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; |
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10 | |
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11 | # exported functions, they croak on error |
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12 | # and expect/generate UTF-8 |
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13 | |
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14 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
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15 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
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16 | |
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17 | # OO-interface |
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18 | |
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19 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
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20 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
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21 | $perl_scalar = $coder->decode ($unicode_json_text); |
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22 | |
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23 | # Note that JSON version 2.0 and above will automatically use JSON::XS |
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24 | # if available, at virtually no speed overhead either, so you should |
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25 | # be able to just: |
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26 | |
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27 | use JSON; |
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28 | |
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29 | # and do the same things, except that you have a pure-perl fallback now. |
6 | |
30 | |
7 | DESCRIPTION |
31 | DESCRIPTION |
8 | This module converts Perl data structures to JSON and vice versa. Its |
32 | 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*. |
33 | 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. |
34 | To reach the latter goal it was written in C. |
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35 | |
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36 | Beginning with version 2.0 of the JSON module, when both JSON and |
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37 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can |
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38 | be overriden) with no overhead due to emulation (by inheritign |
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39 | constructor and methods). If JSON::XS is not available, it will fall |
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40 | back to the compatible JSON::PP module as backend, so using JSON instead |
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41 | of JSON::XS gives you a portable JSON API that can be fast when you need |
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42 | and doesn't require a C compiler when that is a problem. |
11 | |
43 | |
12 | As this is the n-th-something JSON module on CPAN, what was the reason |
44 | As this is the n-th-something JSON module on CPAN, what was the reason |
13 | to write yet another JSON module? While it seems there are many JSON |
45 | to write yet another JSON module? While it seems there are many JSON |
14 | modules, none of them correctly handle all corner cases, and in most |
46 | modules, none of them correctly handle all corner cases, and in most |
15 | cases their maintainers are unresponsive, gone missing, or not listening |
47 | cases their maintainers are unresponsive, gone missing, or not listening |
16 | to bug reports for other reasons. |
48 | to bug reports for other reasons. |
17 | |
49 | |
18 | See COMPARISON, below, for a comparison to some other JSON modules. |
50 | See COMPARISON, below, for a comparison to some other JSON modules. |
19 | |
51 | |
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52 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
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53 | vice versa. |
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54 | |
20 | FEATURES |
55 | FEATURES |
21 | * correct handling of unicode issues |
56 | * correct Unicode handling |
22 | This module knows how to handle Unicode, and even documents how it |
57 | This module knows how to handle Unicode, and even documents how and |
23 | does so. |
58 | when it does so. |
24 | |
59 | |
25 | * round-trip integrity |
60 | * round-trip integrity |
26 | When you serialise a perl data structure using only datatypes |
61 | When you serialise a perl data structure using only datatypes |
27 | supported by JSON, the deserialised data structure is identical on |
62 | 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"). |
63 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" |
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64 | just because it looks like a number). |
29 | |
65 | |
30 | * strict checking of JSON correctness |
66 | * strict checking of JSON correctness |
31 | There is no guessing, no generating of illegal JSON strings by |
67 | There is no guessing, no generating of illegal JSON texts by |
32 | default, and only JSON is accepted as input (the latter is a |
68 | default, and only JSON is accepted as input by default (the latter |
33 | security feature). |
69 | is a security feature). |
34 | |
70 | |
35 | * fast |
71 | * fast |
36 | compared to other JSON modules, this module compares favourably. |
72 | Compared to other JSON modules, this module compares favourably in |
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73 | terms of speed, too. |
37 | |
74 | |
38 | * simple to use |
75 | * simple to use |
39 | This module has both a simple functional interface as well as an OO |
76 | This module has both a simple functional interface as well as an OO |
40 | interface. |
77 | interface. |
41 | |
78 | |
42 | * reasonably versatile output formats |
79 | * reasonably versatile output formats |
43 | You can choose between the most compact format possible, a |
80 | You can choose between the most compact guaranteed single-line |
44 | pure-ascii format, or a pretty-printed format. Or you can combine |
81 | format possible (nice for simple line-based protocols), a pure-ascii |
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82 | format (for when your transport is not 8-bit clean, still supports |
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83 | the whole Unicode range), or a pretty-printed format (for when you |
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84 | want to read that stuff). Or you can combine those features in |
45 | those features in whatever way you like. |
85 | whatever way you like. |
46 | |
86 | |
47 | FUNCTIONAL INTERFACE |
87 | FUNCTIONAL INTERFACE |
48 | The following convinience methods are provided by this module. They are |
88 | The following convenience methods are provided by this module. They are |
49 | exported by default: |
89 | exported by default: |
50 | |
90 | |
51 | $json_string = to_json $perl_scalar |
91 | $json_text = to_json $perl_scalar |
52 | Converts the given Perl data structure (a simple scalar or a |
92 | Converts the given Perl data structure to a UTF-8 encoded, binary |
53 | reference to a hash or array) to a UTF-8 encoded, binary string |
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54 | (that is, the string contains octets only). Croaks on error. |
93 | string (that is, the string contains octets only). Croaks on error. |
55 | |
94 | |
56 | This function call is functionally identical to "JSON::XS->new->utf8 |
95 | This function call is functionally identical to: |
57 | (1)->encode ($perl_scalar)". |
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58 | |
96 | |
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97 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
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98 | |
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99 | except being faster. |
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100 | |
59 | $perl_scalar = from_json $json_string |
101 | $perl_scalar = from_json $json_text |
60 | The opposite of "to_json": expects an UTF-8 (binary) string and |
102 | The opposite of "to_json": expects an UTF-8 (binary) string and |
61 | tries to parse that as an UTF-8 encoded JSON string, returning the |
103 | tries to parse that as an UTF-8 encoded JSON text, returning the |
