| File | /usr/local/lib/perl5/site_perl/5.10.1/darwin-2level/JSON/XS.pm |
| Statements Executed | 20 |
| Statement Execution Time | 1.20ms |
| Calls | P | F | Exclusive Time |
Inclusive Time |
Subroutine |
|---|---|---|---|---|---|
| 1 | 1 | 1 | 525µs | 590µs | DynaLoader::BEGIN@97 |
| 1 | 1 | 1 | 219µs | 229µs | JSON::XS::BEGIN@104 |
| 8 | 1 | 2 | 103µs | 103µs | JSON::XS::encode (xsub) |
| 13 | 2 | 2 | 74µs | 74µs | JSON::XS::new (xsub) |
| 5 | 1 | 2 | 66µs | 66µs | JSON::XS::decode (xsub) |
| 13 | 2 | 2 | 20µs | 20µs | JSON::XS::DESTROY (xsub) |
| 1 | 1 | 1 | 12µs | 39µs | JSON::XS::BEGIN@121 |
| 1 | 1 | 1 | 10µs | 40µs | JSON::XS::Boolean::BEGIN@1461 |
| 1 | 1 | 1 | 7µs | 7µs | JSON::XS::BEGIN@122 |
| 0 | 0 | 0 | 0s | 0s | JSON::XS::Boolean::__ANON__[:1461] |
| 0 | 0 | 0 | 0s | 0s | JSON::XS::Boolean::__ANON__[:1462] |
| 0 | 0 | 0 | 0s | 0s | JSON::XS::Boolean::__ANON__[:1463] |
| 0 | 0 | 0 | 0s | 0s | JSON::XS::false |
| 0 | 0 | 0 | 0s | 0s | JSON::XS::from_json |
| 0 | 0 | 0 | 0s | 0s | JSON::XS::is_bool |
| 0 | 0 | 0 | 0s | 0s | JSON::XS::to_json |
| 0 | 0 | 0 | 0s | 0s | JSON::XS::true |
| Line | State ments |
Time on line |
Calls | Time in subs |
Code |
|---|---|---|---|---|---|
| 1 | 1 | 27µs | =head1 NAME | ||
| 2 | |||||
| 3 | JSON::XS - JSON serialising/deserialising, done correctly and fast | ||||
| 4 | |||||
| 5 | =encoding utf-8 | ||||
| 6 | |||||
| 7 | JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ | ||||
| 8 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) | ||||
| 9 | |||||
| 10 | =head1 SYNOPSIS | ||||
| 11 | |||||
| 12 | use JSON::XS; | ||||
| 13 | |||||
| 14 | # exported functions, they croak on error | ||||
| 15 | # and expect/generate UTF-8 | ||||
| 16 | |||||
| 17 | $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref; | ||||
| 18 | $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text; | ||||
| 19 | |||||
| 20 | # OO-interface | ||||
| 21 | |||||
| 22 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; | ||||
| 23 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); | ||||
| 24 | $perl_scalar = $coder->decode ($unicode_json_text); | ||||
| 25 | |||||
| 26 | # Note that JSON version 2.0 and above will automatically use JSON::XS | ||||
| 27 | # if available, at virtually no speed overhead either, so you should | ||||
| 28 | # be able to just: | ||||
| 29 | |||||
| 30 | use JSON; | ||||
| 31 | |||||
| 32 | # and do the same things, except that you have a pure-perl fallback now. | ||||
| 33 | |||||
| 34 | =head1 DESCRIPTION | ||||
| 35 | |||||
| 36 | This module converts Perl data structures to JSON and vice versa. Its | ||||
| 37 | primary goal is to be I<correct> and its secondary goal is to be | ||||
| 38 | I<fast>. To reach the latter goal it was written in C. | ||||
| 39 | |||||
| 40 | Beginning with version 2.0 of the JSON module, when both JSON and | ||||
| 41 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can be | ||||
| 42 | overridden) with no overhead due to emulation (by inheriting constructor | ||||
| 43 | and methods). If JSON::XS is not available, it will fall back to the | ||||
| 44 | compatible JSON::PP module as backend, so using JSON instead of JSON::XS | ||||
| 45 | gives you a portable JSON API that can be fast when you need and doesn't | ||||
| 46 | require a C compiler when that is a problem. | ||||
| 47 | |||||
| 48 | As this is the n-th-something JSON module on CPAN, what was the reason | ||||
| 49 | to write yet another JSON module? While it seems there are many JSON | ||||
| 50 | modules, none of them correctly handle all corner cases, and in most cases | ||||
| 51 | their maintainers are unresponsive, gone missing, or not listening to bug | ||||
| 52 | reports for other reasons. | ||||
| 53 | |||||
| 54 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and | ||||
| 55 | vice versa. | ||||
| 56 | |||||
| 57 | =head2 FEATURES | ||||
| 58 | |||||
| 59 | =over 4 | ||||
| 60 | |||||
| 61 | =item * correct Unicode handling | ||||
| 62 | |||||
| 63 | This module knows how to handle Unicode, documents how and when it does | ||||
| 64 | so, and even documents what "correct" means. | ||||
| 65 | |||||
| 66 | =item * round-trip integrity | ||||
| 67 | |||||
| 68 | When you serialise a perl data structure using only data types supported | ||||
| 69 | by JSON, the deserialised data structure is identical on the Perl level. | ||||
| 70 | (e.g. the string "2.0" doesn't suddenly become "2" just because it looks | ||||
| 71 | like a number). There minor I<are> exceptions to this, read the MAPPING | ||||
| 72 | section below to learn about those. | ||||
| 73 | |||||
| 74 | =item * strict checking of JSON correctness | ||||
| 75 | |||||
| 76 | There is no guessing, no generating of illegal JSON texts by default, | ||||
| 77 | and only JSON is accepted as input by default (the latter is a security | ||||
| 78 | feature). | ||||
| 79 | |||||
| 80 | =item * fast | ||||
| 81 | |||||
| 82 | Compared to other JSON modules and other serialisers such as Storable, | ||||
| 83 | this module usually compares favourably in terms of speed, too. | ||||
| 84 | |||||
| 85 | =item * simple to use | ||||
| 86 | |||||
| 87 | This module has both a simple functional interface as well as an object | ||||
| 88 | oriented interface interface. | ||||
| 89 | |||||
| 90 | =item * reasonably versatile output formats | ||||
| 91 | |||||
| 92 | You can choose between the most compact guaranteed-single-line format | ||||
| 93 | possible (nice for simple line-based protocols), a pure-ASCII format | ||||
| 94 | (for when your transport is not 8-bit clean, still supports the whole | ||||
| 95 | Unicode range), or a pretty-printed format (for when you want to read that | ||||
| 96 | stuff). Or you can combine those features in whatever way you like. | ||||
| 97 | # spent 590µs (525+65) within DynaLoader::BEGIN@97 which was called
# once (525µs+65µs) by XSLoader::load at line 0 | ||||
| 98 | =back | ||||
| 99 | |||||
| 100 | =cut | ||||
| 101 | |||||
| 102 | package JSON::XS; | ||||
| 103 | |||||
| 104 | 3 | 290µs | 2 | 240µs | # spent 229µs (219+10) within JSON::XS::BEGIN@104 which was called
# once (219µs+10µs) by JSON::BEGIN@2 at line 104 # spent 229µs making 1 call to JSON::XS::BEGIN@104
# spent 10µs making 1 call to common::sense::import |
| 105 | |||||
| 106 | 1 | 600ns | our $VERSION = '2.26'; | ||
| 107 | 1 | 6µs | our @ISA = qw(Exporter); | ||
| 108 | |||||
| 109 | 1 | 900ns | our @EXPORT = qw(encode_json decode_json to_json from_json); | ||
| 110 | |||||
| 111 | sub to_json($) { | ||||
| 112 | require Carp; | ||||
| 113 | 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"); | ||||
| 114 | } | ||||
| 115 | |||||
| 116 | sub from_json($) { | ||||
| 117 | require Carp; | ||||
| 118 | 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"); | ||||
| 119 | } | ||||
| 120 | |||||
| 121 | 3 | 25µs | 2 | 66µs | # spent 39µs (12+27) within JSON::XS::BEGIN@121 which was called
# once (12µs+27µs) by JSON::BEGIN@2 at line 121 # spent 39µs making 1 call to JSON::XS::BEGIN@121
# spent 27µs making 1 call to Exporter::import |
| 122 | 3 | 396µs | 1 | 7µs | # spent 7µs within JSON::XS::BEGIN@122 which was called
# once (7µs+0s) by JSON::BEGIN@2 at line 122 # spent 7µs making 1 call to JSON::XS::BEGIN@122 |
| 123 | |||||
| 124 | =head1 FUNCTIONAL INTERFACE | ||||
| 125 | |||||
| 126 | The following convenience methods are provided by this module. They are | ||||
| 127 | exported by default: | ||||
| 128 | |||||
| 129 | =over 4 | ||||
| 130 | |||||
| 131 | =item $json_text = encode_json $perl_scalar | ||||
| 132 | |||||
| 133 | Converts the given Perl data structure to a UTF-8 encoded, binary string | ||||
| 134 | (that is, the string contains octets only). Croaks on error. | ||||
| 135 | |||||
| 136 | This function call is functionally identical to: | ||||
| 137 | |||||
| 138 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) | ||||
| 139 | |||||
| 140 | Except being faster. | ||||
| 141 | |||||
| 142 | =item $perl_scalar = decode_json $json_text | ||||
| 143 | |||||
| 144 | The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries | ||||
| 145 | to parse that as an UTF-8 encoded JSON text, returning the resulting | ||||
| 146 | reference. Croaks on error. | ||||
| 147 | |||||
| 148 | This function call is functionally identical to: | ||||
| 149 | |||||
| 150 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) | ||||
| 151 | |||||
| 152 | Except being faster. | ||||
| 153 | |||||
| 154 | =item $is_boolean = JSON::XS::is_bool $scalar | ||||
| 155 | |||||
| 156 | Returns true if the passed scalar represents either JSON::XS::true or | ||||
| 157 | JSON::XS::false, two constants that act like C<1> and C<0>, respectively | ||||
| 158 | and are used to represent JSON C<true> and C<false> values in Perl. | ||||
| 159 | |||||
| 160 | See MAPPING, below, for more information on how JSON values are mapped to | ||||
| 161 | Perl. | ||||
| 162 | |||||
| 163 | =back | ||||
| 164 | |||||
| 165 | |||||
| 166 | =head1 A FEW NOTES ON UNICODE AND PERL | ||||
| 167 | |||||
| 168 | Since this often leads to confusion, here are a few very clear words on | ||||
| 169 | how Unicode works in Perl, modulo bugs. | ||||
| 170 | |||||
| 171 | =over 4 | ||||
| 172 | |||||
| 173 | =item 1. Perl strings can store characters with ordinal values > 255. | ||||
| 174 | |||||
| 175 | This enables you to store Unicode characters as single characters in a | ||||
| 176 | Perl string - very natural. | ||||
| 177 | |||||
| 178 | =item 2. Perl does I<not> associate an encoding with your strings. | ||||
| 179 | |||||
| 180 | ... until you force it to, e.g. when matching it against a regex, or | ||||
| 181 | printing the scalar to a file, in which case Perl either interprets your | ||||
| 182 | string as locale-encoded text, octets/binary, or as Unicode, depending | ||||
