… | |
… | |
20 | $perl_scalar = $coder->decode ($unicode_json_text); |
20 | $perl_scalar = $coder->decode ($unicode_json_text); |
21 | |
21 | |
22 | # Note that JSON version 2.0 and above will automatically use JSON::XS |
22 | # Note that JSON version 2.0 and above will automatically use JSON::XS |
23 | # if available, at virtually no speed overhead either, so you should |
23 | # if available, at virtually no speed overhead either, so you should |
24 | # be able to just: |
24 | # be able to just: |
25 | |
25 | |
26 | use JSON; |
26 | use JSON; |
27 | |
27 | |
28 | # and do the same things, except that you have a pure-perl fallback now. |
28 | # and do the same things, except that you have a pure-perl fallback now. |
29 | |
29 | |
30 | DESCRIPTION |
30 | DESCRIPTION |
31 | This module converts Perl data structures to JSON and vice versa. Its |
31 | This module converts Perl data structures to JSON and vice versa. Its |
32 | primary goal is to be *correct* and its secondary goal is to be *fast*. |
32 | primary goal is to be *correct* and its secondary goal is to be *fast*. |
33 | To reach the latter goal it was written in C. |
33 | To reach the latter goal it was written in C. |
34 | |
34 | |
35 | Beginning with version 2.0 of the JSON module, when both JSON and |
35 | Beginning with version 2.0 of the JSON module, when both JSON and |
36 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can |
36 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can |
37 | be overriden) with no overhead due to emulation (by inheritign |
37 | be overridden) with no overhead due to emulation (by inheriting |
38 | constructor and methods). If JSON::XS is not available, it will fall |
38 | constructor and methods). If JSON::XS is not available, it will fall |
39 | back to the compatible JSON::PP module as backend, so using JSON instead |
39 | back to the compatible JSON::PP module as backend, so using JSON instead |
40 | of JSON::XS gives you a portable JSON API that can be fast when you need |
40 | of JSON::XS gives you a portable JSON API that can be fast when you need |
41 | and doesn't require a C compiler when that is a problem. |
41 | and doesn't require a C compiler when that is a problem. |
42 | |
42 | |
… | |
… | |
44 | to write yet another JSON module? While it seems there are many JSON |
44 | to write yet another JSON module? While it seems there are many JSON |
45 | modules, none of them correctly handle all corner cases, and in most |
45 | modules, none of them correctly handle all corner cases, and in most |
46 | cases their maintainers are unresponsive, gone missing, or not listening |
46 | cases their maintainers are unresponsive, gone missing, or not listening |
47 | to bug reports for other reasons. |
47 | to bug reports for other reasons. |
48 | |
48 | |
49 | See COMPARISON, below, for a comparison to some other JSON modules. |
|
|
50 | |
|
|
51 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
49 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
52 | vice versa. |
50 | vice versa. |
53 | |
51 | |
54 | FEATURES |
52 | FEATURES |
55 | * correct Unicode handling |
53 | * correct Unicode handling |
… | |
… | |
57 | This module knows how to handle Unicode, documents how and when it |
55 | This module knows how to handle Unicode, documents how and when it |
58 | does so, and even documents what "correct" means. |
56 | does so, and even documents what "correct" means. |
59 | |
57 | |
60 | * round-trip integrity |
58 | * round-trip integrity |
61 | |
59 | |
62 | When you serialise a perl data structure using only datatypes |
60 | When you serialise a perl data structure using only data types |
63 | supported by JSON, the deserialised data structure is identical on |
61 | supported by JSON and Perl, the deserialised data structure is |
64 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" |
62 | identical on the Perl level. (e.g. the string "2.0" doesn't suddenly |
65 | just because it looks like a number). There minor *are* exceptions |
63 | become "2" just because it looks like a number). There *are* minor |
66 | to this, read the MAPPING section below to learn about those. |
64 | exceptions to this, read the MAPPING section below to learn about |
|
|
65 | those. |
67 | |
66 | |
68 | * strict checking of JSON correctness |
67 | * strict checking of JSON correctness |
69 | |
68 | |
70 | There is no guessing, no generating of illegal JSON texts by |
69 | There is no guessing, no generating of illegal JSON texts by |
