
|
|
440 | |
|
|
441 | Typical names for the single object key are "__class_whatever__", or |
|
|
442 | "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even |
|
|
443 | things like "__class_md5sum(classname)__", to reduce the risk of |
|
|
444 | clashing with real hashes. |
|
|
445 | |
|
|
446 | Example, decode JSON objects of the form "{ "__widget__" => <id> }" |
|
|
447 | into the corresponding $WIDGET{<id>} object: |
|
|
448 | |
|
|
449 | # return whatever is in $WIDGET{5}: |
|
|
450 | JSON::XS |
|
|
451 | ->new |
|
|
452 | ->filter_json_single_key_object (__widget__ => sub { |
|
|
453 | $WIDGET{ $_[0] } |
|
|
454 | }) |
|
|
455 | ->decode ('{"__widget__": 5') |
|
|
456 | |
|
|
457 | # this can be used with a TO_JSON method in some "widget" class |
|
|
458 | # for serialisation to json: |
|
|
459 | sub WidgetBase::TO_JSON { |
|
|
460 | my ($self) = @_; |
|
|
461 | |
|
|
462 | unless ($self->{id}) { |
|
|
463 | $self->{id} = ..get..some..id..; |
|
|
464 | $WIDGET{$self->{id}} = $self; |
|
|
465 | } |
|
|
466 | |
|
|
467 | { __widget__ => $self->{id} } |
|
|
468 | } |
241 | |
469 | |
242 | $json = $json->shrink ([$enable]) |
470 | $json = $json->shrink ([$enable]) |
243 | Perl usually over-allocates memory a bit when allocating space for |
471 | Perl usually over-allocates memory a bit when allocating space for |
244 | strings. This flag optionally resizes strings generated by either |
472 | strings. This flag optionally resizes strings generated by either |
245 | "encode" or "decode" to their minimum size possible. This can save |
473 | "encode" or "decode" to their minimum size possible. This can save |
246 | memory when your JSON texts are either very very long or you have |
474 | memory when your JSON texts are either very very long or you have |
247 | many short strings. It will also try to downgrade any strings to |
475 | many short strings. It will also try to downgrade any strings to |
248 | octet-form if possible: perl stores strings internally either in an |
476 | octet-form if possible: perl stores strings internally either in an |
249 | encoding called UTF-X or in octet-form. The latter cannot store |
477 | encoding called UTF-X or in octet-form. The latter cannot store |
250 | everything but uses less space in general. |
478 | everything but uses less space in general (and some buggy Perl or C |
|
|
479 | code might even rely on that internal representation being used). |
|
|
480 | |
|
|
481 | The actual definition of what shrink does might change in future |
|
|
482 | versions, but it will always try to save space at the expense of |
|
|
483 | time. |
251 | |
484 | |
252 | If $enable is true (or missing), the string returned by "encode" |
485 | If $enable is true (or missing), the string returned by "encode" |
253 | will be shrunk-to-fit, while all strings generated by "decode" will |
486 | will be shrunk-to-fit, while all strings generated by "decode" will |
254 | also be shrunk-to-fit. |
487 | also be shrunk-to-fit. |
255 | |
488 | |
… | |
… | |
260 | converting strings that look like integers or floats into integers |
493 | converting strings that look like integers or floats into integers |
261 | or floats internally (there is no difference on the Perl level), |
494 | or floats internally (there is no difference on the Perl level), |
262 | saving space. |
495 | saving space. |
263 | |
496 | |
264 | $json = $json->max_depth ([$maximum_nesting_depth]) |
497 | $json = $json->max_depth ([$maximum_nesting_depth]) |
265 | Sets the maximum nesting level (default 8192) accepted while |
498 | Sets the maximum nesting level (default 512) accepted while encoding |
266 | encoding or decoding. If the JSON text or Perl data structure has an |
499 | or decoding. If the JSON text or Perl data structure has an equal or |
267 | equal or higher nesting level then this limit, then the encoder and |
500 | higher nesting level then this limit, then the encoder and decoder |
268 | decoder will stop and croak at that point. |
501 | will stop and croak at that point. |
269 | |
502 | |
270 | Nesting level is defined by number of hash- or arrayrefs that the |
503 | Nesting level is defined by number of hash- or arrayrefs that the |
