1 | =head1 NAME |
1 | =head1 NAME |
2 | |
2 | |
3 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
3 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
4 | |
4 | |
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5 | =encoding utf-8 |
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6 | |
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7 | JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ |
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8 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
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9 | |
5 | =head1 SYNOPSIS |
10 | =head1 SYNOPSIS |
6 | |
11 | |
7 | use JSON::XS; |
12 | use JSON::XS; |
8 | |
13 | |
9 | # exported functions, croak on error |
14 | # exported functions, they croak on error |
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15 | # and expect/generate UTF-8 |
10 | |
16 | |
11 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
17 | $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref; |
12 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
18 | $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text; |
13 | |
19 | |
14 | # oo-interface |
20 | # OO-interface |
15 | |
21 | |
16 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
22 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
17 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
23 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
18 | $perl_scalar = $coder->decode ($unicode_json_text); |
24 | $perl_scalar = $coder->decode ($unicode_json_text); |
19 | |
25 | |
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26 | # Note that JSON version 2.0 and above will automatically use JSON::XS |
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27 | # if available, at virtually no speed overhead either, so you should |
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28 | # be able to just: |
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29 | |
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30 | use JSON; |
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31 | |
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32 | # and do the same things, except that you have a pure-perl fallback now. |
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33 | |
20 | =head1 DESCRIPTION |
34 | =head1 DESCRIPTION |
21 | |
35 | |
22 | This module converts Perl data structures to JSON and vice versa. Its |
36 | This module converts Perl data structures to JSON and vice versa. Its |
23 | primary goal is to be I<correct> and its secondary goal is to be |
37 | primary goal is to be I<correct> and its secondary goal is to be |
24 | I<fast>. To reach the latter goal it was written in C. |
38 | I<fast>. To reach the latter goal it was written in C. |
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39 | |
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40 | Beginning with version 2.0 of the JSON module, when both JSON and |
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41 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can be |
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42 | overridden) with no overhead due to emulation (by inheriting constructor |
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43 | and methods). If JSON::XS is not available, it will fall back to the |
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44 | compatible JSON::PP module as backend, so using JSON instead of JSON::XS |
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45 | gives you a portable JSON API that can be fast when you need and doesn't |
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46 | require a C compiler when that is a problem. |
25 | |
47 | |
26 | As this is the n-th-something JSON module on CPAN, what was the reason |
48 | As this is the n-th-something JSON module on CPAN, what was the reason |
27 | to write yet another JSON module? While it seems there are many JSON |
49 | to write yet another JSON module? While it seems there are many JSON |
28 | modules, none of them correctly handle all corner cases, and in most cases |
50 | modules, none of them correctly handle all corner cases, and in most cases |
29 | their maintainers are unresponsive, gone missing, or not listening to bug |
51 | their maintainers are unresponsive, gone missing, or not listening to bug |
30 | reports for other reasons. |
52 | reports for other reasons. |
31 | |
53 | |
32 | See COMPARISON, below, for a comparison to some other JSON modules. |
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33 | |
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34 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
54 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
35 | vice versa. |
55 | vice versa. |
36 | |
56 | |
37 | =head2 FEATURES |
57 | =head2 FEATURES |
38 | |
58 | |
39 | =over 4 |
59 | =over 4 |
40 | |
60 | |
41 | =item * correct handling of unicode issues |
61 | =item * correct Unicode handling |
42 | |
62 | |
43 | This module knows how to handle Unicode, and even documents how and when |
63 | This module knows how to handle Unicode, documents how and when it does |
44 | it does so. |
64 | so, and even documents what "correct" means. |
45 | |
65 | |
46 | =item * round-trip integrity |
66 | =item * round-trip integrity |
47 | |
67 | |
48 | When you serialise a perl data structure using only datatypes supported |
68 | When you serialise a perl data structure using only data types supported |
49 | by JSON, the deserialised data structure is identical on the Perl level. |
69 | by JSON, the deserialised data structure is identical on the Perl level. |
50 | (e.g. the string "2.0" doesn't suddenly become "2"). |
70 | (e.g. the string "2.0" doesn't suddenly become "2" just because it looks |
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71 | like a number). There minor I<are> exceptions to this, read the MAPPING |
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72 | section below to learn about those. |
51 | |
73 | |
52 | =item * strict checking of JSON correctness |
74 | =item * strict checking of JSON correctness |
53 | |
75 | |
54 | There is no guessing, no generating of illegal JSON strings by default, |
76 | There is no guessing, no generating of illegal JSON texts by default, |
55 | and only JSON is accepted as input by default (the latter is a security |
77 | and only JSON is accepted as input by default (the latter is a security |
56 | feature). |
78 | feature). |
57 | |
79 | |
58 | =item * fast |
80 | =item * fast |
59 | |
81 | |
60 | Compared to other JSON modules, this module compares favourably in terms |
82 | Compared to other JSON modules and other serialisers such as Storable, |
61 | of speed, too. |
83 | this module usually compares favourably in terms of speed, too. |
62 | |
84 | |
63 | =item * simple to use |
85 | =item * simple to use |
64 | |
86 | |
65 | This module has both a simple functional interface as well as an OO |
87 | This module has both a simple functional interface as well as an object |
66 | interface. |
88 | oriented interface interface. |
67 | |
89 | |
68 | =item * reasonably versatile output formats |
90 | =item * reasonably versatile output formats |
69 | |
91 | |
70 | You can choose between the most compact guarenteed single-line format |
92 | You can choose between the most compact guaranteed-single-line format |
71 | possible (nice for simple line-based protocols), a pure-ascii format (for |
93 | possible (nice for simple line-based protocols), a pure-ASCII format |
72 | when your transport is not 8-bit clean), or a pretty-printed format (for |
94 | (for when your transport is not 8-bit clean, still supports the whole |
73 | when you want to read that stuff). Or you can combine those features in |
95 | Unicode range), or a pretty-printed format (for when you want to read that |
74 | whatever way you like. |
96 | stuff). Or you can combine those features in whatever way you like. |
75 | |
97 | |
76 | =back |
98 | =back |
77 | |
99 | |
78 | =cut |
100 | =cut |
79 | |
101 | |
80 | package JSON::XS; |
102 | package JSON::XS; |
81 | |
103 | |
82 | BEGIN { |
104 | no warnings; |
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105 | use strict; |
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106 | |
83 | $VERSION = '0.3'; |
107 | our $VERSION = '2.24'; |
84 | @ISA = qw(Exporter); |
108 | our @ISA = qw(Exporter); |
85 | |
109 | |
86 | @EXPORT = qw(to_json from_json); |
110 | our @EXPORT = qw(encode_json decode_json to_json from_json); |
87 | require Exporter; |
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88 | |
111 | |
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112 | sub to_json($) { |
89 | require XSLoader; |
113 | require Carp; |
90 | XSLoader::load JSON::XS::, $VERSION; |
114 | Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call"); |
91 | } |
115 | } |
92 | |
116 | |
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117 | sub from_json($) { |
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118 | require Carp; |
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119 | Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call"); |
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120 | } |
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121 | |
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122 | use Exporter; |
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123 | use XSLoader; |
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124 | |
93 | =head1 FUNCTIONAL INTERFACE |
125 | =head1 FUNCTIONAL INTERFACE |
94 | |
126 | |
95 | The following convinience methods are provided by this module. They are |
127 | The following convenience methods are provided by this module. They are |
96 | exported by default: |
128 | exported by default: |
97 | |
129 | |
98 | =over 4 |
130 | =over 4 |
99 | |
131 | |
100 | =item $json_string = to_json $perl_scalar |
132 | =item $json_text = encode_json $perl_scalar |
101 | |
133 | |
102 | Converts the given Perl data structure (a simple scalar or a reference to |
134 | Converts the given Perl data structure to a UTF-8 encoded, binary string |
103 | a hash or array) to a UTF-8 encoded, binary string (that is, the string contains |
135 | (that is, the string contains octets only). Croaks on error. |
104 | octets only). Croaks on error. |
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105 | |
136 | |
106 | This function call is functionally identical to C<< JSON::XS->new->utf8->encode ($perl_scalar) >>. |
137 | This function call is functionally identical to: |
107 | |
138 | |
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139 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
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140 | |
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141 | Except being faster. |
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142 | |
108 | =item $perl_scalar = from_json $json_string |
143 | =item $perl_scalar = decode_json $json_text |
109 | |
144 | |
110 | The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to |
145 | The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries |
111 | parse that as an UTF-8 encoded JSON string, returning the resulting simple |
146 | to parse that as an UTF-8 encoded JSON text, returning the resulting |
112 | scalar or reference. Croaks on error. |
147 | reference. Croaks on error. |
113 | |
148 | |
114 | This function call is functionally identical to C<< JSON::XS->new->utf8->decode ($json_string) >>. |
149 | This function call is functionally identical to: |
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150 | |
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151 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
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152 | |
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153 | Except being faster. |
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154 | |
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155 | =item $is_boolean = JSON::XS::is_bool $scalar |
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156 | |
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157 | Returns true if the passed scalar represents either JSON::XS::true or |
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158 | JSON::XS::false, two constants that act like C<1> and C<0>, respectively |
