ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/JSON-XS/README
(Generate patch)

Comparing JSON-XS/README (file contents):
Revision 1.22 by root, Wed Dec 5 10:59:27 2007 UTC vs.
Revision 1.26 by root, Tue Jun 3 06:43:45 2008 UTC

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 (JSON::XS will only attempt to parse the JSON text
635 once it is sure it has enough text to get a decisive result, using a
636 very simple but truly incremental parser).
637
638 The following two methods deal with this.
639
640 [void, scalar or list context] = $json->incr_parse ([$string])
641 This is the central parsing function. It can both append new text
642 and extract objects from the stream accumulated so far (both of
643 these functions are optional).
644
645 If $string is given, then this string is appended to the already
646 existing JSON fragment stored in the $json object.
647
648 After that, if the function is called in void context, it will
649 simply return without doing anything further. This can be used to
650 add more text in as many chunks as you want.
651
652 If the method is called in scalar context, then it will try to
653 extract exactly *one* JSON object. If that is successful, it will
654 return this object, otherwise it will return "undef". If there is a
655 parse error, this method will croak just as "decode" would do (one
656 can then use "incr_skip" to skip the errornous part). This is the
657 most common way of using the method.
658
659 And finally, in list context, it will try to extract as many objects
660 from the stream as it can find and return them, or the empty list
661 otherwise. For this to work, there must be no separators between the
662 JSON objects or arrays, instead they must be concatenated
663 back-to-back. If an error occurs, an exception will be raised as in
664 the scalar context case. Note that in this case, any
665 previously-parsed JSON texts will be lost.
666
667 $lvalue_string = $json->incr_text
668 This method returns the currently stored JSON fragment as an lvalue,
669 that is, you can manipulate it. This *only* works when a preceding
670 call to "incr_parse" in *scalar context* successfully returned an
671 object. Under all other circumstances you must not call this
672 function (I mean it. although in simple tests it might actually
673 work, it *will* fail under real world conditions). As a special
674 exception, you can also call this method before having parsed
675 anything.
676
677 This function is useful in two cases: a) finding the trailing text
678 after a JSON object or b) parsing multiple JSON objects separated by
679 non-JSON text (such as commas).
680
681 $json->incr_skip
682 This will reset the state of the incremental parser and will remove
683 the parsed text from the input buffer. This is useful after
684 "incr_parse" died, in which case the input buffer and incremental
685 parser state is left unchanged, to skip the text parsed so far and
686 to reset the parse state.
687
688 $json->incr_reset
689 This completely resets the incremental parser, that is, after this
690 call, it will be as if the parser had never parsed anything.
691
692 This is useful if you want ot repeatedly parse JSON objects and want
693 to ignore any trailing data, which means you have to reset the
694 parser after each successful decode.
695
696 LIMITATIONS
697 All options that affect decoding are supported, except "allow_nonref".
698 The reason for this is that it cannot be made to work sensibly: JSON
699 objects and arrays are self-delimited, i.e. you can concatenate them
700 back to back and still decode them perfectly. This does not hold true
701 for JSON numbers, however.
702
703 For example, is the string 1 a single JSON number, or is it simply the
704 start of 12? Or is 12 a single JSON number, or the concatenation of 1
705 and 2? In neither case you can tell, and this is why JSON::XS takes the
706 conservative route and disallows this case.
707
708 EXAMPLES
709 Some examples will make all this clearer. First, a simple example that
710 works similarly to "decode_prefix": We want to decode the JSON object at
711 the start of a string and identify the portion after the JSON object:
712
713 my $text = "[1,2,3] hello";
714
715 my $json = new JSON::XS;
716
717 my $obj = $json->incr_parse ($text)
718 or die "expected JSON object or array at beginning of string";
719
720 my $tail = $json->incr_text;
721 # $tail now contains " hello"
722
723 Easy, isn't it?
724
725 Now for a more complicated example: Imagine a hypothetical protocol
726 where you read some requests from a TCP stream, and each request is a
727 JSON array, without any separation between them (in fact, it is often
728 useful to use newlines as "separators", as these get interpreted as
729 whitespace at the start of the JSON text, which makes it possible to
730 test said protocol with "telnet"...).
