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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
… …
45 to write yet another JSON module? While it seems there are many JSON 44 to write yet another JSON module? While it seems there are many JSON
46 modules, none of them correctly handle all corner cases, and in most 45 modules, none of them correctly handle all corner cases, and in most
47 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
48 to bug reports for other reasons. 47 to bug reports for other reasons.
49 48
50 See COMPARISON, below, for a comparison to some other JSON modules.
51
52 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 49 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
53 vice versa. 50 vice versa.
54 51
55 FEATURES 52 FEATURES
56 * correct Unicode handling 53 * correct Unicode handling
54
57 This module knows how to handle Unicode, and even documents how and 55 This module knows how to handle Unicode, documents how and when it
58 when it does so. 56 does so, and even documents what "correct" means.
59 57
60 * round-trip integrity 58 * round-trip integrity
59
61 When you serialise a perl data structure using only datatypes 60 When you serialise a perl data structure using only data types
62 supported by JSON, the deserialised data structure is identical on 61 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" 62 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
64 just because it looks like a number). 63 just because it looks like a number). There minor *are* exceptions
64 to this, read the MAPPING section below to learn about those.
65 65
66 * strict checking of JSON correctness 66 * strict checking of JSON correctness
67
67 There is no guessing, no generating of illegal JSON texts by 68 There is no guessing, no generating of illegal JSON texts by
68 default, and only JSON is accepted as input by default (the latter 69 default, and only JSON is accepted as input by default (the latter
69 is a security feature). 70 is a security feature).
70 71
71 * fast 72 * fast
72 Compared to other JSON modules, this module compares favourably in
73 terms of speed, too.
74 73
74 Compared to other JSON modules and other serialisers such as
75 Storable, this module usually compares favourably in terms of speed,
76 too.
77
75 * simple to use 78 * simple to use
79
76 This module has both a simple functional interface as well as an OO 80 This module has both a simple functional interface as well as an
77 interface. 81 object oriented interface interface.
78 82
79 * reasonably versatile output formats 83 * reasonably versatile output formats
84
80 You can choose between the most compact guaranteed single-line 85 You can choose between the most compact guaranteed-single-line
81 format possible (nice for simple line-based protocols), a pure-ascii 86 format possible (nice for simple line-based protocols), a pure-ASCII
82 format (for when your transport is not 8-bit clean, still supports 87 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 88 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 89 want to read that stuff). Or you can combine those features in
85 whatever way you like. 90 whatever way you like.
86 91
… …
94 99
95 This function call is functionally identical to: 100 This function call is functionally identical to:
96 101
97 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 102 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
98 103
99 except being faster. 104 Except being faster.
100 105
101 $perl_scalar = decode_json $json_text 106 $perl_scalar = decode_json $json_text
102 The opposite of "encode_json": expects an UTF-8 (binary) string and 107 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 108 tries to parse that as an UTF-8 encoded JSON text, returning the
104 resulting reference. Croaks on error. 109 resulting reference. Croaks on error.
105 110
106 This function call is functionally identical to: 111 This function call is functionally identical to:
107 112
108 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 113 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
109 114
110 except being faster. 115 Except being faster.
111 116
112 $is_boolean = JSON::XS::is_bool $scalar 117 $is_boolean = JSON::XS::is_bool $scalar
113 Returns true if the passed scalar represents either JSON::XS::true 118 Returns true if the passed scalar represents either JSON::XS::true
114 or JSON::XS::false, two constants that act like 1 and 0, 119 or JSON::XS::false, two constants that act like 1 and 0,
115 respectively and are used to represent JSON "true" and "false" 120 respectively and are used to represent JSON "true" and "false"
… …
125 1. Perl strings can store characters with ordinal values > 255. 130 1. Perl strings can store characters with ordinal values > 255.
126 This enables you to store Unicode characters as single characters in 131 This enables you to store Unicode characters as single characters in
127 a Perl string - very natural. 132 a Perl string - very natural.
128 133
129 2. Perl does *not* associate an encoding with your strings. 134 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 135 ... 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 136 printing the scalar to a file, in which case Perl either interprets
132 your string as locale-encoded text, octets/binary, or as Unicode, 137 your string as locale-encoded text, octets/binary, or as Unicode,
133 depending on various settings. In no case is an encoding stored 138 depending on various settings. In no case is an encoding stored
134 together with your data, it is *use* that decides encoding, not any 139 together with your data, it is *use* that decides encoding, not any
135 magical metadata. 140 magical meta data.
136 141
137 3. The internal utf-8 flag has no meaning with regards to the encoding 142 3. The internal utf-8 flag has no meaning with regards to the encoding
138 of your string. 143 of your string.
