JSON::PP(3) User Contributed Perl Documentation JSON::PP(3)
NAME
JSON::PP - JSON::XS compatible pure-Perl module.
SYNOPSIS
use JSON::PP;
# exported functions, they croak on error
# and expect/generate UTF-8
$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
# OO-interface
$coder = JSON::PP->new->ascii->pretty->allow_nonref;
$json_text = $json->encode( $perl_scalar );
$perl_scalar = $json->decode( $json_text );
$pretty_printed = $json->pretty->encode( $perl_scalar ); # pretty-printing
# Note that JSON version 2.0 and above will automatically use
# JSON::XS or JSON::PP, so you should be able to just:
use JSON;
VERSION
2.27202
JSON::XS 2.27 (~2.30) compatible.
NOTE
JSON::PP had been inculded in JSON distribution (CPAN module). It was
a perl core module in Perl 5.14.
DESCRIPTION
This module is JSON::XS compatible pure Perl module. (Perl 5.8 or
later is recommended)
JSON::XS is the fastest and most proper JSON module on CPAN. It is
written by Marc Lehmann in C, so must be compiled and installed in the
used environment.
JSON::PP is a pure-Perl module and has compatibility to JSON::XS.
FEATURES
o correct unicode handling
This module knows how to handle Unicode (depending on Perl
version).
See to "A FEW NOTES ON UNICODE AND PERL" in JSON::XS and "UNICODE
HANDLING ON PERLS".
o round-trip integrity
When you serialise a perl data structure using only data types
supported by JSON and Perl, the deserialised data structure is
identical on the Perl level. (e.g. the string "2.0" doesn't
suddenly become "2" just because it looks like a number). There are
minor exceptions to this, read the MAPPING section below to learn
about those.
o strict checking of JSON correctness
There is no guessing, no generating of illegal JSON texts by
default, and only JSON is accepted as input by default (the latter
is a security feature). But when some options are set, loose
chcking features are available.
FUNCTIONAL INTERFACE
Some documents are copied and modified from "FUNCTIONAL INTERFACE" in
JSON::XS.
encode_json
$json_text = encode_json $perl_scalar
Converts the given Perl data structure to a UTF-8 encoded, binary
string.
This function call is functionally identical to:
$json_text = JSON::PP->new->utf8->encode($perl_scalar)
decode_json
$perl_scalar = decode_json $json_text
The opposite of "encode_json": expects an UTF-8 (binary) string and
tries to parse that as an UTF-8 encoded JSON text, returning the
resulting reference.
This function call is functionally identical to:
$perl_scalar = JSON::PP->new->utf8->decode($json_text)
JSON::PP::is_bool
$is_boolean = JSON::PP::is_bool($scalar)
Returns true if the passed scalar represents either JSON::PP::true or
JSON::PP::false, two constants that act like 1 and 0 respectively and
are also used to represent JSON "true" and "false" in Perl strings.
JSON::PP::true
Returns JSON true value which is blessed object. It "isa"
JSON::PP::Boolean object.
JSON::PP::false
Returns JSON false value which is blessed object. It "isa"
JSON::PP::Boolean object.
JSON::PP::null
Returns "undef".
See MAPPING, below, for more information on how JSON values are mapped
to Perl.
HOW DO I DECODE A DATA FROM OUTER AND ENCODE TO OUTER
This section supposes that your perl vresion is 5.8 or later.
If you know a JSON text from an outer world - a network, a file
content, and so on, is encoded in UTF-8, you should use "decode_json"
or "JSON" module object with "utf8" enable. And the decoded result will
contain UNICODE characters.
# from network
my $json = JSON::PP->new->utf8;
my $json_text = CGI->new->param( 'json_data' );
my $perl_scalar = $json->decode( $json_text );
# from file content
local $/;
open( my $fh, '<', 'json.data' );
$json_text = <$fh>;
$perl_scalar = decode_json( $json_text );
If an outer data is not encoded in UTF-8, firstly you should "decode"
it.
use Encode;
local $/;
open( my $fh, '<', 'json.data' );
my $encoding = 'cp932';
my $unicode_json_text = decode( $encoding, <$fh> ); # UNICODE
# or you can write the below code.
#
# open( my $fh, "<:encoding($encoding)", 'json.data' );
# $unicode_json_text = <$fh>;
In this case, $unicode_json_text is of course UNICODE string. So you
cannot use "decode_json" nor "JSON" module object with "utf8" enable.