62 | resulting simple scalar or reference. Croaks on error. |
104 | resulting reference. Croaks on error. |
63 | |
105 | |
64 | This function call is functionally identical to "JSON::XS->new->utf8 |
106 | This function call is functionally identical to: |
65 | (1)->decode ($json_string)". |
107 | |
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108 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
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109 | |
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110 | except being faster. |
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111 | |
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112 | $is_boolean = JSON::XS::is_bool $scalar |
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113 | Returns true if the passed scalar represents either JSON::XS::true |
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114 | or JSON::XS::false, two constants that act like 1 and 0, |
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115 | respectively and are used to represent JSON "true" and "false" |
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116 | values in Perl. |
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117 | |
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118 | See MAPPING, below, for more information on how JSON values are |
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119 | mapped to Perl. |
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120 | |
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121 | A FEW NOTES ON UNICODE AND PERL |
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122 | Since this often leads to confusion, here are a few very clear words on |
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123 | how Unicode works in Perl, modulo bugs. |
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124 | |
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125 | 1. Perl strings can store characters with ordinal values > 255. |
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126 | This enables you to store Unicode characters as single characters in |
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127 | a Perl string - very natural. |
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128 | |
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129 | 2. Perl does *not* associate an encoding with your strings. |
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130 | Unless you force it to, e.g. when matching it against a regex, or |
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131 | printing the scalar to a file, in which case Perl either interprets |
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132 | your string as locale-encoded text, octets/binary, or as Unicode, |
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133 | depending on various settings. In no case is an encoding stored |
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134 | together with your data, it is *use* that decides encoding, not any |
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135 | magical metadata. |
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136 | |
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137 | 3. The internal utf-8 flag has no meaning with regards to the encoding |
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138 | of your string. |
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139 | Just ignore that flag unless you debug a Perl bug, a module written |
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140 | in XS or want to dive into the internals of perl. Otherwise it will |
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141 | only confuse you, as, despite the name, it says nothing about how |
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142 | your string is encoded. You can have Unicode strings with that flag |
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143 | set, with that flag clear, and you can have binary data with that |
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144 | flag set and that flag clear. Other possibilities exist, too. |
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145 | |
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146 | If you didn't know about that flag, just the better, pretend it |
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147 | doesn't exist. |
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148 | |
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149 | 4. A "Unicode String" is simply a string where each character can be |
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150 | validly interpreted as a Unicode codepoint. |
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151 | If you have UTF-8 encoded data, it is no longer a Unicode string, |
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152 | but a Unicode string encoded in UTF-8, giving you a binary string. |
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153 | |
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154 | 5. A string containing "high" (> 255) character values is *not* a UTF-8 |
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155 | string. |
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156 | It's a fact. Learn to live with it. |
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157 | |
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158 | I hope this helps :) |
66 | |
159 | |
67 | OBJECT-ORIENTED INTERFACE |
160 | OBJECT-ORIENTED INTERFACE |
68 | The object oriented interface lets you configure your own encoding or |
161 | The object oriented interface lets you configure your own encoding or |
69 | decoding style, within the limits of supported formats. |
162 | decoding style, within the limits of supported formats. |
70 | |
163 | |
… | |
… | |
74 | *disabled*. |
167 | *disabled*. |
75 | |
168 | |
76 | The mutators for flags all return the JSON object again and thus |
169 | The mutators for flags all return the JSON object again and thus |
77 | calls can be chained: |
170 | calls can be chained: |
78 | |
171 | |
79 | my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) |
172 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
80 | => {"a": [1, 2]} |
173 | => {"a": [1, 2]} |
81 | |
174 | |
82 | $json = $json->ascii ($enable) |
175 | $json = $json->ascii ([$enable]) |
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176 | $enabled = $json->get_ascii |
83 | If $enable is true, then the "encode" method will not generate |
177 | If $enable is true (or missing), then the "encode" method will not |
84 | characters outside the code range 0..127. Any unicode characters |
178 | generate characters outside the code range 0..127 (which is ASCII). |
85 | outside that range will be escaped using either a single \uXXXX (BMP |
179 | Any Unicode characters outside that range will be escaped using |
86 | characters) or a double \uHHHH\uLLLLL escape sequence, as per |
180 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
87 | RFC4627. |
181 | escape sequence, as per RFC4627. The resulting encoded JSON text can |
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182 | be treated as a native Unicode string, an ascii-encoded, |
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183 | latin1-encoded or UTF-8 encoded string, or any other superset of |
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184 | ASCII. |
88 | |
185 | |
89 | If $enable is false, then the "encode" method will not escape |
186 | If $enable is false, then the "encode" method will not escape |
90 | Unicode characters unless necessary. |
187 | Unicode characters unless required by the JSON syntax or other |
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188 | flags. This results in a faster and more compact format. |
91 | |
189 | |
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190 | The main use for this flag is to produce JSON texts that can be |
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191 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
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192 | contain any 8 bit characters. |
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193 | |
92 | JSON::XS->new->ascii (1)->encode (chr 0x10401) |
194 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
93 | => \ud801\udc01 |
195 | => ["\ud801\udc01"] |
94 | |
196 | |
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197 | $json = $json->latin1 ([$enable]) |
