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=head1 NAME |
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|
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JSON::XS - JSON serialising/deserialising, done correctly and fast |
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|
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=head1 SYNOPSIS |
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|
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use JSON::XS; |
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|
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=head1 DESCRIPTION |
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|
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This module converts Perl data structures to JSON and vice versa. Its |
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primary goal is to be I<correct> and its secondary goal is to be |
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I<fast>. To reach the latter goal it was written in C. |
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|
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As this is the n-th-something JSON module on CPAN, what was the reason |
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to write yet another JSON module? While it seems there are many JSON |
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modules, none of them correctly handle all corner cases, and in most cases |
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their maintainers are unresponsive, gone missing, or not listening to bug |
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reports for other reasons. |
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|
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See COMPARISON, below, for a comparison to some other JSON modules. |
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|
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=head2 FEATURES |
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|
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=over 4 |
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|
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=item * correct handling of unicode issues |
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|
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This module knows how to handle Unicode, and even documents how it does so. |
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|
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=item * round-trip integrity |
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|
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When you serialise a perl data structure using only datatypes supported |
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by JSON, the deserialised data structure is identical on the Perl level. |
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(e.g. the string "2.0" doesn't suddenly become "2"). |
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|
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=item * strict checking of JSON correctness |
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|
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There is no guessing, no generating of illegal JSON strings by default, |
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and only JSON is accepted as input (the latter is a security feature). |
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|
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=item * fast |
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|
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compared to other JSON modules, this module compares favourably. |
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|
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=item * simple to use |
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|
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This module has both a simple functional interface as well as an OO |
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interface. |
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|
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=item * reasonably versatile output formats |
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|
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You can choose between the most compact format possible, a pure-ascii |
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format, or a pretty-printed format. Or you can combine those features in |
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whatever way you like. |
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|
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=back |
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|
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=cut |
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|
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package JSON::XS; |
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|
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BEGIN { |
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$VERSION = '0.2'; |
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@ISA = qw(Exporter); |
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|
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@EXPORT = qw(to_json from_json); |
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require Exporter; |
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|
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require XSLoader; |
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XSLoader::load JSON::XS::, $VERSION; |
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} |
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|
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=head1 FUNCTIONAL INTERFACE |
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|
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The following convinience methods are provided by this module. They are |
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exported by default: |
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|
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=over 4 |
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|
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=item $json_string = to_json $perl_scalar |
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|
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Converts the given Perl data structure (a simple scalar or a reference to |
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a hash or array) to a UTF-8 encoded, binary string (that is, the string contains |
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octets only). Croaks on error. |
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|
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This function call is functionally identical to C<< JSON::XS->new->utf8 |
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(1)->encode ($perl_scalar) >>. |
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|
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=item $perl_scalar = from_json $json_string |
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|
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The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to |
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parse that as an UTF-8 encoded JSON string, returning the resulting simple |
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scalar or reference. Croaks on error. |
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|
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This function call is functionally identical to C<< JSON::XS->new->utf8 |
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(1)->decode ($json_string) >>. |
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|
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=back |
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|
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=head1 OBJECT-ORIENTED INTERFACE |
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|
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The object oriented interface lets you configure your own encoding or |
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decoding style, within the limits of supported formats. |
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|
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=over 4 |
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|
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=item $json = new JSON::XS |
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|
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Creates a new JSON::XS object that can be used to de/encode JSON |
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strings. All boolean flags described below are by default I<disabled>. |
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|
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The mutators for flags all return the JSON object again and thus calls can |
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be chained: |
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|
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my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) |
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=> {"a": [1, 2]} |
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|
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=item $json = $json->ascii ([$enable]) |
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|
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If C<$enable> is true (or missing), then the C<encode> method will |
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not generate characters outside the code range C<0..127>. Any unicode |
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characters outside that range will be escaped using either a single |
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\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per |
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RFC4627. |
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|
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If C<$enable> is false, then the C<encode> method will not escape Unicode |
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characters unless necessary. |
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|
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JSON::XS->new->ascii (1)->encode (chr 0x10401) |
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=> \ud801\udc01 |
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|
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=item $json = $json->utf8 ([$enable]) |