Instead of them, you use "JSON" module object with "utf8" disable.
$perl_scalar = $json->utf8(0)->decode( $unicode_json_text );
Or "encode 'utf8'" and "decode_json":
$perl_scalar = decode_json( encode( 'utf8', $unicode_json_text ) );
# this way is not efficient.
And now, you want to convert your $perl_scalar into JSON data and send
it to an outer world - a network or a file content, and so on.
Your data usually contains UNICODE strings and you want the converted
data to be encoded in UTF-8, you should use "encode_json" or "JSON"
module object with "utf8" enable.
print encode_json( $perl_scalar ); # to a network? file? or display?
# or
print $json->utf8->encode( $perl_scalar );
If $perl_scalar does not contain UNICODE but $encoding-encoded strings
for some reason, then its characters are regarded as latin1 for perl
(because it does not concern with your $encoding). You cannot use
"encode_json" nor "JSON" module object with "utf8" enable. Instead of
them, you use "JSON" module object with "utf8" disable. Note that the
resulted text is a UNICODE string but no problem to print it.
# $perl_scalar contains $encoding encoded string values
$unicode_json_text = $json->utf8(0)->encode( $perl_scalar );
# $unicode_json_text consists of characters less than 0x100
print $unicode_json_text;
Or "decode $encoding" all string values and "encode_json":
$perl_scalar->{ foo } = decode( $encoding, $perl_scalar->{ foo } );
# ... do it to each string values, then encode_json
$json_text = encode_json( $perl_scalar );
This method is a proper way but probably not efficient.
See to Encode, perluniintro.
METHODS
Basically, check to JSON or JSON::XS.
new
$json = JSON::PP->new
Rturns a new JSON::PP object that can be used to de/encode JSON
strings.
All boolean flags described below are by default disabled.
The mutators for flags all return the JSON object again and thus calls
can be chained:
my $json = JSON::PP->new->utf8->space_after->encode({a => [1,2]})
=> {"a": [1, 2]}
ascii
$json = $json->ascii([$enable])
$enabled = $json->get_ascii
If $enable is true (or missing), then the encode method will not
generate characters outside the code range 0..127. Any Unicode
characters outside that range will be escaped using either a single
\uXXXX or a double \uHHHH\uLLLLL escape sequence, as per RFC4627. (See
to "OBJECT-ORIENTED INTERFACE" in JSON::XS).
In Perl 5.005, there is no character having high value (more than 255).
See to "UNICODE HANDLING ON PERLS".
If $enable is false, then the encode method will not escape Unicode
characters unless required by the JSON syntax or other flags. This
results in a faster and more compact format.
JSON::PP->new->ascii(1)->encode([chr 0x10401])
=> ["\ud801\udc01"]
latin1
$json = $json->latin1([$enable])
$enabled = $json->get_latin1
If $enable is true (or missing), then the encode method will encode the
resulting JSON text as latin1 (or iso-8859-1), escaping any characters
outside the code range 0..255.
If $enable is false, then the encode method will not escape Unicode
characters unless required by the JSON syntax or other flags.
JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
See to "UNICODE HANDLING ON PERLS".
utf8
$json = $json->utf8([$enable])
$enabled = $json->get_utf8
If $enable is true (or missing), then the encode method will encode the
JSON result into UTF-8, as required by many protocols, while the decode
method expects to be handled an UTF-8-encoded string. Please note that
UTF-8-encoded strings do not contain any characters outside the range
0..255, they are thus useful for bytewise/binary I/O.
(In Perl 5.005, any character outside the range 0..255 does not exist.
See to "UNICODE HANDLING ON PERLS".)
In future versions, enabling this option might enable autodetection of
the UTF-16 and UTF-32 encoding families, as described in RFC4627.
If $enable is false, then the encode method will return the JSON string
as a (non-encoded) Unicode string, while decode expects thus a Unicode
string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs to be
done yourself, e.g. using the Encode module.
Example, output UTF-16BE-encoded JSON:
use Encode;
$jsontext = encode "UTF-16BE", JSON::PP->new->encode ($object);
Example, decode UTF-32LE-encoded JSON:
use Encode;
$object = JSON::PP->new->decode (decode "UTF-32LE", $jsontext);
pretty
$json = $json->pretty([$enable])
This enables (or disables) all of the "indent", "space_before" and
"space_after" flags in one call to generate the most readable (or most
compact) form possible.
