… | |
… | |
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, the deserialised data structure is identical on |
64 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" |
62 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" |
65 | just because it looks like a number). There minor *are* exceptions |
63 | just because it looks like a number). There minor *are* exceptions |
66 | to this, read the MAPPING section below to learn about those. |
64 | to this, read the MAPPING section below to learn about those. |
67 | |
65 | |
… | |
… | |
78 | too. |
76 | too. |
79 | |
77 | |
80 | * simple to use |
78 | * simple to use |
81 | |
79 | |
82 | This module has both a simple functional interface as well as an |
80 | This module has both a simple functional interface as well as an |
83 | objetc oriented interface interface. |
81 | object oriented interface interface. |
84 | |
82 | |
85 | * reasonably versatile output formats |
83 | * reasonably versatile output formats |
86 | |
84 | |
87 | You can choose between the most compact guaranteed-single-line |
85 | You can choose between the most compact guaranteed-single-line |
88 | format possible (nice for simple line-based protocols), a pure-ascii |
86 | format possible (nice for simple line-based protocols), a pure-ASCII |
89 | format (for when your transport is not 8-bit clean, still supports |
87 | format (for when your transport is not 8-bit clean, still supports |
90 | the whole Unicode range), or a pretty-printed format (for when you |
88 | the whole Unicode range), or a pretty-printed format (for when you |
91 | want to read that stuff). Or you can combine those features in |
89 | want to read that stuff). Or you can combine those features in |
92 | whatever way you like. |
90 | whatever way you like. |
93 | |
91 | |
… | |
… | |
101 | |
99 | |
102 | This function call is functionally identical to: |
100 | This function call is functionally identical to: |
103 | |
101 | |
104 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
102 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
105 | |
103 | |
106 | except being faster. |
104 | Except being faster. |
107 | |
105 | |
108 | $perl_scalar = decode_json $json_text |
106 | $perl_scalar = decode_json $json_text |
109 | The opposite of "encode_json": expects an UTF-8 (binary) string and |
107 | The opposite of "encode_json": expects an UTF-8 (binary) string and |
110 | tries to parse that as an UTF-8 encoded JSON text, returning the |
108 | tries to parse that as an UTF-8 encoded JSON text, returning the |
111 | resulting reference. Croaks on error. |
109 | resulting reference. Croaks on error. |
112 | |
110 | |
113 | This function call is functionally identical to: |
111 | This function call is functionally identical to: |
114 | |
112 | |
115 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
113 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
116 | |
114 | |
117 | except being faster. |
115 | Except being faster. |
118 | |
116 | |
119 | $is_boolean = JSON::XS::is_bool $scalar |
117 | $is_boolean = JSON::XS::is_bool $scalar |
120 | Returns true if the passed scalar represents either JSON::XS::true |
118 | Returns true if the passed scalar represents either JSON::XS::true |
121 | or JSON::XS::false, two constants that act like 1 and 0, |
119 | or JSON::XS::false, two constants that act like 1 and 0, |
122 | respectively and are used to represent JSON "true" and "false" |
120 | respectively and are used to represent JSON "true" and "false" |
… | |
… | |
152 | |
150 | |
153 | If you didn't know about that flag, just the better, pretend it |
151 | If you didn't know about that flag, just the better, pretend it |
154 | doesn't exist. |
152 | doesn't exist. |
155 | |
153 | |
156 | 4. A "Unicode String" is simply a string where each character can be |
154 | 4. A "Unicode String" is simply a string where each character can be |
157 | validly interpreted as a Unicode codepoint. |
155 | validly interpreted as a Unicode code point. |
158 | If you have UTF-8 encoded data, it is no longer a Unicode string, |
156 | If you have UTF-8 encoded data, it is no longer a Unicode string, |
159 | but a Unicode string encoded in UTF-8, giving you a binary string. |
157 | but a Unicode string encoded in UTF-8, giving you a binary string. |
160 | |
158 | |
161 | 5. A string containing "high" (> 255) character values is *not* a UTF-8 |
159 | 5. A string containing "high" (> 255) character values is *not* a UTF-8 |
162 | string. |
160 | string. |
… | |
… | |
380 | contains the same data, as key-value pairs have no inherent ordering |
378 | contains the same data, as key-value pairs have no inherent ordering |
381 | in Perl. |
379 | in Perl. |
382 | |
380 | |
383 | This setting has no effect when decoding JSON texts. |
381 | This setting has no effect when decoding JSON texts. |
384 | |
382 | |
|
|
383 | This setting has currently no effect on tied hashes. |
|
|
384 | |
385 | $json = $json->allow_nonref ([$enable]) |
385 | $json = $json->allow_nonref ([$enable]) |
386 | $enabled = $json->get_allow_nonref |
386 | $enabled = $json->get_allow_nonref |
387 | If $enable is true (or missing), then the "encode" method can |
387 | If $enable is true (or missing), then the "encode" method can |
