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1 | =encoding utf-8 |
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2 | |
| 1 | =head1 NAME |
3 | =head1 NAME |
| 2 | |
4 | |
| 3 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
5 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
| 4 | |
6 | |
| 5 | 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 |
| … | |
… | |
| 58 | |
60 | |
| 59 | =over 4 |
61 | =over 4 |
| 60 | |
62 | |
| 61 | =item * correct Unicode handling |
63 | =item * correct Unicode handling |
| 62 | |
64 | |
| 63 | This module knows how to handle Unicode, and even documents how and when |
65 | This module knows how to handle Unicode, documents how and when it does |
| 64 | it does so. |
66 | so, and even documents what "correct" means. |
| 65 | |
67 | |
| 66 | =item * round-trip integrity |
68 | =item * round-trip integrity |
| 67 | |
69 | |
| 68 | When you serialise a perl data structure using only datatypes supported |
70 | When you serialise a perl data structure using only datatypes supported |
| 69 | by JSON, the deserialised data structure is identical on the Perl level. |
71 | by JSON, the deserialised data structure is identical on the Perl level. |
| 70 | (e.g. the string "2.0" doesn't suddenly become "2" just because it looks |
72 | (e.g. the string "2.0" doesn't suddenly become "2" just because it looks |
| 71 | like a number). |
73 | like a number). There minor I<are> exceptions to this, read the MAPPING |
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74 | section below to learn about those. |
| 72 | |
75 | |
| 73 | =item * strict checking of JSON correctness |
76 | =item * strict checking of JSON correctness |
| 74 | |
77 | |
| 75 | There is no guessing, no generating of illegal JSON texts by default, |
78 | There is no guessing, no generating of illegal JSON texts by default, |
| 76 | and only JSON is accepted as input by default (the latter is a security |
79 | and only JSON is accepted as input by default (the latter is a security |
| 77 | feature). |
80 | feature). |
| 78 | |
81 | |
| 79 | =item * fast |
82 | =item * fast |
| 80 | |
83 | |
| 81 | Compared to other JSON modules, this module compares favourably in terms |
84 | Compared to other JSON modules and other serialisers such as Storable, |
| 82 | of speed, too. |
85 | this module usually compares favourably in terms of speed, too. |
| 83 | |
86 | |
| 84 | =item * simple to use |
87 | =item * simple to use |
| 85 | |
88 | |
| 86 | This module has both a simple functional interface as well as an OO |
89 | This module has both a simple functional interface as well as an objetc |
| 87 | interface. |
90 | oriented interface interface. |
| 88 | |
91 | |
| 89 | =item * reasonably versatile output formats |
92 | =item * reasonably versatile output formats |
| 90 | |
93 | |
| 91 | You can choose between the most compact guaranteed single-line format |
94 | You can choose between the most compact guaranteed-single-line format |
| 92 | possible (nice for simple line-based protocols), a pure-ascii format |
95 | possible (nice for simple line-based protocols), a pure-ascii format |
| 93 | (for when your transport is not 8-bit clean, still supports the whole |
96 | (for when your transport is not 8-bit clean, still supports the whole |
| 94 | Unicode range), or a pretty-printed format (for when you want to read that |
97 | Unicode range), or a pretty-printed format (for when you want to read that |
| 95 | stuff). Or you can combine those features in whatever way you like. |
98 | stuff). Or you can combine those features in whatever way you like. |
| 96 | |
99 | |
| … | |
… | |
| 174 | This enables you to store Unicode characters as single characters in a |
177 | This enables you to store Unicode characters as single characters in a |
| 175 | Perl string - very natural. |
178 | Perl string - very natural. |
| 176 | |
179 | |
| 177 | =item 2. Perl does I<not> associate an encoding with your strings. |
180 | =item 2. Perl does I<not> associate an encoding with your strings. |
| 178 | |
181 | |
| 179 | Unless you force it to, e.g. when matching it against a regex, or printing |
182 | ... until you force it to, e.g. when matching it against a regex, or |
| 180 | the scalar to a file, in which case Perl either interprets your string as |
183 | printing the scalar to a file, in which case Perl either interprets your |
| 181 | locale-encoded text, octets/binary, or as Unicode, depending on various |
184 | string as locale-encoded text, octets/binary, or as Unicode, depending |
| 182 | settings. In no case is an encoding stored together with your data, it is |
185 | on various settings. In no case is an encoding stored together with your |
| 183 | I<use> that decides encoding, not any magical metadata. |
186 | data, it is I<use> that decides encoding, not any magical meta data. |
| 184 | |
187 | |
| 185 | =item 3. The internal utf-8 flag has no meaning with regards to the |
188 | =item 3. The internal utf-8 flag has no meaning with regards to the |
| 186 | encoding of your string. |
189 | encoding of your string. |
| 187 | |
190 | |
| 188 | Just ignore that flag unless you debug a Perl bug, a module written in |
191 | Just ignore that flag unless you debug a Perl bug, a module written in |
| … | |
… | |
| 706 | |
709 | |
| 707 | A JSON number becomes either an integer, numeric (floating point) or |
710 | A JSON number becomes either an integer, numeric (floating point) or |
| 708 | string scalar in perl, depending on its range and any fractional parts. On |
711 | string scalar in perl, depending on its range and any fractional parts. On |
| 709 | the Perl level, there is no difference between those as Perl handles all |
712 | the Perl level, there is no difference between those as Perl handles all |
| 710 | the conversion details, but an integer may take slightly less memory and |
713 | the conversion details, but an integer may take slightly less memory and |
| 711 | might represent more values exactly than (floating point) numbers. |
714 | might represent more values exactly than floating point numbers. |
| 712 | |
715 | |
| 713 | If the number consists of digits only, JSON::XS will try to represent |
716 | If the number consists of digits only, JSON::XS will try to represent |
| 714 | it as an integer value. If that fails, it will try to represent it as |
717 | it as an integer value. If that fails, it will try to represent it as |
| 715 | a numeric (floating point) value if that is possible without loss of |
718 | a numeric (floating point) value if that is possible without loss of |
| 716 | precision. Otherwise it will preserve the number as a string value. |
719 | precision. Otherwise it will preserve the number as a string value (in |
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720 | which case you lose roundtripping ability, as the JSON number will be |
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721 | re-encoded toa JSON string). |
