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20 $perl_scalar = $coder->decode ($unicode_json_text); 20 $perl_scalar = $coder->decode ($unicode_json_text);
21 21
22 # 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
23 # if available, at virtually no speed overhead either, so you should 23 # if available, at virtually no speed overhead either, so you should
24 # be able to just: 24 # be able to just:
25 25
26 use JSON; 26 use JSON;
27 27
28 # 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.
29 29
30DESCRIPTION 30DESCRIPTION
31 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
32 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*.
33 To reach the latter goal it was written in C. 33 To reach the latter goal it was written in C.
34 34
35 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
36 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
37 be overriden) with no overhead due to emulation (by inheritign 37 be overridden) with no overhead due to emulation (by inheriting
38 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
39 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
40 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
41 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.
42 42
44 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
45 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
46 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
47 to bug reports for other reasons. 47 to bug reports for other reasons.
48 48
49 See COMPARISON, below, for a comparison to some other JSON modules.
50
51 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
52 vice versa. 50 vice versa.
53 51
54 FEATURES 52 FEATURES
55 * correct Unicode handling 53 * correct Unicode handling
57 This module knows how to handle Unicode, documents how and when it 55 This module knows how to handle Unicode, documents how and when it
58 does so, and even documents what "correct" means. 56 does so, and even documents what "correct" means.
59 57
60 * round-trip integrity 58 * round-trip integrity
61 59
62 When you serialise a perl data structure using only datatypes 60 When you serialise a perl data structure using only data types
63 supported by JSON, the deserialised data structure is identical on 61 supported by JSON, the deserialised data structure is identical on
64 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"
65 just because it looks like a number). There minor *are* exceptions 63 just because it looks like a number). There minor *are* exceptions
66 to this, read the MAPPING section below to learn about those. 64 to this, read the MAPPING section below to learn about those.
67 65
78 too. 76 too.
79 77
80 * simple to use 78 * simple to use
81 79
82 This module has both a simple functional interface as well as an 80 This module has both a simple functional interface as well as an
83 objetc oriented interface interface. 81 object oriented interface interface.
84 82
85 * reasonably versatile output formats 83 * reasonably versatile output formats
86 84
87 You can choose between the most compact guaranteed-single-line 85 You can choose between the most compact guaranteed-single-line
88 format possible (nice for simple line-based protocols), a pure-ascii 86 format possible (nice for simple line-based protocols), a pure-ASCII
89 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
90 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
91 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
92 whatever way you like. 90 whatever way you like.
93 91
101 99
102 This function call is functionally identical to: 100 This function call is functionally identical to:
103 101
104 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 102 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
105 103
106 except being faster. 104 Except being faster.
107 105
108 $perl_scalar = decode_json $json_text 106 $perl_scalar = decode_json $json_text
109 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
110 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
111 resulting reference. Croaks on error. 109 resulting reference. Croaks on error.
112 110
113 This function call is functionally identical to: 111 This function call is functionally identical to:
114 112
115 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 113 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
116 114
117 except being faster. 115 Except being faster.
118 116
119 $is_boolean = JSON::XS::is_bool $scalar 117 $is_boolean = JSON::XS::is_bool $scalar
120 Returns true if the passed scalar represents either JSON::XS::true 118 Returns true if the passed scalar represents either JSON::XS::true
121 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,
122 respectively and are used to represent JSON "true" and "false" 120 respectively and are used to represent JSON "true" and "false"
152 150
153 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
154 doesn't exist. 152 doesn't exist.
155 153
156 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
157 validly interpreted as a Unicode codepoint. 155 validly interpreted as a Unicode code point.
158 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,
159 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.
160 158
161 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
162 string. 160 string.
380 contains the same data, as key-value pairs have no inherent ordering 378 contains the same data, as key-value pairs have no inherent ordering
381 in Perl. 379 in Perl.
