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1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4 JSON::XS - 正しくて高速な JSON 4 JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
5 シリアライザ/デシリアライザ
6 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) 5 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7 6
8SYNOPSIS 7SYNOPSIS
9 use JSON::XS; 8 use JSON::XS;
10 9
… …
21 $perl_scalar = $coder->decode ($unicode_json_text); 20 $perl_scalar = $coder->decode ($unicode_json_text);
22 21
23 # Note that JSON version 2.0 and above will automatically use JSON::XS 22 # Note that JSON version 2.0 and above will automatically use JSON::XS
24 # if available, at virtually no speed overhead either, so you should 23 # if available, at virtually no speed overhead either, so you should
25 # be able to just: 24 # be able to just:
26 25
27 use JSON; 26 use JSON;
28 27
29 # and do the same things, except that you have a pure-perl fallback now. 28 # and do the same things, except that you have a pure-perl fallback now.
30 29
31DESCRIPTION 30DESCRIPTION
32 This module converts Perl data structures to JSON and vice versa. Its 31 This module converts Perl data structures to JSON and vice versa. Its
33 primary goal is to be *correct* and its secondary goal is to be *fast*. 32 primary goal is to be *correct* and its secondary goal is to be *fast*.
34 To reach the latter goal it was written in C. 33 To reach the latter goal it was written in C.
35 34
36 Beginning with version 2.0 of the JSON module, when both JSON and 35 Beginning with version 2.0 of the JSON module, when both JSON and
37 JSON::XS are installed, then JSON will fall back on JSON::XS (this can 36 JSON::XS are installed, then JSON will fall back on JSON::XS (this can
38 be overriden) with no overhead due to emulation (by inheritign 37 be overridden) with no overhead due to emulation (by inheriting
39 constructor and methods). If JSON::XS is not available, it will fall 38 constructor and methods). If JSON::XS is not available, it will fall
40 back to the compatible JSON::PP module as backend, so using JSON instead 39 back to the compatible JSON::PP module as backend, so using JSON instead
41 of JSON::XS gives you a portable JSON API that can be fast when you need 40 of JSON::XS gives you a portable JSON API that can be fast when you need
42 and doesn't require a C compiler when that is a problem. 41 and doesn't require a C compiler when that is a problem.
43 42
… …
51 50
52 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 51 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
53 vice versa. 52 vice versa.
54 53
55 FEATURES 54 FEATURES
56 * correct Unicode handling 55 * correct Unicode handling
56
57 This module knows how to handle Unicode, and even documents how and 57 This module knows how to handle Unicode, documents how and when it
58 when it does so. 58 does so, and even documents what "correct" means.
59 59
60 * round-trip integrity 60 * round-trip integrity
61
61 When you serialise a perl data structure using only datatypes 62 When you serialise a perl data structure using only data types
62 supported by JSON, the deserialised data structure is identical on 63 supported by JSON, the deserialised data structure is identical on
63 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" 64 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
64 just because it looks like a number). 65 just because it looks like a number). There minor *are* exceptions
66 to this, read the MAPPING section below to learn about those.
65 67
66 * strict checking of JSON correctness 68 * strict checking of JSON correctness
69
67 There is no guessing, no generating of illegal JSON texts by 70 There is no guessing, no generating of illegal JSON texts by
68 default, and only JSON is accepted as input by default (the latter 71 default, and only JSON is accepted as input by default (the latter
69 is a security feature). 72 is a security feature).
70 73
71 * fast 74 * fast
72 Compared to other JSON modules, this module compares favourably in
73 terms of speed, too.
74 75
76 Compared to other JSON modules and other serialisers such as
77 Storable, this module usually compares favourably in terms of speed,
78 too.
79
75 * simple to use 80 * simple to use
81
76 This module has both a simple functional interface as well as an OO 82 This module has both a simple functional interface as well as an
77 interface. 83 object oriented interface interface.
78 84
79 * reasonably versatile output formats 85 * reasonably versatile output formats
86
80 You can choose between the most compact guaranteed single-line 87 You can choose between the most compact guaranteed-single-line
81 format possible (nice for simple line-based protocols), a pure-ascii 88 format possible (nice for simple line-based protocols), a pure-ASCII
82 format (for when your transport is not 8-bit clean, still supports 89 format (for when your transport is not 8-bit clean, still supports
83 the whole Unicode range), or a pretty-printed format (for when you 90 the whole Unicode range), or a pretty-printed format (for when you
84 want to read that stuff). Or you can combine those features in 91 want to read that stuff). Or you can combine those features in
85 whatever way you like. 92 whatever way you like.
86 93
… …
94 101
95 This function call is functionally identical to: 102 This function call is functionally identical to:
96 103
97 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 104 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
98 105
99 except being faster. 106 Except being faster.
100 107
101 $perl_scalar = decode_json $json_text 108 $perl_scalar = decode_json $json_text
102 The opposite of "encode_json": expects an UTF-8 (binary) string and 109 The opposite of "encode_json": expects an UTF-8 (binary) string and
103 tries to parse that as an UTF-8 encoded JSON text, returning the 110 tries to parse that as an UTF-8 encoded JSON text, returning the
104 resulting reference. Croaks on error. 111 resulting reference. Croaks on error.
105 112
106 This function call is functionally identical to: 113 This function call is functionally identical to:
107 114
108 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 115 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
109 116
110 except being faster. 117 Except being faster.
111 118
112 $is_boolean = JSON::XS::is_bool $scalar 119 $is_boolean = JSON::XS::is_bool $scalar
113 Returns true if the passed scalar represents either JSON::XS::true 120 Returns true if the passed scalar represents either JSON::XS::true
114 or JSON::XS::false, two constants that act like 1 and 0, 121 or JSON::XS::false, two constants that act like 1 and 0,
115 respectively and are used to represent JSON "true" and "false" 122 respectively and are used to represent JSON "true" and "false"
… …
125 1. Perl strings can store characters with ordinal values > 255. 132 1. Perl strings can store characters with ordinal values > 255.