388 | convert a non-reference into its corresponding string, number or |
388 | convert a non-reference into its corresponding string, number or |
389 | null JSON value, which is an extension to RFC4627. Likewise, |
389 | null JSON value, which is an extension to RFC4627. Likewise, |
… | |
… | |
397 | Example, encode a Perl scalar as JSON value with enabled |
397 | Example, encode a Perl scalar as JSON value with enabled |
398 | "allow_nonref", resulting in an invalid JSON text: |
398 | "allow_nonref", resulting in an invalid JSON text: |
399 | |
399 | |
400 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
400 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
401 | => "Hello, World!" |
401 | => "Hello, World!" |
|
|
402 | |
|
|
403 | $json = $json->allow_unknown ([$enable]) |
|
|
404 | $enabled = $json->get_allow_unknown |
|
|
405 | If $enable is true (or missing), then "encode" will *not* throw an |
|
|
406 | exception when it encounters values it cannot represent in JSON (for |
|
|
407 | example, filehandles) but instead will encode a JSON "null" value. |
|
|
408 | Note that blessed objects are not included here and are handled |
|
|
409 | separately by c<allow_nonref>. |
|
|
410 | |
|
|
411 | If $enable is false (the default), then "encode" will throw an |
|
|
412 | exception when it encounters anything it cannot encode as JSON. |
|
|
413 | |
|
|
414 | This option does not affect "decode" in any way, and it is |
|
|
415 | recommended to leave it off unless you know your communications |
|
|
416 | partner. |
402 | |
417 | |
403 | $json = $json->allow_blessed ([$enable]) |
418 | $json = $json->allow_blessed ([$enable]) |
404 | $enabled = $json->get_allow_blessed |
419 | $enabled = $json->get_allow_blessed |
405 | If $enable is true (or missing), then the "encode" method will not |
420 | If $enable is true (or missing), then the "encode" method will not |
406 | barf when it encounters a blessed reference. Instead, the value of |
421 | barf when it encounters a blessed reference. Instead, the value of |
… | |
… | |
541 | saving space. |
556 | saving space. |
542 | |
557 | |
543 | $json = $json->max_depth ([$maximum_nesting_depth]) |
558 | $json = $json->max_depth ([$maximum_nesting_depth]) |
544 | $max_depth = $json->get_max_depth |
559 | $max_depth = $json->get_max_depth |
545 | Sets the maximum nesting level (default 512) accepted while encoding |
560 | Sets the maximum nesting level (default 512) accepted while encoding |
546 | or decoding. If the JSON text or Perl data structure has an equal or |
561 | or decoding. If a higher nesting level is detected in JSON text or a |
547 | higher nesting level then this limit, then the encoder and decoder |
562 | Perl data structure, then the encoder and decoder will stop and |
548 | will stop and croak at that point. |
563 | croak at that point. |
549 | |
564 | |
550 | Nesting level is defined by number of hash- or arrayrefs that the |
565 | Nesting level is defined by number of hash- or arrayrefs that the |
551 | encoder needs to traverse to reach a given point or the number of |
566 | encoder needs to traverse to reach a given point or the number of |
552 | "{" or "[" characters without their matching closing parenthesis |
567 | "{" or "[" characters without their matching closing parenthesis |
553 | crossed to reach a given character in a string. |
568 | crossed to reach a given character in a string. |
554 | |
569 | |
555 | Setting the maximum depth to one disallows any nesting, so that |
570 | Setting the maximum depth to one disallows any nesting, so that |
556 | ensures that the object is only a single hash/object or array. |
571 | ensures that the object is only a single hash/object or array. |
557 | |
572 | |
558 | The argument to "max_depth" will be rounded up to the next highest |
|
|
559 | power of two. If no argument is given, the highest possible setting |
573 | If no argument is given, the highest possible setting will be used, |
560 | will be used, which is rarely useful. |
574 | which is rarely useful. |
|
|
575 | |
|
|
576 | Note that nesting is implemented by recursion in C. The default |
|
|
577 | value has been chosen to be as large as typical operating systems |
|
|
578 | allow without crashing. |
561 | |
579 | |
562 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
580 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
563 | useful. |
581 | useful. |
564 | |
582 | |
565 | $json = $json->max_size ([$maximum_string_size]) |
583 | $json = $json->max_size ([$maximum_string_size]) |
566 | $max_size = $json->get_max_size |
584 | $max_size = $json->get_max_size |
567 | Set the maximum length a JSON text may have (in bytes) where |
585 | Set the maximum length a JSON text may have (in bytes) where |
568 | decoding is being attempted. The default is 0, meaning no limit. |
586 | decoding is being attempted. The default is 0, meaning no limit. |
569 | When "decode" is called on a string longer then this number of |
587 | When "decode" is called on a string that is longer then this many |
570 | characters it will not attempt to decode the string but throw an |
588 | bytes, it will not attempt to decode the string but throw an |
571 | exception. This setting has no effect on "encode" (yet). |
589 | exception. This setting has no effect on "encode" (yet). |
