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1.1 |
=head1 NAME |
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JSON::XS - JSON serialising/deserialising, done correctly and fast |
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=head1 SYNOPSIS |
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use JSON::XS; |
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1.22 |
# exported functions, they croak on error |
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# and expect/generate UTF-8 |
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1.12 |
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$utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
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$perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
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1.22 |
# objToJson and jsonToObj aliases to to_json and from_json |
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# are exported for compatibility to the JSON module, |
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# but should not be used in new code. |
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1.21 |
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1.22 |
# OO-interface |
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1.12 |
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$coder = JSON::XS->new->ascii->pretty->allow_nonref; |
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$pretty_printed_unencoded = $coder->encode ($perl_scalar); |
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$perl_scalar = $coder->decode ($unicode_json_text); |
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1.1 |
=head1 DESCRIPTION |
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1.2 |
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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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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See COMPARISON, below, for a comparison to some other JSON modules. |
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1.10 |
See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
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vice versa. |
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1.2 |
=head2 FEATURES |
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1.1 |
=over 4 |
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1.21 |
=item * correct unicode handling |
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1.2 |
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1.10 |
This module knows how to handle Unicode, and even documents how and when |
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it does so. |
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1.2 |
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=item * round-trip integrity |
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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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1.21 |
(e.g. the string "2.0" doesn't suddenly become "2" just because it looks |
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like a number). |
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1.2 |
|
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=item * strict checking of JSON correctness |
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1.16 |
There is no guessing, no generating of illegal JSON texts by default, |
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1.10 |
and only JSON is accepted as input by default (the latter is a security |
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feature). |
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1.2 |
|
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=item * fast |
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1.10 |
Compared to other JSON modules, this module compares favourably in terms |
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of speed, too. |
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1.2 |
|
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=item * simple to use |
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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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=item * reasonably versatile output formats |
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1.10 |
You can choose between the most compact guarenteed single-line format |
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1.21 |
possible (nice for simple line-based protocols), a pure-ascii format |
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(for when your transport is not 8-bit clean, still supports the whole |
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unicode range), or a pretty-printed format (for when you want to read that |
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stuff). Or you can combine those features in whatever way you like. |
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1.2 |
|
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=back |
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1.1 |
=cut |
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package JSON::XS; |
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1.20 |
use strict; |
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1.44 |
our $VERSION = '1.4'; |
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1.43 |
our @ISA = qw(Exporter); |
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1.1 |
|
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1.43 |
our @EXPORT = qw(to_json from_json objToJson jsonToObj); |
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1.1 |
|
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1.43 |
use Exporter; |
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use XSLoader; |
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1.1 |
|