139 Just ignore that flag unless you debug a Perl bug, a module written 144 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 145 in XS or want to dive into the internals of perl. Otherwise it will
… …
145 150
146 If you didn't know about that flag, just the better, pretend it 151 If you didn't know about that flag, just the better, pretend it
147 doesn't exist. 152 doesn't exist.
148 153
149 4. A "Unicode String" is simply a string where each character can be 154 4. A "Unicode String" is simply a string where each character can be
150 validly interpreted as a Unicode codepoint. 155 validly interpreted as a Unicode code point.
151 If you have UTF-8 encoded data, it is no longer a Unicode string, 156 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. 157 but a Unicode string encoded in UTF-8, giving you a binary string.
153 158
154 5. A string containing "high" (> 255) character values is *not* a UTF-8 159 5. A string containing "high" (> 255) character values is *not* a UTF-8
155 string. 160 string.
… …
185 190
186 If $enable is false, then the "encode" method will not escape 191 If $enable is false, then the "encode" method will not escape
187 Unicode characters unless required by the JSON syntax or other 192 Unicode characters unless required by the JSON syntax or other
188 flags. This results in a faster and more compact format. 193 flags. This results in a faster and more compact format.
189 194
195 See also the section *ENCODING/CODESET FLAG NOTES* later in this
196 document.
197
190 The main use for this flag is to produce JSON texts that can be 198 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 199 transmitted over a 7-bit channel, as the encoded JSON texts will not
192 contain any 8 bit characters. 200 contain any 8 bit characters.
193 201
194 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 202 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
… …
205 superset of latin1. 213 superset of latin1.
206 214
207 If $enable is false, then the "encode" method will not escape 215 If $enable is false, then the "encode" method will not escape
208 Unicode characters unless required by the JSON syntax or other 216 Unicode characters unless required by the JSON syntax or other
209 flags. 217 flags.
218
219 See also the section *ENCODING/CODESET FLAG NOTES* later in this
220 document.
210 221
211 The main use for this flag is efficiently encoding binary data as 222 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 223 JSON text, as most octets will not be escaped, resulting in a
213 smaller encoded size. The disadvantage is that the resulting JSON 224 smaller encoded size. The disadvantage is that the resulting JSON
214 text is encoded in latin1 (and must correctly be treated as such 225 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 245 If $enable is false, then the "encode" method will return the JSON
235 string as a (non-encoded) Unicode string, while "decode" expects 246 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 247 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. 248 UTF-16) needs to be done yourself, e.g. using the Encode module.
238 249
250 See also the section *ENCODING/CODESET FLAG NOTES* later in this
251 document.
252
239 Example, output UTF-16BE-encoded JSON: 253 Example, output UTF-16BE-encoded JSON:
240 254
241 use Encode; 255 use Encode;
242 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 256 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
243 257
… …
318 If $enable is false (the default), then "decode" will only accept 332 If $enable is false (the default), then "decode" will only accept
319 valid JSON texts. 333 valid JSON texts.
320 334
321 Currently accepted extensions are: 335 Currently accepted extensions are:
322 336
323 * list items can have an end-comma 337 * list items can have an end-comma
338
324 JSON *separates* array elements and key-value pairs with commas. 339 JSON *separates* array elements and key-value pairs with commas.
325 This can be annoying if you write JSON texts manually and want 340 This can be annoying if you write JSON texts manually and want
326 to be able to quickly append elements, so this extension accepts 341 to be able to quickly append elements, so this extension accepts
327 comma at the end of such items not just between them: 342 comma at the end of such items not just between them:
328 343
… …
333 { 348 {
334 "k1": "v1", 349 "k1": "v1",
335 "k2": "v2", <- this comma not normally allowed 350 "k2": "v2", <- this comma not normally allowed
336 } 351 }
337 352
338 * shell-style '#'-comments 353 * shell-style '#'-comments
354
339 Whenever JSON allows whitespace, shell-style comments are 355 Whenever JSON allows whitespace, shell-style comments are
340 additionally allowed. They are terminated by the first 356 additionally allowed. They are terminated by the first
341 carriage-return or line-feed character, after which more 357 carriage-return or line-feed character, after which more
342 white-space and comments are allowed. 358 white-space and comments are allowed.
343 359
… …
379 Example, encode a Perl scalar as JSON value with enabled 395 Example, encode a Perl scalar as JSON value with enabled
380 "allow_nonref", resulting in an invalid JSON text: 396 "allow_nonref", resulting in an invalid JSON text:
381 397
382 JSON::XS->new->allow_nonref->encode ("Hello, World!") 398 JSON::XS->new->allow_nonref->encode ("Hello, World!")
383 => "Hello, World!" 399 => "Hello, World!"
