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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
… …
588 and you need to know where the JSON text ends. 606 and you need to know where the JSON text ends.
589 607
590 JSON::XS->new->decode_prefix ("[1] the tail") 608 JSON::XS->new->decode_prefix ("[1] the tail")
591 => ([], 3) 609 => ([], 3)
592 610
611INCREMENTAL PARSING
612 [This section and the API it details is still EXPERIMENTAL]
613
614 In some cases, there is the need for incremental parsing of JSON texts.
615 While this module always has to keep both JSON text and resulting Perl
616 data structure in memory at one time, it does allow you to parse a JSON
617 stream incrementally. It does so by accumulating text until it has a
618 full JSON object, which it then can decode. This process is similar to
619 using "decode_prefix" to see if a full JSON object is available, but is
620 much more efficient (JSON::XS will only attempt to parse the JSON text
621 once it is sure it has enough text to get a decisive result, using a
622 very simple but truly incremental parser).
623
624 The following two methods deal with this.
625
626 [void, scalar or list context] = $json->incr_parse ([$string])
627 This is the central parsing function. It can both append new text
628 and extract objects from the stream accumulated so far (both of
629 these functions are optional).
630
631 If $string is given, then this string is appended to the already
632 existing JSON fragment stored in the $json object.
633
634 After that, if the function is called in void context, it will
635 simply return without doing anything further. This can be used to
636 add more text in as many chunks as you want.
637
638 If the method is called in scalar context, then it will try to
639 extract exactly *one* JSON object. If that is successful, it will
640 return this object, otherwise it will return "undef". If there is a
641 parse error, this method will croak just as "decode" would do (one
642 can then use "incr_skip" to skip the errornous part). This is the
643 most common way of using the method.
644
645 And finally, in list context, it will try to extract as many objects
646 from the stream as it can find and return them, or the empty list
647 otherwise. For this to work, there must be no separators between the
648 JSON objects or arrays, instead they must be concatenated
649 back-to-back. If an error occurs, an exception will be raised as in
650 the scalar context case. Note that in this case, any
651 previously-parsed JSON texts will be lost.
652
653 $lvalue_string = $json->incr_text
654 This method returns the currently stored JSON fragment as an lvalue,
655 that is, you can manipulate it. This *only* works when a preceding
656 call to "incr_parse" in *scalar context* successfully returned an
657 object. Under all other circumstances you must not call this
658 function (I mean it. although in simple tests it might actually
659 work, it *will* fail under real world conditions). As a special
660 exception, you can also call this method before having parsed
661 anything.
662
663 This function is useful in two cases: a) finding the trailing text
664 after a JSON object or b) parsing multiple JSON objects separated by
665 non-JSON text (such as commas).
666
667 $json->incr_skip
668 This will reset the state of the incremental parser and will remove
669 the parsed text from the input buffer. This is useful after
670 "incr_parse" died, in which case the input buffer and incremental
671 parser state is left unchanged, to skip the text parsed so far and
672 to reset the parse state.
673
674 LIMITATIONS
675 All options that affect decoding are supported, except "allow_nonref".
676 The reason for this is that it cannot be made to work sensibly: JSON
677 objects and arrays are self-delimited, i.e. you can concatenate them
678 back to back and still decode them perfectly. This does not hold true
679 for JSON numbers, however.
680
681 For example, is the string 1 a single JSON number, or is it simply the
682 start of 12? Or is 12 a single JSON number, or the concatenation of 1
683 and 2? In neither case you can tell, and this is why JSON::XS takes the
684 conservative route and disallows this case.