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159 | and are used to represent JSON C<true> and C<false> values in Perl. |
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160 | |
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161 | See MAPPING, below, for more information on how JSON values are mapped to |
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162 | Perl. |
115 | |
163 | |
116 | =back |
164 | =back |
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165 | |
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166 | |
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167 | =head1 A FEW NOTES ON UNICODE AND PERL |
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168 | |
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169 | Since this often leads to confusion, here are a few very clear words on |
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170 | how Unicode works in Perl, modulo bugs. |
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171 | |
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172 | =over 4 |
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173 | |
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174 | =item 1. Perl strings can store characters with ordinal values > 255. |
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175 | |
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176 | This enables you to store Unicode characters as single characters in a |
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177 | Perl string - very natural. |
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178 | |
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179 | =item 2. Perl does I<not> associate an encoding with your strings. |
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180 | |
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181 | ... until you force it to, e.g. when matching it against a regex, or |
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182 | printing the scalar to a file, in which case Perl either interprets your |
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183 | string as locale-encoded text, octets/binary, or as Unicode, depending |
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184 | on various settings. In no case is an encoding stored together with your |
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185 | data, it is I<use> that decides encoding, not any magical meta data. |
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186 | |
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187 | =item 3. The internal utf-8 flag has no meaning with regards to the |
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188 | encoding of your string. |
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189 | |
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190 | Just ignore that flag unless you debug a Perl bug, a module written in |
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191 | XS or want to dive into the internals of perl. Otherwise it will only |
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192 | confuse you, as, despite the name, it says nothing about how your string |
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193 | is encoded. You can have Unicode strings with that flag set, with that |
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194 | flag clear, and you can have binary data with that flag set and that flag |
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195 | clear. Other possibilities exist, too. |
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196 | |
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197 | If you didn't know about that flag, just the better, pretend it doesn't |
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198 | exist. |
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199 | |
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200 | =item 4. A "Unicode String" is simply a string where each character can be |
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201 | validly interpreted as a Unicode code point. |
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202 | |
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203 | If you have UTF-8 encoded data, it is no longer a Unicode string, but a |
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204 | Unicode string encoded in UTF-8, giving you a binary string. |
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205 | |
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206 | =item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string. |
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207 | |
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208 | It's a fact. Learn to live with it. |
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209 | |
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210 | =back |
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211 | |
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212 | I hope this helps :) |
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213 | |
117 | |
214 | |
118 | =head1 OBJECT-ORIENTED INTERFACE |
215 | =head1 OBJECT-ORIENTED INTERFACE |
119 | |
216 | |
120 | The object oriented interface lets you configure your own encoding or |
217 | The object oriented interface lets you configure your own encoding or |
121 | decoding style, within the limits of supported formats. |
218 | decoding style, within the limits of supported formats. |
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128 | strings. All boolean flags described below are by default I<disabled>. |
225 | strings. All boolean flags described below are by default I<disabled>. |
129 | |
226 | |
130 | The mutators for flags all return the JSON object again and thus calls can |
227 | The mutators for flags all return the JSON object again and thus calls can |
131 | be chained: |
228 | be chained: |
132 | |
229 | |
133 | my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) |
230 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
134 | => {"a": [1, 2]} |
231 | => {"a": [1, 2]} |
135 | |
232 | |
136 | =item $json = $json->ascii ([$enable]) |
233 | =item $json = $json->ascii ([$enable]) |
137 | |
234 | |
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235 | =item $enabled = $json->get_ascii |
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236 | |
138 | If C<$enable> is true (or missing), then the C<encode> method will |
237 | If C<$enable> is true (or missing), then the C<encode> method will not |
139 | not generate characters outside the code range C<0..127>. Any unicode |
238 | generate characters outside the code range C<0..127> (which is ASCII). Any |
140 | characters outside that range will be escaped using either a single |
239 | Unicode characters outside that range will be escaped using either a |
141 | \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per |
240 | single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, |
142 | RFC4627. |
241 | as per RFC4627. The resulting encoded JSON text can be treated as a native |
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242 | Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string, |
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243 | or any other superset of ASCII. |
143 | |
244 | |
144 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
245 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
145 | characters unless necessary. |
246 | characters unless required by the JSON syntax or other flags. This results |
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247 | in a faster and more compact format. |
146 | |
248 | |
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249 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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250 | document. |
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251 | |
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252 | The main use for this flag is to produce JSON texts that can be |
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253 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
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254 | contain any 8 bit characters. |
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255 | |
147 | JSON::XS->new->ascii (1)->encode (chr 0x10401) |
256 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
148 | => \ud801\udc01 |
257 | => ["\ud801\udc01"] |
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258 | |
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259 | =item $json = $json->latin1 ([$enable]) |
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260 | |
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261 | =item $enabled = $json->get_latin1 |
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262 | |
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263 | If C<$enable> is true (or missing), then the C<encode> method will encode |
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264 | the resulting JSON text as latin1 (or iso-8859-1), escaping any characters |
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265 | outside the code range C<0..255>. The resulting string can be treated as a |
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266 | latin1-encoded JSON text or a native Unicode string. The C<decode> method |
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267 | will not be affected in any way by this flag, as C<decode> by default |
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268 | expects Unicode, which is a strict superset of latin1. |
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269 | |
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270 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
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271 | characters unless required by the JSON syntax or other flags. |
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272 | |
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273 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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274 | document. |
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275 | |
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276 | The main use for this flag is efficiently encoding binary data as JSON |
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277 | text, as most octets will not be escaped, resulting in a smaller encoded |
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278 | size. The disadvantage is that the resulting JSON text is encoded |
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279 | in latin1 (and must correctly be treated as such when storing and |
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280 | transferring), a rare encoding for JSON. It is therefore most useful when |
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281 | you want to store data structures known to contain binary data efficiently |
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282 | in files or databases, not when talking to other JSON encoders/decoders. |
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283 | |
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284 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
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285 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
149 | |
286 | |
150 | =item $json = $json->utf8 ([$enable]) |
287 | =item $json = $json->utf8 ([$enable]) |
151 | |
288 | |
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289 | =item $enabled = $json->get_utf8 |
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290 | |
152 | If C<$enable> is true (or missing), then the C<encode> method will encode |
291 | If C<$enable> is true (or missing), then the C<encode> method will encode |
153 | the JSON string into UTF-8, as required by many protocols, while the |
292 | the JSON result into UTF-8, as required by many protocols, while the |
154 | C<decode> method expects to be handled an UTF-8-encoded string. Please |
293 | C<decode> method expects to be handled an UTF-8-encoded string. Please |
155 | note that UTF-8-encoded strings do not contain any characters outside the |