| 717 | |
722 | |
| 718 | Numbers containing a fractional or exponential part will always be |
723 | Numbers containing a fractional or exponential part will always be |
| 719 | represented as numeric (floating point) values, possibly at a loss of |
724 | represented as numeric (floating point) values, possibly at a loss of |
| 720 | precision. |
725 | precision (in which case you might lose perfect roundtripping ability, but |
| 721 | |
726 | the JSON number will still be re-encoded as a JSON number). |
| 722 | This might create round-tripping problems as numbers might become strings, |
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| 723 | but as Perl is typeless there is no other way to do it. |
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| 724 | |
727 | |
| 725 | =item true, false |
728 | =item true, false |
| 726 | |
729 | |
| 727 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
730 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
| 728 | respectively. They are overloaded to act almost exactly like the numbers |
731 | respectively. They are overloaded to act almost exactly like the numbers |
| … | |
… | |
| 819 | :). |
822 | :). |
| 820 | |
823 | |
| 821 | =back |
824 | =back |
| 822 | |
825 | |
| 823 | |
826 | |
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827 | =head1 ENCODING/CODESET FLAG NOTES |
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828 | |
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829 | The interested reader might have seen a number of flags that signify |
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830 | encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be |
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831 | some confusion on what these do, so here is a short comparison: |
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832 | |
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833 | C<utf8> controls wether the JSON text created by C<encode> (and expected |
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834 | by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only |
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835 | control wether C<encode> escapes character values outside their respective |
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836 | codeset range. Neither of these flags conflict with each other, although |
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837 | some combinations make less sense than others. |
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838 | |
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839 | Care has been taken to make all flags symmetrical with respect to |
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840 | C<encode> and C<decode>, that is, texts encoded with any combination of |
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841 | these flag values will be correctly decoded when the same flags are used |
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842 | - in general, if you use different flag settings while encoding vs. when |
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843 | decoding you likely have a bug somewhere. |
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844 | |
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845 | Below comes a verbose discussion of these flags. Note that a "codeset" is |
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846 | simply an abstract set of character-codepoint pairs, while an encoding |
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847 | takes those codepoint numbers and I<encodes> them, in our case into |
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848 | octets. Unicode is (among other things) a codeset, UTF-8 is an encoding, |
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849 | and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at |
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850 | the same time, which can be confusing. |
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851 | |
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852 | =over 4 |
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853 | |
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854 | =item C<utf8> flag disabled |
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855 | |
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856 | When C<utf8> is disabled (the default), then C<encode>/C<decode> generate |
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857 | and expect Unicode strings, that is, characters with high ordinal Unicode |
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858 | values (> 255) will be encoded as such characters, and likewise such |
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859 | characters are decoded as-is, no canges to them will be done, except |
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860 | "(re-)interpreting" them as Unicode codepoints or Unicode characters, |
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861 | respectively (to Perl, these are the same thing in strings unless you do |
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862 | funny/weird/dumb stuff). |
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863 | |
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864 | This is useful when you want to do the encoding yourself (e.g. when you |
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865 | want to have UTF-16 encoded JSON texts) or when some other layer does |
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866 | the encoding for you (for example, when printing to a terminal using a |
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867 | filehandle that transparently encodes to UTF-8 you certainly do NOT want |
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868 | to UTF-8 encode your data first and have Perl encode it another time). |
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869 | |
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870 | =item C<utf8> flag enabled |
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871 | |
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872 | If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all |
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873 | characters using the corresponding UTF-8 multi-byte sequence, and will |
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874 | expect your input strings to be encoded as UTF-8, that is, no "character" |
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875 | of the input string must have any value > 255, as UTF-8 does not allow |
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876 | that. |
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877 | |
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878 | The C<utf8> flag therefore switches between two modes: disabled means you |