685
686 EXAMPLES
687 Some examples will make all this clearer. First, a simple example that
688 works similarly to "decode_prefix": We want to decode the JSON object at
689 the start of a string and identify the portion after the JSON object:
690
691 my $text = "[1,2,3] hello";
692
693 my $json = new JSON::XS;
694
695 my $obj = $json->incr_parse ($text)
696 or die "expected JSON object or array at beginning of string";
697
698 my $tail = $json->incr_text;
699 # $tail now contains " hello"
700
701 Easy, isn't it?
702
703 Now for a more complicated example: Imagine a hypothetical protocol
704 where you read some requests from a TCP stream, and each request is a
705 JSON array, without any separation between them (in fact, it is often
706 useful to use newlines as "separators", as these get interpreted as
707 whitespace at the start of the JSON text, which makes it possible to
708 test said protocol with "telnet"...).
709
710 Here is how you'd do it (it is trivial to write this in an event-based
711 manner):
712
713 my $json = new JSON::XS;
714
715 # read some data from the socket
716 while (sysread $socket, my $buf, 4096) {
717
718 # split and decode as many requests as possible
719 for my $request ($json->incr_parse ($buf)) {
720 # act on the $request
721 }
722 }
723
724 Another complicated example: Assume you have a string with JSON objects
725 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
726 [3]"). To parse them, we have to skip the commas between the JSON texts,
727 and here is where the lvalue-ness of "incr_text" comes in useful:
728
729 my $text = "[1],[2], [3]";
730 my $json = new JSON::XS;
731
732 # void context, so no parsing done
733 $json->incr_parse ($text);
734
735 # now extract as many objects as possible. note the
736 # use of scalar context so incr_text can be called.
737 while (my $obj = $json->incr_parse) {
738 # do something with $obj
739
740 # now skip the optional comma
741 $json->incr_text =~ s/^ \s* , //x;
742 }
743
744 Now lets go for a very complex example: Assume that you have a gigantic
745 JSON array-of-objects, many gigabytes in size, and you want to parse it,
746 but you cannot load it into memory fully (this has actually happened in
747 the real world :).
748
749 Well, you lost, you have to implement your own JSON parser. But JSON::XS
750 can still help you: You implement a (very simple) array parser and let
751 JSON decode the array elements, which are all full JSON objects on their
752 own (this wouldn't work if the array elements could be JSON numbers, for
753 example):
754
755 my $json = new JSON::XS;
756
757 # open the monster
758 open my $fh, "<bigfile.json"
759 or die "bigfile: $!";
760
761 # first parse the initial "["
762 for (;;) {
763 sysread $fh, my $buf, 65536
764 or die "read error: $!";
765 $json->incr_parse ($buf); # void context, so no parsing
766
767 # Exit the loop once we found and removed(!) the initial "[".
768 # In essence, we are (ab-)using the $json object as a simple scalar
769 # we append data to.
770 last if $json->incr_text =~ s/^ \s* \[ //x;
771 }
772
773 # now we have the skipped the initial "[", so continue
774 # parsing all the elements.
775 for (;;) {
776 # in this loop we read data until we got a single JSON object
777 for (;;) {
778 if (my $obj = $json->incr_parse) {
779 # do something with $obj
780 last;
781 }
782
783 # add more data
784 sysread $fh, my $buf, 65536
785 or die "read error: $!";
786 $json->incr_parse ($buf); # void context, so no parsing
787 }
788
789 # in this loop we read data until we either found and parsed the
790 # separating "," between elements, or the final "]"
791 for (;;) {
792 # first skip whitespace
793 $json->incr_text =~ s/^\s*//;
794
795 # if we find "]", we are done
796 if ($json->incr_text =~ s/^\]//) {
797 print "finished.\n";
798 exit;
799 }
800
801 # if we find ",", we can continue with the next element
802 if ($json->incr_text =~ s/^,//) {
803 last;
804 }
805
806 # if we find anything else, we have a parse error!
807 if (length $json->incr_text) {
808 die "parse error near ", $json->incr_text;
809 }
810
811 # else add more data
812 sysread $fh, my $buf, 65536
813 or die "read error: $!";
814 $json->incr_parse ($buf); # void context, so no parsing
815 }
816
817 This is a complex example, but most of the complexity comes from the
818 fact that we are trying to be correct (bear with me if I am wrong, I
819 never ran the above example :).