71 | default, and only JSON is accepted as input by default (the latter |
70 | default, and only JSON is accepted as input by default (the latter |
… | |
… | |
78 | too. |
77 | too. |
79 | |
78 | |
80 | * simple to use |
79 | * simple to use |
81 | |
80 | |
82 | This module has both a simple functional interface as well as an |
81 | This module has both a simple functional interface as well as an |
83 | objetc oriented interface interface. |
82 | object oriented interface interface. |
84 | |
83 | |
85 | * reasonably versatile output formats |
84 | * reasonably versatile output formats |
86 | |
85 | |
87 | You can choose between the most compact guaranteed-single-line |
86 | You can choose between the most compact guaranteed-single-line |
88 | format possible (nice for simple line-based protocols), a pure-ascii |
87 | format possible (nice for simple line-based protocols), a pure-ASCII |
89 | format (for when your transport is not 8-bit clean, still supports |
88 | format (for when your transport is not 8-bit clean, still supports |
90 | the whole Unicode range), or a pretty-printed format (for when you |
89 | the whole Unicode range), or a pretty-printed format (for when you |
91 | want to read that stuff). Or you can combine those features in |
90 | want to read that stuff). Or you can combine those features in |
92 | whatever way you like. |
91 | whatever way you like. |
93 | |
92 | |
… | |
… | |
101 | |
100 | |
102 | This function call is functionally identical to: |
101 | This function call is functionally identical to: |
103 | |
102 | |
104 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
103 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
105 | |
104 | |
106 | except being faster. |
105 | Except being faster. |
107 | |
106 | |
108 | $perl_scalar = decode_json $json_text |
107 | $perl_scalar = decode_json $json_text |
109 | The opposite of "encode_json": expects an UTF-8 (binary) string and |
108 | The opposite of "encode_json": expects an UTF-8 (binary) string and |
110 | tries to parse that as an UTF-8 encoded JSON text, returning the |
109 | tries to parse that as an UTF-8 encoded JSON text, returning the |
111 | resulting reference. Croaks on error. |
110 | resulting reference. Croaks on error. |
112 | |
111 | |
113 | This function call is functionally identical to: |
112 | This function call is functionally identical to: |
114 | |
113 | |
115 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
114 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
116 | |
115 | |
117 | except being faster. |
116 | Except being faster. |
118 | |
117 | |
119 | $is_boolean = JSON::XS::is_bool $scalar |
118 | $is_boolean = JSON::XS::is_bool $scalar |
120 | Returns true if the passed scalar represents either JSON::XS::true |
119 | Returns true if the passed scalar represents either JSON::XS::true |
121 | or JSON::XS::false, two constants that act like 1 and 0, |
120 | or JSON::XS::false, two constants that act like 1 and 0, |
122 | respectively and are used to represent JSON "true" and "false" |
121 | respectively and are used to represent JSON "true" and "false" |
… | |
… | |
152 | |
151 | |
153 | If you didn't know about that flag, just the better, pretend it |
152 | If you didn't know about that flag, just the better, pretend it |
154 | doesn't exist. |
153 | doesn't exist. |
155 | |
154 | |
156 | 4. A "Unicode String" is simply a string where each character can be |
155 | 4. A "Unicode String" is simply a string where each character can be |
157 | validly interpreted as a Unicode codepoint. |
156 | validly interpreted as a Unicode code point. |
158 | If you have UTF-8 encoded data, it is no longer a Unicode string, |
157 | If you have UTF-8 encoded data, it is no longer a Unicode string, |
159 | but a Unicode string encoded in UTF-8, giving you a binary string. |
158 | but a Unicode string encoded in UTF-8, giving you a binary string. |
160 | |
159 | |
161 | 5. A string containing "high" (> 255) character values is *not* a UTF-8 |
160 | 5. A string containing "high" (> 255) character values is *not* a UTF-8 |
162 | string. |
161 | string. |
… | |
… | |
370 | output JSON objects by sorting their keys. This is adding a |
369 | output JSON objects by sorting their keys. This is adding a |
371 | comparatively high overhead. |
370 | comparatively high overhead. |
372 | |
371 | |
373 | If $enable is false, then the "encode" method will output key-value |
372 | If $enable is false, then the "encode" method will output key-value |
374 | pairs in the order Perl stores them (which will likely change |