400
401 $json = $json->allow_unknown ([$enable])
402 $enabled = $json->get_allow_unknown
403 If $enable is true (or missing), then "encode" will *not* throw an
404 exception when it encounters values it cannot represent in JSON (for
405 example, filehandles) but instead will encode a JSON "null" value.
406 Note that blessed objects are not included here and are handled
407 separately by c<allow_nonref>.
408
409 If $enable is false (the default), then "encode" will throw an
410 exception when it encounters anything it cannot encode as JSON.
411
412 This option does not affect "decode" in any way, and it is
413 recommended to leave it off unless you know your communications
414 partner.
384 415
385 $json = $json->allow_blessed ([$enable]) 416 $json = $json->allow_blessed ([$enable])
386 $enabled = $json->get_allow_blessed 417 $enabled = $json->get_allow_blessed
387 If $enable is true (or missing), then the "encode" method will not 418 If $enable is true (or missing), then the "encode" method will not
388 barf when it encounters a blessed reference. Instead, the value of 419 barf when it encounters a blessed reference. Instead, the value of
… …
523 saving space. 554 saving space.
524 555
525 $json = $json->max_depth ([$maximum_nesting_depth]) 556 $json = $json->max_depth ([$maximum_nesting_depth])
526 $max_depth = $json->get_max_depth 557 $max_depth = $json->get_max_depth
527 Sets the maximum nesting level (default 512) accepted while encoding 558 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 559 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 560 Perl data structure, then the encoder and decoder will stop and
530 will stop and croak at that point. 561 croak at that point.
531 562
532 Nesting level is defined by number of hash- or arrayrefs that the 563 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 564 encoder needs to traverse to reach a given point or the number of
534 "{" or "[" characters without their matching closing parenthesis 565 "{" or "[" characters without their matching closing parenthesis
535 crossed to reach a given character in a string. 566 crossed to reach a given character in a string.
536 567
537 Setting the maximum depth to one disallows any nesting, so that 568 Setting the maximum depth to one disallows any nesting, so that
538 ensures that the object is only a single hash/object or array. 569 ensures that the object is only a single hash/object or array.
539 570
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 571 If no argument is given, the highest possible setting will be used,
542 will be used, which is rarely useful. 572 which is rarely useful.
573
574 Note that nesting is implemented by recursion in C. The default
575 value has been chosen to be as large as typical operating systems
576 allow without crashing.
543 577
544 See SECURITY CONSIDERATIONS, below, for more info on why this is 578 See SECURITY CONSIDERATIONS, below, for more info on why this is
545 useful. 579 useful.
546 580
547 $json = $json->max_size ([$maximum_string_size]) 581 $json = $json->max_size ([$maximum_string_size])
548 $max_size = $json->get_max_size 582 $max_size = $json->get_max_size
549 Set the maximum length a JSON text may have (in bytes) where 583 Set the maximum length a JSON text may have (in bytes) where
550 decoding is being attempted. The default is 0, meaning no limit. 584 decoding is being attempted. The default is 0, meaning no limit.
551 When "decode" is called on a string longer then this number of 585 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 586 bytes, it will not attempt to decode the string but throw an
553 exception. This setting has no effect on "encode" (yet). 587 exception. This setting has no effect on "encode" (yet).
554 588
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 589 If no argument is given, the limit check will be deactivated (same
558 specified). 590 as when 0 is specified).
559 591
560 See SECURITY CONSIDERATIONS, below, for more info on why this is 592 See SECURITY CONSIDERATIONS, below, for more info on why this is
561 useful. 593 useful.
562 594
563 $json_text = $json->encode ($perl_scalar) 595 $json_text = $json->encode ($perl_scalar)
… …
588 and you need to know where the JSON text ends. 620 and you need to know where the JSON text ends.
589 621
590 JSON::XS->new->decode_prefix ("[1] the tail") 622 JSON::XS->new->decode_prefix ("[1] the tail")
591 => ([], 3) 623 => ([], 3)
592 624
625INCREMENTAL PARSING
626 In some cases, there is the need for incremental parsing of JSON texts.
627 While this module always has to keep both JSON text and resulting Perl
628 data structure in memory at one time, it does allow you to parse a JSON
629 stream incrementally. It does so by accumulating text until it has a
630 full JSON object, which it then can decode. This process is similar to
631 using "decode_prefix" to see if a full JSON object is available, but is
632 much more efficient (and can be implemented with a minimum of method
633 calls).
634
635 JSON::XS will only attempt to parse the JSON text once it is sure it has
636 enough text to get a decisive result, using a very simple but truly
637 incremental parser. This means that it sometimes won't stop as early as
638 the full parser, for example, it doesn't detect parenthese mismatches.
