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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 $utf8_encoded_json_text; |
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1.22 |
# OO-interface |
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1.12 |
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$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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1.58 |
our $VERSION = '1.5'; |
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1.43 |
our @ISA = qw(Exporter); |
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1.1 |
|
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1.49 |
our @EXPORT = qw(to_json from_json); |
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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<$enable> is true (or missing), then the C<encode> method can convert a |
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1.3 |
non-reference into its corresponding string, number or null JSON value, |
303 |
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which is an extension to RFC4627. Likewise, C<decode> will accept those JSON |
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values instead of croaking. |
305 |
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If C<$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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|
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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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1.46 |
methods called by the Perl core (== not by the user of the object) are |
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1.44 |
usually in upper case letters and to avoid collisions with the C<to_json> |
344 |
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function. |
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|
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1.45 |
This setting does not yet influence C<decode> in any way, but in the |
347 |
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future, global hooks might get installed that influence C<decode> and are |
348 |
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enabled by this setting. |
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|
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root |
1.44 |
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 |
1.52 |
=item $json = $json->filter_json_object ([$coderef->($hashref)]) |
354 |
root |
1.51 |
|
355 |
|
|
When C<$coderef> is specified, it will be called from C<decode> each |
356 |
|
|
time it decodes a JSON object. The only argument is a reference to the |
357 |
|
|
newly-created hash. If the code references returns a single scalar (which |
358 |
|
|
need not be a reference), this value (i.e. a copy of that scalar to avoid |
359 |
|
|
aliasing) is inserted into the deserialised data structure. If it returns |
360 |
|
|
an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the |
361 |
|
|
original deserialised hash will be inserted. This setting can slow down |
362 |
|
|
decoding considerably. |
363 |
|
|
|
364 |
root |
1.52 |
When C<$coderef> is omitted or undefined, any existing callback will |
365 |
|
|
be removed and C<decode> will not change the deserialised hash in any |
366 |
|
|
way. |
367 |
root |
1.51 |
|
368 |
|
|
Example, convert all JSON objects into the integer 5: |
369 |
|
|
|
370 |
|
|
my $js = JSON::XS->new->filter_json_object (sub { 5 }); |
371 |
|
|
# returns [5] |
372 |
|
|
$js->decode ('[{}]') |
373 |
root |
1.52 |
# throw an exception because allow_nonref is not enabled |
374 |
|
|
# so a lone 5 is not allowed. |
375 |
root |
1.51 |
$js->decode ('{"a":1, "b":2}'); |
376 |
|
|
|
377 |
root |
1.52 |
=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)]) |
378 |
root |
1.51 |
|
379 |
root |
1.52 |
