JSON::PP(3pm) Perl Programmers Reference Guide JSON::PP(3pm)
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
$json = JSON::PP->new->ascii->pretty->allow_nonref;
$pretty_printed_json_text = $json->encode( $perl_scalar );
$perl_scalar = $json->decode( $json_text );
# 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;
DESCRIPTION
JSON::PP is a pure perl JSON decoder/encoder, and (almost) compatible
to much faster JSON::XS written by Marc Lehmann in C. JSON::PP works as
a fallback module when you use JSON module without having installed
JSON::XS.
Because of this fallback feature of JSON.pm, JSON::PP tries not to be
more JavaScript-friendly than JSON::XS (i.e. not to escape extra
characters such as U+2028 and U+2029, etc), in order for you not to
lose such JavaScript-friendliness silently when you use JSON.pm and
install JSON::XS for speed or by accident. If you need JavaScript-
friendly RFC7159-compliant pure perl module, try JSON::Tiny, which is
derived from Mojolicious web framework and is also smaller and faster
than JSON::PP.
JSON::PP has been in the Perl core since Perl 5.14, mainly for CPAN
toolchain modules to parse META.json.
FUNCTIONAL INTERFACE
This section is taken from JSON::XS almost verbatim. "encode_json" and
"decode_json" are exported by default.
encode_json
$json_text = encode_json $perl_scalar
Converts the given Perl data structure to a UTF-8 encoded, binary
string (that is, the string contains octets only). Croaks on error.
This function call is functionally identical to:
$json_text = JSON::PP->new->utf8->encode($perl_scalar)
Except being faster.
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. Croaks on error.
This function call is functionally identical to:
$perl_scalar = JSON::PP->new->utf8->decode($json_text)
Except being faster.
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.
On perl 5.36 and above, will also return true when given one of perl's
standard boolean values, such as the result of a comparison.
See MAPPING, below, for more information on how JSON values are mapped
to Perl.
OBJECT-ORIENTED INTERFACE
This section is also taken from JSON::XS.
The object oriented interface lets you configure your own encoding or
decoding style, within the limits of supported formats.
new
$json = JSON::PP->new
Creates a new JSON::PP object that can be used to de/encode JSON
strings. All boolean flags described below are by default disabled
(with the exception of "allow_nonref", which defaults to enabled since
version 4.0).
The mutators for flags all return the JSON::PP 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 (which is ASCII). Any
Unicode characters outside that range will be escaped using either a
single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape
sequence, as per RFC4627. The resulting encoded JSON text can be
treated as a native Unicode string, an ascii-encoded, latin1-encoded or
UTF-8 encoded string, or any other superset of ASCII.
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.
See also the section ENCODING/CODESET FLAG NOTES later in this
document.
The main use for this flag is to produce JSON texts that can be
transmitted over a 7-bit channel, as the encoded JSON texts will not
contain any 8 bit characters.
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. The resulting string can be
treated as a latin1-encoded JSON text or a native Unicode string. The
"decode" method will not be affected in any way by this flag, as
"decode" by default expects Unicode, which is a strict superset of
latin1.
If $enable is false, then the "encode" method will not escape Unicode
characters unless required by the JSON syntax or other flags.
See also the section ENCODING/CODESET FLAG NOTES later in this
document.
The main use for this flag is efficiently encoding binary data as JSON
text, as most octets will not be escaped, resulting in a smaller
encoded size. The disadvantage is that the resulting JSON text is
encoded in latin1 (and must correctly be treated as such when storing
and transferring), a rare encoding for JSON. It is therefore most
useful when you want to store data structures known to contain binary
data efficiently in files or databases, not when talking to other JSON
encoders/decoders.
JSON::PP->new->latin1->encode (["\x{89}\x{abc}"]
=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
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
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.
See also the section ENCODING/CODESET FLAG NOTES later in this
document.
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" (and in the future possibly more) flags in one call to
generate the most readable (or most compact) form possible.
indent
$json = $json->indent([$enable])
$enabled = $json->get_indent
If $enable is true (or missing), then the "encode" method will use a
multiline format as output, putting every array member or object/hash
key-value pair into its own line, indenting them properly.
If $enable is false, no newlines or indenting will be produced, and the
resulting JSON text is guaranteed not to contain any "newlines".
This setting has no effect when decoding JSON texts.