Equivalent to:
$json->indent->space_before->space_after
indent
$json = $json->indent([$enable])
$enabled = $json->get_indent
The default indent space length is three. You can use "indent_length"
to change the length.
space_before
$json = $json->space_before([$enable])
$enabled = $json->get_space_before
If $enable is true (or missing), then the "encode" method will add an
extra optional space before the ":" separating keys from values in JSON
objects.
If $enable is false, then the "encode" method will not add any extra
space at those places.
This setting has no effect when decoding JSON texts.
Example, space_before enabled, space_after and indent disabled:
{"key" :"value"}
space_after
$json = $json->space_after([$enable])
$enabled = $json->get_space_after
If $enable is true (or missing), then the "encode" method will add an
extra optional space after the ":" separating keys from values in JSON
objects and extra whitespace after the "," separating key-value pairs
and array members.
If $enable is false, then the "encode" method will not add any extra
space at those places.
This setting has no effect when decoding JSON texts.
Example, space_before and indent disabled, space_after enabled:
{"key": "value"}
relaxed
$json = $json->relaxed([$enable])
$enabled = $json->get_relaxed
If $enable is true (or missing), then "decode" will accept some
extensions to normal JSON syntax (see below). "encode" will not be
affected in anyway. Be aware that this option makes you accept invalid
JSON texts as if they were valid!. I suggest only to use this option to
parse application-specific files written by humans (configuration
files, resource files etc.)
If $enable is false (the default), then "decode" will only accept valid
JSON texts.
Currently accepted extensions are:
o list items can have an end-comma
JSON separates array elements and key-value pairs with commas. This
can be annoying if you write JSON texts manually and want to be
able to quickly append elements, so this extension accepts comma at
the end of such items not just between them:
[
1,
2, <- this comma not normally allowed
]
{
"k1": "v1",
"k2": "v2", <- this comma not normally allowed
}
o shell-style '#'-comments
Whenever JSON allows whitespace, shell-style comments are
additionally allowed. They are terminated by the first carriage-
return or line-feed character, after which more white-space and
comments are allowed.
[
1, # this comment not allowed in JSON
# neither this one...
]
canonical
$json = $json->canonical([$enable])
$enabled = $json->get_canonical
If $enable is true (or missing), then the "encode" method will output
JSON objects by sorting their keys. This is adding a comparatively high
overhead.
If $enable is false, then the "encode" method will output key-value
pairs in the order Perl stores them (which will likely change between
runs of the same script).
This option is useful if you want the same data structure to be encoded
as the same JSON text (given the same overall settings). If it is
disabled, the same hash might be encoded differently even if contains
the same data, as key-value pairs have no inherent ordering in Perl.
This setting has no effect when decoding JSON texts.
If you want your own sorting routine, you can give a code referece or a
subroutine name to "sort_by". See to "JSON::PP OWN METHODS".
allow_nonref
$json = $json->allow_nonref([$enable])
$enabled = $json->get_allow_nonref
If $enable is true (or missing), then the "encode" method can convert a
non-reference into its corresponding string, number or null JSON value,
which is an extension to RFC4627. Likewise, "decode" will accept those
JSON values instead of croaking.
If $enable is false, then the "encode" method will croak if it isn't
passed an arrayref or hashref, as JSON texts must either be an object
or array. Likewise, "decode" will croak if given something that is not
a JSON object or array.
JSON::PP->new->allow_nonref->encode ("Hello, World!")
=> "Hello, World!"
allow_unknown
$json = $json->allow_unknown ([$enable])
$enabled = $json->get_allow_unknown
If $enable is true (or missing), then "encode" will *not* throw an
exception when it encounters values it cannot represent in JSON (for
example, filehandles) but instead will encode a JSON "null" value.
Note that blessed objects are not included here and are handled
separately by c<allow_nonref>.
If $enable is false (the default), then "encode" will throw an
exception when it encounters anything it cannot encode as JSON.
This option does not affect "decode" in any way, and it is recommended
to leave it off unless you know your communications partner.
allow_blessed
$json = $json->allow_blessed([$enable])
$enabled = $json->get_allow_blessed
If $enable is true (or missing), then the "encode" method will not barf
when it encounters a blessed reference. Instead, the value of the
convert_blessed option will decide whether "null" ("convert_blessed"
disabled or no "TO_JSON" method found) or a representation of the
object ("convert_blessed" enabled and "TO_JSON" method found) is being
encoded. Has no effect on "decode".