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1.2 |
=head1 FUNCTIONAL INTERFACE |
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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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=over 4 |
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1.16 |
=item $json_text = to_json $perl_scalar |
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1.2 |
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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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1.16 |
This function call is functionally identical to: |
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1.2 |
|
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1.16 |
$json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
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except being faster. |
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=item $perl_scalar = from_json $json_text |
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1.2 |
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The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to |
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1.16 |
parse that as an UTF-8 encoded JSON text, returning the resulting simple |
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1.2 |
scalar or reference. Croaks on error. |
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1.16 |
This function call is functionally identical to: |
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$perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
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except being faster. |
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1.2 |
|
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1.43 |
=item $is_boolean = JSON::XS::is_bool $scalar |
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Returns true if the passed scalar represents either JSON::XS::true or |
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JSON::XS::false, two constants that act like C<1> and C<0>, respectively |
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and are used to represent JSON C<true> and C<false> values in Perl. |
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See MAPPING, below, for more information on how JSON values are mapped to |
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Perl. |
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1.2 |
=back |
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1.23 |
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1.2 |
=head1 OBJECT-ORIENTED INTERFACE |
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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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=over 4 |
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=item $json = new JSON::XS |
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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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1.1 |
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1.2 |
The mutators for flags all return the JSON object again and thus calls can |
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be chained: |
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1.16 |
my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
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1.3 |
=> {"a": [1, 2]} |
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1.2 |
|
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1.7 |
=item $json = $json->ascii ([$enable]) |
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1.2 |
|
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1.16 |
If C<$enable> is true (or missing), then the C<encode> method will not |
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generate characters outside the code range C<0..127> (which is ASCII). Any |
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unicode characters outside that range will be escaped using either a |
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single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, |
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1.32 |
as per RFC4627. The resulting encoded JSON text can be treated as a native |
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unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string, |
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or any other superset of ASCII. |
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1.2 |
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If C<$enable> is false, then the C<encode> method will not escape Unicode |
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1.33 |
characters unless required by the JSON syntax or other flags. This results |
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in a faster and more compact format. |
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The main use for this flag is to produce JSON texts that can be |
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transmitted over a 7-bit channel, as the encoded JSON texts will not |
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contain any 8 bit characters. |
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1.2 |
|
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1.16 |
JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
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=> ["\ud801\udc01"] |
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1.3 |
|
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1.33 |
=item $json = $json->latin1 ([$enable]) |
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If C<$enable> is true (or missing), then the C<encode> method will encode |
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the resulting JSON text as latin1 (or iso-8859-1), escaping any characters |