271 | encoder needs to traverse to reach a given point or the number of |
504 | encoder needs to traverse to reach a given point or the number of |
272 | "{" or "[" characters without their matching closing parenthesis |
505 | "{" or "[" characters without their matching closing parenthesis |
273 | crossed to reach a given character in a string. |
506 | crossed to reach a given character in a string. |
274 | |
507 | |
275 | Setting the maximum depth to one disallows any nesting, so that |
508 | Setting the maximum depth to one disallows any nesting, so that |
276 | ensures that the object is only a single hash/object or array. |
509 | ensures that the object is only a single hash/object or array. |
277 | |
510 | |
278 | The argument to "max_depth" will be rounded up to the next nearest |
511 | The argument to "max_depth" will be rounded up to the next highest |
279 | power of two. |
512 | power of two. If no argument is given, the highest possible setting |
|
|
513 | will be used, which is rarely useful. |
|
|
514 | |
|
|
515 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
|
|
516 | useful. |
|
|
517 | |
|
|
518 | $json = $json->max_size ([$maximum_string_size]) |
|
|
519 | Set the maximum length a JSON text may have (in bytes) where |
|
|
520 | decoding is being attempted. The default is 0, meaning no limit. |
|
|
521 | When "decode" is called on a string longer then this number of |
|
|
522 | characters it will not attempt to decode the string but throw an |
|
|
523 | exception. This setting has no effect on "encode" (yet). |
|
|
524 | |
|
|
525 | The argument to "max_size" will be rounded up to the next highest |
|
|
526 | power of two (so may be more than requested). If no argument is |
|
|
527 | given, the limit check will be deactivated (same as when 0 is |
|
|
528 | specified). |
280 | |
529 | |
281 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
530 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
282 | useful. |
531 | useful. |
283 | |
532 | |
284 | $json_text = $json->encode ($perl_scalar) |
533 | $json_text = $json->encode ($perl_scalar) |
… | |
… | |
296 | |
545 | |
297 | JSON numbers and strings become simple Perl scalars. JSON arrays |
546 | JSON numbers and strings become simple Perl scalars. JSON arrays |
298 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
547 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
299 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
548 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
300 | |
549 | |
|
|
550 | ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
|
|
551 | This works like the "decode" method, but instead of raising an |
|
|
552 | exception when there is trailing garbage after the first JSON |
|
|
553 | object, it will silently stop parsing there and return the number of |
|
|
554 | characters consumed so far. |
|
|
555 | |
|
|
556 | This is useful if your JSON texts are not delimited by an outer |
|
|
557 | protocol (which is not the brightest thing to do in the first place) |
|
|
558 | and you need to know where the JSON text ends. |
|
|
559 | |
|
|
560 | JSON::XS->new->decode_prefix ("[1] the tail") |
|
|
561 | => ([], 3) |
|
|
562 | |
301 | MAPPING |
563 | MAPPING |
302 | This section describes how JSON::XS maps Perl values to JSON values and |
564 | This section describes how JSON::XS maps Perl values to JSON values and |
303 | vice versa. These mappings are designed to "do the right thing" in most |
565 | vice versa. These mappings are designed to "do the right thing" in most |
304 | circumstances automatically, preserving round-tripping characteristics |
566 | circumstances automatically, preserving round-tripping characteristics |
305 | (what you put in comes out as something equivalent). |
567 | (what you put in comes out as something equivalent). |
306 | |
568 | |
307 | For the more enlightened: note that in the following descriptions, |
569 | For the more enlightened: note that in the following descriptions, |
308 | lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* |
570 | lowercase *perl* refers to the Perl interpreter, while uppercase *Perl* |
309 | refers to the abstract Perl language itself. |