639 The only thing it guarantees is that it starts decoding as soon as a
640 syntactically valid JSON text has been seen. This means you need to set
641 resource limits (e.g. "max_size") to ensure the parser will stop parsing
642 in the presence if syntax errors.
643
644 The following methods implement this incremental parser.
645
646 [void, scalar or list context] = $json->incr_parse ([$string])
647 This is the central parsing function. It can both append new text
648 and extract objects from the stream accumulated so far (both of
649 these functions are optional).
650
651 If $string is given, then this string is appended to the already
652 existing JSON fragment stored in the $json object.
653
654 After that, if the function is called in void context, it will
655 simply return without doing anything further. This can be used to
656 add more text in as many chunks as you want.
657
658 If the method is called in scalar context, then it will try to
659 extract exactly *one* JSON object. If that is successful, it will
660 return this object, otherwise it will return "undef". If there is a
661 parse error, this method will croak just as "decode" would do (one
662 can then use "incr_skip" to skip the errornous part). This is the
663 most common way of using the method.
664
665 And finally, in list context, it will try to extract as many objects
666 from the stream as it can find and return them, or the empty list
667 otherwise. For this to work, there must be no separators between the
668 JSON objects or arrays, instead they must be concatenated
669 back-to-back. If an error occurs, an exception will be raised as in
670 the scalar context case. Note that in this case, any
671 previously-parsed JSON texts will be lost.
672
673 $lvalue_string = $json->incr_text
674 This method returns the currently stored JSON fragment as an lvalue,
675 that is, you can manipulate it. This *only* works when a preceding
676 call to "incr_parse" in *scalar context* successfully returned an
677 object. Under all other circumstances you must not call this
678 function (I mean it. although in simple tests it might actually
679 work, it *will* fail under real world conditions). As a special
680 exception, you can also call this method before having parsed
681 anything.
682
683 This function is useful in two cases: a) finding the trailing text
684 after a JSON object or b) parsing multiple JSON objects separated by
685 non-JSON text (such as commas).
686
687 $json->incr_skip
688 This will reset the state of the incremental parser and will remove
689 the parsed text from the input buffer. This is useful after
690 "incr_parse" died, in which case the input buffer and incremental
691 parser state is left unchanged, to skip the text parsed so far and
692 to reset the parse state.
693
694 $json->incr_reset
695 This completely resets the incremental parser, that is, after this
696 call, it will be as if the parser had never parsed anything.
697
698 This is useful if you want ot repeatedly parse JSON objects and want
699 to ignore any trailing data, which means you have to reset the
700 parser after each successful decode.
701
702 LIMITATIONS
703 All options that affect decoding are supported, except "allow_nonref".
704 The reason for this is that it cannot be made to work sensibly: JSON
705 objects and arrays are self-delimited, i.e. you can concatenate them
706 back to back and still decode them perfectly. This does not hold true
707 for JSON numbers, however.
708
709 For example, is the string 1 a single JSON number, or is it simply the
710 start of 12? Or is 12 a single JSON number, or the concatenation of 1
711 and 2? In neither case you can tell, and this is why JSON::XS takes the
712 conservative route and disallows this case.
713
714 EXAMPLES
715 Some examples will make all this clearer. First, a simple example that
716 works similarly to "decode_prefix": We want to decode the JSON object at
717 the start of a string and identify the portion after the JSON object:
718
719 my $text = "[1,2,3] hello";
720
721 my $json = new JSON::XS;
722
723 my $obj = $json->incr_parse ($text)
724 or die "expected JSON object or array at beginning of string";
725
726 my $tail = $json->incr_text;
727 # $tail now contains " hello"
728
729 Easy, isn't it?
730
731 Now for a more complicated example: Imagine a hypothetical protocol
732 where you read some requests from a TCP stream, and each request is a
733 JSON array, without any separation between them (in fact, it is often
734 useful to use newlines as "separators", as these get interpreted as
735 whitespace at the start of the JSON text, which makes it possible to
736 test said protocol with "telnet"...).
737
738 Here is how you'd do it (it is trivial to write this in an event-based
739 manner):
740
741 my $json = new JSON::XS;
742
743 # read some data from the socket
744 while (sysread $socket, my $buf, 4096) {
745
746 # split and decode as many requests as possible
747 for my $request ($json->incr_parse ($buf)) {
748 # act on the $request
749 }
750 }
751
752 Another complicated example: Assume you have a string with JSON objects
753 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
754 [3]"). To parse them, we have to skip the commas between the JSON texts,
755 and here is where the lvalue-ness of "incr_text" comes in useful:
756
757 my $text = "[1],[2], [3]";
758 my $json = new JSON::XS;
759
760 # void context, so no parsing done
761 $json->incr_parse ($text);
762
763 # now extract as many objects as possible. note the
764 # use of scalar context so incr_text can be called.