373 | pairs in the order Perl stores them (which will likely change |
375 | between runs of the same script). |
374 | between runs of the same script, and can change even within the same |
|
|
375 | run from 5.18 onwards). |
376 | |
376 | |
377 | This option is useful if you want the same data structure to be |
377 | This option is useful if you want the same data structure to be |
378 | encoded as the same JSON text (given the same overall settings). If |
378 | encoded as the same JSON text (given the same overall settings). If |
379 | it is disabled, the same hash might be encoded differently even if |
379 | it is disabled, the same hash might be encoded differently even if |
380 | contains the same data, as key-value pairs have no inherent ordering |
380 | contains the same data, as key-value pairs have no inherent ordering |
381 | in Perl. |
381 | in Perl. |
382 | |
382 | |
383 | This setting has no effect when decoding JSON texts. |
383 | This setting has no effect when decoding JSON texts. |
|
|
384 | |
|
|
385 | This setting has currently no effect on tied hashes. |
384 | |
386 | |
385 | $json = $json->allow_nonref ([$enable]) |
387 | $json = $json->allow_nonref ([$enable]) |
386 | $enabled = $json->get_allow_nonref |
388 | $enabled = $json->get_allow_nonref |
387 | If $enable is true (or missing), then the "encode" method can |
389 | If $enable is true (or missing), then the "encode" method can |
388 | convert a non-reference into its corresponding string, number or |
390 | convert a non-reference into its corresponding string, number or |
… | |
… | |
623 | |
625 | |
624 | JSON::XS->new->decode_prefix ("[1] the tail") |
626 | JSON::XS->new->decode_prefix ("[1] the tail") |
625 | => ([], 3) |
627 | => ([], 3) |
626 | |
628 | |
627 | INCREMENTAL PARSING |
629 | INCREMENTAL 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. |
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 |
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 |
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 |
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 |
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 |
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 |
636 | much more efficient (and can be implemented with a minimum of method |
637 | once it is sure it has enough text to get a decisive result, using a |
637 | calls). |
638 | very simple but truly incremental parser). |
|
|
639 | |
638 | |
640 | The following two methods deal with this. |
639 | JSON::XS will only attempt to parse the JSON text once it is sure it has |
|
|
640 | enough text to get a decisive result, using a very simple but truly |
|
|
641 | incremental parser. This means that it sometimes won't stop as early as |
|
|
642 | the full parser, for example, it doesn't detect mismatched parentheses. |
|
|
643 | The only thing it guarantees is that it starts decoding as soon as a |
|
|
644 | syntactically valid JSON text has been seen. This means you need to set |
|
|
645 | resource limits (e.g. "max_size") to ensure the parser will stop parsing |
|
|
646 | in the presence if syntax errors. |
|
|
647 | |
|
|
648 | The following methods implement this incremental parser. |
641 | |
649 | |
642 | [void, scalar or list context] = $json->incr_parse ([$string]) |
650 | [void, scalar or list context] = $json->incr_parse ([$string]) |
643 | This is the central parsing function. It can both append new text |
651 | This is the central parsing function. It can both append new text |
644 | and extract objects from the stream accumulated so far (both of |
652 | and extract objects from the stream accumulated so far (both of |
645 | these functions are optional). |
653 | these functions are optional). |
… | |
… | |
663 | otherwise. For this to work, there must be no separators between the |
671 | otherwise. For this to work, there must be no separators between the |
664 | JSON objects or arrays, instead they must be concatenated |
672 | JSON objects or arrays, instead they must be concatenated |
665 | back-to-back. If an error occurs, an exception will be raised as in |
673 | 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 |
674 | the scalar context case. Note that in this case, any |
667 | previously-parsed JSON texts will be lost. |
675 | previously-parsed JSON texts will be lost. |
|
|
676 | |
|
|
677 | Example: Parse some JSON arrays/objects in a given string and return |
|
|
678 | them. |
|
|
679 | |
|
|
680 | my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]"); |
668 | |