126 This enables you to store Unicode characters as single characters in 133 This enables you to store Unicode characters as single characters in
127 a Perl string - very natural. 134 a Perl string - very natural.
128 135
129 2. Perl does *not* associate an encoding with your strings. 136 2. Perl does *not* associate an encoding with your strings.
130 Unless you force it to, e.g. when matching it against a regex, or 137 ... until you force it to, e.g. when matching it against a regex, or
131 printing the scalar to a file, in which case Perl either interprets 138 printing the scalar to a file, in which case Perl either interprets
132 your string as locale-encoded text, octets/binary, or as Unicode, 139 your string as locale-encoded text, octets/binary, or as Unicode,
133 depending on various settings. In no case is an encoding stored 140 depending on various settings. In no case is an encoding stored
134 together with your data, it is *use* that decides encoding, not any 141 together with your data, it is *use* that decides encoding, not any
135 magical metadata. 142 magical meta data.
136 143
137 3. The internal utf-8 flag has no meaning with regards to the encoding 144 3. The internal utf-8 flag has no meaning with regards to the encoding
138 of your string. 145 of your string.
139 Just ignore that flag unless you debug a Perl bug, a module written 146 Just ignore that flag unless you debug a Perl bug, a module written
140 in XS or want to dive into the internals of perl. Otherwise it will 147 in XS or want to dive into the internals of perl. Otherwise it will
… …
145 152
146 If you didn't know about that flag, just the better, pretend it 153 If you didn't know about that flag, just the better, pretend it
147 doesn't exist. 154 doesn't exist.
148 155
149 4. A "Unicode String" is simply a string where each character can be 156 4. A "Unicode String" is simply a string where each character can be
150 validly interpreted as a Unicode codepoint. 157 validly interpreted as a Unicode code point.
151 If you have UTF-8 encoded data, it is no longer a Unicode string, 158 If you have UTF-8 encoded data, it is no longer a Unicode string,
152 but a Unicode string encoded in UTF-8, giving you a binary string. 159 but a Unicode string encoded in UTF-8, giving you a binary string.
153 160
154 5. A string containing "high" (> 255) character values is *not* a UTF-8 161 5. A string containing "high" (> 255) character values is *not* a UTF-8
155 string. 162 string.
… …
185 192
186 If $enable is false, then the "encode" method will not escape 193 If $enable is false, then the "encode" method will not escape
187 Unicode characters unless required by the JSON syntax or other 194 Unicode characters unless required by the JSON syntax or other
188 flags. This results in a faster and more compact format. 195 flags. This results in a faster and more compact format.
189 196
197 See also the section *ENCODING/CODESET FLAG NOTES* later in this
198 document.
199
190 The main use for this flag is to produce JSON texts that can be 200 The main use for this flag is to produce JSON texts that can be
191 transmitted over a 7-bit channel, as the encoded JSON texts will not 201 transmitted over a 7-bit channel, as the encoded JSON texts will not
192 contain any 8 bit characters. 202 contain any 8 bit characters.
193 203
194 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 204 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
… …
205 superset of latin1. 215 superset of latin1.
206 216
207 If $enable is false, then the "encode" method will not escape 217 If $enable is false, then the "encode" method will not escape
208 Unicode characters unless required by the JSON syntax or other 218 Unicode characters unless required by the JSON syntax or other
209 flags. 219 flags.
220
221 See also the section *ENCODING/CODESET FLAG NOTES* later in this
222 document.
210 223
211 The main use for this flag is efficiently encoding binary data as 224 The main use for this flag is efficiently encoding binary data as
212 JSON text, as most octets will not be escaped, resulting in a 225 JSON text, as most octets will not be escaped, resulting in a
213 smaller encoded size. The disadvantage is that the resulting JSON 226 smaller encoded size. The disadvantage is that the resulting JSON
214 text is encoded in latin1 (and must correctly be treated as such 227 text is encoded in latin1 (and must correctly be treated as such
… …
234 If $enable is false, then the "encode" method will return the JSON 247 If $enable is false, then the "encode" method will return the JSON
235 string as a (non-encoded) Unicode string, while "decode" expects 248 string as a (non-encoded) Unicode string, while "decode" expects
236 thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or 249 thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
237 UTF-16) needs to be done yourself, e.g. using the Encode module. 250 UTF-16) needs to be done yourself, e.g. using the Encode module.
238 251
252 See also the section *ENCODING/CODESET FLAG NOTES* later in this
253 document.
254
239 Example, output UTF-16BE-encoded JSON: 255 Example, output UTF-16BE-encoded JSON:
240 256
241 use Encode; 257 use Encode;
242 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 258 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
243 259
… …
318 If $enable is false (the default), then "decode" will only accept 334 If $enable is false (the default), then "decode" will only accept
319 valid JSON texts. 335 valid JSON texts.
320 336
321 Currently accepted extensions are: 337 Currently accepted extensions are:
322 338
323 * list items can have an end-comma 339 * list items can have an end-comma
340
324 JSON *separates* array elements and key-value pairs with commas. 341 JSON *separates* array elements and key-value pairs with commas.
325 This can be annoying if you write JSON texts manually and want 342 This can be annoying if you write JSON texts manually and want
326 to be able to quickly append elements, so this extension accepts 343 to be able to quickly append elements, so this extension accepts
327 comma at the end of such items not just between them: 344 comma at the end of such items not just between them:
328 345
… …
333 { 350 {
334 "k1": "v1", 351 "k1": "v1",
335 "k2": "v2", <- this comma not normally allowed 352 "k2": "v2", <- this comma not normally allowed
336 } 353 }
337 354
338 * shell-style '#'-comments 355 * shell-style '#'-comments
356
339 Whenever JSON allows whitespace, shell-style comments are 357 Whenever JSON allows whitespace, shell-style comments are
340 additionally allowed. They are terminated by the first 358 additionally allowed. They are terminated by the first
341 carriage-return or line-feed character, after which more 359 carriage-return or line-feed character, after which more
342 white-space and comments are allowed. 360 white-space and comments are allowed.