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. You will also most
likely combine this setting with "space_after".
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...
]
o C-style multiple-line '/* */'-comments (JSON::PP only)
Whenever JSON allows whitespace, C-style multiple-line comments are
additionally allowed. Everything between "/*" and "*/" is a
comment, after which more white-space and comments are allowed.
[
1, /* this comment not allowed in JSON */
/* neither this one... */
]
o C++-style one-line '//'-comments (JSON::PP only)
Whenever JSON allows whitespace, C++-style one-line 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...
]
o literal ASCII TAB characters in strings
Literal ASCII TAB characters are now allowed in strings (and
treated as "\t").
[
"Hello\tWorld",
"Hello<TAB>World", # literal <TAB> would not normally be allowed
]
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, and can change even within the same run from
5.18 onwards).
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.
This setting has currently no effect on tied hashes.
allow_nonref
$json = $json->allow_nonref([$enable])
$enabled = $json->get_allow_nonref
Unlike other boolean options, this opotion is enabled by default
beginning with version 4.0.
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.
Example, encode a Perl scalar as JSON value without enabled
"allow_nonref", resulting in an error:
JSON::PP->new->allow_nonref(0)->encode ("Hello, World!")
=> hash- or arrayref expected...
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_blessed>.
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
See "OBJECT SERIALISATION" for details.
If $enable is true (or missing), then the "encode" method will not barf
when it encounters a blessed reference that it cannot convert
otherwise. Instead, a JSON "null" value is encoded instead of the
object.
If $enable is false (the default), then "encode" will throw an
exception when it encounters a blessed object that it cannot convert
otherwise.
This setting has no effect on "decode".
convert_blessed
$json = $json->convert_blessed([$enable])
$enabled = $json->get_convert_blessed
See "OBJECT SERIALISATION" for details.
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.
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 any
"to_json" function or method.
If $enable is false (the default), then "encode" will not consider this
type of conversion.
This setting has no effect on "decode".
allow_tags
$json = $json->allow_tags([$enable])
$enabled = $json->get_allow_tags
See "OBJECT SERIALISATION" for details.
If $enable is true (or missing), then "encode", upon encountering a
blessed object, will check for the availability of the "FREEZE" method
on the object's class. If found, it will be used to serialise the
object into a nonstandard tagged JSON value (that JSON decoders cannot
decode).
It also causes "decode" to parse such tagged JSON values and
deserialise them via a call to the "THAW" method.
If $enable is false (the default), then "encode" will not consider this
type of conversion, and tagged JSON values will cause a parse error in
"decode", as if tags were not part of the grammar.
boolean_values
$json->boolean_values([$false, $true])
($false, $true) = $json->get_boolean_values
By default, JSON booleans will be decoded as overloaded
$JSON::PP::false and $JSON::PP::true objects.
With this method you can specify your own boolean values for decoding -
on decode, JSON "false" will be decoded as a copy of $false, and JSON
"true" will be decoded as $true ("copy" here is the same thing as
assigning a value to another variable, i.e. "$copy = $false").
This is useful when you want to pass a decoded data structure directly
to other serialisers like YAML, Data::MessagePack and so on.
Note that this works only when you "decode". You can set incompatible
boolean objects (like boolean), but when you "encode" a data structure
with such boolean objects, you still need to enable "convert_blessed"
(and add a "TO_JSON" method if necessary).
Calling this method without any arguments will reset the booleans to
their default values.
"get_boolean_values" will return both $false and $true values, or the
empty list when they are set to the default.
core_bools
$json->core_bools([$enable]);
If $enable is true (or missing), then "decode", will produce standard
perl boolean values. Equivalent to calling:
$json->boolean_values(!!1, !!0)
"get_core_bools" will return true if this has been set. On perl 5.36,
it will also return true if the boolean values have been set to perl's
core booleans using the "boolean_values" method.
The methods "unblessed_bool" and "get_unblessed_bool" are provided as
aliases for compatibility with Cpanel::JSON::XS.
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 is a reference to the
newly-created hash. If the code references returns a single scalar
(which need not be a reference), this value (or rather a copy of it) 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('[{}]');
# returns 5
$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
If $enable is true (or missing), the string returned by "encode" will
be shrunk (i.e. downgraded if possible).
The actual definition of what shrink does might change in future
versions, but it will always try to save space at the expense of time.