571 | refers to the abstract Perl language itself. |
310 | |
572 | |
311 | JSON -> PERL |
573 | JSON -> PERL |
312 | object |
574 | object |
313 | A JSON object becomes a reference to a hash in Perl. No ordering of |
575 | A JSON object becomes a reference to a hash in Perl. No ordering of |
314 | object keys is preserved (JSON does not preserver object key |
576 | object keys is preserved (JSON does not preserve object key ordering |
315 | ordering itself). |
577 | itself). |
316 | |
578 | |
317 | array |
579 | array |
318 | A JSON array becomes a reference to an array in Perl. |
580 | A JSON array becomes a reference to an array in Perl. |
319 | |
581 | |
320 | string |
582 | string |
321 | A JSON string becomes a string scalar in Perl - Unicode codepoints |
583 | A JSON string becomes a string scalar in Perl - Unicode codepoints |
322 | in JSON are represented by the same codepoints in the Perl string, |
584 | in JSON are represented by the same codepoints in the Perl string, |
323 | so no manual decoding is necessary. |
585 | so no manual decoding is necessary. |
324 | |
586 | |
325 | number |
587 | number |
326 | A JSON number becomes either an integer or numeric (floating point) |
588 | A JSON number becomes either an integer, numeric (floating point) or |
327 | scalar in perl, depending on its range and any fractional parts. On |
589 | string scalar in perl, depending on its range and any fractional |
328 | the Perl level, there is no difference between those as Perl handles |
590 | parts. On the Perl level, there is no difference between those as |
329 | all the conversion details, but an integer may take slightly less |
591 | Perl handles all the conversion details, but an integer may take |
330 | memory and might represent more values exactly than (floating point) |
592 | slightly less memory and might represent more values exactly than |
331 | numbers. |
593 | (floating point) numbers. |
|
|
594 | |
|
|
595 | If the number consists of digits only, JSON::XS will try to |
|
|
596 | represent it as an integer value. If that fails, it will try to |
|
|
597 | represent it as a numeric (floating point) value if that is possible |
|
|
598 | without loss of precision. Otherwise it will preserve the number as |
|
|
599 | a string value. |
|
|
600 | |
|
|
601 | Numbers containing a fractional or exponential part will always be |
|
|
602 | represented as numeric (floating point) values, possibly at a loss |
|
|
603 | of precision. |
|
|
604 | |
|
|
605 | This might create round-tripping problems as numbers might become |
|
|
606 | strings, but as Perl is typeless there is no other way to do it. |
332 | |
607 | |
333 | true, false |
608 | true, false |
334 | These JSON atoms become 0, 1, respectively. Information is lost in |
609 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
335 | this process. Future versions might represent those values |
610 | respectively. They are overloaded to act almost exactly like the |
336 | differently, but they will be guarenteed to act like these integers |
611 | numbers 1 and 0. You can check whether a scalar is a JSON boolean by |
337 | would normally in Perl. |
612 | using the "JSON::XS::is_bool" function. |
338 | |
613 | |
339 | null |
614 | null |
340 | A JSON null atom becomes "undef" in Perl. |
615 | A JSON null atom becomes "undef" in Perl. |
341 | |
616 | |
342 | PERL -> JSON |
617 | PERL -> JSON |
… | |
… | |
344 | truly typeless language, so we can only guess which JSON type is meant |
619 | truly typeless language, so we can only guess which JSON type is meant |
345 | by a Perl value. |
620 | by a Perl value. |
346 | |
621 | |
347 | hash references |
622 | hash references |
348 | Perl hash references become JSON objects. As there is no inherent |
623 | Perl hash references become JSON objects. As there is no inherent |
349 | ordering in hash keys, they will usually be encoded in a |
624 | ordering in hash keys (or JSON objects), they will usually be |
350 | pseudo-random order that can change between runs of the same program |
625 | encoded in a pseudo-random order that can change between runs of the |
351 | but stays generally the same within a single run of a program. |
