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1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4 JSON::XS - 正しくて高速な JSON 4 JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
5 シリアライザ/デシリアライザ
6 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) 5 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7 6
8SYNOPSIS 7SYNOPSIS
9 use JSON::XS; 8 use JSON::XS;
10 9
… …
21 $perl_scalar = $coder->decode ($unicode_json_text); 20 $perl_scalar = $coder->decode ($unicode_json_text);
22 21
23 # Note that JSON version 2.0 and above will automatically use JSON::XS 22 # Note that JSON version 2.0 and above will automatically use JSON::XS
24 # if available, at virtually no speed overhead either, so you should 23 # if available, at virtually no speed overhead either, so you should
25 # be able to just: 24 # be able to just:
26 25
27 use JSON; 26 use JSON;
28 27
29 # and do the same things, except that you have a pure-perl fallback now. 28 # and do the same things, except that you have a pure-perl fallback now.
30 29
31DESCRIPTION 30DESCRIPTION
32 This module converts Perl data structures to JSON and vice versa. Its 31 This module converts Perl data structures to JSON and vice versa. Its
… …
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 datatypes
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 objetc 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.
… …
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
… …
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 [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 :).
836
593MAPPING 837MAPPING
594 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
595 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
596 circumstances automatically, preserving round-tripping characteristics 840 circumstances automatically, preserving round-tripping characteristics
597 (what you put in comes out as something equivalent). 841 (what you put in comes out as something equivalent).
… …
618 A JSON number becomes either an integer, numeric (floating point) or 862 A JSON number becomes either an integer, numeric (floating point) or
619 string scalar in perl, depending on its range and any fractional 863 string scalar in perl, depending on its range and any fractional
620 parts. On the Perl level, there is no difference between those as 864 parts. On the Perl level, there is no difference between those as
621 Perl handles all the conversion details, but an integer may take 865 Perl handles all the conversion details, but an integer may take
622 slightly less memory and might represent more values exactly than 866 slightly less memory and might represent more values exactly than
623 (floating point) numbers. 867 floating point numbers.
624 868
625 If the number consists of digits only, JSON::XS will try to 869 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 870 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 871 represent it as a numeric (floating point) value if that is possible
628 without loss of precision. Otherwise it will preserve the number as 872 without loss of precision. Otherwise it will preserve the number as
629 a string value. 873 a string value (in which case you lose roundtripping ability, as the
874 JSON number will be re-encoded toa JSON string).
630 875
631 Numbers containing a fractional or exponential part will always be 876 Numbers containing a fractional or exponential part will always be
632 represented as numeric (floating point) values, possibly at a loss 877 represented as numeric (floating point) values, possibly at a loss
633 of precision. 878 of precision (in which case you might lose perfect roundtripping
634 879 ability, but the JSON number will still be re-encoded as a JSON
635 This might create round-tripping problems as numbers might become 880 number).
636 strings, but as Perl is typeless there is no other way to do it.
637 881
638 true, false 882 true, false
639 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 883 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
640 respectively. They are overloaded to act almost exactly like the 884 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 885 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
… …
676 JSON::XS::true, JSON::XS::false 920 JSON::XS::true, JSON::XS::false
677 These special values become JSON true and JSON false values, 921 These special values become JSON true and JSON false values,
678 respectively. You can also use "\1" and "\0" directly if you want. 922 respectively. You can also use "\1" and "\0" directly if you want.
679 923
680 blessed objects 924 blessed objects
681 Blessed objects are not allowed. JSON::XS currently tries to encode 925 Blessed objects are not directly representable in JSON. See the
682 their underlying representation (hash- or arrayref), but this 926 "allow_blessed" and "convert_blessed" methods on various options on
683 behaviour might change in future versions. 927 how to deal with this: basically, you can choose between throwing an
928 exception, encoding the reference as if it weren't blessed, or
929 provide your own serialiser method.