If $enable is false, then JSON::PP does nothing.
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.
Setting the maximum depth to one disallows any nesting, so that ensures
that the object is only a single hash/object or array.
If no argument is given, the highest possible setting will be used,
which is rarely useful.
See "SECURITY CONSIDERATIONS" in JSON::XS for more info on why this is
useful.
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 "SECURITY CONSIDERATIONS" in JSON::XS for more info on why this is
useful.
encode
$json_text = $json->encode($perl_scalar)
Converts the given Perl value or data structure to its JSON
representation. Croaks on error.
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.
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.
This is useful if your JSON texts are not delimited by an outer
protocol and you need to know where the JSON text ends.
JSON::PP->new->decode_prefix ("[1] the tail")
=> ([1], 3)
FLAGS FOR JSON::PP ONLY
The following flags and properties are for JSON::PP only. If you use
any of these, you can't make your application run faster by replacing
JSON::PP with JSON::XS. If you need these and also speed boost, you
might want to try Cpanel::JSON::XS, a fork of JSON::XS by Reini Urban,
which supports some of these (with a different set of
incompatibilities). Most of these historical flags are only kept for
backward compatibility, and should not be used in a new application.
allow_singlequote
$json = $json->allow_singlequote([$enable])
$enabled = $json->get_allow_singlequote
If $enable is true (or missing), then "decode" will accept invalid JSON
texts that contain strings that begin and end with single quotation
marks. "encode" will not be affected in any way. 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.
$json->allow_singlequote->decode(qq|{"foo":'bar'}|);
$json->allow_singlequote->decode(qq|{'foo':"bar"}|);
$json->allow_singlequote->decode(qq|{'foo':'bar'}|);
allow_barekey
$json = $json->allow_barekey([$enable])
$enabled = $json->get_allow_barekey
If $enable is true (or missing), then "decode" will accept invalid JSON
texts that contain JSON objects whose names don't begin and end with
quotation marks. "encode" will not be affected in any way. 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.
$json->allow_barekey->decode(qq|{foo:"bar"}|);
allow_bignum
$json = $json->allow_bignum([$enable])
$enabled = $json->get_allow_bignum
If $enable is true (or missing), then "decode" will convert big
integers Perl cannot handle as integer into Math::BigInt objects and
convert floating numbers into Math::BigFloat objects. "encode" will
convert "Math::BigInt" and "Math::BigFloat" objects into JSON numbers.
$json->allow_nonref->allow_bignum;
$bigfloat = $json->decode('2.000000000000000000000000001');
print $json->encode($bigfloat);
# => 2.000000000000000000000000001
See also MAPPING.
loose
$json = $json->loose([$enable])
$enabled = $json->get_loose
If $enable is true (or missing), then "decode" will accept invalid JSON
texts that contain unescaped [\x00-\x1f\x22\x5c] characters. "encode"
will not be affected in any way. 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.
$json->loose->decode(qq|["abc
def"]|);
escape_slash
$json = $json->escape_slash([$enable])
$enabled = $json->get_escape_slash
If $enable is true (or missing), then "encode" will explicitly escape
slash (solidus; "U+002F") characters to reduce the risk of XSS (cross
site scripting) that may be caused by "</script>" in a JSON text, with
the cost of bloating the size of JSON texts.
This option may be useful when you embed JSON in HTML, but embedding
arbitrary JSON in HTML (by some HTML template toolkit or by string
interpolation) is risky in general. You must escape necessary
characters in correct order, depending on the context.
"decode" will not be affected in any way.
indent_length
$json = $json->indent_length($number_of_spaces)
$length = $json->get_indent_length
This option is only useful when you also enable "indent" or "pretty".
JSON::XS indents with three spaces when you "encode" (if requested by
"indent" or "pretty"), and the number cannot be changed. JSON::PP
allows you to change/get the number of indent spaces with these
mutator/accessor. The default number of spaces is three (the same as
JSON::XS), and the acceptable range is from 0 (no indentation; it'd be
better to disable indentation by indent(0)) to 15.
sort_by
$json = $json->sort_by($code_ref)
$json = $json->sort_by($subroutine_name)
If you just want to sort keys (names) in JSON objects when you
"encode", enable "canonical" option (see above) that allows you to sort
object keys alphabetically.
If you do need to sort non-alphabetically for whatever reasons, you can
give a code reference (or a subroutine name) to "sort_by", then the
argument will be passed to Perl's "sort" built-in function.