343 361
… …
379 Example, encode a Perl scalar as JSON value with enabled 397 Example, encode a Perl scalar as JSON value with enabled
380 "allow_nonref", resulting in an invalid JSON text: 398 "allow_nonref", resulting in an invalid JSON text:
381 399
382 JSON::XS->new->allow_nonref->encode ("Hello, World!") 400 JSON::XS->new->allow_nonref->encode ("Hello, World!")
383 => "Hello, World!" 401 => "Hello, World!"
402
403 $json = $json->allow_unknown ([$enable])
404 $enabled = $json->get_allow_unknown
405 If $enable is true (or missing), then "encode" will *not* throw an
406 exception when it encounters values it cannot represent in JSON (for
407 example, filehandles) but instead will encode a JSON "null" value.
408 Note that blessed objects are not included here and are handled
409 separately by c<allow_nonref>.
410
411 If $enable is false (the default), then "encode" will throw an
412 exception when it encounters anything it cannot encode as JSON.
413
414 This option does not affect "decode" in any way, and it is
415 recommended to leave it off unless you know your communications
416 partner.
384 417
385 $json = $json->allow_blessed ([$enable]) 418 $json = $json->allow_blessed ([$enable])
386 $enabled = $json->get_allow_blessed 419 $enabled = $json->get_allow_blessed
387 If $enable is true (or missing), then the "encode" method will not 420 If $enable is true (or missing), then the "encode" method will not
388 barf when it encounters a blessed reference. Instead, the value of 421 barf when it encounters a blessed reference. Instead, the value of
… …
523 saving space. 556 saving space.
524 557
525 $json = $json->max_depth ([$maximum_nesting_depth]) 558 $json = $json->max_depth ([$maximum_nesting_depth])
526 $max_depth = $json->get_max_depth 559 $max_depth = $json->get_max_depth
527 Sets the maximum nesting level (default 512) accepted while encoding 560 Sets the maximum nesting level (default 512) accepted while encoding
528 or decoding. If the JSON text or Perl data structure has an equal or 561 or decoding. If a higher nesting level is detected in JSON text or a
529 higher nesting level then this limit, then the encoder and decoder 562 Perl data structure, then the encoder and decoder will stop and
530 will stop and croak at that point. 563 croak at that point.
531 564
532 Nesting level is defined by number of hash- or arrayrefs that the 565 Nesting level is defined by number of hash- or arrayrefs that the
533 encoder needs to traverse to reach a given point or the number of 566 encoder needs to traverse to reach a given point or the number of
534 "{" or "[" characters without their matching closing parenthesis 567 "{" or "[" characters without their matching closing parenthesis
535 crossed to reach a given character in a string. 568 crossed to reach a given character in a string.
536 569
537 Setting the maximum depth to one disallows any nesting, so that 570 Setting the maximum depth to one disallows any nesting, so that
538 ensures that the object is only a single hash/object or array. 571 ensures that the object is only a single hash/object or array.
539 572
540 The argument to "max_depth" will be rounded up to the next highest
541 power of two. If no argument is given, the highest possible setting 573 If no argument is given, the highest possible setting will be used,
542 will be used, which is rarely useful. 574 which is rarely useful.
575
576 Note that nesting is implemented by recursion in C. The default
577 value has been chosen to be as large as typical operating systems
578 allow without crashing.
543 579
544 See SECURITY CONSIDERATIONS, below, for more info on why this is 580 See SECURITY CONSIDERATIONS, below, for more info on why this is
545 useful. 581 useful.
546 582
547 $json = $json->max_size ([$maximum_string_size]) 583 $json = $json->max_size ([$maximum_string_size])
548 $max_size = $json->get_max_size 584 $max_size = $json->get_max_size
549 Set the maximum length a JSON text may have (in bytes) where 585 Set the maximum length a JSON text may have (in bytes) where
550 decoding is being attempted. The default is 0, meaning no limit. 586 decoding is being attempted. The default is 0, meaning no limit.
551 When "decode" is called on a string longer then this number of 587 When "decode" is called on a string that is longer then this many
552 characters it will not attempt to decode the string but throw an 588 bytes, it will not attempt to decode the string but throw an
553 exception. This setting has no effect on "encode" (yet). 589 exception. This setting has no effect on "encode" (yet).
554 590
555 The argument to "max_size" will be rounded up to the next highest
556 power of two (so may be more than requested). If no argument is
557 given, the limit check will be deactivated (same as when 0 is 591 If no argument is given, the limit check will be deactivated (same
558 specified). 592 as when 0 is specified).
559 593
560 See SECURITY CONSIDERATIONS, below, for more info on why this is 594 See SECURITY CONSIDERATIONS, below, for more info on why this is
561 useful. 595 useful.
562 596
563 $json_text = $json->encode ($perl_scalar) 597 $json_text = $json->encode ($perl_scalar)
… …
588 and you need to know where the JSON text ends. 622 and you need to know where the JSON text ends.
589 623
590 JSON::XS->new->decode_prefix ("[1] the tail") 624 JSON::XS->new->decode_prefix ("[1] the tail")
591 => ([], 3) 625 => ([], 3)
592 626
627INCREMENTAL PARSING
628 In some cases, there is the need for incremental parsing of JSON texts.
629 While this module always has to keep both JSON text and resulting Perl
630 data structure in memory at one time, it does allow you to parse a JSON
631 stream incrementally. It does so by accumulating text until it has a
632 full JSON object, which it then can decode. This process is similar to
633 using "decode_prefix" to see if a full JSON object is available, but is
634 much more efficient (and can be implemented with a minimum of method
635 calls).