| 183 | on various settings. In no case is an encoding stored together with your | ||||
| 184 | data, it is I<use> that decides encoding, not any magical meta data. | ||||
| 185 | |||||
| 186 | =item 3. The internal utf-8 flag has no meaning with regards to the | ||||
| 187 | encoding of your string. | ||||
| 188 | |||||
| 189 | Just ignore that flag unless you debug a Perl bug, a module written in | ||||
| 190 | XS or want to dive into the internals of perl. Otherwise it will only | ||||
| 191 | confuse you, as, despite the name, it says nothing about how your string | ||||
| 192 | is encoded. You can have Unicode strings with that flag set, with that | ||||
| 193 | flag clear, and you can have binary data with that flag set and that flag | ||||
| 194 | clear. Other possibilities exist, too. | ||||
| 195 | |||||
| 196 | If you didn't know about that flag, just the better, pretend it doesn't | ||||
| 197 | exist. | ||||
| 198 | |||||
| 199 | =item 4. A "Unicode String" is simply a string where each character can be | ||||
| 200 | validly interpreted as a Unicode code point. | ||||
| 201 | |||||
| 202 | If you have UTF-8 encoded data, it is no longer a Unicode string, but a | ||||
| 203 | Unicode string encoded in UTF-8, giving you a binary string. | ||||
| 204 | |||||
| 205 | =item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string. | ||||
| 206 | |||||
| 207 | It's a fact. Learn to live with it. | ||||
| 208 | |||||
| 209 | =back | ||||
| 210 | |||||
| 211 | I hope this helps :) | ||||
| 212 | |||||
| 213 | |||||
| 214 | =head1 OBJECT-ORIENTED INTERFACE | ||||
| 215 | |||||
| 216 | The object oriented interface lets you configure your own encoding or | ||||
| 217 | decoding style, within the limits of supported formats. | ||||
| 218 | |||||
| 219 | =over 4 | ||||
| 220 | |||||
| 221 | =item $json = new JSON::XS | ||||
| 222 | |||||
| 223 | Creates a new JSON::XS object that can be used to de/encode JSON | ||||
| 224 | strings. All boolean flags described below are by default I<disabled>. | ||||
| 225 | |||||
| 226 | The mutators for flags all return the JSON object again and thus calls can | ||||
| 227 | be chained: | ||||
| 228 | |||||
| 229 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) | ||||
| 230 | => {"a": [1, 2]} | ||||
| 231 | |||||
| 232 | =item $json = $json->ascii ([$enable]) | ||||
| 233 | |||||
| 234 | =item $enabled = $json->get_ascii | ||||
| 235 | |||||
| 236 | If C<$enable> is true (or missing), then the C<encode> method will not | ||||
| 237 | generate characters outside the code range C<0..127> (which is ASCII). Any | ||||
| 238 | Unicode characters outside that range will be escaped using either a | ||||
| 239 | single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, | ||||
| 240 | as per RFC4627. The resulting encoded JSON text can be treated as a native | ||||
| 241 | Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string, | ||||
| 242 | or any other superset of ASCII. | ||||
| 243 | |||||
| 244 | If C<$enable> is false, then the C<encode> method will not escape Unicode | ||||
| 245 | characters unless required by the JSON syntax or other flags. This results | ||||
| 246 | in a faster and more compact format. | ||||
| 247 | |||||
| 248 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this | ||||
| 249 | document. | ||||
| 250 | |||||
| 251 | The main use for this flag is to produce JSON texts that can be | ||||
| 252 | transmitted over a 7-bit channel, as the encoded JSON texts will not | ||||
| 253 | contain any 8 bit characters. | ||||
| 254 | |||||
| 255 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) | ||||
| 256 | => ["\ud801\udc01"] | ||||
| 257 | |||||
| 258 | =item $json = $json->latin1 ([$enable]) | ||||
| 259 | |||||
| 260 | =item $enabled = $json->get_latin1 | ||||
| 261 | |||||
| 262 | If C<$enable> is true (or missing), then the C<encode> method will encode | ||||
| 263 | the resulting JSON text as latin1 (or iso-8859-1), escaping any characters | ||||
| 264 | outside the code range C<0..255>. The resulting string can be treated as a | ||||
| 265 | latin1-encoded JSON text or a native Unicode string. The C<decode> method | ||||
| 266 | will not be affected in any way by this flag, as C<decode> by default | ||||
| 267 | expects Unicode, which is a strict superset of latin1. | ||||
| 268 | |||||
| 269 | If C<$enable> is false, then the C<encode> method will not escape Unicode | ||||
| 270 | characters unless required by the JSON syntax or other flags. | ||||
| 271 | |||||
| 272 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this | ||||
| 273 | document. | ||||
| 274 | |||||
| 275 | The main use for this flag is efficiently encoding binary data as JSON | ||||
| 276 | text, as most octets will not be escaped, resulting in a smaller encoded | ||||
| 277 | size. The disadvantage is that the resulting JSON text is encoded | ||||
| 278 | in latin1 (and must correctly be treated as such when storing and | ||||
| 279 | transferring), a rare encoding for JSON. It is therefore most useful when | ||||
| 280 | you want to store data structures known to contain binary data efficiently | ||||
| 281 | in files or databases, not when talking to other JSON encoders/decoders. | ||||
| 282 | |||||
| 283 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] | ||||
| 284 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) | ||||
| 285 | |||||
| 286 | =item $json = $json->utf8 ([$enable]) | ||||
| 287 | |||||
| 288 | =item $enabled = $json->get_utf8 | ||||
| 289 | |||||
| 290 | If C<$enable> is true (or missing), then the C<encode> method will encode | ||||
| 291 | the JSON result into UTF-8, as required by many protocols, while the | ||||
| 292 | C<decode> method expects to be handled an UTF-8-encoded string. Please | ||||
| 293 | note that UTF-8-encoded strings do not contain any characters outside the | ||||
| 294 | range C<0..255>, they are thus useful for bytewise/binary I/O. In future | ||||
| 295 | versions, enabling this option might enable autodetection of the UTF-16 | ||||
| 296 | and UTF-32 encoding families, as described in RFC4627. | ||||
| 297 | |||||
| 298 | If C<$enable> is false, then the C<encode> method will return the JSON | ||||
| 299 | string as a (non-encoded) Unicode string, while C<decode> expects thus a | ||||
| 300 | Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs | ||||
| 301 | to be done yourself, e.g. using the Encode module. | ||||
| 302 | |||||
| 303 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this | ||||
| 304 | document. | ||||
| 305 | |||||
| 306 | Example, output UTF-16BE-encoded JSON: | ||||
| 307 | |||||
| 308 | use Encode; | ||||
| 309 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); | ||||
| 310 | |||||
| 311 | Example, decode UTF-32LE-encoded JSON: | ||||
| 312 | |||||
| 313 | use Encode; | ||||
| 314 | $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); | ||||
| 315 | |||||
| 316 | =item $json = $json->pretty ([$enable]) | ||||
| 317 | |||||
| 318 | This enables (or disables) all of the C<indent>, C<space_before> and | ||||
| 319 | C<space_after> (and in the future possibly more) flags in one call to | ||||
| 320 | generate the most readable (or most compact) form possible. | ||||
| 321 | |||||
| 322 | Example, pretty-print some simple structure: | ||||
| 323 | |||||
| 324 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) | ||||
| 325 | => | ||||
| 326 | { | ||||
| 327 | "a" : [ | ||||
| 328 | 1, | ||||
| 329 | 2 | ||||
| 330 | ] | ||||
| 331 | } | ||||
| 332 | |||||
| 333 | =item $json = $json->indent ([$enable]) | ||||
| 334 | |||||
| 335 | =item $enabled = $json->get_indent | ||||
| 336 | |||||
| 337 | If C<$enable> is true (or missing), then the C<encode> method will use a multiline | ||||
| 338 | format as output, putting every array member or object/hash key-value pair | ||||
| 339 | into its own line, indenting them properly. | ||||
| 340 | |||||
| 341 | If C<$enable> is false, no newlines or indenting will be produced, and the | ||||
| 342 | resulting JSON text is guaranteed not to contain any C<newlines>. | ||||
| 343 | |||||
| 344 | This setting has no effect when decoding JSON texts. | ||||
| 345 | |||||
| 346 | =item $json = $json->space_before ([$enable]) | ||||
| 347 | |||||
| 348 | =item $enabled = $json->get_space_before | ||||
| 349 | |||||
| 350 | If C<$enable> is true (or missing), then the C<encode> method will add an extra | ||||
| 351 | optional space before the C<:> separating keys from values in JSON objects. | ||||
| 352 | |||||
| 353 | If C<$enable> is false, then the C<encode> method will not add any extra | ||||
| 354 | space at those places. | ||||
| 355 | |||||
| 356 | This setting has no effect when decoding JSON texts. You will also | ||||
| 357 | most likely combine this setting with C<space_after>. | ||||
| 358 | |||||
| 359 | Example, space_before enabled, space_after and indent disabled: | ||||
| 360 | |||||
| 361 | {"key" :"value"} | ||||
| 362 | |||||
| 363 | =item $json = $json->space_after ([$enable]) | ||||
| 364 | |||||
| 365 | =item $enabled = $json->get_space_after | ||||
| 366 | |||||
| 367 | If C<$enable> is true (or missing), then the C<encode> method will add an extra | ||||
| 368 | optional space after the C<:> separating keys from values in JSON objects | ||||
| 369 | and extra whitespace after the C<,> separating key-value pairs and array | ||||
| 370 | members. | ||||
| 371 | |||||
| 372 | If C<$enable> is false, then the C<encode> method will not add any extra | ||||
| 373 | space at those places. | ||||
| 374 | |||||
| 375 | This setting has no effect when decoding JSON texts. | ||||
| 376 | |||||
| 377 | Example, space_before and indent disabled, space_after enabled: | ||||
| 378 | |||||
| 379 | {"key": "value"} | ||||
| 380 | |||||
| 381 | =item $json = $json->relaxed ([$enable]) | ||||
| 382 | |||||