765 while (my $obj = $json->incr_parse) {
766 # do something with $obj
767
768 # now skip the optional comma
769 $json->incr_text =~ s/^ \s* , //x;
770 }
771
772 Now lets go for a very complex example: Assume that you have a gigantic
773 JSON array-of-objects, many gigabytes in size, and you want to parse it,
774 but you cannot load it into memory fully (this has actually happened in
775 the real world :).
776
777 Well, you lost, you have to implement your own JSON parser. But JSON::XS
778 can still help you: You implement a (very simple) array parser and let
779 JSON decode the array elements, which are all full JSON objects on their
780 own (this wouldn't work if the array elements could be JSON numbers, for
781 example):
782
783 my $json = new JSON::XS;
784
785 # open the monster
786 open my $fh, "<bigfile.json"
787 or die "bigfile: $!";
788
789 # first parse the initial "["
790 for (;;) {
791 sysread $fh, my $buf, 65536
792 or die "read error: $!";
793 $json->incr_parse ($buf); # void context, so no parsing
794
795 # Exit the loop once we found and removed(!) the initial "[".
796 # In essence, we are (ab-)using the $json object as a simple scalar
797 # we append data to.
798 last if $json->incr_text =~ s/^ \s* \[ //x;
799 }
800
801 # now we have the skipped the initial "[", so continue
802 # parsing all the elements.
803 for (;;) {
804 # in this loop we read data until we got a single JSON object
805 for (;;) {
806 if (my $obj = $json->incr_parse) {
807 # do something with $obj
808 last;
809 }
810
811 # add more data
812 sysread $fh, my $buf, 65536
813 or die "read error: $!";
814 $json->incr_parse ($buf); # void context, so no parsing
815 }
816
817 # in this loop we read data until we either found and parsed the
818 # separating "," between elements, or the final "]"
819 for (;;) {
820 # first skip whitespace
821 $json->incr_text =~ s/^\s*//;
822
823 # if we find "]", we are done
824 if ($json->incr_text =~ s/^\]//) {
825 print "finished.\n";
826 exit;
827 }
828
829 # if we find ",", we can continue with the next element
830 if ($json->incr_text =~ s/^,//) {
831 last;
832 }
833
834 # if we find anything else, we have a parse error!
835 if (length $json->incr_text) {
836 die "parse error near ", $json->incr_text;
837 }
838
839 # else add more data
840 sysread $fh, my $buf, 65536
841 or die "read error: $!";
842 $json->incr_parse ($buf); # void context, so no parsing
843 }
844
845 This is a complex example, but most of the complexity comes from the
846 fact that we are trying to be correct (bear with me if I am wrong, I
847 never ran the above example :).
848
593MAPPING 849MAPPING
594 This section describes how JSON::XS maps Perl values to JSON values and 850 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 851 vice versa. These mappings are designed to "do the right thing" in most
596 circumstances automatically, preserving round-tripping characteristics 852 circumstances automatically, preserving round-tripping characteristics
597 (what you put in comes out as something equivalent). 853 (what you put in comes out as something equivalent).
… …
618 A JSON number becomes either an integer, numeric (floating point) or 874 A JSON number becomes either an integer, numeric (floating point) or
619 string scalar in perl, depending on its range and any fractional 875 string scalar in perl, depending on its range and any fractional
620 parts. On the Perl level, there is no difference between those as 876 parts. On the Perl level, there is no difference between those as
621 Perl handles all the conversion details, but an integer may take 877 Perl handles all the conversion details, but an integer may take
622 slightly less memory and might represent more values exactly than 878 slightly less memory and might represent more values exactly than
623 (floating point) numbers. 879 floating point numbers.
624 880
625 If the number consists of digits only, JSON::XS will try to 881 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 882 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 883 represent it as a numeric (floating point) value if that is possible
628 without loss of precision. Otherwise it will preserve the number as 884 without loss of precision. Otherwise it will preserve the number as
629 a string value. 885 a string value (in which case you lose roundtripping ability, as the
886 JSON number will be re-encoded toa JSON string).
630 887
631 Numbers containing a fractional or exponential part will always be 888 Numbers containing a fractional or exponential part will always be
632 represented as numeric (floating point) values, possibly at a loss 889 represented as numeric (floating point) values, possibly at a loss
633 of precision. 890 of precision (in which case you might lose perfect roundtripping
634 891 ability, but the JSON number will still be re-encoded as a JSON
635 This might create round-tripping problems as numbers might become 892 number).
636 strings, but as Perl is typeless there is no other way to do it.