Works remotely similar to C<filter_json_object>, but is only called for |
380 |
|
|
JSON objects having a single key named C<$key>. |
381 |
root |
1.51 |
|
382 |
|
|
This C<$coderef> is called before the one specified via |
383 |
root |
1.52 |
C<filter_json_object>, if any. It gets passed the single value in the JSON |
384 |
|
|
object. If it returns a single value, it will be inserted into the data |
385 |
|
|
structure. If it returns nothing (not even C<undef> but the empty list), |
386 |
|
|
the callback from C<filter_json_object> will be called next, as if no |
387 |
|
|
single-key callback were specified. |
388 |
|
|
|
389 |
|
|
If C<$coderef> is omitted or undefined, the corresponding callback will be |
390 |
|
|
disabled. There can only ever be one callback for a given key. |
391 |
root |
1.51 |
|
392 |
|
|
As this callback gets called less often then the C<filter_json_object> |
393 |
|
|
one, decoding speed will not usually suffer as much. Therefore, single-key |
394 |
|
|
objects make excellent targets to serialise Perl objects into, especially |
395 |
|
|
as single-key JSON objects are as close to the type-tagged value concept |
396 |
|
|
as JSON gets (its basically an ID/VALUE tuple). Of course, JSON does not |
397 |
|
|
support this in any way, so you need to make sure your data never looks |
398 |
|
|
like a serialised Perl hash. |
399 |
|
|
|
400 |
|
|
Typical names for the single object key are C<__class_whatever__>, or |
401 |
|
|
C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even |
402 |
|
|
things like C<__class_md5sum(classname)__>, to reduce the risk of clashing |
403 |
|
|
with real hashes. |
404 |
|
|
|
405 |
|
|
Example, decode JSON objects of the form C<< { "__widget__" => <id> } >> |
406 |
|
|
into the corresponding C<< $WIDGET{<id>} >> object: |
407 |
|
|
|
408 |
|
|
# return whatever is in $WIDGET{5}: |
409 |
|
|
JSON::XS |
410 |
|
|
->new |
411 |
root |
1.52 |
->filter_json_single_key_object (__widget__ => sub { |
412 |
|
|
$WIDGET{ $_[0] } |
413 |
root |
1.51 |
}) |
414 |
|
|
->decode ('{"__widget__": 5') |
415 |
|
|
|
416 |
|
|
# this can be used with a TO_JSON method in some "widget" class |
417 |
|
|
# for serialisation to json: |
418 |
|
|
sub WidgetBase::TO_JSON { |
419 |
|
|
my ($self) = @_; |
420 |
|
|
|
421 |
|
|
unless ($self->{id}) { |
422 |
|
|
$self->{id} = ..get..some..id..; |
423 |
|
|
$WIDGET{$self->{id}} = $self; |
424 |
|
|
} |
425 |
|
|
|
426 |
|
|
{ __widget__ => $self->{id} } |
427 |
|
|
} |
428 |
|
|
|
429 |
root |
1.7 |
=item $json = $json->shrink ([$enable]) |
430 |
|
|
|
431 |
|
|
Perl usually over-allocates memory a bit when allocating space for |
432 |
root |
1.24 |
strings. This flag optionally resizes strings generated by either |
433 |
root |
1.7 |
C<encode> or C<decode> to their minimum size possible. This can save |
434 |
root |
1.16 |
memory when your JSON texts are either very very long or you have many |
435 |
root |
1.8 |
short strings. It will also try to downgrade any strings to octet-form |
436 |
|
|
if possible: perl stores strings internally either in an encoding called |
437 |
|
|
UTF-X or in octet-form. The latter cannot store everything but uses less |
438 |
root |
1.24 |
space in general (and some buggy Perl or C code might even rely on that |
439 |
|
|
internal representation being used). |
440 |
root |
1.7 |
|
441 |
root |
1.24 |
The actual definition of what shrink does might change in future versions, |
442 |
|
|
but it will always try to save space at the expense of time. |
443 |
|
|
|
444 |
|
|
If C<$enable> is true (or missing), the string returned by C<encode> will |
445 |
|
|
be shrunk-to-fit, while all strings generated by C<decode> will also be |
446 |
|
|
shrunk-to-fit. |
447 |
root |
1.7 |
|
448 |
|
|
If C<$enable> is false, then the normal perl allocation algorithms are used. |
449 |
|
|
If you work with your data, then this is likely to be faster. |
450 |
|
|
|
451 |
|
|