If $enable is false (the default), then "encode" will throw an
exception when it encounters a blessed object.
convert_blessed
$json = $json->convert_blessed([$enable])
$enabled = $json->get_convert_blessed
If $enable is true (or missing), then "encode", upon encountering a
blessed object, will check for the availability of the "TO_JSON" method
on the object's class. If found, it will be called in scalar context
and the resulting scalar will be encoded instead of the object. If no
"TO_JSON" method is found, the value of "allow_blessed" will decide
what to do.
The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
returns other blessed objects, those will be handled in the same way.
"TO_JSON" must take care of not causing an endless recursion cycle (==
crash) in this case. The name of "TO_JSON" was chosen because other
methods called by the Perl core (== not by the user of the object) are
usually in upper case letters and to avoid collisions with the
"to_json" function or method.
This setting does not yet influence "decode" in any way.
If $enable is false, then the "allow_blessed" setting will decide what
to do when a blessed object is found.
filter_json_object
$json = $json->filter_json_object([$coderef])
When $coderef is specified, it will be called from "decode" each time
it decodes a JSON object. The only argument passed to the coderef is a
reference to the newly-created hash. If the code references returns a
single scalar (which need not be a reference), this value (i.e. a copy
of that scalar to avoid aliasing) is inserted into the deserialised
data structure. If it returns an empty list (NOTE: not "undef", which
is a valid scalar), the original deserialised hash will be inserted.
This setting can slow down decoding considerably.
When $coderef is omitted or undefined, any existing callback will be
removed and "decode" will not change the deserialised hash in any way.
Example, convert all JSON objects into the integer 5:
my $js = JSON::PP->new->filter_json_object (sub { 5 });
# returns [5]
$js->decode ('[{}]'); # the given subroutine takes a hash reference.
# throw an exception because allow_nonref is not enabled
# so a lone 5 is not allowed.
$js->decode ('{"a":1, "b":2}');
filter_json_single_key_object
$json = $json->filter_json_single_key_object($key [=> $coderef])
Works remotely similar to "filter_json_object", but is only called for
JSON objects having a single key named $key.
This $coderef is called before the one specified via
"filter_json_object", if any. It gets passed the single value in the
JSON object. If it returns a single value, it will be inserted into the
data structure. If it returns nothing (not even "undef" but the empty
list), the callback from "filter_json_object" will be called next, as
if no single-key callback were specified.
If $coderef is omitted or undefined, the corresponding callback will be
disabled. There can only ever be one callback for a given key.
As this callback gets called less often then the "filter_json_object"
one, decoding speed will not usually suffer as much. Therefore, single-
key objects make excellent targets to serialise Perl objects into,
especially as single-key JSON objects are as close to the type-tagged
value concept as JSON gets (it's basically an ID/VALUE tuple). Of
course, JSON does not support this in any way, so you need to make sure
your data never looks like a serialised Perl hash.
Typical names for the single object key are "__class_whatever__", or
"$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
things like "__class_md5sum(classname)__", to reduce the risk of
clashing with real hashes.
Example, decode JSON objects of the form "{ "__widget__" => <id> }"
into the corresponding $WIDGET{<id>} object:
# return whatever is in $WIDGET{5}:
JSON::PP
->new
->filter_json_single_key_object (__widget__ => sub {
$WIDGET{ $_[0] }
})
->decode ('{"__widget__": 5')
# this can be used with a TO_JSON method in some "widget" class
# for serialisation to json:
sub WidgetBase::TO_JSON {
my ($self) = @_;
unless ($self->{id}) {
$self->{id} = ..get..some..id..;
$WIDGET{$self->{id}} = $self;
}
{ __widget__ => $self->{id} }
}
shrink
$json = $json->shrink([$enable])
$enabled = $json->get_shrink
In JSON::XS, this flag resizes strings generated by either "encode" or
"decode" to their minimum size possible. It will also try to downgrade
any strings to octet-form if possible.
In JSON::PP, it is noop about resizing strings but tries
"utf8::downgrade" to the returned string by "encode". See to utf8.
