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1 | =head1 NAME |
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2 | |
| 1 | =encoding utf-8 |
3 | =encoding utf-8 |
| 2 | |
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| 3 | =head1 NAME |
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| 4 | |
4 | |
| 5 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
5 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
| 6 | |
6 | |
| 7 | JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ |
7 | JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ |
| 8 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
8 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
| … | |
… | |
| 681 | => ([], 3) |
681 | => ([], 3) |
| 682 | |
682 | |
| 683 | =back |
683 | =back |
| 684 | |
684 | |
| 685 | |
685 | |
|
|
686 | =head1 INCREMENTAL PARSING |
|
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687 | |
|
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688 | [This section is still EXPERIMENTAL] |
|
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689 | |
|
|
690 | In some cases, there is the need for incremental parsing of JSON |
|
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691 | texts. While this module always has to keep both JSON text and resulting |
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692 | Perl data structure in memory at one time, it does allow you to parse a |
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693 | JSON stream incrementally. It does so by accumulating text until it has |
|
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694 | a full JSON object, which it then can decode. This process is similar to |
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695 | using C<decode_prefix> to see if a full JSON object is available, but is |
|
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696 | much more efficient (JSON::XS will only attempt to parse the JSON text |
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697 | once it is sure it has enough text to get a decisive result, using a very |
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698 | simple but truly incremental parser). |
|
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699 | |
|
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700 | The following two methods deal with this. |
|
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701 | |
|
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702 | =over 4 |
|
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703 | |
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704 | =item [void, scalar or list context] = $json->incr_parse ([$string]) |
|
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705 | |
|
|
706 | This is the central parsing function. It can both append new text and |
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707 | extract objects from the stream accumulated so far (both of these |
|
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708 | functions are optional). |
|
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709 | |
|
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710 | If C<$string> is given, then this string is appended to the already |
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711 | existing JSON fragment stored in the C<$json> object. |
|
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712 | |
|
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713 | After that, if the function is called in void context, it will simply |
|
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714 | return without doing anything further. This can be used to add more text |
|
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715 | in as many chunks as you want. |
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716 | |
|
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717 | If the method is called in scalar context, then it will try to extract |
|
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718 | exactly I<one> JSON object. If that is successful, it will return this |
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719 | object, otherwise it will return C<undef>. This is the most common way of |
|
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720 | using the method. |
|
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721 | |
|
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722 | And finally, in list context, it will try to extract as many objects |
|
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723 | from the stream as it can find and return them, or the empty list |
|
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724 | otherwise. For this to work, there must be no separators between the JSON |
|
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725 | objects or arrays, instead they must be concatenated back-to-back. |
|
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726 | |
|
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727 | =item $lvalue_string = $json->incr_text |
|
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728 | |
|
|
729 | This method returns the currently stored JSON fragment as an lvalue, that |