In the future, this setting might control other things, such as converting |
452 |
|
|
strings that look like integers or floats into integers or floats |
453 |
|
|
internally (there is no difference on the Perl level), saving space. |
454 |
|
|
|
455 |
root |
1.23 |
=item $json = $json->max_depth ([$maximum_nesting_depth]) |
456 |
|
|
|
457 |
root |
1.28 |
Sets the maximum nesting level (default C<512>) accepted while encoding |
458 |
root |
1.23 |
or decoding. If the JSON text or Perl data structure has an equal or |
459 |
|
|
higher nesting level then this limit, then the encoder and decoder will |
460 |
|
|
stop and croak at that point. |
461 |
|
|
|
462 |
|
|
Nesting level is defined by number of hash- or arrayrefs that the encoder |
463 |
|
|
needs to traverse to reach a given point or the number of C<{> or C<[> |
464 |
|
|
characters without their matching closing parenthesis crossed to reach a |
465 |
|
|
given character in a string. |
466 |
|
|
|
467 |
|
|
Setting the maximum depth to one disallows any nesting, so that ensures |
468 |
|
|
that the object is only a single hash/object or array. |
469 |
|
|
|
470 |
root |
1.47 |
The argument to C<max_depth> will be rounded up to the next highest power |
471 |
|
|
of two. If no argument is given, the highest possible setting will be |
472 |
|
|
used, which is rarely useful. |
473 |
|
|
|
474 |
|
|
See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
475 |
|
|
|
476 |
|
|
=item $json = $json->max_size ([$maximum_string_size]) |
477 |
|
|
|
478 |
|
|
Set the maximum length a JSON text may have (in bytes) where decoding is |
479 |
|
|
being attempted. The default is C<0>, meaning no limit. When C<decode> |
480 |
|
|
is called on a string longer then this number of characters it will not |
481 |
|
|
attempt to decode the string but throw an exception. This setting has no |
482 |
|
|
effect on C<encode> (yet). |
483 |
|
|
|
484 |
|
|
The argument to C<max_size> will be rounded up to the next B<highest> |
485 |
|
|
power of two (so may be more than requested). If no argument is given, the |
486 |
|
|
limit check will be deactivated (same as when C<0> is specified). |
487 |
root |
1.23 |
|
488 |
|
|
See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
489 |
|
|
|
490 |
root |
1.16 |
=item $json_text = $json->encode ($perl_scalar) |
491 |
root |
1.2 |
|
492 |
|
|
Converts the given Perl data structure (a simple scalar or a reference |
493 |
|
|
to a hash or array) to its JSON representation. Simple scalars will be |
494 |
|
|
converted into JSON string or number sequences, while references to arrays |
495 |
|
|
become JSON arrays and references to hashes become JSON objects. Undefined |
496 |
|
|
Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
497 |
|
|
nor C<false> values will be generated. |
498 |
root |
1.1 |
|
499 |
root |
1.16 |
=item $perl_scalar = $json->decode ($json_text) |
500 |
root |
1.1 |
|
501 |
root |
1.16 |
The opposite of C<encode>: expects a JSON text and tries to parse it, |
502 |
root |
1.2 |
returning the resulting simple scalar or reference. Croaks on error. |
503 |
root |
1.1 |
|
504 |
root |
1.2 |
JSON numbers and strings become simple Perl scalars. JSON arrays become |
505 |
|
|
Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
506 |
|
|
C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
507 |
root |
1.1 |
|
508 |
root |
1.34 |
=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
509 |
|
|
|
510 |
|
|
This works like the C<decode> method, but instead of raising an exception |
511 |
|
|
when there is trailing garbage after the first JSON object, it will |
512 |
|
|
silently stop parsing there and return the number of characters consumed |
513 |
|
|
so far. |
514 |
|
|
|
515 |
|
|
This is useful if your JSON texts are not delimited by an outer protocol |
516 |
|
|
(which is not the brightest thing to do in the first place) and you need |
517 |
|
|