681 | |
669 | $lvalue_string = $json->incr_text |
682 | $lvalue_string = $json->incr_text |
670 | This method returns the currently stored JSON fragment as an lvalue, |
683 | This method returns the currently stored JSON fragment as an lvalue, |
671 | that is, you can manipulate it. This *only* works when a preceding |
684 | that is, you can manipulate it. This *only* works when a preceding |
672 | call to "incr_parse" in *scalar context* successfully returned an |
685 | call to "incr_parse" in *scalar context* successfully returned an |
… | |
… | |
680 | after a JSON object or b) parsing multiple JSON objects separated by |
693 | after a JSON object or b) parsing multiple JSON objects separated by |
681 | non-JSON text (such as commas). |
694 | non-JSON text (such as commas). |
682 | |
695 | |
683 | $json->incr_skip |
696 | $json->incr_skip |
684 | This will reset the state of the incremental parser and will remove |
697 | This will reset the state of the incremental parser and will remove |
685 | the parsed text from the input buffer. This is useful after |
698 | the parsed text from the input buffer so far. This is useful after |
686 | "incr_parse" died, in which case the input buffer and incremental |
699 | "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 |
700 | parser state is left unchanged, to skip the text parsed so far and |
688 | to reset the parse state. |
701 | to reset the parse state. |
|
|
702 | |
|
|
703 | The difference to "incr_reset" is that only text until the parse |
|
|
704 | error occured is removed. |
|
|
705 | |
|
|
706 | $json->incr_reset |
|
|
707 | This completely resets the incremental parser, that is, after this |
|
|
708 | call, it will be as if the parser had never parsed anything. |
|
|
709 | |
|
|
710 | This is useful if you want to repeatedly parse JSON objects and want |
|
|
711 | to ignore any trailing data, which means you have to reset the |
|
|
712 | parser after each successful decode. |
689 | |
713 | |
690 | LIMITATIONS |
714 | LIMITATIONS |
691 | All options that affect decoding are supported, except "allow_nonref". |
715 | 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 |
716 | 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 |
717 | objects and arrays are self-delimited, i.e. you can concatenate them |
… | |
… | |
876 | Numbers containing a fractional or exponential part will always be |
900 | Numbers containing a fractional or exponential part will always be |
877 | represented as numeric (floating point) values, possibly at a loss |
901 | represented as numeric (floating point) values, possibly at a loss |
878 | of precision (in which case you might lose perfect roundtripping |
902 | of precision (in which case you might lose perfect roundtripping |
879 | ability, but the JSON number will still be re-encoded as a JSON |
903 | ability, but the JSON number will still be re-encoded as a JSON |
880 | number). |
904 | number). |
|
|
905 | |
|
|
906 | Note that precision is not accuracy - binary floating point values |
|
|
907 | cannot represent most decimal fractions exactly, and when converting |
|
|
908 | from and to floating point, JSON::XS only guarantees precision up to |
|
|
909 | but not including the leats significant bit. |
881 | |
910 | |
882 | true, false |
911 | true, false |
883 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
912 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
884 | respectively. They are overloaded to act almost exactly like the |
913 | respectively. They are overloaded to act almost exactly like the |
885 | numbers 1 and 0. You can check whether a scalar is a JSON boolean by |
914 | numbers 1 and 0. You can check whether a scalar is a JSON boolean by |
… | |
… | |
913 | an exception to be thrown, except for references to the integers 0 |
942 | an exception to be thrown, except for references to the integers 0 |
914 | and 1, which get turned into "false" and "true" atoms in JSON. You |
943 | and 1, which get turned into "false" and "true" atoms in JSON. You |
915 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
944 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
916 | readability. |
945 | readability. |
917 | |
946 | |
918 | encode_json [\0,JSON::XS::true] # yields [false,true] |
947 | encode_json [\0, JSON::XS::true] # yields [false,true] |
919 | |
948 | |
920 | JSON::XS::true, JSON::XS::false |
949 | JSON::XS::true, JSON::XS::false |
921 | These special values become JSON true and JSON false values, |
950 | These special values become JSON true and JSON false values, |