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198 | $enabled = $json->get_latin1 |
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199 | If $enable is true (or missing), then the "encode" method will |
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200 | encode the resulting JSON text as latin1 (or iso-8859-1), escaping |
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201 | any characters outside the code range 0..255. The resulting string |
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202 | can be treated as a latin1-encoded JSON text or a native Unicode |
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203 | string. The "decode" method will not be affected in any way by this |
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204 | flag, as "decode" by default expects Unicode, which is a strict |
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205 | superset of latin1. |
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206 | |
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207 | If $enable is false, then the "encode" method will not escape |
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208 | Unicode characters unless required by the JSON syntax or other |
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209 | flags. |
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210 | |
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211 | The main use for this flag is efficiently encoding binary data as |
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212 | JSON text, as most octets will not be escaped, resulting in a |
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213 | smaller encoded size. The disadvantage is that the resulting JSON |
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214 | text is encoded in latin1 (and must correctly be treated as such |
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215 | when storing and transferring), a rare encoding for JSON. It is |
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216 | therefore most useful when you want to store data structures known |
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217 | to contain binary data efficiently in files or databases, not when |
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218 | talking to other JSON encoders/decoders. |
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219 | |
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220 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
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221 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
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222 | |
95 | $json = $json->utf8 ($enable) |
223 | $json = $json->utf8 ([$enable]) |
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224 | $enabled = $json->get_utf8 |
96 | If $enable is true, then the "encode" method will encode the JSON |
225 | If $enable is true (or missing), then the "encode" method will |
97 | string into UTF-8, as required by many protocols, while the "decode" |
226 | encode the JSON result into UTF-8, as required by many protocols, |
98 | method expects to be handled an UTF-8-encoded string. Please note |
227 | 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 |
228 | 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. |
229 | characters outside the range 0..255, they are thus useful for |
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230 | bytewise/binary I/O. In future versions, enabling this option might |
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231 | enable autodetection of the UTF-16 and UTF-32 encoding families, as |
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232 | described in RFC4627. |
101 | |
233 | |
102 | If $enable is false, then the "encode" method will return the JSON |
234 | If $enable is false, then the "encode" method will return the JSON |
103 | string as a (non-encoded) unicode string, while "decode" expects |
235 | 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 |
236 | 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. |
237 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
106 | |
238 | |
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239 | Example, output UTF-16BE-encoded JSON: |
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240 | |
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241 | use Encode; |
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242 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
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243 | |
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244 | Example, decode UTF-32LE-encoded JSON: |
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245 | |
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246 | use Encode; |
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247 | $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); |
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248 | |
107 | $json = $json->pretty ($enable) |
249 | $json = $json->pretty ([$enable]) |
108 | This enables (or disables) all of the "indent", "space_before" and |
250 | 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 |
251 | "space_after" (and in the future possibly more) flags in one call to |
110 | generate the most readable (or most compact) form possible. |
252 | generate the most readable (or most compact) form possible. |
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253 | |
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254 | Example, pretty-print some simple structure: |
111 | |
255 | |
112 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
256 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
113 | => |
257 | => |
114 | { |
258 | { |
115 | "a" : [ |
259 | "a" : [ |
116 | 1, |
260 | 1, |
117 | 2 |
261 | 2 |
118 | ] |
262 | ] |
119 | } |
263 | } |
120 | |
264 | |
121 | $json = $json->indent ($enable) |
265 | $json = $json->indent ([$enable]) |
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266 | $enabled = $json->get_indent |
122 | If $enable is true, then the "encode" method will use a multiline |
267 | If $enable is true (or missing), then the "encode" method will use a |
123 | format as output, putting every array member or object/hash |
268 | multiline format as output, putting every array member or |
124 | key-value pair into its own line, identing them properly. |
269 | object/hash key-value pair into its own line, indenting them |
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270 | properly. |
125 | |
271 | |
126 | If $enable is false, no newlines or indenting will be produced, and |
272 | If $enable is false, no newlines or indenting will be produced, and |
127 | the resulting JSON strings is guarenteed not to contain any |
273 | the resulting JSON text is guaranteed not to contain any "newlines". |
128 | "newlines". |
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129 | |
274 | |
130 | This setting has no effect when decoding JSON strings. |
275 | This setting has no effect when decoding JSON texts. |
131 | |
276 | |
132 | $json = $json->space_before ($enable) |
277 | $json = $json->space_before ([$enable]) |
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278 | $enabled = $json->get_space_before |
133 | If $enable is true, then the "encode" method will add an extra |
279 | If $enable is true (or missing), then the "encode" method will add |
134 | optional space before the ":" separating keys from values in JSON |
280 | an extra optional space before the ":" separating keys from values |
135 | objects. |
281 | in JSON objects. |
136 | |
282 | |
137 | If $enable is false, then the "encode" method will not add any extra |
283 | If $enable is false, then the "encode" method will not add any extra |
138 | space at those places. |
284 | space at those places. |
139 | |
285 | |
140 | This setting has no effect when decoding JSON strings. You will also |
286 | This setting has no effect when decoding JSON texts. You will also |
141 | most likely combine this setting with "space_after". |
287 | most likely combine this setting with "space_after". |
142 | |
288 | |
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289 | Example, space_before enabled, space_after and indent disabled: |
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290 | |
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291 | {"key" :"value"} |
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292 | |
143 | $json = $json->space_after ($enable) |