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outside the code range C<0..255>. The resulting string can be treated as a |
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latin1-encoded JSON text or a native unicode string. The C<decode> method |
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will not be affected in any way by this flag, as C<decode> by default |
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expects unicode, which is a strict superset of latin1. |
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If C<$enable> is false, then the C<encode> method will not escape Unicode |
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characters unless required by the JSON syntax or other flags. |
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The main use for this flag is efficiently encoding binary data as JSON |
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text, as most octets will not be escaped, resulting in a smaller encoded |
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size. The disadvantage is that the resulting JSON text is encoded |
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in latin1 (and must correctly be treated as such when storing and |
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transfering), a rare encoding for JSON. It is therefore most useful when |
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you want to store data structures known to contain binary data efficiently |
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in files or databases, not when talking to other JSON encoders/decoders. |
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JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
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=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
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1.7 |
=item $json = $json->utf8 ([$enable]) |
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1.2 |
|
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1.7 |
If C<$enable> is true (or missing), then the C<encode> method will encode |
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1.16 |
the JSON result into UTF-8, as required by many protocols, while the |
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1.7 |
C<decode> method expects to be handled an UTF-8-encoded string. Please |
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note that UTF-8-encoded strings do not contain any characters outside the |
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1.16 |
range C<0..255>, they are thus useful for bytewise/binary I/O. In future |
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versions, enabling this option might enable autodetection of the UTF-16 |
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and UTF-32 encoding families, as described in RFC4627. |
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1.2 |
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If C<$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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1.16 |
Example, output UTF-16BE-encoded JSON: |
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use Encode; |
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$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
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Example, decode UTF-32LE-encoded JSON: |
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use Encode; |
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$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); |
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1.12 |
|
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1.7 |
=item $json = $json->pretty ([$enable]) |
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1.2 |
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This enables (or disables) all of the C<indent>, C<space_before> and |
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1.3 |
C<space_after> (and in the future possibly more) flags in one call to |
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1.2 |
generate the most readable (or most compact) form possible. |
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1.12 |
Example, pretty-print some simple structure: |
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1.3 |
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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1.7 |
=item $json = $json->indent ([$enable]) |
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1.2 |
|
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1.7 |
If C<$enable> is true (or missing), then the C<encode> method will use a multiline |
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1.2 |
format as output, putting every array member or object/hash key-value pair |
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into its own line, identing them properly. |
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If C<$enable> is false, no newlines or indenting will be produced, and the |
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1.16 |
resulting JSON text is guarenteed not to contain any C<newlines>. |
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1.2 |
|
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1.16 |
This setting has no effect when decoding JSON texts. |
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1.2 |
|
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1.7 |
=item $json = $json->space_before ([$enable]) |
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1.2 |
|
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1.7 |
If C<$enable> is true (or missing), then the C<encode> method will add an extra |
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1.2 |
optional space before the C<:> separating keys from values in JSON objects. |
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If C<$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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1.16 |