636
637 JSON::XS will only attempt to parse the JSON text once it is sure it has
638 enough text to get a decisive result, using a very simple but truly
639 incremental parser. This means that it sometimes won't stop as early as
640 the full parser, for example, it doesn't detect parenthese mismatches.
641 The only thing it guarantees is that it starts decoding as soon as a
642 syntactically valid JSON text has been seen. This means you need to set
643 resource limits (e.g. "max_size") to ensure the parser will stop parsing
644 in the presence if syntax errors.
645
646 The following methods implement this incremental parser.
647
648 [void, scalar or list context] = $json->incr_parse ([$string])
649 This is the central parsing function. It can both append new text
650 and extract objects from the stream accumulated so far (both of
651 these functions are optional).
652
653 If $string is given, then this string is appended to the already
654 existing JSON fragment stored in the $json object.
655
656 After that, if the function is called in void context, it will
657 simply return without doing anything further. This can be used to
658 add more text in as many chunks as you want.
659
660 If the method is called in scalar context, then it will try to
661 extract exactly *one* JSON object. If that is successful, it will
662 return this object, otherwise it will return "undef". If there is a
663 parse error, this method will croak just as "decode" would do (one
664 can then use "incr_skip" to skip the errornous part). This is the
665 most common way of using the method.
666
667 And finally, in list context, it will try to extract as many objects
668 from the stream as it can find and return them, or the empty list
669 otherwise. For this to work, there must be no separators between the
670 JSON objects or arrays, instead they must be concatenated
671 back-to-back. If an error occurs, an exception will be raised as in
672 the scalar context case. Note that in this case, any
673 previously-parsed JSON texts will be lost.
674
675 $lvalue_string = $json->incr_text
676 This method returns the currently stored JSON fragment as an lvalue,
677 that is, you can manipulate it. This *only* works when a preceding
678 call to "incr_parse" in *scalar context* successfully returned an
679 object. Under all other circumstances you must not call this
680 function (I mean it. although in simple tests it might actually
681 work, it *will* fail under real world conditions). As a special
682 exception, you can also call this method before having parsed
683 anything.
684
685 This function is useful in two cases: a) finding the trailing text
686 after a JSON object or b) parsing multiple JSON objects separated by
687 non-JSON text (such as commas).
688
689 $json->incr_skip
690 This will reset the state of the incremental parser and will remove
691 the parsed text from the input buffer. This is useful after
692 "incr_parse" died, in which case the input buffer and incremental
693 parser state is left unchanged, to skip the text parsed so far and
694 to reset the parse state.
695
696 $json->incr_reset
697 This completely resets the incremental parser, that is, after this
698 call, it will be as if the parser had never parsed anything.
699
700 This is useful if you want ot repeatedly parse JSON objects and want
701 to ignore any trailing data, which means you have to reset the
702 parser after each successful decode.
703
704 LIMITATIONS
705 All options that affect decoding are supported, except "allow_nonref".
706 The reason for this is that it cannot be made to work sensibly: JSON
707 objects and arrays are self-delimited, i.e. you can concatenate them
708 back to back and still decode them perfectly. This does not hold true
709 for JSON numbers, however.
710
711 For example, is the string 1 a single JSON number, or is it simply the
712 start of 12? Or is 12 a single JSON number, or the concatenation of 1
713 and 2? In neither case you can tell, and this is why JSON::XS takes the
714 conservative route and disallows this case.
715
716 EXAMPLES
717 Some examples will make all this clearer. First, a simple example that
718 works similarly to "decode_prefix": We want to decode the JSON object at
719 the start of a string and identify the portion after the JSON object:
720
721 my $text = "[1,2,3] hello";
722
723 my $json = new JSON::XS;
724
725 my $obj = $json->incr_parse ($text)
726 or die "expected JSON object or array at beginning of string";
727
728 my $tail = $json->incr_text;
729 # $tail now contains " hello"
730
731 Easy, isn't it?
732
733 Now for a more complicated example: Imagine a hypothetical protocol
734 where you read some requests from a TCP stream, and each request is a
735 JSON array, without any separation between them (in fact, it is often
736 useful to use newlines as "separators", as these get interpreted as
737 whitespace at the start of the JSON text, which makes it possible to
738 test said protocol with "telnet"...).
739
740 Here is how you'd do it (it is trivial to write this in an event-based
741 manner):
742
743 my $json = new JSON::XS;
744
745 # read some data from the socket
746 while (sysread $socket, my $buf, 4096) {
747
748 # split and decode as many requests as possible
749 for my $request ($json->incr_parse ($buf)) {
750 # act on the $request
751 }
752 }
753
754 Another complicated example: Assume you have a string with JSON objects
755 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
756 [3]"). To parse them, we have to skip the commas between the JSON texts,
757 and here is where the lvalue-ness of "incr_text" comes in useful:
758
759 my $text = "[1],[2], [3]";
760 my $json = new JSON::XS;
761
762 # void context, so no parsing done
763 $json->incr_parse ($text);
764
765 # now extract as many objects as possible. note the
766 # use of scalar context so incr_text can be called.
767 while (my $obj = $json->incr_parse) {
768 # do something with $obj
769
770 # now skip the optional comma
771 $json->incr_text =~ s/^ \s* , //x;
772 }
773
774 Now lets go for a very complex example: Assume that you have a gigantic
775 JSON array-of-objects, many gigabytes in size, and you want to parse it,
776 but you cannot load it into memory fully (this has actually happened in
777 the real world :).