As the sorting is done in the JSON::PP scope, you usually need to
prepend "JSON::PP::" to the subroutine name, and the special variables
$a and $b used in the subrontine used by "sort" function.
Example:
my %ORDER = (id => 1, class => 2, name => 3);
$json->sort_by(sub {
($ORDER{$JSON::PP::a} // 999) <=> ($ORDER{$JSON::PP::b} // 999)
or $JSON::PP::a cmp $JSON::PP::b
});
print $json->encode([
{name => 'CPAN', id => 1, href => 'http://cpan.org'}
]);
# [{"id":1,"name":"CPAN","href":"http://cpan.org"}]
Note that "sort_by" affects all the plain hashes in the data structure.
If you need finer control, "tie" necessary hashes with a module that
implements ordered hash (such as Hash::Ordered and Tie::IxHash).
"canonical" and "sort_by" don't affect the key order in "tie"d hashes.
use Hash::Ordered;
tie my %hash, 'Hash::Ordered',
(name => 'CPAN', id => 1, href => 'http://cpan.org');
print $json->encode([\%hash]);
# [{"name":"CPAN","id":1,"href":"http://cpan.org"}] # order is kept
INCREMENTAL PARSING
This section is also taken from JSON::XS.
In some cases, there is the need for incremental parsing of JSON texts.
While this module always has to keep both JSON text and resulting Perl
data structure in memory at one time, it 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).
JSON::PP 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 mismatched parentheses.
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 erroneous 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 (other than
whitespace) 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::PP->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.
That means you can only use this function to look at or manipulate text
before or after complete JSON objects, not while the parser is in the
middle of parsing a JSON object.
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).
incr_skip
$json->incr_skip
This will reset the state of the incremental parser and will remove the
parsed text from the input buffer so far. 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.
The difference to "incr_reset" is that only text until the parse error
occurred is removed.
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 to repeatedly parse JSON objects and want to
ignore any trailing data, which means you have to reset the parser
after each successful decode.
MAPPING
Most of this section is also taken from JSON::XS.
This section describes how JSON::PP maps Perl values to JSON values and
vice versa. These mappings are designed to "do the right thing" in most
circumstances automatically, preserving round-tripping characteristics
(what you put in comes out as something equivalent).
For the more enlightened: note that in the following descriptions,
lowercase perl refers to the Perl interpreter, while uppercase Perl
refers to the abstract Perl language itself.
JSON -> PERL
object
A JSON object becomes a reference to a hash in Perl. No ordering of
object keys is preserved (JSON does not preserve 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::PP 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 to a 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::PP only guarantees
precision up to but not including the least significant bit.
When "allow_bignum" is enabled, big integer values and any numeric
values will be converted into Math::BigInt and Math::BigFloat
objects respectively, without becoming string scalars or losing
precision.
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 whether a scalar is a JSON boolean
by using the "JSON::PP::is_bool" function.
null
A JSON null atom becomes "undef" in Perl.
shell-style comments ("# text")
As a nonstandard extension to the JSON syntax that is enabled by
the "relaxed" setting, shell-style comments are allowed. They can
start anywhere outside strings and go till the end of the line.
tagged values ("(tag)value").
Another nonstandard extension to the JSON syntax, enabled with the
"allow_tags" setting, are tagged values. In this implementation,
the tag must be a perl package/class name encoded as a JSON string,
and the value must be a JSON array encoding optional constructor
arguments.
See "OBJECT SERIALISATION", below, for details.
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. JSON::PP can optionally sort the
hash keys (determined by the canonical flag and/or sort_by
property), so the same data structure will serialise to the same
JSON text (given same settings and version of JSON::PP), 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::PP::false" and "JSON::PP::true" to improve
readability.
to_json [\0, JSON::PP::true] # yields [false,true]
JSON::PP::true, JSON::PP::false
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
This special value becomes JSON null.
blessed objects
Blessed objects are not directly representable in JSON, but
"JSON::PP" allows various ways of handling objects. See "OBJECT
SERIALISATION", below, for details.
simple scalars
Simple Perl scalars (any scalar that is not a reference) are the
most difficult objects to encode: 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 JSON 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
# (but for older perls)
You can force the type to be a JSON 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 choice is yours.
You can not currently force the type in other, less obscure, ways.