This setting has no effect when decoding JSON texts. You will also |
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most likely combine this setting with C<space_after>. |
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1.2 |
|
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1.12 |
Example, space_before enabled, space_after and indent disabled: |
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{"key" :"value"} |
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1.7 |
=item $json = $json->space_after ([$enable]) |
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1.2 |
|
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1.7 |
If C<$enable> is true (or missing), then the C<encode> method will add an extra |
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1.2 |
optional space after the C<:> separating keys from values in JSON objects |
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and extra whitespace after the C<,> separating key-value pairs and array |
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members. |
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If C<$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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1.16 |
This setting has no effect when decoding JSON texts. |
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1.2 |
|
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1.12 |
Example, space_before and indent disabled, space_after enabled: |
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{"key": "value"} |
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1.7 |
=item $json = $json->canonical ([$enable]) |
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1.2 |
|
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1.7 |
If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
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1.2 |
by sorting their keys. This is adding a comparatively high overhead. |
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If C<$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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This option is useful if you want the same data structure to be encoded as |
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1.16 |
the same JSON text (given the same overall settings). If it is disabled, |
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1.2 |
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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1.16 |
This setting has no effect when decoding JSON texts. |
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1.2 |
|
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1.7 |
=item $json = $json->allow_nonref ([$enable]) |
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1.3 |
|
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1.7 |
If C<$enable> is true (or missing), then the C<encode> method can convert a |
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1.3 |
non-reference into its corresponding string, number or null JSON value, |
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which is an extension to RFC4627. Likewise, C<decode> will accept those JSON |
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values instead of croaking. |
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If C<$enable> is false, then the C<encode> method will croak if it isn't |
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1.16 |
passed an arrayref or hashref, as JSON texts must either be an object |
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1.3 |
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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1.12 |
Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, |
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resulting in an invalid JSON text: |
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JSON::XS->new->allow_nonref->encode ("Hello, World!") |
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=> "Hello, World!" |
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1.44 |
=item $json = $json->allow_blessed ([$enable]) |
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If C<$enable> is true (or missing), then the C<encode> method will not |
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barf when it encounters a blessed reference. Instead, the value of the |
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B<convert_blessed> option will decide wether C<null> (C<convert_blessed> |
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disabled or no C<to_json> method found) or a representation of the |
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object (C<convert_blessed> enabled and C<to_json> method found) is being |
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encoded. Has no effect on C<decode>. |
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If C<$enable> is false (the default), then C<encode> will throw an |
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exception when it encounters a blessed object. |
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=item $json = $json->convert_blessed ([$enable]) |
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If C<$enable> is true (or missing), then C<encode>, upon encountering a |
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blessed object, will check for the availability of the C<TO_JSON> method |
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on the object's class. If found, it will be called in scalar context |
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and the resulting scalar will be encoded instead of the object. If no |
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C<TO_JSON> method is found, the value of C<allow_blessed> will decide what |
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to do. |