778
779 Well, you lost, you have to implement your own JSON parser. But JSON::XS
780 can still help you: You implement a (very simple) array parser and let
781 JSON decode the array elements, which are all full JSON objects on their
782 own (this wouldn't work if the array elements could be JSON numbers, for
783 example):
784
785 my $json = new JSON::XS;
786
787 # open the monster
788 open my $fh, "<bigfile.json"
789 or die "bigfile: $!";
790
791 # first parse the initial "["
792 for (;;) {
793 sysread $fh, my $buf, 65536
794 or die "read error: $!";
795 $json->incr_parse ($buf); # void context, so no parsing
796
797 # Exit the loop once we found and removed(!) the initial "[".
798 # In essence, we are (ab-)using the $json object as a simple scalar
799 # we append data to.
800 last if $json->incr_text =~ s/^ \s* \[ //x;
801 }
802
803 # now we have the skipped the initial "[", so continue
804 # parsing all the elements.
805 for (;;) {
806 # in this loop we read data until we got a single JSON object
807 for (;;) {
808 if (my $obj = $json->incr_parse) {
809 # do something with $obj
810 last;
811 }
812
813 # add more data
814 sysread $fh, my $buf, 65536
815 or die "read error: $!";
816 $json->incr_parse ($buf); # void context, so no parsing
817 }
818
819 # in this loop we read data until we either found and parsed the
820 # separating "," between elements, or the final "]"
821 for (;;) {
822 # first skip whitespace
823 $json->incr_text =~ s/^\s*//;
824
825 # if we find "]", we are done
826 if ($json->incr_text =~ s/^\]//) {
827 print "finished.\n";
828 exit;
829 }
830
831 # if we find ",", we can continue with the next element
832 if ($json->incr_text =~ s/^,//) {
833 last;
834 }
835
836 # if we find anything else, we have a parse error!
837 if (length $json->incr_text) {
838 die "parse error near ", $json->incr_text;
839 }
840
841 # else add more data
842 sysread $fh, my $buf, 65536
843 or die "read error: $!";
844 $json->incr_parse ($buf); # void context, so no parsing
845 }
846
847 This is a complex example, but most of the complexity comes from the
848 fact that we are trying to be correct (bear with me if I am wrong, I
849 never ran the above example :).
850
593MAPPING 851MAPPING
594 This section describes how JSON::XS maps Perl values to JSON values and 852 This section describes how JSON::XS maps Perl values to JSON values and
595 vice versa. These mappings are designed to "do the right thing" in most 853 vice versa. These mappings are designed to "do the right thing" in most
596 circumstances automatically, preserving round-tripping characteristics 854 circumstances automatically, preserving round-tripping characteristics
597 (what you put in comes out as something equivalent). 855 (what you put in comes out as something equivalent).
… …
618 A JSON number becomes either an integer, numeric (floating point) or 876 A JSON number becomes either an integer, numeric (floating point) or
619 string scalar in perl, depending on its range and any fractional 877 string scalar in perl, depending on its range and any fractional
620 parts. On the Perl level, there is no difference between those as 878 parts. On the Perl level, there is no difference between those as
621 Perl handles all the conversion details, but an integer may take 879 Perl handles all the conversion details, but an integer may take
622 slightly less memory and might represent more values exactly than 880 slightly less memory and might represent more values exactly than
623 (floating point) numbers. 881 floating point numbers.
624 882
625 If the number consists of digits only, JSON::XS will try to 883 If the number consists of digits only, JSON::XS will try to
626 represent it as an integer value. If that fails, it will try to 884 represent it as an integer value. If that fails, it will try to
627 represent it as a numeric (floating point) value if that is possible 885 represent it as a numeric (floating point) value if that is possible
628 without loss of precision. Otherwise it will preserve the number as 886 without loss of precision. Otherwise it will preserve the number as
629 a string value. 887 a string value (in which case you lose roundtripping ability, as the
888 JSON number will be re-encoded toa JSON string).
630 889
631 Numbers containing a fractional or exponential part will always be 890 Numbers containing a fractional or exponential part will always be
632 represented as numeric (floating point) values, possibly at a loss 891 represented as numeric (floating point) values, possibly at a loss
633 of precision. 892 of precision (in which case you might lose perfect roundtripping
634 893 ability, but the JSON number will still be re-encoded as a JSON
635 This might create round-tripping problems as numbers might become 894 number).
636 strings, but as Perl is typeless there is no other way to do it.
637 895
638 true, false 896 true, false
639 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 897 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
640 respectively. They are overloaded to act almost exactly like the 898 respectively. They are overloaded to act almost exactly like the
641 numbers 1 and 0. You can check whether a scalar is a JSON boolean by 899 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
… …
669 an exception to be thrown, except for references to the integers 0 927 an exception to be thrown, except for references to the integers 0
670 and 1, which get turned into "false" and "true" atoms in JSON. You 928 and 1, which get turned into "false" and "true" atoms in JSON. You
671 can also use "JSON::XS::false" and "JSON::XS::true" to improve 929 can also use "JSON::XS::false" and "JSON::XS::true" to improve
672 readability. 930 readability.
673 931
674 encode_json [\0,JSON::XS::true] # yields [false,true] 932 encode_json [\0, JSON::XS::true] # yields [false,true]
675 933
676 JSON::XS::true, JSON::XS::false 934 JSON::XS::true, JSON::XS::false
677 These special values become JSON true and JSON false values, 935 These special values become JSON true and JSON false values,
678 respectively. You can also use "\1" and "\0" directly if you want. 936 respectively. You can also use "\1" and "\0" directly if you want.
679 937
680 blessed objects 938 blessed objects
681 Blessed objects are not allowed. JSON::XS currently tries to encode 939 Blessed objects are not directly representable in JSON. See the
682 their underlying representation (hash- or arrayref), but this 940 "allow_blessed" and "convert_blessed" methods on various options on
683 behaviour might change in future versions. 941 how to deal with this: basically, you can choose between throwing an
942 exception, encoding the reference as if it weren't blessed, or
943 provide your own serialiser method.