820
593MAPPING 821MAPPING
594 This section describes how JSON::XS maps Perl values to JSON values and 822 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 823 vice versa. These mappings are designed to "do the right thing" in most
596 circumstances automatically, preserving round-tripping characteristics 824 circumstances automatically, preserving round-tripping characteristics
597 (what you put in comes out as something equivalent). 825 (what you put in comes out as something equivalent).
… …
618 A JSON number becomes either an integer, numeric (floating point) or 846 A JSON number becomes either an integer, numeric (floating point) or
619 string scalar in perl, depending on its range and any fractional 847 string scalar in perl, depending on its range and any fractional
620 parts. On the Perl level, there is no difference between those as 848 parts. On the Perl level, there is no difference between those as
621 Perl handles all the conversion details, but an integer may take 849 Perl handles all the conversion details, but an integer may take
622 slightly less memory and might represent more values exactly than 850 slightly less memory and might represent more values exactly than
623 (floating point) numbers. 851 floating point numbers.
624 852
625 If the number consists of digits only, JSON::XS will try to 853 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 854 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 855 represent it as a numeric (floating point) value if that is possible
628 without loss of precision. Otherwise it will preserve the number as 856 without loss of precision. Otherwise it will preserve the number as
629 a string value. 857 a string value (in which case you lose roundtripping ability, as the
858 JSON number will be re-encoded toa JSON string).
630 859
631 Numbers containing a fractional or exponential part will always be 860 Numbers containing a fractional or exponential part will always be
632 represented as numeric (floating point) values, possibly at a loss 861 represented as numeric (floating point) values, possibly at a loss
633 of precision. 862 of precision (in which case you might lose perfect roundtripping
634 863 ability, but the JSON number will still be re-encoded as a JSON
635 This might create round-tripping problems as numbers might become 864 number).
636 strings, but as Perl is typeless there is no other way to do it.
637 865
638 true, false 866 true, false
639 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 867 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
640 respectively. They are overloaded to act almost exactly like the 868 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 869 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
… …
676 JSON::XS::true, JSON::XS::false 904 JSON::XS::true, JSON::XS::false
677 These special values become JSON true and JSON false values, 905 These special values become JSON true and JSON false values,
678 respectively. You can also use "\1" and "\0" directly if you want. 906 respectively. You can also use "\1" and "\0" directly if you want.
679 907
680 blessed objects 908 blessed objects
681 Blessed objects are not allowed. JSON::XS currently tries to encode 909 Blessed objects are not directly representable in JSON. See the
682 their underlying representation (hash- or arrayref), but this 910 "allow_blessed" and "convert_blessed" methods on various options on
683 behaviour might change in future versions. 911 how to deal with this: basically, you can choose between throwing an
912 exception, encoding the reference as if it weren't blessed, or
913 provide your own serialiser method.
684 914
685 simple scalars 915 simple scalars
686 Simple Perl scalars (any scalar that is not a reference) are the 916 Simple Perl scalars (any scalar that is not a reference) are the
687 most difficult objects to encode: JSON::XS will encode undefined 917 most difficult objects to encode: JSON::XS will encode undefined
688 scalars as JSON null value, scalars that have last been used in a 918 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 919 string context before encoding as JSON strings, and anything else as
690 number value: 920 number value:
691 921
692 # dump as number 922 # dump as number
693 encode_json [2] # yields [2] 923 encode_json [2] # yields [2]
694 encode_json [-3.0e17] # yields [-3e+17] 924 encode_json [-3.0e17] # yields [-3e+17]
… …
713 my $x = "3"; # some variable containing a string 943 my $x = "3"; # some variable containing a string
714 $x += 0; # numify it, ensuring it will be dumped as a number 944 $x += 0; # numify it, ensuring it will be dumped as a number
715 $x *= 1; # same thing, the choice is yours. 945 $x *= 1; # same thing, the choice is yours.