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The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> |
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returns other blessed objects, those will be handled in the same |
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way. C<TO_JSON> must take care of not causing an endless recursion cycle |
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(== crash) in this case. The name of C<TO_JSON> was chosen because other |
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methods called by the Perl core (== not the user of the object) are |
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usually in upper case letters and to avoid collisions with the C<to_json> |
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function. |
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|
If C<$enable> is false, then the C<allow_blessed> setting will decide what |
351 |
|
|
to do when a blessed object is found. |
352 |
|
|
|
353 |
root |
1.7 |
=item $json = $json->shrink ([$enable]) |
354 |
|
|
|
355 |
|
|
Perl usually over-allocates memory a bit when allocating space for |
356 |
root |
1.24 |
strings. This flag optionally resizes strings generated by either |
357 |
root |
1.7 |
C<encode> or C<decode> to their minimum size possible. This can save |
358 |
root |
1.16 |
memory when your JSON texts are either very very long or you have many |
359 |
root |
1.8 |
short strings. It will also try to downgrade any strings to octet-form |
360 |
|
|
if possible: perl stores strings internally either in an encoding called |
361 |
|
|
UTF-X or in octet-form. The latter cannot store everything but uses less |
362 |
root |
1.24 |
space in general (and some buggy Perl or C code might even rely on that |
363 |
|
|
internal representation being used). |
364 |
root |
1.7 |
|
365 |
root |
1.24 |
The actual definition of what shrink does might change in future versions, |
366 |
|
|
but it will always try to save space at the expense of time. |
367 |
|
|
|
368 |
|
|
If C<$enable> is true (or missing), the string returned by C<encode> will |
369 |
|
|
be shrunk-to-fit, while all strings generated by C<decode> will also be |
370 |
|
|
shrunk-to-fit. |
371 |
root |
1.7 |
|
372 |
|
|
If C<$enable> is false, then the normal perl allocation algorithms are used. |
373 |
|
|
If you work with your data, then this is likely to be faster. |
374 |
|
|
|
375 |
|
|
In the future, this setting might control other things, such as converting |
376 |
|
|
strings that look like integers or floats into integers or floats |
377 |
|
|
internally (there is no difference on the Perl level), saving space. |
378 |
|
|
|
379 |
root |
1.23 |
=item $json = $json->max_depth ([$maximum_nesting_depth]) |
380 |
|
|
|
381 |
root |
1.28 |
Sets the maximum nesting level (default C<512>) accepted while encoding |
382 |
root |
1.23 |
or decoding. If the JSON text or Perl data structure has an equal or |
383 |
|
|
higher nesting level then this limit, then the encoder and decoder will |
384 |
|
|
stop and croak at that point. |
385 |
|
|
|
386 |
|
|
Nesting level is defined by number of hash- or arrayrefs that the encoder |
387 |
|
|
needs to traverse to reach a given point or the number of C<{> or C<[> |
388 |
|
|
characters without their matching closing parenthesis crossed to reach a |
389 |
|
|
given character in a string. |
390 |
|
|
|
391 |
|
|
Setting the maximum depth to one disallows any nesting, so that ensures |
392 |
|
|
that the object is only a single hash/object or array. |
393 |
|
|
|
394 |
|
|
The argument to C<max_depth> will be rounded up to the next nearest power |
395 |
|
|
of two. |
396 |
|
|
|
397 |
|
|
See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
398 |
|
|
|
399 |
root |
1.16 |
=item $json_text = $json->encode ($perl_scalar) |
400 |
root |
1.2 |
|
401 |
|
|
Converts the given Perl data structure (a simple scalar or a reference |
402 |
|
|
to a hash or array) to its JSON representation. Simple scalars will be |
403 |
|
|
converted into JSON string or number sequences, while references to arrays |
404 |
|
|
become JSON arrays and references to hashes become JSON objects. Undefined |
405 |
|
|
Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
406 |
|
|
nor C<false> values will be generated. |
407 |
root |
1.1 |
|
408 |
root |
1.16 |
=item $perl_scalar = $json->decode ($json_text) |
409 |
root |
1.1 |
|
410 |
root |
1.16 |
The opposite of C<encode>: expects a JSON text and tries to parse it, |
411 |
root |
1.2 |
returning the resulting simple scalar or reference. Croaks on error. |
412 |
root |
1.1 |
|
413 |
root |
1.2 |
JSON numbers and strings become simple Perl scalars. JSON arrays become |
414 |
|
|
Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
415 |
|
|
C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
416 |
root |
1.1 |
|
417 |
root |
1.34 |
=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
418 |
|
|
|
419 |
|
|
This works like the C<decode> method, but instead of raising an exception |
420 |
|
|
when there is trailing garbage after the first JSON object, it will |
421 |
|
|
silently stop parsing there and return the number of characters consumed |
422 |
|
|
so far. |
423 |
|
|
|
424 |
|
|
This is useful if your JSON texts are not delimited by an outer protocol |
425 |
|
|
(which is not the brightest thing to do in the first place) and you need |
426 |
|
|
to know where the JSON text ends. |
427 |
|
|
|
428 |
|
|
JSON::XS->new->decode_prefix ("[1] the tail") |
429 |
|
|
=> ([], 3) |
430 |
|
|
|
431 |
root |
1.1 |
=back |
432 |
|
|
|
433 |
root |
1.23 |
|
434 |
root |
1.10 |
=head1 MAPPING |
435 |
|
|
|
436 |
|
|
This section describes how JSON::XS maps Perl values to JSON values and |
437 |
|
|
vice versa. These mappings are designed to "do the right thing" in most |
438 |
|
|
circumstances automatically, preserving round-tripping characteristics |
439 |
|
|
(what you put in comes out as something equivalent). |