See to "OBJECT-ORIENTED INTERFACE" in JSON::XS
max_depth
$json = $json->max_depth([$maximum_nesting_depth])
$max_depth = $json->get_max_depth
Sets the maximum nesting level (default 512) accepted while encoding or
decoding. If a higher nesting level is detected in JSON text or a Perl
data structure, then the encoder and decoder will stop and croak at
that point.
Nesting level is defined by number of hash- or arrayrefs that the
encoder needs to traverse to reach a given point or the number of "{"
or "[" characters without their matching closing parenthesis crossed to
reach a given character in a string.
If no argument is given, the highest possible setting will be used,
which is rarely useful.
See "SSECURITY CONSIDERATIONS" in JSON::XS for more info on why this is
useful.
When a large value (100 or more) was set and it de/encodes a deep
nested object/text, it may raise a warning 'Deep recursion on
subroutin' at the perl runtime phase.
max_size
$json = $json->max_size([$maximum_string_size])
$max_size = $json->get_max_size
Set the maximum length a JSON text may have (in bytes) where decoding
is being attempted. The default is 0, meaning no limit. When "decode"
is called on a string that is longer then this many bytes, it will not
attempt to decode the string but throw an exception. This setting has
no effect on "encode" (yet).
If no argument is given, the limit check will be deactivated (same as
when 0 is specified).
See "SSECURITY CONSIDERATIONS" in JSON::XS for more info on why this is
useful.
encode
$json_text = $json->encode($perl_scalar)
Converts the given Perl data structure (a simple scalar or a reference
to a hash or array) to its JSON representation. Simple scalars will be
converted into JSON string or number sequences, while references to
arrays become JSON arrays and references to hashes become JSON objects.
Undefined Perl values (e.g. "undef") become JSON "null" values.
References to the integers 0 and 1 are converted into "true" and
"false".
decode
$perl_scalar = $json->decode($json_text)
The opposite of "encode": expects a JSON text and tries to parse it,
returning the resulting simple scalar or reference. Croaks on error.
JSON numbers and strings become simple Perl scalars. JSON arrays become
Perl arrayrefs and JSON objects become Perl hashrefs. "true" becomes 1
("JSON::true"), "false" becomes 0 ("JSON::false") and "null" becomes
"undef".
decode_prefix
($perl_scalar, $characters) = $json->decode_prefix($json_text)
This works like the "decode" method, but instead of raising an
exception when there is trailing garbage after the first JSON object,
it will silently stop parsing there and return the number of characters
consumed so far.
JSON->new->decode_prefix ("[1] the tail")
=> ([], 3)
INCREMENTAL PARSING
Most of this section are copied and modified from "INCREMENTAL PARSING"
in JSON::XS.
In some cases, there is the need for incremental parsing of JSON texts.
This module does allow you to parse a JSON stream incrementally. It
does so by accumulating text until it has a full JSON object, which it
then can decode. This process is similar to using "decode_prefix" to
see if a full JSON object is available, but is much more efficient (and
can be implemented with a minimum of method calls).
This module will only attempt to parse the JSON text once it is sure it
has enough text to get a decisive result, using a very simple but truly
incremental parser. This means that it sometimes won't stop as early as
the full parser, for example, it doesn't detect parenthese mismatches.
The only thing it guarantees is that it starts decoding as soon as a
syntactically valid JSON text has been seen. This means you need to set
resource limits (e.g. "max_size") to ensure the parser will stop
parsing in the presence if syntax errors.
The following methods implement this incremental parser.
incr_parse
$json->incr_parse( [$string] ) # void context
$obj_or_undef = $json->incr_parse( [$string] ) # scalar context
@obj_or_empty = $json->incr_parse( [$string] ) # list context
This is the central parsing function. It can both append new text and
extract objects from the stream accumulated so far (both of these
functions are optional).
If $string is given, then this string is appended to the already
existing JSON fragment stored in the $json object.
After that, if the function is called in void context, it will simply
return without doing anything further. This can be used to add more
text in as many chunks as you want.
If the method is called in scalar context, then it will try to extract
exactly one JSON object. If that is successful, it will return this
object, otherwise it will return "undef". If there is a parse error,
this method will croak just as "decode" would do (one can then use
"incr_skip" to skip the errornous part). This is the most common way of
using the method.
And finally, in list context, it will try to extract as many objects
from the stream as it can find and return them, or the empty list
otherwise. For this to work, there must be no separators between the
JSON objects or arrays, instead they must be concatenated back-to-back.