293 | $json = $json->space_after ([$enable]) |
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294 | $enabled = $json->get_space_after |
144 | If $enable is true, then the "encode" method will add an extra |
295 | If $enable is true (or missing), then the "encode" method will add |
145 | optional space after the ":" separating keys from values in JSON |
296 | an extra optional space after the ":" separating keys from values in |
146 | objects and extra whitespace after the "," separating key-value |
297 | JSON objects and extra whitespace after the "," separating key-value |
147 | pairs and array members. |
298 | pairs and array members. |
148 | |
299 | |
149 | If $enable is false, then the "encode" method will not add any extra |
300 | If $enable is false, then the "encode" method will not add any extra |
150 | space at those places. |
301 | space at those places. |
151 | |
302 | |
152 | This setting has no effect when decoding JSON strings. |
303 | This setting has no effect when decoding JSON texts. |
153 | |
304 | |
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305 | Example, space_before and indent disabled, space_after enabled: |
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306 | |
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307 | {"key": "value"} |
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308 | |
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309 | $json = $json->relaxed ([$enable]) |
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310 | $enabled = $json->get_relaxed |
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311 | If $enable is true (or missing), then "decode" will accept some |
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312 | extensions to normal JSON syntax (see below). "encode" will not be |
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313 | affected in anyway. *Be aware that this option makes you accept |
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314 | invalid JSON texts as if they were valid!*. I suggest only to use |
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315 | this option to parse application-specific files written by humans |
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316 | (configuration files, resource files etc.) |
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317 | |
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318 | If $enable is false (the default), then "decode" will only accept |
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319 | valid JSON texts. |
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320 | |
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321 | Currently accepted extensions are: |
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322 | |
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323 | * list items can have an end-comma |
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324 | JSON *separates* array elements and key-value pairs with commas. |
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325 | This can be annoying if you write JSON texts manually and want |
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326 | to be able to quickly append elements, so this extension accepts |
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327 | comma at the end of such items not just between them: |
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328 | |
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329 | [ |
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330 | 1, |
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331 | 2, <- this comma not normally allowed |
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332 | ] |
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333 | { |
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334 | "k1": "v1", |
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335 | "k2": "v2", <- this comma not normally allowed |
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336 | } |
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337 | |
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338 | * shell-style '#'-comments |
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339 | Whenever JSON allows whitespace, shell-style comments are |
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340 | additionally allowed. They are terminated by the first |
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341 | carriage-return or line-feed character, after which more |
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342 | white-space and comments are allowed. |
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343 | |
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344 | [ |
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345 | 1, # this comment not allowed in JSON |
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346 | # neither this one... |
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347 | ] |
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348 | |
154 | $json = $json->canonical ($enable) |
349 | $json = $json->canonical ([$enable]) |
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350 | $enabled = $json->get_canonical |
155 | If $enable is true, then the "encode" method will output JSON |
351 | If $enable is true (or missing), then the "encode" method will |
156 | objects by sorting their keys. This is adding a comparatively high |
352 | output JSON objects by sorting their keys. This is adding a |
157 | overhead. |
353 | comparatively high overhead. |
158 | |
354 | |
159 | If $enable is false, then the "encode" method will output key-value |
355 | If $enable is false, then the "encode" method will output key-value |
160 | pairs in the order Perl stores them (which will likely change |
356 | pairs in the order Perl stores them (which will likely change |
161 | between runs of the same script). |
357 | between runs of the same script). |
162 | |
358 | |
163 | This option is useful if you want the same data structure to be |
359 | This option is useful if you want the same data structure to be |
164 | encoded as the same JSON string (given the same overall settings). |
360 | encoded as the same JSON text (given the same overall settings). If |
165 | If it is disabled, the same hash migh be encoded differently even if |
361 | it is disabled, the same hash might be encoded differently even if |
166 | contains the same data, as key-value pairs have no inherent ordering |
362 | contains the same data, as key-value pairs have no inherent ordering |
167 | in Perl. |
363 | in Perl. |
168 | |
364 | |
169 | This setting has no effect when decoding JSON strings. |
365 | This setting has no effect when decoding JSON texts. |
170 | |
366 | |
171 | $json = $json->allow_nonref ($enable) |
367 | $json = $json->allow_nonref ([$enable]) |
|
|
368 | $enabled = $json->get_allow_nonref |
172 | If $enable is true, then the "encode" method can convert a |
369 | If $enable is true (or missing), then the "encode" method can |
173 | non-reference into its corresponding string, number or null JSON |
370 | convert a non-reference into its corresponding string, number or |
174 | value, which is an extension to RFC4627. Likewise, "decode" will |
371 | null JSON value, which is an extension to RFC4627. Likewise, |
175 | accept those JSON values instead of croaking. |
372 | "decode" will accept those JSON values instead of croaking. |
176 | |
373 | |
177 | If $enable is false, then the "encode" method will croak if it isn't |
374 | 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 |
375 | passed an arrayref or hashref, as JSON texts must either be an |
179 | object or array. Likewise, "decode" will croak if given something |
376 | object or array. Likewise, "decode" will croak if given something |
180 | that is not a JSON object or array. |
377 | that is not a JSON object or array. |
181 | |
378 | |
|
|
379 | Example, encode a Perl scalar as JSON value with enabled |
|
|
380 | "allow_nonref", resulting in an invalid JSON text: |
|
|
381 | |
|
|
382 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
|
|
383 | => "Hello, World!" |
|
|
384 | |
|
|
385 | $json = $json->allow_blessed ([$enable]) |
|
|
386 | $enabled = $json->get_allow_blessed |
|
|
387 | If $enable is true (or missing), then the "encode" method will not |
|
|
388 | barf when it encounters a blessed reference. Instead, the value of |
|
|
389 | the convert_blessed option will decide whether "null" |
|
|