731
732 Here is how you'd do it (it is trivial to write this in an event-based
733 manner):
734
735 my $json = new JSON::XS;
736
737 # read some data from the socket
738 while (sysread $socket, my $buf, 4096) {
739
740 # split and decode as many requests as possible
741 for my $request ($json->incr_parse ($buf)) {
742 # act on the $request
743 }
744 }
745
746 Another complicated example: Assume you have a string with JSON objects
747 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
748 [3]"). To parse them, we have to skip the commas between the JSON texts,
749 and here is where the lvalue-ness of "incr_text" comes in useful:
750
751 my $text = "[1],[2], [3]";
752 my $json = new JSON::XS;
753
754 # void context, so no parsing done
755 $json->incr_parse ($text);
756
757 # now extract as many objects as possible. note the
758 # use of scalar context so incr_text can be called.
759 while (my $obj = $json->incr_parse) {
760 # do something with $obj
761
762 # now skip the optional comma
763 $json->incr_text =~ s/^ \s* , //x;
764 }
765
766 Now lets go for a very complex example: Assume that you have a gigantic
767 JSON array-of-objects, many gigabytes in size, and you want to parse it,
768 but you cannot load it into memory fully (this has actually happened in
769 the real world :).
770
771 Well, you lost, you have to implement your own JSON parser. But JSON::XS
772 can still help you: You implement a (very simple) array parser and let
773 JSON decode the array elements, which are all full JSON objects on their
774 own (this wouldn't work if the array elements could be JSON numbers, for
775 example):
776
777 my $json = new JSON::XS;
778
779 # open the monster
780 open my $fh, "<bigfile.json"
781 or die "bigfile: $!";
782
783 # first parse the initial "["
784 for (;;) {
785 sysread $fh, my $buf, 65536
786 or die "read error: $!";
787 $json->incr_parse ($buf); # void context, so no parsing
788
789 # Exit the loop once we found and removed(!) the initial "[".
790 # In essence, we are (ab-)using the $json object as a simple scalar
791 # we append data to.
792 last if $json->incr_text =~ s/^ \s* \[ //x;
793 }
794
795 # now we have the skipped the initial "[", so continue
796 # parsing all the elements.
797 for (;;) {
798 # in this loop we read data until we got a single JSON object
799 for (;;) {
800 if (my $obj = $json->incr_parse) {
801 # do something with $obj
802 last;
803 }
804
805 # add more data
806 sysread $fh, my $buf, 65536
807 or die "read error: $!";
808 $json->incr_parse ($buf); # void context, so no parsing
809 }
810
811 # in this loop we read data until we either found and parsed the
812 # separating "," between elements, or the final "]"
813 for (;;) {
814 # first skip whitespace
815 $json->incr_text =~ s/^\s*//;
816
817 # if we find "]", we are done
818 if ($json->incr_text =~ s/^\]//) {
819 print "finished.\n";
820 exit;
821 }
822
823 # if we find ",", we can continue with the next element
824 if ($json->incr_text =~ s/^,//) {
825 last;
826 }
827
828 # if we find anything else, we have a parse error!
829 if (length $json->incr_text) {
830 die "parse error near ", $json->incr_text;
831 }
832
833 # else add more data
834 sysread $fh, my $buf, 65536
835 or die "read error: $!";
836 $json->incr_parse ($buf); # void context, so no parsing
837 }
838
839 This is a complex example, but most of the complexity comes from the
840 fact that we are trying to be correct (bear with me if I am wrong, I
841 never ran the above example :).
842
593MAPPING 843MAPPING
594 This section describes how JSON::XS maps Perl values to JSON values and 844 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 845 vice versa. These mappings are designed to "do the right thing" in most
596 circumstances automatically, preserving round-tripping characteristics 846 circumstances automatically, preserving round-tripping characteristics
597 (what you put in comes out as something equivalent). 847 (what you put in comes out as something equivalent).