294 | note that UTF-8-encoded strings do not contain any characters outside the |
156 | range C<0..255>, they are thus useful for bytewise/binary I/O. |
295 | range C<0..255>, they are thus useful for bytewise/binary I/O. In future |
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296 | versions, enabling this option might enable autodetection of the UTF-16 |
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297 | and UTF-32 encoding families, as described in RFC4627. |
157 | |
298 | |
158 | If C<$enable> is false, then the C<encode> method will return the JSON |
299 | If C<$enable> is false, then the C<encode> method will return the JSON |
159 | string as a (non-encoded) unicode string, while C<decode> expects thus a |
300 | string as a (non-encoded) Unicode string, while C<decode> expects thus a |
160 | unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
301 | Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
161 | to be done yourself, e.g. using the Encode module. |
302 | to be done yourself, e.g. using the Encode module. |
162 | |
303 | |
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304 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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305 | document. |
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306 | |
163 | Example, output UTF-16-encoded JSON: |
307 | Example, output UTF-16BE-encoded JSON: |
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308 | |
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309 | use Encode; |
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310 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
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311 | |
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312 | Example, decode UTF-32LE-encoded JSON: |
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313 | |
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314 | use Encode; |
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315 | $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); |
164 | |
316 | |
165 | =item $json = $json->pretty ([$enable]) |
317 | =item $json = $json->pretty ([$enable]) |
166 | |
318 | |
167 | This enables (or disables) all of the C<indent>, C<space_before> and |
319 | This enables (or disables) all of the C<indent>, C<space_before> and |
168 | C<space_after> (and in the future possibly more) flags in one call to |
320 | C<space_after> (and in the future possibly more) flags in one call to |
… | |
… | |
179 | ] |
331 | ] |
180 | } |
332 | } |
181 | |
333 | |
182 | =item $json = $json->indent ([$enable]) |
334 | =item $json = $json->indent ([$enable]) |
183 | |
335 | |
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336 | =item $enabled = $json->get_indent |
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337 | |
184 | If C<$enable> is true (or missing), then the C<encode> method will use a multiline |
338 | If C<$enable> is true (or missing), then the C<encode> method will use a multiline |
185 | format as output, putting every array member or object/hash key-value pair |
339 | format as output, putting every array member or object/hash key-value pair |
186 | into its own line, identing them properly. |
340 | into its own line, indenting them properly. |
187 | |
341 | |
188 | If C<$enable> is false, no newlines or indenting will be produced, and the |
342 | If C<$enable> is false, no newlines or indenting will be produced, and the |
189 | resulting JSON strings is guarenteed not to contain any C<newlines>. |
343 | resulting JSON text is guaranteed not to contain any C<newlines>. |
190 | |
344 | |
191 | This setting has no effect when decoding JSON strings. |
345 | This setting has no effect when decoding JSON texts. |
192 | |
346 | |
193 | =item $json = $json->space_before ([$enable]) |
347 | =item $json = $json->space_before ([$enable]) |
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348 | |
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349 | =item $enabled = $json->get_space_before |
194 | |
350 | |
195 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
351 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
196 | optional space before the C<:> separating keys from values in JSON objects. |
352 | optional space before the C<:> separating keys from values in JSON objects. |
197 | |
353 | |
198 | If C<$enable> is false, then the C<encode> method will not add any extra |
354 | If C<$enable> is false, then the C<encode> method will not add any extra |
199 | space at those places. |
355 | space at those places. |
200 | |
356 | |
201 | This setting has no effect when decoding JSON strings. You will also most |
357 | This setting has no effect when decoding JSON texts. You will also |
202 | likely combine this setting with C<space_after>. |
358 | most likely combine this setting with C<space_after>. |
203 | |
359 | |
204 | Example, space_before enabled, space_after and indent disabled: |
360 | Example, space_before enabled, space_after and indent disabled: |
205 | |
361 | |
206 | {"key" :"value"} |
362 | {"key" :"value"} |
207 | |
363 | |
208 | =item $json = $json->space_after ([$enable]) |
364 | =item $json = $json->space_after ([$enable]) |
|
|
365 | |
|
|
366 | =item $enabled = $json->get_space_after |
209 | |
367 | |
210 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
368 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
211 | optional space after the C<:> separating keys from values in JSON objects |
369 | optional space after the C<:> separating keys from values in JSON objects |
212 | and extra whitespace after the C<,> separating key-value pairs and array |
370 | and extra whitespace after the C<,> separating key-value pairs and array |
213 | members. |
371 | members. |
214 | |
372 | |
215 | If C<$enable> is false, then the C<encode> method will not add any extra |
373 | If C<$enable> is false, then the C<encode> method will not add any extra |
216 | space at those places. |
374 | space at those places. |
217 | |
375 | |
218 | This setting has no effect when decoding JSON strings. |
376 | This setting has no effect when decoding JSON texts. |
219 | |
377 | |
220 | Example, space_before and indent disabled, space_after enabled: |
378 | Example, space_before and indent disabled, space_after enabled: |
221 | |
379 | |
222 | {"key": "value"} |
380 | {"key": "value"} |
223 | |
381 | |
|
|
382 | =item $json = $json->relaxed ([$enable]) |
|
|
383 | |
|
|
384 | =item $enabled = $json->get_relaxed |
|
|
385 | |
|
|
386 | If C<$enable> is true (or missing), then C<decode> will accept some |
|
|
387 | extensions to normal JSON syntax (see below). C<encode> will not be |
|
|
388 | affected in anyway. I<Be aware that this option makes you accept invalid |
|
|
389 | JSON texts as if they were valid!>. I suggest only to use this option to |
|
|
390 | parse application-specific files written by humans (configuration files, |
|
|
391 | resource files etc.) |
|
|
392 | |
|
|
393 | If C<$enable> is false (the default), then C<decode> will only accept |
|
|
394 | valid JSON texts. |
|
|
395 | |
|
|
396 | Currently accepted extensions are: |
|
|
397 | |
|
|
398 | =over 4 |
|
|
399 | |
|
|
400 | =item * list items can have an end-comma |
|
|
401 | |
|
|
402 | JSON I<separates> array elements and key-value pairs with commas. This |
|
|
403 | can be annoying if you write JSON texts manually and want to be able to |
|
|
404 | quickly append elements, so this extension accepts comma at the end of |
|
|
405 | such items not just between them: |
|
|
406 | |
|
|
407 | [ |
|
|
408 | 1, |
|
|
409 | 2, <- this comma not normally allowed |
|
|
410 | ] |
|
|
411 | { |
|
|
412 | "k1": "v1", |
|
|
413 | "k2": "v2", <- this comma not normally allowed |
|
|
414 | } |
|
|
415 | |
|
|
416 | =item * shell-style '#'-comments |
|
|
417 | |
|
|
418 | Whenever JSON allows whitespace, shell-style comments are additionally |
|
|
419 | allowed. They are terminated by the first carriage-return or line-feed |
|
|
420 | character, after which more white-space and comments are allowed. |
|
|
421 | |
|
|
422 | [ |
|
|
423 | 1, # this comment not allowed in JSON |
|
|
424 | # neither this one... |
|
|
425 | ] |
|
|
426 | |
|
|
427 | =back |
|
|
428 | |
224 | =item $json = $json->canonical ([$enable]) |
429 | =item $json = $json->canonical ([$enable]) |
|
|
430 | |
|
|
431 | =item $enabled = $json->get_canonical |
225 | |
432 | |
226 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
433 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
227 | by sorting their keys. This is adding a comparatively high overhead. |
434 | by sorting their keys. This is adding a comparatively high overhead. |
228 | |
435 | |
229 | If C<$enable> is false, then the C<encode> method will output key-value |
436 | If C<$enable> is false, then the C<encode> method will output key-value |
230 | pairs in the order Perl stores them (which will likely change between runs |
437 | pairs in the order Perl stores them (which will likely change between runs |
231 | of the same script). |
438 | of the same script). |
232 | |
439 | |
233 | This option is useful if you want the same data structure to be encoded as |
440 | This option is useful if you want the same data structure to be encoded as |
234 | the same JSON string (given the same overall settings). If it is disabled, |
441 | the same JSON text (given the same overall settings). If it is disabled, |
235 | the same hash migh be encoded differently even if contains the same data, |
442 | the same hash might be encoded differently even if contains the same data, |
236 | as key-value pairs have no inherent ordering in Perl. |
443 | as key-value pairs have no inherent ordering in Perl. |
237 | |
444 | |
238 | This setting has no effect when decoding JSON strings. |
445 | This setting has no effect when decoding JSON texts. |
239 | |
446 | |
240 | =item $json = $json->allow_nonref ([$enable]) |
447 | =item $json = $json->allow_nonref ([$enable]) |
|
|
448 | |
|
|
449 | =item $enabled = $json->get_allow_nonref |
241 | |
450 | |
242 | If C<$enable> is true (or missing), then the C<encode> method can convert a |
451 | If C<$enable> is true (or missing), then the C<encode> method can convert a |
243 | non-reference into its corresponding string, number or null JSON value, |
452 | non-reference into its corresponding string, number or null JSON value, |
244 | which is an extension to RFC4627. Likewise, C<decode> will accept those JSON |
453 | which is an extension to RFC4627. Likewise, C<decode> will accept those JSON |
245 | values instead of croaking. |
454 | values instead of croaking. |
246 | |
455 | |
247 | If C<$enable> is false, then the C<encode> method will croak if it isn't |
456 | If C<$enable> is false, then the C<encode> method will croak if it isn't |
248 | passed an arrayref or hashref, as JSON strings must either be an object |
457 | passed an arrayref or hashref, as JSON texts must either be an object |
249 | or array. Likewise, C<decode> will croak if given something that is not a |
458 | or array. Likewise, C<decode> will croak if given something that is not a |
250 | JSON object or array. |
459 | JSON object or array. |
251 | |
460 | |
252 | Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, |
461 | Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, |
253 | resulting in an invalid JSON text: |
462 | resulting in an invalid JSON text: |
254 | |
463 | |
255 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
464 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
256 | => "Hello, World!" |
465 | => "Hello, World!" |
257 | |
466 | |
|
|
467 | =item $json = $json->allow_unknown ([$enable]) |
|
|
468 | |
|
|
469 | =item $enabled = $json->get_allow_unknown |
|
|
470 | |
|
|
471 | If C<$enable> is true (or missing), then C<encode> will I<not> throw an |
|
|
472 | exception when it encounters values it cannot represent in JSON (for |
|
|
473 | example, filehandles) but instead will encode a JSON C<null> value. Note |
|
|
474 | that blessed objects are not included here and are handled separately by |
|
|
475 | c<allow_nonref>. |
|
|
476 | |
|
|
477 | If C<$enable> is false (the default), then C<encode> will throw an |
|
|
478 | exception when it encounters anything it cannot encode as JSON. |
|
|
479 | |
|
|