390 | ("convert_blessed" disabled or no "TO_JSON" method found) or a |
|
|
391 | representation of the object ("convert_blessed" enabled and |
|
|
392 | "TO_JSON" method found) is being encoded. Has no effect on "decode". |
|
|
393 | |
|
|
394 | If $enable is false (the default), then "encode" will throw an |
|
|
395 | exception when it encounters a blessed object. |
|
|
396 | |
|
|
397 | $json = $json->convert_blessed ([$enable]) |
|
|
398 | $enabled = $json->get_convert_blessed |
|
|
399 | If $enable is true (or missing), then "encode", upon encountering a |
|
|
400 | blessed object, will check for the availability of the "TO_JSON" |
|
|
401 | method on the object's class. If found, it will be called in scalar |
|
|
402 | context and the resulting scalar will be encoded instead of the |
|
|
403 | object. If no "TO_JSON" method is found, the value of |
|
|
404 | "allow_blessed" will decide what to do. |
|
|
405 | |
|
|
406 | The "TO_JSON" method may safely call die if it wants. If "TO_JSON" |
|
|
407 | returns other blessed objects, those will be handled in the same |
|
|
408 | way. "TO_JSON" must take care of not causing an endless recursion |
|
|
409 | cycle (== crash) in this case. The name of "TO_JSON" was chosen |
|
|
410 | because other methods called by the Perl core (== not by the user of |
|
|
411 | the object) are usually in upper case letters and to avoid |
|
|
412 | collisions with the "to_json" function. |
|
|
413 | |
|
|
414 | This setting does not yet influence "decode" in any way, but in the |
|
|
415 | future, global hooks might get installed that influence "decode" and |
|
|
416 | are enabled by this setting. |
|
|
417 | |
|
|
418 | If $enable is false, then the "allow_blessed" setting will decide |
|
|
419 | what to do when a blessed object is found. |
|
|
420 | |
|
|
421 | $json = $json->filter_json_object ([$coderef->($hashref)]) |
|
|
422 | When $coderef is specified, it will be called from "decode" each |
|
|
423 | time it decodes a JSON object. The only argument is a reference to |
|
|
424 | the newly-created hash. If the code references returns a single |
|
|
425 | scalar (which need not be a reference), this value (i.e. a copy of |
|
|
426 | that scalar to avoid aliasing) is inserted into the deserialised |
|
|
427 | data structure. If it returns an empty list (NOTE: *not* "undef", |
|
|
428 | which is a valid scalar), the original deserialised hash will be |
|
|
429 | inserted. This setting can slow down decoding considerably. |
|
|
430 | |
|
|
431 | When $coderef is omitted or undefined, any existing callback will be |
|
|
432 | removed and "decode" will not change the deserialised hash in any |
|
|
433 | way. |
|
|
434 | |
|
|
435 | Example, convert all JSON objects into the integer 5: |
|
|
436 | |
|
|
437 | my $js = JSON::XS->new->filter_json_object (sub { 5 }); |
|
|
438 | # returns [5] |
|
|
439 | $js->decode ('[{}]') |
|
|
440 | # throw an exception because allow_nonref is not enabled |
|
|
441 | # so a lone 5 is not allowed. |
|
|
442 | $js->decode ('{"a":1, "b":2}'); |
|
|
443 | |
|
|
444 | $json = $json->filter_json_single_key_object ($key [=> |
|
|
445 | $coderef->($value)]) |
|
|
446 | Works remotely similar to "filter_json_object", but is only called |
|
|
447 | for JSON objects having a single key named $key. |
|
|
448 | |
|
|
449 | This $coderef is called before the one specified via |
|
|
450 | "filter_json_object", if any. It gets passed the single value in the |
|
|
451 | JSON object. If it returns a single value, it will be inserted into |
|
|
452 | the data structure. If it returns nothing (not even "undef" but the |
|
|
453 | empty list), the callback from "filter_json_object" will be called |
|
|
454 | next, as if no single-key callback were specified. |
|
|
455 | |
|
|
456 | If $coderef is omitted or undefined, the corresponding callback will |
|
|
457 | be disabled. There can only ever be one callback for a given key. |
|
|
458 | |
|
|
459 | As this callback gets called less often then the |
|
|
460 | "filter_json_object" one, decoding speed will not usually suffer as |
|
|
461 | much. Therefore, single-key objects make excellent targets to |
|
|
462 | serialise Perl objects into, especially as single-key JSON objects |
|
|
463 | are as close to the type-tagged value concept as JSON gets (it's |
|
|
464 | basically an ID/VALUE tuple). Of course, JSON does not support this |
|
|
465 | in any way, so you need to make sure your data never looks like a |
|
|
466 | serialised Perl hash. |
|
|
467 | |
|
|
468 | Typical names for the single object key are "__class_whatever__", or |
|
|
469 | "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even |
|
|
470 | things like "__class_md5sum(classname)__", to reduce the risk of |
|
|
471 | clashing with real hashes. |
|
|
472 | |
|
|
473 | Example, decode JSON objects of the form "{ "__widget__" => <id> }" |
|
|
474 | into the corresponding $WIDGET{<id>} object: |
|
|
475 | |
|
|
476 | # return whatever is in $WIDGET{5}: |
|
|
477 | JSON::XS |
|
|
478 | ->new |
|
|
479 | ->filter_json_single_key_object (__widget__ => sub { |
|
|
480 | $WIDGET{ $_[0] } |
|
|
481 | }) |
|
|
482 | ->decode ('{"__widget__": 5') |
|
|
483 | |
|
|
484 | # this can be used with a TO_JSON method in some "widget" class |
|
|
485 | # for serialisation to json: |
|
|
486 | sub WidgetBase::TO_JSON { |
|
|
487 | my ($self) = @_; |
|
|
488 | |
|
|
489 | unless ($self->{id}) { |
|
|
490 | $self->{id} = ..get..some..id..; |
|
|
491 | $WIDGET{$self->{id}} = $self; |
|
|
492 | } |
|
|
493 | |
|
|
494 | { __widget__ => $self->{id} } |
|
|
495 | } |
|
|
496 | |
|
|
497 | $json = $json->shrink ([$enable]) |
|
|
498 | $enabled = $json->get_shrink |
|
|
499 | Perl usually over-allocates memory a bit when allocating space for |
|
|
500 | strings. This flag optionally resizes strings generated by either |
|
|
501 | "encode" or "decode" to their minimum size possible. This can save |
|
|
502 | memory when your JSON texts are either very very long or you have |
|
|
503 | many short strings. It will also try to downgrade any strings to |
|
|
504 | octet-form if possible: perl stores strings internally either in an |
|
|
505 | encoding called UTF-X or in octet-form. The latter cannot store |
|
|
506 | everything but uses less space in general (and some buggy Perl or C |
|
|
507 | code might even rely on that internal representation being used). |
|
|
508 | |
|
|
509 | The actual definition of what shrink does might change in future |
|
|
510 | versions, but it will always try to save space at the expense of |
|
|
511 | time. |
|
|
512 | |
|
|
513 | If $enable is true (or missing), the string returned by "encode" |
|
|
514 | will be shrunk-to-fit, while all strings generated by "decode" will |
|
|
515 | also be shrunk-to-fit. |
|
|
516 | |
|
|
517 | If $enable is false, then the normal perl allocation algorithms are |
|
|
518 | used. If you work with your data, then this is likely to be faster. |
|
|
519 | |
|
|
520 | In the future, this setting might control other things, such as |
|
|
521 | converting strings that look like integers or floats into integers |
|
|
522 | or floats internally (there is no difference on the Perl level), |
|
|
523 | saving space. |
|
|
524 | |
|
|
525 | $json = $json->max_depth ([$maximum_nesting_depth]) |
|
|
526 | $max_depth = $json->get_max_depth |
|
|
527 | Sets the maximum nesting level (default 512) accepted while encoding |
|
|
528 | or decoding. If the JSON text or Perl data structure has an equal or |
|
|
529 | higher nesting level then this limit, then the encoder and decoder |
|
|
530 | will stop and croak at that point. |
|
|
531 | |
|
|
532 | Nesting level is defined by number of hash- or arrayrefs that the |
|
|
533 | encoder needs to traverse to reach a given point or the number of |
|
|
534 | "{" or "[" characters without their matching closing parenthesis |
|
|
535 | crossed to reach a given character in a string. |
|
|
536 | |
|
|
537 | Setting the maximum depth to one disallows any nesting, so that |
|
|
538 | ensures that the object is only a single hash/object or array. |
|
|
539 | |
|
|
540 | The argument to "max_depth" will be rounded up to the next highest |
|
|
541 | power of two. If no argument is given, the highest possible setting |
|
|
542 | will be used, which is rarely useful. |
|
|
543 | |
|
|
544 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
|
|
545 | useful. |
|
|
546 | |
|
|
547 | $json = $json->max_size ([$maximum_string_size]) |
|
|
548 | $max_size = $json->get_max_size |