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730 | is, you can manipulate it. This I<only> works when a preceding call to |
|
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731 | C<incr_parse> in I<scalar context> successfully returned an object. Under |
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732 | all other circumstances you must not call this function (I mean it. |
|
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733 | although in simple tests it might actually work, it I<will> fail under |
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734 | real world conditions). As a special exception, you can also call this |
|
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735 | method before having parsed anything. |
|
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736 | |
|
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737 | This function is useful in two cases: a) finding the trailing text after a |
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738 | JSON object or b) parsing multiple JSON objects separated by non-JSON text |
|
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739 | (such as commas). |
|
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740 | |
|
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741 | =back |
|
|
742 | |
|
|
743 | =head2 LIMITATIONS |
|
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744 | |
|
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745 | All options that affect decoding are supported, except |
|
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746 | C<allow_nonref>. The reason for this is that it cannot be made to |
|
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747 | work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate |
|
|
748 | them back to back and still decode them perfectly. This does not hold true |
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749 | for JSON numbers, however. |
|
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750 | |
|
|
751 | For example, is the string C<1> a single JSON number, or is it simply the |
|
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752 | start of C<12>? Or is C<12> a single JSON number, or the concatenation |
|
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753 | of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS |
|
|
754 | takes the conservative route and disallows this case. |
|
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755 | |
|
|
756 | =head2 EXAMPLES |
|
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757 | |
|
|
758 | Some examples will make all this clearer. First, a simple example that |
|
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759 | works similarly to C<decode_prefix>: We want to decode the JSON object at |
|
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760 | the start of a string and identify the portion after the JSON object: |
|
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761 | |
|
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762 | my $text = "[1,2,3] hello"; |
|
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763 | |
|
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764 | my $json = new JSON::XS; |
|
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765 | |
|
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766 | my $obj = $json->incr_parse ($text) |
|
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767 | or die "expected JSON object or array at beginning of string"; |
|
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768 | |
|
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769 | my $tail = $json->incr_text; |
|
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770 | # $tail now contains " hello" |
|
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771 | |
|
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772 | Easy, isn't it? |
|
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773 | |
|
|
774 | Now for a more complicated example: Imagine a hypothetical protocol where |
|
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775 | you read some requests from a TCP stream, and each request is a JSON |
|
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776 | array, without any separation between them (in fact, it is often useful to |
|
|
777 | use newlines as "separators", as these get interpreted as whitespace at |
|
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778 | the start of the JSON text, which makes it possible to test said protocol |
|
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779 | with C<telnet>...). |
|
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780 | |
|
|
781 | Here is how you'd do it (it is trivial to write this in an event-based |
|
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782 | manner): |
|
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783 | |
|
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784 | my $json = new JSON::XS; |
|
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785 | |
|
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786 | # read some data from the socket |
|
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787 | while (sysread $socket, my $buf, 4096) { |
