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Revision 1.23 by root, Wed Mar 19 22:31:00 2008 UTC vs.
Revision 1.25 by root, Wed Apr 16 18:38:38 2008 UTC

… …
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 [This section and the API it details is still EXPERIMENTAL]
629
630 In some cases, there is the need for incremental parsing of JSON texts.
631 While this module always has to keep both JSON text and resulting Perl
632 data structure in memory at one time, it does allow you to parse a JSON
633 stream incrementally. It does so by accumulating text until it has a
634 full JSON object, which it then can decode. This process is similar to
635 using "decode_prefix" to see if a full JSON object is available, but is
636 much more efficient (JSON::XS will only attempt to parse the JSON text
637 once it is sure it has enough text to get a decisive result, using a
638 very simple but truly incremental parser).
639
640 The following two methods deal with this.
641
642 [void, scalar or list context] = $json->incr_parse ([$string])
643 This is the central parsing function. It can both append new text
644 and extract objects from the stream accumulated so far (both of
645 these functions are optional).
646
647 If $string is given, then this string is appended to the already
648 existing JSON fragment stored in the $json object.
649
650 After that, if the function is called in void context, it will
651 simply return without doing anything further. This can be used to
652 add more text in as many chunks as you want.
653
654 If the method is called in scalar context, then it will try to
655 extract exactly *one* JSON object. If that is successful, it will
656 return this object, otherwise it will return "undef". If there is a
657 parse error, this method will croak just as "decode" would do (one
658 can then use "incr_skip" to skip the errornous part). This is the
659 most common way of using the method.
660
661 And finally, in list context, it will try to extract as many objects
662 from the stream as it can find and return them, or the empty list
663 otherwise. For this to work, there must be no separators between the
664 JSON objects or arrays, instead they must be concatenated
665 back-to-back. If an error occurs, an exception will be raised as in
666 the scalar context case. Note that in this case, any
667 previously-parsed JSON texts will be lost.
668
669 $lvalue_string = $json->incr_text
670 This method returns the currently stored JSON fragment as an lvalue,
671 that is, you can manipulate it. This *only* works when a preceding
672 call to "incr_parse" in *scalar context* successfully returned an
673 object. Under all other circumstances you must not call this
674 function (I mean it. although in simple tests it might actually
675 work, it *will* fail under real world conditions). As a special
676 exception, you can also call this method before having parsed
677 anything.
678
679 This function is useful in two cases: a) finding the trailing text
680 after a JSON object or b) parsing multiple JSON objects separated by
681 non-JSON text (such as commas).
682
683 $json->incr_skip
684 This will reset the state of the incremental parser and will remove
685 the parsed text from the input buffer. This is useful after
686 "incr_parse" died, in which case the input buffer and incremental
687 parser state is left unchanged, to skip the text parsed so far and
688 to reset the parse state.
689
690 LIMITATIONS
691 All options that affect decoding are supported, except "allow_nonref".
692 The reason for this is that it cannot be made to work sensibly: JSON
693 objects and arrays are self-delimited, i.e. you can concatenate them
694 back to back and still decode them perfectly. This does not hold true
695 for JSON numbers, however.
696
697 For example, is the string 1 a single JSON number, or is it simply the
698 start of 12? Or is 12 a single JSON number, or the concatenation of 1
699 and 2? In neither case you can tell, and this is why JSON::XS takes the
700 conservative route and disallows this case.
701
702 EXAMPLES
703 Some examples will make all this clearer. First, a simple example that
704 works similarly to "decode_prefix": We want to decode the JSON object at
705 the start of a string and identify the portion after the JSON object:
706
707 my $text = "[1,2,3] hello";
708
709 my $json = new JSON::XS;
710
711 my $obj = $json->incr_parse ($text)
712 or die "expected JSON object or array at beginning of string";
713
714 my $tail = $json->incr_text;
715 # $tail now contains " hello"
716
717 Easy, isn't it?
718
719 Now for a more complicated example: Imagine a hypothetical protocol
720 where you read some requests from a TCP stream, and each request is a
721 JSON array, without any separation between them (in fact, it is often
722 useful to use newlines as "separators", as these get interpreted as
723 whitespace at the start of the JSON text, which makes it possible to
724 test said protocol with "telnet"...).
725
726 Here is how you'd do it (it is trivial to write this in an event-based
727 manner):
728
729 my $json = new JSON::XS;
730
731 # read some data from the socket
732 while (sysread $socket, my $buf, 4096) {
733
734 # split and decode as many requests as possible
735 for my $request ($json->incr_parse ($buf)) {
736 # act on the $request
737 }
738 }
739
740 Another complicated example: Assume you have a string with JSON objects
741 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
742 [3]"). To parse them, we have to skip the commas between the JSON texts,
743 and here is where the lvalue-ness of "incr_text" comes in useful:
744
745 my $text = "[1],[2], [3]";
746 my $json = new JSON::XS;
747
748 # void context, so no parsing done
749 $json->incr_parse ($text);
750
751 # now extract as many objects as possible. note the
752 # use of scalar context so incr_text can be called.