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|
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If C<$enable> is true (or missing), then the C<encode> method will encode |
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the JSON string into UTF-8, as required by many protocols, while the |
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C<decode> method expects to be handled an UTF-8-encoded string. Please |
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note that UTF-8-encoded strings do not contain any characters outside the |
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range C<0..255>, they are thus useful for bytewise/binary I/O. |
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|
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If C<$enable> is false, then the C<encode> method will return the JSON |
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string as a (non-encoded) unicode string, while C<decode> expects thus a |
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unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
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to be done yourself, e.g. using the Encode module. |
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|
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=item $json = $json->pretty ([$enable]) |
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|
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This enables (or disables) all of the C<indent>, C<space_before> and |
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C<space_after> (and in the future possibly more) flags in one call to |
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generate the most readable (or most compact) form possible. |
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|
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my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
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=> |
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{ |
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"a" : [ |
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1, |
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2 |
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] |
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} |
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|
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=item $json = $json->indent ([$enable]) |
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|
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If C<$enable> is true (or missing), then the C<encode> method will use a multiline |
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format as output, putting every array member or object/hash key-value pair |
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into its own line, identing them properly. |
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|
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If C<$enable> is false, no newlines or indenting will be produced, and the |
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resulting JSON strings is guarenteed not to contain any C<newlines>. |
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|
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This setting has no effect when decoding JSON strings. |
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|
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=item $json = $json->space_before ([$enable]) |
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|
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If C<$enable> is true (or missing), then the C<encode> method will add an extra |
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optional space before the C<:> separating keys from values in JSON objects. |
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|
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If C<$enable> is false, then the C<encode> method will not add any extra |
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space at those places. |
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|
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This setting has no effect when decoding JSON strings. You will also most |
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likely combine this setting with C<space_after>. |
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|
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=item $json = $json->space_after ([$enable]) |
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|
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If C<$enable> is true (or missing), then the C<encode> method will add an extra |
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optional space after the C<:> separating keys from values in JSON objects |
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and extra whitespace after the C<,> separating key-value pairs and array |
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members. |
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|
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If C<$enable> is false, then the C<encode> method will not add any extra |
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space at those places. |
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|
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This setting has no effect when decoding JSON strings. |
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|
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=item $json = $json->canonical ([$enable]) |
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|
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If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
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by sorting their keys. This is adding a comparatively high overhead. |
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|
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If C<$enable> is false, then the C<encode> method will output key-value |
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pairs in the order Perl stores them (which will likely change between runs |
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of the same script). |
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|
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This option is useful if you want the same data structure to be encoded as |
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the same JSON string (given the same overall settings). If it is disabled, |
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the same hash migh be encoded differently even if contains the same data, |
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as key-value pairs have no inherent ordering in Perl. |
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|
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This setting has no effect when decoding JSON strings. |
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|
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=item $json = $json->allow_nonref ([$enable]) |
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|
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If C<$enable> is true (or missing), then the C<encode> method can convert a |
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non-reference into its corresponding string, number or null JSON value, |
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which is an extension to RFC4627. Likewise, C<decode> will accept those JSON |
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values instead of croaking. |
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|
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If C<$enable> is false, then the C<encode> method will croak if it isn't |
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passed an arrayref or hashref, as JSON strings must either be an object |
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or array. Likewise, C<decode> will croak if given something that is not a |
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JSON object or array. |
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|
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=item $json = $json->shrink ([$enable]) |
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|
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Perl usually over-allocates memory a bit when allocating space for |
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strings. This flag optionally resizes strings generated by either |
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C<encode> or C<decode> to their minimum size possible. This can save |
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memory when your JSON strings are either very very long or you have many |
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short strings. It will also try to downgrade any strings to octet-form |
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if possible: perl stores strings internally either in an encoding called |
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UTF-X or in octet-form. The latter cannot store everything but uses less |
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space in general. |
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|
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If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit, |
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while all strings generated by C<decode> will also be shrunk-to-fit. |
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|
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If C<$enable> is false, then the normal perl allocation algorithms are used. |
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If you work with your data, then this is likely to be faster. |
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|
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In the future, this setting might control other things, such as converting |
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strings that look like integers or floats into integers or floats |
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internally (there is no difference on the Perl level), saving space. |
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|
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=item $json_string = $json->encode ($perl_scalar) |
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|
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Converts the given Perl data structure (a simple scalar or a reference |
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to a hash or array) to its JSON representation. Simple scalars will be |