to know where the JSON text ends. |
518 |
|
|
|
519 |
|
|
JSON::XS->new->decode_prefix ("[1] the tail") |
520 |
|
|
=> ([], 3) |
521 |
|
|
|
522 |
root |
1.1 |
=back |
523 |
|
|
|
524 |
root |
1.23 |
|
525 |
root |
1.10 |
=head1 MAPPING |
526 |
|
|
|
527 |
|
|
This section describes how JSON::XS maps Perl values to JSON values and |
528 |
|
|
vice versa. These mappings are designed to "do the right thing" in most |
529 |
|
|
circumstances automatically, preserving round-tripping characteristics |
530 |
|
|
(what you put in comes out as something equivalent). |
531 |
|
|
|
532 |
|
|
For the more enlightened: note that in the following descriptions, |
533 |
|
|
lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> |
534 |
|
|
refers to the abstract Perl language itself. |
535 |
|
|
|
536 |
root |
1.39 |
|
537 |
root |
1.10 |
=head2 JSON -> PERL |
538 |
|
|
|
539 |
|
|
=over 4 |
540 |
|
|
|
541 |
|
|
=item object |
542 |
|
|
|
543 |
|
|
A JSON object becomes a reference to a hash in Perl. No ordering of object |
544 |
root |
1.14 |
keys is preserved (JSON does not preserver object key ordering itself). |
545 |
root |
1.10 |
|
546 |
|
|
=item array |
547 |
|
|
|
548 |
|
|
A JSON array becomes a reference to an array in Perl. |
549 |
|
|
|
550 |
|
|
=item string |
551 |
|
|
|
552 |
|
|
A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON |
553 |
|
|
are represented by the same codepoints in the Perl string, so no manual |
554 |
|
|
decoding is necessary. |
555 |
|
|
|
556 |
|
|
=item number |
557 |
|
|
|
558 |
root |
1.56 |
A JSON number becomes either an integer, numeric (floating point) or |
559 |
|
|
string scalar in perl, depending on its range and any fractional parts. On |
560 |
|
|
the Perl level, there is no difference between those as Perl handles all |
561 |
|
|
the conversion details, but an integer may take slightly less memory and |
562 |
|
|
might represent more values exactly than (floating point) numbers. |
563 |
|
|
|
564 |
|
|
If the number consists of digits only, JSON::XS will try to represent |
565 |
|
|
it as an integer value. If that fails, it will try to represent it as |
566 |
|
|
a numeric (floating point) value if that is possible without loss of |
567 |
|
|
precision. Otherwise it will preserve the number as a string value. |
568 |
|
|
|
569 |
|
|
Numbers containing a fractional or exponential part will always be |
570 |
|
|
represented as numeric (floating point) values, possibly at a loss of |
571 |
|
|
precision. |
572 |
|
|
|
573 |
|
|
This might create round-tripping problems as numbers might become strings, |
574 |
|
|
but as Perl is typeless there is no other way to do it. |
575 |
root |
1.10 |
|
576 |
|
|
=item true, false |
577 |
|
|
|
578 |
root |
1.43 |
These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
579 |
|
|
respectively. They are overloaded to act almost exactly like the numbers |
580 |
|
|
C<1> and C<0>. You can check wether a scalar is a JSON boolean by using |
581 |
|
|
the C<JSON::XS::is_bool> function. |
582 |
root |
1.10 |
|
583 |
|
|
=item null |
584 |
|
|
|
585 |
|
|
A JSON null atom becomes C<undef> in Perl. |
586 |
|
|
|
587 |
|
|
=back |
588 |
|
|
|
589 |
root |
1.39 |
|
590 |
root |
1.10 |
=head2 PERL -> JSON |
591 |
|
|
|
592 |
|
|
The mapping from Perl to JSON is slightly more difficult, as Perl is a |
593 |
|
|
truly typeless language, so we can only guess which JSON type is meant by |
594 |
|
|
a Perl value. |
595 |
|
|
|
596 |
|
|
=over 4 |
597 |
|
|
|
598 |
|
|
=item hash references |
599 |
|
|
|
600 |
|
|
Perl hash references become JSON objects. As there is no inherent ordering |
601 |
root |
1.25 |
in hash keys (or JSON objects), they will usually be encoded in a |
602 |
|
|
pseudo-random order that can change between runs of the same program but |
603 |
|
|
stays generally the same within a single run of a program. JSON::XS can |
604 |
|
|