|
|
549 | Set the maximum length a JSON text may have (in bytes) where |
|
|
550 | decoding is being attempted. The default is 0, meaning no limit. |
|
|
551 | When "decode" is called on a string longer then this number of |
|
|
552 | characters it will not attempt to decode the string but throw an |
|
|
553 | exception. This setting has no effect on "encode" (yet). |
|
|
554 | |
|
|
555 | The argument to "max_size" will be rounded up to the next highest |
|
|
556 | power of two (so may be more than requested). If no argument is |
|
|
557 | given, the limit check will be deactivated (same as when 0 is |
|
|
558 | specified). |
|
|
559 | |
|
|
560 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
|
|
561 | useful. |
|
|
562 | |
182 | $json_string = $json->encode ($perl_scalar) |
563 | $json_text = $json->encode ($perl_scalar) |
183 | Converts the given Perl data structure (a simple scalar or a |
564 | Converts the given Perl data structure (a simple scalar or a |
184 | reference to a hash or array) to its JSON representation. Simple |
565 | reference to a hash or array) to its JSON representation. Simple |
185 | scalars will be converted into JSON string or number sequences, |
566 | scalars will be converted into JSON string or number sequences, |
186 | while references to arrays become JSON arrays and references to |
567 | while references to arrays become JSON arrays and references to |
187 | hashes become JSON objects. Undefined Perl values (e.g. "undef") |
568 | hashes become JSON objects. Undefined Perl values (e.g. "undef") |
188 | become JSON "null" values. Neither "true" nor "false" values will be |
569 | become JSON "null" values. Neither "true" nor "false" values will be |
189 | generated. |
570 | generated. |
190 | |
571 | |
191 | $perl_scalar = $json->decode ($json_string) |
572 | $perl_scalar = $json->decode ($json_text) |
192 | The opposite of "encode": expects a JSON string and tries to parse |
573 | The opposite of "encode": expects a JSON text and tries to parse it, |
193 | it, returning the resulting simple scalar or reference. Croaks on |
574 | returning the resulting simple scalar or reference. Croaks on error. |
194 | error. |
|
|
195 | |
575 | |
196 | JSON numbers and strings become simple Perl scalars. JSON arrays |
576 | JSON numbers and strings become simple Perl scalars. JSON arrays |
197 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
577 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
198 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
578 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
|
|
579 | |
|
|
580 | ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
|
|
581 | This works like the "decode" method, but instead of raising an |
|
|
582 | exception when there is trailing garbage after the first JSON |
|
|
583 | object, it will silently stop parsing there and return the number of |
|
|
584 | characters consumed so far. |
|
|
585 | |
|
|
586 | This is useful if your JSON texts are not delimited by an outer |
|
|
587 | protocol (which is not the brightest thing to do in the first place) |
|
|
588 | and you need to know where the JSON text ends. |
|
|
589 | |
|
|
590 | JSON::XS->new->decode_prefix ("[1] the tail") |
|
|
591 | => ([], 3) |
|
|
592 | |
|
|
593 | MAPPING |
|
|
594 | This section describes how JSON::XS maps Perl values to JSON values and |
|
|
595 | vice versa. These mappings are designed to "do the right thing" in most |
|
|
596 | circumstances automatically, preserving round-tripping characteristics |
|
|
597 | (what you put in comes out as something equivalent). |
|
|
598 | |
|
|
599 | For the more enlightened: note that in the following descriptions, |
|
|
600 | lowercase *perl* refers to the Perl interpreter, while uppercase *Perl* |
|
|
601 | refers to the abstract Perl language itself. |
|
|
602 | |
|
|
603 | JSON -> PERL |
|
|
604 | object |
|
|
605 | A JSON object becomes a reference to a hash in Perl. No ordering of |
|
|
606 | object keys is preserved (JSON does not preserve object key ordering |
|
|
607 | itself). |
|
|
608 | |
|
|
609 | array |
|
|
610 | A JSON array becomes a reference to an array in Perl. |
|
|
611 | |
|
|
612 | string |
|
|
613 | A JSON string becomes a string scalar in Perl - Unicode codepoints |
|
|
614 | in JSON are represented by the same codepoints in the Perl string, |
|
|
615 | so no manual decoding is necessary. |
|
|
616 | |
|
|
617 | number |
|
|
618 | A JSON number becomes either an integer, numeric (floating point) or |
|
|
619 | string scalar in perl, depending on its range and any fractional |
|
|
620 | parts. On the Perl level, there is no difference between those as |
|
|
621 | Perl handles all the conversion details, but an integer may take |
|
|
622 | slightly less memory and might represent more values exactly than |
|
|
623 | (floating point) numbers. |
|
|
624 | |
|
|
625 | If the number consists of digits only, JSON::XS will try to |
|
|
626 | represent it as an integer value. If that fails, it will try to |
|
|
627 | represent it as a numeric (floating point) value if that is possible |
|
|
628 | without loss of precision. Otherwise it will preserve the number as |
|
|
629 | a string value. |
|
|
630 | |
|
|
631 | Numbers containing a fractional or exponential part will always be |
|
|
632 | represented as numeric (floating point) values, possibly at a loss |
|
|
633 | of precision. |
|
|
634 | |
|
|
635 | This might create round-tripping problems as numbers might become |
|
|
636 | strings, but as Perl is typeless there is no other way to do it. |
|
|
637 | |
|
|
638 | true, false |
|
|
639 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
|
|
640 | respectively. They are overloaded to act almost exactly like the |
|
|
641 | numbers 1 and 0. You can check whether a scalar is a JSON boolean by |
|
|
642 | using the "JSON::XS::is_bool" function. |
|
|
643 | |
|
|
644 | null |
|
|
645 | A JSON null atom becomes "undef" in Perl. |
|
|
646 | |
|
|
647 | PERL -> JSON |
|
|
648 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
|
|
649 | truly typeless language, so we can only guess which JSON type is meant |
|
|
650 | by a Perl value. |
|
|
651 | |
|
|
652 | hash references |
|
|
653 | Perl hash references become JSON objects. As there is no inherent |
|
|
654 | ordering in hash keys (or JSON objects), they will usually be |
|
|
655 | encoded in a pseudo-random order that can change between runs of the |
|
|
656 | same program but stays generally the same within a single run of a |
|
|
657 | program. JSON::XS can optionally sort the hash keys (determined by |
|
|
658 | the *canonical* flag), so the same datastructure will serialise to |
|
|
659 | the same JSON text (given same settings and version of JSON::XS), |
|
|
660 | but this incurs a runtime overhead and is only rarely useful, e.g. |
|
|
661 | when you want to compare some JSON text against another for |
|
|
662 | equality. |
|
|
663 | |
|
|
664 | array references |
|
|
665 | Perl array references become JSON arrays. |
|
|
666 | |
|
|
667 | other references |
|
|
668 | Other unblessed references are generally not allowed and will cause |
|
|
669 | an exception to be thrown, except for references to the integers 0 |
|
|
670 | and 1, which get turned into "false" and "true" atoms in JSON. You |
|
|
671 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
|
|
672 | readability. |
|
|
673 | |
|
|
674 | to_json [\0,JSON::XS::true] # yields [false,true] |
|
|
675 | |
|
|
676 | JSON::XS::true, JSON::XS::false |
|
|
677 | These special values become JSON true and JSON false values, |
|
|
678 | respectively. You can also use "\1" and "\0" directly if you want. |
|
|
679 | |
|
|
680 | blessed objects |
|
|
681 | Blessed objects are not allowed. JSON::XS currently tries to encode |
|
|
682 | their underlying representation (hash- or arrayref), but this |
|
|
683 | behaviour might change in future versions. |
|
|
684 | |
|
|
685 | simple scalars |
|
|
686 | Simple Perl scalars (any scalar that is not a reference) are the |
|
|
687 | most difficult objects to encode: JSON::XS will encode undefined |
|
|
688 | scalars as JSON null value, scalars that have last been used in a |
|
|
689 | string context before encoding as JSON strings and anything else as |
|
|
690 | number value: |
|
|
691 | |
|
|
692 | # dump as number |
|
|
693 | to_json [2] # yields [2] |
|
|
694 | to_json [-3.0e17] # yields [-3e+17] |
|
|
695 | my $value = 5; to_json [$value] # yields [5] |
|
|
696 | |
|
|