753 while (my $obj = $json->incr_parse) {
754 # do something with $obj
755
756 # now skip the optional comma
757 $json->incr_text =~ s/^ \s* , //x;
758 }
759
760 Now lets go for a very complex example: Assume that you have a gigantic
761 JSON array-of-objects, many gigabytes in size, and you want to parse it,
762 but you cannot load it into memory fully (this has actually happened in
763 the real world :).
764
765 Well, you lost, you have to implement your own JSON parser. But JSON::XS
766 can still help you: You implement a (very simple) array parser and let
767 JSON decode the array elements, which are all full JSON objects on their
768 own (this wouldn't work if the array elements could be JSON numbers, for
769 example):
770
771 my $json = new JSON::XS;
772
773 # open the monster
774 open my $fh, "<bigfile.json"
775 or die "bigfile: $!";
776
777 # first parse the initial "["
778 for (;;) {
779 sysread $fh, my $buf, 65536
780 or die "read error: $!";
781 $json->incr_parse ($buf); # void context, so no parsing
782
783 # Exit the loop once we found and removed(!) the initial "[".
784 # In essence, we are (ab-)using the $json object as a simple scalar
785 # we append data to.
786 last if $json->incr_text =~ s/^ \s* \[ //x;
787 }
788
789 # now we have the skipped the initial "[", so continue
790 # parsing all the elements.
791 for (;;) {
792 # in this loop we read data until we got a single JSON object
793 for (;;) {
794 if (my $obj = $json->incr_parse) {
795 # do something with $obj
796 last;
797 }
798
799 # add more data
800 sysread $fh, my $buf, 65536
801 or die "read error: $!";
802 $json->incr_parse ($buf); # void context, so no parsing
803 }
804
805 # in this loop we read data until we either found and parsed the
806 # separating "," between elements, or the final "]"
807 for (;;) {
808 # first skip whitespace
809 $json->incr_text =~ s/^\s*//;
810
811 # if we find "]", we are done
812 if ($json->incr_text =~ s/^\]//) {
813 print "finished.\n";
814 exit;
815 }
816
817 # if we find ",", we can continue with the next element
818 if ($json->incr_text =~ s/^,//) {
819 last;
820 }
821
822 # if we find anything else, we have a parse error!
823 if (length $json->incr_text) {
824 die "parse error near ", $json->incr_text;
825 }
826
827 # else add more data
828 sysread $fh, my $buf, 65536
829 or die "read error: $!";
830 $json->incr_parse ($buf); # void context, so no parsing
831 }
832
833 This is a complex example, but most of the complexity comes from the
834 fact that we are trying to be correct (bear with me if I am wrong, I
835 never ran the above example :).
610 836
611MAPPING 837MAPPING
612 This section describes how JSON::XS maps Perl values to JSON values and 838 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 839 vice versa. These mappings are designed to "do the right thing" in most
614 circumstances automatically, preserving round-tripping characteristics 840 circumstances automatically, preserving round-tripping characteristics
… …
734 $x += 0; # numify it, ensuring it will be dumped as a number 960 $x += 0; # numify it, ensuring it will be dumped as a number
735 $x *= 1; # same thing, the choice is yours. 961 $x *= 1; # same thing, the choice is yours.
736 962
737 You can not currently force the type in other, less obscure, ways. 963 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 964 Tell me if you need this capability (but don't forget to explain why
739 its needed :). 965 it's needed :).
740 966
741ENCODING/CODESET FLAG NOTES 967ENCODING/CODESET FLAG NOTES
742 The interested reader might have seen a number of flags that signify 968 The interested reader might have seen a number of flags that signify
743 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be 969 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
744 some confusion on what these do, so here is a short comparison: 970 some confusion on what these do, so here is a short comparison:
745 971
746 "utf8" controls wether the JSON text created by "encode" (and expected 972 "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 973 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
748 control wether "encode" escapes character values outside their 974 control whether "encode" escapes character values outside their
749 respective codeset range. Neither of these flags conflict with each 975 respective codeset range. Neither of these flags conflict with each
750 other, although some combinations make less sense than others. 976 other, although some combinations make less sense than others.