626 | same program but stays generally the same within a single run of a |
352 | JSON::XS can optionally sort the hash keys (determined by the |
627 | program. JSON::XS can optionally sort the hash keys (determined by |
353 | *canonical* flag), so the same datastructure will serialise to the |
628 | the *canonical* flag), so the same datastructure will serialise to |
354 | same JSON text (given same settings and version of JSON::XS), but |
629 | the same JSON text (given same settings and version of JSON::XS), |
355 | this incurs a runtime overhead. |
630 | but this incurs a runtime overhead and is only rarely useful, e.g. |
|
|
631 | when you want to compare some JSON text against another for |
|
|
632 | equality. |
356 | |
633 | |
357 | array references |
634 | array references |
358 | Perl array references become JSON arrays. |
635 | Perl array references become JSON arrays. |
|
|
636 | |
|
|
637 | other references |
|
|
638 | Other unblessed references are generally not allowed and will cause |
|
|
639 | an exception to be thrown, except for references to the integers 0 |
|
|
640 | and 1, which get turned into "false" and "true" atoms in JSON. You |
|
|
641 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
|
|
642 | readability. |
|
|
643 | |
|
|
644 | to_json [\0,JSON::XS::true] # yields [false,true] |
|
|
645 | |
|
|
646 | JSON::XS::true, JSON::XS::false |
|
|
647 | These special values become JSON true and JSON false values, |
|
|
648 | respectively. You can also use "\1" and "\0" directly if you want. |
359 | |
649 | |
360 | blessed objects |
650 | blessed objects |
361 | Blessed objects are not allowed. JSON::XS currently tries to encode |
651 | Blessed objects are not allowed. JSON::XS currently tries to encode |
362 | their underlying representation (hash- or arrayref), but this |
652 | their underlying representation (hash- or arrayref), but this |
363 | behaviour might change in future versions. |
653 | behaviour might change in future versions. |
… | |
… | |
379 | to_json [$value] # yields ["5"] |
669 | to_json [$value] # yields ["5"] |
380 | |
670 | |
381 | # undef becomes null |
671 | # undef becomes null |
382 | to_json [undef] # yields [null] |
672 | to_json [undef] # yields [null] |
383 | |
673 | |
384 | You can force the type to be a string by stringifying it: |
674 | You can force the type to be a JSON string by stringifying it: |
385 | |
675 | |
386 | my $x = 3.1; # some variable containing a number |
676 | my $x = 3.1; # some variable containing a number |
387 | "$x"; # stringified |
677 | "$x"; # stringified |
388 | $x .= ""; # another, more awkward way to stringify |
678 | $x .= ""; # another, more awkward way to stringify |
389 | print $x; # perl does it for you, too, quite often |
679 | print $x; # perl does it for you, too, quite often |
390 | |
680 | |
391 | You can force the type to be a number by numifying it: |
681 | You can force the type to be a JSON number by numifying it: |
392 | |
682 | |
393 | my $x = "3"; # some variable containing a string |
683 | my $x = "3"; # some variable containing a string |
394 | $x += 0; # numify it, ensuring it will be dumped as a number |
684 | $x += 0; # numify it, ensuring it will be dumped as a number |
395 | $x *= 1; # same thing, the choise is yours. |
685 | $x *= 1; # same thing, the choice is yours. |
396 | |
686 | |
397 | You can not currently output JSON booleans or force the type in |
687 | You can not currently force the type in other, less obscure, ways. |
398 | other, less obscure, ways. Tell me if you need this capability. |
688 | Tell me if you need this capability. |
399 | |
|
|
400 | circular data structures |
|
|
401 | Those will be encoded until memory or stackspace runs out. |
|
|
402 | |
689 | |
403 | COMPARISON |
690 | COMPARISON |
404 | As already mentioned, this module was created because none of the |
691 | As already mentioned, this module was created because none of the |
405 | existing JSON modules could be made to work correctly. First I will |
692 | existing JSON modules could be made to work correctly. First I will |
406 | describe the problems (or pleasures) I encountered with various existing |