| 383 | =item $enabled = $json->get_relaxed | ||||
| 384 | |||||
| 385 | If C<$enable> is true (or missing), then C<decode> will accept some | ||||
| 386 | extensions to normal JSON syntax (see below). C<encode> will not be | ||||
| 387 | affected in anyway. I<Be aware that this option makes you accept invalid | ||||
| 388 | JSON texts as if they were valid!>. I suggest only to use this option to | ||||
| 389 | parse application-specific files written by humans (configuration files, | ||||
| 390 | resource files etc.) | ||||
| 391 | |||||
| 392 | If C<$enable> is false (the default), then C<decode> will only accept | ||||
| 393 | valid JSON texts. | ||||
| 394 | |||||
| 395 | Currently accepted extensions are: | ||||
| 396 | |||||
| 397 | =over 4 | ||||
| 398 | |||||
| 399 | =item * list items can have an end-comma | ||||
| 400 | |||||
| 401 | JSON I<separates> array elements and key-value pairs with commas. This | ||||
| 402 | can be annoying if you write JSON texts manually and want to be able to | ||||
| 403 | quickly append elements, so this extension accepts comma at the end of | ||||
| 404 | such items not just between them: | ||||
| 405 | |||||
| 406 | [ | ||||
| 407 | 1, | ||||
| 408 | 2, <- this comma not normally allowed | ||||
| 409 | ] | ||||
| 410 | { | ||||
| 411 | "k1": "v1", | ||||
| 412 | "k2": "v2", <- this comma not normally allowed | ||||
| 413 | } | ||||
| 414 | |||||
| 415 | =item * shell-style '#'-comments | ||||
| 416 | |||||
| 417 | Whenever JSON allows whitespace, shell-style comments are additionally | ||||
| 418 | allowed. They are terminated by the first carriage-return or line-feed | ||||
| 419 | character, after which more white-space and comments are allowed. | ||||
| 420 | |||||
| 421 | [ | ||||
| 422 | 1, # this comment not allowed in JSON | ||||
| 423 | # neither this one... | ||||
| 424 | ] | ||||
| 425 | |||||
| 426 | =back | ||||
| 427 | |||||
| 428 | =item $json = $json->canonical ([$enable]) | ||||
| 429 | |||||
| 430 | =item $enabled = $json->get_canonical | ||||
| 431 | |||||
| 432 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects | ||||
| 433 | by sorting their keys. This is adding a comparatively high overhead. | ||||
| 434 | |||||
| 435 | If C<$enable> is false, then the C<encode> method will output key-value | ||||
| 436 | pairs in the order Perl stores them (which will likely change between runs | ||||
| 437 | of the same script). | ||||
| 438 | |||||
| 439 | This option is useful if you want the same data structure to be encoded as | ||||
| 440 | the same JSON text (given the same overall settings). If it is disabled, | ||||
| 441 | the same hash might be encoded differently even if contains the same data, | ||||
| 442 | as key-value pairs have no inherent ordering in Perl. | ||||
| 443 | |||||
| 444 | This setting has no effect when decoding JSON texts. | ||||
| 445 | |||||
| 446 | This setting has currently no effect on tied hashes. | ||||
| 447 | |||||
| 448 | =item $json = $json->allow_nonref ([$enable]) | ||||
| 449 | |||||
| 450 | =item $enabled = $json->get_allow_nonref | ||||
| 451 | |||||
| 452 | If C<$enable> is true (or missing), then the C<encode> method can convert a | ||||
| 453 | non-reference into its corresponding string, number or null JSON value, | ||||
| 454 | which is an extension to RFC4627. Likewise, C<decode> will accept those JSON | ||||
| 455 | values instead of croaking. | ||||
| 456 | |||||
| 457 | If C<$enable> is false, then the C<encode> method will croak if it isn't | ||||
| 458 | passed an arrayref or hashref, as JSON texts must either be an object | ||||
| 459 | or array. Likewise, C<decode> will croak if given something that is not a | ||||
| 460 | JSON object or array. | ||||
| 461 | |||||
| 462 | Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, | ||||
| 463 | resulting in an invalid JSON text: | ||||
| 464 | |||||
| 465 | JSON::XS->new->allow_nonref->encode ("Hello, World!") | ||||
| 466 | => "Hello, World!" | ||||
| 467 | |||||
| 468 | =item $json = $json->allow_unknown ([$enable]) | ||||
| 469 | |||||
| 470 | =item $enabled = $json->get_allow_unknown | ||||
| 471 | |||||
| 472 | If C<$enable> is true (or missing), then C<encode> will I<not> throw an | ||||
| 473 | exception when it encounters values it cannot represent in JSON (for | ||||
| 474 | example, filehandles) but instead will encode a JSON C<null> value. Note | ||||
| 475 | that blessed objects are not included here and are handled separately by | ||||
| 476 | c<allow_nonref>. | ||||
| 477 | |||||
| 478 | If C<$enable> is false (the default), then C<encode> will throw an | ||||
| 479 | exception when it encounters anything it cannot encode as JSON. | ||||
| 480 | |||||
| 481 | This option does not affect C<decode> in any way, and it is recommended to | ||||
| 482 | leave it off unless you know your communications partner. | ||||
| 483 | |||||
| 484 | =item $json = $json->allow_blessed ([$enable]) | ||||
| 485 | |||||
| 486 | =item $enabled = $json->get_allow_blessed | ||||
| 487 | |||||
| 488 | If C<$enable> is true (or missing), then the C<encode> method will not | ||||
| 489 | barf when it encounters a blessed reference. Instead, the value of the | ||||
| 490 | B<convert_blessed> option will decide whether C<null> (C<convert_blessed> | ||||
| 491 | disabled or no C<TO_JSON> method found) or a representation of the | ||||
| 492 | object (C<convert_blessed> enabled and C<TO_JSON> method found) is being | ||||
| 493 | encoded. Has no effect on C<decode>. | ||||
| 494 | |||||
| 495 | If C<$enable> is false (the default), then C<encode> will throw an | ||||
| 496 | exception when it encounters a blessed object. | ||||
| 497 | |||||
| 498 | =item $json = $json->convert_blessed ([$enable]) | ||||
| 499 | |||||
| 500 | =item $enabled = $json->get_convert_blessed | ||||
| 501 | |||||
| 502 | If C<$enable> is true (or missing), then C<encode>, upon encountering a | ||||
| 503 | blessed object, will check for the availability of the C<TO_JSON> method | ||||
| 504 | on the object's class. If found, it will be called in scalar context | ||||
| 505 | and the resulting scalar will be encoded instead of the object. If no | ||||
| 506 | C<TO_JSON> method is found, the value of C<allow_blessed> will decide what | ||||
| 507 | to do. | ||||
| 508 | |||||
| 509 | The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> | ||||
| 510 | returns other blessed objects, those will be handled in the same | ||||
| 511 | way. C<TO_JSON> must take care of not causing an endless recursion cycle | ||||
| 512 | (== crash) in this case. The name of C<TO_JSON> was chosen because other | ||||
| 513 | methods called by the Perl core (== not by the user of the object) are | ||||
| 514 | usually in upper case letters and to avoid collisions with any C<to_json> | ||||
| 515 | function or method. | ||||
| 516 | |||||
| 517 | This setting does not yet influence C<decode> in any way, but in the | ||||
| 518 | future, global hooks might get installed that influence C<decode> and are | ||||
| 519 | enabled by this setting. | ||||
| 520 | |||||
| 521 | If C<$enable> is false, then the C<allow_blessed> setting will decide what | ||||
| 522 | to do when a blessed object is found. | ||||
| 523 | |||||
| 524 | =item $json = $json->filter_json_object ([$coderef->($hashref)]) | ||||
| 525 | |||||
| 526 | When C<$coderef> is specified, it will be called from C<decode> each | ||||
| 527 | time it decodes a JSON object. The only argument is a reference to the | ||||
| 528 | newly-created hash. If the code references returns a single scalar (which | ||||
| 529 | need not be a reference), this value (i.e. a copy of that scalar to avoid | ||||
| 530 | aliasing) is inserted into the deserialised data structure. If it returns | ||||
| 531 | an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the | ||||
| 532 | original deserialised hash will be inserted. This setting can slow down | ||||
| 533 | decoding considerably. | ||||
| 534 | |||||
| 535 | When C<$coderef> is omitted or undefined, any existing callback will | ||||
| 536 | be removed and C<decode> will not change the deserialised hash in any | ||||
| 537 | way. | ||||
| 538 | |||||
| 539 | Example, convert all JSON objects into the integer 5: | ||||
| 540 | |||||
| 541 | my $js = JSON::XS->new->filter_json_object (sub { 5 }); | ||||
| 542 | # returns [5] | ||||
| 543 | $js->decode ('[{}]') | ||||
| 544 | # throw an exception because allow_nonref is not enabled | ||||
| 545 | # so a lone 5 is not allowed. | ||||
| 546 | $js->decode ('{"a":1, "b":2}'); | ||||
| 547 | |||||
| 548 | =item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)]) | ||||
| 549 | |||||
| 550 | Works remotely similar to C<filter_json_object>, but is only called for | ||||
| 551 | JSON objects having a single key named C<$key>. | ||||
| 552 | |||||
| 553 | This C<$coderef> is called before the one specified via | ||||
| 554 | C<filter_json_object>, if any. It gets passed the single value in the JSON | ||||
| 555 | object. If it returns a single value, it will be inserted into the data | ||||
| 556 | structure. If it returns nothing (not even C<undef> but the empty list), | ||||
| 557 | the callback from C<filter_json_object> will be called next, as if no | ||||
| 558 | single-key callback were specified. | ||||
| 559 | |||||
| 560 | If C<$coderef> is omitted or undefined, the corresponding callback will be | ||||
| 561 | disabled. There can only ever be one callback for a given key. | ||||
| 562 | |||||
| 563 | As this callback gets called less often then the C<filter_json_object> | ||||
| 564 | one, decoding speed will not usually suffer as much. Therefore, single-key | ||||
| 565 | objects make excellent targets to serialise Perl objects into, especially | ||||
| 566 | as single-key JSON objects are as close to the type-tagged value concept | ||||