716 946
717 You can not currently force the type in other, less obscure, ways. 947 You can not currently force the type in other, less obscure, ways.
718 Tell me if you need this capability. 948 Tell me if you need this capability (but don't forget to explain why
949 it's needed :).
719 950
720COMPARISON 951ENCODING/CODESET FLAG NOTES
721 As already mentioned, this module was created because none of the 952 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 953 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
723 describe the problems (or pleasures) I encountered with various existing 954 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.
726 955
727 JSON 1.07 956 "utf8" controls whether the JSON text created by "encode" (and expected
728 Slow (but very portable, as it is written in pure Perl). 957 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
958 control whether "encode" escapes character values outside their
959 respective codeset range. Neither of these flags conflict with each
960 other, although some combinations make less sense than others.
729 961
730 Undocumented/buggy Unicode handling (how JSON handles Unicode values 962 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 963 "encode" and "decode", that is, texts encoded with any combination of
732 doing en-/decoding oneself, but Unicode escapes are not working 964 these flag values will be correctly decoded when the same flags are used
965 - in general, if you use different flag settings while encoding vs. when
966 decoding you likely have a bug somewhere.
967
968 Below comes a verbose discussion of these flags. Note that a "codeset"
969 is simply an abstract set of character-codepoint pairs, while an
970 encoding takes those codepoint numbers and *encodes* them, in our case
971 into octets. Unicode is (among other things) a codeset, UTF-8 is an
972 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
973 encodings at the same time, which can be confusing.
974
975 "utf8" flag disabled
976 When "utf8" is disabled (the default), then "encode"/"decode"
977 generate and expect Unicode strings, that is, characters with high
978 ordinal Unicode values (> 255) will be encoded as such characters,
979 and likewise such characters are decoded as-is, no canges to them
980 will be done, except "(re-)interpreting" them as Unicode codepoints
981 or Unicode characters, respectively (to Perl, these are the same
982 thing in strings unless you do funny/weird/dumb stuff).
983
984 This is useful when you want to do the encoding yourself (e.g. when
985 you want to have UTF-16 encoded JSON texts) or when some other layer
986 does the encoding for you (for example, when printing to a terminal
987 using a filehandle that transparently encodes to UTF-8 you certainly
988 do NOT want to UTF-8 encode your data first and have Perl encode it
989 another time).
990
991 "utf8" flag enabled
992 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
993 characters using the corresponding UTF-8 multi-byte sequence, and
994 will expect your input strings to be encoded as UTF-8, that is, no
995 "character" of the input string must have any value > 255, as UTF-8
996 does not allow that.
997
998 The "utf8" flag therefore switches between two modes: disabled means
999 you will get a Unicode string in Perl, enabled means you get an
1000 UTF-8 encoded octet/binary string in Perl.
1001
1002 "latin1" or "ascii" flags enabled
1003 With "latin1" (or "ascii") enabled, "encode" will escape characters
1004 with ordinal values > 255 (> 127 with "ascii") and encode the
1005 remaining characters as specified by the "utf8" flag.
1006
1007 If "utf8" is disabled, then the result is also correctly encoded in
1008 those character sets (as both are proper subsets of Unicode, meaning
1009 that a Unicode string with all character values < 256 is the same
1010 thing as a ISO-8859-1 string, and a Unicode string with all
1011 character values < 128 is the same thing as an ASCII string in
733 properly). 1012 Perl).
734 1013
735 No round-tripping (strings get clobbered if they look like numbers, 1014 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 1015 regardless of these flags, just some more characters will be escaped
737 will decode into the number 2. 1016 using "\uXXXX" then before.
738 1017
739 JSON::PC 0.01 1018 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
740 Very fast. 1019 encoding, while ASCII-encoded strings are. That is because the
1020 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1021 *codeset* being a subset of Unicode), while ASCII is.