572 | |
590 | |
573 | The argument to "max_size" will be rounded up to the next highest |
|
|
574 | power of two (so may be more than requested). If no argument is |
|
|
575 | given, the limit check will be deactivated (same as when 0 is |
591 | If no argument is given, the limit check will be deactivated (same |
576 | specified). |
592 | as when 0 is specified). |
577 | |
593 | |
578 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
594 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
579 | useful. |
595 | useful. |
580 | |
596 | |
581 | $json_text = $json->encode ($perl_scalar) |
597 | $json_text = $json->encode ($perl_scalar) |
… | |
… | |
605 | protocol (which is not the brightest thing to do in the first place) |
621 | protocol (which is not the brightest thing to do in the first place) |
606 | and you need to know where the JSON text ends. |
622 | and you need to know where the JSON text ends. |
607 | |
623 | |
608 | JSON::XS->new->decode_prefix ("[1] the tail") |
624 | JSON::XS->new->decode_prefix ("[1] the tail") |
609 | => ([], 3) |
625 | => ([], 3) |
|
|
626 | |
|
|
627 | INCREMENTAL PARSING |
|
|
628 | In some cases, there is the need for incremental parsing of JSON texts. |
|
|
629 | While this module always has to keep both JSON text and resulting Perl |
|
|
630 | data structure in memory at one time, it does allow you to parse a JSON |
|
|
631 | stream incrementally. It does so by accumulating text until it has a |
|
|
632 | full JSON object, which it then can decode. This process is similar to |
|
|
633 | using "decode_prefix" to see if a full JSON object is available, but is |
|
|
634 | much more efficient (and can be implemented with a minimum of method |
|
|
635 | calls). |
|
|
636 | |
|
|
637 | JSON::XS will only attempt to parse the JSON text once it is sure it has |
|
|
638 | enough text to get a decisive result, using a very simple but truly |
|
|
639 | incremental parser. This means that it sometimes won't stop as early as |
|
|
640 | the full parser, for example, it doesn't detect parenthese mismatches. |
|
|
641 | The only thing it guarantees is that it starts decoding as soon as a |
|
|
642 | syntactically valid JSON text has been seen. This means you need to set |
|
|
643 | resource limits (e.g. "max_size") to ensure the parser will stop parsing |
|
|
644 | in the presence if syntax errors. |
|
|
645 | |
|
|
646 | The following methods implement this incremental parser. |
|
|
647 | |
|
|
648 | [void, scalar or list context] = $json->incr_parse ([$string]) |
|
|
649 | This is the central parsing function. It can both append new text |
|
|
650 | and extract objects from the stream accumulated so far (both of |
|
|
651 | these functions are optional). |
|
|
652 | |
|
|
653 | If $string is given, then this string is appended to the already |
|
|
654 | existing JSON fragment stored in the $json object. |
|
|
655 | |
|
|
656 | After that, if the function is called in void context, it will |
|
|
657 | simply return without doing anything further. This can be used to |
|
|
658 | add more text in as many chunks as you want. |
|
|
659 | |
|
|
660 | If the method is called in scalar context, then it will try to |
|
|
661 | extract exactly *one* JSON object. If that is successful, it will |
|
|
662 | return this object, otherwise it will return "undef". If there is a |
|
|
663 | parse error, this method will croak just as "decode" would do (one |
|
|
664 | can then use "incr_skip" to skip the errornous part). This is the |
|
|
665 | most common way of using the method. |
|
|
666 | |
|
|
667 | And finally, in list context, it will try to extract as many objects |
|
|
668 | from the stream as it can find and return them, or the empty list |
|
|
669 | otherwise. For this to work, there must be no separators between the |
|
|
670 | JSON objects or arrays, instead they must be concatenated |
|
|
671 | back-to-back. If an error occurs, an exception will be raised as in |
|
|
672 | the scalar context case. Note that in this case, any |
|
|
673 | previously-parsed JSON texts will be lost. |
|
|
674 | |
|
|
675 | $lvalue_string = $json->incr_text |
|
|
676 | This method returns the currently stored JSON fragment as an lvalue, |
|
|
677 | that is, you can manipulate it. This *only* works when a preceding |
|
|
678 | call to "incr_parse" in *scalar context* successfully returned an |
|
|
679 | object. Under all other circumstances you must not call this |
|
|
680 | function (I mean it. although in simple tests it might actually |
|
|
681 | work, it *will* fail under real world conditions). As a special |
|
|
682 | exception, you can also call this method before having parsed |
|
|
683 | anything. |
|
|
684 | |
|
|
685 | This function is useful in two cases: a) finding the trailing text |
|
|
686 | after a JSON object or b) parsing multiple JSON objects separated by |
|
|
687 | non-JSON text (such as commas). |
|
|
688 | |
|
|
689 | $json->incr_skip |
|
|
690 | This will reset the state of the incremental parser and will remove |
|
|
691 | the parsed text from the input buffer so far. This is useful after |
|
|
692 | "incr_parse" died, in which case the input buffer and incremental |
|
|
693 | parser state is left unchanged, to skip the text parsed so far and |
|
|
694 | to reset the parse state. |