480 | This option does not affect C<decode> in any way, and it is recommended to |
|
|
481 | leave it off unless you know your communications partner. |
|
|
482 | |
|
|
483 | =item $json = $json->allow_blessed ([$enable]) |
|
|
484 | |
|
|
485 | =item $enabled = $json->get_allow_blessed |
|
|
486 | |
|
|
487 | If C<$enable> is true (or missing), then the C<encode> method will not |
|
|
488 | barf when it encounters a blessed reference. Instead, the value of the |
|
|
489 | B<convert_blessed> option will decide whether C<null> (C<convert_blessed> |
|
|
490 | disabled or no C<TO_JSON> method found) or a representation of the |
|
|
491 | object (C<convert_blessed> enabled and C<TO_JSON> method found) is being |
|
|
492 | encoded. Has no effect on C<decode>. |
|
|
493 | |
|
|
494 | If C<$enable> is false (the default), then C<encode> will throw an |
|
|
495 | exception when it encounters a blessed object. |
|
|
496 | |
|
|
497 | =item $json = $json->convert_blessed ([$enable]) |
|
|
498 | |
|
|
499 | =item $enabled = $json->get_convert_blessed |
|
|
500 | |
|
|
501 | If C<$enable> is true (or missing), then C<encode>, upon encountering a |
|
|
502 | blessed object, will check for the availability of the C<TO_JSON> method |
|
|
503 | on the object's class. If found, it will be called in scalar context |
|
|
504 | and the resulting scalar will be encoded instead of the object. If no |
|
|
505 | C<TO_JSON> method is found, the value of C<allow_blessed> will decide what |
|
|
506 | to do. |
|
|
507 | |
|
|
508 | The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> |
|
|
509 | returns other blessed objects, those will be handled in the same |
|
|
510 | way. C<TO_JSON> must take care of not causing an endless recursion cycle |
|
|
511 | (== crash) in this case. The name of C<TO_JSON> was chosen because other |
|
|
512 | methods called by the Perl core (== not by the user of the object) are |
|
|
513 | usually in upper case letters and to avoid collisions with any C<to_json> |
|
|
514 | function or method. |
|
|
515 | |
|
|
516 | This setting does not yet influence C<decode> in any way, but in the |
|
|
517 | future, global hooks might get installed that influence C<decode> and are |
|
|
518 | enabled by this setting. |
|
|
519 | |
|
|
520 | If C<$enable> is false, then the C<allow_blessed> setting will decide what |
|
|
521 | to do when a blessed object is found. |
|
|
522 | |
|
|
523 | =item $json = $json->filter_json_object ([$coderef->($hashref)]) |
|
|
524 | |
|
|
525 | When C<$coderef> is specified, it will be called from C<decode> each |
|
|
526 | time it decodes a JSON object. The only argument is a reference to the |
|
|
527 | newly-created hash. If the code references returns a single scalar (which |
|
|
528 | need not be a reference), this value (i.e. a copy of that scalar to avoid |
|
|
529 | aliasing) is inserted into the deserialised data structure. If it returns |
|
|
530 | an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the |
|
|
531 | original deserialised hash will be inserted. This setting can slow down |
|
|
532 | decoding considerably. |
|
|
533 | |
|
|
534 | When C<$coderef> is omitted or undefined, any existing callback will |
|
|
535 | be removed and C<decode> will not change the deserialised hash in any |
|
|
536 | way. |
|
|
537 | |
|
|
538 | Example, convert all JSON objects into the integer 5: |
|
|
539 | |
|
|
540 | my $js = JSON::XS->new->filter_json_object (sub { 5 }); |
|
|
541 | # returns [5] |
|
|
542 | $js->decode ('[{}]') |
|
|
543 | # throw an exception because allow_nonref is not enabled |
|
|
544 | # so a lone 5 is not allowed. |
|
|
545 | $js->decode ('{"a":1, "b":2}'); |
|
|
546 | |
|
|
547 | =item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)]) |
|
|
548 | |
|
|
549 | Works remotely similar to C<filter_json_object>, but is only called for |
|
|
550 | JSON objects having a single key named C<$key>. |
|
|
551 | |
|
|
552 | This C<$coderef> is called before the one specified via |
|
|
553 | C<filter_json_object>, if any. It gets passed the single value in the JSON |
|
|
554 | object. If it returns a single value, it will be inserted into the data |
|
|
555 | structure. If it returns nothing (not even C<undef> but the empty list), |
|
|
556 | the callback from C<filter_json_object> will be called next, as if no |
|
|
557 | single-key callback were specified. |
|
|
558 | |
|
|
559 | If C<$coderef> is omitted or undefined, the corresponding callback will be |
|
|
560 | disabled. There can only ever be one callback for a given key. |
|
|
561 | |
|
|
562 | As this callback gets called less often then the C<filter_json_object> |
|
|
563 | one, decoding speed will not usually suffer as much. Therefore, single-key |
|
|
564 | objects make excellent targets to serialise Perl objects into, especially |
|
|
565 | as single-key JSON objects are as close to the type-tagged value concept |
|
|
566 | as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not |
|
|
567 | support this in any way, so you need to make sure your data never looks |
|
|
568 | like a serialised Perl hash. |
|
|
569 | |
|
|
570 | Typical names for the single object key are C<__class_whatever__>, or |
|
|
571 | C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even |
|
|
572 | things like C<__class_md5sum(classname)__>, to reduce the risk of clashing |
|
|
573 | with real hashes. |
|
|
574 | |
|
|
575 | Example, decode JSON objects of the form C<< { "__widget__" => <id> } >> |
|
|
576 | into the corresponding C<< $WIDGET{<id>} >> object: |
|
|
577 | |
|
|
578 | # return whatever is in $WIDGET{5}: |
|
|
579 | JSON::XS |
|
|
580 | ->new |
|
|
581 | ->filter_json_single_key_object (__widget__ => sub { |
|
|
582 | $WIDGET{ $_[0] } |
|
|
583 | }) |
|
|
584 | ->decode ('{"__widget__": 5') |
|
|
585 | |
|
|
586 | # this can be used with a TO_JSON method in some "widget" class |
|
|
587 | # for serialisation to json: |
|
|
588 | sub WidgetBase::TO_JSON { |
|
|
589 | my ($self) = @_; |
|
|
590 | |
|
|
591 | unless ($self->{id}) { |
|
|
592 | $self->{id} = ..get..some..id..; |
|
|
593 | $WIDGET{$self->{id}} = $self; |
|
|
594 | } |
|
|
595 | |
|
|
596 | { __widget__ => $self->{id} } |
|
|
597 | } |
|
|
598 | |
258 | =item $json = $json->shrink ([$enable]) |
599 | =item $json = $json->shrink ([$enable]) |
259 | |
600 | |
|
|
601 | =item $enabled = $json->get_shrink |
|
|
602 | |
260 | Perl usually over-allocates memory a bit when allocating space for |
603 | Perl usually over-allocates memory a bit when allocating space for |
261 | strings. This flag optionally resizes strings generated by either |
604 | strings. This flag optionally resizes strings generated by either |
262 | C<encode> or C<decode> to their minimum size possible. This can save |
605 | C<encode> or C<decode> to their minimum size possible. This can save |
263 | memory when your JSON strings are either very very long or you have many |
606 | memory when your JSON texts are either very very long or you have many |
264 | short strings. It will also try to downgrade any strings to octet-form |
607 | short strings. It will also try to downgrade any strings to octet-form |
265 | if possible: perl stores strings internally either in an encoding called |
608 | if possible: perl stores strings internally either in an encoding called |
266 | UTF-X or in octet-form. The latter cannot store everything but uses less |
609 | UTF-X or in octet-form. The latter cannot store everything but uses less |
267 | space in general. |
610 | space in general (and some buggy Perl or C code might even rely on that |
|
|
611 | internal representation being used). |
268 | |
612 | |
|
|
613 | The actual definition of what shrink does might change in future versions, |
|
|
614 | but it will always try to save space at the expense of time. |
|
|
615 | |
269 | If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit, |
616 | If C<$enable> is true (or missing), the string returned by C<encode> will |
270 | while all strings generated by C<decode> will also be shrunk-to-fit. |
617 | be shrunk-to-fit, while all strings generated by C<decode> will also be |
|
|
618 | shrunk-to-fit. |
271 | |
619 | |
272 | If C<$enable> is false, then the normal perl allocation algorithms are used. |
620 | If C<$enable> is false, then the normal perl allocation algorithms are used. |
273 | If you work with your data, then this is likely to be faster. |
621 | If you work with your data, then this is likely to be faster. |
274 | |
622 | |
275 | In the future, this setting might control other things, such as converting |
623 | In the future, this setting might control other things, such as converting |
276 | strings that look like integers or floats into integers or floats |
624 | strings that look like integers or floats into integers or floats |
277 | internally (there is no difference on the Perl level), saving space. |
625 | internally (there is no difference on the Perl level), saving space. |
278 | |
626 | |
|
|
627 | =item $json = $json->max_depth ([$maximum_nesting_depth]) |
|
|
628 | |
|
|
629 | =item $max_depth = $json->get_max_depth |
|
|
630 | |
|
|
631 | Sets the maximum nesting level (default C<512>) accepted while encoding |
|
|
632 | or decoding. If a higher nesting level is detected in JSON text or a Perl |
|
|
633 | data structure, then the encoder and decoder will stop and croak at that |
|
|
634 | point. |
|
|
635 | |
|
|
636 | Nesting level is defined by number of hash- or arrayrefs that the encoder |
|
|
637 | needs to traverse to reach a given point or the number of C<{> or C<[> |
|
|
638 | characters without their matching closing parenthesis crossed to reach a |
|
|
639 | given character in a string. |
|
|
640 | |
|
|
641 | Setting the maximum depth to one disallows any nesting, so that ensures |
|
|
642 | that the object is only a single hash/object or array. |
|
|
643 | |
|
|
644 | If no argument is given, the highest possible setting will be used, which |
|
|
645 | is rarely useful. |
|
|
646 | |
|
|
647 | Note that nesting is implemented by recursion in C. The default value has |
|
|
648 | been chosen to be as large as typical operating systems allow without |
|
|
649 | crashing. |
|
|
650 | |
|
|
651 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
|
|
652 | |
|
|
653 | =item $json = $json->max_size ([$maximum_string_size]) |
|
|
654 | |
|
|
655 | =item $max_size = $json->get_max_size |
|
|
656 | |
|
|
657 | Set the maximum length a JSON text may have (in bytes) where decoding is |
|
|
658 | being attempted. The default is C<0>, meaning no limit. When C<decode> |
|
|
659 | is called on a string that is longer then this many bytes, it will not |
|
|
660 | attempt to decode the string but throw an exception. This setting has no |
|
|
661 | effect on C<encode> (yet). |
|
|
662 | |
|
|
663 | If no argument is given, the limit check will be deactivated (same as when |
|
|
664 | C<0> is specified). |
|
|
665 | |
|
|
666 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
|
|
667 | |
279 | =item $json_string = $json->encode ($perl_scalar) |
668 | =item $json_text = $json->encode ($perl_scalar) |
280 | |
669 | |
281 | Converts the given Perl data structure (a simple scalar or a reference |
670 | Converts the given Perl data structure (a simple scalar or a reference |
282 | to a hash or array) to its JSON representation. Simple scalars will be |
671 | to a hash or array) to its JSON representation. Simple scalars will be |
283 | converted into JSON string or number sequences, while references to arrays |
672 | converted into JSON string or number sequences, while references to arrays |
284 | become JSON arrays and references to hashes become JSON objects. Undefined |
673 | become JSON arrays and references to hashes become JSON objects. Undefined |
285 | Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
674 | Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
286 | nor C<false> values will be generated. |
675 | nor C<false> values will be generated. |
287 | |
676 | |
288 | =item $perl_scalar = $json->decode ($json_string) |
677 | =item $perl_scalar = $json->decode ($json_text) |
289 | |
678 | |
290 | The opposite of C<encode>: expects a JSON string and tries to parse it, |
679 | The opposite of C<encode>: expects a JSON text and tries to parse it, |
291 | returning the resulting simple scalar or reference. Croaks on error. |