684 944
685 simple scalars 945 simple scalars
686 Simple Perl scalars (any scalar that is not a reference) are the 946 Simple Perl scalars (any scalar that is not a reference) are the
687 most difficult objects to encode: JSON::XS will encode undefined 947 most difficult objects to encode: JSON::XS will encode undefined
688 scalars as JSON null value, scalars that have last been used in a 948 scalars as JSON "null" values, scalars that have last been used in a
689 string context before encoding as JSON strings and anything else as 949 string context before encoding as JSON strings, and anything else as
690 number value: 950 number value:
691 951
692 # dump as number 952 # dump as number
693 encode_json [2] # yields [2] 953 encode_json [2] # yields [2]
694 encode_json [-3.0e17] # yields [-3e+17] 954 encode_json [-3.0e17] # yields [-3e+17]
… …
713 my $x = "3"; # some variable containing a string 973 my $x = "3"; # some variable containing a string
714 $x += 0; # numify it, ensuring it will be dumped as a number 974 $x += 0; # numify it, ensuring it will be dumped as a number
715 $x *= 1; # same thing, the choice is yours. 975 $x *= 1; # same thing, the choice is yours.
716 976
717 You can not currently force the type in other, less obscure, ways. 977 You can not currently force the type in other, less obscure, ways.
718 Tell me if you need this capability. 978 Tell me if you need this capability (but don't forget to explain why
979 it's needed :).
719 980
720COMPARISON 981ENCODING/CODESET FLAG NOTES
721 As already mentioned, this module was created because none of the 982 The interested reader might have seen a number of flags that signify
722 existing JSON modules could be made to work correctly. First I will 983 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
723 describe the problems (or pleasures) I encountered with various existing 984 some confusion on what these do, so here is a short comparison:
724 JSON modules, followed by some benchmark values. JSON::XS was designed
725 not to suffer from any of these problems or limitations.
726 985
727 JSON 1.07 986 "utf8" controls whether the JSON text created by "encode" (and expected
728 Slow (but very portable, as it is written in pure Perl). 987 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
988 control whether "encode" escapes character values outside their
989 respective codeset range. Neither of these flags conflict with each
990 other, although some combinations make less sense than others.
729 991
730 Undocumented/buggy Unicode handling (how JSON handles Unicode values 992 Care has been taken to make all flags symmetrical with respect to
731 is undocumented. One can get far by feeding it Unicode strings and 993 "encode" and "decode", that is, texts encoded with any combination of
732 doing en-/decoding oneself, but Unicode escapes are not working 994 these flag values will be correctly decoded when the same flags are used
995 - in general, if you use different flag settings while encoding vs. when
996 decoding you likely have a bug somewhere.
997
998 Below comes a verbose discussion of these flags. Note that a "codeset"
999 is simply an abstract set of character-codepoint pairs, while an
1000 encoding takes those codepoint numbers and *encodes* them, in our case
1001 into octets. Unicode is (among other things) a codeset, UTF-8 is an
1002 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
1003 encodings at the same time, which can be confusing.
1004
1005 "utf8" flag disabled
1006 When "utf8" is disabled (the default), then "encode"/"decode"
1007 generate and expect Unicode strings, that is, characters with high
1008 ordinal Unicode values (> 255) will be encoded as such characters,
1009 and likewise such characters are decoded as-is, no canges to them
1010 will be done, except "(re-)interpreting" them as Unicode codepoints
1011 or Unicode characters, respectively (to Perl, these are the same
1012 thing in strings unless you do funny/weird/dumb stuff).
1013
1014 This is useful when you want to do the encoding yourself (e.g. when
1015 you want to have UTF-16 encoded JSON texts) or when some other layer
1016 does the encoding for you (for example, when printing to a terminal
1017 using a filehandle that transparently encodes to UTF-8 you certainly
1018 do NOT want to UTF-8 encode your data first and have Perl encode it
1019 another time).
1020
1021 "utf8" flag enabled
1022 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1023 characters using the corresponding UTF-8 multi-byte sequence, and
1024 will expect your input strings to be encoded as UTF-8, that is, no
1025 "character" of the input string must have any value > 255, as UTF-8
1026 does not allow that.
1027
1028 The "utf8" flag therefore switches between two modes: disabled means
1029 you will get a Unicode string in Perl, enabled means you get an
1030 UTF-8 encoded octet/binary string in Perl.
1031
1032 "latin1" or "ascii" flags enabled
1033 With "latin1" (or "ascii") enabled, "encode" will escape characters
1034 with ordinal values > 255 (> 127 with "ascii") and encode the
1035 remaining characters as specified by the "utf8" flag.
1036
1037 If "utf8" is disabled, then the result is also correctly encoded in
1038 those character sets (as both are proper subsets of Unicode, meaning
1039 that a Unicode string with all character values < 256 is the same
1040 thing as a ISO-8859-1 string, and a Unicode string with all
1041 character values < 128 is the same thing as an ASCII string in
733 properly). 1042 Perl).
734 1043
735 No round-tripping (strings get clobbered if they look like numbers, 1044 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
736 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 1045 regardless of these flags, just some more characters will be escaped
737 will decode into the number 2. 1046 using "\uXXXX" then before.
738 1047
739 JSON::PC 0.01 1048 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
740 Very fast. 1049 encoding, while ASCII-encoded strings are. That is because the
1050 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1051 *codeset* being a subset of Unicode), while ASCII is.
741 1052
742 Undocumented/buggy Unicode handling. 1053 Surprisingly, "decode" will ignore these flags and so treat all
1054 input values as governed by the "utf8" flag. If it is disabled, this
1055 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1056 strict subsets of Unicode. If it is enabled, you can correctly
1057 decode UTF-8 encoded strings.
743 1058
744 No round-tripping. 1059 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1060 flag - they only govern when the JSON output engine escapes a
1061 character or not.