922 | respectively. You can also use "\1" and "\0" directly if you want. |
951 | respectively. You can also use "\1" and "\0" directly if you want. |
923 | |
952 | |
… | |
… | |
961 | $x *= 1; # same thing, the choice is yours. |
990 | $x *= 1; # same thing, the choice is yours. |
962 | |
991 | |
963 | You can not currently force the type in other, less obscure, ways. |
992 | You can not currently force the type in other, less obscure, ways. |
964 | Tell me if you need this capability (but don't forget to explain why |
993 | Tell me if you need this capability (but don't forget to explain why |
965 | it's needed :). |
994 | it's needed :). |
|
|
995 | |
|
|
996 | Note that numerical precision has the same meaning as under Perl (so |
|
|
997 | binary to decimal conversion follows the same rules as in Perl, |
|
|
998 | which can differ to other languages). Also, your perl interpreter |
|
|
999 | might expose extensions to the floating point numbers of your |
|
|
1000 | platform, such as infinities or NaN's - these cannot be represented |
|
|
1001 | in JSON, and it is an error to pass those in. |
966 | |
1002 | |
967 | ENCODING/CODESET FLAG NOTES |
1003 | ENCODING/CODESET FLAG NOTES |
968 | The interested reader might have seen a number of flags that signify |
1004 | The interested reader might have seen a number of flags that signify |
969 | encodings or codesets - "utf8", "latin1" and "ascii". There seems to be |
1005 | encodings or codesets - "utf8", "latin1" and "ascii". There seems to be |
970 | some confusion on what these do, so here is a short comparison: |
1006 | some confusion on what these do, so here is a short comparison: |
… | |
… | |
1057 | structure back. This is useful when your channel for JSON transfer |
1093 | structure back. This is useful when your channel for JSON transfer |
1058 | is not 8-bit clean or the encoding might be mangled in between (e.g. |
1094 | is not 8-bit clean or the encoding might be mangled in between (e.g. |
1059 | in mail), and works because ASCII is a proper subset of most 8-bit |
1095 | in mail), and works because ASCII is a proper subset of most 8-bit |
1060 | and multibyte encodings in use in the world. |
1096 | and multibyte encodings in use in the world. |
1061 | |
1097 | |
|
|
1098 | JSON and ECMAscript |
|
|
1099 | JSON syntax is based on how literals are represented in javascript (the |
|
|
1100 | not-standardised predecessor of ECMAscript) which is presumably why it |
|
|
1101 | is called "JavaScript Object Notation". |
|
|
1102 | |
|
|
1103 | However, JSON is not a subset (and also not a superset of course) of |
|
|
1104 | ECMAscript (the standard) or javascript (whatever browsers actually |
|
|
1105 | implement). |
|
|
1106 | |
|
|
1107 | If you want to use javascript's "eval" function to "parse" JSON, you |
|
|
1108 | might run into parse errors for valid JSON texts, or the resulting data |
|
|
1109 | structure might not be queryable: |
|
|
1110 | |
|
|
1111 | One of the problems is that U+2028 and U+2029 are valid characters |
|
|
1112 | inside JSON strings, but are not allowed in ECMAscript string literals, |
|
|
1113 | so the following Perl fragment will not output something that can be |
|
|
1114 | guaranteed to be parsable by javascript's "eval": |
|
|
1115 | |
|
|
1116 | use JSON::XS; |
|
|
1117 | |
|
|
1118 | print encode_json [chr 0x2028]; |
|
|
1119 | |
|
|
1120 | The right fix for this is to use a proper JSON parser in your javascript |
|
|
1121 | programs, and not rely on "eval" (see for example Douglas Crockford's |
|
|
1122 | json2.js parser). |
|
|
1123 | |
|
|
1124 | If this is not an option, you can, as a stop-gap measure, simply encode |
|
|
1125 | to ASCII-only JSON: |
|
|
1126 | |
|
|
1127 | use JSON::XS; |
|
|
1128 | |
|
|
1129 | print JSON::XS->new->ascii->encode ([chr 0x2028]); |
|
|
1130 | |
|
|
1131 | Note that this will enlarge the resulting JSON text quite a bit if you |
|
|
1132 | have many non-ASCII characters. You might be tempted to run some regexes |
|
|
1133 | to only escape U+2028 and U+2029, e.g.: |
|
|
1134 | |
|
|
1135 | # DO NOT USE THIS! |
|
|
1136 | my $json = JSON::XS->new->utf8->encode ([chr 0x2028]); |
|
|
1137 | $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028 |
|
|
1138 | $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029 |
|
|
1139 | print $json; |
|
|
1140 | |
|
|
1141 | Note that *this is a bad idea*: the above only works for U+2028 and |
|
|
1142 | U+2029 and thus only for fully ECMAscript-compliant parsers. Many |