optionally sort the hash keys (determined by the I<canonical> flag), so |
605 |
|
|
the same datastructure will serialise to the same JSON text (given same |
606 |
|
|
settings and version of JSON::XS), but this incurs a runtime overhead |
607 |
|
|
and is only rarely useful, e.g. when you want to compare some JSON text |
608 |
|
|
against another for equality. |
609 |
root |
1.10 |
|
610 |
|
|
=item array references |
611 |
|
|
|
612 |
|
|
Perl array references become JSON arrays. |
613 |
|
|
|
614 |
root |
1.25 |
=item other references |
615 |
|
|
|
616 |
|
|
Other unblessed references are generally not allowed and will cause an |
617 |
|
|
exception to be thrown, except for references to the integers C<0> and |
618 |
|
|
C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
619 |
|
|
also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
620 |
|
|
|
621 |
|
|
to_json [\0,JSON::XS::true] # yields [false,true] |
622 |
|
|
|
623 |
root |
1.43 |
=item JSON::XS::true, JSON::XS::false |
624 |
|
|
|
625 |
|
|
These special values become JSON true and JSON false values, |
626 |
|
|
respectively. You cna alos use C<\1> and C<\0> directly if you want. |
627 |
|
|
|
628 |
root |
1.10 |
=item blessed objects |
629 |
|
|
|
630 |
|
|
Blessed objects are not allowed. JSON::XS currently tries to encode their |
631 |
|
|
underlying representation (hash- or arrayref), but this behaviour might |
632 |
|
|
change in future versions. |
633 |
|
|
|
634 |
|
|
=item simple scalars |
635 |
|
|
|
636 |
|
|
Simple Perl scalars (any scalar that is not a reference) are the most |
637 |
|
|
difficult objects to encode: JSON::XS will encode undefined scalars as |
638 |
|
|
JSON null value, scalars that have last been used in a string context |
639 |
|
|
before encoding as JSON strings and anything else as number value: |
640 |
|
|
|
641 |
|
|
# dump as number |
642 |
|
|
to_json [2] # yields [2] |
643 |
|
|
to_json [-3.0e17] # yields [-3e+17] |
644 |
|
|
my $value = 5; to_json [$value] # yields [5] |
645 |
|
|
|
646 |
|
|
# used as string, so dump as string |
647 |
|
|
print $value; |
648 |
|
|
to_json [$value] # yields ["5"] |
649 |
|
|
|
650 |
|
|
# undef becomes null |
651 |
|
|
to_json [undef] # yields [null] |
652 |
|
|
|
653 |
|
|
You can force the type to be a string by stringifying it: |
654 |
|
|
|
655 |
|
|
my $x = 3.1; # some variable containing a number |
656 |
|
|
"$x"; # stringified |
657 |
|
|
$x .= ""; # another, more awkward way to stringify |
658 |
|
|
print $x; # perl does it for you, too, quite often |
659 |
|
|
|
660 |
|
|
You can force the type to be a number by numifying it: |
661 |
|
|
|
662 |
|
|
my $x = "3"; # some variable containing a string |
663 |
|
|
$x += 0; # numify it, ensuring it will be dumped as a number |
664 |
|
|
$x *= 1; # same thing, the choise is yours. |
665 |
|
|
|
666 |
|
|
You can not currently output JSON booleans or force the type in other, |
667 |
|
|
less obscure, ways. Tell me if you need this capability. |
668 |
|
|
|
669 |
|
|
=back |
670 |
|
|
|
671 |
root |
1.23 |
|
672 |
root |
1.3 |
=head1 COMPARISON |
673 |
|
|
|
674 |
|
|
As already mentioned, this module was created because none of the existing |
675 |
|
|
JSON modules could be made to work correctly. First I will describe the |
676 |
|
|
problems (or pleasures) I encountered with various existing JSON modules, |
677 |
root |
1.4 |
followed by some benchmark values. JSON::XS was designed not to suffer |
678 |
|
|
from any of these problems or limitations. |
679 |
root |
1.3 |
|
680 |
|
|
=over 4 |
681 |
|
|
|
682 |
root |
1.5 |
=item JSON 1.07 |
683 |
root |
1.3 |
|
684 |
|
|
Slow (but very portable, as it is written in pure Perl). |
685 |
|
|
|
686 |
|
|
Undocumented/buggy Unicode handling (how JSON handles unicode values is |
687 |
|
|
undocumented. One can get far by feeding it unicode strings and doing |
688 |
|
|
en-/decoding oneself, but unicode escapes are not working properly). |