745 1062
746 Has problems handling many Perl values (e.g. regex results and other 1063 The main use for "latin1" is to relatively efficiently store binary
747 magic values will make it croak). 1064 data as JSON, at the expense of breaking compatibility with most
1065 JSON decoders.
748 1066
749 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1067 The main use for "ascii" is to force the output to not contain
750 which is not a valid JSON text. 1068 characters with values > 127, which means you can interpret the
751 1069 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
752 Unmaintained (maintainer unresponsive for many months, bugs are not 1070 any character set and 8-bit-encoding, and still get the same data
753 getting fixed). 1071 structure back. This is useful when your channel for JSON transfer
754 1072 is not 8-bit clean or the encoding might be mangled in between (e.g.
755 JSON::Syck 0.21 1073 in mail), and works because ASCII is a proper subset of most 8-bit
756 Very buggy (often crashes). 1074 and multibyte encodings in use in the world.
757
758 Very inflexible (no human-readable format supported, format pretty
759 much undocumented. I need at least a format for easy reading by
760 humans and a single-line compact format for use in a protocol, and
761 preferably a way to generate ASCII-only JSON texts).
762
763 Completely broken (and confusingly documented) Unicode handling
764 (Unicode escapes are not working properly, you need to set
765 ImplicitUnicode to *different* values on en- and decoding to get
766 symmetric behaviour).
767
768 No round-tripping (simple cases work, but this depends on whether
769 the scalar value was used in a numeric context or not).
770
771 Dumping hashes may skip hash values depending on iterator state.
772
773 Unmaintained (maintainer unresponsive for many months, bugs are not
774 getting fixed).
775
776 Does not check input for validity (i.e. will accept non-JSON input
777 and return "something" instead of raising an exception. This is a
778 security issue: imagine two banks transferring money between each
779 other using JSON. One bank might parse a given non-JSON request and
780 deduct money, while the other might reject the transaction with a
781 syntax error. While a good protocol will at least recover, that is
782 extra unnecessary work and the transaction will still not succeed).
783
784 JSON::DWIW 0.04
785 Very fast. Very natural. Very nice.
786
787 Undocumented Unicode handling (but the best of the pack. Unicode
788 escapes still don't get parsed properly).
789
790 Very inflexible.
791
792 No round-tripping.
793
794 Does not generate valid JSON texts (key strings are often unquoted,
795 empty keys result in nothing being output)
796
797 Does not check input for validity.
798 1075
799 JSON and YAML 1076 JSON and YAML
800 You often hear that JSON is a subset (or a close subset) of YAML. This 1077 You often hear that JSON is a subset of YAML. This is, however, a mass
801 is, however, a mass hysteria and very far from the truth. In general, 1078 hysteria(*) and very far from the truth (as of the time of this
802 there is no way to configure JSON::XS to output a data structure as 1079 writing), so let me state it clearly: *in general, there is no way to
803 valid YAML. 1080 configure JSON::XS to output a data structure as valid YAML* that works
1081 in all cases.
804 1082
805 If you really must use JSON::XS to generate YAML, you should use this 1083 If you really must use JSON::XS to generate YAML, you should use this
806 algorithm (subject to change in future versions): 1084 algorithm (subject to change in future versions):
807 1085
808 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1086 my $to_yaml = JSON::XS->new->utf8->space_after (1);
809 my $yaml = $to_yaml->encode ($ref) . "\n"; 1087 my $yaml = $to_yaml->encode ($ref) . "\n";
810 1088
811 This will usually generate JSON texts that also parse as valid YAML. 1089 This will *usually* generate JSON texts that also parse as valid YAML.
812 Please note that YAML has hardcoded limits on (simple) object key 1090 Please note that YAML has hardcoded limits on (simple) object key
813 lengths that JSON doesn't have, so you should make sure that your hash 1091 lengths that JSON doesn't have and also has different and incompatible
1092 unicode handling, so you should make sure that your hash keys are
814 keys are noticeably shorter than the 1024 characters YAML allows. 1093 noticeably shorter than the 1024 "stream characters" YAML allows and
1094 that you do not have characters with codepoint values outside the
1095 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1096 sequences in strings (which JSON::XS does not *currently* generate, but
1097 other JSON generators might).
815 1098
816 There might be other incompatibilities that I am not aware of. In 1099 There might be other incompatibilities that I am not aware of (or the
1100 YAML specification has been changed yet again - it does so quite often).
817 general you should not try to generate YAML with a JSON generator or 1101 In general you should not try to generate YAML with a JSON generator or
818 vice versa, or try to parse JSON with a YAML parser or vice versa: 1102 vice versa, or try to parse JSON with a YAML parser or vice versa:
819 chances are high that you will run into severe interoperability 1103 chances are high that you will run into severe interoperability problems
820 problems. 1104 when you least expect it.
1105
1106 (*) I have been pressured multiple times by Brian Ingerson (one of the
1107 authors of the YAML specification) to remove this paragraph, despite
1108 him acknowledging that the actual incompatibilities exist. As I was
1109 personally bitten by this "JSON is YAML" lie, I refused and said I
1110 will continue to educate people about these issues, so others do not
1111 run into the same problem again and again. After this, Brian called
1112 me a (quote)*complete and worthless idiot*(unquote).
1113
1114 In my opinion, instead of pressuring and insulting people who
1115 actually clarify issues with YAML and the wrong statements of some
1116 of its proponents, I would kindly suggest reading the JSON spec
1117 (which is not that difficult or long) and finally make YAML
1118 compatible to it, and educating users about the changes, instead of
1119 spreading lies about the real compatibility for many *years* and
1120 trying to silence people who point out that it isn't true.