741 1022
742 Undocumented/buggy Unicode handling. 1023 Surprisingly, "decode" will ignore these flags and so treat all
1024 input values as governed by the "utf8" flag. If it is disabled, this
1025 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1026 strict subsets of Unicode. If it is enabled, you can correctly
1027 decode UTF-8 encoded strings.
743 1028
744 No round-tripping. 1029 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1030 flag - they only govern when the JSON output engine escapes a
1031 character or not.
745 1032
746 Has problems handling many Perl values (e.g. regex results and other 1033 The main use for "latin1" is to relatively efficiently store binary
747 magic values will make it croak). 1034 data as JSON, at the expense of breaking compatibility with most
1035 JSON decoders.
748 1036
749 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1037 The main use for "ascii" is to force the output to not contain
750 which is not a valid JSON text. 1038 characters with values > 127, which means you can interpret the
751 1039 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
752 Unmaintained (maintainer unresponsive for many months, bugs are not 1040 any character set and 8-bit-encoding, and still get the same data
753 getting fixed). 1041 structure back. This is useful when your channel for JSON transfer
754 1042 is not 8-bit clean or the encoding might be mangled in between (e.g.
755 JSON::Syck 0.21 1043 in mail), and works because ASCII is a proper subset of most 8-bit
756 Very buggy (often crashes). 1044 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 1045
799 JSON and YAML 1046 JSON and YAML
800 You often hear that JSON is a subset (or a close subset) of YAML. This 1047 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, 1048 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 1049 writing), so let me state it clearly: *in general, there is no way to
803 valid YAML. 1050 configure JSON::XS to output a data structure as valid YAML* that works
1051 in all cases.
804 1052
805 If you really must use JSON::XS to generate YAML, you should use this 1053 If you really must use JSON::XS to generate YAML, you should use this
806 algorithm (subject to change in future versions): 1054 algorithm (subject to change in future versions):
807 1055
808 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1056 my $to_yaml = JSON::XS->new->utf8->space_after (1);
809 my $yaml = $to_yaml->encode ($ref) . "\n"; 1057 my $yaml = $to_yaml->encode ($ref) . "\n";
810 1058
811 This will usually generate JSON texts that also parse as valid YAML. 1059 This will *usually* generate JSON texts that also parse as valid YAML.
812 Please note that YAML has hardcoded limits on (simple) object key 1060 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 1061 lengths that JSON doesn't have and also has different and incompatible
1062 unicode handling, so you should make sure that your hash keys are
814 keys are noticeably shorter than the 1024 characters YAML allows. 1063 noticeably shorter than the 1024 "stream characters" YAML allows and
1064 that you do not have characters with codepoint values outside the
1065 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1066 sequences in strings (which JSON::XS does not *currently* generate, but
1067 other JSON generators might).
815 1068
816 There might be other incompatibilities that I am not aware of. In 1069 There might be other incompatibilities that I am not aware of (or the
1070 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 1071 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: 1072 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 1073 chances are high that you will run into severe interoperability problems
820 problems. 1074 when you least expect it.
1075
1076 (*) I have been pressured multiple times by Brian Ingerson (one of the
1077 authors of the YAML specification) to remove this paragraph, despite
1078 him acknowledging that the actual incompatibilities exist. As I was
1079 personally bitten by this "JSON is YAML" lie, I refused and said I
1080 will continue to educate people about these issues, so others do not
1081 run into the same problem again and again. After this, Brian called
1082 me a (quote)*complete and worthless idiot*(unquote).
1083
1084 In my opinion, instead of pressuring and insulting people who
1085 actually clarify issues with YAML and the wrong statements of some
1086 of its proponents, I would kindly suggest reading the JSON spec
1087 (which is not that difficult or long) and finally make YAML
1088 compatible to it, and educating users about the changes, instead of
1089 spreading lies about the real compatibility for many *years* and
1090 trying to silence people who point out that it isn't true.