382 380
383 This setting has no effect when decoding JSON texts. 381 This setting has no effect when decoding JSON texts.
384 382
383 This setting has currently no effect on tied hashes.
384
385 $json = $json->allow_nonref ([$enable]) 385 $json = $json->allow_nonref ([$enable])
386 $enabled = $json->get_allow_nonref 386 $enabled = $json->get_allow_nonref
387 If $enable is true (or missing), then the "encode" method can 387 If $enable is true (or missing), then the "encode" method can
388 convert a non-reference into its corresponding string, number or 388 convert a non-reference into its corresponding string, number or
389 null JSON value, which is an extension to RFC4627. Likewise, 389 null JSON value, which is an extension to RFC4627. Likewise,
397 Example, encode a Perl scalar as JSON value with enabled 397 Example, encode a Perl scalar as JSON value with enabled
398 "allow_nonref", resulting in an invalid JSON text: 398 "allow_nonref", resulting in an invalid JSON text:
399 399
400 JSON::XS->new->allow_nonref->encode ("Hello, World!") 400 JSON::XS->new->allow_nonref->encode ("Hello, World!")
401 => "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.
402 417
403 $json = $json->allow_blessed ([$enable]) 418 $json = $json->allow_blessed ([$enable])
404 $enabled = $json->get_allow_blessed 419 $enabled = $json->get_allow_blessed
405 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
406 barf when it encounters a blessed reference. Instead, the value of 421 barf when it encounters a blessed reference. Instead, the value of
541 saving space. 556 saving space.
542 557
543 $json = $json->max_depth ([$maximum_nesting_depth]) 558 $json = $json->max_depth ([$maximum_nesting_depth])
544 $max_depth = $json->get_max_depth 559 $max_depth = $json->get_max_depth
545 Sets the maximum nesting level (default 512) accepted while encoding 560 Sets the maximum nesting level (default 512) accepted while encoding
546 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
547 higher nesting level then this limit, then the encoder and decoder 562 Perl data structure, then the encoder and decoder will stop and
548 will stop and croak at that point. 563 croak at that point.
549 564
550 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
551 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
552 "{" or "[" characters without their matching closing parenthesis 567 "{" or "[" characters without their matching closing parenthesis
553 crossed to reach a given character in a string. 568 crossed to reach a given character in a string.
554 569
555 Setting the maximum depth to one disallows any nesting, so that 570 Setting the maximum depth to one disallows any nesting, so that
556 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.
557 572
558 The argument to "max_depth" will be rounded up to the next highest
559 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,
560 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.
561 579
562 See SECURITY CONSIDERATIONS, below, for more info on why this is 580 See SECURITY CONSIDERATIONS, below, for more info on why this is
563 useful. 581 useful.
564 582
565 $json = $json->max_size ([$maximum_string_size]) 583 $json = $json->max_size ([$maximum_string_size])
566 $max_size = $json->get_max_size 584 $max_size = $json->get_max_size
567 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
568 decoding is being attempted. The default is 0, meaning no limit. 586 decoding is being attempted. The default is 0, meaning no limit.
569 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
570 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
571 exception. This setting has no effect on "encode" (yet). 589 exception. This setting has no effect on "encode" (yet).
572 590
573 The argument to "max_size" will be rounded up to the next highest
574 power of two (so may be more than requested). If no argument is
575 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
576 specified). 592 as when 0 is specified).
577 593
578 See SECURITY CONSIDERATIONS, below, for more info on why this is 594 See SECURITY CONSIDERATIONS, below, for more info on why this is
579 useful. 595 useful.
580 596
581 $json_text = $json->encode ($perl_scalar) 597 $json_text = $json->encode ($perl_scalar)
605 protocol (which is not the brightest thing to do in the first place) 621 protocol (which is not the brightest thing to do in the first place)
606 and you need to know where the JSON text ends. 622 and you need to know where the JSON text ends.