440 |
|
|
|
441 |
|
|
For the more enlightened: note that in the following descriptions, |
442 |
|
|
lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> |
443 |
|
|
refers to the abstract Perl language itself. |
444 |
|
|
|
445 |
root |
1.39 |
|
446 |
root |
1.10 |
=head2 JSON -> PERL |
447 |
|
|
|
448 |
|
|
=over 4 |
449 |
|
|
|
450 |
|
|
=item object |
451 |
|
|
|
452 |
|
|
A JSON object becomes a reference to a hash in Perl. No ordering of object |
453 |
root |
1.14 |
keys is preserved (JSON does not preserver object key ordering itself). |
454 |
root |
1.10 |
|
455 |
|
|
=item array |
456 |
|
|
|
457 |
|
|
A JSON array becomes a reference to an array in Perl. |
458 |
|
|
|
459 |
|
|
=item string |
460 |
|
|
|
461 |
|
|
A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON |
462 |
|
|
are represented by the same codepoints in the Perl string, so no manual |
463 |
|
|
decoding is necessary. |
464 |
|
|
|
465 |
|
|
=item number |
466 |
|
|
|
467 |
|
|
A JSON number becomes either an integer or numeric (floating point) |
468 |
|
|
scalar in perl, depending on its range and any fractional parts. On the |
469 |
|
|
Perl level, there is no difference between those as Perl handles all the |
470 |
|
|
conversion details, but an integer may take slightly less memory and might |
471 |
|
|
represent more values exactly than (floating point) numbers. |
472 |
|
|
|
473 |
|
|
=item true, false |
474 |
|
|
|
475 |
root |
1.43 |
These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
476 |
|
|
respectively. They are overloaded to act almost exactly like the numbers |
477 |
|
|
C<1> and C<0>. You can check wether a scalar is a JSON boolean by using |
478 |
|
|
the C<JSON::XS::is_bool> function. |
479 |
root |
1.10 |
|
480 |
|
|
=item null |
481 |
|
|
|
482 |
|
|
A JSON null atom becomes C<undef> in Perl. |
483 |
|
|
|
484 |
|
|
=back |
485 |
|
|
|
486 |
root |
1.39 |
|
487 |
root |
1.10 |
=head2 PERL -> JSON |
488 |
|
|
|
489 |
|
|
The mapping from Perl to JSON is slightly more difficult, as Perl is a |
490 |
|
|
truly typeless language, so we can only guess which JSON type is meant by |
491 |
|
|
a Perl value. |
492 |
|
|
|
493 |
|
|
=over 4 |
494 |
|
|
|
495 |
|
|
=item hash references |
496 |
|
|
|
497 |
|
|
Perl hash references become JSON objects. As there is no inherent ordering |
498 |
root |
1.25 |
in hash keys (or JSON objects), they will usually be encoded in a |
499 |
|
|
pseudo-random order that can change between runs of the same program but |
500 |
|
|
stays generally the same within a single run of a program. JSON::XS can |
501 |
|
|
optionally sort the hash keys (determined by the I<canonical> flag), so |
502 |
|
|
the same datastructure will serialise to the same JSON text (given same |
503 |
|
|
settings and version of JSON::XS), but this incurs a runtime overhead |
504 |
|
|
and is only rarely useful, e.g. when you want to compare some JSON text |
505 |
|
|
against another for equality. |
506 |
root |
1.10 |
|
507 |
|
|
=item array references |
508 |
|
|
|
509 |
|
|
Perl array references become JSON arrays. |
510 |
|
|
|
511 |
root |
1.25 |
=item other references |
512 |
|
|
|
513 |
|
|
Other unblessed references are generally not allowed and will cause an |
514 |
|
|
exception to be thrown, except for references to the integers C<0> and |
515 |
|
|
C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
516 |
|
|
also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
517 |
|
|
|
518 |
|
|
to_json [\0,JSON::XS::true] # yields [false,true] |
519 |
|
|
|
520 |
root |
1.43 |
=item JSON::XS::true, JSON::XS::false |
521 |
|
|
|
522 |
|
|
These special values become JSON true and JSON false values, |
523 |
|
|
respectively. You cna alos use C<\1> and C<\0> directly if you want. |
524 |
|
|
|
525 |
root |
1.10 |
=item blessed objects |
526 |
|
|
|
527 |
|
|
Blessed objects are not allowed. JSON::XS currently tries to encode their |
528 |
|
|
underlying representation (hash- or arrayref), but this behaviour might |
529 |
|
|
change in future versions. |
530 |
|
|
|
531 |
|
|
=item simple scalars |
532 |
|
|
|
533 |
|
|
Simple Perl scalars (any scalar that is not a reference) are the most |
534 |
|
|
difficult objects to encode: JSON::XS will encode undefined scalars as |
535 |
|
|
JSON null value, scalars that have last been used in a string context |
536 |
|
|
before encoding as JSON strings and anything else as number value: |
537 |
|
|
|
538 |
|
|
# dump as number |
539 |
|
|
to_json [2] # yields [2] |
540 |
|
|
to_json [-3.0e17] # yields [-3e+17] |
541 |
|
|
my $value = 5; to_json [$value] # yields [5] |
542 |
|
|
|
543 |
|
|
# used as string, so dump as string |
544 |
|
|
print $value; |
545 |
|
|
to_json [$value] # yields ["5"] |
546 |
|
|
|
547 |
|
|
# undef becomes null |
548 |
|
|
to_json [undef] # yields [null] |
549 |
|
|
|
550 |
|
|
You can force the type to be a string by stringifying it: |
551 |
|
|
|
552 |
|
|
my $x = 3.1; # some variable containing a number |
553 |
|
|
"$x"; # stringified |
554 |
|
|
$x .= ""; # another, more awkward way to stringify |
555 |
|
|
print $x; # perl does it for you, too, quite often |
556 |
|
|
|
557 |
|
|
You can force the type to be a number by numifying it: |
558 |
|
|
|
559 |
|
|
my $x = "3"; # some variable containing a string |
560 |
|
|
$x += 0; # numify it, ensuring it will be dumped as a number |
561 |
|
|
$x *= 1; # same thing, the choise is yours. |
562 |
|
|
|
563 |
|
|
You can not currently output JSON booleans or force the type in other, |
564 |
|
|
less obscure, ways. Tell me if you need this capability. |
565 |
|
|
|
566 |
|
|
=back |
567 |
|
|
|
568 |
root |
1.23 |
|
569 |
root |
1.3 |
=head1 COMPARISON |
570 |
|
|
|
571 |
|
|
As already mentioned, this module was created because none of the existing |
572 |
|
|
JSON modules could be made to work correctly. First I will describe the |
573 |
|
|
problems (or pleasures) I encountered with various existing JSON modules, |
574 |
root |
1.4 |