697 | # used as string, so dump as string |
|
|
698 | print $value; |
|
|
699 | to_json [$value] # yields ["5"] |
|
|
700 | |
|
|
701 | # undef becomes null |
|
|
702 | to_json [undef] # yields [null] |
|
|
703 | |
|
|
704 | You can force the type to be a JSON string by stringifying it: |
|
|
705 | |
|
|
706 | my $x = 3.1; # some variable containing a number |
|
|
707 | "$x"; # stringified |
|
|
708 | $x .= ""; # another, more awkward way to stringify |
|
|
709 | print $x; # perl does it for you, too, quite often |
|
|
710 | |
|
|
711 | You can force the type to be a JSON number by numifying it: |
|
|
712 | |
|
|
713 | my $x = "3"; # some variable containing a string |
|
|
714 | $x += 0; # numify it, ensuring it will be dumped as a number |
|
|
715 | $x *= 1; # same thing, the choice is yours. |
|
|
716 | |
|
|
717 | You can not currently force the type in other, less obscure, ways. |
|
|
718 | Tell me if you need this capability. |
199 | |
719 | |
200 | COMPARISON |
720 | COMPARISON |
201 | As already mentioned, this module was created because none of the |
721 | As already mentioned, this module was created because none of the |
202 | existing JSON modules could be made to work correctly. First I will |
722 | existing JSON modules could be made to work correctly. First I will |
203 | describe the problems (or pleasures) I encountered with various existing |
723 | describe the problems (or pleasures) I encountered with various existing |
204 | JSON modules, followed by some benchmark values. JSON::XS was designed |
724 | JSON modules, followed by some benchmark values. JSON::XS was designed |
205 | not to suffer from any of these problems or limitations. |
725 | not to suffer from any of these problems or limitations. |
206 | |
726 | |
207 | JSON |
727 | JSON 1.07 |
208 | Slow (but very portable, as it is written in pure Perl). |
728 | Slow (but very portable, as it is written in pure Perl). |
209 | |
729 | |
210 | Undocumented/buggy Unicode handling (how JSON handles unicode values |
730 | Undocumented/buggy Unicode handling (how JSON handles Unicode values |
211 | is undocumented. One can get far by feeding it unicode strings and |
731 | is undocumented. One can get far by feeding it Unicode strings and |
212 | doing en-/decoding oneself, but unicode escapes are not working |
732 | doing en-/decoding oneself, but Unicode escapes are not working |
213 | properly). |
733 | properly). |
214 | |
734 | |
215 | No roundtripping (strings get clobbered if they look like numbers, |
735 | No round-tripping (strings get clobbered if they look like numbers, |
216 | e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that |
736 | e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that |
217 | will decode into the number 2. |
737 | will decode into the number 2. |
218 | |
738 | |
219 | JSON::PC |
739 | JSON::PC 0.01 |
220 | Very fast. |
740 | Very fast. |
221 | |
741 | |
222 | Undocumented/buggy Unicode handling. |
742 | Undocumented/buggy Unicode handling. |
223 | |
743 | |
224 | No roundtripping. |
744 | No round-tripping. |
225 | |
745 | |
226 | Has problems handling many Perl values (e.g. regex results and other |
746 | Has problems handling many Perl values (e.g. regex results and other |
227 | magic values will make it croak). |
747 | magic values will make it croak). |
228 | |
748 | |
229 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
749 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
230 | which is not a valid JSON string. |
750 | which is not a valid JSON text. |
231 | |
751 | |
232 | Unmaintained (maintainer unresponsive for many months, bugs are not |
752 | Unmaintained (maintainer unresponsive for many months, bugs are not |
233 | getting fixed). |
753 | getting fixed). |
234 | |
754 | |
235 | JSON::Syck |
755 | JSON::Syck 0.21 |
236 | Very buggy (often crashes). |
756 | Very buggy (often crashes). |
237 | |
757 | |
238 | Very inflexible (no human-readable format supported, format pretty |
758 | Very inflexible (no human-readable format supported, format pretty |
239 | much undocumented. I need at least a format for easy reading by |
759 | much undocumented. I need at least a format for easy reading by |
240 | humans and a single-line compact format for use in a protocol, and |
760 | humans and a single-line compact format for use in a protocol, and |
241 | preferably a way to generate ASCII-only JSON strings). |
761 | preferably a way to generate ASCII-only JSON texts). |
242 | |
762 | |
243 | Completely broken (and confusingly documented) Unicode handling |
763 | Completely broken (and confusingly documented) Unicode handling |
244 | (unicode escapes are not working properly, you need to set |
764 | (Unicode escapes are not working properly, you need to set |
245 | ImplicitUnicode to *different* values on en- and decoding to get |
765 | ImplicitUnicode to *different* values on en- and decoding to get |
246 | symmetric behaviour). |
766 | symmetric behaviour). |
247 | |
767 | |
248 | No roundtripping (simple cases work, but this depends on wether the |
768 | No round-tripping (simple cases work, but this depends on whether |
249 | scalar value was used in a numeric context or not). |
769 | the scalar value was used in a numeric context or not). |
250 | |
770 | |
251 | Dumping hashes may skip hash values depending on iterator state. |
771 | Dumping hashes may skip hash values depending on iterator state. |
252 | |
772 | |
253 | Unmaintained (maintainer unresponsive for many months, bugs are not |
773 | Unmaintained (maintainer unresponsive for many months, bugs are not |
254 | getting fixed). |
774 | getting fixed). |
255 | |
775 | |
256 | Does not check input for validity (i.e. will accept non-JSON input |
776 | Does not check input for validity (i.e. will accept non-JSON input |
257 | and return "something" instead of raising an exception. This is a |
777 | and return "something" instead of raising an exception. This is a |
258 | security issue: imagine two banks transfering money between each |
778 | security issue: imagine two banks transferring money between each |
259 | other using JSON. One bank might parse a given non-JSON request and |
779 | other using JSON. One bank might parse a given non-JSON request and |
260 | deduct money, while the other might reject the transaction with a |
780 | deduct money, while the other might reject the transaction with a |
261 | syntax error. While a good protocol will at least recover, that is |
781 | syntax error. While a good protocol will at least recover, that is |
262 | extra unnecessary work and the transaction will still not succeed). |
782 | extra unnecessary work and the transaction will still not succeed). |
263 | |
783 | |
264 | JSON::DWIW |
784 | JSON::DWIW 0.04 |
265 | Very fast. Very natural. Very nice. |
785 | Very fast. Very natural. Very nice. |
266 | |
786 | |
267 | Undocumented unicode handling (but the best of the pack. Unicode |
787 | Undocumented Unicode handling (but the best of the pack. Unicode |
268 | escapes still don't get parsed properly). |
788 | escapes still don't get parsed properly). |
269 | |
789 | |
270 | Very inflexible. |
790 | Very inflexible. |
271 | |
791 | |
272 | No roundtripping. |
792 | No round-tripping. |
273 | |
793 | |
274 | Does not generate valid JSON (key strings are often unquoted, empty |
794 | Does not generate valid JSON texts (key strings are often unquoted, |
275 | keys result in nothing being output) |
795 | empty keys result in nothing being output) |
276 | |
796 | |
277 | Does not check input for validity. |
797 | Does not check input for validity. |
|
|
798 | |
|
|
799 | JSON and YAML |
|
|
800 | You often hear that JSON is a subset (or a close subset) of YAML. This |
|
|
801 | is, however, a mass hysteria and very far from the truth. In general, |
|
|
802 | there is no way to configure JSON::XS to output a data structure as |
|
|
803 | valid YAML. |
|
|
804 | |
|
|
805 | If you really must use JSON::XS to generate YAML, you should use this |
|
|
806 | algorithm (subject to change in future versions): |
|
|
807 | |
|
|
808 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
|
|
809 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
|
|
810 | |
|
|
811 | This will usually generate JSON texts that also parse as valid YAML. |
|
|
812 | Please note that YAML has hardcoded limits on (simple) object key |
|
|
813 | lengths that JSON doesn't have, so you should make sure that your hash |
|
|
814 | keys are noticeably shorter than the 1024 characters YAML allows. |
|
|
815 | |