693 | describe the problems (or pleasures) I encountered with various existing |
… | |
… | |
408 | not to suffer from any of these problems or limitations. |
695 | not to suffer from any of these problems or limitations. |
409 | |
696 | |
410 | JSON 1.07 |
697 | JSON 1.07 |
411 | Slow (but very portable, as it is written in pure Perl). |
698 | Slow (but very portable, as it is written in pure Perl). |
412 | |
699 | |
413 | Undocumented/buggy Unicode handling (how JSON handles unicode values |
700 | Undocumented/buggy Unicode handling (how JSON handles Unicode values |
414 | is undocumented. One can get far by feeding it unicode strings and |
701 | is undocumented. One can get far by feeding it Unicode strings and |
415 | doing en-/decoding oneself, but unicode escapes are not working |
702 | doing en-/decoding oneself, but Unicode escapes are not working |
416 | properly). |
703 | properly). |
417 | |
704 | |
418 | No roundtripping (strings get clobbered if they look like numbers, |
705 | No round-tripping (strings get clobbered if they look like numbers, |
419 | e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that |
706 | e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that |
420 | will decode into the number 2. |
707 | will decode into the number 2. |
421 | |
708 | |
422 | JSON::PC 0.01 |
709 | JSON::PC 0.01 |
423 | Very fast. |
710 | Very fast. |
424 | |
711 | |
425 | Undocumented/buggy Unicode handling. |
712 | Undocumented/buggy Unicode handling. |
426 | |
713 | |
427 | No roundtripping. |
714 | No round-tripping. |
428 | |
715 | |
429 | Has problems handling many Perl values (e.g. regex results and other |
716 | Has problems handling many Perl values (e.g. regex results and other |
430 | magic values will make it croak). |
717 | magic values will make it croak). |
431 | |
718 | |
432 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
719 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
… | |
… | |
442 | much undocumented. I need at least a format for easy reading by |
729 | much undocumented. I need at least a format for easy reading by |
443 | humans and a single-line compact format for use in a protocol, and |
730 | humans and a single-line compact format for use in a protocol, and |
444 | preferably a way to generate ASCII-only JSON texts). |
731 | preferably a way to generate ASCII-only JSON texts). |
445 | |
732 | |
446 | Completely broken (and confusingly documented) Unicode handling |
733 | Completely broken (and confusingly documented) Unicode handling |
447 | (unicode escapes are not working properly, you need to set |
734 | (Unicode escapes are not working properly, you need to set |
448 | ImplicitUnicode to *different* values on en- and decoding to get |
735 | ImplicitUnicode to *different* values on en- and decoding to get |
449 | symmetric behaviour). |
736 | symmetric behaviour). |
450 | |
737 | |
451 | No roundtripping (simple cases work, but this depends on wether the |
738 | No round-tripping (simple cases work, but this depends on whether |
452 | scalar value was used in a numeric context or not). |
739 | the scalar value was used in a numeric context or not). |
453 | |
740 | |
454 | Dumping hashes may skip hash values depending on iterator state. |
741 | Dumping hashes may skip hash values depending on iterator state. |
455 | |
742 | |
456 | Unmaintained (maintainer unresponsive for many months, bugs are not |
743 | Unmaintained (maintainer unresponsive for many months, bugs are not |
457 | getting fixed). |
744 | getting fixed). |
458 | |
745 | |
459 | Does not check input for validity (i.e. will accept non-JSON input |
746 | Does not check input for validity (i.e. will accept non-JSON input |
460 | and return "something" instead of raising an exception. This is a |
747 | and return "something" instead of raising an exception. This is a |
461 | security issue: imagine two banks transfering money between each |
748 | security issue: imagine two banks transferring money between each |
462 | other using JSON. One bank might parse a given non-JSON request and |
749 | other using JSON. One bank might parse a given non-JSON request and |
463 | deduct money, while the other might reject the transaction with a |