followed by some benchmark values. JSON::XS was designed not to suffer |
575 |
|
|
from any of these problems or limitations. |
576 |
root |
1.3 |
|
577 |
|
|
=over 4 |
578 |
|
|
|
579 |
root |
1.5 |
=item JSON 1.07 |
580 |
root |
1.3 |
|
581 |
|
|
Slow (but very portable, as it is written in pure Perl). |
582 |
|
|
|
583 |
|
|
Undocumented/buggy Unicode handling (how JSON handles unicode values is |
584 |
|
|
undocumented. One can get far by feeding it unicode strings and doing |
585 |
|
|
en-/decoding oneself, but unicode escapes are not working properly). |
586 |
|
|
|
587 |
|
|
No roundtripping (strings get clobbered if they look like numbers, e.g. |
588 |
|
|
the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will |
589 |
|
|
decode into the number 2. |
590 |
|
|
|
591 |
root |
1.5 |
=item JSON::PC 0.01 |
592 |
root |
1.3 |
|
593 |
|
|
Very fast. |
594 |
|
|
|
595 |
|
|
Undocumented/buggy Unicode handling. |
596 |
|
|
|
597 |
|
|
No roundtripping. |
598 |
|
|
|
599 |
root |
1.4 |
Has problems handling many Perl values (e.g. regex results and other magic |
600 |
|
|
values will make it croak). |
601 |
root |
1.3 |
|
602 |
|
|
Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
603 |
root |
1.16 |
which is not a valid JSON text. |
604 |
root |
1.3 |
|
605 |
|
|
Unmaintained (maintainer unresponsive for many months, bugs are not |
606 |
|
|
getting fixed). |
607 |
|
|
|
608 |
root |
1.5 |
=item JSON::Syck 0.21 |
609 |
root |
1.3 |
|
610 |
|
|
Very buggy (often crashes). |
611 |
|
|
|
612 |
root |
1.4 |
Very inflexible (no human-readable format supported, format pretty much |
613 |
|
|
undocumented. I need at least a format for easy reading by humans and a |
614 |
|
|
single-line compact format for use in a protocol, and preferably a way to |
615 |
root |
1.16 |
generate ASCII-only JSON texts). |
616 |
root |
1.3 |
|
617 |
|
|
Completely broken (and confusingly documented) Unicode handling (unicode |
618 |
|
|
escapes are not working properly, you need to set ImplicitUnicode to |
619 |
|
|
I<different> values on en- and decoding to get symmetric behaviour). |
620 |
|
|
|
621 |
|
|
No roundtripping (simple cases work, but this depends on wether the scalar |
622 |
|
|
value was used in a numeric context or not). |
623 |
|
|
|
624 |
|
|
Dumping hashes may skip hash values depending on iterator state. |
625 |
|
|
|
626 |
|
|
Unmaintained (maintainer unresponsive for many months, bugs are not |
627 |
|
|
getting fixed). |
628 |
|
|
|
629 |
|
|
Does not check input for validity (i.e. will accept non-JSON input and |
630 |
|
|
return "something" instead of raising an exception. This is a security |
631 |
|
|
issue: imagine two banks transfering money between each other using |
632 |
|
|
JSON. One bank might parse a given non-JSON request and deduct money, |
633 |
|
|
while the other might reject the transaction with a syntax error. While a |
634 |
|
|
good protocol will at least recover, that is extra unnecessary work and |
635 |
|
|
the transaction will still not succeed). |
636 |
|
|
|
637 |
root |
1.5 |
=item JSON::DWIW 0.04 |
638 |
root |
1.3 |
|
639 |
|
|
Very fast. Very natural. Very nice. |
640 |
|
|
|
641 |
|
|
Undocumented unicode handling (but the best of the pack. Unicode escapes |
642 |
|
|
still don't get parsed properly). |
643 |
|
|
|
644 |
|
|
Very inflexible. |
645 |
|
|
|
646 |
|
|
No roundtripping. |
647 |
|
|
|
648 |
root |
1.16 |
Does not generate valid JSON texts (key strings are often unquoted, empty keys |
649 |
root |
1.4 |
result in nothing being output) |
650 |
|
|
|
651 |
root |
1.3 |
Does not check input for validity. |
652 |
|
|
|
653 |
|
|
=back |
654 |
|
|
|
655 |
root |
1.39 |
|
656 |
|
|
=head2 JSON and YAML |
657 |
|
|
|
658 |
|
|
You often hear that JSON is a subset (or a close subset) of YAML. This is, |
659 |
|
|
however, a mass hysteria and very far from the truth. In general, there is |
660 |
|
|
no way to configure JSON::XS to output a data structure as valid YAML. |
661 |
|
|
|
662 |
root |
1.41 |
If you really must use JSON::XS to generate YAML, you should use this |
663 |
root |
1.39 |
algorithm (subject to change in future versions): |
664 |
|
|
|
665 |
|
|
my $to_yaml = JSON::XS->new->utf8->space_after (1); |
666 |
|
|
my $yaml = $to_yaml->encode ($ref) . "\n"; |
667 |
|
|
|
668 |
|
|
This will usually generate JSON texts that also parse as valid |
669 |
root |
1.41 |
YAML. Please note that YAML has hardcoded limits on (simple) object key |
670 |
|
|
lengths that JSON doesn't have, so you should make sure that your hash |
671 |
|
|
keys are noticably shorter than the 1024 characters YAML allows. |
672 |
root |
1.39 |
|
673 |
|
|
There might be other incompatibilities that I am not aware of. In general |
674 |
|
|
you should not try to generate YAML with a JSON generator or vice versa, |
675 |
root |
1.41 |
or try to parse JSON with a YAML parser or vice versa: chances are high |
676 |
|
|
that you will run into severe interoperability problems. |
677 |
root |
1.39 |
|
678 |
|
|
|
679 |
root |
1.3 |
=head2 SPEED |
680 |
|
|
|
681 |
root |
1.4 |
It seems that JSON::XS is surprisingly fast, as shown in the following |
682 |
|
|
tables. They have been generated with the help of the C<eg/bench> program |
683 |
|
|
in the JSON::XS distribution, to make it easy to compare on your own |
684 |
|
|
system. |
685 |
|
|
|
686 |
root |
1.37 |
First comes a comparison between various modules using a very short |
687 |
|
|
single-line JSON string: |
688 |
root |
1.18 |
|
689 |
root |
1.37 |
{"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
690 |
root |
1.38 |
"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
691 |
root |
1.18 |
|
692 |
root |
1.39 |
It shows the number of encodes/decodes per second (JSON::XS uses |
693 |
|
|
the functional interface, while JSON::XS/2 uses the OO interface |
694 |
|
|
with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables |
695 |
|
|
shrink). Higher is better: |
696 |
root |
1.4 |
|
697 |