680 | returning the resulting simple scalar or reference. Croaks on error. |
292 | |
681 | |
293 | JSON numbers and strings become simple Perl scalars. JSON arrays become |
682 | JSON numbers and strings become simple Perl scalars. JSON arrays become |
294 | Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
683 | Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
295 | C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
684 | C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
296 | |
685 | |
|
|
686 | =item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
|
|
687 | |
|
|
688 | This works like the C<decode> method, but instead of raising an exception |
|
|
689 | when there is trailing garbage after the first JSON object, it will |
|
|
690 | silently stop parsing there and return the number of characters consumed |
|
|
691 | so far. |
|
|
692 | |
|
|
693 | This is useful if your JSON texts are not delimited by an outer protocol |
|
|
694 | (which is not the brightest thing to do in the first place) and you need |
|
|
695 | to know where the JSON text ends. |
|
|
696 | |
|
|
697 | JSON::XS->new->decode_prefix ("[1] the tail") |
|
|
698 | => ([], 3) |
|
|
699 | |
297 | =back |
700 | =back |
|
|
701 | |
|
|
702 | |
|
|
703 | =head1 INCREMENTAL PARSING |
|
|
704 | |
|
|
705 | In some cases, there is the need for incremental parsing of JSON |
|
|
706 | texts. While this module always has to keep both JSON text and resulting |
|
|
707 | Perl data structure in memory at one time, it does allow you to parse a |
|
|
708 | JSON stream incrementally. It does so by accumulating text until it has |
|
|
709 | a full JSON object, which it then can decode. This process is similar to |
|
|
710 | using C<decode_prefix> to see if a full JSON object is available, but |
|
|
711 | is much more efficient (and can be implemented with a minimum of method |
|
|
712 | calls). |
|
|
713 | |
|
|
714 | JSON::XS will only attempt to parse the JSON text once it is sure it |
|
|
715 | has enough text to get a decisive result, using a very simple but |
|
|
716 | truly incremental parser. This means that it sometimes won't stop as |
|
|
717 | early as the full parser, for example, it doesn't detect parenthese |
|
|
718 | mismatches. The only thing it guarantees is that it starts decoding as |
|
|
719 | soon as a syntactically valid JSON text has been seen. This means you need |
|
|
720 | to set resource limits (e.g. C<max_size>) to ensure the parser will stop |
|
|
721 | parsing in the presence if syntax errors. |
|
|
722 | |
|
|
723 | The following methods implement this incremental parser. |
|
|
724 | |
|
|
725 | =over 4 |
|
|
726 | |
|
|
727 | =item [void, scalar or list context] = $json->incr_parse ([$string]) |
|
|
728 | |
|
|
729 | This is the central parsing function. It can both append new text and |
|
|
730 | extract objects from the stream accumulated so far (both of these |
|
|
731 | functions are optional). |
|
|
732 | |
|
|
733 | If C<$string> is given, then this string is appended to the already |
|
|
734 | existing JSON fragment stored in the C<$json> object. |
|
|
735 | |
|
|
736 | After that, if the function is called in void context, it will simply |
|
|
737 | return without doing anything further. This can be used to add more text |
|
|
738 | in as many chunks as you want. |
|
|
739 | |
|
|
740 | If the method is called in scalar context, then it will try to extract |
|
|
741 | exactly I<one> JSON object. If that is successful, it will return this |
|
|
742 | object, otherwise it will return C<undef>. If there is a parse error, |
|
|
743 | this method will croak just as C<decode> would do (one can then use |
|
|
744 | C<incr_skip> to skip the errornous part). This is the most common way of |
|
|
745 | using the method. |
|
|
746 | |
|
|
747 | And finally, in list context, it will try to extract as many objects |
|
|
748 | from the stream as it can find and return them, or the empty list |
|
|
749 | otherwise. For this to work, there must be no separators between the JSON |
|
|
750 | objects or arrays, instead they must be concatenated back-to-back. If |
|
|
751 | an error occurs, an exception will be raised as in the scalar context |
|
|
752 | case. Note that in this case, any previously-parsed JSON texts will be |
|
|
753 | lost. |
|
|
754 | |
|
|
755 | =item $lvalue_string = $json->incr_text |
|
|
756 | |
|
|
757 | This method returns the currently stored JSON fragment as an lvalue, that |
|
|
758 | is, you can manipulate it. This I<only> works when a preceding call to |
|
|
759 | C<incr_parse> in I<scalar context> successfully returned an object. Under |
|
|
760 | all other circumstances you must not call this function (I mean it. |
|
|
761 | although in simple tests it might actually work, it I<will> fail under |
|
|
762 | real world conditions). As a special exception, you can also call this |
|
|
763 | method before having parsed anything. |
|
|
764 | |
|
|
765 | This function is useful in two cases: a) finding the trailing text after a |
|
|
766 | JSON object or b) parsing multiple JSON objects separated by non-JSON text |
|
|
767 | (such as commas). |
|
|
768 | |
|
|
769 | =item $json->incr_skip |
|
|
770 | |
|
|
771 | This will reset the state of the incremental parser and will remove |
|
|
772 | the parsed text from the input buffer so far. This is useful after |
|
|
773 | C<incr_parse> died, in which case the input buffer and incremental parser |
|
|
774 | state is left unchanged, to skip the text parsed so far and to reset the |
|
|
775 | parse state. |
|
|
776 | |
|
|
777 | The difference to C<incr_reset> is that only text until the parse error |
|
|
778 | occured is removed. |
|
|
779 | |
|
|
780 | =item $json->incr_reset |
|
|
781 | |
|
|
782 | This completely resets the incremental parser, that is, after this call, |
|
|
783 | it will be as if the parser had never parsed anything. |
|
|
784 | |
|
|
785 | This is useful if you want to repeatedly parse JSON objects and want to |
|
|
786 | ignore any trailing data, which means you have to reset the parser after |
|
|
787 | each successful decode. |
|
|
788 | |
|
|
789 | =back |
|
|
790 | |
|
|
791 | =head2 LIMITATIONS |
|
|
792 | |
|
|
793 | All options that affect decoding are supported, except |
|
|
794 | C<allow_nonref>. The reason for this is that it cannot be made to |
|
|
795 | work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate |
|
|
796 | them back to back and still decode them perfectly. This does not hold true |
|
|
797 | for JSON numbers, however. |
|
|
798 | |
|
|
799 | For example, is the string C<1> a single JSON number, or is it simply the |
|
|
800 | start of C<12>? Or is C<12> a single JSON number, or the concatenation |
|
|
801 | of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS |
|
|
802 | takes the conservative route and disallows this case. |
|
|
803 | |
|
|
804 | =head2 EXAMPLES |
|
|
805 | |
|
|
806 | Some examples will make all this clearer. First, a simple example that |
|
|
807 | works similarly to C<decode_prefix>: We want to decode the JSON object at |
|
|
808 | the start of a string and identify the portion after the JSON object: |
|
|
809 | |
|
|
810 | my $text = "[1,2,3] hello"; |
|
|
811 | |
|
|
812 | my $json = new JSON::XS; |
|
|
813 | |
|
|
814 | my $obj = $json->incr_parse ($text) |
|
|
815 | or die "expected JSON object or array at beginning of string"; |
|
|
816 | |
|
|
817 | my $tail = $json->incr_text; |
|
|
818 | # $tail now contains " hello" |
|
|
819 | |
|
|
820 | Easy, isn't it? |
|
|
821 | |
|
|
822 | Now for a more complicated example: Imagine a hypothetical protocol where |
|
|
823 | you read some requests from a TCP stream, and each request is a JSON |
|
|
824 | array, without any separation between them (in fact, it is often useful to |
|
|
825 | use newlines as "separators", as these get interpreted as whitespace at |
|
|
826 | the start of the JSON text, which makes it possible to test said protocol |
|
|
827 | with C<telnet>...). |
|
|
828 | |
|
|
829 | Here is how you'd do it (it is trivial to write this in an event-based |
|
|
830 | manner): |
|
|
831 | |
|
|
832 | my $json = new JSON::XS; |
|
|
833 | |
|
|
834 | # read some data from the socket |
|
|
835 | while (sysread $socket, my $buf, 4096) { |
|
|
836 | |
|
|
837 | # split and decode as many requests as possible |
|
|
838 | for my $request ($json->incr_parse ($buf)) { |
|
|
839 | # act on the $request |
|
|
840 | } |
|
|
841 | } |
|
|
842 | |
|
|
843 | Another complicated example: Assume you have a string with JSON objects |
|
|
844 | or arrays, all separated by (optional) comma characters (e.g. C<[1],[2], |
|
|
845 | [3]>). To parse them, we have to skip the commas between the JSON texts, |
|
|
846 | and here is where the lvalue-ness of C<incr_text> comes in useful: |
|
|
847 | |
|
|
848 | my $text = "[1],[2], [3]"; |
|
|
849 | my $json = new JSON::XS; |
|
|
850 | |
|
|
851 | # void context, so no parsing done |
|
|
852 | $json->incr_parse ($text); |
|
|
853 | |
|
|
854 | # now extract as many objects as possible. note the |
|
|
855 | # use of scalar context so incr_text can be called. |
|
|
856 | while (my $obj = $json->incr_parse) { |
|
|
857 | # do something with $obj |
|
|
858 | |
|
|
859 | # now skip the optional comma |
|
|
860 | $json->incr_text =~ s/^ \s* , //x; |
|
|
861 | } |
|
|
862 | |
|
|
863 | Now lets go for a very complex example: Assume that you have a gigantic |
|
|
864 | JSON array-of-objects, many gigabytes in size, and you want to parse it, |
|
|
865 | but you cannot load it into memory fully (this has actually happened in |
|
|
866 | the real world :). |
|
|
867 | |
|
|
868 | Well, you lost, you have to implement your own JSON parser. But JSON::XS |
|
|
869 | can still help you: You implement a (very simple) array parser and let |
|
|
870 | JSON decode the array elements, which are all full JSON objects on their |
|
|
871 | own (this wouldn't work if the array elements could be JSON numbers, for |
|
|
872 | example): |
|
|
873 | |
|
|
874 | my $json = new JSON::XS; |
|
|
875 | |
|
|
876 | # open the monster |
|
|
877 | open my $fh, "<bigfile.json" |
|
|
878 | or die "bigfile: $!"; |
|
|
879 | |
|
|
880 | # first parse the initial "[" |
|
|
881 | for (;;) { |
|
|
882 | sysread $fh, my $buf, 65536 |
|
|
883 | or die "read error: $!"; |
|
|
884 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
885 | |
|
|
886 | # Exit the loop once we found and removed(!) the initial "[". |
|
|
887 | # In essence, we are (ab-)using the $json object as a simple scalar |
|
|
888 | # we append data to. |
|
|
889 | last if $json->incr_text =~ s/^ \s* \[ //x; |
|
|
890 | } |
|
|
891 | |
|
|
892 | # now we have the skipped the initial "[", so continue |
|
|
893 | # parsing all the elements. |
|
|
894 | for (;;) { |
|
|
895 | # in this loop we read data until we got a single JSON object |
|
|
896 | for (;;) { |
|
|
897 | if (my $obj = $json->incr_parse) { |
|
|
898 | # do something with $obj |
|
|
899 | last; |
|
|
900 | } |
|
|
901 | |
|
|
902 | # add more data |
|
|
903 | sysread $fh, my $buf, 65536 |
|
|
904 | or die "read error: $!"; |
|
|
905 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
906 | } |
|
|
907 | |
|
|
908 | # in this loop we read data until we either found and parsed the |
|
|
909 | # separating "," between elements, or the final "]" |
|
|
910 | for (;;) { |
|
|
911 | # first skip whitespace |
|
|
912 | $json->incr_text =~ s/^\s*//; |
|
|
913 | |
|
|
914 | # if we find "]", we are done |
|
|
915 | if ($json->incr_text =~ s/^\]//) { |
|
|
916 | print "finished.\n"; |
|
|
917 | exit; |
|
|
918 | } |
|
|
919 | |
|
|
920 | # if we find ",", we can continue with the next element |
|
|
921 | if ($json->incr_text =~ s/^,//) { |
|
|
922 | last; |
|
|
923 | } |
|
|
924 | |
|
|
925 | # if we find anything else, we have a parse error! |
|
|
926 | if (length $json->incr_text) { |
|
|
927 | die "parse error near ", $json->incr_text; |
|
|
928 | } |
|
|
929 | |
|
|
930 | # else add more data |
|
|
931 | sysread $fh, my $buf, 65536 |
|
|
932 | or die "read error: $!"; |
|
|
933 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
934 | } |
|
|
935 | |
|
|
936 | This is a complex example, but most of the complexity comes from the fact |
|
|
937 | that we are trying to be correct (bear with me if I am wrong, I never ran |