|
|
695 | |
|
|
696 | The difference to "incr_reset" is that only text until the parse |
|
|
697 | error occured is removed. |
|
|
698 | |
|
|
699 | $json->incr_reset |
|
|
700 | This completely resets the incremental parser, that is, after this |
|
|
701 | call, it will be as if the parser had never parsed anything. |
|
|
702 | |
|
|
703 | This is useful if you want to repeatedly parse JSON objects and want |
|
|
704 | to ignore any trailing data, which means you have to reset the |
|
|
705 | parser after each successful decode. |
|
|
706 | |
|
|
707 | LIMITATIONS |
|
|
708 | All options that affect decoding are supported, except "allow_nonref". |
|
|
709 | The reason for this is that it cannot be made to work sensibly: JSON |
|
|
710 | objects and arrays are self-delimited, i.e. you can concatenate them |
|
|
711 | back to back and still decode them perfectly. This does not hold true |
|
|
712 | for JSON numbers, however. |
|
|
713 | |
|
|
714 | For example, is the string 1 a single JSON number, or is it simply the |
|
|
715 | start of 12? Or is 12 a single JSON number, or the concatenation of 1 |
|
|
716 | and 2? In neither case you can tell, and this is why JSON::XS takes the |
|
|
717 | conservative route and disallows this case. |
|
|
718 | |
|
|
719 | EXAMPLES |
|
|
720 | Some examples will make all this clearer. First, a simple example that |
|
|
721 | works similarly to "decode_prefix": We want to decode the JSON object at |
|
|
722 | the start of a string and identify the portion after the JSON object: |
|
|
723 | |
|
|
724 | my $text = "[1,2,3] hello"; |
|
|
725 | |
|
|
726 | my $json = new JSON::XS; |
|
|
727 | |
|
|
728 | my $obj = $json->incr_parse ($text) |
|
|
729 | or die "expected JSON object or array at beginning of string"; |
|
|
730 | |
|
|
731 | my $tail = $json->incr_text; |
|
|
732 | # $tail now contains " hello" |
|
|
733 | |
|
|
734 | Easy, isn't it? |
|
|
735 | |
|
|
736 | Now for a more complicated example: Imagine a hypothetical protocol |
|
|
737 | where you read some requests from a TCP stream, and each request is a |
|
|
738 | JSON array, without any separation between them (in fact, it is often |
|
|
739 | useful to use newlines as "separators", as these get interpreted as |
|
|
740 | whitespace at the start of the JSON text, which makes it possible to |
|
|
741 | test said protocol with "telnet"...). |
|
|
742 | |
|
|
743 | Here is how you'd do it (it is trivial to write this in an event-based |
|
|
744 | manner): |
|
|
745 | |
|
|
746 | my $json = new JSON::XS; |
|
|
747 | |
|
|
748 | # read some data from the socket |
|
|
749 | while (sysread $socket, my $buf, 4096) { |
|
|
750 | |
|
|
751 | # split and decode as many requests as possible |
|
|
752 | for my $request ($json->incr_parse ($buf)) { |
|
|
753 | # act on the $request |
|
|
754 | } |
|
|
755 | } |
|
|
756 | |
|
|
757 | Another complicated example: Assume you have a string with JSON objects |
|
|
758 | or arrays, all separated by (optional) comma characters (e.g. "[1],[2], |
|
|
759 | [3]"). To parse them, we have to skip the commas between the JSON texts, |
|
|
760 | and here is where the lvalue-ness of "incr_text" comes in useful: |
|
|
761 | |
|
|
762 | my $text = "[1],[2], [3]"; |
|
|
763 | my $json = new JSON::XS; |
|
|
764 | |
|
|
765 | # void context, so no parsing done |
|
|
766 | $json->incr_parse ($text); |
|
|
767 | |
|
|
768 | # now extract as many objects as possible. note the |
|
|
769 | # use of scalar context so incr_text can be called. |
|
|
770 | while (my $obj = $json->incr_parse) { |
|
|
771 | # do something with $obj |
|
|
772 | |
|
|
773 | # now skip the optional comma |
|
|
774 | $json->incr_text =~ s/^ \s* , //x; |
|
|
775 | } |
|
|
776 | |
|
|
777 | Now lets go for a very complex example: Assume that you have a gigantic |
|
|
778 | JSON array-of-objects, many gigabytes in size, and you want to parse it, |
|
|
779 | but you cannot load it into memory fully (this has actually happened in |
|
|
780 | the real world :). |
|
|
781 | |
|
|
782 | Well, you lost, you have to implement your own JSON parser. But JSON::XS |
|
|
783 | can still help you: You implement a (very simple) array parser and let |
|
|
784 | JSON decode the array elements, which are all full JSON objects on their |
|
|
785 | own (this wouldn't work if the array elements could be JSON numbers, for |
|
|
786 | example): |
|
|
787 | |
|
|
788 | my $json = new JSON::XS; |
|
|
789 | |
|
|
790 | # open the monster |
|
|
791 | open my $fh, "<bigfile.json" |
|
|
792 | or die "bigfile: $!"; |
|
|
793 | |
|
|
794 | # first parse the initial "[" |
|
|
795 | for (;;) { |
|
|
796 | sysread $fh, my $buf, 65536 |
|
|
797 | or die "read error: $!"; |
|
|
798 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
799 | |
|
|
800 | # Exit the loop once we found and removed(!) the initial "[". |
|
|
801 | # In essence, we are (ab-)using the $json object as a simple scalar |
|
|
802 | # we append data to. |
|
|
803 | last if $json->incr_text =~ s/^ \s* \[ //x; |
|
|
804 | } |
|
|
805 | |
|
|
806 | # now we have the skipped the initial "[", so continue |
|
|
807 | # parsing all the elements. |
|
|
808 | for (;;) { |
|
|
809 | # in this loop we read data until we got a single JSON object |
|
|
810 | for (;;) { |
|
|