637 893
638 true, false 894 true, false
639 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 895 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
640 respectively. They are overloaded to act almost exactly like the 896 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 897 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 0 925 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 926 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 927 can also use "JSON::XS::false" and "JSON::XS::true" to improve
672 readability. 928 readability.
673 929
674 encode_json [\0,JSON::XS::true] # yields [false,true] 930 encode_json [\0, JSON::XS::true] # yields [false,true]
675 931
676 JSON::XS::true, JSON::XS::false 932 JSON::XS::true, JSON::XS::false
677 These special values become JSON true and JSON false values, 933 These special values become JSON true and JSON false values,
678 respectively. You can also use "\1" and "\0" directly if you want. 934 respectively. You can also use "\1" and "\0" directly if you want.
679 935
680 blessed objects 936 blessed objects
681 Blessed objects are not allowed. JSON::XS currently tries to encode 937 Blessed objects are not directly representable in JSON. See the
682 their underlying representation (hash- or arrayref), but this 938 "allow_blessed" and "convert_blessed" methods on various options on
683 behaviour might change in future versions. 939 how to deal with this: basically, you can choose between throwing an
940 exception, encoding the reference as if it weren't blessed, or
941 provide your own serialiser method.
684 942
685 simple scalars 943 simple scalars
686 Simple Perl scalars (any scalar that is not a reference) are the 944 Simple Perl scalars (any scalar that is not a reference) are the
687 most difficult objects to encode: JSON::XS will encode undefined 945 most difficult objects to encode: JSON::XS will encode undefined
688 scalars as JSON null value, scalars that have last been used in a 946 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 947 string context before encoding as JSON strings, and anything else as
690 number value: 948 number value:
691 949
692 # dump as number 950 # dump as number
693 encode_json [2] # yields [2] 951 encode_json [2] # yields [2]
694 encode_json [-3.0e17] # yields [-3e+17] 952 encode_json [-3.0e17] # yields [-3e+17]
… …
713 my $x = "3"; # some variable containing a string 971 my $x = "3"; # some variable containing a string
714 $x += 0; # numify it, ensuring it will be dumped as a number 972 $x += 0; # numify it, ensuring it will be dumped as a number
715 $x *= 1; # same thing, the choice is yours. 973 $x *= 1; # same thing, the choice is yours.
716 974
717 You can not currently force the type in other, less obscure, ways. 975 You can not currently force the type in other, less obscure, ways.
718 Tell me if you need this capability. 976 Tell me if you need this capability (but don't forget to explain why
977 it's needed :).
719 978
720COMPARISON 979ENCODING/CODESET FLAG NOTES
721 As already mentioned, this module was created because none of the 980 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 981 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
723 describe the problems (or pleasures) I encountered with various existing 982 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.
726 983
727 JSON 1.07 984 "utf8" controls whether the JSON text created by "encode" (and expected
728 Slow (but very portable, as it is written in pure Perl). 985 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
986 control whether "encode" escapes character values outside their
987 respective codeset range. Neither of these flags conflict with each
988 other, although some combinations make less sense than others.
729 989
730 Undocumented/buggy Unicode handling (how JSON handles Unicode values 990 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 991 "encode" and "decode", that is, texts encoded with any combination of
732 doing en-/decoding oneself, but Unicode escapes are not working 992 these flag values will be correctly decoded when the same flags are used
993 - in general, if you use different flag settings while encoding vs. when
994 decoding you likely have a bug somewhere.
995
996 Below comes a verbose discussion of these flags. Note that a "codeset"
997 is simply an abstract set of character-codepoint pairs, while an
998 encoding takes those codepoint numbers and *encodes* them, in our case
999 into octets. Unicode is (among other things) a codeset, UTF-8 is an
1000 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
1001 encodings at the same time, which can be confusing.
1002
1003 "utf8" flag disabled
1004 When "utf8" is disabled (the default), then "encode"/"decode"
1005 generate and expect Unicode strings, that is, characters with high
1006 ordinal Unicode values (> 255) will be encoded as such characters,
1007 and likewise such characters are decoded as-is, no canges to them
1008 will be done, except "(re-)interpreting" them as Unicode codepoints
1009 or Unicode characters, respectively (to Perl, these are the same
1010 thing in strings unless you do funny/weird/dumb stuff).
1011
1012 This is useful when you want to do the encoding yourself (e.g. when
1013 you want to have UTF-16 encoded JSON texts) or when some other layer
1014 does the encoding for you (for example, when printing to a terminal
1015 using a filehandle that transparently encodes to UTF-8 you certainly
1016 do NOT want to UTF-8 encode your data first and have Perl encode it
1017 another time).