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879 | will get a Unicode string in Perl, enabled means you get an UTF-8 encoded |
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880 | octet/binary string in Perl. |
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881 | |
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882 | =item C<latin1> or C<ascii> flags enabled |
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883 | |
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884 | With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters |
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885 | with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining |
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886 | characters as specified by the C<utf8> flag. |
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887 | |
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888 | If C<utf8> is disabled, then the result is also correctly encoded in those |
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889 | character sets (as both are proper subsets of Unicode, meaning that a |
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890 | Unicode string with all character values < 256 is the same thing as a |
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891 | ISO-8859-1 string, and a Unicode string with all character values < 128 is |
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892 | the same thing as an ASCII string in Perl). |
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893 | |
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894 | If C<utf8> is enabled, you still get a correct UTF-8-encoded string, |
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895 | regardless of these flags, just some more characters will be escaped using |
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896 | C<\uXXXX> then before. |
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897 | |
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898 | Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8 |
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899 | encoding, while ASCII-encoded strings are. That is because the ISO-8859-1 |
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900 | encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being |
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901 | a subset of Unicode), while ASCII is. |
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902 | |
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903 | Surprisingly, C<decode> will ignore these flags and so treat all input |
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904 | values as governed by the C<utf8> flag. If it is disabled, this allows you |
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905 | to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of |
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906 | Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings. |
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907 | |
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908 | So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag - |
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909 | they only govern when the JSON output engine escapes a character or not. |
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910 | |
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911 | The main use for C<latin1> is to relatively efficiently store binary data |
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912 | as JSON, at the expense of breaking compatibility with most JSON decoders. |
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913 | |
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914 | The main use for C<ascii> is to force the output to not contain characters |
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915 | with values > 127, which means you can interpret the resulting string |
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916 | as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and |
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917 | 8-bit-encoding, and still get the same data structure back. This is useful |
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918 | when your channel for JSON transfer is not 8-bit clean or the encoding |
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919 | might be mangled in between (e.g. in mail), and works because ASCII is a |
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920 | proper subset of most 8-bit and multibyte encodings in use in the world. |
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921 | |
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922 | =back |
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923 | |
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924 | |
| 824 | =head1 COMPARISON |
925 | =head1 COMPARISON |
| 825 | |
926 | |
| 826 | As already mentioned, this module was created because none of the existing |
927 | As already mentioned, this module was created because none of the existing |
| 827 | JSON modules could be made to work correctly. First I will describe the |
928 | JSON modules could be made to work correctly. First I will describe the |
| 828 | problems (or pleasures) I encountered with various existing JSON modules, |
929 | problems (or pleasures) I encountered with various existing JSON modules, |
| 829 | followed by some benchmark values. JSON::XS was designed not to suffer |
930 | followed by some benchmark values. JSON::XS was designed not to suffer |
| 830 | from any of these problems or limitations. |
931 | from any of these problems or limitations. |
| 831 | |
932 | |
| 832 | =over 4 |
933 | =over 4 |
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934 | |
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935 | =item JSON 2.xx |
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936 | |
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937 | A marvellous piece of engineering, this module either uses JSON::XS |
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938 | directly when available (so will be 100% compatible with it, including |
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939 | speed), or it uses JSON::PP, which is basically JSON::XS translated to |
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940 | Pure Perl, which should be 100% compatible with JSON::XS, just a bit |
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941 | slower. |
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942 | |
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943 | You cannot really lose by using this module. |
| 833 | |
944 | |
| 834 | =item JSON 1.07 |
945 | =item JSON 1.07 |
| 835 | |
946 | |
| 836 | Slow (but very portable, as it is written in pure Perl). |
947 | Slow (but very portable, as it is written in pure Perl). |
| 837 | |
948 | |