811 | if (my $obj = $json->incr_parse) { |
|
|
812 | # do something with $obj |
|
|
813 | last; |
|
|
814 | } |
|
|
815 | |
|
|
816 | # add more data |
|
|
817 | sysread $fh, my $buf, 65536 |
|
|
818 | or die "read error: $!"; |
|
|
819 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
820 | } |
|
|
821 | |
|
|
822 | # in this loop we read data until we either found and parsed the |
|
|
823 | # separating "," between elements, or the final "]" |
|
|
824 | for (;;) { |
|
|
825 | # first skip whitespace |
|
|
826 | $json->incr_text =~ s/^\s*//; |
|
|
827 | |
|
|
828 | # if we find "]", we are done |
|
|
829 | if ($json->incr_text =~ s/^\]//) { |
|
|
830 | print "finished.\n"; |
|
|
831 | exit; |
|
|
832 | } |
|
|
833 | |
|
|
834 | # if we find ",", we can continue with the next element |
|
|
835 | if ($json->incr_text =~ s/^,//) { |
|
|
836 | last; |
|
|
837 | } |
|
|
838 | |
|
|
839 | # if we find anything else, we have a parse error! |
|
|
840 | if (length $json->incr_text) { |
|
|
841 | die "parse error near ", $json->incr_text; |
|
|
842 | } |
|
|
843 | |
|
|
844 | # else add more data |
|
|
845 | sysread $fh, my $buf, 65536 |
|
|
846 | or die "read error: $!"; |
|
|
847 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
848 | } |
|
|
849 | |
|
|
850 | This is a complex example, but most of the complexity comes from the |
|
|
851 | fact that we are trying to be correct (bear with me if I am wrong, I |
|
|
852 | never ran the above example :). |
610 | |
853 | |
611 | MAPPING |
854 | MAPPING |
612 | This section describes how JSON::XS maps Perl values to JSON values and |
855 | This section describes how JSON::XS maps Perl values to JSON values and |
613 | vice versa. These mappings are designed to "do the right thing" in most |
856 | vice versa. These mappings are designed to "do the right thing" in most |
614 | circumstances automatically, preserving round-tripping characteristics |
857 | circumstances automatically, preserving round-tripping characteristics |
… | |
… | |
687 | an exception to be thrown, except for references to the integers 0 |
930 | an exception to be thrown, except for references to the integers 0 |
688 | and 1, which get turned into "false" and "true" atoms in JSON. You |
931 | and 1, which get turned into "false" and "true" atoms in JSON. You |
689 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
932 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
690 | readability. |
933 | readability. |
691 | |
934 | |
692 | encode_json [\0,JSON::XS::true] # yields [false,true] |
935 | encode_json [\0, JSON::XS::true] # yields [false,true] |
693 | |
936 | |
694 | JSON::XS::true, JSON::XS::false |
937 | JSON::XS::true, JSON::XS::false |
695 | These special values become JSON true and JSON false values, |
938 | These special values become JSON true and JSON false values, |
696 | respectively. You can also use "\1" and "\0" directly if you want. |
939 | respectively. You can also use "\1" and "\0" directly if you want. |
697 | |
940 | |
… | |
… | |
734 | $x += 0; # numify it, ensuring it will be dumped as a number |
977 | $x += 0; # numify it, ensuring it will be dumped as a number |
735 | $x *= 1; # same thing, the choice is yours. |
978 | $x *= 1; # same thing, the choice is yours. |
736 | |
979 | |
737 | You can not currently force the type in other, less obscure, ways. |
980 | You can not currently force the type in other, less obscure, ways. |
738 | Tell me if you need this capability (but don't forget to explain why |
981 | Tell me if you need this capability (but don't forget to explain why |
739 | its needed :). |
982 | it's needed :). |
740 | |
983 | |
741 | ENCODING/CODESET FLAG NOTES |
984 | ENCODING/CODESET FLAG NOTES |
742 | The interested reader might have seen a number of flags that signify |
985 | The interested reader might have seen a number of flags that signify |
743 | encodings or codesets - "utf8", "latin1" and "ascii". There seems to be |
986 | encodings or codesets - "utf8", "latin1" and "ascii". There seems to be |
744 | some confusion on what these do, so here is a short comparison: |
987 | some confusion on what these do, so here is a short comparison: |
745 | |
988 | |
746 | "utf8" controls wether the JSON text created by "encode" (and expected |
989 | "utf8" controls whether the JSON text created by "encode" (and expected |
747 | by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only |
990 | by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only |
748 | control wether "encode" escapes character values outside their |
991 | control whether "encode" escapes character values outside their |
749 | respective codeset range. Neither of these flags conflict with each |
992 | respective codeset range. Neither of these flags conflict with each |
750 | other, although some combinations make less sense than others. |
993 | other, although some combinations make less sense than others. |
751 | |
994 | |
752 | Care has been taken to make all flags symmetrical with respect to |
995 | Care has been taken to make all flags symmetrical with respect to |
753 | "encode" and "decode", that is, texts encoded with any combination of |
996 | "encode" and "decode", that is, texts encoded with any combination of |
… | |
… | |
831 | structure back. This is useful when your channel for JSON transfer |