684 930
685 simple scalars 931 simple scalars
686 Simple Perl scalars (any scalar that is not a reference) are the 932 Simple Perl scalars (any scalar that is not a reference) are the
687 most difficult objects to encode: JSON::XS will encode undefined 933 most difficult objects to encode: JSON::XS will encode undefined
688 scalars as JSON null value, scalars that have last been used in a 934 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 935 string context before encoding as JSON strings, and anything else as
690 number value: 936 number value:
691 937
692 # dump as number 938 # dump as number
693 encode_json [2] # yields [2] 939 encode_json [2] # yields [2]
694 encode_json [-3.0e17] # yields [-3e+17] 940 encode_json [-3.0e17] # yields [-3e+17]
… …
713 my $x = "3"; # some variable containing a string 959 my $x = "3"; # some variable containing a string
714 $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
715 $x *= 1; # same thing, the choice is yours. 961 $x *= 1; # same thing, the choice is yours.
716 962
717 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.
718 Tell me if you need this capability. 964 Tell me if you need this capability (but don't forget to explain why
965 it's needed :).
719 966
720COMPARISON 967ENCODING/CODESET FLAG NOTES
721 As already mentioned, this module was created because none of the 968 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 969 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
723 describe the problems (or pleasures) I encountered with various existing 970 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.
726 971
727 JSON 1.07 972 "utf8" controls whether the JSON text created by "encode" (and expected
728 Slow (but very portable, as it is written in pure Perl). 973 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
974 control whether "encode" escapes character values outside their
975 respective codeset range. Neither of these flags conflict with each
976 other, although some combinations make less sense than others.
729 977
730 Undocumented/buggy Unicode handling (how JSON handles Unicode values 978 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 979 "encode" and "decode", that is, texts encoded with any combination of
732 doing en-/decoding oneself, but Unicode escapes are not working 980 these flag values will be correctly decoded when the same flags are used
981 - in general, if you use different flag settings while encoding vs. when
982 decoding you likely have a bug somewhere.
983
984 Below comes a verbose discussion of these flags. Note that a "codeset"
985 is simply an abstract set of character-codepoint pairs, while an
986 encoding takes those codepoint numbers and *encodes* them, in our case
987 into octets. Unicode is (among other things) a codeset, UTF-8 is an
988 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
989 encodings at the same time, which can be confusing.
990
991 "utf8" flag disabled
992 When "utf8" is disabled (the default), then "encode"/"decode"
993 generate and expect Unicode strings, that is, characters with high
994 ordinal Unicode values (> 255) will be encoded as such characters,
995 and likewise such characters are decoded as-is, no canges to them
996 will be done, except "(re-)interpreting" them as Unicode codepoints
997 or Unicode characters, respectively (to Perl, these are the same
998 thing in strings unless you do funny/weird/dumb stuff).
999
1000 This is useful when you want to do the encoding yourself (e.g. when
1001 you want to have UTF-16 encoded JSON texts) or when some other layer
1002 does the encoding for you (for example, when printing to a terminal
1003 using a filehandle that transparently encodes to UTF-8 you certainly
1004 do NOT want to UTF-8 encode your data first and have Perl encode it
1005 another time).
1006
1007 "utf8" flag enabled
1008 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1009 characters using the corresponding UTF-8 multi-byte sequence, and
1010 will expect your input strings to be encoded as UTF-8, that is, no
1011 "character" of the input string must have any value > 255, as UTF-8
1012 does not allow that.
1013
1014 The "utf8" flag therefore switches between two modes: disabled means
1015 you will get a Unicode string in Perl, enabled means you get an
1016 UTF-8 encoded octet/binary string in Perl.
1017
1018 "latin1" or "ascii" flags enabled
1019 With "latin1" (or "ascii") enabled, "encode" will escape characters
1020 with ordinal values > 255 (> 127 with "ascii") and encode the
1021 remaining characters as specified by the "utf8" flag.
1022
1023 If "utf8" is disabled, then the result is also correctly encoded in
1024 those character sets (as both are proper subsets of Unicode, meaning
1025 that a Unicode string with all character values < 256 is the same
1026 thing as a ISO-8859-1 string, and a Unicode string with all
1027 character values < 128 is the same thing as an ASCII string in
733 properly). 1028 Perl).