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converted into JSON string or number sequences, while references to arrays |
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become JSON arrays and references to hashes become JSON objects. Undefined |
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Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
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nor C<false> values will be generated. |
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|
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=item $perl_scalar = $json->decode ($json_string) |
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|
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The opposite of C<encode>: expects a JSON string and tries to parse it, |
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returning the resulting simple scalar or reference. Croaks on error. |
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|
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JSON numbers and strings become simple Perl scalars. JSON arrays become |
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Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
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C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
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|
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=back |
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|
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=head1 COMPARISON |
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|
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As already mentioned, this module was created because none of the existing |
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JSON modules could be made to work correctly. First I will describe the |
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problems (or pleasures) I encountered with various existing JSON modules, |
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followed by some benchmark values. JSON::XS was designed not to suffer |
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from any of these problems or limitations. |
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|
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=over 4 |
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|
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=item JSON 1.07 |
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|
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Slow (but very portable, as it is written in pure Perl). |
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|
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Undocumented/buggy Unicode handling (how JSON handles unicode values is |
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undocumented. One can get far by feeding it unicode strings and doing |
| 280 |
en-/decoding oneself, but unicode escapes are not working properly). |
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|
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No roundtripping (strings get clobbered if they look like numbers, e.g. |
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the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will |
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decode into the number 2. |
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|
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=item JSON::PC 0.01 |
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|
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Very fast. |
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|
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Undocumented/buggy Unicode handling. |
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|
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No roundtripping. |
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|
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Has problems handling many Perl values (e.g. regex results and other magic |
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values will make it croak). |
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|
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Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
| 298 |
which is not a valid JSON string. |
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|
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Unmaintained (maintainer unresponsive for many months, bugs are not |
| 301 |
getting fixed). |
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|
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=item JSON::Syck 0.21 |
| 304 |
|
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Very buggy (often crashes). |
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|
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Very inflexible (no human-readable format supported, format pretty much |
| 308 |
undocumented. I need at least a format for easy reading by humans and a |
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single-line compact format for use in a protocol, and preferably a way to |
| 310 |
generate ASCII-only JSON strings). |
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|
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Completely broken (and confusingly documented) Unicode handling (unicode |
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escapes are not working properly, you need to set ImplicitUnicode to |
| 314 |
I<different> values on en- and decoding to get symmetric behaviour). |
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|
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No roundtripping (simple cases work, but this depends on wether the scalar |
| 317 |
value was used in a numeric context or not). |
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|
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Dumping hashes may skip hash values depending on iterator state. |
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|
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Unmaintained (maintainer unresponsive for many months, bugs are not |
| 322 |
getting fixed). |
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|
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Does not check input for validity (i.e. will accept non-JSON input and |
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return "something" instead of raising an exception. This is a security |
| 326 |
issue: imagine two banks transfering money between each other using |
| 327 |
JSON. One bank might parse a given non-JSON request and deduct money, |
| 328 |
while the other might reject the transaction with a syntax error. While a |
| 329 |
good protocol will at least recover, that is extra unnecessary work and |
| 330 |
the transaction will still not succeed). |
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|
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=item JSON::DWIW 0.04 |
| 333 |
|
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Very fast. Very natural. Very nice. |
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|
| 336 |
Undocumented unicode handling (but the best of the pack. Unicode escapes |
| 337 |
still don't get parsed properly). |
| 338 |
|
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Very inflexible. |
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|
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No roundtripping. |
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|
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Does not generate valid JSON (key strings are often unquoted, empty keys |
| 344 |
result in nothing being output) |
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|
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Does not check input for validity. |
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|
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=back |
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|
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=head2 SPEED |
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|
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It seems that JSON::XS is surprisingly fast, as shown in the following |
| 353 |
tables. They have been generated with the help of the C<eg/bench> program |
| 354 |
in the JSON::XS distribution, to make it easy to compare on your own |
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system. |
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|
| 357 |
First is a comparison between various modules using a very simple JSON |
| 358 |
string, showing the number of encodes/decodes per second (JSON::XS is |
| 359 |
the functional interface, while JSON::XS/2 is the OO interface with |
| 360 |
pretty-printing and hashkey sorting enabled). |
| 361 |
|
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module | encode | decode | |
| 363 |
-----------|------------|------------| |
| 364 |
JSON | 14006 | 6820 | |
| 365 |
JSON::DWIW | 200937 | 120386 | |
| 366 |
JSON::PC | 85065 | 129366 | |
| 367 |
JSON::Syck | 59898 | 44232 | |
| 368 |
JSON::XS | 1171478 | 342435 | |
| 369 |
JSON::XS/2 | 730760 | 328714 | |
| 370 |
-----------+------------+------------+ |
| 371 |
|
| 372 |
That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 |
| 373 |
times faster than JSON, even with pretty-printing and key sorting. |
| 374 |
|
| 375 |
Using a longer test string (roughly 8KB, generated from Yahoo! Locals |
| 376 |
search API (http://nanoref.com/yahooapis/mgPdGg): |
| 377 |
|
| 378 |
module | encode | decode | |
| 379 |
-----------|------------|------------| |
| 380 |
JSON | 673 | 38 | |
| 381 |
JSON::DWIW | 5271 | 770 | |
| 382 |
JSON::PC | 9901 | 2491 | |
| 383 |
JSON::Syck | 2360 | 786 | |
| 384 |
JSON::XS | 37398 | 3202 | |
| 385 |
JSON::XS/2 | 13765 | 3153 | |
| 386 |
-----------+------------+------------+ |
| 387 |
|
| 388 |
Again, JSON::XS leads by far in the encoding case, while still beating |
| 389 |
every other module in the decoding case. |
| 390 |
|
| 391 |
Last example is an almost 8MB large hash with many large binary values |
| 392 |
(PNG files), resulting in a lot of escaping: |
| 393 |
|
| 394 |
=head1 BUGS |
| 395 |
|
| 396 |
While the goal of this module is to be correct, that unfortunately does |
| 397 |
not mean its bug-free, only that I think its design is bug-free. It is |
| 398 |
still very young and not well-tested. If you keep reporting bugs they will |
| 399 |
be fixed swiftly, though. |
| 400 |
|
| 401 |
=cut |
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|
| 403 |
1; |
| 404 |
|
| 405 |
=head1 AUTHOR |
| 406 |
|
| 407 |
Marc Lehmann <schmorp@schmorp.de> |
| 408 |
http://home.schmorp.de/ |
| 409 |
|
| 410 |
=cut |
| 411 |
|