607 623
608 JSON::XS->new->decode_prefix ("[1] the tail") 624 JSON::XS->new->decode_prefix ("[1] the tail")
609 => ([], 3) 625 => ([], 3)
626
627INCREMENTAL PARSING
628 In some cases, there is the need for incremental parsing of JSON texts.
629 While this module always has to keep both JSON text and resulting Perl
630 data structure in memory at one time, it does allow you to parse a JSON
631 stream incrementally. It does so by accumulating text until it has a
632 full JSON object, which it then can decode. This process is similar to
633 using "decode_prefix" to see if a full JSON object is available, but is
634 much more efficient (and can be implemented with a minimum of method
635 calls).
636
637 JSON::XS will only attempt to parse the JSON text once it is sure it has
638 enough text to get a decisive result, using a very simple but truly
639 incremental parser. This means that it sometimes won't stop as early as
640 the full parser, for example, it doesn't detect parenthese mismatches.
641 The only thing it guarantees is that it starts decoding as soon as a
642 syntactically valid JSON text has been seen. This means you need to set
643 resource limits (e.g. "max_size") to ensure the parser will stop parsing
644 in the presence if syntax errors.
645
646 The following methods implement this incremental parser.
647
648 [void, scalar or list context] = $json->incr_parse ([$string])
649 This is the central parsing function. It can both append new text
650 and extract objects from the stream accumulated so far (both of
651 these functions are optional).
652
653 If $string is given, then this string is appended to the already
654 existing JSON fragment stored in the $json object.
655
656 After that, if the function is called in void context, it will
657 simply return without doing anything further. This can be used to
658 add more text in as many chunks as you want.
659
660 If the method is called in scalar context, then it will try to
661 extract exactly *one* JSON object. If that is successful, it will
662 return this object, otherwise it will return "undef". If there is a
663 parse error, this method will croak just as "decode" would do (one
664 can then use "incr_skip" to skip the errornous part). This is the
665 most common way of using the method.
666
667 And finally, in list context, it will try to extract as many objects
668 from the stream as it can find and return them, or the empty list
669 otherwise. For this to work, there must be no separators between the
670 JSON objects or arrays, instead they must be concatenated
671 back-to-back. If an error occurs, an exception will be raised as in
672 the scalar context case. Note that in this case, any
673 previously-parsed JSON texts will be lost.
674
675 $lvalue_string = $json->incr_text
676 This method returns the currently stored JSON fragment as an lvalue,
677 that is, you can manipulate it. This *only* works when a preceding
678 call to "incr_parse" in *scalar context* successfully returned an
679 object. Under all other circumstances you must not call this
680 function (I mean it. although in simple tests it might actually
681 work, it *will* fail under real world conditions). As a special
682 exception, you can also call this method before having parsed
683 anything.
684
685 This function is useful in two cases: a) finding the trailing text
686 after a JSON object or b) parsing multiple JSON objects separated by
687 non-JSON text (such as commas).
688
689 $json->incr_skip
690 This will reset the state of the incremental parser and will remove
691 the parsed text from the input buffer so far. This is useful after
692 "incr_parse" died, in which case the input buffer and incremental
693 parser state is left unchanged, to skip the text parsed so far and
694 to reset the parse state.
695
696 The difference to "incr_reset" is that only text until the parse
697 error occured is removed.
698
699 $json->incr_reset
700 This completely resets the incremental parser, that is, after this
701 call, it will be as if the parser had never parsed anything.
702
703 This is useful if you want to repeatedly parse JSON objects and want
704 to ignore any trailing data, which means you have to reset the
705 parser after each successful decode.
706
707 LIMITATIONS
708 All options that affect decoding are supported, except "allow_nonref".
709 The reason for this is that it cannot be made to work sensibly: JSON
710 objects and arrays are self-delimited, i.e. you can concatenate them
711 back to back and still decode them perfectly. This does not hold true
712 for JSON numbers, however.
713
714 For example, is the string 1 a single JSON number, or is it simply the
715 start of 12? Or is 12 a single JSON number, or the concatenation of 1
716 and 2? In neither case you can tell, and this is why JSON::XS takes the
717 conservative route and disallows this case.