689 |
|
|
|
690 |
|
|
No roundtripping (strings get clobbered if they look like numbers, e.g. |
691 |
|
|
the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will |
692 |
|
|
decode into the number 2. |
693 |
|
|
|
694 |
root |
1.5 |
=item JSON::PC 0.01 |
695 |
root |
1.3 |
|
696 |
|
|
Very fast. |
697 |
|
|
|
698 |
|
|
Undocumented/buggy Unicode handling. |
699 |
|
|
|
700 |
|
|
No roundtripping. |
701 |
|
|
|
702 |
root |
1.4 |
Has problems handling many Perl values (e.g. regex results and other magic |
703 |
|
|
values will make it croak). |
704 |
root |
1.3 |
|
705 |
|
|
Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
706 |
root |
1.16 |
which is not a valid JSON text. |
707 |
root |
1.3 |
|
708 |
|
|
Unmaintained (maintainer unresponsive for many months, bugs are not |
709 |
|
|
getting fixed). |
710 |
|
|
|
711 |
root |
1.5 |
=item JSON::Syck 0.21 |
712 |
root |
1.3 |
|
713 |
|
|
Very buggy (often crashes). |
714 |
|
|
|
715 |
root |
1.4 |
Very inflexible (no human-readable format supported, format pretty much |
716 |
|
|
undocumented. I need at least a format for easy reading by humans and a |
717 |
|
|
single-line compact format for use in a protocol, and preferably a way to |
718 |
root |
1.16 |
generate ASCII-only JSON texts). |
719 |
root |
1.3 |
|
720 |
|
|
Completely broken (and confusingly documented) Unicode handling (unicode |
721 |
|
|
escapes are not working properly, you need to set ImplicitUnicode to |
722 |
|
|
I<different> values on en- and decoding to get symmetric behaviour). |
723 |
|
|
|
724 |
|
|
No roundtripping (simple cases work, but this depends on wether the scalar |
725 |
|
|
value was used in a numeric context or not). |
726 |
|
|
|
727 |
|
|
Dumping hashes may skip hash values depending on iterator state. |
728 |
|
|
|
729 |
|
|
Unmaintained (maintainer unresponsive for many months, bugs are not |
730 |
|
|
getting fixed). |
731 |
|
|
|
732 |
|
|
Does not check input for validity (i.e. will accept non-JSON input and |
733 |
|
|
return "something" instead of raising an exception. This is a security |
734 |
|
|
issue: imagine two banks transfering money between each other using |
735 |
|
|
JSON. One bank might parse a given non-JSON request and deduct money, |
736 |
|
|
while the other might reject the transaction with a syntax error. While a |
737 |
|
|
good protocol will at least recover, that is extra unnecessary work and |
738 |
|
|
the transaction will still not succeed). |
739 |
|
|
|
740 |
root |
1.5 |
=item JSON::DWIW 0.04 |
741 |
root |
1.3 |
|
742 |
|
|
Very fast. Very natural. Very nice. |
743 |
|
|
|
744 |
|
|
Undocumented unicode handling (but the best of the pack. Unicode escapes |
745 |
|
|
still don't get parsed properly). |
746 |
|
|
|
747 |
|
|
Very inflexible. |
748 |
|
|
|
749 |
|
|
No roundtripping. |
750 |
|
|
|
751 |
root |
1.16 |
Does not generate valid JSON texts (key strings are often unquoted, empty keys |
752 |
root |
1.4 |
result in nothing being output) |
753 |
|
|
|
754 |
root |
1.3 |
Does not check input for validity. |
755 |
|
|
|
756 |
|
|
=back |
757 |
|
|
|
758 |
root |
1.39 |
|
759 |
|
|
=head2 JSON and YAML |
760 |
|
|
|
761 |
|
|
You often hear that JSON is a subset (or a close subset) of YAML. This is, |
762 |
|
|
however, a mass hysteria and very far from the truth. In general, there is |
763 |
|
|
no way to configure JSON::XS to output a data structure as valid YAML. |
764 |
|
|
|
765 |
root |
1.41 |
If you really must use JSON::XS to generate YAML, you should use this |
766 |
root |
1.39 |
algorithm (subject to change in future versions): |
767 |
|
|
|
768 |
|
|
my $to_yaml = JSON::XS->new->utf8->space_after (1); |
769 |
|
|
my $yaml = $to_yaml->encode ($ref) . "\n"; |
770 |
|
|
|
771 |
|
|
This will usually generate JSON texts that also parse as valid |
772 |
root |
1.41 |
YAML. Please note that YAML has hardcoded limits on (simple) object key |
773 |
|
|