1074 | structure back. This is useful when your channel for JSON transfer |
832 | is not 8-bit clean or the encoding might be mangled in between (e.g. |
1075 | is not 8-bit clean or the encoding might be mangled in between (e.g. |
833 | in mail), and works because ASCII is a proper subset of most 8-bit |
1076 | in mail), and works because ASCII is a proper subset of most 8-bit |
834 | and multibyte encodings in use in the world. |
1077 | and multibyte encodings in use in the world. |
835 | |
1078 | |
836 | COMPARISON |
1079 | JSON and ECMAscript |
837 | As already mentioned, this module was created because none of the |
1080 | JSON syntax is based on how literals are represented in javascript (the |
838 | existing JSON modules could be made to work correctly. First I will |
1081 | not-standardised predecessor of ECMAscript) which is presumably why it |
839 | describe the problems (or pleasures) I encountered with various existing |
1082 | is called "JavaScript Object Notation". |
840 | JSON modules, followed by some benchmark values. JSON::XS was designed |
|
|
841 | not to suffer from any of these problems or limitations. |
|
|
842 | |
1083 | |
843 | JSON 2.xx |
1084 | However, JSON is not a subset (and also not a superset of course) of |
844 | A marvellous piece of engineering, this module either uses JSON::XS |
1085 | ECMAscript (the standard) or javascript (whatever browsers actually |
845 | directly when available (so will be 100% compatible with it, |
1086 | implement). |
846 | including speed), or it uses JSON::PP, which is basically JSON::XS |
|
|
847 | translated to Pure Perl, which should be 100% compatible with |
|
|
848 | JSON::XS, just a bit slower. |
|
|
849 | |
1087 | |
850 | You cannot really lose by using this module, especially as it tries |
1088 | If you want to use javascript's "eval" function to "parse" JSON, you |
851 | very hard to work even with ancient Perl versions, while JSON::XS |
1089 | might run into parse errors for valid JSON texts, or the resulting data |
852 | does not. |
1090 | structure might not be queryable: |
853 | |
1091 | |
854 | JSON 1.07 |
1092 | One of the problems is that U+2028 and U+2029 are valid characters |
855 | Slow (but very portable, as it is written in pure Perl). |
1093 | inside JSON strings, but are not allowed in ECMAscript string literals, |
|
|
1094 | so the following Perl fragment will not output something that can be |
|
|
1095 | guaranteed to be parsable by javascript's "eval": |
856 | |
1096 | |
857 | Undocumented/buggy Unicode handling (how JSON handles Unicode values |
1097 | use JSON::XS; |
858 | is undocumented. One can get far by feeding it Unicode strings and |
|
|
859 | doing en-/decoding oneself, but Unicode escapes are not working |
|
|
860 | properly). |
|
|
861 | |
1098 | |
862 | No round-tripping (strings get clobbered if they look like numbers, |
1099 | print encode_json [chr 0x2028]; |
863 | e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that |
|
|
864 | will decode into the number 2. |
|
|
865 | |
1100 | |
866 | JSON::PC 0.01 |
1101 | The right fix for this is to use a proper JSON parser in your javascript |
867 | Very fast. |
1102 | programs, and not rely on "eval" (see for example Douglas Crockford's |
|
|
1103 | json2.js parser). |
868 | |
1104 | |
869 | Undocumented/buggy Unicode handling. |
1105 | If this is not an option, you can, as a stop-gap measure, simply encode |
|
|
1106 | to ASCII-only JSON: |
870 | |
1107 | |
871 | No round-tripping. |
1108 | use JSON::XS; |
872 | |
1109 | |
873 | Has problems handling many Perl values (e.g. regex results and other |
1110 | print JSON::XS->new->ascii->encode ([chr 0x2028]); |
874 | magic values will make it croak). |
|
|
875 | |
1111 | |
876 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
1112 | Note that this will enlarge the resulting JSON text quite a bit if you |
877 | which is not a valid JSON text. |
1113 | have many non-ASCII characters. You might be tempted to run some regexes |
|
|
1114 | to only escape U+2028 and U+2029, e.g.: |
878 | |
1115 | |
879 | Unmaintained (maintainer unresponsive for many months, bugs are not |
1116 | # DO NOT USE THIS! |
880 | getting fixed). |
1117 | my $json = JSON::XS->new->utf8->encode ([chr 0x2028]); |
|
|
1118 | $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028 |
|
|
1119 | $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029 |
|
|
1120 | print $json; |
881 | |
1121 | |
882 | JSON::Syck 0.21 |
1122 | Note that *this is a bad idea*: the above only works for U+2028 and |
883 | Very buggy (often crashes). |
1123 | U+2029 and thus only for fully ECMAscript-compliant parsers. Many |
|
|
1124 | existing javascript implementations, however, have issues with other |
|
|
1125 | characters as well - using "eval" naively simply *will* cause problems. |
884 | |
1126 | |
885 | Very inflexible (no human-readable format supported, format pretty |
1127 | Another problem is that some javascript implementations reserve some |
886 | much undocumented. I need at least a format for easy reading by |
1128 | property names for their own purposes (which probably makes them |
887 | humans and a single-line compact format for use in a protocol, and |
1129 | non-ECMAscript-compliant). For example, Iceweasel reserves the |