… …
618 A JSON number becomes either an integer, numeric (floating point) or 868 A JSON number becomes either an integer, numeric (floating point) or
619 string scalar in perl, depending on its range and any fractional 869 string scalar in perl, depending on its range and any fractional
620 parts. On the Perl level, there is no difference between those as 870 parts. On the Perl level, there is no difference between those as
621 Perl handles all the conversion details, but an integer may take 871 Perl handles all the conversion details, but an integer may take
622 slightly less memory and might represent more values exactly than 872 slightly less memory and might represent more values exactly than
623 (floating point) numbers. 873 floating point numbers.
624 874
625 If the number consists of digits only, JSON::XS will try to 875 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 876 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 877 represent it as a numeric (floating point) value if that is possible
628 without loss of precision. Otherwise it will preserve the number as 878 without loss of precision. Otherwise it will preserve the number as
629 a string value. 879 a string value (in which case you lose roundtripping ability, as the
880 JSON number will be re-encoded toa JSON string).
630 881
631 Numbers containing a fractional or exponential part will always be 882 Numbers containing a fractional or exponential part will always be
632 represented as numeric (floating point) values, possibly at a loss 883 represented as numeric (floating point) values, possibly at a loss
633 of precision. 884 of precision (in which case you might lose perfect roundtripping
634 885 ability, but the JSON number will still be re-encoded as a JSON
635 This might create round-tripping problems as numbers might become 886 number).
636 strings, but as Perl is typeless there is no other way to do it.
637 887
638 true, false 888 true, false
639 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 889 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
640 respectively. They are overloaded to act almost exactly like the 890 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 891 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 0 919 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 920 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 921 can also use "JSON::XS::false" and "JSON::XS::true" to improve
672 readability. 922 readability.
673 923
674 encode_json [\0,JSON::XS::true] # yields [false,true] 924 encode_json [\0, JSON::XS::true] # yields [false,true]
675 925
676 JSON::XS::true, JSON::XS::false 926 JSON::XS::true, JSON::XS::false
677 These special values become JSON true and JSON false values, 927 These special values become JSON true and JSON false values,
678 respectively. You can also use "\1" and "\0" directly if you want. 928 respectively. You can also use "\1" and "\0" directly if you want.
679 929
680 blessed objects 930 blessed objects
681 Blessed objects are not allowed. JSON::XS currently tries to encode 931 Blessed objects are not directly representable in JSON. See the
682 their underlying representation (hash- or arrayref), but this 932 "allow_blessed" and "convert_blessed" methods on various options on
683 behaviour might change in future versions. 933 how to deal with this: basically, you can choose between throwing an
934 exception, encoding the reference as if it weren't blessed, or
935 provide your own serialiser method.
684 936
685 simple scalars 937 simple scalars
686 Simple Perl scalars (any scalar that is not a reference) are the 938 Simple Perl scalars (any scalar that is not a reference) are the
687 most difficult objects to encode: JSON::XS will encode undefined 939 most difficult objects to encode: JSON::XS will encode undefined
688 scalars as JSON null value, scalars that have last been used in a 940 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 941 string context before encoding as JSON strings, and anything else as
690 number value: 942 number value:
691 943
692 # dump as number 944 # dump as number
693 encode_json [2] # yields [2] 945 encode_json [2] # yields [2]
694 encode_json [-3.0e17] # yields [-3e+17] 946 encode_json [-3.0e17] # yields [-3e+17]
… …
713 my $x = "3"; # some variable containing a string 965 my $x = "3"; # some variable containing a string
714 $x += 0; # numify it, ensuring it will be dumped as a number 966 $x += 0; # numify it, ensuring it will be dumped as a number
715 $x *= 1; # same thing, the choice is yours. 967 $x *= 1; # same thing, the choice is yours.
716 968
717 You can not currently force the type in other, less obscure, ways. 969 You can not currently force the type in other, less obscure, ways.