750 | deduct money, while the other might reject the transaction with a |
464 | syntax error. While a good protocol will at least recover, that is |
751 | syntax error. While a good protocol will at least recover, that is |
465 | extra unnecessary work and the transaction will still not succeed). |
752 | extra unnecessary work and the transaction will still not succeed). |
466 | |
753 | |
467 | JSON::DWIW 0.04 |
754 | JSON::DWIW 0.04 |
468 | Very fast. Very natural. Very nice. |
755 | Very fast. Very natural. Very nice. |
469 | |
756 | |
470 | Undocumented unicode handling (but the best of the pack. Unicode |
757 | Undocumented Unicode handling (but the best of the pack. Unicode |
471 | escapes still don't get parsed properly). |
758 | escapes still don't get parsed properly). |
472 | |
759 | |
473 | Very inflexible. |
760 | Very inflexible. |
474 | |
761 | |
475 | No roundtripping. |
762 | No round-tripping. |
476 | |
763 | |
477 | Does not generate valid JSON texts (key strings are often unquoted, |
764 | Does not generate valid JSON texts (key strings are often unquoted, |
478 | empty keys result in nothing being output) |
765 | empty keys result in nothing being output) |
479 | |
766 | |
480 | Does not check input for validity. |
767 | Does not check input for validity. |
|
|
768 | |
|
|
769 | JSON and YAML |
|
|
770 | You often hear that JSON is a subset (or a close subset) of YAML. This |
|
|
771 | is, however, a mass hysteria and very far from the truth. In general, |
|
|
772 | there is no way to configure JSON::XS to output a data structure as |
|
|
773 | valid YAML. |
|
|
774 | |
|
|
775 | If you really must use JSON::XS to generate YAML, you should use this |
|
|
776 | algorithm (subject to change in future versions): |
|
|
777 | |
|
|
778 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
|
|
779 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
|
|
780 | |
|
|
781 | This will usually generate JSON texts that also parse as valid YAML. |
|
|
782 | Please note that YAML has hardcoded limits on (simple) object key |
|
|
783 | lengths that JSON doesn't have, so you should make sure that your hash |
|
|
784 | keys are noticeably shorter than the 1024 characters YAML allows. |
|
|
785 | |
|
|
786 | There might be other incompatibilities that I am not aware of. In |
|
|
787 | general you should not try to generate YAML with a JSON generator or |
|
|
788 | vice versa, or try to parse JSON with a YAML parser or vice versa: |
|
|
789 | chances are high that you will run into severe interoperability |
|
|
790 | problems. |
481 | |
791 | |
482 | SPEED |
792 | SPEED |
483 | It seems that JSON::XS is surprisingly fast, as shown in the following |
793 | It seems that JSON::XS is surprisingly fast, as shown in the following |
484 | tables. They have been generated with the help of the "eg/bench" program |
794 | tables. They have been generated with the help of the "eg/bench" program |
485 | in the JSON::XS distribution, to make it easy to compare on your own |
795 | in the JSON::XS distribution, to make it easy to compare on your own |
486 | system. |
796 | system. |
487 | |
797 | |
488 | First comes a comparison between various modules using a very short JSON |
798 | First comes a comparison between various modules using a very short |
489 | string: |
799 | single-line JSON string: |
490 | |
800 | |
491 | {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} |
801 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
|
|
802 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
492 | |
803 | |
493 | It shows the number of encodes/decodes per second (JSON::XS uses the |
804 | It shows the number of encodes/decodes per second (JSON::XS uses the |
494 | functional interface, while JSON::XS/2 uses the OO interface with |
805 | functional interface, while JSON::XS/2 uses the OO interface with |
495 | pretty-printing and hashkey sorting enabled). Higher is better: |
806 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
|
|
807 | Higher is better: |
496 | |
808 | |
|
|
809 | Storable | 15779.925 | 14169.946 | |
|
|
810 | -----------+------------+------------+ |
497 | module | encode | decode | |
811 | module | encode | decode | |