821 1121
822 SPEED 1122 SPEED
823 It seems that JSON::XS is surprisingly fast, as shown in the following 1123 It seems that JSON::XS is surprisingly fast, as shown in the following
824 tables. They have been generated with the help of the "eg/bench" program 1124 tables. They have been generated with the help of the "eg/bench" program
825 in the JSON::XS distribution, to make it easy to compare on your own 1125 in the JSON::XS distribution, to make it easy to compare on your own
826 system. 1126 system.
827 1127
828 First comes a comparison between various modules using a very short 1128 First comes a comparison between various modules using a very short
829 single-line JSON string: 1129 single-line JSON string (also available at
1130 <http://dist.schmorp.de/misc/json/short.json>).
830 1131
831 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1132 {"method": "handleMessage", "params": ["user1",
832 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1133 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1134 true, false]}
833 1135
834 It shows the number of encodes/decodes per second (JSON::XS uses the 1136 It shows the number of encodes/decodes per second (JSON::XS uses the
835 functional interface, while JSON::XS/2 uses the OO interface with 1137 functional interface, while JSON::XS/2 uses the OO interface with
836 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1138 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
837 Higher is better: 1139 Higher is better:
… …
853 encoding, about three times faster on decoding, and over forty times 1155 encoding, about three times faster on decoding, and over forty times
854 faster than JSON, even with pretty-printing and key sorting. It also 1156 faster than JSON, even with pretty-printing and key sorting. It also
855 compares favourably to Storable for small amounts of data. 1157 compares favourably to Storable for small amounts of data.
856 1158
857 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1159 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
858 search API (http://nanoref.com/yahooapis/mgPdGg): 1160 search API (<http://dist.schmorp.de/misc/json/long.json>).
859 1161
860 module | encode | decode | 1162 module | encode | decode |
861 -----------|------------|------------| 1163 -----------|------------|------------|
862 JSON 1.x | 55.260 | 34.971 | 1164 JSON 1.x | 55.260 | 34.971 |
863 JSON::DWIW | 825.228 | 1082.513 | 1165 JSON::DWIW | 825.228 | 1082.513 |
… …
900 Third, JSON::XS recurses using the C stack when decoding objects and 1202 Third, JSON::XS recurses using the C stack when decoding objects and
901 arrays. The C stack is a limited resource: for instance, on my amd64 1203 arrays. The C stack is a limited resource: for instance, on my amd64
902 machine with 8MB of stack size I can decode around 180k nested arrays 1204 machine with 8MB of stack size I can decode around 180k nested arrays
903 but only 14k nested JSON objects (due to perl itself recursing deeply on 1205 but only 14k nested JSON objects (due to perl itself recursing deeply on
904 croak to free the temporary). If that is exceeded, the program crashes. 1206 croak to free the temporary). If that is exceeded, the program crashes.
905 to be conservative, the default nesting limit is set to 512. If your 1207 To be conservative, the default nesting limit is set to 512. If your
906 process has a smaller stack, you should adjust this setting accordingly 1208 process has a smaller stack, you should adjust this setting accordingly
907 with the "max_depth" method. 1209 with the "max_depth" method.
908 1210
909 And last but least, something else could bomb you that I forgot to think 1211 Something else could bomb you, too, that I forgot to think of. In that
910 of. In that case, you get to keep the pieces. I am always open for 1212 case, you get to keep the pieces. I am always open for hints, though...
911 hints, though... 1213
1214 Also keep in mind that JSON::XS might leak contents of your Perl data
1215 structures in its error messages, so when you serialise sensitive
1216 information you might want to make sure that exceptions thrown by
1217 JSON::XS will not end up in front of untrusted eyes.
912 1218
913 If you are using JSON::XS to return packets to consumption by JavaScript 1219 If you are using JSON::XS to return packets to consumption by JavaScript
914 scripts in a browser you should have a look at 1220 scripts in a browser you should have a look at
915 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1221 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
916 you are vulnerable to some common attack vectors (which really are 1222 you are vulnerable to some common attack vectors (which really are
917 browser design bugs, but it is still you who will have to deal with it, 1223 browser design bugs, but it is still you who will have to deal with it,
918 as major browser developers care only for features, not about doing 1224 as major browser developers care only for features, not about getting
919 security right). 1225 security right).
920 1226
921THREADS 1227THREADS
922 This module is *not* guaranteed to be thread safe and there are no plans 1228 This module is *not* guaranteed to be thread safe and there are no plans
923 to change this until Perl gets thread support (as opposed to the 1229 to change this until Perl gets thread support (as opposed to the
924 horribly slow so-called "threads" which are simply slow and bloated 1230 horribly slow so-called "threads" which are simply slow and bloated
925 process simulations - use fork, its *much* faster, cheaper, better). 1231 process simulations - use fork, it's *much* faster, cheaper, better).
926 1232
927 (It might actually work, but you have been warned). 1233 (It might actually work, but you have been warned).
928 1234
929BUGS 1235BUGS
930 While the goal of this module is to be correct, that unfortunately does 1236 While the goal of this module is to be correct, that unfortunately does
931 not mean its bug-free, only that I think its design is bug-free. It is 1237 not mean it's bug-free, only that I think its design is bug-free. If you
932 still relatively early in its development. If you keep reporting bugs
933 they will be fixed swiftly, though. 1238 keep reporting bugs they will be fixed swiftly, though.
934 1239
935 Please refrain from using rt.cpan.org or any other bug reporting 1240 Please refrain from using rt.cpan.org or any other bug reporting
936 service. I put the contact address into my modules for a reason. 1241 service. I put the contact address into my modules for a reason.
1242
1243SEE ALSO
1244 The json_xs command line utility for quick experiments.
937 1245
938AUTHOR 1246AUTHOR
939 Marc Lehmann <schmorp@schmorp.de> 1247 Marc Lehmann <schmorp@schmorp.de>
940 http://home.schmorp.de/ 1248 http://home.schmorp.de/
941 1249

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