718 Tell me if you need this capability. 970 Tell me if you need this capability (but don't forget to explain why
971 it's needed :).
719 972
720COMPARISON 973ENCODING/CODESET FLAG NOTES
721 As already mentioned, this module was created because none of the 974 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 975 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
723 describe the problems (or pleasures) I encountered with various existing 976 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.
726 977
727 JSON 1.07 978 "utf8" controls whether the JSON text created by "encode" (and expected
728 Slow (but very portable, as it is written in pure Perl). 979 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
980 control whether "encode" escapes character values outside their
981 respective codeset range. Neither of these flags conflict with each
982 other, although some combinations make less sense than others.
729 983
730 Undocumented/buggy Unicode handling (how JSON handles Unicode values 984 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 985 "encode" and "decode", that is, texts encoded with any combination of
732 doing en-/decoding oneself, but Unicode escapes are not working 986 these flag values will be correctly decoded when the same flags are used
987 - in general, if you use different flag settings while encoding vs. when
988 decoding you likely have a bug somewhere.
989
990 Below comes a verbose discussion of these flags. Note that a "codeset"
991 is simply an abstract set of character-codepoint pairs, while an
992 encoding takes those codepoint numbers and *encodes* them, in our case
993 into octets. Unicode is (among other things) a codeset, UTF-8 is an
994 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
995 encodings at the same time, which can be confusing.
996
997 "utf8" flag disabled
998 When "utf8" is disabled (the default), then "encode"/"decode"
999 generate and expect Unicode strings, that is, characters with high
1000 ordinal Unicode values (> 255) will be encoded as such characters,
1001 and likewise such characters are decoded as-is, no canges to them
1002 will be done, except "(re-)interpreting" them as Unicode codepoints
1003 or Unicode characters, respectively (to Perl, these are the same
1004 thing in strings unless you do funny/weird/dumb stuff).
1005
1006 This is useful when you want to do the encoding yourself (e.g. when
1007 you want to have UTF-16 encoded JSON texts) or when some other layer
1008 does the encoding for you (for example, when printing to a terminal
1009 using a filehandle that transparently encodes to UTF-8 you certainly
1010 do NOT want to UTF-8 encode your data first and have Perl encode it
1011 another time).
1012
1013 "utf8" flag enabled
1014 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1015 characters using the corresponding UTF-8 multi-byte sequence, and
1016 will expect your input strings to be encoded as UTF-8, that is, no
1017 "character" of the input string must have any value > 255, as UTF-8
1018 does not allow that.
1019
1020 The "utf8" flag therefore switches between two modes: disabled means
1021 you will get a Unicode string in Perl, enabled means you get an
1022 UTF-8 encoded octet/binary string in Perl.
1023
1024 "latin1" or "ascii" flags enabled
1025 With "latin1" (or "ascii") enabled, "encode" will escape characters
1026 with ordinal values > 255 (> 127 with "ascii") and encode the
1027 remaining characters as specified by the "utf8" flag.
1028
1029 If "utf8" is disabled, then the result is also correctly encoded in
1030 those character sets (as both are proper subsets of Unicode, meaning
1031 that a Unicode string with all character values < 256 is the same
1032 thing as a ISO-8859-1 string, and a Unicode string with all
1033 character values < 128 is the same thing as an ASCII string in
733 properly). 1034 Perl).
734 1035
735 No round-tripping (strings get clobbered if they look like numbers, 1036 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 1037 regardless of these flags, just some more characters will be escaped
737 will decode into the number 2. 1038 using "\uXXXX" then before.
738 1039
739 JSON::PC 0.01 1040 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
740 Very fast. 1041 encoding, while ASCII-encoded strings are. That is because the
1042 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1043 *codeset* being a subset of Unicode), while ASCII is.
741 1044
742 Undocumented/buggy Unicode handling. 1045 Surprisingly, "decode" will ignore these flags and so treat all
1046 input values as governed by the "utf8" flag. If it is disabled, this
1047 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1048 strict subsets of Unicode. If it is enabled, you can correctly
1049 decode UTF-8 encoded strings.