Since version 2.91_01, JSON::PP uses a different number detection
logic that converts a scalar that is possible to turn into a number
safely. The new logic is slightly faster, and tends to help people
who use older perl or who want to encode complicated data
structure. However, this may results in a different JSON text from
the one JSON::XS encodes (and thus may break tests that compare
entire JSON texts). If you do need the previous behavior for
compatibility or for finer control, set PERL_JSON_PP_USE_B
environmental variable to true before you "use" JSON::PP (or
JSON.pm).
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.
JSON::PP (and JSON::XS) trusts what you pass to "encode" method (or
"encode_json" function) is a clean, validated data structure with
values that can be represented as valid JSON values only, because
it's not from an external data source (as opposed to JSON texts you
pass to "decode" or "decode_json", which JSON::PP considers tainted
and doesn't trust). As JSON::PP doesn't know exactly what you and
consumers of your JSON texts want the unexpected values to be (you
may want to convert them into null, or to stringify them with or
without normalisation (string representation of infinities/NaN may
vary depending on platforms), or to croak without conversion),
you're advised to do what you and your consumers need before you
encode, and also not to numify values that may start with values
that look like a number (including infinities/NaN), without
validating.
OBJECT SERIALISATION
As JSON cannot directly represent Perl objects, you have to choose
between a pure JSON representation (without the ability to deserialise
the object automatically again), and a nonstandard extension to the
JSON syntax, tagged values.
SERIALISATION
What happens when "JSON::PP" encounters a Perl object depends on the
"allow_blessed", "convert_blessed", "allow_tags" and "allow_bignum"
settings, which are used in this order:
1. "allow_tags" is enabled and the object has a "FREEZE" method.
In this case, "JSON::PP" creates a tagged JSON value, using a
nonstandard extension to the JSON syntax.
This works by invoking the "FREEZE" method on the object, with the
first argument being the object to serialise, and the second
argument being the constant string "JSON" to distinguish it from
other serialisers.
The "FREEZE" method can return any number of values (i.e. zero or
more). These values and the paclkage/classname of the object will
then be encoded as a tagged JSON value in the following format:
("classname")[FREEZE return values...]
e.g.:
("URI")["http://www.google.com/"]
("MyDate")[2013,10,29]
("ImageData::JPEG")["Z3...VlCg=="]
For example, the hypothetical "My::Object" "FREEZE" method might
use the objects "type" and "id" members to encode the object:
sub My::Object::FREEZE {
my ($self, $serialiser) = @_;
($self->{type}, $self->{id})
}
2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
In this case, the "TO_JSON" method of the object is invoked in
scalar context. It must return a single scalar that can be directly
encoded into JSON. This scalar replaces the object in the JSON
text.
For example, the following "TO_JSON" method will convert all URI
objects to JSON strings when serialised. The fact that these values
originally were URI objects is lost.
sub URI::TO_JSON {
my ($uri) = @_;
$uri->as_string
}
3. "allow_bignum" is enabled and the object is a "Math::BigInt" or
"Math::BigFloat".
The object will be serialised as a JSON number value.
4. "allow_blessed" is enabled.
The object will be serialised as a JSON null value.
5. none of the above
If none of the settings are enabled or the respective methods are
missing, "JSON::PP" throws an exception.
DESERIALISATION
For deserialisation there are only two cases to consider: either
nonstandard tagging was used, in which case "allow_tags" decides, or
objects cannot be automatically be deserialised, in which case you can
use postprocessing or the "filter_json_object" or
"filter_json_single_key_object" callbacks to get some real objects our
of your JSON.
This section only considers the tagged value case: a tagged JSON object
is encountered during decoding and "allow_tags" is disabled, a parse
error will result (as if tagged values were not part of the grammar).
If "allow_tags" is enabled, "JSON::PP" will look up the "THAW" method
of the package/classname used during serialisation (it will not attempt
to load the package as a Perl module). If there is no such method, the
decoding will fail with an error.
Otherwise, the "THAW" method is invoked with the classname as first
argument, the constant string "JSON" as second argument, and all the
values from the JSON array (the values originally returned by the
"FREEZE" method) as remaining arguments.
The method must then return the object. While technically you can
return any Perl scalar, you might have to enable the "allow_nonref"
setting to make that work in all cases, so better return an actual
blessed reference.