888 | preferably a way to generate ASCII-only JSON texts). |
1130 | "__proto__" property name for it's own purposes. |
889 | |
1131 | |
890 | Completely broken (and confusingly documented) Unicode handling |
1132 | If that is a problem, you could parse try to filter the resulting JSON |
891 | (Unicode escapes are not working properly, you need to set |
1133 | output for these property strings, e.g.: |
892 | ImplicitUnicode to *different* values on en- and decoding to get |
|
|
893 | symmetric behaviour). |
|
|
894 | |
1134 | |
895 | No round-tripping (simple cases work, but this depends on whether |
1135 | $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; |
896 | the scalar value was used in a numeric context or not). |
|
|
897 | |
1136 | |
898 | Dumping hashes may skip hash values depending on iterator state. |
1137 | This works because "__proto__" is not valid outside of strings, so every |
|
|
1138 | occurence of ""__proto__"\s*:" must be a string used as property name. |
899 | |
1139 | |
900 | Unmaintained (maintainer unresponsive for many months, bugs are not |
1140 | If you know of other incompatibilities, please let me know. |
901 | getting fixed). |
|
|
902 | |
|
|
903 | Does not check input for validity (i.e. will accept non-JSON input |
|
|
904 | and return "something" instead of raising an exception. This is a |
|
|
905 | security issue: imagine two banks transferring money between each |
|
|
906 | other using JSON. One bank might parse a given non-JSON request and |
|
|
907 | deduct money, while the other might reject the transaction with a |
|
|
908 | syntax error. While a good protocol will at least recover, that is |
|
|
909 | extra unnecessary work and the transaction will still not succeed). |
|
|
910 | |
|
|
911 | JSON::DWIW 0.04 |
|
|
912 | Very fast. Very natural. Very nice. |
|
|
913 | |
|
|
914 | Undocumented Unicode handling (but the best of the pack. Unicode |
|
|
915 | escapes still don't get parsed properly). |
|
|
916 | |
|
|
917 | Very inflexible. |
|
|
918 | |
|
|
919 | No round-tripping. |
|
|
920 | |
|
|
921 | Does not generate valid JSON texts (key strings are often unquoted, |
|
|
922 | empty keys result in nothing being output) |
|
|
923 | |
|
|
924 | Does not check input for validity. |
|
|
925 | |
1141 | |
926 | JSON and YAML |
1142 | JSON and YAML |
927 | You often hear that JSON is a subset of YAML. This is, however, a mass |
1143 | You often hear that JSON is a subset of YAML. This is, however, a mass |
928 | hysteria(*) and very far from the truth (as of the time of this |
1144 | hysteria(*) and very far from the truth (as of the time of this |
929 | writing), so let me state it clearly: *in general, there is no way to |
1145 | writing), so let me state it clearly: *in general, there is no way to |
… | |
… | |
937 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
1153 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
938 | |
1154 | |
939 | This will *usually* generate JSON texts that also parse as valid YAML. |
1155 | This will *usually* generate JSON texts that also parse as valid YAML. |
940 | Please note that YAML has hardcoded limits on (simple) object key |
1156 | Please note that YAML has hardcoded limits on (simple) object key |
941 | lengths that JSON doesn't have and also has different and incompatible |
1157 | lengths that JSON doesn't have and also has different and incompatible |
942 | unicode handling, so you should make sure that your hash keys are |
1158 | unicode character escape syntax, so you should make sure that your hash |
943 | noticeably shorter than the 1024 "stream characters" YAML allows and |
1159 | keys are noticeably shorter than the 1024 "stream characters" YAML |
944 | that you do not have characters with codepoint values outside the |
1160 | allows and that you do not have characters with codepoint values outside |
945 | Unicode BMP (basic multilingual page). YAML also does not allow "\/" |
1161 | the Unicode BMP (basic multilingual page). YAML also does not allow "\/" |
946 | sequences in strings (which JSON::XS does not *currently* generate, but |
1162 | sequences in strings (which JSON::XS does not *currently* generate, but |
947 | other JSON generators might). |
1163 | other JSON generators might). |
948 | |
1164 | |
949 | There might be other incompatibilities that I am not aware of (or the |
1165 | There might be other incompatibilities that I am not aware of (or the |
950 | YAML specification has been changed yet again - it does so quite often). |
1166 | YAML specification has been changed yet again - it does so quite often). |
… | |
… | |
967 | (which is not that difficult or long) and finally make YAML |
1183 | (which is not that difficult or long) and finally make YAML |
968 | compatible to it, and educating users about the changes, instead of |
1184 | compatible to it, and educating users about the changes, instead of |
969 | spreading lies about the real compatibility for many *years* and |
1185 | spreading lies about the real compatibility for many *years* and |
970 | trying to silence people who point out that it isn't true. |
1186 | trying to silence people who point out that it isn't true. |
971 | |
1187 | |
|
|
1188 | Addendum/2009: the YAML 1.2 spec is still incomaptible with JSON, |