If an error occurs, an exception will be raised as in the scalar
context case. Note that in this case, any previously-parsed JSON texts
will be lost.
Example: Parse some JSON arrays/objects in a given string and return
them.
my @objs = JSON->new->incr_parse ("[5][7][1,2]");
incr_text
$lvalue_string = $json->incr_text
This method returns the currently stored JSON fragment as an lvalue,
that is, you can manipulate it. This only works when a preceding call
to "incr_parse" in scalar context successfully returned an object.
Under all other circumstances you must not call this function (I mean
it. although in simple tests it might actually work, it will fail
under real world conditions). As a special exception, you can also call
this method before having parsed anything.
This function is useful in two cases: a) finding the trailing text
after a JSON object or b) parsing multiple JSON objects separated by
non-JSON text (such as commas).
$json->incr_text =~ s/\s*,\s*//;
In Perl 5.005, "lvalue" attribute is not available. You must write
codes like the below:
$string = $json->incr_text;
$string =~ s/\s*,\s*//;
$json->incr_text( $string );
incr_skip
$json->incr_skip
This will reset the state of the incremental parser and will remove the
parsed text from the input buffer. This is useful after "incr_parse"
died, in which case the input buffer and incremental parser state is
left unchanged, to skip the text parsed so far and to reset the parse
state.
incr_reset
$json->incr_reset
This completely resets the incremental parser, that is, after this
call, it will be as if the parser had never parsed anything.
This is useful if you want ot repeatedly parse JSON objects and want to
ignore any trailing data, which means you have to reset the parser
after each successful decode.
See to "INCREMENTAL PARSING" in JSON::XS for examples.
JSON::PP OWN METHODS
allow_singlequote
$json = $json->allow_singlequote([$enable])
If $enable is true (or missing), then "decode" will accept JSON strings
quoted by single quotations that are invalid JSON format.
$json->allow_singlequote->decode({"foo":'bar'});
$json->allow_singlequote->decode({'foo':"bar"});
$json->allow_singlequote->decode({'foo':'bar'});
As same as the "relaxed" option, this option may be used to parse
application-specific files written by humans.
allow_barekey
$json = $json->allow_barekey([$enable])
If $enable is true (or missing), then "decode" will accept bare keys of
JSON object that are invalid JSON format.
As same as the "relaxed" option, this option may be used to parse
application-specific files written by humans.
$json->allow_barekey->decode('{foo:"bar"}');
allow_bignum
$json = $json->allow_bignum([$enable])
If $enable is true (or missing), then "decode" will convert the big
integer Perl cannot handle as integer into a Math::BigInt object and
convert a floating number (any) into a Math::BigFloat.
On the contary, "encode" converts "Math::BigInt" objects and
"Math::BigFloat" objects into JSON numbers with "allow_blessed" enable.
$json->allow_nonref->allow_blessed->allow_bignum;
$bigfloat = $json->decode('2.000000000000000000000000001');
print $json->encode($bigfloat);
# => 2.000000000000000000000000001
See to "MAPPING" in JSON::XS aboout the normal conversion of JSON
number.
loose
$json = $json->loose([$enable])
The unescaped [\x00-\x1f\x22\x2f\x5c] strings are invalid in JSON
strings and the module doesn't allow to "decode" to these (except for
\x2f). If $enable is true (or missing), then "decode" will accept
these unescaped strings.
$json->loose->decode(qq|["abc
def"]|);
See "SSECURITY CONSIDERATIONS" in JSON::XS.
escape_slash
$json = $json->escape_slash([$enable])
According to JSON Grammar, slash (U+002F) is escaped. But default
JSON::PP (as same as JSON::XS) encodes strings without escaping slash.
If $enable is true (or missing), then "encode" will escape slashes.
indent_length
$json = $json->indent_length($length)
JSON::XS indent space length is 3 and cannot be changed. JSON::PP set
the indent space length with the given $length. The default is 3. The
acceptable range is 0 to 15.
sort_by
$json = $json->sort_by($function_name)
$json = $json->sort_by($subroutine_ref)
If $function_name or $subroutine_ref are set, its sort routine are used
in encoding JSON objects.
