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JSON::PP(3perl) - phpMan
JSON::PP(3perl) Perl Programmers Reference Guide JSON::PP(3perl)
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
· 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".
· 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.
· 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:
· 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
}
· 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 v5.20.2 2014-12-27 JSON::PP(3perl)
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