| 567 | as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not | ||||
| 568 | support this in any way, so you need to make sure your data never looks | ||||
| 569 | like a serialised Perl hash. | ||||
| 570 | |||||
| 571 | Typical names for the single object key are C<__class_whatever__>, or | ||||
| 572 | C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even | ||||
| 573 | things like C<__class_md5sum(classname)__>, to reduce the risk of clashing | ||||
| 574 | with real hashes. | ||||
| 575 | |||||
| 576 | Example, decode JSON objects of the form C<< { "__widget__" => <id> } >> | ||||
| 577 | into the corresponding C<< $WIDGET{<id>} >> object: | ||||
| 578 | |||||
| 579 | # return whatever is in $WIDGET{5}: | ||||
| 580 | JSON::XS | ||||
| 581 | ->new | ||||
| 582 | ->filter_json_single_key_object (__widget__ => sub { | ||||
| 583 | $WIDGET{ $_[0] } | ||||
| 584 | }) | ||||
| 585 | ->decode ('{"__widget__": 5') | ||||
| 586 | |||||
| 587 | # this can be used with a TO_JSON method in some "widget" class | ||||
| 588 | # for serialisation to json: | ||||
| 589 | sub WidgetBase::TO_JSON { | ||||
| 590 | my ($self) = @_; | ||||
| 591 | |||||
| 592 | unless ($self->{id}) { | ||||
| 593 | $self->{id} = ..get..some..id..; | ||||
| 594 | $WIDGET{$self->{id}} = $self; | ||||
| 595 | } | ||||
| 596 | |||||
| 597 | { __widget__ => $self->{id} } | ||||
| 598 | } | ||||
| 599 | |||||
| 600 | =item $json = $json->shrink ([$enable]) | ||||
| 601 | |||||
| 602 | =item $enabled = $json->get_shrink | ||||
| 603 | |||||
| 604 | Perl usually over-allocates memory a bit when allocating space for | ||||
| 605 | strings. This flag optionally resizes strings generated by either | ||||
| 606 | C<encode> or C<decode> to their minimum size possible. This can save | ||||
| 607 | memory when your JSON texts are either very very long or you have many | ||||
| 608 | short strings. It will also try to downgrade any strings to octet-form | ||||
| 609 | if possible: perl stores strings internally either in an encoding called | ||||
| 610 | UTF-X or in octet-form. The latter cannot store everything but uses less | ||||
| 611 | space in general (and some buggy Perl or C code might even rely on that | ||||
| 612 | internal representation being used). | ||||
| 613 | |||||
| 614 | The actual definition of what shrink does might change in future versions, | ||||
| 615 | but it will always try to save space at the expense of time. | ||||
| 616 | |||||
| 617 | If C<$enable> is true (or missing), the string returned by C<encode> will | ||||
| 618 | be shrunk-to-fit, while all strings generated by C<decode> will also be | ||||
| 619 | shrunk-to-fit. | ||||
| 620 | |||||
| 621 | If C<$enable> is false, then the normal perl allocation algorithms are used. | ||||
| 622 | If you work with your data, then this is likely to be faster. | ||||
| 623 | |||||
| 624 | In the future, this setting might control other things, such as converting | ||||
| 625 | strings that look like integers or floats into integers or floats | ||||
| 626 | internally (there is no difference on the Perl level), saving space. | ||||
| 627 | |||||
| 628 | =item $json = $json->max_depth ([$maximum_nesting_depth]) | ||||
| 629 | |||||
| 630 | =item $max_depth = $json->get_max_depth | ||||
| 631 | |||||
| 632 | Sets the maximum nesting level (default C<512>) accepted while encoding | ||||
| 633 | or decoding. If a higher nesting level is detected in JSON text or a Perl | ||||
| 634 | data structure, then the encoder and decoder will stop and croak at that | ||||
| 635 | point. | ||||
| 636 | |||||
| 637 | Nesting level is defined by number of hash- or arrayrefs that the encoder | ||||
| 638 | needs to traverse to reach a given point or the number of C<{> or C<[> | ||||
| 639 | characters without their matching closing parenthesis crossed to reach a | ||||
| 640 | given character in a string. | ||||
| 641 | |||||
| 642 | Setting the maximum depth to one disallows any nesting, so that ensures | ||||
| 643 | that the object is only a single hash/object or array. | ||||
| 644 | |||||
| 645 | If no argument is given, the highest possible setting will be used, which | ||||
| 646 | is rarely useful. | ||||
| 647 | |||||
| 648 | Note that nesting is implemented by recursion in C. The default value has | ||||
| 649 | been chosen to be as large as typical operating systems allow without | ||||
| 650 | crashing. | ||||
| 651 | |||||
| 652 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. | ||||
| 653 | |||||
| 654 | =item $json = $json->max_size ([$maximum_string_size]) | ||||
| 655 | |||||
| 656 | =item $max_size = $json->get_max_size | ||||
| 657 | |||||
| 658 | Set the maximum length a JSON text may have (in bytes) where decoding is | ||||
| 659 | being attempted. The default is C<0>, meaning no limit. When C<decode> | ||||
| 660 | is called on a string that is longer then this many bytes, it will not | ||||
| 661 | attempt to decode the string but throw an exception. This setting has no | ||||
| 662 | effect on C<encode> (yet). | ||||
| 663 | |||||
| 664 | If no argument is given, the limit check will be deactivated (same as when | ||||
| 665 | C<0> is specified). | ||||
| 666 | |||||
| 667 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. | ||||
| 668 | |||||
| 669 | =item $json_text = $json->encode ($perl_scalar) | ||||
| 670 | |||||
| 671 | Converts the given Perl data structure (a simple scalar or a reference | ||||
| 672 | to a hash or array) to its JSON representation. Simple scalars will be | ||||
| 673 | converted into JSON string or number sequences, while references to arrays | ||||
| 674 | become JSON arrays and references to hashes become JSON objects. Undefined | ||||
| 675 | Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> | ||||
| 676 | nor C<false> values will be generated. | ||||
| 677 | |||||
| 678 | =item $perl_scalar = $json->decode ($json_text) | ||||
| 679 | |||||
| 680 | The opposite of C<encode>: expects a JSON text and tries to parse it, | ||||
| 681 | returning the resulting simple scalar or reference. Croaks on error. | ||||
| 682 | |||||
| 683 | JSON numbers and strings become simple Perl scalars. JSON arrays become | ||||
| 684 | Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes | ||||
| 685 | C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. | ||||
| 686 | |||||
| 687 | =item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) | ||||
| 688 | |||||
| 689 | This works like the C<decode> method, but instead of raising an exception | ||||
| 690 | when there is trailing garbage after the first JSON object, it will | ||||
| 691 | silently stop parsing there and return the number of characters consumed | ||||
| 692 | so far. | ||||
| 693 | |||||
| 694 | This is useful if your JSON texts are not delimited by an outer protocol | ||||
| 695 | (which is not the brightest thing to do in the first place) and you need | ||||
| 696 | to know where the JSON text ends. | ||||
| 697 | |||||
| 698 | JSON::XS->new->decode_prefix ("[1] the tail") | ||||
| 699 | => ([], 3) | ||||
| 700 | |||||
| 701 | =back | ||||
| 702 | |||||
| 703 | |||||
| 704 | =head1 INCREMENTAL PARSING | ||||
| 705 | |||||
| 706 | In some cases, there is the need for incremental parsing of JSON | ||||
| 707 | texts. While this module always has to keep both JSON text and resulting | ||||
| 708 | Perl data structure in memory at one time, it does allow you to parse a | ||||
| 709 | JSON stream incrementally. It does so by accumulating text until it has | ||||
| 710 | a full JSON object, which it then can decode. This process is similar to | ||||
| 711 | using C<decode_prefix> to see if a full JSON object is available, but | ||||
| 712 | is much more efficient (and can be implemented with a minimum of method | ||||
| 713 | calls). | ||||
| 714 | |||||
| 715 | JSON::XS will only attempt to parse the JSON text once it is sure it | ||||
| 716 | has enough text to get a decisive result, using a very simple but | ||||
| 717 | truly incremental parser. This means that it sometimes won't stop as | ||||
| 718 | early as the full parser, for example, it doesn't detect parenthese | ||||
| 719 | mismatches. The only thing it guarantees is that it starts decoding as | ||||
| 720 | soon as a syntactically valid JSON text has been seen. This means you need | ||||
| 721 | to set resource limits (e.g. C<max_size>) to ensure the parser will stop | ||||
| 722 | parsing in the presence if syntax errors. | ||||
| 723 | |||||
| 724 | The following methods implement this incremental parser. | ||||
| 725 | |||||
| 726 | =over 4 | ||||
| 727 | |||||
| 728 | =item [void, scalar or list context] = $json->incr_parse ([$string]) | ||||
| 729 | |||||
| 730 | This is the central parsing function. It can both append new text and | ||||
| 731 | extract objects from the stream accumulated so far (both of these | ||||
| 732 | functions are optional). | ||||
| 733 | |||||
| 734 | If C<$string> is given, then this string is appended to the already | ||||
| 735 | existing JSON fragment stored in the C<$json> object. | ||||
| 736 | |||||
| 737 | After that, if the function is called in void context, it will simply | ||||
| 738 | return without doing anything further. This can be used to add more text | ||||
| 739 | in as many chunks as you want. | ||||
| 740 | |||||
| 741 | If the method is called in scalar context, then it will try to extract | ||||
| 742 | exactly I<one> JSON object. If that is successful, it will return this | ||||
| 743 | object, otherwise it will return C<undef>. If there is a parse error, | ||||
| 744 | this method will croak just as C<decode> would do (one can then use | ||||
| 745 | C<incr_skip> to skip the errornous part). This is the most common way of | ||||
| 746 | using the method. | ||||
| 747 | |||||
| 748 | And finally, in list context, it will try to extract as many objects | ||||