|
|
938 | the above example :). |
|
|
939 | |
|
|
940 | |
298 | |
941 | |
299 | =head1 MAPPING |
942 | =head1 MAPPING |
300 | |
943 | |
301 | This section describes how JSON::XS maps Perl values to JSON values and |
944 | This section describes how JSON::XS maps Perl values to JSON values and |
302 | vice versa. These mappings are designed to "do the right thing" in most |
945 | vice versa. These mappings are designed to "do the right thing" in most |
303 | circumstances automatically, preserving round-tripping characteristics |
946 | circumstances automatically, preserving round-tripping characteristics |
304 | (what you put in comes out as something equivalent). |
947 | (what you put in comes out as something equivalent). |
305 | |
948 | |
306 | For the more enlightened: note that in the following descriptions, |
949 | For the more enlightened: note that in the following descriptions, |
307 | lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> |
950 | lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl> |
308 | refers to the abstract Perl language itself. |
951 | refers to the abstract Perl language itself. |
309 | |
952 | |
|
|
953 | |
310 | =head2 JSON -> PERL |
954 | =head2 JSON -> PERL |
311 | |
955 | |
312 | =over 4 |
956 | =over 4 |
313 | |
957 | |
314 | =item object |
958 | =item object |
315 | |
959 | |
316 | A JSON object becomes a reference to a hash in Perl. No ordering of object |
960 | A JSON object becomes a reference to a hash in Perl. No ordering of object |
317 | keys is preserved. |
961 | keys is preserved (JSON does not preserve object key ordering itself). |
318 | |
962 | |
319 | =item array |
963 | =item array |
320 | |
964 | |
321 | A JSON array becomes a reference to an array in Perl. |
965 | A JSON array becomes a reference to an array in Perl. |
322 | |
966 | |
… | |
… | |
326 | are represented by the same codepoints in the Perl string, so no manual |
970 | are represented by the same codepoints in the Perl string, so no manual |
327 | decoding is necessary. |
971 | decoding is necessary. |
328 | |
972 | |
329 | =item number |
973 | =item number |
330 | |
974 | |
331 | A JSON number becomes either an integer or numeric (floating point) |
975 | A JSON number becomes either an integer, numeric (floating point) or |
332 | scalar in perl, depending on its range and any fractional parts. On the |
976 | string scalar in perl, depending on its range and any fractional parts. On |
333 | Perl level, there is no difference between those as Perl handles all the |
977 | the Perl level, there is no difference between those as Perl handles all |
334 | conversion details, but an integer may take slightly less memory and might |
978 | the conversion details, but an integer may take slightly less memory and |
335 | represent more values exactly than (floating point) numbers. |
979 | might represent more values exactly than floating point numbers. |
|
|
980 | |
|
|
981 | If the number consists of digits only, JSON::XS will try to represent |
|
|
982 | it as an integer value. If that fails, it will try to represent it as |
|
|
983 | a numeric (floating point) value if that is possible without loss of |
|
|
984 | precision. Otherwise it will preserve the number as a string value (in |
|
|
985 | which case you lose roundtripping ability, as the JSON number will be |
|
|
986 | re-encoded toa JSON string). |
|
|
987 | |
|
|
988 | Numbers containing a fractional or exponential part will always be |
|
|
989 | represented as numeric (floating point) values, possibly at a loss of |
|
|
990 | precision (in which case you might lose perfect roundtripping ability, but |
|
|
991 | the JSON number will still be re-encoded as a JSON number). |
336 | |
992 | |
337 | =item true, false |
993 | =item true, false |
338 | |
994 | |
339 | These JSON atoms become C<0>, C<1>, respectively. Information is lost in |
995 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
340 | this process. Future versions might represent those values differently, |
996 | respectively. They are overloaded to act almost exactly like the numbers |
341 | but they will be guarenteed to act like these integers would normally in |
997 | C<1> and C<0>. You can check whether a scalar is a JSON boolean by using |
342 | Perl. |
998 | the C<JSON::XS::is_bool> function. |
343 | |
999 | |
344 | =item null |
1000 | =item null |
345 | |
1001 | |
346 | A JSON null atom becomes C<undef> in Perl. |
1002 | A JSON null atom becomes C<undef> in Perl. |
347 | |
1003 | |
348 | =back |
1004 | =back |
|
|
1005 | |
349 | |
1006 | |
350 | =head2 PERL -> JSON |
1007 | =head2 PERL -> JSON |
351 | |
1008 | |
352 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
1009 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
353 | truly typeless language, so we can only guess which JSON type is meant by |
1010 | truly typeless language, so we can only guess which JSON type is meant by |
… | |
… | |
356 | =over 4 |
1013 | =over 4 |
357 | |
1014 | |
358 | =item hash references |
1015 | =item hash references |
359 | |
1016 | |
360 | Perl hash references become JSON objects. As there is no inherent ordering |
1017 | Perl hash references become JSON objects. As there is no inherent ordering |
361 | in hash keys, they will usually be encoded in a pseudo-random order that |
1018 | in hash keys (or JSON objects), they will usually be encoded in a |
362 | can change between runs of the same program but stays generally the same |
1019 | pseudo-random order that can change between runs of the same program but |
363 | within the single run of a program. JSON::XS can optionally sort the hash |
1020 | stays generally the same within a single run of a program. JSON::XS can |
364 | keys (determined by the I<canonical> flag), so the same datastructure |
1021 | optionally sort the hash keys (determined by the I<canonical> flag), so |
365 | will serialise to the same JSON text (given same settings and version of |
1022 | the same datastructure will serialise to the same JSON text (given same |
366 | JSON::XS), but this incurs a runtime overhead. |
1023 | settings and version of JSON::XS), but this incurs a runtime overhead |
|
|
1024 | and is only rarely useful, e.g. when you want to compare some JSON text |
|
|
1025 | against another for equality. |
367 | |
1026 | |
368 | =item array references |
1027 | =item array references |
369 | |
1028 | |
370 | Perl array references become JSON arrays. |
1029 | Perl array references become JSON arrays. |
371 | |
1030 | |
|
|
1031 | =item other references |
|
|
1032 | |
|
|
1033 | Other unblessed references are generally not allowed and will cause an |
|
|
1034 | exception to be thrown, except for references to the integers C<0> and |
|
|
1035 | C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
|
|
1036 | also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
|
|
1037 | |
|
|
1038 | encode_json [\0, JSON::XS::true] # yields [false,true] |
|
|
1039 | |
|
|
1040 | =item JSON::XS::true, JSON::XS::false |
|
|
1041 | |
|
|
1042 | These special values become JSON true and JSON false values, |
|
|
1043 | respectively. You can also use C<\1> and C<\0> directly if you want. |
|
|
1044 | |
372 | =item blessed objects |
1045 | =item blessed objects |
373 | |
1046 | |
374 | Blessed objects are not allowed. JSON::XS currently tries to encode their |
1047 | Blessed objects are not directly representable in JSON. See the |
375 | underlying representation (hash- or arrayref), but this behaviour might |
1048 | C<allow_blessed> and C<convert_blessed> methods on various options on |
376 | change in future versions. |
1049 | how to deal with this: basically, you can choose between throwing an |
|
|
1050 | exception, encoding the reference as if it weren't blessed, or provide |
|
|
1051 | your own serialiser method. |
377 | |
1052 | |
378 | =item simple scalars |
1053 | =item simple scalars |
379 | |
1054 | |
380 | Simple Perl scalars (any scalar that is not a reference) are the most |
1055 | Simple Perl scalars (any scalar that is not a reference) are the most |
381 | difficult objects to encode: JSON::XS will encode undefined scalars as |
1056 | difficult objects to encode: JSON::XS will encode undefined scalars as |
382 | JSON null value, scalars that have last been used in a string context |
1057 | JSON C<null> values, scalars that have last been used in a string context |
383 | before encoding as JSON strings and anything else as number value: |
1058 | before encoding as JSON strings, and anything else as number value: |
384 | |
1059 | |
385 | # dump as number |
1060 | # dump as number |
386 | to_json [2] # yields [2] |
1061 | encode_json [2] # yields [2] |
387 | to_json [-3.0e17] # yields [-3e+17] |
1062 | encode_json [-3.0e17] # yields [-3e+17] |
388 | my $value = 5; to_json [$value] # yields [5] |
1063 | my $value = 5; encode_json [$value] # yields [5] |
389 | |
1064 | |
390 | # used as string, so dump as string |
1065 | # used as string, so dump as string |
391 | print $value; |
1066 | print $value; |
392 | to_json [$value] # yields ["5"] |
1067 | encode_json [$value] # yields ["5"] |
393 | |
1068 | |
394 | # undef becomes null |
1069 | # undef becomes null |
395 | to_json [undef] # yields [null] |
1070 | encode_json [undef] # yields [null] |
396 | |
1071 | |
397 | You can force the type to be a string by stringifying it: |
1072 | You can force the type to be a JSON string by stringifying it: |
398 | |
1073 | |
399 | my $x = 3.1; # some variable containing a number |
1074 | my $x = 3.1; # some variable containing a number |
400 | "$x"; # stringified |
1075 | "$x"; # stringified |
401 | $x .= ""; # another, more awkward way to stringify |
1076 | $x .= ""; # another, more awkward way to stringify |
402 | print $x; # perl does it for you, too, quite often |
1077 | print $x; # perl does it for you, too, quite often |
403 | |
1078 | |
404 | You can force the type to be a number by numifying it: |
1079 | You can force the type to be a JSON number by numifying it: |
405 | |
1080 | |
406 | my $x = "3"; # some variable containing a string |
1081 | my $x = "3"; # some variable containing a string |
407 | $x += 0; # numify it, ensuring it will be dumped as a number |
1082 | $x += 0; # numify it, ensuring it will be dumped as a number |
408 | $x *= 1; # same thing, the choise is yours. |
1083 | $x *= 1; # same thing, the choice is yours. |
409 | |
1084 | |
410 | You can not currently output JSON booleans or force the type in other, |
1085 | You can not currently force the type in other, less obscure, ways. Tell me |
411 | less obscure, ways. Tell me if you need this capability. |
1086 | if you need this capability (but don't forget to explain why it's needed |
412 | |
1087 | :). |
413 | =item circular data structures |
|
|
414 | |
|
|
415 | Those will be encoded until memory or stackspace runs out. |
|
|
416 | |
1088 | |
417 | =back |
1089 | =back |
418 | |
1090 | |
419 | =head1 COMPARISON |
|
|
420 | |
1091 | |
421 | As already mentioned, this module was created because none of the existing |
1092 | =head1 ENCODING/CODESET FLAG NOTES |
422 | JSON modules could be made to work correctly. First I will describe the |
1093 | |
423 | problems (or pleasures) I encountered with various existing JSON modules, |
1094 | The interested reader might have seen a number of flags that signify |
424 | followed by some benchmark values. JSON::XS was designed not to suffer |
1095 | encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be |
425 | from any of these problems or limitations. |
1096 | some confusion on what these do, so here is a short comparison: |
|
|
1097 | |
|
|
1098 | C<utf8> controls whether the JSON text created by C<encode> (and expected |
|
|
1099 | by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only |
|
|
1100 | control whether C<encode> escapes character values outside their respective |
|
|
1101 | codeset range. Neither of these flags conflict with each other, although |
|
|
1102 | some combinations make less sense than others. |
|
|
1103 | |
|
|
1104 | Care has been taken to make all flags symmetrical with respect to |
|
|
1105 | C<encode> and C<decode>, that is, texts encoded with any combination of |
|
|
1106 | these flag values will be correctly decoded when the same flags are used |
|
|
1107 | - in general, if you use different flag settings while encoding vs. when |