751 977
752 Care has been taken to make all flags symmetrical with respect to 978 Care has been taken to make all flags symmetrical with respect to
753 "encode" and "decode", that is, texts encoded with any combination of 979 "encode" and "decode", that is, texts encoded with any combination of
… …
830 any character set and 8-bit-encoding, and still get the same data 1056 any character set and 8-bit-encoding, and still get the same data
831 structure back. This is useful when your channel for JSON transfer 1057 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. 1058 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 1059 in mail), and works because ASCII is a proper subset of most 8-bit
834 and multibyte encodings in use in the world. 1060 and multibyte encodings in use in the world.
835
836COMPARISON
837 As already mentioned, this module was created because none of the
838 existing JSON modules could be made to work correctly. First I will
839 describe the problems (or pleasures) I encountered with various existing
840 JSON modules, followed by some benchmark values. JSON::XS was designed
841 not to suffer from any of these problems or limitations.
842
843 JSON 2.xx
844 A marvellous piece of engineering, this module either uses JSON::XS
845 directly when available (so will be 100% compatible with it,
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
850 You cannot really lose by using this module, especially as it tries
851 very hard to work even with ancient Perl versions, while JSON::XS
852 does not.
853
854 JSON 1.07
855 Slow (but very portable, as it is written in pure Perl).
856
857 Undocumented/buggy Unicode handling (how JSON handles Unicode values
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
862 No round-tripping (strings get clobbered if they look like numbers,
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
866 JSON::PC 0.01
867 Very fast.
868
869 Undocumented/buggy Unicode handling.
870
871 No round-tripping.
872
873 Has problems handling many Perl values (e.g. regex results and other
874 magic values will make it croak).
875
876 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
877 which is not a valid JSON text.
878
879 Unmaintained (maintainer unresponsive for many months, bugs are not
880 getting fixed).
881
882 JSON::Syck 0.21
883 Very buggy (often crashes).
884
885 Very inflexible (no human-readable format supported, format pretty
886 much undocumented. I need at least a format for easy reading by
887 humans and a single-line compact format for use in a protocol, and
888 preferably a way to generate ASCII-only JSON texts).
889
890 Completely broken (and confusingly documented) Unicode handling
891 (Unicode escapes are not working properly, you need to set
892 ImplicitUnicode to *different* values on en- and decoding to get
893 symmetric behaviour).
894
895 No round-tripping (simple cases work, but this depends on whether
896 the scalar value was used in a numeric context or not).
897
898 Dumping hashes may skip hash values depending on iterator state.
899
900 Unmaintained (maintainer unresponsive for many months, bugs are not
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 1061
926 JSON and YAML 1062 JSON and YAML
927 You often hear that JSON is a subset of YAML. This is, however, a mass 1063 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 1064 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 1065 writing), so let me state it clearly: *in general, there is no way to
… …
977 1113
978 First comes a comparison between various modules using a very short 1114 First comes a comparison between various modules using a very short
979 single-line JSON string (also available at 1115 single-line JSON string (also available at
980 <http://dist.schmorp.de/misc/json/short.json>). 1116 <http://dist.schmorp.de/misc/json/short.json>).
981 1117
982 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1118 {"method": "handleMessage", "params": ["user1",
983 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1119 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1120 true, false]}
984 1121
985 It shows the number of encodes/decodes per second (JSON::XS uses the 1122 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 1123 functional interface, while JSON::XS/2 uses the OO interface with
987 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1124 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
988 Higher is better: 1125 Higher is better:
… …
1075 1212
1076THREADS 1213THREADS
1077 This module is *not* guaranteed to be thread safe and there are no plans 1214 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 1215 to change this until Perl gets thread support (as opposed to the
1079 horribly slow so-called "threads" which are simply slow and bloated 1216 horribly slow so-called "threads" which are simply slow and bloated
1080 process simulations - use fork, its *much* faster, cheaper, better). 1217 process simulations - use fork, it's *much* faster, cheaper, better).
1081 1218
1082 (It might actually work, but you have been warned). 1219 (It might actually work, but you have been warned).
1083 1220
1084BUGS 1221BUGS
1085 While the goal of this module is to be correct, that unfortunately does 1222 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 1223 not mean it's bug-free, only that I think its design is bug-free. It is
1087 still relatively early in its development. If you keep reporting bugs 1224 still relatively early in its development. If you keep reporting bugs
1088 they will be fixed swiftly, though. 1225 they will be fixed swiftly, though.
1089 1226
1090 Please refrain from using rt.cpan.org or any other bug reporting 1227 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. 1228 service. I put the contact address into my modules for a reason.
1229
1230SEE ALSO
1231 The json_xs command line utility for quick experiments.
1092 1232
1093AUTHOR 1233AUTHOR
1094 Marc Lehmann <schmorp@schmorp.de> 1234 Marc Lehmann <schmorp@schmorp.de>
1095 http://home.schmorp.de/ 1235 http://home.schmorp.de/
1096 1236

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