|
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788 | |
|
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789 | # split and decode as many requests as possible |
|
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790 | for my $request ($json->incr_parse ($buf)) { |
|
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791 | # act on the $request |
|
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792 | } |
|
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793 | } |
|
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794 | |
|
|
795 | Another complicated example: Assume you have a string with JSON objects |
|
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796 | or arrays, all separated by (optional) comma characters (e.g. C<[1],[2], |
|
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797 | [3]>). To parse them, we have to skip the commas between the JSON texts, |
|
|
798 | and here is where the lvalue-ness of C<incr_text> comes in useful: |
|
|
799 | |
|
|
800 | my $text = "[1],[2], [3]"; |
|
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801 | my $json = new JSON::XS; |
|
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802 | |
|
|
803 | # void context, so no parsing done |
|
|
804 | $json->incr_parse ($text); |
|
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805 | |
|
|
806 | # now extract as many objects as possible. note the |
|
|
807 | # use of scalar context so incr_text can be called. |
|
|
808 | while (my $obj = $json->incr_parse) { |
|
|
809 | # do something with $obj |
|
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810 | |
|
|
811 | # now skip the optional comma |
|
|
812 | $json->incr_text =~ s/^ \s* , //x; |
|
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813 | } |
|
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814 | |
|
|
815 | Now lets go for a very complex example: Assume that you have a gigantic |
|
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816 | JSON array-of-objects, many gigabytes in size, and you want to parse it, |
|
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817 | but you cannot load it into memory fully (this has actually happened in |
|
|
818 | the real world :). |
|
|
819 | |
|
|
820 | Well, you lost, you have to implement your own JSON parser. But JSON::XS |
|
|
821 | can still help you: You implement a (very simple) array parser and let |
|
|
822 | JSON decode the array elements, which are all full JSON objects on their |
|
|
823 | own (this wouldn't work if the array elements could be JSON numbers, for |
|
|
824 | example): |
|
|
825 | |
|
|
826 | my $json = new JSON::XS; |
|
|
827 | |
|
|
828 | # open the monster |
|
|
829 | open my $fh, "<bigfile.json" |
|
|
830 | or die "bigfile: $!"; |
|
|
831 | |
|
|
832 | # first parse the initial "[" |
|
|
833 | for (;;) { |
|
|
834 | sysread $fh, my $buf, 65536 |
|
|
835 | or die "read error: $!"; |
|
|
836 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
837 | |
|
|
838 | # Exit the loop once we found and removed(!) the initial "[". |
|
|
839 | # In essence, we are (ab-)using the $json object as a simple scalar |
|
|
840 | # we append data to. |
|
|
841 | last if $json->incr_text =~ s/^ \s* \[ //x; |
|
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842 | } |
|
|
843 | |
|
|
844 | # now we have the skipped the initial "[", so continue |
|
|
845 | # parsing all the elements. |
|
|
846 | for (;;) { |
|
|
847 | # in this loop we read data until we got a single JSON object |
|
|
848 | for (;;) { |
|
|
849 | if (my $obj = $json->incr_parse) { |
|
|
850 | # do something with $obj |
|
|
851 | last; |
|
|
852 | } |
|
|
853 | |
|
|
854 | # add more data |
|
|
855 | sysread $fh, my $buf, 65536 |
|
|
856 | or die "read error: $!"; |
|
|
857 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
858 | } |
|
|
859 | |
|
|
860 | # in this loop we read data until we either found and parsed the |
|
|
861 | # separating "," between elements, or the final "]" |
|
|
862 | for (;;) { |
|
|
863 | # first skip whitespace |
|
|
864 | $json->incr_text =~ s/^\s*//; |
|
|
865 | |
|
|
866 | # if we find "]", we are done |
|
|
867 | if ($json->incr_text =~ s/^\]//) { |
|
|
868 | print "finished.\n"; |
|
|
869 | exit; |
|
|
870 | } |
|
|
871 | |
|
|
872 | # if we find ",", we can continue with the next element |
|
|
873 | if ($json->incr_text =~ s/^,//) { |
|
|
874 | last; |
|
|
875 | } |
|
|
876 | |
|
|
877 | # if we find anything else, we have a parse error! |
|
|
878 | if (length $json->incr_text) { |
|
|
879 | die "parse error near ", $json->incr_text; |
|
|
880 | } |
|
|
881 | |
|
|
882 | # else add more data |
|
|
883 | sysread $fh, my $buf, 65536 |
|
|
884 | or die "read error: $!"; |
|
|
885 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
886 | } |
|
|
887 | |
|
|
888 | This is a complex example, but most of the complexity comes from the fact |
|
|
889 | that we are trying to be correct (bear with me if I am wrong, I never ran |
|
|
890 | the above example :). |
|
|
891 | |
|
|
892 | |
|
|
893 | |
| 686 | =head1 MAPPING |
894 | =head1 MAPPING |
| 687 | |
895 | |
| 688 | This section describes how JSON::XS maps Perl values to JSON values and |