718
719 EXAMPLES
720 Some examples will make all this clearer. First, a simple example that
721 works similarly to "decode_prefix": We want to decode the JSON object at
722 the start of a string and identify the portion after the JSON object:
723
724 my $text = "[1,2,3] hello";
725
726 my $json = new JSON::XS;
727
728 my $obj = $json->incr_parse ($text)
729 or die "expected JSON object or array at beginning of string";
730
731 my $tail = $json->incr_text;
732 # $tail now contains " hello"
733
734 Easy, isn't it?
735
736 Now for a more complicated example: Imagine a hypothetical protocol
737 where you read some requests from a TCP stream, and each request is a
738 JSON array, without any separation between them (in fact, it is often
739 useful to use newlines as "separators", as these get interpreted as
740 whitespace at the start of the JSON text, which makes it possible to
741 test said protocol with "telnet"...).
742
743 Here is how you'd do it (it is trivial to write this in an event-based
744 manner):
745
746 my $json = new JSON::XS;
747
748 # read some data from the socket
749 while (sysread $socket, my $buf, 4096) {
750
751 # split and decode as many requests as possible
752 for my $request ($json->incr_parse ($buf)) {
753 # act on the $request
754 }
755 }
756
757 Another complicated example: Assume you have a string with JSON objects
758 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
759 [3]"). To parse them, we have to skip the commas between the JSON texts,
760 and here is where the lvalue-ness of "incr_text" comes in useful:
761
762 my $text = "[1],[2], [3]";
763 my $json = new JSON::XS;
764
765 # void context, so no parsing done
766 $json->incr_parse ($text);
767
768 # now extract as many objects as possible. note the
769 # use of scalar context so incr_text can be called.
770 while (my $obj = $json->incr_parse) {
771 # do something with $obj
772
773 # now skip the optional comma
774 $json->incr_text =~ s/^ \s* , //x;
775 }
776
777 Now lets go for a very complex example: Assume that you have a gigantic
778 JSON array-of-objects, many gigabytes in size, and you want to parse it,
779 but you cannot load it into memory fully (this has actually happened in
780 the real world :).
781
782 Well, you lost, you have to implement your own JSON parser. But JSON::XS
783 can still help you: You implement a (very simple) array parser and let
784 JSON decode the array elements, which are all full JSON objects on their
785 own (this wouldn't work if the array elements could be JSON numbers, for
786 example):
787
788 my $json = new JSON::XS;
789
790 # open the monster
791 open my $fh, "<bigfile.json"
792 or die "bigfile: $!";
793
794 # first parse the initial "["
795 for (;;) {
796 sysread $fh, my $buf, 65536
797 or die "read error: $!";
798 $json->incr_parse ($buf); # void context, so no parsing
799
800 # Exit the loop once we found and removed(!) the initial "[".
801 # In essence, we are (ab-)using the $json object as a simple scalar
802 # we append data to.
803 last if $json->incr_text =~ s/^ \s* \[ //x;
804 }
805
806 # now we have the skipped the initial "[", so continue
807 # parsing all the elements.
808 for (;;) {
809 # in this loop we read data until we got a single JSON object
810 for (;;) {
811 if (my $obj = $json->incr_parse) {
812 # do something with $obj
813 last;
814 }
815
816 # add more data
817 sysread $fh, my $buf, 65536
818 or die "read error: $!";
819 $json->incr_parse ($buf); # void context, so no parsing
820 }
821
822 # in this loop we read data until we either found and parsed the
823 # separating "," between elements, or the final "]"
824 for (;;) {
825 # first skip whitespace
826 $json->incr_text =~ s/^\s*//;
827
828 # if we find "]", we are done
829 if ($json->incr_text =~ s/^\]//) {
830 print "finished.\n";
831 exit;
832 }
833
834 # if we find ",", we can continue with the next element
835 if ($json->incr_text =~ s/^,//) {
836 last;
837 }
838
839 # if we find anything else, we have a parse error!