$js = $pc->sort_by(sub { $JSON::PP::a cmp $JSON::PP::b })->encode($obj);
# is($js, q|{"a":1,"b":2,"c":3,"d":4,"e":5,"f":6,"g":7,"h":8,"i":9}|);
$js = $pc->sort_by('own_sort')->encode($obj);
# is($js, q|{"a":1,"b":2,"c":3,"d":4,"e":5,"f":6,"g":7,"h":8,"i":9}|);
sub JSON::PP::own_sort { $JSON::PP::a cmp $JSON::PP::b }
As the sorting routine runs in the JSON::PP scope, the given subroutine
name and the special variables $a, $b will begin 'JSON::PP::'.
If $integer is set, then the effect is same as "canonical" on.
INTERNAL
For developers.
PP_encode_box
Returns
{
depth => $depth,
indent_count => $indent_count,
}
PP_decode_box
Returns
{
text => $text,
at => $at,
ch => $ch,
len => $len,
depth => $depth,
encoding => $encoding,
is_valid_utf8 => $is_valid_utf8,
};
MAPPING
This section is copied from JSON::XS and modified to "JSON::PP".
JSON::XS and JSON::PP mapping mechanisms are almost equivalent.
See to "MAPPING" in JSON::XS.
JSON -> PERL
object
A JSON object becomes a reference to a hash in Perl. No ordering of
object keys is preserved (JSON does not preserver object key
ordering itself).
array
A JSON array becomes a reference to an array in Perl.
string
A JSON string becomes a string scalar in Perl - Unicode codepoints
in JSON are represented by the same codepoints in the Perl string,
so no manual decoding is necessary.
number
A JSON number becomes either an integer, numeric (floating point)
or string scalar in perl, depending on its range and any fractional
parts. On the Perl level, there is no difference between those as
Perl handles all the conversion details, but an integer may take
slightly less memory and might represent more values exactly than
floating point numbers.
If the number consists of digits only, "JSON" will try to represent
it as an integer value. If that fails, it will try to represent it
as a numeric (floating point) value if that is possible without
loss of precision. Otherwise it will preserve the number as a
string value (in which case you lose roundtripping ability, as the
JSON number will be re-encoded toa JSON string).
Numbers containing a fractional or exponential part will always be
represented as numeric (floating point) values, possibly at a loss
of precision (in which case you might lose perfect roundtripping
ability, but the JSON number will still be re-encoded as a JSON
number).
Note that precision is not accuracy - binary floating point values
cannot represent most decimal fractions exactly, and when
converting from and to floating point, "JSON" only guarantees
precision up to but not including the leats significant bit.
When "allow_bignum" is enable, the big integers and the numeric can
be optionally converted into Math::BigInt and Math::BigFloat
objects.
true, false
These JSON atoms become "JSON::PP::true" and "JSON::PP::false",
respectively. They are overloaded to act almost exactly like the
numbers 1 and 0. You can check wether a scalar is a JSON boolean by
using the "JSON::is_bool" function.
print JSON::PP::true . "\n";
=> true
print JSON::PP::true + 1;
=> 1
ok(JSON::true eq '1');
ok(JSON::true == 1);
"JSON" will install these missing overloading features to the
backend modules.
null
A JSON null atom becomes "undef" in Perl.
"JSON::PP::null" returns "unddef".
PERL -> JSON
The mapping from Perl to JSON is slightly more difficult, as Perl is a
truly typeless language, so we can only guess which JSON type is meant
by a Perl value.
hash references
Perl hash references become JSON objects. As there is no inherent
ordering in hash keys (or JSON objects), they will usually be
encoded in a pseudo-random order that can change between runs of
the same program but stays generally the same within a single run
of a program. "JSON" optionally sort the hash keys (determined by
the canonical flag), so the same datastructure will serialise to
the same JSON text (given same settings and version of JSON::XS),
but this incurs a runtime overhead and is only rarely useful, e.g.
when you want to compare some JSON text against another for
equality.
array references
Perl array references become JSON arrays.
other references
Other unblessed references are generally not allowed and will cause
an exception to be thrown, except for references to the integers 0
and 1, which get turned into "false" and "true" atoms in JSON. You
can also use "JSON::false" and "JSON::true" to improve readability.
to_json [\0,JSON::PP::true] # yields [false,true]
JSON::PP::true, JSON::PP::false, JSON::PP::null
These special values become JSON true and JSON false values,
respectively. You can also use "\1" and "\0" directly if you want.