|
|
1143 | existing javascript implementations, however, have issues with other |
|
|
1144 | characters as well - using "eval" naively simply *will* cause problems. |
|
|
1145 | |
|
|
1146 | Another problem is that some javascript implementations reserve some |
|
|
1147 | property names for their own purposes (which probably makes them |
|
|
1148 | non-ECMAscript-compliant). For example, Iceweasel reserves the |
|
|
1149 | "__proto__" property name for its own purposes. |
|
|
1150 | |
|
|
1151 | If that is a problem, you could parse try to filter the resulting JSON |
|
|
1152 | output for these property strings, e.g.: |
|
|
1153 | |
|
|
1154 | $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; |
|
|
1155 | |
|
|
1156 | This works because "__proto__" is not valid outside of strings, so every |
|
|
1157 | occurence of ""__proto__"\s*:" must be a string used as property name. |
|
|
1158 | |
|
|
1159 | If you know of other incompatibilities, please let me know. |
|
|
1160 | |
1062 | JSON and YAML |
1161 | JSON and YAML |
1063 | You often hear that JSON is a subset of YAML. This is, however, a mass |
1162 | You often hear that JSON is a subset of YAML. This is, however, a mass |
1064 | hysteria(*) and very far from the truth (as of the time of this |
1163 | hysteria(*) and very far from the truth (as of the time of this |
1065 | writing), so let me state it clearly: *in general, there is no way to |
1164 | writing), so let me state it clearly: *in general, there is no way to |
1066 | configure JSON::XS to output a data structure as valid YAML* that works |
1165 | configure JSON::XS to output a data structure as valid YAML* that works |
… | |
… | |
1073 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
1172 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
1074 | |
1173 | |
1075 | This will *usually* generate JSON texts that also parse as valid YAML. |
1174 | This will *usually* generate JSON texts that also parse as valid YAML. |
1076 | Please note that YAML has hardcoded limits on (simple) object key |
1175 | Please note that YAML has hardcoded limits on (simple) object key |
1077 | lengths that JSON doesn't have and also has different and incompatible |
1176 | 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 |
1177 | unicode character escape syntax, so you should make sure that your hash |
1079 | noticeably shorter than the 1024 "stream characters" YAML allows and |
1178 | keys are noticeably shorter than the 1024 "stream characters" YAML |
1080 | that you do not have characters with codepoint values outside the |
1179 | allows and that you do not have characters with codepoint values outside |
1081 | Unicode BMP (basic multilingual page). YAML also does not allow "\/" |
1180 | the Unicode BMP (basic multilingual page). YAML also does not allow "\/" |
1082 | sequences in strings (which JSON::XS does not *currently* generate, but |
1181 | sequences in strings (which JSON::XS does not *currently* generate, but |
1083 | other JSON generators might). |
1182 | other JSON generators might). |
1084 | |
1183 | |
1085 | There might be other incompatibilities that I am not aware of (or the |
1184 | 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). |
1185 | YAML specification has been changed yet again - it does so quite often). |
… | |
… | |
1103 | (which is not that difficult or long) and finally make YAML |
1202 | (which is not that difficult or long) and finally make YAML |
1104 | compatible to it, and educating users about the changes, instead of |
1203 | compatible to it, and educating users about the changes, instead of |
1105 | spreading lies about the real compatibility for many *years* and |
1204 | spreading lies about the real compatibility for many *years* and |
1106 | trying to silence people who point out that it isn't true. |
1205 | trying to silence people who point out that it isn't true. |
1107 | |
1206 | |
|
|
1207 | Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, |
|
|
1208 | even though the incompatibilities have been documented (and are |
|
|
1209 | known to Brian) for many years and the spec makes explicit claims |
|
|
1210 | that YAML is a superset of JSON. It would be so easy to fix, but |
|
|
1211 | apparently, bullying people and corrupting userdata is so much |
|
|
1212 | easier. |
|
|
1213 | |
1108 | SPEED |
1214 | SPEED |
1109 | It seems that JSON::XS is surprisingly fast, as shown in the following |
1215 | It seems that JSON::XS is surprisingly fast, as shown in the following |