840 if (length $json->incr_text) {
841 die "parse error near ", $json->incr_text;
842 }
843
844 # else add more data
845 sysread $fh, my $buf, 65536
846 or die "read error: $!";
847 $json->incr_parse ($buf); # void context, so no parsing
848 }
849
850 This is a complex example, but most of the complexity comes from the
851 fact that we are trying to be correct (bear with me if I am wrong, I
852 never ran the above example :).
610 853
611MAPPING 854MAPPING
612 This section describes how JSON::XS maps Perl values to JSON values and 855 This section describes how JSON::XS maps Perl values to JSON values and
613 vice versa. These mappings are designed to "do the right thing" in most 856 vice versa. These mappings are designed to "do the right thing" in most
614 circumstances automatically, preserving round-tripping characteristics 857 circumstances automatically, preserving round-tripping characteristics
687 an exception to be thrown, except for references to the integers 0 930 an exception to be thrown, except for references to the integers 0
688 and 1, which get turned into "false" and "true" atoms in JSON. You 931 and 1, which get turned into "false" and "true" atoms in JSON. You
689 can also use "JSON::XS::false" and "JSON::XS::true" to improve 932 can also use "JSON::XS::false" and "JSON::XS::true" to improve
690 readability. 933 readability.
691 934
692 encode_json [\0,JSON::XS::true] # yields [false,true] 935 encode_json [\0, JSON::XS::true] # yields [false,true]
693 936
694 JSON::XS::true, JSON::XS::false 937 JSON::XS::true, JSON::XS::false
695 These special values become JSON true and JSON false values, 938 These special values become JSON true and JSON false values,
696 respectively. You can also use "\1" and "\0" directly if you want. 939 respectively. You can also use "\1" and "\0" directly if you want.
697 940
734 $x += 0; # numify it, ensuring it will be dumped as a number 977 $x += 0; # numify it, ensuring it will be dumped as a number
735 $x *= 1; # same thing, the choice is yours. 978 $x *= 1; # same thing, the choice is yours.
736 979
737 You can not currently force the type in other, less obscure, ways. 980 You can not currently force the type in other, less obscure, ways.
738 Tell me if you need this capability (but don't forget to explain why 981 Tell me if you need this capability (but don't forget to explain why
739 its needed :). 982 it's needed :).
740 983
741ENCODING/CODESET FLAG NOTES 984ENCODING/CODESET FLAG NOTES
742 The interested reader might have seen a number of flags that signify 985 The interested reader might have seen a number of flags that signify
743 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be 986 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
744 some confusion on what these do, so here is a short comparison: 987 some confusion on what these do, so here is a short comparison:
745 988
746 "utf8" controls wether the JSON text created by "encode" (and expected 989 "utf8" controls whether the JSON text created by "encode" (and expected
747 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only 990 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
748 control wether "encode" escapes character values outside their 991 control whether "encode" escapes character values outside their
749 respective codeset range. Neither of these flags conflict with each 992 respective codeset range. Neither of these flags conflict with each
750 other, although some combinations make less sense than others. 993 other, although some combinations make less sense than others.
751 994
752 Care has been taken to make all flags symmetrical with respect to 995 Care has been taken to make all flags symmetrical with respect to
753 "encode" and "decode", that is, texts encoded with any combination of 996 "encode" and "decode", that is, texts encoded with any combination of
831 structure back. This is useful when your channel for JSON transfer 1074 structure back. This is useful when your channel for JSON transfer
832 is not 8-bit clean or the encoding might be mangled in between (e.g. 1075 is not 8-bit clean or the encoding might be mangled in between (e.g.
833 in mail), and works because ASCII is a proper subset of most 8-bit 1076 in mail), and works because ASCII is a proper subset of most 8-bit
834 and multibyte encodings in use in the world. 1077 and multibyte encodings in use in the world.
835 1078
836COMPARISON 1079 JSON and ECMAscript
837 As already mentioned, this module was created because none of the 1080 JSON syntax is based on how literals are represented in javascript (the
838 existing JSON modules could be made to work correctly. First I will 1081 not-standardised predecessor of ECMAscript) which is presumably why it
839 describe the problems (or pleasures) I encountered with various existing 1082 is called "JavaScript Object Notation".