lengths that JSON doesn't have, so you should make sure that your hash |
774 |
|
|
keys are noticably shorter than the 1024 characters YAML allows. |
775 |
root |
1.39 |
|
776 |
|
|
There might be other incompatibilities that I am not aware of. In general |
777 |
|
|
you should not try to generate YAML with a JSON generator or vice versa, |
778 |
root |
1.41 |
or try to parse JSON with a YAML parser or vice versa: chances are high |
779 |
|
|
that you will run into severe interoperability problems. |
780 |
root |
1.39 |
|
781 |
|
|
|
782 |
root |
1.3 |
=head2 SPEED |
783 |
|
|
|
784 |
root |
1.4 |
It seems that JSON::XS is surprisingly fast, as shown in the following |
785 |
|
|
tables. They have been generated with the help of the C<eg/bench> program |
786 |
|
|
in the JSON::XS distribution, to make it easy to compare on your own |
787 |
|
|
system. |
788 |
|
|
|
789 |
root |
1.37 |
First comes a comparison between various modules using a very short |
790 |
|
|
single-line JSON string: |
791 |
root |
1.18 |
|
792 |
root |
1.37 |
{"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
793 |
root |
1.38 |
"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
794 |
root |
1.18 |
|
795 |
root |
1.39 |
It shows the number of encodes/decodes per second (JSON::XS uses |
796 |
|
|
the functional interface, while JSON::XS/2 uses the OO interface |
797 |
|
|
with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables |
798 |
|
|
shrink). Higher is better: |
799 |
root |
1.4 |
|
800 |
root |
1.48 |
Storable | 15779.925 | 14169.946 | |
801 |
|
|
-----------+------------+------------+ |
802 |
root |
1.4 |
module | encode | decode | |
803 |
|
|
-----------|------------|------------| |
804 |
root |
1.48 |
JSON | 4990.842 | 4088.813 | |
805 |
|
|
JSON::DWIW | 51653.990 | 71575.154 | |
806 |
|
|
JSON::PC | 65948.176 | 74631.744 | |
807 |
|
|
JSON::PP | 8931.652 | 3817.168 | |
808 |
|
|
JSON::Syck | 24877.248 | 27776.848 | |
809 |
|
|
JSON::XS | 388361.481 | 227951.304 | |
810 |
|
|
JSON::XS/2 | 227951.304 | 218453.333 | |
811 |
|
|
JSON::XS/3 | 338250.323 | 218453.333 | |
812 |
|
|
Storable | 16500.016 | 135300.129 | |
813 |
root |
1.4 |
-----------+------------+------------+ |
814 |
|
|
|
815 |
root |
1.37 |
That is, JSON::XS is about five times faster than JSON::DWIW on encoding, |
816 |
root |
1.38 |
about three times faster on decoding, and over fourty times faster |
817 |
root |
1.37 |
than JSON, even with pretty-printing and key sorting. It also compares |
818 |
|
|
favourably to Storable for small amounts of data. |
819 |
root |
1.4 |
|
820 |
root |
1.13 |
Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
821 |
root |
1.4 |
search API (http://nanoref.com/yahooapis/mgPdGg): |
822 |
|
|
|
823 |
|
|
module | encode | decode | |
824 |
|
|
-----------|------------|------------| |
825 |
root |
1.48 |
JSON | 55.260 | 34.971 | |
826 |
|
|
JSON::DWIW | 825.228 | 1082.513 | |
827 |
|
|
JSON::PC | 3571.444 | 2394.829 | |
828 |
|
|
JSON::PP | 210.987 | 32.574 | |
829 |
|
|
JSON::Syck | 552.551 | 787.544 | |
830 |
|
|
JSON::XS | 5780.463 | 4854.519 | |
831 |
|
|
JSON::XS/2 | 3869.998 | 4798.975 | |
832 |
|
|
JSON::XS/3 | 5862.880 | 4798.975 | |
833 |
|
|
Storable | 4445.002 | 5235.027 | |
834 |
root |
1.4 |
-----------+------------+------------+ |
835 |
|
|
|
836 |
root |
1.40 |
Again, JSON::XS leads by far (except for Storable which non-surprisingly |
837 |
|
|
decodes faster). |
838 |
root |
1.4 |
|
839 |
root |
1.18 |
On large strings containing lots of high unicode characters, some modules |
840 |
|
|
(such as JSON::PC) seem to decode faster than JSON::XS, but the result |
841 |
|
|
will be broken due to missing (or wrong) unicode handling. Others refuse |
842 |
|
|
to decode or encode properly, so it was impossible to prepare a fair |
843 |
|
|
comparison table for that case. |
844 |
root |
1.13 |
|
845 |
root |
1.11 |
|
846 |
root |
1.23 |