|
|
module | encode | decode | |
698 |
|
|
-----------|------------|------------| |
699 |
root |
1.38 |
JSON | 7645.468 | 4208.613 | |
700 |
root |
1.40 |
JSON::DWIW | 40721.398 | 77101.176 | |
701 |
root |
1.38 |
JSON::PC | 65948.176 | 78251.940 | |
702 |
root |
1.40 |
JSON::Syck | 22844.793 | 26479.192 | |
703 |
root |
1.38 |
JSON::XS | 388361.481 | 199728.762 | |
704 |
|
|
JSON::XS/2 | 218453.333 | 192399.266 | |
705 |
|
|
JSON::XS/3 | 338250.323 | 192399.266 | |
706 |
root |
1.40 |
Storable | 15779.925 | 14169.946 | |
707 |
root |
1.4 |
-----------+------------+------------+ |
708 |
|
|
|
709 |
root |
1.37 |
That is, JSON::XS is about five times faster than JSON::DWIW on encoding, |
710 |
root |
1.38 |
about three times faster on decoding, and over fourty times faster |
711 |
root |
1.37 |
than JSON, even with pretty-printing and key sorting. It also compares |
712 |
|
|
favourably to Storable for small amounts of data. |
713 |
root |
1.4 |
|
714 |
root |
1.13 |
Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
715 |
root |
1.4 |
search API (http://nanoref.com/yahooapis/mgPdGg): |
716 |
|
|
|
717 |
|
|
module | encode | decode | |
718 |
|
|
-----------|------------|------------| |
719 |
root |
1.37 |
JSON | 254.685 | 37.665 | |
720 |
root |
1.40 |
JSON::DWIW | 843.343 | 1049.731 | |
721 |
root |
1.37 |
JSON::PC | 3602.116 | 2307.352 | |
722 |
root |
1.40 |
JSON::Syck | 505.107 | 787.899 | |
723 |
|
|
JSON::XS | 5747.196 | 3690.220 | |
724 |
|
|
JSON::XS/2 | 3968.121 | 3676.634 | |
725 |
|
|
JSON::XS/3 | 6105.246 | 3662.508 | |
726 |
|
|
Storable | 4417.337 | 5285.161 | |
727 |
root |
1.4 |
-----------+------------+------------+ |
728 |
|
|
|
729 |
root |
1.40 |
Again, JSON::XS leads by far (except for Storable which non-surprisingly |
730 |
|
|
decodes faster). |
731 |
root |
1.4 |
|
732 |
root |
1.18 |
On large strings containing lots of high unicode characters, some modules |
733 |
|
|
(such as JSON::PC) seem to decode faster than JSON::XS, but the result |
734 |
|
|
will be broken due to missing (or wrong) unicode handling. Others refuse |
735 |
|
|
to decode or encode properly, so it was impossible to prepare a fair |
736 |
|
|
comparison table for that case. |
737 |
root |
1.13 |
|
738 |
root |
1.11 |
|
739 |
root |
1.23 |
=head1 SECURITY CONSIDERATIONS |
740 |
|
|
|
741 |
|
|
When you are using JSON in a protocol, talking to untrusted potentially |
742 |
|
|
hostile creatures requires relatively few measures. |
743 |
|
|
|
744 |
|
|
First of all, your JSON decoder should be secure, that is, should not have |
745 |
|
|
any buffer overflows. Obviously, this module should ensure that and I am |
746 |
|
|
trying hard on making that true, but you never know. |
747 |
|
|
|
748 |
|
|
Second, you need to avoid resource-starving attacks. That means you should |
749 |
|
|
limit the size of JSON texts you accept, or make sure then when your |
750 |
|
|
resources run out, thats just fine (e.g. by using a separate process that |
751 |
|
|
can crash safely). The size of a JSON text in octets or characters is |
752 |
|
|
usually a good indication of the size of the resources required to decode |
753 |
|
|
it into a Perl structure. |
754 |
|
|
|
755 |
|
|
Third, JSON::XS recurses using the C stack when decoding objects and |
756 |
|
|
arrays. The C stack is a limited resource: for instance, on my amd64 |
757 |
root |
1.28 |
machine with 8MB of stack size I can decode around 180k nested arrays but |
758 |
|
|
only 14k nested JSON objects (due to perl itself recursing deeply on croak |
759 |
|
|
to free the temporary). If that is exceeded, the program crashes. to be |
760 |
|
|
conservative, the default nesting limit is set to 512. If your process |
761 |
|
|
has a smaller stack, you should adjust this setting accordingly with the |
762 |
|
|
C<max_depth> method. |
763 |
root |
1.23 |
|
764 |
|
|
And last but least, something else could bomb you that I forgot to think |
765 |
root |
1.30 |
of. In that case, you get to keep the pieces. I am always open for hints, |
766 |
root |
1.23 |
though... |
767 |
|
|
|
768 |
root |
1.42 |
If you are using JSON::XS to return packets to consumption |
769 |
|
|
by javascript scripts in a browser you should have a look at |
770 |
|
|
L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether |
771 |
|
|
you are vulnerable to some common attack vectors (which really are browser |
772 |
|
|
design bugs, but it is still you who will have to deal with it, as major |
773 |
|
|
browser developers care only for features, not about doing security |
774 |
|
|
right). |
775 |
|
|
|
776 |
root |
1.11 |
|
777 |
root |
1.4 |
=head1 BUGS |
778 |
|
|
|
779 |
|
|
While the goal of this module is to be correct, that unfortunately does |
780 |
|
|
not mean its bug-free, only that I think its design is bug-free. It is |
781 |
root |
1.23 |
still relatively early in its development. If you keep reporting bugs they |
782 |
|
|
will be fixed swiftly, though. |
783 |
root |
1.4 |
|
784 |
root |
1.2 |
=cut |
785 |
|
|
|
786 |
root |
1.43 |
our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; |
787 |
|
|
our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; |
788 |
|
|
|
789 |
|
|
sub true() { $true } |
790 |
|
|
sub false() { $false } |
791 |
|
|
|
792 |
|
|
sub is_bool($) { |
793 |
|
|
UNIVERSAL::isa $_[0], "JSON::XS::Boolean" |
794 |
root |
1.44 |
# or UNIVERSAL::isa $_[0], "JSON::Literal" |
795 |
root |
1.43 |
} |
796 |
|
|
|
797 |
|
|
XSLoader::load "JSON::XS", $VERSION; |
798 |
|
|
|
799 |
|
|
package JSON::XS::Boolean; |
800 |
|
|
|
801 |
|
|
use overload |
802 |
|
|
"0+" => sub { ${$_[0]} }, |
803 |
|
|
"++" => sub { $_[0] = ${$_[0]} + 1 }, |
804 |
|
|
"--" => sub { $_[0] = ${$_[0]} - 1 }, |
805 |
|
|
fallback => 1; |
806 |
root |
1.25 |
|
807 |
root |
1.2 |
1; |
808 |
|
|
|
809 |
root |
1.1 |
=head1 AUTHOR |
810 |
|
|
|
811 |
|
|
Marc Lehmann <schmorp@schmorp.de> |
812 |
|
|
http://home.schmorp.de/ |
813 |
|
|
|
814 |
|
|
=cut |
815 |
|
|
|