|
|
816 | There might be other incompatibilities that I am not aware of. In |
|
|
817 | general you should not try to generate YAML with a JSON generator or |
|
|
818 | vice versa, or try to parse JSON with a YAML parser or vice versa: |
|
|
819 | chances are high that you will run into severe interoperability |
|
|
820 | problems. |
278 | |
821 | |
279 | SPEED |
822 | SPEED |
280 | It seems that JSON::XS is surprisingly fast, as shown in the following |
823 | It seems that JSON::XS is surprisingly fast, as shown in the following |
281 | tables. They have been generated with the help of the "eg/bench" program |
824 | tables. They have been generated with the help of the "eg/bench" program |
282 | in the JSON::XS distribution, to make it easy to compare on your own |
825 | in the JSON::XS distribution, to make it easy to compare on your own |
283 | system. |
826 | system. |
284 | |
827 | |
285 | First is a comparison between various modules using a very simple JSON |
828 | First comes a comparison between various modules using a very short |
|
|
829 | single-line JSON string: |
|
|
830 | |
|
|
831 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
|
|
832 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
|
|
833 | |
286 | string, showing the number of encodes/decodes per second (JSON::XS is |
834 | It shows the number of encodes/decodes per second (JSON::XS uses the |
287 | the functional interface, while JSON::XS/2 is the OO interface with |
835 | functional interface, while JSON::XS/2 uses the OO interface with |
288 | pretty-printing and hashkey sorting enabled). |
836 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
|
|
837 | Higher is better: |
289 | |
838 | |
290 | module | encode | decode | |
839 | module | encode | decode | |
291 | -----------|------------|------------| |
840 | -----------|------------|------------| |
292 | JSON | 14006 | 6820 | |
841 | JSON 1.x | 4990.842 | 4088.813 | |
293 | JSON::DWIW | 200937 | 120386 | |
842 | JSON::DWIW | 51653.990 | 71575.154 | |
294 | JSON::PC | 85065 | 129366 | |
843 | JSON::PC | 65948.176 | 74631.744 | |
295 | JSON::Syck | 59898 | 44232 | |
844 | JSON::PP | 8931.652 | 3817.168 | |
296 | JSON::XS | 1171478 | 342435 | |
845 | JSON::Syck | 24877.248 | 27776.848 | |
297 | JSON::XS/2 | 730760 | 328714 | |
846 | JSON::XS | 388361.481 | 227951.304 | |
|
|
847 | JSON::XS/2 | 227951.304 | 218453.333 | |
|
|
848 | JSON::XS/3 | 338250.323 | 218453.333 | |
|
|
849 | Storable | 16500.016 | 135300.129 | |
298 | -----------+------------+------------+ |
850 | -----------+------------+------------+ |
299 | |
851 | |
300 | That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 |
852 | That is, JSON::XS is about five times faster than JSON::DWIW on |
|
|
853 | encoding, about three times faster on decoding, and over forty times |
301 | times faster than JSON, even with pretty-printing and key sorting. |
854 | faster than JSON, even with pretty-printing and key sorting. It also |
|
|
855 | compares favourably to Storable for small amounts of data. |
302 | |
856 | |
303 | Using a longer test string (roughly 8KB, generated from Yahoo! Locals |
857 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
304 | search API (http://nanoref.com/yahooapis/mgPdGg): |
858 | search API (http://nanoref.com/yahooapis/mgPdGg): |
305 | |
859 | |
306 | module | encode | decode | |
860 | module | encode | decode | |
307 | -----------|------------|------------| |
861 | -----------|------------|------------| |
308 | JSON | 673 | 38 | |
862 | JSON 1.x | 55.260 | 34.971 | |
309 | JSON::DWIW | 5271 | 770 | |
863 | JSON::DWIW | 825.228 | 1082.513 | |
|
|
864 | JSON::PC | 3571.444 | 2394.829 | |
310 | JSON::PC | 9901 | 2491 | |
865 | JSON::PP | 210.987 | 32.574 | |
311 | JSON::Syck | 2360 | 786 | |
866 | JSON::Syck | 552.551 | 787.544 | |
312 | JSON::XS | 37398 | 3202 | |
867 | JSON::XS | 5780.463 | 4854.519 | |
313 | JSON::XS/2 | 13765 | 3153 | |
868 | JSON::XS/2 | 3869.998 | 4798.975 | |
|
|
869 | JSON::XS/3 | 5862.880 | 4798.975 | |
|
|
870 | Storable | 4445.002 | 5235.027 | |
314 | -----------+------------+------------+ |
871 | -----------+------------+------------+ |
315 | |
872 | |
316 | Again, JSON::XS leads by far in the encoding case, while still beating |
873 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
317 | every other module in the decoding case. |
874 | decodes faster). |
318 | |
875 | |
319 | Last example is an almost 8MB large hash with many large binary values |
876 | On large strings containing lots of high Unicode characters, some |
320 | (PNG files), resulting in a lot of escaping: |
877 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
|
|
878 | result will be broken due to missing (or wrong) Unicode handling. Others |
|
|
879 | refuse to decode or encode properly, so it was impossible to prepare a |
|
|
880 | fair comparison table for that case. |
|
|
881 | |
|
|
882 | SECURITY CONSIDERATIONS |
|
|
883 | When you are using JSON in a protocol, talking to untrusted potentially |
|
|
884 | hostile creatures requires relatively few measures. |
|
|
885 | |
|
|
886 | First of all, your JSON decoder should be secure, that is, should not |
|
|
887 | have any buffer overflows. Obviously, this module should ensure that and |
|
|
888 | I am trying hard on making that true, but you never know. |
|
|
889 | |
|
|
890 | Second, you need to avoid resource-starving attacks. That means you |
|
|
891 | should limit the size of JSON texts you accept, or make sure then when |
|
|
892 | your resources run out, that's just fine (e.g. by using a separate |
|
|
893 | process that can crash safely). The size of a JSON text in octets or |
|
|
894 | characters is usually a good indication of the size of the resources |
|
|
895 | required to decode it into a Perl structure. While JSON::XS can check |
|
|
896 | the size of the JSON text, it might be too late when you already have it |
|
|
897 | in memory, so you might want to check the size before you accept the |
|
|
898 | string. |
|
|
899 | |
|
|
900 | Third, JSON::XS recurses using the C stack when decoding objects and |
|
|
901 | arrays. The C stack is a limited resource: for instance, on my amd64 |
|
|
902 | machine with 8MB of stack size I can decode around 180k nested arrays |
|
|
903 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
|
|
904 | croak to free the temporary). If that is exceeded, the program crashes. |
|
|
905 | to be conservative, the default nesting limit is set to 512. If your |
|
|
906 | process has a smaller stack, you should adjust this setting accordingly |
|
|
907 | with the "max_depth" method. |
|
|
908 | |
|
|
909 | And last but least, something else could bomb you that I forgot to think |
|
|
910 | of. In that case, you get to keep the pieces. I am always open for |
|
|
911 | hints, though... |
|
|
912 | |
|
|
913 | If you are using JSON::XS to return packets to consumption by JavaScript |
|
|
914 | scripts in a browser you should have a look at |
|
|
915 | <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
|
|
916 | you are vulnerable to some common attack vectors (which really are |
|
|
917 | browser design bugs, but it is still you who will have to deal with it, |
|
|
918 | as major browser developers care only for features, not about doing |
|
|
919 | security right). |
|
|
920 | |
|
|
921 | THREADS |
|
|
922 | This module is *not* guaranteed to be thread safe and there are no plans |
|
|
923 | to change this until Perl gets thread support (as opposed to the |
|
|
924 | horribly slow so-called "threads" which are simply slow and bloated |
|
|
925 | process simulations - use fork, its *much* faster, cheaper, better). |
|
|
926 | |
|
|
927 | (It might actually work, but you have been warned). |
321 | |
928 | |
322 | BUGS |
929 | BUGS |
323 | While the goal of this module is to be correct, that unfortunately does |
930 | 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 |
931 | 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 |
932 | still relatively early in its development. If you keep reporting bugs |
326 | will be fixed swiftly, though. |
933 | they will be fixed swiftly, though. |
|
|
934 | |
|
|
935 | Please refrain from using rt.cpan.org or any other bug reporting |
|
|
936 | service. I put the contact address into my modules for a reason. |
327 | |
937 | |
328 | AUTHOR |
938 | AUTHOR |
329 | Marc Lehmann <schmorp@schmorp.de> |
939 | Marc Lehmann <schmorp@schmorp.de> |
330 | http://home.schmorp.de/ |
940 | http://home.schmorp.de/ |
331 | |
941 | |