| 749 | from the stream as it can find and return them, or the empty list | ||||
| 750 | otherwise. For this to work, there must be no separators between the JSON | ||||
| 751 | objects or arrays, instead they must be concatenated back-to-back. If | ||||
| 752 | an error occurs, an exception will be raised as in the scalar context | ||||
| 753 | case. Note that in this case, any previously-parsed JSON texts will be | ||||
| 754 | lost. | ||||
| 755 | |||||
| 756 | =item $lvalue_string = $json->incr_text | ||||
| 757 | |||||
| 758 | This method returns the currently stored JSON fragment as an lvalue, that | ||||
| 759 | is, you can manipulate it. This I<only> works when a preceding call to | ||||
| 760 | C<incr_parse> in I<scalar context> successfully returned an object. Under | ||||
| 761 | all other circumstances you must not call this function (I mean it. | ||||
| 762 | although in simple tests it might actually work, it I<will> fail under | ||||
| 763 | real world conditions). As a special exception, you can also call this | ||||
| 764 | method before having parsed anything. | ||||
| 765 | |||||
| 766 | This function is useful in two cases: a) finding the trailing text after a | ||||
| 767 | JSON object or b) parsing multiple JSON objects separated by non-JSON text | ||||
| 768 | (such as commas). | ||||
| 769 | |||||
| 770 | =item $json->incr_skip | ||||
| 771 | |||||
| 772 | This will reset the state of the incremental parser and will remove | ||||
| 773 | the parsed text from the input buffer so far. This is useful after | ||||
| 774 | C<incr_parse> died, in which case the input buffer and incremental parser | ||||
| 775 | state is left unchanged, to skip the text parsed so far and to reset the | ||||
| 776 | parse state. | ||||
| 777 | |||||
| 778 | The difference to C<incr_reset> is that only text until the parse error | ||||
| 779 | occured is removed. | ||||
| 780 | |||||
| 781 | =item $json->incr_reset | ||||
| 782 | |||||
| 783 | This completely resets the incremental parser, that is, after this call, | ||||
| 784 | it will be as if the parser had never parsed anything. | ||||
| 785 | |||||
| 786 | This is useful if you want to repeatedly parse JSON objects and want to | ||||
| 787 | ignore any trailing data, which means you have to reset the parser after | ||||
| 788 | each successful decode. | ||||
| 789 | |||||
| 790 | =back | ||||
| 791 | |||||
| 792 | =head2 LIMITATIONS | ||||
| 793 | |||||
| 794 | All options that affect decoding are supported, except | ||||
| 795 | C<allow_nonref>. The reason for this is that it cannot be made to | ||||
| 796 | work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate | ||||
| 797 | them back to back and still decode them perfectly. This does not hold true | ||||
| 798 | for JSON numbers, however. | ||||
| 799 | |||||
| 800 | For example, is the string C<1> a single JSON number, or is it simply the | ||||
| 801 | start of C<12>? Or is C<12> a single JSON number, or the concatenation | ||||
| 802 | of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS | ||||
| 803 | takes the conservative route and disallows this case. | ||||
| 804 | |||||
| 805 | =head2 EXAMPLES | ||||
| 806 | |||||
| 807 | Some examples will make all this clearer. First, a simple example that | ||||
| 808 | works similarly to C<decode_prefix>: We want to decode the JSON object at | ||||
| 809 | the start of a string and identify the portion after the JSON object: | ||||
| 810 | |||||
| 811 | my $text = "[1,2,3] hello"; | ||||
| 812 | |||||
| 813 | my $json = new JSON::XS; | ||||
| 814 | |||||
| 815 | my $obj = $json->incr_parse ($text) | ||||
| 816 | or die "expected JSON object or array at beginning of string"; | ||||
| 817 | |||||
| 818 | my $tail = $json->incr_text; | ||||
| 819 | # $tail now contains " hello" | ||||
| 820 | |||||
| 821 | Easy, isn't it? | ||||
| 822 | |||||
| 823 | Now for a more complicated example: Imagine a hypothetical protocol where | ||||
| 824 | you read some requests from a TCP stream, and each request is a JSON | ||||
| 825 | array, without any separation between them (in fact, it is often useful to | ||||
| 826 | use newlines as "separators", as these get interpreted as whitespace at | ||||
| 827 | the start of the JSON text, which makes it possible to test said protocol | ||||
| 828 | with C<telnet>...). | ||||
| 829 | |||||
| 830 | Here is how you'd do it (it is trivial to write this in an event-based | ||||
| 831 | manner): | ||||
| 832 | |||||
| 833 | my $json = new JSON::XS; | ||||
| 834 | |||||
| 835 | # read some data from the socket | ||||
| 836 | while (sysread $socket, my $buf, 4096) { | ||||
| 837 | |||||
| 838 | # split and decode as many requests as possible | ||||
| 839 | for my $request ($json->incr_parse ($buf)) { | ||||
| 840 | # act on the $request | ||||
| 841 | } | ||||
| 842 | } | ||||
| 843 | |||||
| 844 | Another complicated example: Assume you have a string with JSON objects | ||||
| 845 | or arrays, all separated by (optional) comma characters (e.g. C<[1],[2], | ||||
| 846 | [3]>). To parse them, we have to skip the commas between the JSON texts, | ||||
| 847 | and here is where the lvalue-ness of C<incr_text> comes in useful: | ||||
| 848 | |||||
| 849 | my $text = "[1],[2], [3]"; | ||||
| 850 | my $json = new JSON::XS; | ||||
| 851 | |||||
| 852 | # void context, so no parsing done | ||||
| 853 | $json->incr_parse ($text); | ||||
| 854 | |||||
| 855 | # now extract as many objects as possible. note the | ||||
| 856 | # use of scalar context so incr_text can be called. | ||||
| 857 | while (my $obj = $json->incr_parse) { | ||||
| 858 | # do something with $obj | ||||
| 859 | |||||
| 860 | # now skip the optional comma | ||||
| 861 | $json->incr_text =~ s/^ \s* , //x; | ||||
| 862 | } | ||||
| 863 | |||||
| 864 | Now lets go for a very complex example: Assume that you have a gigantic | ||||
| 865 | JSON array-of-objects, many gigabytes in size, and you want to parse it, | ||||
| 866 | but you cannot load it into memory fully (this has actually happened in | ||||
| 867 | the real world :). | ||||
| 868 | |||||
| 869 | Well, you lost, you have to implement your own JSON parser. But JSON::XS | ||||
| 870 | can still help you: You implement a (very simple) array parser and let | ||||
| 871 | JSON decode the array elements, which are all full JSON objects on their | ||||
| 872 | own (this wouldn't work if the array elements could be JSON numbers, for | ||||
| 873 | example): | ||||
| 874 | |||||
| 875 | my $json = new JSON::XS; | ||||
| 876 | |||||
| 877 | # open the monster | ||||
| 878 | open my $fh, "<bigfile.json" | ||||
| 879 | or die "bigfile: $!"; | ||||
| 880 | |||||
| 881 | # first parse the initial "[" | ||||
| 882 | for (;;) { | ||||
| 883 | sysread $fh, my $buf, 65536 | ||||
| 884 | or die "read error: $!"; | ||||
| 885 | $json->incr_parse ($buf); # void context, so no parsing | ||||
| 886 | |||||
| 887 | # Exit the loop once we found and removed(!) the initial "[". | ||||
| 888 | # In essence, we are (ab-)using the $json object as a simple scalar | ||||
| 889 | # we append data to. | ||||
| 890 | last if $json->incr_text =~ s/^ \s* \[ //x; | ||||
| 891 | } | ||||
| 892 | |||||
| 893 | # now we have the skipped the initial "[", so continue | ||||
| 894 | # parsing all the elements. | ||||
| 895 | for (;;) { | ||||
| 896 | # in this loop we read data until we got a single JSON object | ||||
| 897 | for (;;) { | ||||
| 898 | if (my $obj = $json->incr_parse) { | ||||
| 899 | # do something with $obj | ||||
| 900 | last; | ||||
| 901 | } | ||||
| 902 | |||||
| 903 | # add more data | ||||
| 904 | sysread $fh, my $buf, 65536 | ||||
| 905 | or die "read error: $!"; | ||||
| 906 | $json->incr_parse ($buf); # void context, so no parsing | ||||
| 907 | } | ||||
| 908 | |||||
| 909 | # in this loop we read data until we either found and parsed the | ||||
| 910 | # separating "," between elements, or the final "]" | ||||
| 911 | for (;;) { | ||||
| 912 | # first skip whitespace | ||||
| 913 | $json->incr_text =~ s/^\s*//; | ||||
| 914 | |||||
| 915 | # if we find "]", we are done | ||||
| 916 | if ($json->incr_text =~ s/^\]//) { | ||||
| 917 | print "finished.\n"; | ||||
| 918 | exit; | ||||
| 919 | } | ||||
| 920 | |||||
| 921 | # if we find ",", we can continue with the next element | ||||
| 922 | if ($json->incr_text =~ s/^,//) { | ||||
| 923 | last; | ||||
| 924 | } | ||||
| 925 | |||||
| 926 | # if we find anything else, we have a parse error! | ||||
| 927 | if (length $json->incr_text) { | ||||
| 928 | die "parse error near ", $json->incr_text; | ||||
| 929 | } | ||||
| 930 | |||||
| 931 | # else add more data | ||||
| 932 | sysread $fh, my $buf, 65536 | ||||
| 933 | or die "read error: $!"; | ||||
| 934 | $json->incr_parse ($buf); # void context, so no parsing | ||||
| 935 | } | ||||
| 936 | |||||
| 937 | This is a complex example, but most of the complexity comes from the fact | ||||
| 938 | that we are trying to be correct (bear with me if I am wrong, I never ran | ||||
| 939 | the above example :). | ||||
| 940 | |||||
| 941 | |||||
| 942 | |||||
| 943 | =head1 MAPPING | ||||
| 944 | |||||
| 945 | This section describes how JSON::XS maps Perl values to JSON values and | ||||
| 946 | vice versa. These mappings are designed to "do the right thing" in most | ||||
| 947 | circumstances automatically, preserving round-tripping characteristics | ||||
| 948 | (what you put in comes out as something equivalent). | ||||
| 949 | |||||
| 950 | For the more enlightened: note that in the following descriptions, | ||||
| 951 | lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl> | ||||
| 952 | refers to the abstract Perl language itself. | ||||
| 953 | |||||
| 954 | |||||
| 955 | =head2 JSON -> PERL | ||||
| 956 | |||||
| 957 | =over 4 | ||||
| 958 | |||||