|
|
1189 | even though the incompatibilities have been documented (and are |
|
|
1190 | known to Brian) for many years and the spec makes explicit claims |
|
|
1191 | that YAML is a superset of JSON. It would be so easy to fix, but |
|
|
1192 | apparently, bullying and corrupting userdata is so much easier. |
|
|
1193 | |
972 | SPEED |
1194 | SPEED |
973 | It seems that JSON::XS is surprisingly fast, as shown in the following |
1195 | It seems that JSON::XS is surprisingly fast, as shown in the following |
974 | tables. They have been generated with the help of the "eg/bench" program |
1196 | tables. They have been generated with the help of the "eg/bench" program |
975 | in the JSON::XS distribution, to make it easy to compare on your own |
1197 | in the JSON::XS distribution, to make it easy to compare on your own |
976 | system. |
1198 | system. |
977 | |
1199 | |
978 | First comes a comparison between various modules using a very short |
1200 | First comes a comparison between various modules using a very short |
979 | single-line JSON string (also available at |
1201 | single-line JSON string (also available at |
980 | <http://dist.schmorp.de/misc/json/short.json>). |
1202 | <http://dist.schmorp.de/misc/json/short.json>). |
981 | |
1203 | |
982 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
1204 | {"method": "handleMessage", "params": ["user1", |
983 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
1205 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
|
|
1206 | true, false]} |
984 | |
1207 | |
985 | It shows the number of encodes/decodes per second (JSON::XS uses the |
1208 | It shows the number of encodes/decodes per second (JSON::XS uses the |
986 | functional interface, while JSON::XS/2 uses the OO interface with |
1209 | functional interface, while JSON::XS/2 uses the OO interface with |
987 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
1210 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
988 | Higher is better: |
1211 | Higher is better: |
… | |
… | |
1065 | information you might want to make sure that exceptions thrown by |
1288 | information you might want to make sure that exceptions thrown by |
1066 | JSON::XS will not end up in front of untrusted eyes. |
1289 | JSON::XS will not end up in front of untrusted eyes. |
1067 | |
1290 | |
1068 | If you are using JSON::XS to return packets to consumption by JavaScript |
1291 | If you are using JSON::XS to return packets to consumption by JavaScript |
1069 | scripts in a browser you should have a look at |
1292 | scripts in a browser you should have a look at |
1070 | <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
1293 | <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> |
1071 | you are vulnerable to some common attack vectors (which really are |
1294 | to see whether you are vulnerable to some common attack vectors (which |
1072 | browser design bugs, but it is still you who will have to deal with it, |
1295 | really are browser design bugs, but it is still you who will have to |
1073 | as major browser developers care only for features, not about getting |
1296 | deal with it, as major browser developers care only for features, not |
1074 | security right). |
1297 | about getting security right). |
1075 | |
1298 | |
1076 | THREADS |
1299 | THREADS |
1077 | This module is *not* guaranteed to be thread safe and there are no plans |
1300 | This module is *not* guaranteed to be thread safe and there are no plans |
1078 | to change this until Perl gets thread support (as opposed to the |
1301 | to change this until Perl gets thread support (as opposed to the |
1079 | horribly slow so-called "threads" which are simply slow and bloated |
1302 | horribly slow so-called "threads" which are simply slow and bloated |
1080 | process simulations - use fork, its *much* faster, cheaper, better). |
1303 | process simulations - use fork, it's *much* faster, cheaper, better). |
1081 | |
1304 | |
1082 | (It might actually work, but you have been warned). |
1305 | (It might actually work, but you have been warned). |
1083 | |
1306 | |
1084 | BUGS |
1307 | BUGS |
1085 | While the goal of this module is to be correct, that unfortunately does |
1308 | While the goal of this module is to be correct, that unfortunately does |
1086 | not mean its bug-free, only that I think its design is bug-free. It is |
1309 | not mean it's bug-free, only that I think its design is bug-free. If you |
1087 | still relatively early in its development. If you keep reporting bugs |
|
|
1088 | they will be fixed swiftly, though. |
1310 | keep reporting bugs they will be fixed swiftly, though. |
1089 | |
1311 | |
1090 | Please refrain from using rt.cpan.org or any other bug reporting |
1312 | Please refrain from using rt.cpan.org or any other bug reporting |
1091 | service. I put the contact address into my modules for a reason. |
1313 | service. I put the contact address into my modules for a reason. |
|
|
1314 | |
|
|
1315 | SEE ALSO |
|
|
1316 | The json_xs command line utility for quick experiments. |
1092 | |
1317 | |
1093 | AUTHOR |
1318 | AUTHOR |
1094 | Marc Lehmann <schmorp@schmorp.de> |
1319 | Marc Lehmann <schmorp@schmorp.de> |
1095 | http://home.schmorp.de/ |
1320 | http://home.schmorp.de/ |
1096 | |
1321 | |