1018
1019 "utf8" flag enabled
1020 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1021 characters using the corresponding UTF-8 multi-byte sequence, and
1022 will expect your input strings to be encoded as UTF-8, that is, no
1023 "character" of the input string must have any value > 255, as UTF-8
1024 does not allow that.
1025
1026 The "utf8" flag therefore switches between two modes: disabled means
1027 you will get a Unicode string in Perl, enabled means you get an
1028 UTF-8 encoded octet/binary string in Perl.
1029
1030 "latin1" or "ascii" flags enabled
1031 With "latin1" (or "ascii") enabled, "encode" will escape characters
1032 with ordinal values > 255 (> 127 with "ascii") and encode the
1033 remaining characters as specified by the "utf8" flag.
1034
1035 If "utf8" is disabled, then the result is also correctly encoded in
1036 those character sets (as both are proper subsets of Unicode, meaning
1037 that a Unicode string with all character values < 256 is the same
1038 thing as a ISO-8859-1 string, and a Unicode string with all
1039 character values < 128 is the same thing as an ASCII string in
733 properly). 1040 Perl).
734 1041
735 No round-tripping (strings get clobbered if they look like numbers, 1042 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 1043 regardless of these flags, just some more characters will be escaped
737 will decode into the number 2. 1044 using "\uXXXX" then before.
738 1045
739 JSON::PC 0.01 1046 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
740 Very fast. 1047 encoding, while ASCII-encoded strings are. That is because the
1048 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1049 *codeset* being a subset of Unicode), while ASCII is.
741 1050
742 Undocumented/buggy Unicode handling. 1051 Surprisingly, "decode" will ignore these flags and so treat all
1052 input values as governed by the "utf8" flag. If it is disabled, this
1053 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1054 strict subsets of Unicode. If it is enabled, you can correctly
1055 decode UTF-8 encoded strings.
743 1056
744 No round-tripping. 1057 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1058 flag - they only govern when the JSON output engine escapes a
1059 character or not.
745 1060
746 Has problems handling many Perl values (e.g. regex results and other 1061 The main use for "latin1" is to relatively efficiently store binary
747 magic values will make it croak). 1062 data as JSON, at the expense of breaking compatibility with most
1063 JSON decoders.
748 1064
749 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1065 The main use for "ascii" is to force the output to not contain
750 which is not a valid JSON text. 1066 characters with values > 127, which means you can interpret the
751 1067 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
752 Unmaintained (maintainer unresponsive for many months, bugs are not 1068 any character set and 8-bit-encoding, and still get the same data
753 getting fixed). 1069 structure back. This is useful when your channel for JSON transfer
754 1070 is not 8-bit clean or the encoding might be mangled in between (e.g.
755 JSON::Syck 0.21 1071 in mail), and works because ASCII is a proper subset of most 8-bit
756 Very buggy (often crashes). 1072 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 1073
799 JSON and YAML 1074 JSON and YAML
800 You often hear that JSON is a subset (or a close subset) of YAML. This 1075 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, 1076 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 1077 writing), so let me state it clearly: *in general, there is no way to
803 valid YAML. 1078 configure JSON::XS to output a data structure as valid YAML* that works
1079 in all cases.
804 1080
805 If you really must use JSON::XS to generate YAML, you should use this 1081 If you really must use JSON::XS to generate YAML, you should use this
806 algorithm (subject to change in future versions): 1082 algorithm (subject to change in future versions):
807 1083
808 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1084 my $to_yaml = JSON::XS->new->utf8->space_after (1);
809 my $yaml = $to_yaml->encode ($ref) . "\n"; 1085 my $yaml = $to_yaml->encode ($ref) . "\n";
810 1086
811 This will usually generate JSON texts that also parse as valid YAML. 1087 This will *usually* generate JSON texts that also parse as valid YAML.
812 Please note that YAML has hardcoded limits on (simple) object key 1088 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 1089 lengths that JSON doesn't have and also has different and incompatible
1090 unicode handling, so you should make sure that your hash keys are
814 keys are noticeably shorter than the 1024 characters YAML allows. 1091 noticeably shorter than the 1024 "stream characters" YAML allows and
1092 that you do not have characters with codepoint values outside the
1093 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1094 sequences in strings (which JSON::XS does not *currently* generate, but
1095 other JSON generators might).
815 1096
816 There might be other incompatibilities that I am not aware of. In 1097 There might be other incompatibilities that I am not aware of (or the
1098 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 1099 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: 1100 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 1101 chances are high that you will run into severe interoperability problems
820 problems. 1102 when you least expect it.
1103
1104 (*) I have been pressured multiple times by Brian Ingerson (one of the
1105 authors of the YAML specification) to remove this paragraph, despite
1106 him acknowledging that the actual incompatibilities exist. As I was
1107 personally bitten by this "JSON is YAML" lie, I refused and said I
1108 will continue to educate people about these issues, so others do not
1109 run into the same problem again and again. After this, Brian called
1110 me a (quote)*complete and worthless idiot*(unquote).