JSON::PP::null returns "undef".
blessed objects
Blessed objects are not directly representable in JSON. See the
"allow_blessed" and "convert_blessed" methods on various options on
how to deal with this: basically, you can choose between throwing
an exception, encoding the reference as if it weren't blessed, or
provide your own serialiser method.
See to convert_blessed.
simple scalars
Simple Perl scalars (any scalar that is not a reference) are the
most difficult objects to encode: JSON::XS and JSON::PP will encode
undefined scalars as JSON "null" values, scalars that have last
been used in a string context before encoding as JSON strings, and
anything else as number value:
# dump as number
encode_json [2] # yields [2]
encode_json [-3.0e17] # yields [-3e+17]
my $value = 5; encode_json [$value] # yields [5]
# used as string, so dump as string
print $value;
encode_json [$value] # yields ["5"]
# undef becomes null
encode_json [undef] # yields [null]
You can force the type to be a string by stringifying it:
my $x = 3.1; # some variable containing a number
"$x"; # stringified
$x .= ""; # another, more awkward way to stringify
print $x; # perl does it for you, too, quite often
You can force the type to be a number by numifying it:
my $x = "3"; # some variable containing a string
$x += 0; # numify it, ensuring it will be dumped as a number
$x *= 1; # same thing, the choise is yours.
You can not currently force the type in other, less obscure, ways.
Note that numerical precision has the same meaning as under Perl
(so binary to decimal conversion follows the same rules as in Perl,
which can differ to other languages). Also, your perl interpreter
might expose extensions to the floating point numbers of your
platform, such as infinities or NaN's - these cannot be represented
in JSON, and it is an error to pass those in.
Big Number
When "allow_bignum" is enable, "encode" converts "Math::BigInt"
objects and "Math::BigFloat" objects into JSON numbers.
UNICODE HANDLING ON PERLS
If you do not know about Unicode on Perl well, please check "A FEW
NOTES ON UNICODE AND PERL" in JSON::XS.
Perl 5.8 and later
Perl can handle Unicode and the JSON::PP de/encode methods also work
properly.
$json->allow_nonref->encode(chr hex 3042);
$json->allow_nonref->encode(chr hex 12345);
Reuturns "\u3042" and "\ud808\udf45" respectively.
$json->allow_nonref->decode('"\u3042"');
$json->allow_nonref->decode('"\ud808\udf45"');
Returns UTF-8 encoded strings with UTF8 flag, regarded as "U+3042" and
"U+12345".
Note that the versions from Perl 5.8.0 to 5.8.2, Perl built-in "join"
was broken, so JSON::PP wraps the "join" with a subroutine. Thus
JSON::PP works slow in the versions.
Perl 5.6
Perl can handle Unicode and the JSON::PP de/encode methods also work.
Perl 5.005
Perl 5.005 is a byte sementics world -- all strings are sequences of
bytes. That means the unicode handling is not available.
In encoding,
$json->allow_nonref->encode(chr hex 3042); # hex 3042 is 12354.
$json->allow_nonref->encode(chr hex 12345); # hex 12345 is 74565.
Returns "B" and "E", as "chr" takes a value more than 255, it treats as
"$value % 256", so the above codes are equivalent to :
$json->allow_nonref->encode(chr 66);
$json->allow_nonref->encode(chr 69);
In decoding,
$json->decode('"\u00e3\u0081\u0082"');
The returned is a byte sequence "0xE3 0x81 0x82" for UTF-8 encoded
japanese character ("HIRAGANA LETTER A"). And if it is represented in
Unicode code point, "U+3042".
Next,
$json->decode('"\u3042"');
We ordinary expect the returned value is a Unicode character "U+3042".
But here is 5.005 world. This is "0xE3 0x81 0x82".
$json->decode('"\ud808\udf45"');
This is not a character "U+12345" but bytes - "0xf0 0x92 0x8d 0x85".
TODO
speed
memory saving
SEE ALSO
Most of the document are copied and modified from JSON::XS doc.
JSON::XS
RFC4627 (<http://www.ietf.org/rfc/rfc4627.txt>;)
AUTHOR
Makamaka Hannyaharamitu, <makamaka[at]cpan.org>
COPYRIGHT AND LICENSE
Copyright 2007-2013 by Makamaka Hannyaharamitu
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.16.3 2013-03-13 JSON::PP(3)
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