| 959 | =item object | ||||
| 960 | |||||
| 961 | A JSON object becomes a reference to a hash in Perl. No ordering of object | ||||
| 962 | keys is preserved (JSON does not preserve object key ordering itself). | ||||
| 963 | |||||
| 964 | =item array | ||||
| 965 | |||||
| 966 | A JSON array becomes a reference to an array in Perl. | ||||
| 967 | |||||
| 968 | =item string | ||||
| 969 | |||||
| 970 | A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON | ||||
| 971 | are represented by the same codepoints in the Perl string, so no manual | ||||
| 972 | decoding is necessary. | ||||
| 973 | |||||
| 974 | =item number | ||||
| 975 | |||||
| 976 | A JSON number becomes either an integer, numeric (floating point) or | ||||
| 977 | string scalar in perl, depending on its range and any fractional parts. On | ||||
| 978 | the Perl level, there is no difference between those as Perl handles all | ||||
| 979 | the conversion details, but an integer may take slightly less memory and | ||||
| 980 | might represent more values exactly than floating point numbers. | ||||
| 981 | |||||
| 982 | If the number consists of digits only, JSON::XS will try to represent | ||||
| 983 | it as an integer value. If that fails, it will try to represent it as | ||||
| 984 | a numeric (floating point) value if that is possible without loss of | ||||
| 985 | precision. Otherwise it will preserve the number as a string value (in | ||||
| 986 | which case you lose roundtripping ability, as the JSON number will be | ||||
| 987 | re-encoded toa JSON string). | ||||
| 988 | |||||
| 989 | Numbers containing a fractional or exponential part will always be | ||||
| 990 | represented as numeric (floating point) values, possibly at a loss of | ||||
| 991 | precision (in which case you might lose perfect roundtripping ability, but | ||||
| 992 | the JSON number will still be re-encoded as a JSON number). | ||||
| 993 | |||||
| 994 | =item true, false | ||||
| 995 | |||||
| 996 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, | ||||
| 997 | respectively. They are overloaded to act almost exactly like the numbers | ||||
| 998 | C<1> and C<0>. You can check whether a scalar is a JSON boolean by using | ||||
| 999 | the C<JSON::XS::is_bool> function. | ||||
| 1000 | |||||
| 1001 | =item null | ||||
| 1002 | |||||
| 1003 | A JSON null atom becomes C<undef> in Perl. | ||||
| 1004 | |||||
| 1005 | =back | ||||
| 1006 | |||||
| 1007 | |||||
| 1008 | =head2 PERL -> JSON | ||||
| 1009 | |||||
| 1010 | The mapping from Perl to JSON is slightly more difficult, as Perl is a | ||||
| 1011 | truly typeless language, so we can only guess which JSON type is meant by | ||||
| 1012 | a Perl value. | ||||
| 1013 | |||||
| 1014 | =over 4 | ||||
| 1015 | |||||
| 1016 | =item hash references | ||||
| 1017 | |||||
| 1018 | Perl hash references become JSON objects. As there is no inherent ordering | ||||
| 1019 | in hash keys (or JSON objects), they will usually be encoded in a | ||||
| 1020 | pseudo-random order that can change between runs of the same program but | ||||
| 1021 | stays generally the same within a single run of a program. JSON::XS can | ||||
| 1022 | optionally sort the hash keys (determined by the I<canonical> flag), so | ||||
| 1023 | the same datastructure will serialise to the same JSON text (given same | ||||
| 1024 | settings and version of JSON::XS), but this incurs a runtime overhead | ||||
| 1025 | and is only rarely useful, e.g. when you want to compare some JSON text | ||||
| 1026 | against another for equality. | ||||
| 1027 | |||||
| 1028 | =item array references | ||||
| 1029 | |||||
| 1030 | Perl array references become JSON arrays. | ||||
| 1031 | |||||
| 1032 | =item other references | ||||
| 1033 | |||||
| 1034 | Other unblessed references are generally not allowed and will cause an | ||||
| 1035 | exception to be thrown, except for references to the integers C<0> and | ||||
| 1036 | C<1>, which get turned into C<false> and C<true> atoms in JSON. You can | ||||
| 1037 | also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. | ||||
| 1038 | |||||
| 1039 | encode_json [\0, JSON::XS::true] # yields [false,true] | ||||
| 1040 | |||||
| 1041 | =item JSON::XS::true, JSON::XS::false | ||||
| 1042 | |||||
| 1043 | These special values become JSON true and JSON false values, | ||||
| 1044 | respectively. You can also use C<\1> and C<\0> directly if you want. | ||||
| 1045 | |||||
| 1046 | =item blessed objects | ||||
| 1047 | |||||
| 1048 | Blessed objects are not directly representable in JSON. See the | ||||
| 1049 | C<allow_blessed> and C<convert_blessed> methods on various options on | ||||
| 1050 | how to deal with this: basically, you can choose between throwing an | ||||
| 1051 | exception, encoding the reference as if it weren't blessed, or provide | ||||
| 1052 | your own serialiser method. | ||||
| 1053 | |||||
| 1054 | =item simple scalars | ||||
| 1055 | |||||
| 1056 | Simple Perl scalars (any scalar that is not a reference) are the most | ||||
| 1057 | difficult objects to encode: JSON::XS will encode undefined scalars as | ||||
| 1058 | JSON C<null> values, scalars that have last been used in a string context | ||||
| 1059 | before encoding as JSON strings, and anything else as number value: | ||||
| 1060 | |||||
| 1061 | # dump as number | ||||
| 1062 | encode_json [2] # yields [2] | ||||
| 1063 | encode_json [-3.0e17] # yields [-3e+17] | ||||
| 1064 | my $value = 5; encode_json [$value] # yields [5] | ||||
| 1065 | |||||
| 1066 | # used as string, so dump as string | ||||
| 1067 | print $value; | ||||
| 1068 | encode_json [$value] # yields ["5"] | ||||
| 1069 | |||||
| 1070 | # undef becomes null | ||||
| 1071 | encode_json [undef] # yields [null] | ||||
| 1072 | |||||
| 1073 | You can force the type to be a JSON string by stringifying it: | ||||
| 1074 | |||||
| 1075 | my $x = 3.1; # some variable containing a number | ||||
| 1076 | "$x"; # stringified | ||||
| 1077 | $x .= ""; # another, more awkward way to stringify | ||||
| 1078 | print $x; # perl does it for you, too, quite often | ||||
| 1079 | |||||
| 1080 | You can force the type to be a JSON number by numifying it: | ||||
| 1081 | |||||
| 1082 | my $x = "3"; # some variable containing a string | ||||
| 1083 | $x += 0; # numify it, ensuring it will be dumped as a number | ||||
| 1084 | $x *= 1; # same thing, the choice is yours. | ||||
| 1085 | |||||
| 1086 | You can not currently force the type in other, less obscure, ways. Tell me | ||||
| 1087 | if you need this capability (but don't forget to explain why it's needed | ||||
| 1088 | :). | ||||
| 1089 | |||||
| 1090 | =back | ||||
| 1091 | |||||
| 1092 | |||||
| 1093 | =head1 ENCODING/CODESET FLAG NOTES | ||||
| 1094 | |||||
| 1095 | The interested reader might have seen a number of flags that signify | ||||
| 1096 | encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be | ||||
| 1097 | some confusion on what these do, so here is a short comparison: | ||||
| 1098 | |||||
| 1099 | C<utf8> controls whether the JSON text created by C<encode> (and expected | ||||
| 1100 | by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only | ||||
| 1101 | control whether C<encode> escapes character values outside their respective | ||||
| 1102 | codeset range. Neither of these flags conflict with each other, although | ||||
| 1103 | some combinations make less sense than others. | ||||
| 1104 | |||||
| 1105 | Care has been taken to make all flags symmetrical with respect to | ||||
| 1106 | C<encode> and C<decode>, that is, texts encoded with any combination of | ||||
| 1107 | these flag values will be correctly decoded when the same flags are used | ||||
| 1108 | - in general, if you use different flag settings while encoding vs. when | ||||
| 1109 | decoding you likely have a bug somewhere. | ||||
| 1110 | |||||
| 1111 | Below comes a verbose discussion of these flags. Note that a "codeset" is | ||||
| 1112 | simply an abstract set of character-codepoint pairs, while an encoding | ||||
| 1113 | takes those codepoint numbers and I<encodes> them, in our case into | ||||
| 1114 | octets. Unicode is (among other things) a codeset, UTF-8 is an encoding, | ||||
| 1115 | and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at | ||||
| 1116 | the same time, which can be confusing. | ||||
| 1117 | |||||
| 1118 | =over 4 | ||||
| 1119 | |||||
| 1120 | =item C<utf8> flag disabled | ||||
| 1121 | |||||
| 1122 | When C<utf8> is disabled (the default), then C<encode>/C<decode> generate | ||||
| 1123 | and expect Unicode strings, that is, characters with high ordinal Unicode | ||||
| 1124 | values (> 255) will be encoded as such characters, and likewise such | ||||
| 1125 | characters are decoded as-is, no canges to them will be done, except | ||||
| 1126 | "(re-)interpreting" them as Unicode codepoints or Unicode characters, | ||||
| 1127 | respectively (to Perl, these are the same thing in strings unless you do | ||||
| 1128 | funny/weird/dumb stuff). | ||||
| 1129 | |||||
| 1130 | This is useful when you want to do the encoding yourself (e.g. when you | ||||
| 1131 | want to have UTF-16 encoded JSON texts) or when some other layer does | ||||
| 1132 | the encoding for you (for example, when printing to a terminal using a | ||||
| 1133 | filehandle that transparently encodes to UTF-8 you certainly do NOT want | ||||
| 1134 | to UTF-8 encode your data first and have Perl encode it another time). | ||||
| 1135 | |||||
| 1136 | =item C<utf8> flag enabled | ||||
| 1137 | |||||
| 1138 | If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all | ||||
| 1139 | characters using the corresponding UTF-8 multi-byte sequence, and will | ||||
| 1140 | expect your input strings to be encoded as UTF-8, that is, no "character" | ||||
| 1141 | of the input string must have any value > 255, as UTF-8 does not allow | ||||