|
|
1108 | decoding you likely have a bug somewhere. |
|
|
1109 | |
|
|
1110 | Below comes a verbose discussion of these flags. Note that a "codeset" is |
|
|
1111 | simply an abstract set of character-codepoint pairs, while an encoding |
|
|
1112 | takes those codepoint numbers and I<encodes> them, in our case into |
|
|
1113 | octets. Unicode is (among other things) a codeset, UTF-8 is an encoding, |
|
|
1114 | and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at |
|
|
1115 | the same time, which can be confusing. |
426 | |
1116 | |
427 | =over 4 |
1117 | =over 4 |
428 | |
1118 | |
429 | =item JSON 1.07 |
1119 | =item C<utf8> flag disabled |
430 | |
1120 | |
431 | Slow (but very portable, as it is written in pure Perl). |
1121 | When C<utf8> is disabled (the default), then C<encode>/C<decode> generate |
|
|
1122 | and expect Unicode strings, that is, characters with high ordinal Unicode |
|
|
1123 | values (> 255) will be encoded as such characters, and likewise such |
|
|
1124 | characters are decoded as-is, no canges to them will be done, except |
|
|
1125 | "(re-)interpreting" them as Unicode codepoints or Unicode characters, |
|
|
1126 | respectively (to Perl, these are the same thing in strings unless you do |
|
|
1127 | funny/weird/dumb stuff). |
432 | |
1128 | |
433 | Undocumented/buggy Unicode handling (how JSON handles unicode values is |
1129 | This is useful when you want to do the encoding yourself (e.g. when you |
434 | undocumented. One can get far by feeding it unicode strings and doing |
1130 | want to have UTF-16 encoded JSON texts) or when some other layer does |
435 | en-/decoding oneself, but unicode escapes are not working properly). |
1131 | the encoding for you (for example, when printing to a terminal using a |
|
|
1132 | filehandle that transparently encodes to UTF-8 you certainly do NOT want |
|
|
1133 | to UTF-8 encode your data first and have Perl encode it another time). |
436 | |
1134 | |
437 | No roundtripping (strings get clobbered if they look like numbers, e.g. |
1135 | =item C<utf8> flag enabled |
438 | the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will |
|
|
439 | decode into the number 2. |
|
|
440 | |
1136 | |
441 | =item JSON::PC 0.01 |
1137 | If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all |
|
|
1138 | characters using the corresponding UTF-8 multi-byte sequence, and will |
|
|
1139 | expect your input strings to be encoded as UTF-8, that is, no "character" |
|
|
1140 | of the input string must have any value > 255, as UTF-8 does not allow |
|
|
1141 | that. |
442 | |
1142 | |
443 | Very fast. |
1143 | The C<utf8> flag therefore switches between two modes: disabled means you |
|
|
1144 | will get a Unicode string in Perl, enabled means you get an UTF-8 encoded |
|
|
1145 | octet/binary string in Perl. |
444 | |
1146 | |
445 | Undocumented/buggy Unicode handling. |
1147 | =item C<latin1> or C<ascii> flags enabled |
446 | |
1148 | |
447 | No roundtripping. |
1149 | With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters |
|
|
1150 | with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining |
|
|
1151 | characters as specified by the C<utf8> flag. |
448 | |
1152 | |
449 | Has problems handling many Perl values (e.g. regex results and other magic |
1153 | If C<utf8> is disabled, then the result is also correctly encoded in those |
450 | values will make it croak). |
1154 | character sets (as both are proper subsets of Unicode, meaning that a |
|
|
1155 | Unicode string with all character values < 256 is the same thing as a |
|
|
1156 | ISO-8859-1 string, and a Unicode string with all character values < 128 is |
|
|
1157 | the same thing as an ASCII string in Perl). |
451 | |
1158 | |
452 | Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
1159 | If C<utf8> is enabled, you still get a correct UTF-8-encoded string, |
453 | which is not a valid JSON string. |
1160 | regardless of these flags, just some more characters will be escaped using |
|
|
1161 | C<\uXXXX> then before. |
454 | |
1162 | |
455 | Unmaintained (maintainer unresponsive for many months, bugs are not |
1163 | Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8 |
456 | getting fixed). |
1164 | encoding, while ASCII-encoded strings are. That is because the ISO-8859-1 |
|
|
1165 | encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being |
|
|
1166 | a subset of Unicode), while ASCII is. |
457 | |
1167 | |
458 | =item JSON::Syck 0.21 |
1168 | Surprisingly, C<decode> will ignore these flags and so treat all input |
|
|
1169 | values as governed by the C<utf8> flag. If it is disabled, this allows you |
|
|
1170 | to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of |
|
|
1171 | Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings. |
459 | |
1172 | |
460 | Very buggy (often crashes). |
1173 | So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag - |
|
|
1174 | they only govern when the JSON output engine escapes a character or not. |
461 | |
1175 | |
462 | Very inflexible (no human-readable format supported, format pretty much |
1176 | The main use for C<latin1> is to relatively efficiently store binary data |
463 | undocumented. I need at least a format for easy reading by humans and a |
1177 | as JSON, at the expense of breaking compatibility with most JSON decoders. |
464 | single-line compact format for use in a protocol, and preferably a way to |
|
|
465 | generate ASCII-only JSON strings). |
|
|
466 | |
1178 | |
467 | Completely broken (and confusingly documented) Unicode handling (unicode |
1179 | The main use for C<ascii> is to force the output to not contain characters |
468 | escapes are not working properly, you need to set ImplicitUnicode to |
1180 | with values > 127, which means you can interpret the resulting string |
469 | I<different> values on en- and decoding to get symmetric behaviour). |
1181 | as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and |
470 | |
1182 | 8-bit-encoding, and still get the same data structure back. This is useful |
471 | No roundtripping (simple cases work, but this depends on wether the scalar |
1183 | when your channel for JSON transfer is not 8-bit clean or the encoding |
472 | value was used in a numeric context or not). |
1184 | might be mangled in between (e.g. in mail), and works because ASCII is a |
473 | |
1185 | proper subset of most 8-bit and multibyte encodings in use in the world. |
474 | Dumping hashes may skip hash values depending on iterator state. |
|
|
475 | |
|
|
476 | Unmaintained (maintainer unresponsive for many months, bugs are not |
|
|
477 | getting fixed). |
|
|
478 | |
|
|
479 | Does not check input for validity (i.e. will accept non-JSON input and |
|
|
480 | return "something" instead of raising an exception. This is a security |
|
|
481 | issue: imagine two banks transfering money between each other using |
|
|
482 | JSON. One bank might parse a given non-JSON request and deduct money, |
|
|
483 | while the other might reject the transaction with a syntax error. While a |
|
|
484 | good protocol will at least recover, that is extra unnecessary work and |
|
|
485 | the transaction will still not succeed). |
|
|
486 | |
|
|
487 | =item JSON::DWIW 0.04 |
|
|
488 | |
|
|
489 | Very fast. Very natural. Very nice. |
|
|
490 | |
|
|
491 | Undocumented unicode handling (but the best of the pack. Unicode escapes |
|
|
492 | still don't get parsed properly). |
|
|
493 | |
|
|
494 | Very inflexible. |
|
|
495 | |
|
|
496 | No roundtripping. |
|
|
497 | |
|
|
498 | Does not generate valid JSON (key strings are often unquoted, empty keys |
|
|
499 | result in nothing being output) |
|
|
500 | |
|
|
501 | Does not check input for validity. |
|
|
502 | |
1186 | |
503 | =back |
1187 | =back |
|
|
1188 | |
|
|
1189 | |
|
|
1190 | =head2 JSON and ECMAscript |
|
|
1191 | |
|
|
1192 | JSON syntax is based on how literals are represented in javascript (the |
|
|
1193 | not-standardised predecessor of ECMAscript) which is presumably why it is |
|
|
1194 | called "JavaScript Object Notation". |
|
|
1195 | |
|
|
1196 | However, JSON is not a subset (and also not a superset of course) of |
|
|
1197 | ECMAscript (the standard) or javascript (whatever browsers actually |
|
|
1198 | implement). |
|
|
1199 | |
|
|
1200 | If you want to use javascript's C<eval> function to "parse" JSON, you |
|
|
1201 | might run into parse errors for valid JSON texts, or the resulting data |
|
|
1202 | structure might not be queryable: |
|
|
1203 | |
|
|
1204 | One of the problems is that U+2028 and U+2029 are valid characters inside |
|
|
1205 | JSON strings, but are not allowed in ECMAscript string literals, so the |
|
|
1206 | following Perl fragment will not output something that can be guaranteed |
|
|
1207 | to be parsable by javascript's C<eval>: |
|
|
1208 | |
|
|
1209 | use JSON::XS; |
|
|
1210 | |
|
|
1211 | print encode_json [chr 0x2028]; |
|
|
1212 | |
|
|
1213 | The right fix for this is to use a proper JSON parser in your javascript |
|
|
1214 | programs, and not rely on C<eval> (see for example Douglas Crockford's |
|
|
1215 | F<json2.js> parser). |
|
|
1216 | |
|
|
1217 | If this is not an option, you can, as a stop-gap measure, simply encode to |
|
|
1218 | ASCII-only JSON: |
|
|
1219 | |
|
|
1220 | use JSON::XS; |
|
|
1221 | |
|
|
1222 | print JSON::XS->new->ascii->encode ([chr 0x2028]); |
|
|
1223 | |
|
|
1224 | Note that this will enlarge the resulting JSON text quite a bit if you |
|
|
1225 | have many non-ASCII characters. You might be tempted to run some regexes |
|
|
1226 | to only escape U+2028 and U+2029, e.g.: |
|
|
1227 | |
|
|
1228 | # DO NOT USE THIS! |
|
|
1229 | my $json = JSON::XS->new->utf8->encode ([chr 0x2028]); |
|
|
1230 | $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028 |
|
|
1231 | $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029 |
|
|
1232 | print $json; |
|
|
1233 | |
|
|
1234 | Note that I<this is a bad idea>: the above only works for U+2028 and |
|
|
1235 | U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing |
|
|
1236 | javascript implementations, however, have issues with other characters as |
|
|
1237 | well - using C<eval> naively simply I<will> cause problems. |
|
|
1238 | |
|
|
1239 | Another problem is that some javascript implementations reserve |
|
|
1240 | some property names for their own purposes (which probably makes |
|
|
1241 | them non-ECMAscript-compliant). For example, Iceweasel reserves the |
|
|
1242 | C<__proto__> property name for it's own purposes. |
|
|
1243 | |
|
|
1244 | If that is a problem, you could parse try to filter the resulting JSON |
|
|
1245 | output for these property strings, e.g.: |
|
|
1246 | |
|
|
1247 | $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; |
|
|
1248 | |
|
|
1249 | This works because C<__proto__> is not valid outside of strings, so every |
|
|
1250 | occurence of C<"__proto__"\s*:> must be a string used as property name. |
|
|
1251 | |
|
|
1252 | If you know of other incompatibilities, please let me know. |
|
|
1253 | |
|
|
1254 | |
|
|
1255 | =head2 JSON and YAML |
|
|
1256 | |
|
|
1257 | You often hear that JSON is a subset of YAML. This is, however, a mass |
|
|
1258 | hysteria(*) and very far from the truth (as of the time of this writing), |
|
|
1259 | so let me state it clearly: I<in general, there is no way to configure |
|
|
1260 | JSON::XS to output a data structure as valid YAML> that works in all |
|
|
1261 | cases. |
|
|
1262 | |
|
|
1263 | If you really must use JSON::XS to generate YAML, you should use this |
|
|
1264 | algorithm (subject to change in future versions): |
|
|
1265 | |
|
|
1266 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
|
|
1267 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
|
|
1268 | |
|
|
1269 | This will I<usually> generate JSON texts that also parse as valid |
|
|
1270 | YAML. Please note that YAML has hardcoded limits on (simple) object key |
|
|
1271 | lengths that JSON doesn't have and also has different and incompatible |
|
|
1272 | unicode handling, so you should make sure that your hash keys are |
|
|
1273 | noticeably shorter than the 1024 "stream characters" YAML allows and that |
|
|
1274 | you do not have characters with codepoint values outside the Unicode BMP |
|
|
1275 | (basic multilingual page). YAML also does not allow C<\/> sequences in |