896 | This section describes how JSON::XS maps Perl values to JSON values and |
| 689 | vice versa. These mappings are designed to "do the right thing" in most |
897 | vice versa. These mappings are designed to "do the right thing" in most |
| 690 | circumstances automatically, preserving round-tripping characteristics |
898 | circumstances automatically, preserving round-tripping characteristics |
| … | |
… | |
| 825 | my $x = "3"; # some variable containing a string |
1033 | my $x = "3"; # some variable containing a string |
| 826 | $x += 0; # numify it, ensuring it will be dumped as a number |
1034 | $x += 0; # numify it, ensuring it will be dumped as a number |
| 827 | $x *= 1; # same thing, the choice is yours. |
1035 | $x *= 1; # same thing, the choice is yours. |
| 828 | |
1036 | |
| 829 | You can not currently force the type in other, less obscure, ways. Tell me |
1037 | You can not currently force the type in other, less obscure, ways. Tell me |
| 830 | if you need this capability (but don't forget to explain why its needed |
1038 | if you need this capability (but don't forget to explain why it's needed |
| 831 | :). |
1039 | :). |
| 832 | |
1040 | |
| 833 | =back |
1041 | =back |
| 834 | |
1042 | |
| 835 | |
1043 | |
| … | |
… | |
| 837 | |
1045 | |
| 838 | The interested reader might have seen a number of flags that signify |
1046 | The interested reader might have seen a number of flags that signify |
| 839 | encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be |
1047 | encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be |
| 840 | some confusion on what these do, so here is a short comparison: |
1048 | some confusion on what these do, so here is a short comparison: |
| 841 | |
1049 | |
| 842 | C<utf8> controls wether the JSON text created by C<encode> (and expected |
1050 | C<utf8> controls whether the JSON text created by C<encode> (and expected |
| 843 | by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only |
1051 | by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only |
| 844 | control wether C<encode> escapes character values outside their respective |
1052 | control whether C<encode> escapes character values outside their respective |
| 845 | codeset range. Neither of these flags conflict with each other, although |
1053 | codeset range. Neither of these flags conflict with each other, although |
| 846 | some combinations make less sense than others. |
1054 | some combinations make less sense than others. |
| 847 | |
1055 | |
| 848 | Care has been taken to make all flags symmetrical with respect to |
1056 | Care has been taken to make all flags symmetrical with respect to |
| 849 | C<encode> and C<decode>, that is, texts encoded with any combination of |
1057 | C<encode> and C<decode>, that is, texts encoded with any combination of |
| … | |
… | |
| 1193 | =head1 THREADS |
1401 | =head1 THREADS |
| 1194 | |
1402 | |
| 1195 | This module is I<not> guaranteed to be thread safe and there are no |
1403 | This module is I<not> guaranteed to be thread safe and there are no |
| 1196 | plans to change this until Perl gets thread support (as opposed to the |
1404 | plans to change this until Perl gets thread support (as opposed to the |
| 1197 | horribly slow so-called "threads" which are simply slow and bloated |
1405 | horribly slow so-called "threads" which are simply slow and bloated |
| 1198 | process simulations - use fork, its I<much> faster, cheaper, better). |
1406 | process simulations - use fork, it's I<much> faster, cheaper, better). |
| 1199 | |
1407 | |
| 1200 | (It might actually work, but you have been warned). |
1408 | (It might actually work, but you have been warned). |
| 1201 | |
1409 | |
| 1202 | |
1410 | |
| 1203 | =head1 BUGS |
1411 | =head1 BUGS |
| 1204 | |
1412 | |
| 1205 | While the goal of this module is to be correct, that unfortunately does |
1413 | While the goal of this module is to be correct, that unfortunately does |
| 1206 | not mean its bug-free, only that I think its design is bug-free. It is |
1414 | not mean it's bug-free, only that I think its design is bug-free. It is |
| 1207 | still relatively early in its development. If you keep reporting bugs they |
1415 | still relatively early in its development. If you keep reporting bugs they |
| 1208 | will be fixed swiftly, though. |
1416 | will be fixed swiftly, though. |
| 1209 | |
1417 | |
| 1210 | Please refrain from using rt.cpan.org or any other bug reporting |
1418 | Please refrain from using rt.cpan.org or any other bug reporting |
| 1211 | service. I put the contact address into my modules for a reason. |
1419 | service. I put the contact address into my modules for a reason. |
| … | |
… | |
| 1233 | "--" => sub { $_[0] = ${$_[0]} - 1 }, |
1441 | "--" => sub { $_[0] = ${$_[0]} - 1 }, |
| 1234 | fallback => 1; |
1442 | fallback => 1; |
| 1235 | |
1443 | |
| 1236 | 1; |
1444 | 1; |
| 1237 | |
1445 | |
|
|
1446 | =head1 SEE ALSO |
|
|
1447 | |
|
|
1448 | The F<json_xs> command line utility for quick experiments. |
|
|
1449 | |
| 1238 | =head1 AUTHOR |
1450 | =head1 AUTHOR |
| 1239 | |
1451 | |
| 1240 | Marc Lehmann <schmorp@schmorp.de> |
1452 | Marc Lehmann <schmorp@schmorp.de> |
| 1241 | http://home.schmorp.de/ |
1453 | http://home.schmorp.de/ |
| 1242 | |
1454 | |