743 1050
744 No round-tripping. 1051 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1052 flag - they only govern when the JSON output engine escapes a
1053 character or not.
745 1054
746 Has problems handling many Perl values (e.g. regex results and other 1055 The main use for "latin1" is to relatively efficiently store binary
747 magic values will make it croak). 1056 data as JSON, at the expense of breaking compatibility with most
1057 JSON decoders.
748 1058
749 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1059 The main use for "ascii" is to force the output to not contain
750 which is not a valid JSON text. 1060 characters with values > 127, which means you can interpret the
751 1061 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
752 Unmaintained (maintainer unresponsive for many months, bugs are not 1062 any character set and 8-bit-encoding, and still get the same data
753 getting fixed). 1063 structure back. This is useful when your channel for JSON transfer
754 1064 is not 8-bit clean or the encoding might be mangled in between (e.g.
755 JSON::Syck 0.21 1065 in mail), and works because ASCII is a proper subset of most 8-bit
756 Very buggy (often crashes). 1066 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 1067
799 JSON and YAML 1068 JSON and YAML
800 You often hear that JSON is a subset (or a close subset) of YAML. This 1069 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, 1070 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 1071 writing), so let me state it clearly: *in general, there is no way to
803 valid YAML. 1072 configure JSON::XS to output a data structure as valid YAML* that works
1073 in all cases.
804 1074
805 If you really must use JSON::XS to generate YAML, you should use this 1075 If you really must use JSON::XS to generate YAML, you should use this
806 algorithm (subject to change in future versions): 1076 algorithm (subject to change in future versions):
807 1077
808 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1078 my $to_yaml = JSON::XS->new->utf8->space_after (1);
809 my $yaml = $to_yaml->encode ($ref) . "\n"; 1079 my $yaml = $to_yaml->encode ($ref) . "\n";
810 1080
811 This will usually generate JSON texts that also parse as valid YAML. 1081 This will *usually* generate JSON texts that also parse as valid YAML.
812 Please note that YAML has hardcoded limits on (simple) object key 1082 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 1083 lengths that JSON doesn't have and also has different and incompatible
1084 unicode handling, so you should make sure that your hash keys are
814 keys are noticeably shorter than the 1024 characters YAML allows. 1085 noticeably shorter than the 1024 "stream characters" YAML allows and
1086 that you do not have characters with codepoint values outside the
1087 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1088 sequences in strings (which JSON::XS does not *currently* generate, but
1089 other JSON generators might).
815 1090
816 There might be other incompatibilities that I am not aware of. In 1091 There might be other incompatibilities that I am not aware of (or the
1092 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 1093 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: 1094 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 1095 chances are high that you will run into severe interoperability problems
820 problems. 1096 when you least expect it.
1097
1098 (*) I have been pressured multiple times by Brian Ingerson (one of the
1099 authors of the YAML specification) to remove this paragraph, despite
1100 him acknowledging that the actual incompatibilities exist. As I was
1101 personally bitten by this "JSON is YAML" lie, I refused and said I
1102 will continue to educate people about these issues, so others do not
1103 run into the same problem again and again. After this, Brian called
1104 me a (quote)*complete and worthless idiot*(unquote).
1105
1106 In my opinion, instead of pressuring and insulting people who
1107 actually clarify issues with YAML and the wrong statements of some
1108 of its proponents, I would kindly suggest reading the JSON spec
1109 (which is not that difficult or long) and finally make YAML
1110 compatible to it, and educating users about the changes, instead of
1111 spreading lies about the real compatibility for many *years* and
1112 trying to silence people who point out that it isn't true.
821 1113
822 SPEED 1114 SPEED
823 It seems that JSON::XS is surprisingly fast, as shown in the following 1115 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 1116 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 1117 in the JSON::XS distribution, to make it easy to compare on your own
826 system. 1118 system.