|
|
1276 | strings (which JSON::XS does not I<currently> generate, but other JSON |
|
|
1277 | generators might). |
|
|
1278 | |
|
|
1279 | There might be other incompatibilities that I am not aware of (or the YAML |
|
|
1280 | specification has been changed yet again - it does so quite often). In |
|
|
1281 | general you should not try to generate YAML with a JSON generator or vice |
|
|
1282 | versa, or try to parse JSON with a YAML parser or vice versa: chances are |
|
|
1283 | high that you will run into severe interoperability problems when you |
|
|
1284 | least expect it. |
|
|
1285 | |
|
|
1286 | =over 4 |
|
|
1287 | |
|
|
1288 | =item (*) |
|
|
1289 | |
|
|
1290 | I have been pressured multiple times by Brian Ingerson (one of the |
|
|
1291 | authors of the YAML specification) to remove this paragraph, despite him |
|
|
1292 | acknowledging that the actual incompatibilities exist. As I was personally |
|
|
1293 | bitten by this "JSON is YAML" lie, I refused and said I will continue to |
|
|
1294 | educate people about these issues, so others do not run into the same |
|
|
1295 | problem again and again. After this, Brian called me a (quote)I<complete |
|
|
1296 | and worthless idiot>(unquote). |
|
|
1297 | |
|
|
1298 | In my opinion, instead of pressuring and insulting people who actually |
|
|
1299 | clarify issues with YAML and the wrong statements of some of its |
|
|
1300 | proponents, I would kindly suggest reading the JSON spec (which is not |
|
|
1301 | that difficult or long) and finally make YAML compatible to it, and |
|
|
1302 | educating users about the changes, instead of spreading lies about the |
|
|
1303 | real compatibility for many I<years> and trying to silence people who |
|
|
1304 | point out that it isn't true. |
|
|
1305 | |
|
|
1306 | =back |
|
|
1307 | |
504 | |
1308 | |
505 | =head2 SPEED |
1309 | =head2 SPEED |
506 | |
1310 | |
507 | It seems that JSON::XS is surprisingly fast, as shown in the following |
1311 | It seems that JSON::XS is surprisingly fast, as shown in the following |
508 | tables. They have been generated with the help of the C<eg/bench> program |
1312 | tables. They have been generated with the help of the C<eg/bench> program |
509 | in the JSON::XS distribution, to make it easy to compare on your own |
1313 | in the JSON::XS distribution, to make it easy to compare on your own |
510 | system. |
1314 | system. |
511 | |
1315 | |
512 | First comes a comparison between various modules using a very short JSON |
1316 | First comes a comparison between various modules using |
513 | string (83 bytes), showing the number of encodes/decodes per second |
1317 | a very short single-line JSON string (also available at |
|
|
1318 | L<http://dist.schmorp.de/misc/json/short.json>). |
|
|
1319 | |
|
|
1320 | {"method": "handleMessage", "params": ["user1", |
|
|
1321 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
|
|
1322 | true, false]} |
|
|
1323 | |
|
|
1324 | It shows the number of encodes/decodes per second (JSON::XS uses |
514 | (JSON::XS is the functional interface, while JSON::XS/2 is the OO |
1325 | the functional interface, while JSON::XS/2 uses the OO interface |
515 | interface with pretty-printing and hashkey sorting enabled). Higher is |
1326 | with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables |
516 | better: |
1327 | shrink). Higher is better: |
517 | |
1328 | |
518 | module | encode | decode | |
1329 | module | encode | decode | |
519 | -----------|------------|------------| |
1330 | -----------|------------|------------| |
520 | JSON | 14006 | 6820 | |
1331 | JSON 1.x | 4990.842 | 4088.813 | |
521 | JSON::DWIW | 200937 | 120386 | |
1332 | JSON::DWIW | 51653.990 | 71575.154 | |
522 | JSON::PC | 85065 | 129366 | |
1333 | JSON::PC | 65948.176 | 74631.744 | |
523 | JSON::Syck | 59898 | 44232 | |
1334 | JSON::PP | 8931.652 | 3817.168 | |
524 | JSON::XS | 1171478 | 342435 | |
1335 | JSON::Syck | 24877.248 | 27776.848 | |
525 | JSON::XS/2 | 730760 | 328714 | |
1336 | JSON::XS | 388361.481 | 227951.304 | |
|
|
1337 | JSON::XS/2 | 227951.304 | 218453.333 | |
|
|
1338 | JSON::XS/3 | 338250.323 | 218453.333 | |
|
|
1339 | Storable | 16500.016 | 135300.129 | |
526 | -----------+------------+------------+ |
1340 | -----------+------------+------------+ |
527 | |
1341 | |
528 | That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 |
1342 | That is, JSON::XS is about five times faster than JSON::DWIW on encoding, |
|
|
1343 | about three times faster on decoding, and over forty times faster |
529 | times faster than JSON, even with pretty-printing and key sorting. |
1344 | than JSON, even with pretty-printing and key sorting. It also compares |
|
|
1345 | favourably to Storable for small amounts of data. |
530 | |
1346 | |
531 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1347 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
532 | search API (http://nanoref.com/yahooapis/mgPdGg): |
1348 | search API (L<http://dist.schmorp.de/misc/json/long.json>). |
533 | |
1349 | |
534 | module | encode | decode | |
1350 | module | encode | decode | |
535 | -----------|------------|------------| |
1351 | -----------|------------|------------| |
536 | JSON | 673 | 38 | |
1352 | JSON 1.x | 55.260 | 34.971 | |
537 | JSON::DWIW | 5271 | 770 | |
1353 | JSON::DWIW | 825.228 | 1082.513 | |
538 | JSON::PC | 9901 | 2491 | |
1354 | JSON::PC | 3571.444 | 2394.829 | |
539 | JSON::Syck | 2360 | 786 | |
1355 | JSON::PP | 210.987 | 32.574 | |
540 | JSON::XS | 37398 | 3202 | |
1356 | JSON::Syck | 552.551 | 787.544 | |
541 | JSON::XS/2 | 13765 | 3153 | |
1357 | JSON::XS | 5780.463 | 4854.519 | |
|
|
1358 | JSON::XS/2 | 3869.998 | 4798.975 | |
|
|
1359 | JSON::XS/3 | 5862.880 | 4798.975 | |
|
|
1360 | Storable | 4445.002 | 5235.027 | |
542 | -----------+------------+------------+ |
1361 | -----------+------------+------------+ |
543 | |
1362 | |
544 | Again, JSON::XS leads by far in the encoding case, while still beating |
1363 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
545 | every other module in the decoding case. |
1364 | decodes faster). |
546 | |
1365 | |
547 | On large strings containing lots of unicode characters, some modules |
1366 | On large strings containing lots of high Unicode characters, some modules |
548 | (such as JSON::PC) decode faster than JSON::XS, but the result will be |
1367 | (such as JSON::PC) seem to decode faster than JSON::XS, but the result |
549 | broken due to missing unicode handling. Others refuse to decode or encode |
1368 | will be broken due to missing (or wrong) Unicode handling. Others refuse |
550 | properly, so it was impossible to prepare a fair comparison table for that |
1369 | to decode or encode properly, so it was impossible to prepare a fair |
551 | case. |
1370 | comparison table for that case. |
552 | |
1371 | |
553 | =head1 RESOURCE LIMITS |
|
|
554 | |
1372 | |
555 | JSON::XS does not impose any limits on the size of JSON texts or Perl |
1373 | =head1 SECURITY CONSIDERATIONS |
556 | values they represent - if your machine can handle it, JSON::XS will |
1374 | |
557 | encode or decode it. Future versions might optionally impose structure |
1375 | When you are using JSON in a protocol, talking to untrusted potentially |
558 | depth and memory use resource limits. |
1376 | hostile creatures requires relatively few measures. |
|
|
1377 | |
|
|
1378 | First of all, your JSON decoder should be secure, that is, should not have |
|
|
1379 | any buffer overflows. Obviously, this module should ensure that and I am |
|
|
1380 | trying hard on making that true, but you never know. |
|
|
1381 | |
|
|
1382 | Second, you need to avoid resource-starving attacks. That means you should |
|
|
1383 | limit the size of JSON texts you accept, or make sure then when your |
|
|
1384 | resources run out, that's just fine (e.g. by using a separate process that |
|
|
1385 | can crash safely). The size of a JSON text in octets or characters is |
|
|
1386 | usually a good indication of the size of the resources required to decode |
|
|
1387 | it into a Perl structure. While JSON::XS can check the size of the JSON |
|
|
1388 | text, it might be too late when you already have it in memory, so you |
|
|
1389 | might want to check the size before you accept the string. |
|
|
1390 | |
|
|
1391 | Third, JSON::XS recurses using the C stack when decoding objects and |
|
|
1392 | arrays. The C stack is a limited resource: for instance, on my amd64 |
|
|
1393 | machine with 8MB of stack size I can decode around 180k nested arrays but |
|
|
1394 | only 14k nested JSON objects (due to perl itself recursing deeply on croak |
|
|
1395 | to free the temporary). If that is exceeded, the program crashes. To be |
|
|
1396 | conservative, the default nesting limit is set to 512. If your process |
|
|
1397 | has a smaller stack, you should adjust this setting accordingly with the |
|
|
1398 | C<max_depth> method. |
|
|
1399 | |
|
|
1400 | Something else could bomb you, too, that I forgot to think of. In that |
|
|
1401 | case, you get to keep the pieces. I am always open for hints, though... |
|
|
1402 | |
|
|
1403 | Also keep in mind that JSON::XS might leak contents of your Perl data |
|
|
1404 | structures in its error messages, so when you serialise sensitive |
|
|
1405 | information you might want to make sure that exceptions thrown by JSON::XS |
|
|
1406 | will not end up in front of untrusted eyes. |
|
|
1407 | |
|
|
1408 | If you are using JSON::XS to return packets to consumption |
|
|
1409 | by JavaScript scripts in a browser you should have a look at |
|
|
1410 | L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
|
|
1411 | you are vulnerable to some common attack vectors (which really are browser |
|
|
1412 | design bugs, but it is still you who will have to deal with it, as major |
|
|
1413 | browser developers care only for features, not about getting security |
|
|
1414 | right). |
|
|
1415 | |
|
|
1416 | |
|
|
1417 | =head1 THREADS |
|
|
1418 | |
|
|
1419 | This module is I<not> guaranteed to be thread safe and there are no |
|
|
1420 | plans to change this until Perl gets thread support (as opposed to the |
|
|
1421 | horribly slow so-called "threads" which are simply slow and bloated |
|
|
1422 | process simulations - use fork, it's I<much> faster, cheaper, better). |
|
|
1423 | |
|
|
1424 | (It might actually work, but you have been warned). |
|
|
1425 | |
559 | |
1426 | |
560 | =head1 BUGS |
1427 | =head1 BUGS |
561 | |
1428 | |
562 | While the goal of this module is to be correct, that unfortunately does |
1429 | While the goal of this module is to be correct, that unfortunately does |
563 | not mean its bug-free, only that I think its design is bug-free. It is |
1430 | not mean it's bug-free, only that I think its design is bug-free. If you |
564 | still very young and not well-tested. If you keep reporting bugs they will |
1431 | keep reporting bugs they will be fixed swiftly, though. |
565 | be fixed swiftly, though. |
1432 | |
|
|
1433 | Please refrain from using rt.cpan.org or any other bug reporting |
|
|
1434 | service. I put the contact address into my modules for a reason. |
566 | |
1435 | |
567 | =cut |
1436 | =cut |
568 | |
1437 | |
|
|
1438 | our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; |
|
|
1439 | our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; |
|
|
1440 | |
|
|
1441 | sub true() { $true } |
|
|
1442 | sub false() { $false } |
|
|
1443 | |
|
|
1444 | sub is_bool($) { |
|
|
1445 | UNIVERSAL::isa $_[0], "JSON::XS::Boolean" |
|
|
1446 | # or UNIVERSAL::isa $_[0], "JSON::Literal" |
|
|
1447 | } |
|
|
1448 | |
|
|
1449 | XSLoader::load "JSON::XS", $VERSION; |
|
|
1450 | |
|
|
1451 | package JSON::XS::Boolean; |
|
|
1452 | |
|
|
1453 | use overload |
|
|
1454 | "0+" => sub { ${$_[0]} }, |
|
|
1455 | "++" => sub { $_[0] = ${$_[0]} + 1 }, |
|
|
1456 | "--" => sub { $_[0] = ${$_[0]} - 1 }, |
|
|
1457 | fallback => 1; |
|
|
1458 | |
569 | 1; |
1459 | 1; |
|
|
1460 | |
|
|
1461 | =head1 SEE ALSO |
|
|
1462 | |
|
|
1463 | The F<json_xs> command line utility for quick experiments. |
570 | |
1464 | |
571 | =head1 AUTHOR |
1465 | =head1 AUTHOR |
572 | |
1466 | |
573 | Marc Lehmann <schmorp@schmorp.de> |
1467 | Marc Lehmann <schmorp@schmorp.de> |
574 | http://home.schmorp.de/ |
1468 | http://home.schmorp.de/ |