840 JSON modules, followed by some benchmark values. JSON::XS was designed
841 not to suffer from any of these problems or limitations.
842 1083
843 JSON 2.xx 1084 However, JSON is not a subset (and also not a superset of course) of
844 A marvellous piece of engineering, this module either uses JSON::XS 1085 ECMAscript (the standard) or javascript (whatever browsers actually
845 directly when available (so will be 100% compatible with it, 1086 implement).
846 including speed), or it uses JSON::PP, which is basically JSON::XS
847 translated to Pure Perl, which should be 100% compatible with
848 JSON::XS, just a bit slower.
849 1087
850 You cannot really lose by using this module, especially as it tries 1088 If you want to use javascript's "eval" function to "parse" JSON, you
851 very hard to work even with ancient Perl versions, while JSON::XS 1089 might run into parse errors for valid JSON texts, or the resulting data
852 does not. 1090 structure might not be queryable:
853 1091
854 JSON 1.07 1092 One of the problems is that U+2028 and U+2029 are valid characters
855 Slow (but very portable, as it is written in pure Perl). 1093 inside JSON strings, but are not allowed in ECMAscript string literals,
1094 so the following Perl fragment will not output something that can be
1095 guaranteed to be parsable by javascript's "eval":
856 1096
857 Undocumented/buggy Unicode handling (how JSON handles Unicode values 1097 use JSON::XS;
858 is undocumented. One can get far by feeding it Unicode strings and
859 doing en-/decoding oneself, but Unicode escapes are not working
860 properly).
861 1098
862 No round-tripping (strings get clobbered if they look like numbers, 1099 print encode_json [chr 0x2028];
863 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
864 will decode into the number 2.
865 1100
866 JSON::PC 0.01 1101 The right fix for this is to use a proper JSON parser in your javascript
867 Very fast. 1102 programs, and not rely on "eval" (see for example Douglas Crockford's
1103 json2.js parser).
868 1104
869 Undocumented/buggy Unicode handling. 1105 If this is not an option, you can, as a stop-gap measure, simply encode
1106 to ASCII-only JSON:
870 1107
871 No round-tripping. 1108 use JSON::XS;
872 1109
873 Has problems handling many Perl values (e.g. regex results and other 1110 print JSON::XS->new->ascii->encode ([chr 0x2028]);
874 magic values will make it croak).
875 1111
876 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1112 Note that this will enlarge the resulting JSON text quite a bit if you
877 which is not a valid JSON text. 1113 have many non-ASCII characters. You might be tempted to run some regexes
1114 to only escape U+2028 and U+2029, e.g.:
878 1115
879 Unmaintained (maintainer unresponsive for many months, bugs are not 1116 # DO NOT USE THIS!
880 getting fixed). 1117 my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
1118 $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
1119 $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
1120 print $json;
881 1121
882 JSON::Syck 0.21 1122 Note that *this is a bad idea*: the above only works for U+2028 and
883 Very buggy (often crashes). 1123 U+2029 and thus only for fully ECMAscript-compliant parsers. Many
1124 existing javascript implementations, however, have issues with other
1125 characters as well - using "eval" naively simply *will* cause problems.
884 1126
885 Very inflexible (no human-readable format supported, format pretty 1127 Another problem is that some javascript implementations reserve some
886 much undocumented. I need at least a format for easy reading by 1128 property names for their own purposes (which probably makes them
887 humans and a single-line compact format for use in a protocol, and 1129 non-ECMAscript-compliant). For example, Iceweasel reserves the
888 preferably a way to generate ASCII-only JSON texts). 1130 "__proto__" property name for it's own purposes.
889 1131
890 Completely broken (and confusingly documented) Unicode handling 1132 If that is a problem, you could parse try to filter the resulting JSON
891 (Unicode escapes are not working properly, you need to set 1133 output for these property strings, e.g.:
892 ImplicitUnicode to *different* values on en- and decoding to get
893 symmetric behaviour).