498 | -----------|------------|------------| |
812 | -----------|------------|------------| |
499 | JSON | 11488.516 | 7823.035 | |
813 | JSON | 4990.842 | 4088.813 | |
500 | JSON::DWIW | 94708.054 | 129094.260 | |
814 | JSON::DWIW | 51653.990 | 71575.154 | |
501 | JSON::PC | 63884.157 | 128528.212 | |
815 | JSON::PC | 65948.176 | 74631.744 | |
|
|
816 | JSON::PP | 8931.652 | 3817.168 | |
502 | JSON::Syck | 34898.677 | 42096.911 | |
817 | JSON::Syck | 24877.248 | 27776.848 | |
503 | JSON::XS | 654027.064 | 396423.669 | |
818 | JSON::XS | 388361.481 | 227951.304 | |
504 | JSON::XS/2 | 371564.190 | 371725.613 | |
819 | JSON::XS/2 | 227951.304 | 218453.333 | |
|
|
820 | JSON::XS/3 | 338250.323 | 218453.333 | |
|
|
821 | Storable | 16500.016 | 135300.129 | |
505 | -----------+------------+------------+ |
822 | -----------+------------+------------+ |
506 | |
823 | |
507 | That is, JSON::XS is more than six times faster than JSON::DWIW on |
824 | That is, JSON::XS is about five times faster than JSON::DWIW on |
508 | encoding, more than three times faster on decoding, and about thirty |
825 | encoding, about three times faster on decoding, and over forty times |
509 | times faster than JSON, even with pretty-printing and key sorting. |
826 | faster than JSON, even with pretty-printing and key sorting. It also |
|
|
827 | compares favourably to Storable for small amounts of data. |
510 | |
828 | |
511 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
829 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
512 | search API (http://nanoref.com/yahooapis/mgPdGg): |
830 | search API (http://nanoref.com/yahooapis/mgPdGg): |
513 | |
831 | |
514 | module | encode | decode | |
832 | module | encode | decode | |
515 | -----------|------------|------------| |
833 | -----------|------------|------------| |
516 | JSON | 273.023 | 44.674 | |
834 | JSON | 55.260 | 34.971 | |
517 | JSON::DWIW | 1089.383 | 1145.704 | |
835 | JSON::DWIW | 825.228 | 1082.513 | |
518 | JSON::PC | 3097.419 | 2393.921 | |
836 | JSON::PC | 3571.444 | 2394.829 | |
519 | JSON::Syck | 514.060 | 843.053 | |
837 | JSON::PP | 210.987 | 32.574 | |
520 | JSON::XS | 6479.668 | 3636.364 | |
838 | JSON::Syck | 552.551 | 787.544 | |
521 | JSON::XS/2 | 3774.221 | 3599.124 | |
839 | JSON::XS | 5780.463 | 4854.519 | |
|
|
840 | JSON::XS/2 | 3869.998 | 4798.975 | |
|
|
841 | JSON::XS/3 | 5862.880 | 4798.975 | |
|
|
842 | Storable | 4445.002 | 5235.027 | |
522 | -----------+------------+------------+ |
843 | -----------+------------+------------+ |
523 | |
844 | |
524 | Again, JSON::XS leads by far. |
845 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
|
|
846 | decodes faster). |
525 | |
847 | |
526 | On large strings containing lots of high unicode characters, some |
848 | On large strings containing lots of high Unicode characters, some |
527 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
849 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
528 | result will be broken due to missing (or wrong) unicode handling. Others |
850 | result will be broken due to missing (or wrong) Unicode handling. Others |
529 | refuse to decode or encode properly, so it was impossible to prepare a |
851 | refuse to decode or encode properly, so it was impossible to prepare a |
530 | fair comparison table for that case. |
852 | fair comparison table for that case. |
531 | |
853 | |
532 | SECURITY CONSIDERATIONS |
854 | SECURITY CONSIDERATIONS |
533 | When you are using JSON in a protocol, talking to untrusted potentially |
855 | When you are using JSON in a protocol, talking to untrusted potentially |
… | |
… | |
537 | have any buffer overflows. Obviously, this module should ensure that and |
859 | have any buffer overflows. Obviously, this module should ensure that and |
538 | I am trying hard on making that true, but you never know. |
860 | I am trying hard on making that true, but you never know. |
539 | |
861 | |
540 | Second, you need to avoid resource-starving attacks. That means you |
862 | Second, you need to avoid resource-starving attacks. That means you |
541 | should limit the size of JSON texts you accept, or make sure then when |