1110 | tables. They have been generated with the help of the "eg/bench" program |
1216 | tables. They have been generated with the help of the "eg/bench" program |
1111 | in the JSON::XS distribution, to make it easy to compare on your own |
1217 | in the JSON::XS distribution, to make it easy to compare on your own |
1112 | system. |
1218 | system. |
… | |
… | |
1115 | single-line JSON string (also available at |
1221 | single-line JSON string (also available at |
1116 | <http://dist.schmorp.de/misc/json/short.json>). |
1222 | <http://dist.schmorp.de/misc/json/short.json>). |
1117 | |
1223 | |
1118 | {"method": "handleMessage", "params": ["user1", |
1224 | {"method": "handleMessage", "params": ["user1", |
1119 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
1225 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
1120 | true, false]} |
1226 | 1, 0]} |
1121 | |
1227 | |
1122 | It shows the number of encodes/decodes per second (JSON::XS uses the |
1228 | It shows the number of encodes/decodes per second (JSON::XS uses the |
1123 | functional interface, while JSON::XS/2 uses the OO interface with |
1229 | functional interface, while JSON::XS/2 uses the OO interface with |
1124 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
1230 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink. |
1125 | Higher is better: |
1231 | JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses |
|
|
1232 | the from_json method). Higher is better: |
1126 | |
1233 | |
1127 | module | encode | decode | |
1234 | module | encode | decode | |
1128 | -----------|------------|------------| |
1235 | --------------|------------|------------| |
1129 | JSON 1.x | 4990.842 | 4088.813 | |
1236 | JSON::DWIW/DS | 86302.551 | 102300.098 | |
1130 | JSON::DWIW | 51653.990 | 71575.154 | |
1237 | JSON::DWIW/FJ | 86302.551 | 75983.768 | |
1131 | JSON::PC | 65948.176 | 74631.744 | |
1238 | JSON::PP | 15827.562 | 6638.658 | |
1132 | JSON::PP | 8931.652 | 3817.168 | |
1239 | JSON::Syck | 63358.066 | 47662.545 | |
1133 | JSON::Syck | 24877.248 | 27776.848 | |
1240 | JSON::XS | 511500.488 | 511500.488 | |
1134 | JSON::XS | 388361.481 | 227951.304 | |
1241 | JSON::XS/2 | 291271.111 | 388361.481 | |
1135 | JSON::XS/2 | 227951.304 | 218453.333 | |
1242 | JSON::XS/3 | 361577.931 | 361577.931 | |
1136 | JSON::XS/3 | 338250.323 | 218453.333 | |
1243 | Storable | 66788.280 | 265462.278 | |
1137 | Storable | 16500.016 | 135300.129 | |
|
|
1138 | -----------+------------+------------+ |
1244 | --------------+------------+------------+ |
1139 | |
1245 | |
1140 | That is, JSON::XS is about five times faster than JSON::DWIW on |
1246 | That is, JSON::XS is almost six times faster than JSON::DWIW on |
1141 | encoding, about three times faster on decoding, and over forty times |
1247 | encoding, about five times faster on decoding, and over thirty to |
1142 | faster than JSON, even with pretty-printing and key sorting. It also |
1248 | seventy times faster than JSON's pure perl implementation. It also |
1143 | compares favourably to Storable for small amounts of data. |
1249 | compares favourably to Storable for small amounts of data. |
1144 | |
1250 | |
1145 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1251 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1146 | search API (<http://dist.schmorp.de/misc/json/long.json>). |
1252 | search API (<http://dist.schmorp.de/misc/json/long.json>). |
1147 | |
1253 | |
1148 | module | encode | decode | |
1254 | module | encode | decode | |
1149 | -----------|------------|------------| |
1255 | --------------|------------|------------| |
1150 | JSON 1.x | 55.260 | 34.971 | |
1256 | JSON::DWIW/DS | 1647.927 | 2673.916 | |
1151 | JSON::DWIW | 825.228 | 1082.513 | |
1257 | JSON::DWIW/FJ | 1630.249 | 2596.128 | |
1152 | JSON::PC | 3571.444 | 2394.829 | |
|
|
1153 | JSON::PP | 210.987 | 32.574 | |
1258 | JSON::PP | 400.640 | 62.311 | |
1154 | JSON::Syck | 552.551 | 787.544 | |
1259 | JSON::Syck | 1481.040 | 1524.869 | |
1155 | JSON::XS | 5780.463 | 4854.519 | |
1260 | JSON::XS | 20661.596 | 9541.183 | |
1156 | JSON::XS/2 | 3869.998 | 4798.975 | |
1261 | JSON::XS/2 | 10683.403 | 9416.938 | |
1157 | JSON::XS/3 | 5862.880 | 4798.975 | |
1262 | JSON::XS/3 | 20661.596 | 9400.054 | |
1158 | Storable | 4445.002 | 5235.027 | |
1263 | Storable | 19765.806 | 10000.725 | |
1159 | -----------+------------+------------+ |
1264 | --------------+------------+------------+ |
1160 | |
1265 | |
1161 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
1266 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