734 1029
735 No round-tripping (strings get clobbered if they look like numbers, 1030 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 1031 regardless of these flags, just some more characters will be escaped
737 will decode into the number 2. 1032 using "\uXXXX" then before.
738 1033
739 JSON::PC 0.01 1034 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
740 Very fast. 1035 encoding, while ASCII-encoded strings are. That is because the
1036 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1037 *codeset* being a subset of Unicode), while ASCII is.
741 1038
742 Undocumented/buggy Unicode handling. 1039 Surprisingly, "decode" will ignore these flags and so treat all
1040 input values as governed by the "utf8" flag. If it is disabled, this
1041 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1042 strict subsets of Unicode. If it is enabled, you can correctly
1043 decode UTF-8 encoded strings.
743 1044
744 No round-tripping. 1045 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1046 flag - they only govern when the JSON output engine escapes a
1047 character or not.
745 1048
746 Has problems handling many Perl values (e.g. regex results and other 1049 The main use for "latin1" is to relatively efficiently store binary
747 magic values will make it croak). 1050 data as JSON, at the expense of breaking compatibility with most
1051 JSON decoders.
748 1052
749 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1053 The main use for "ascii" is to force the output to not contain
750 which is not a valid JSON text. 1054 characters with values > 127, which means you can interpret the
751 1055 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
752 Unmaintained (maintainer unresponsive for many months, bugs are not 1056 any character set and 8-bit-encoding, and still get the same data
753 getting fixed). 1057 structure back. This is useful when your channel for JSON transfer
754 1058 is not 8-bit clean or the encoding might be mangled in between (e.g.
755 JSON::Syck 0.21 1059 in mail), and works because ASCII is a proper subset of most 8-bit
756 Very buggy (often crashes). 1060 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 1061
799 JSON and YAML 1062 JSON and YAML
800 You often hear that JSON is a subset (or a close subset) of YAML. This 1063 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, 1064 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 1065 writing), so let me state it clearly: *in general, there is no way to
803 valid YAML. 1066 configure JSON::XS to output a data structure as valid YAML* that works
1067 in all cases.
804 1068
805 If you really must use JSON::XS to generate YAML, you should use this 1069 If you really must use JSON::XS to generate YAML, you should use this
806 algorithm (subject to change in future versions): 1070 algorithm (subject to change in future versions):
807 1071
808 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1072 my $to_yaml = JSON::XS->new->utf8->space_after (1);
809 my $yaml = $to_yaml->encode ($ref) . "\n"; 1073 my $yaml = $to_yaml->encode ($ref) . "\n";
810 1074
811 This will usually generate JSON texts that also parse as valid YAML. 1075 This will *usually* generate JSON texts that also parse as valid YAML.
812 Please note that YAML has hardcoded limits on (simple) object key 1076 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 1077 lengths that JSON doesn't have and also has different and incompatible
1078 unicode handling, so you should make sure that your hash keys are
814 keys are noticeably shorter than the 1024 characters YAML allows. 1079 noticeably shorter than the 1024 "stream characters" YAML allows and
1080 that you do not have characters with codepoint values outside the
1081 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1082 sequences in strings (which JSON::XS does not *currently* generate, but
1083 other JSON generators might).
815 1084
816 There might be other incompatibilities that I am not aware of. In 1085 There might be other incompatibilities that I am not aware of (or the
1086 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 1087 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: 1088 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 1089 chances are high that you will run into severe interoperability problems
820 problems. 1090 when you least expect it.
1091
1092 (*) I have been pressured multiple times by Brian Ingerson (one of the
1093 authors of the YAML specification) to remove this paragraph, despite
1094 him acknowledging that the actual incompatibilities exist. As I was
1095 personally bitten by this "JSON is YAML" lie, I refused and said I
1096 will continue to educate people about these issues, so others do not
1097 run into the same problem again and again. After this, Brian called
1098 me a (quote)*complete and worthless idiot*(unquote).