1111
1112 In my opinion, instead of pressuring and insulting people who
1113 actually clarify issues with YAML and the wrong statements of some
1114 of its proponents, I would kindly suggest reading the JSON spec
1115 (which is not that difficult or long) and finally make YAML
1116 compatible to it, and educating users about the changes, instead of
1117 spreading lies about the real compatibility for many *years* and
1118 trying to silence people who point out that it isn't true.
821 1119
822 SPEED 1120 SPEED
823 It seems that JSON::XS is surprisingly fast, as shown in the following 1121 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 1122 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 1123 in the JSON::XS distribution, to make it easy to compare on your own
826 system. 1124 system.
827 1125
828 First comes a comparison between various modules using a very short 1126 First comes a comparison between various modules using a very short
829 single-line JSON string: 1127 single-line JSON string (also available at
1128 <http://dist.schmorp.de/misc/json/short.json>).
830 1129
831 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1130 {"method": "handleMessage", "params": ["user1",
832 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1131 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1132 true, false]}
833 1133
834 It shows the number of encodes/decodes per second (JSON::XS uses the 1134 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 1135 functional interface, while JSON::XS/2 uses the OO interface with
836 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1136 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
837 Higher is better: 1137 Higher is better:
… …
853 encoding, about three times faster on decoding, and over forty times 1153 encoding, about three times faster on decoding, and over forty times
854 faster than JSON, even with pretty-printing and key sorting. It also 1154 faster than JSON, even with pretty-printing and key sorting. It also
855 compares favourably to Storable for small amounts of data. 1155 compares favourably to Storable for small amounts of data.
856 1156
857 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1157 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
858 search API (http://nanoref.com/yahooapis/mgPdGg): 1158 search API (<http://dist.schmorp.de/misc/json/long.json>).
859 1159
860 module | encode | decode | 1160 module | encode | decode |
861 -----------|------------|------------| 1161 -----------|------------|------------|
862 JSON 1.x | 55.260 | 34.971 | 1162 JSON 1.x | 55.260 | 34.971 |
863 JSON::DWIW | 825.228 | 1082.513 | 1163 JSON::DWIW | 825.228 | 1082.513 |
… …
900 Third, JSON::XS recurses using the C stack when decoding objects and 1200 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 1201 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 1202 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 1203 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. 1204 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 1205 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 1206 process has a smaller stack, you should adjust this setting accordingly
907 with the "max_depth" method. 1207 with the "max_depth" method.
908 1208
909 And last but least, something else could bomb you that I forgot to think 1209 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 1210 case, you get to keep the pieces. I am always open for hints, though...
911 hints, though... 1211
1212 Also keep in mind that JSON::XS might leak contents of your Perl data
1213 structures in its error messages, so when you serialise sensitive
1214 information you might want to make sure that exceptions thrown by
1215 JSON::XS will not end up in front of untrusted eyes.
912 1216
913 If you are using JSON::XS to return packets to consumption by JavaScript 1217 If you are using JSON::XS to return packets to consumption by JavaScript
914 scripts in a browser you should have a look at 1218 scripts in a browser you should have a look at
915 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1219 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
916 you are vulnerable to some common attack vectors (which really are 1220 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, 1221 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 1222 as major browser developers care only for features, not about getting
919 security right). 1223 security right).
920 1224
921THREADS 1225THREADS
922 This module is *not* guaranteed to be thread safe and there are no plans 1226 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 1227 to change this until Perl gets thread support (as opposed to the
924 horribly slow so-called "threads" which are simply slow and bloated 1228 horribly slow so-called "threads" which are simply slow and bloated
925 process simulations - use fork, its *much* faster, cheaper, better). 1229 process simulations - use fork, it's *much* faster, cheaper, better).
926 1230
927 (It might actually work, but you have been warned). 1231 (It might actually work, but you have been warned).
928 1232
929BUGS 1233BUGS
930 While the goal of this module is to be correct, that unfortunately does 1234 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 1235 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. 1236 keep reporting bugs they will be fixed swiftly, though.
934 1237
935 Please refrain from using rt.cpan.org or any other bug reporting 1238 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. 1239 service. I put the contact address into my modules for a reason.
1240
1241SEE ALSO
1242 The json_xs command line utility for quick experiments.
937 1243
938AUTHOR 1244AUTHOR
939 Marc Lehmann <schmorp@schmorp.de> 1245 Marc Lehmann <schmorp@schmorp.de>
940 http://home.schmorp.de/ 1246 http://home.schmorp.de/
941 1247

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