=head1 SECURITY CONSIDERATIONS |
847 |
|
|
|
848 |
|
|
When you are using JSON in a protocol, talking to untrusted potentially |
849 |
|
|
hostile creatures requires relatively few measures. |
850 |
|
|
|
851 |
|
|
First of all, your JSON decoder should be secure, that is, should not have |
852 |
|
|
any buffer overflows. Obviously, this module should ensure that and I am |
853 |
|
|
trying hard on making that true, but you never know. |
854 |
|
|
|
855 |
|
|
Second, you need to avoid resource-starving attacks. That means you should |
856 |
|
|
limit the size of JSON texts you accept, or make sure then when your |
857 |
|
|
resources run out, thats just fine (e.g. by using a separate process that |
858 |
|
|
can crash safely). The size of a JSON text in octets or characters is |
859 |
|
|
usually a good indication of the size of the resources required to decode |
860 |
root |
1.47 |
it into a Perl structure. While JSON::XS can check the size of the JSON |
861 |
|
|
text, it might be too late when you already have it in memory, so you |
862 |
|
|
might want to check the size before you accept the string. |
863 |
root |
1.23 |
|
864 |
|
|
Third, JSON::XS recurses using the C stack when decoding objects and |
865 |
|
|
arrays. The C stack is a limited resource: for instance, on my amd64 |
866 |
root |
1.28 |
machine with 8MB of stack size I can decode around 180k nested arrays but |
867 |
|
|
only 14k nested JSON objects (due to perl itself recursing deeply on croak |
868 |
|
|
to free the temporary). If that is exceeded, the program crashes. to be |
869 |
|
|
conservative, the default nesting limit is set to 512. If your process |
870 |
|
|
has a smaller stack, you should adjust this setting accordingly with the |
871 |
|
|
C<max_depth> method. |
872 |
root |
1.23 |
|
873 |
|
|
And last but least, something else could bomb you that I forgot to think |
874 |
root |
1.30 |
of. In that case, you get to keep the pieces. I am always open for hints, |
875 |
root |
1.23 |
though... |
876 |
|
|
|
877 |
root |
1.42 |
If you are using JSON::XS to return packets to consumption |
878 |
|
|
by javascript scripts in a browser you should have a look at |
879 |
|
|
L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether |
880 |
|
|
you are vulnerable to some common attack vectors (which really are browser |
881 |
|
|
design bugs, but it is still you who will have to deal with it, as major |
882 |
|
|
browser developers care only for features, not about doing security |
883 |
|
|
right). |
884 |
|
|
|
885 |
root |
1.11 |
|
886 |
root |
1.4 |
=head1 BUGS |
887 |
|
|
|
888 |
|
|
While the goal of this module is to be correct, that unfortunately does |
889 |
|
|
not mean its bug-free, only that I think its design is bug-free. It is |
890 |
root |
1.23 |
still relatively early in its development. If you keep reporting bugs they |
891 |
|
|
will be fixed swiftly, though. |
892 |
root |
1.4 |
|
893 |
root |
1.2 |
=cut |
894 |
|
|
|
895 |
root |
1.53 |
our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; |
896 |
|
|
our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; |
897 |
root |
1.43 |
|
898 |
|
|
sub true() { $true } |
899 |
|
|
sub false() { $false } |
900 |
|
|
|
901 |
|
|
sub is_bool($) { |
902 |
|
|
UNIVERSAL::isa $_[0], "JSON::XS::Boolean" |
903 |
root |
1.44 |
# or UNIVERSAL::isa $_[0], "JSON::Literal" |
904 |
root |
1.43 |
} |
905 |
|
|
|
906 |
|
|
XSLoader::load "JSON::XS", $VERSION; |
907 |
|
|
|
908 |
|
|
package JSON::XS::Boolean; |
909 |
|
|
|
910 |
|
|
use overload |
911 |
|
|
"0+" => sub { ${$_[0]} }, |
912 |
|
|
"++" => sub { $_[0] = ${$_[0]} + 1 }, |
913 |
|
|
"--" => sub { $_[0] = ${$_[0]} - 1 }, |
914 |
|
|
fallback => 1; |
915 |
root |
1.25 |
|
916 |
root |
1.2 |
1; |
917 |
|
|
|
918 |
root |
1.1 |
=head1 AUTHOR |
919 |
|
|
|
920 |
|
|
Marc Lehmann <schmorp@schmorp.de> |
921 |
|
|
http://home.schmorp.de/ |
922 |
|
|
|
923 |
|
|
=cut |
924 |
|
|
|