827 1119
828 First comes a comparison between various modules using a very short 1120 First comes a comparison between various modules using a very short
829 single-line JSON string: 1121 single-line JSON string (also available at
1122 <http://dist.schmorp.de/misc/json/short.json>).
830 1123
831 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1124 {"method": "handleMessage", "params": ["user1",
832 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1125 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1126 true, false]}
833 1127
834 It shows the number of encodes/decodes per second (JSON::XS uses the 1128 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 1129 functional interface, while JSON::XS/2 uses the OO interface with
836 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1130 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
837 Higher is better: 1131 Higher is better:
… …
853 encoding, about three times faster on decoding, and over forty times 1147 encoding, about three times faster on decoding, and over forty times
854 faster than JSON, even with pretty-printing and key sorting. It also 1148 faster than JSON, even with pretty-printing and key sorting. It also
855 compares favourably to Storable for small amounts of data. 1149 compares favourably to Storable for small amounts of data.
856 1150
857 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1151 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
858 search API (http://nanoref.com/yahooapis/mgPdGg): 1152 search API (<http://dist.schmorp.de/misc/json/long.json>).
859 1153
860 module | encode | decode | 1154 module | encode | decode |
861 -----------|------------|------------| 1155 -----------|------------|------------|
862 JSON 1.x | 55.260 | 34.971 | 1156 JSON 1.x | 55.260 | 34.971 |
863 JSON::DWIW | 825.228 | 1082.513 | 1157 JSON::DWIW | 825.228 | 1082.513 |
… …
900 Third, JSON::XS recurses using the C stack when decoding objects and 1194 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 1195 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 1196 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 1197 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. 1198 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 1199 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 1200 process has a smaller stack, you should adjust this setting accordingly
907 with the "max_depth" method. 1201 with the "max_depth" method.
908 1202
909 And last but least, something else could bomb you that I forgot to think 1203 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 1204 case, you get to keep the pieces. I am always open for hints, though...
911 hints, though... 1205
1206 Also keep in mind that JSON::XS might leak contents of your Perl data
1207 structures in its error messages, so when you serialise sensitive
1208 information you might want to make sure that exceptions thrown by
1209 JSON::XS will not end up in front of untrusted eyes.
912 1210
913 If you are using JSON::XS to return packets to consumption by JavaScript 1211 If you are using JSON::XS to return packets to consumption by JavaScript
914 scripts in a browser you should have a look at 1212 scripts in a browser you should have a look at
915 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1213 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
916 you are vulnerable to some common attack vectors (which really are 1214 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, 1215 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 1216 as major browser developers care only for features, not about getting
919 security right). 1217 security right).
920 1218
921THREADS 1219THREADS
922 This module is *not* guaranteed to be thread safe and there are no plans 1220 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 1221 to change this until Perl gets thread support (as opposed to the
924 horribly slow so-called "threads" which are simply slow and bloated 1222 horribly slow so-called "threads" which are simply slow and bloated
925 process simulations - use fork, its *much* faster, cheaper, better). 1223 process simulations - use fork, it's *much* faster, cheaper, better).
926 1224
927 (It might actually work, but you have been warned). 1225 (It might actually work, but you have been warned).
928 1226
929BUGS 1227BUGS
930 While the goal of this module is to be correct, that unfortunately does 1228 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 1229 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. 1230 keep reporting bugs they will be fixed swiftly, though.
934 1231
935 Please refrain from using rt.cpan.org or any other bug reporting 1232 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. 1233 service. I put the contact address into my modules for a reason.
1234
1235SEE ALSO
1236 The json_xs command line utility for quick experiments.
937 1237
938AUTHOR 1238AUTHOR
939 Marc Lehmann <schmorp@schmorp.de> 1239 Marc Lehmann <schmorp@schmorp.de>
940 http://home.schmorp.de/ 1240 http://home.schmorp.de/
941 1241

Diff Legend

– Removed lines
+ Added lines
< Changed lines
> Changed lines