863 | should limit the size of JSON texts you accept, or make sure then when |
542 | your resources run out, thats just fine (e.g. by using a separate |
864 | your resources run out, that's just fine (e.g. by using a separate |
543 | process that can crash safely). The size of a JSON text in octets or |
865 | process that can crash safely). The size of a JSON text in octets or |
544 | characters is usually a good indication of the size of the resources |
866 | characters is usually a good indication of the size of the resources |
545 | required to decode it into a Perl structure. |
867 | required to decode it into a Perl structure. While JSON::XS can check |
|
|
868 | the size of the JSON text, it might be too late when you already have it |
|
|
869 | in memory, so you might want to check the size before you accept the |
|
|
870 | string. |
546 | |
871 | |
547 | Third, JSON::XS recurses using the C stack when decoding objects and |
872 | Third, JSON::XS recurses using the C stack when decoding objects and |
548 | arrays. The C stack is a limited resource: for instance, on my amd64 |
873 | arrays. The C stack is a limited resource: for instance, on my amd64 |
549 | machine with 8MB of stack size I can decode around 180k nested arrays |
874 | machine with 8MB of stack size I can decode around 180k nested arrays |
550 | but only 14k nested JSON objects. If that is exceeded, the program |
875 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
|
|
876 | croak to free the temporary). If that is exceeded, the program crashes. |
551 | crashes. Thats why the default nesting limit is set to 8192. If your |
877 | to be conservative, the default nesting limit is set to 512. If your |
552 | process has a smaller stack, you should adjust this setting accordingly |
878 | process has a smaller stack, you should adjust this setting accordingly |
553 | with the "max_depth" method. |
879 | with the "max_depth" method. |
554 | |
880 | |
555 | And last but least, something else could bomb you that I forgot to think |
881 | And last but least, something else could bomb you that I forgot to think |
556 | of. In that case, you get to keep the pieces. I am alway sopen for |
882 | of. In that case, you get to keep the pieces. I am always open for |
557 | hints, though... |
883 | hints, though... |
|
|
884 | |
|
|
885 | If you are using JSON::XS to return packets to consumption by JavaScript |
|
|
886 | scripts in a browser you should have a look at |
|
|
887 | <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
|
|
888 | you are vulnerable to some common attack vectors (which really are |
|
|
889 | browser design bugs, but it is still you who will have to deal with it, |
|
|
890 | as major browser developers care only for features, not about doing |
|
|
891 | security right). |
|
|
892 | |
|
|
893 | THREADS |
|
|
894 | This module is *not* guaranteed to be thread safe and there are no plans |
|
|
895 | to change this until Perl gets thread support (as opposed to the |
|
|
896 | horribly slow so-called "threads" which are simply slow and bloated |
|
|
897 | process simulations - use fork, its *much* faster, cheaper, better). |
|
|
898 | |
|
|
899 | (It might actually work, but you have been warned). |
558 | |
900 | |
559 | BUGS |
901 | BUGS |
560 | While the goal of this module is to be correct, that unfortunately does |
902 | While the goal of this module is to be correct, that unfortunately does |
561 | not mean its bug-free, only that I think its design is bug-free. It is |
903 | not mean its bug-free, only that I think its design is bug-free. It is |
562 | still relatively early in its development. If you keep reporting bugs |
904 | still relatively early in its development. If you keep reporting bugs |
563 | they will be fixed swiftly, though. |
905 | they will be fixed swiftly, though. |
564 | |
906 | |
|
|
907 | Please refrain from using rt.cpan.org or any other bug reporting |
|
|
908 | service. I put the contact address into my modules for a reason. |
|
|
909 | |
565 | AUTHOR |
910 | AUTHOR |
566 | Marc Lehmann <schmorp@schmorp.de> |
911 | Marc Lehmann <schmorp@schmorp.de> |
567 | http://home.schmorp.de/ |
912 | http://home.schmorp.de/ |
568 | |
913 | |