821 1091
822 SPEED 1092 SPEED
823 It seems that JSON::XS is surprisingly fast, as shown in the following 1093 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 1094 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 1095 in the JSON::XS distribution, to make it easy to compare on your own
826 system. 1096 system.
827 1097
828 First comes a comparison between various modules using a very short 1098 First comes a comparison between various modules using a very short
829 single-line JSON string: 1099 single-line JSON string (also available at
1100 <http://dist.schmorp.de/misc/json/short.json>).
830 1101
831 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1102 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
832 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1103 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
833 1104
834 It shows the number of encodes/decodes per second (JSON::XS uses the 1105 It shows the number of encodes/decodes per second (JSON::XS uses the
… …
853 encoding, about three times faster on decoding, and over forty times 1124 encoding, about three times faster on decoding, and over forty times
854 faster than JSON, even with pretty-printing and key sorting. It also 1125 faster than JSON, even with pretty-printing and key sorting. It also
855 compares favourably to Storable for small amounts of data. 1126 compares favourably to Storable for small amounts of data.
856 1127
857 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1128 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
858 search API (http://nanoref.com/yahooapis/mgPdGg): 1129 search API (<http://dist.schmorp.de/misc/json/long.json>).
859 1130
860 module | encode | decode | 1131 module | encode | decode |
861 -----------|------------|------------| 1132 -----------|------------|------------|
862 JSON 1.x | 55.260 | 34.971 | 1133 JSON 1.x | 55.260 | 34.971 |
863 JSON::DWIW | 825.228 | 1082.513 | 1134 JSON::DWIW | 825.228 | 1082.513 |
… …
900 Third, JSON::XS recurses using the C stack when decoding objects and 1171 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 1172 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 1173 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 1174 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. 1175 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 1176 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 1177 process has a smaller stack, you should adjust this setting accordingly
907 with the "max_depth" method. 1178 with the "max_depth" method.
908 1179
909 And last but least, something else could bomb you that I forgot to think 1180 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 1181 case, you get to keep the pieces. I am always open for hints, though...
911 hints, though... 1182
1183 Also keep in mind that JSON::XS might leak contents of your Perl data
1184 structures in its error messages, so when you serialise sensitive
1185 information you might want to make sure that exceptions thrown by
1186 JSON::XS will not end up in front of untrusted eyes.
912 1187
913 If you are using JSON::XS to return packets to consumption by JavaScript 1188 If you are using JSON::XS to return packets to consumption by JavaScript
914 scripts in a browser you should have a look at 1189 scripts in a browser you should have a look at
915 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1190 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
916 you are vulnerable to some common attack vectors (which really are 1191 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, 1192 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 1193 as major browser developers care only for features, not about getting
919 security right). 1194 security right).
920 1195
921THREADS 1196THREADS
922 This module is *not* guaranteed to be thread safe and there are no plans 1197 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 1198 to change this until Perl gets thread support (as opposed to the
924 horribly slow so-called "threads" which are simply slow and bloated 1199 horribly slow so-called "threads" which are simply slow and bloated
925 process simulations - use fork, its *much* faster, cheaper, better). 1200 process simulations - use fork, it's *much* faster, cheaper, better).
926 1201
927 (It might actually work, but you have been warned). 1202 (It might actually work, but you have been warned).
928 1203
929BUGS 1204BUGS
930 While the goal of this module is to be correct, that unfortunately does 1205 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 1206 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 1207 still relatively early in its development. If you keep reporting bugs
933 they will be fixed swiftly, though. 1208 they will be fixed swiftly, though.
934 1209
935 Please refrain from using rt.cpan.org or any other bug reporting 1210 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. 1211 service. I put the contact address into my modules for a reason.
1212
1213SEE ALSO
1214 The json_xs command line utility for quick experiments.
937 1215
938AUTHOR 1216AUTHOR
939 Marc Lehmann <schmorp@schmorp.de> 1217 Marc Lehmann <schmorp@schmorp.de>
940 http://home.schmorp.de/ 1218 http://home.schmorp.de/
941 1219

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