894 1134
895 No round-tripping (simple cases work, but this depends on whether 1135 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
896 the scalar value was used in a numeric context or not).
897 1136
898 Dumping hashes may skip hash values depending on iterator state. 1137 This works because "__proto__" is not valid outside of strings, so every
1138 occurence of ""__proto__"\s*:" must be a string used as property name.
899 1139
900 Unmaintained (maintainer unresponsive for many months, bugs are not 1140 If you know of other incompatibilities, please let me know.
901 getting fixed).
902
903 Does not check input for validity (i.e. will accept non-JSON input
904 and return "something" instead of raising an exception. This is a
905 security issue: imagine two banks transferring money between each
906 other using JSON. One bank might parse a given non-JSON request and
907 deduct money, while the other might reject the transaction with a
908 syntax error. While a good protocol will at least recover, that is
909 extra unnecessary work and the transaction will still not succeed).
910
911 JSON::DWIW 0.04
912 Very fast. Very natural. Very nice.
913
914 Undocumented Unicode handling (but the best of the pack. Unicode
915 escapes still don't get parsed properly).
916
917 Very inflexible.
918
919 No round-tripping.
920
921 Does not generate valid JSON texts (key strings are often unquoted,
922 empty keys result in nothing being output)
923
924 Does not check input for validity.
925 1141
926 JSON and YAML 1142 JSON and YAML
927 You often hear that JSON is a subset of YAML. This is, however, a mass 1143 You often hear that JSON is a subset of YAML. This is, however, a mass
928 hysteria(*) and very far from the truth (as of the time of this 1144 hysteria(*) and very far from the truth (as of the time of this
929 writing), so let me state it clearly: *in general, there is no way to 1145 writing), so let me state it clearly: *in general, there is no way to
937 my $yaml = $to_yaml->encode ($ref) . "\n"; 1153 my $yaml = $to_yaml->encode ($ref) . "\n";
938 1154
939 This will *usually* generate JSON texts that also parse as valid YAML. 1155 This will *usually* generate JSON texts that also parse as valid YAML.
940 Please note that YAML has hardcoded limits on (simple) object key 1156 Please note that YAML has hardcoded limits on (simple) object key
941 lengths that JSON doesn't have and also has different and incompatible 1157 lengths that JSON doesn't have and also has different and incompatible
942 unicode handling, so you should make sure that your hash keys are 1158 unicode character escape syntax, so you should make sure that your hash
943 noticeably shorter than the 1024 "stream characters" YAML allows and 1159 keys are noticeably shorter than the 1024 "stream characters" YAML
944 that you do not have characters with codepoint values outside the 1160 allows and that you do not have characters with codepoint values outside
945 Unicode BMP (basic multilingual page). YAML also does not allow "\/" 1161 the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
946 sequences in strings (which JSON::XS does not *currently* generate, but 1162 sequences in strings (which JSON::XS does not *currently* generate, but
947 other JSON generators might). 1163 other JSON generators might).
948 1164
949 There might be other incompatibilities that I am not aware of (or the 1165 There might be other incompatibilities that I am not aware of (or the
950 YAML specification has been changed yet again - it does so quite often). 1166 YAML specification has been changed yet again - it does so quite often).
967 (which is not that difficult or long) and finally make YAML 1183 (which is not that difficult or long) and finally make YAML
968 compatible to it, and educating users about the changes, instead of 1184 compatible to it, and educating users about the changes, instead of
969 spreading lies about the real compatibility for many *years* and 1185 spreading lies about the real compatibility for many *years* and
970 trying to silence people who point out that it isn't true. 1186 trying to silence people who point out that it isn't true.
971 1187
1188 Addendum/2009: the YAML 1.2 spec is still incomaptible with JSON,
1189 even though the incompatibilities have been documented (and are
1190 known to Brian) for many years and the spec makes explicit claims
1191 that YAML is a superset of JSON. It would be so easy to fix, but
1192 apparently, bullying and corrupting userdata is so much easier.