| 1142 | that. | ||||
| 1143 | |||||
| 1144 | The C<utf8> flag therefore switches between two modes: disabled means you | ||||
| 1145 | will get a Unicode string in Perl, enabled means you get an UTF-8 encoded | ||||
| 1146 | octet/binary string in Perl. | ||||
| 1147 | |||||
| 1148 | =item C<latin1> or C<ascii> flags enabled | ||||
| 1149 | |||||
| 1150 | With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters | ||||
| 1151 | with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining | ||||
| 1152 | characters as specified by the C<utf8> flag. | ||||
| 1153 | |||||
| 1154 | If C<utf8> is disabled, then the result is also correctly encoded in those | ||||
| 1155 | character sets (as both are proper subsets of Unicode, meaning that a | ||||
| 1156 | Unicode string with all character values < 256 is the same thing as a | ||||
| 1157 | ISO-8859-1 string, and a Unicode string with all character values < 128 is | ||||
| 1158 | the same thing as an ASCII string in Perl). | ||||
| 1159 | |||||
| 1160 | If C<utf8> is enabled, you still get a correct UTF-8-encoded string, | ||||
| 1161 | regardless of these flags, just some more characters will be escaped using | ||||
| 1162 | C<\uXXXX> then before. | ||||
| 1163 | |||||
| 1164 | Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8 | ||||
| 1165 | encoding, while ASCII-encoded strings are. That is because the ISO-8859-1 | ||||
| 1166 | encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being | ||||
| 1167 | a subset of Unicode), while ASCII is. | ||||
| 1168 | |||||
| 1169 | Surprisingly, C<decode> will ignore these flags and so treat all input | ||||
| 1170 | values as governed by the C<utf8> flag. If it is disabled, this allows you | ||||
| 1171 | to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of | ||||
| 1172 | Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings. | ||||
| 1173 | |||||
| 1174 | So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag - | ||||
| 1175 | they only govern when the JSON output engine escapes a character or not. | ||||
| 1176 | |||||
| 1177 | The main use for C<latin1> is to relatively efficiently store binary data | ||||
| 1178 | as JSON, at the expense of breaking compatibility with most JSON decoders. | ||||
| 1179 | |||||
| 1180 | The main use for C<ascii> is to force the output to not contain characters | ||||
| 1181 | with values > 127, which means you can interpret the resulting string | ||||
| 1182 | as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and | ||||
| 1183 | 8-bit-encoding, and still get the same data structure back. This is useful | ||||
| 1184 | when your channel for JSON transfer is not 8-bit clean or the encoding | ||||
| 1185 | might be mangled in between (e.g. in mail), and works because ASCII is a | ||||
| 1186 | proper subset of most 8-bit and multibyte encodings in use in the world. | ||||
| 1187 | |||||
| 1188 | =back | ||||
| 1189 | |||||
| 1190 | |||||
| 1191 | =head2 JSON and ECMAscript | ||||
| 1192 | |||||
| 1193 | JSON syntax is based on how literals are represented in javascript (the | ||||
| 1194 | not-standardised predecessor of ECMAscript) which is presumably why it is | ||||
| 1195 | called "JavaScript Object Notation". | ||||
| 1196 | |||||
| 1197 | However, JSON is not a subset (and also not a superset of course) of | ||||
| 1198 | ECMAscript (the standard) or javascript (whatever browsers actually | ||||
| 1199 | implement). | ||||
| 1200 | |||||
| 1201 | If you want to use javascript's C<eval> function to "parse" JSON, you | ||||
| 1202 | might run into parse errors for valid JSON texts, or the resulting data | ||||
| 1203 | structure might not be queryable: | ||||
| 1204 | |||||
| 1205 | One of the problems is that U+2028 and U+2029 are valid characters inside | ||||
| 1206 | JSON strings, but are not allowed in ECMAscript string literals, so the | ||||
| 1207 | following Perl fragment will not output something that can be guaranteed | ||||
| 1208 | to be parsable by javascript's C<eval>: | ||||
| 1209 | |||||
| 1210 | use JSON::XS; | ||||
| 1211 | |||||
| 1212 | print encode_json [chr 0x2028]; | ||||
| 1213 | |||||
| 1214 | The right fix for this is to use a proper JSON parser in your javascript | ||||
| 1215 | programs, and not rely on C<eval> (see for example Douglas Crockford's | ||||
| 1216 | F<json2.js> parser). | ||||
| 1217 | |||||
| 1218 | If this is not an option, you can, as a stop-gap measure, simply encode to | ||||
| 1219 | ASCII-only JSON: | ||||
| 1220 | |||||
| 1221 | use JSON::XS; | ||||
| 1222 | |||||
| 1223 | print JSON::XS->new->ascii->encode ([chr 0x2028]); | ||||
| 1224 | |||||
| 1225 | Note that this will enlarge the resulting JSON text quite a bit if you | ||||
| 1226 | have many non-ASCII characters. You might be tempted to run some regexes | ||||
| 1227 | to only escape U+2028 and U+2029, e.g.: | ||||
| 1228 | |||||
| 1229 | # DO NOT USE THIS! | ||||
| 1230 | my $json = JSON::XS->new->utf8->encode ([chr 0x2028]); | ||||
| 1231 | $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028 | ||||
| 1232 | $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029 | ||||
| 1233 | print $json; | ||||
| 1234 | |||||
| 1235 | Note that I<this is a bad idea>: the above only works for U+2028 and | ||||
| 1236 | U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing | ||||
| 1237 | javascript implementations, however, have issues with other characters as | ||||
| 1238 | well - using C<eval> naively simply I<will> cause problems. | ||||
| 1239 | |||||
| 1240 | Another problem is that some javascript implementations reserve | ||||
| 1241 | some property names for their own purposes (which probably makes | ||||
| 1242 | them non-ECMAscript-compliant). For example, Iceweasel reserves the | ||||
| 1243 | C<__proto__> property name for it's own purposes. | ||||
| 1244 | |||||
| 1245 | If that is a problem, you could parse try to filter the resulting JSON | ||||
| 1246 | output for these property strings, e.g.: | ||||
| 1247 | |||||
| 1248 | $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; | ||||
| 1249 | |||||
| 1250 | This works because C<__proto__> is not valid outside of strings, so every | ||||
| 1251 | occurence of C<"__proto__"\s*:> must be a string used as property name. | ||||
| 1252 | |||||
| 1253 | If you know of other incompatibilities, please let me know. | ||||
| 1254 | |||||
| 1255 | |||||
| 1256 | =head2 JSON and YAML | ||||
| 1257 | |||||
| 1258 | You often hear that JSON is a subset of YAML. This is, however, a mass | ||||
| 1259 | hysteria(*) and very far from the truth (as of the time of this writing), | ||||
| 1260 | so let me state it clearly: I<in general, there is no way to configure | ||||
| 1261 | JSON::XS to output a data structure as valid YAML> that works in all | ||||
| 1262 | cases. | ||||
| 1263 | |||||
| 1264 | If you really must use JSON::XS to generate YAML, you should use this | ||||
| 1265 | algorithm (subject to change in future versions): | ||||
| 1266 | |||||
| 1267 | my $to_yaml = JSON::XS->new->utf8->space_after (1); | ||||
| 1268 | my $yaml = $to_yaml->encode ($ref) . "\n"; | ||||
| 1269 | |||||
| 1270 | This will I<usually> generate JSON texts that also parse as valid | ||||
| 1271 | YAML. Please note that YAML has hardcoded limits on (simple) object key | ||||
| 1272 | lengths that JSON doesn't have and also has different and incompatible | ||||
| 1273 | unicode character escape syntax, so you should make sure that your hash | ||||
| 1274 | keys are noticeably shorter than the 1024 "stream characters" YAML allows | ||||
| 1275 | and that you do not have characters with codepoint values outside the | ||||
| 1276 | Unicode BMP (basic multilingual page). YAML also does not allow C<\/> | ||||
| 1277 | sequences in strings (which JSON::XS does not I<currently> generate, but | ||||
| 1278 | other JSON generators might). | ||||
| 1279 | |||||
| 1280 | There might be other incompatibilities that I am not aware of (or the YAML | ||||
| 1281 | specification has been changed yet again - it does so quite often). In | ||||
| 1282 | general you should not try to generate YAML with a JSON generator or vice | ||||
| 1283 | versa, or try to parse JSON with a YAML parser or vice versa: chances are | ||||
| 1284 | high that you will run into severe interoperability problems when you | ||||
| 1285 | least expect it. | ||||
| 1286 | |||||
| 1287 | =over 4 | ||||
| 1288 | |||||
| 1289 | =item (*) | ||||
| 1290 | |||||
| 1291 | I have been pressured multiple times by Brian Ingerson (one of the | ||||
| 1292 | authors of the YAML specification) to remove this paragraph, despite him | ||||
| 1293 | acknowledging that the actual incompatibilities exist. As I was personally | ||||
| 1294 | bitten by this "JSON is YAML" lie, I refused and said I will continue to | ||||
| 1295 | educate people about these issues, so others do not run into the same | ||||
| 1296 | problem again and again. After this, Brian called me a (quote)I<complete | ||||
| 1297 | and worthless idiot>(unquote). | ||||
| 1298 | |||||
| 1299 | In my opinion, instead of pressuring and insulting people who actually | ||||
| 1300 | clarify issues with YAML and the wrong statements of some of its | ||||
| 1301 | proponents, I would kindly suggest reading the JSON spec (which is not | ||||
| 1302 | that difficult or long) and finally make YAML compatible to it, and | ||||
| 1303 | educating users about the changes, instead of spreading lies about the | ||||
| 1304 | real compatibility for many I<years> and trying to silence people who | ||||
| 1305 | point out that it isn't true. | ||||
| 1306 | |||||
| 1307 | Addendum/2009: the YAML 1.2 spec is still incomaptible with JSON, even | ||||
| 1308 | though the incompatibilities have been documented (and are known to | ||||
| 1309 | Brian) for many years and the spec makes explicit claims that YAML is a | ||||