1162 | decodes faster). |
1267 | decodes a bit faster). |
1163 | |
1268 | |
1164 | On large strings containing lots of high Unicode characters, some |
1269 | On large strings containing lots of high Unicode characters, some |
1165 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
1270 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
1166 | result will be broken due to missing (or wrong) Unicode handling. Others |
1271 | result will be broken due to missing (or wrong) Unicode handling. Others |
1167 | refuse to decode or encode properly, so it was impossible to prepare a |
1272 | refuse to decode or encode properly, so it was impossible to prepare a |
… | |
… | |
1202 | information you might want to make sure that exceptions thrown by |
1307 | information you might want to make sure that exceptions thrown by |
1203 | JSON::XS will not end up in front of untrusted eyes. |
1308 | JSON::XS will not end up in front of untrusted eyes. |
1204 | |
1309 | |
1205 | If you are using JSON::XS to return packets to consumption by JavaScript |
1310 | If you are using JSON::XS to return packets to consumption by JavaScript |
1206 | scripts in a browser you should have a look at |
1311 | scripts in a browser you should have a look at |
1207 | <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
1312 | <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> |
1208 | you are vulnerable to some common attack vectors (which really are |
1313 | to see whether you are vulnerable to some common attack vectors (which |
1209 | browser design bugs, but it is still you who will have to deal with it, |
1314 | really are browser design bugs, but it is still you who will have to |
1210 | as major browser developers care only for features, not about getting |
1315 | deal with it, as major browser developers care only for features, not |
1211 | security right). |
1316 | about getting security right). |
1212 | |
1317 | |
1213 | THREADS |
1318 | THREADS |
1214 | This module is *not* guaranteed to be thread safe and there are no plans |
1319 | This module is *not* guaranteed to be thread safe and there are no plans |
1215 | to change this until Perl gets thread support (as opposed to the |
1320 | to change this until Perl gets thread support (as opposed to the |
1216 | horribly slow so-called "threads" which are simply slow and bloated |
1321 | horribly slow so-called "threads" which are simply slow and bloated |
1217 | process simulations - use fork, it's *much* faster, cheaper, better). |
1322 | process simulations - use fork, it's *much* faster, cheaper, better). |
1218 | |
1323 | |
1219 | (It might actually work, but you have been warned). |
1324 | (It might actually work, but you have been warned). |
1220 | |
1325 | |
|
|
1326 | THE PERILS OF SETLOCALE |
|
|
1327 | Sometimes people avoid the Perl locale support and directly call the |
|
|
1328 | system's setlocale function with "LC_ALL". |
|
|
1329 | |
|
|
1330 | This breaks both perl and modules such as JSON::XS, as stringification |
|
|
1331 | of numbers no longer works correcly (e.g. "$x = 0.1; print "$x"+1" might |
|
|
1332 | print 1, and JSON::XS might output illegal JSON as JSON::XS relies on |
|
|
1333 | perl to stringify numbers). |
|
|
1334 | |
|
|
1335 | The solution is simple: don't call "setlocale", or use it for only those |
|
|
1336 | categories you need, such as "LC_MESSAGES" or "LC_CTYPE". |
|
|
1337 | |
|
|
1338 | If you need "LC_NUMERIC", you should enable it only around the code that |
|
|
1339 | actually needs it (avoiding stringification of numbers), and restore it |
|
|
1340 | afterwards. |
|
|
1341 | |
1221 | BUGS |
1342 | BUGS |
1222 | While the goal of this module is to be correct, that unfortunately does |
1343 | While the goal of this module is to be correct, that unfortunately does |
1223 | not mean it's bug-free, only that I think its design is bug-free. It is |
1344 | not mean it's bug-free, only that I think its design is bug-free. If you |
1224 | still relatively early in its development. If you keep reporting bugs |
|
|
1225 | they will be fixed swiftly, though. |
1345 | keep reporting bugs they will be fixed swiftly, though. |
1226 | |
1346 | |
1227 | Please refrain from using rt.cpan.org or any other bug reporting |
1347 | Please refrain from using rt.cpan.org or any other bug reporting |
1228 | service. I put the contact address into my modules for a reason. |
1348 | service. I put the contact address into my modules for a reason. |
1229 | |
1349 | |
1230 | SEE ALSO |
1350 | SEE ALSO |