1099
1100 In my opinion, instead of pressuring and insulting people who
1101 actually clarify issues with YAML and the wrong statements of some
1102 of its proponents, I would kindly suggest reading the JSON spec
1103 (which is not that difficult or long) and finally make YAML
1104 compatible to it, and educating users about the changes, instead of
1105 spreading lies about the real compatibility for many *years* and
1106 trying to silence people who point out that it isn't true.
821 1107
822 SPEED 1108 SPEED
823 It seems that JSON::XS is surprisingly fast, as shown in the following 1109 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 1110 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 1111 in the JSON::XS distribution, to make it easy to compare on your own
826 system. 1112 system.
827 1113
828 First comes a comparison between various modules using a very short 1114 First comes a comparison between various modules using a very short
829 single-line JSON string: 1115 single-line JSON string (also available at
1116 <http://dist.schmorp.de/misc/json/short.json>).
830 1117
831 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1118 {"method": "handleMessage", "params": ["user1",
832 "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]}
833 1121
834 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
835 functional interface, while JSON::XS/2 uses the OO interface with 1123 functional interface, while JSON::XS/2 uses the OO interface with
836 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1124 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
837 Higher is better: 1125 Higher is better:
… …
853 encoding, about three times faster on decoding, and over forty times 1141 encoding, about three times faster on decoding, and over forty times
854 faster than JSON, even with pretty-printing and key sorting. It also 1142 faster than JSON, even with pretty-printing and key sorting. It also
855 compares favourably to Storable for small amounts of data. 1143 compares favourably to Storable for small amounts of data.
856 1144
857 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1145 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
858 search API (http://nanoref.com/yahooapis/mgPdGg): 1146 search API (<http://dist.schmorp.de/misc/json/long.json>).
859 1147
860 module | encode | decode | 1148 module | encode | decode |
861 -----------|------------|------------| 1149 -----------|------------|------------|
862 JSON 1.x | 55.260 | 34.971 | 1150 JSON 1.x | 55.260 | 34.971 |
863 JSON::DWIW | 825.228 | 1082.513 | 1151 JSON::DWIW | 825.228 | 1082.513 |
… …
900 Third, JSON::XS recurses using the C stack when decoding objects and 1188 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 1189 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 1190 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 1191 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. 1192 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 1193 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 1194 process has a smaller stack, you should adjust this setting accordingly
907 with the "max_depth" method. 1195 with the "max_depth" method.
908 1196
909 And last but least, something else could bomb you that I forgot to think 1197 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 1198 case, you get to keep the pieces. I am always open for hints, though...
911 hints, though... 1199
1200 Also keep in mind that JSON::XS might leak contents of your Perl data
1201 structures in its error messages, so when you serialise sensitive
1202 information you might want to make sure that exceptions thrown by
1203 JSON::XS will not end up in front of untrusted eyes.
912 1204
913 If you are using JSON::XS to return packets to consumption by JavaScript 1205 If you are using JSON::XS to return packets to consumption by JavaScript
914 scripts in a browser you should have a look at 1206 scripts in a browser you should have a look at
915 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1207 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
916 you are vulnerable to some common attack vectors (which really are 1208 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, 1209 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 1210 as major browser developers care only for features, not about getting
919 security right). 1211 security right).
920 1212
921THREADS 1213THREADS
922 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
923 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
924 horribly slow so-called "threads" which are simply slow and bloated 1216 horribly slow so-called "threads" which are simply slow and bloated
925 process simulations - use fork, its *much* faster, cheaper, better). 1217 process simulations - use fork, it's *much* faster, cheaper, better).
926 1218
927 (It might actually work, but you have been warned). 1219 (It might actually work, but you have been warned).
928 1220
929BUGS 1221BUGS
930 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
931 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
932 still relatively early in its development. If you keep reporting bugs 1224 still relatively early in its development. If you keep reporting bugs
933 they will be fixed swiftly, though. 1225 they will be fixed swiftly, though.
934 1226
935 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
936 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.
937 1232
938AUTHOR 1233AUTHOR
939 Marc Lehmann <schmorp@schmorp.de> 1234 Marc Lehmann <schmorp@schmorp.de>
940 http://home.schmorp.de/ 1235 http://home.schmorp.de/
941 1236

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