| 1310 | superset of JSON. It would be so easy to fix, but apparently, bullying and | ||||
| 1311 | corrupting userdata is so much easier. | ||||
| 1312 | |||||
| 1313 | =back | ||||
| 1314 | |||||
| 1315 | |||||
| 1316 | =head2 SPEED | ||||
| 1317 | |||||
| 1318 | It seems that JSON::XS is surprisingly fast, as shown in the following | ||||
| 1319 | tables. They have been generated with the help of the C<eg/bench> program | ||||
| 1320 | in the JSON::XS distribution, to make it easy to compare on your own | ||||
| 1321 | system. | ||||
| 1322 | |||||
| 1323 | First comes a comparison between various modules using | ||||
| 1324 | a very short single-line JSON string (also available at | ||||
| 1325 | L<http://dist.schmorp.de/misc/json/short.json>). | ||||
| 1326 | |||||
| 1327 | {"method": "handleMessage", "params": ["user1", | ||||
| 1328 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, | ||||
| 1329 | true, false]} | ||||
| 1330 | |||||
| 1331 | It shows the number of encodes/decodes per second (JSON::XS uses | ||||
| 1332 | the functional interface, while JSON::XS/2 uses the OO interface | ||||
| 1333 | with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables | ||||
| 1334 | shrink). Higher is better: | ||||
| 1335 | |||||
| 1336 | module | encode | decode | | ||||
| 1337 | -----------|------------|------------| | ||||
| 1338 | JSON 1.x | 4990.842 | 4088.813 | | ||||
| 1339 | JSON::DWIW | 51653.990 | 71575.154 | | ||||
| 1340 | JSON::PC | 65948.176 | 74631.744 | | ||||
| 1341 | JSON::PP | 8931.652 | 3817.168 | | ||||
| 1342 | JSON::Syck | 24877.248 | 27776.848 | | ||||
| 1343 | JSON::XS | 388361.481 | 227951.304 | | ||||
| 1344 | JSON::XS/2 | 227951.304 | 218453.333 | | ||||
| 1345 | JSON::XS/3 | 338250.323 | 218453.333 | | ||||
| 1346 | Storable | 16500.016 | 135300.129 | | ||||
| 1347 | -----------+------------+------------+ | ||||
| 1348 | |||||
| 1349 | That is, JSON::XS is about five times faster than JSON::DWIW on encoding, | ||||
| 1350 | about three times faster on decoding, and over forty times faster | ||||
| 1351 | than JSON, even with pretty-printing and key sorting. It also compares | ||||
| 1352 | favourably to Storable for small amounts of data. | ||||
| 1353 | |||||
| 1354 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals | ||||
| 1355 | search API (L<http://dist.schmorp.de/misc/json/long.json>). | ||||
| 1356 | |||||
| 1357 | module | encode | decode | | ||||
| 1358 | -----------|------------|------------| | ||||
| 1359 | JSON 1.x | 55.260 | 34.971 | | ||||
| 1360 | JSON::DWIW | 825.228 | 1082.513 | | ||||
| 1361 | JSON::PC | 3571.444 | 2394.829 | | ||||
| 1362 | JSON::PP | 210.987 | 32.574 | | ||||
| 1363 | JSON::Syck | 552.551 | 787.544 | | ||||
| 1364 | JSON::XS | 5780.463 | 4854.519 | | ||||
| 1365 | JSON::XS/2 | 3869.998 | 4798.975 | | ||||
| 1366 | JSON::XS/3 | 5862.880 | 4798.975 | | ||||
| 1367 | Storable | 4445.002 | 5235.027 | | ||||
| 1368 | -----------+------------+------------+ | ||||
| 1369 | |||||
| 1370 | Again, JSON::XS leads by far (except for Storable which non-surprisingly | ||||
| 1371 | decodes faster). | ||||
| 1372 | |||||
| 1373 | On large strings containing lots of high Unicode characters, some modules | ||||
| 1374 | (such as JSON::PC) seem to decode faster than JSON::XS, but the result | ||||
| 1375 | will be broken due to missing (or wrong) Unicode handling. Others refuse | ||||
| 1376 | to decode or encode properly, so it was impossible to prepare a fair | ||||
| 1377 | comparison table for that case. | ||||
| 1378 | |||||
| 1379 | |||||
| 1380 | =head1 SECURITY CONSIDERATIONS | ||||
| 1381 | |||||
| 1382 | When you are using JSON in a protocol, talking to untrusted potentially | ||||
| 1383 | hostile creatures requires relatively few measures. | ||||
| 1384 | |||||
| 1385 | First of all, your JSON decoder should be secure, that is, should not have | ||||
| 1386 | any buffer overflows. Obviously, this module should ensure that and I am | ||||
| 1387 | trying hard on making that true, but you never know. | ||||
| 1388 | |||||
| 1389 | Second, you need to avoid resource-starving attacks. That means you should | ||||
| 1390 | limit the size of JSON texts you accept, or make sure then when your | ||||
| 1391 | resources run out, that's just fine (e.g. by using a separate process that | ||||
| 1392 | can crash safely). The size of a JSON text in octets or characters is | ||||
| 1393 | usually a good indication of the size of the resources required to decode | ||||
| 1394 | it into a Perl structure. While JSON::XS can check the size of the JSON | ||||
| 1395 | text, it might be too late when you already have it in memory, so you | ||||
| 1396 | might want to check the size before you accept the string. | ||||
| 1397 | |||||
| 1398 | Third, JSON::XS recurses using the C stack when decoding objects and | ||||
| 1399 | arrays. The C stack is a limited resource: for instance, on my amd64 | ||||
| 1400 | machine with 8MB of stack size I can decode around 180k nested arrays but | ||||
| 1401 | only 14k nested JSON objects (due to perl itself recursing deeply on croak | ||||
| 1402 | to free the temporary). If that is exceeded, the program crashes. To be | ||||
| 1403 | conservative, the default nesting limit is set to 512. If your process | ||||
| 1404 | has a smaller stack, you should adjust this setting accordingly with the | ||||
| 1405 | C<max_depth> method. | ||||
| 1406 | |||||
| 1407 | Something else could bomb you, too, that I forgot to think of. In that | ||||
| 1408 | case, you get to keep the pieces. I am always open for hints, though... | ||||
| 1409 | |||||
| 1410 | Also keep in mind that JSON::XS might leak contents of your Perl data | ||||
| 1411 | structures in its error messages, so when you serialise sensitive | ||||
| 1412 | information you might want to make sure that exceptions thrown by JSON::XS | ||||
| 1413 | will not end up in front of untrusted eyes. | ||||
| 1414 | |||||
| 1415 | If you are using JSON::XS to return packets to consumption | ||||
| 1416 | by JavaScript scripts in a browser you should have a look at | ||||
| 1417 | L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether | ||||
| 1418 | you are vulnerable to some common attack vectors (which really are browser | ||||
| 1419 | design bugs, but it is still you who will have to deal with it, as major | ||||
| 1420 | browser developers care only for features, not about getting security | ||||
| 1421 | right). | ||||
| 1422 | |||||
| 1423 | |||||
| 1424 | =head1 THREADS | ||||
| 1425 | |||||
| 1426 | This module is I<not> guaranteed to be thread safe and there are no | ||||
| 1427 | plans to change this until Perl gets thread support (as opposed to the | ||||
| 1428 | horribly slow so-called "threads" which are simply slow and bloated | ||||
| 1429 | process simulations - use fork, it's I<much> faster, cheaper, better). | ||||
| 1430 | |||||
| 1431 | (It might actually work, but you have been warned). | ||||
| 1432 | |||||
| 1433 | |||||
| 1434 | =head1 BUGS | ||||
| 1435 | |||||
| 1436 | While the goal of this module is to be correct, that unfortunately does | ||||
| 1437 | not mean it's bug-free, only that I think its design is bug-free. If you | ||||
| 1438 | keep reporting bugs they will be fixed swiftly, though. | ||||
| 1439 | |||||
| 1440 | Please refrain from using rt.cpan.org or any other bug reporting | ||||
| 1441 | service. I put the contact address into my modules for a reason. | ||||
| 1442 | |||||
| 1443 | =cut | ||||
| 1444 | |||||
| 1445 | 1 | 22µs | our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; | ||
| 1446 | 1 | 700ns | our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; | ||
| 1447 | |||||
| 1448 | sub true() { $true } | ||||
| 1449 | sub false() { $false } | ||||
| 1450 | |||||
| 1451 | sub is_bool($) { | ||||
| 1452 | UNIVERSAL::isa $_[0], "JSON::XS::Boolean" | ||||
| 1453 | # or UNIVERSAL::isa $_[0], "JSON::Literal" | ||||
| 1454 | } | ||||
| 1455 | |||||
| 1456 | 1 | 390µs | 1 | 1.00ms | XSLoader::load "JSON::XS", $VERSION; # spent 1.00ms making 1 call to XSLoader::load |
| 1457 | |||||
| 1458 | package JSON::XS::Boolean; | ||||
| 1459 | |||||
| 1460 | use overload | ||||
| 1461 | # spent 40µs (10+30) within JSON::XS::Boolean::BEGIN@1461 which was called
# once (10µs+30µs) by JSON::BEGIN@2 at line 1464 | ||||
| 1462 | "++" => sub { $_[0] = ${$_[0]} + 1 }, | ||||
| 1463 | "--" => sub { $_[0] = ${$_[0]} - 1 }, | ||||
| 1464 | 3 | 35µs | 2 | 69µs | fallback => 1; # spent 40µs making 1 call to JSON::XS::Boolean::BEGIN@1461
# spent 30µs making 1 call to overload::import |
| 1465 | |||||
| 1466 | 1 | 12µs | 1; | ||
| 1467 | |||||
| 1468 | =head1 SEE ALSO | ||||
| 1469 | |||||
| 1470 | The F<json_xs> command line utility for quick experiments. | ||||
| 1471 | |||||
| 1472 | =head1 AUTHOR | ||||
| 1473 | |||||
| 1474 | Marc Lehmann <schmorp@schmorp.de> | ||||
| 1475 | http://home.schmorp.de/ | ||||
| 1476 | |||||
| 1477 | =cut | ||||
| 1478 | |||||
# spent 20µs within JSON::XS::DESTROY which was called 13 times, avg 2µs/call:
# 8 times (13µs+0s) by JSON::to_json at line 165 of ../lib/SimpleDB/Class/Types.pm, avg 2µs/call
# 5 times (7µs+0s) by JSON::from_json at line 213 of ../lib/SimpleDB/Class/Types.pm, avg 1µs/call | |||||
# spent 66µs within JSON::XS::decode which was called 5 times, avg 13µs/call:
# 5 times (66µs+0s) by JSON::from_json at line 154 of JSON.pm, avg 13µs/call | |||||
# spent 103µs within JSON::XS::encode which was called 8 times, avg 13µs/call:
# 8 times (103µs+0s) by JSON::to_json at line 140 of JSON.pm, avg 13µs/call | |||||
# spent 74µs within JSON::XS::new which was called 13 times, avg 6µs/call:
# 8 times (54µs+0s) by JSON::to_json at line 131 of JSON.pm, avg 7µs/call
# 5 times (20µs+0s) by JSON::from_json at line 145 of JSON.pm, avg 4µs/call |