1193
972 SPEED 1194 SPEED
973 It seems that JSON::XS is surprisingly fast, as shown in the following 1195 It seems that JSON::XS is surprisingly fast, as shown in the following
974 tables. They have been generated with the help of the "eg/bench" program 1196 tables. They have been generated with the help of the "eg/bench" program
975 in the JSON::XS distribution, to make it easy to compare on your own 1197 in the JSON::XS distribution, to make it easy to compare on your own
976 system. 1198 system.
977 1199
978 First comes a comparison between various modules using a very short 1200 First comes a comparison between various modules using a very short
979 single-line JSON string (also available at 1201 single-line JSON string (also available at
980 <http://dist.schmorp.de/misc/json/short.json>). 1202 <http://dist.schmorp.de/misc/json/short.json>).
981 1203
982 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1204 {"method": "handleMessage", "params": ["user1",
983 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1205 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1206 true, false]}
984 1207
985 It shows the number of encodes/decodes per second (JSON::XS uses the 1208 It shows the number of encodes/decodes per second (JSON::XS uses the
986 functional interface, while JSON::XS/2 uses the OO interface with 1209 functional interface, while JSON::XS/2 uses the OO interface with
987 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1210 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
988 Higher is better: 1211 Higher is better:
1065 information you might want to make sure that exceptions thrown by 1288 information you might want to make sure that exceptions thrown by
1066 JSON::XS will not end up in front of untrusted eyes. 1289 JSON::XS will not end up in front of untrusted eyes.
1067 1290
1068 If you are using JSON::XS to return packets to consumption by JavaScript 1291 If you are using JSON::XS to return packets to consumption by JavaScript
1069 scripts in a browser you should have a look at 1292 scripts in a browser you should have a look at
1070 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1293 <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
1071 you are vulnerable to some common attack vectors (which really are 1294 to see whether you are vulnerable to some common attack vectors (which
1072 browser design bugs, but it is still you who will have to deal with it, 1295 really are browser design bugs, but it is still you who will have to
1073 as major browser developers care only for features, not about getting 1296 deal with it, as major browser developers care only for features, not
1074 security right). 1297 about getting security right).
1075 1298
1076THREADS 1299THREADS
1077 This module is *not* guaranteed to be thread safe and there are no plans 1300 This module is *not* guaranteed to be thread safe and there are no plans
1078 to change this until Perl gets thread support (as opposed to the 1301 to change this until Perl gets thread support (as opposed to the
1079 horribly slow so-called "threads" which are simply slow and bloated 1302 horribly slow so-called "threads" which are simply slow and bloated
1080 process simulations - use fork, its *much* faster, cheaper, better). 1303 process simulations - use fork, it's *much* faster, cheaper, better).
1081 1304
1082 (It might actually work, but you have been warned). 1305 (It might actually work, but you have been warned).
1083 1306
1084BUGS 1307BUGS
1085 While the goal of this module is to be correct, that unfortunately does 1308 While the goal of this module is to be correct, that unfortunately does
1086 not mean its bug-free, only that I think its design is bug-free. It is 1309 not mean it's bug-free, only that I think its design is bug-free. If you
1087 still relatively early in its development. If you keep reporting bugs
1088 they will be fixed swiftly, though. 1310 keep reporting bugs they will be fixed swiftly, though.
1089 1311
1090 Please refrain from using rt.cpan.org or any other bug reporting 1312 Please refrain from using rt.cpan.org or any other bug reporting
1091 service. I put the contact address into my modules for a reason. 1313 service. I put the contact address into my modules for a reason.
1314
1315SEE ALSO
1316 The json_xs command line utility for quick experiments.
1092 1317
1093AUTHOR 1318AUTHOR
1094 Marc Lehmann <schmorp@schmorp.de> 1319 Marc Lehmann <schmorp@schmorp.de>
1095 http://home.schmorp.de/ 1320 http://home.schmorp.de/
1096 1321

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