As an example, let's implement a "THAW" function that regenerates the
"My::Object" from the "FREEZE" example earlier:
sub My::Object::THAW {
my ($class, $serialiser, $type, $id) = @_;
$class->new (type => $type, id => $id)
}
ENCODING/CODESET FLAG NOTES
This section is taken from JSON::XS.
The interested reader might have seen a number of flags that signify
encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
some confusion on what these do, so here is a short comparison:
"utf8" controls whether the JSON text created by "encode" (and expected
by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
control whether "encode" escapes character values outside their
respective codeset range. Neither of these flags conflict with each
other, although some combinations make less sense than others.
Care has been taken to make all flags symmetrical with respect to
"encode" and "decode", that is, texts encoded with any combination of
these flag values will be correctly decoded when the same flags are
used - in general, if you use different flag settings while encoding
vs. when decoding you likely have a bug somewhere.
Below comes a verbose discussion of these flags. Note that a "codeset"
is simply an abstract set of character-codepoint pairs, while an
encoding takes those codepoint numbers and encodes them, in our case
into octets. Unicode is (among other things) a codeset, UTF-8 is an
encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
encodings at the same time, which can be confusing.
"utf8" flag disabled
When "utf8" is disabled (the default), then "encode"/"decode"
generate and expect Unicode strings, that is, characters with high
ordinal Unicode values (> 255) will be encoded as such characters,
and likewise such characters are decoded as-is, no changes to them
will be done, except "(re-)interpreting" them as Unicode codepoints
or Unicode characters, respectively (to Perl, these are the same
thing in strings unless you do funny/weird/dumb stuff).
This is useful when you want to do the encoding yourself (e.g. when
you want to have UTF-16 encoded JSON texts) or when some other
layer does the encoding for you (for example, when printing to a
terminal using a filehandle that transparently encodes to UTF-8 you
certainly do NOT want to UTF-8 encode your data first and have Perl
encode it another time).
"utf8" flag enabled
If the "utf8"-flag is enabled, "encode"/"decode" will encode all
characters using the corresponding UTF-8 multi-byte sequence, and
will expect your input strings to be encoded as UTF-8, that is, no
"character" of the input string must have any value > 255, as UTF-8
does not allow that.
The "utf8" flag therefore switches between two modes: disabled
means you will get a Unicode string in Perl, enabled means you get
an UTF-8 encoded octet/binary string in Perl.
"latin1" or "ascii" flags enabled
With "latin1" (or "ascii") enabled, "encode" will escape characters
with ordinal values > 255 (> 127 with "ascii") and encode the
remaining characters as specified by the "utf8" flag.
If "utf8" is disabled, then the result is also correctly encoded in
those character sets (as both are proper subsets of Unicode,
meaning that a Unicode string with all character values < 256 is
the same thing as a ISO-8859-1 string, and a Unicode string with
all character values < 128 is the same thing as an ASCII string in
Perl).
If "utf8" is enabled, you still get a correct UTF-8-encoded string,
regardless of these flags, just some more characters will be
escaped using "\uXXXX" then before.
Note that ISO-8859-1-encoded strings are not compatible with UTF-8
encoding, while ASCII-encoded strings are. That is because the
ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the
ISO-8859-1 codeset being a subset of Unicode), while ASCII is.
Surprisingly, "decode" will ignore these flags and so treat all
input values as governed by the "utf8" flag. If it is disabled,
this allows you to decode ISO-8859-1- and ASCII-encoded strings, as
both strict subsets of Unicode. If it is enabled, you can correctly
decode UTF-8 encoded strings.
So neither "latin1" nor "ascii" are incompatible with the "utf8"
flag - they only govern when the JSON output engine escapes a
character or not.
The main use for "latin1" is to relatively efficiently store binary
data as JSON, at the expense of breaking compatibility with most
JSON decoders.
The main use for "ascii" is to force the output to not contain
characters with values > 127, which means you can interpret the
resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
any character set and 8-bit-encoding, and still get the same data
structure back. This is useful when your channel for JSON transfer
is not 8-bit clean or the encoding might be mangled in between
(e.g. in mail), and works because ASCII is a proper subset of most
8-bit and multibyte encodings in use in the world.
BUGS
Please report bugs on a specific behavior of this module to RT or
GitHub issues (preferred):
<https://github.com/makamaka/JSON-PP/issues>
<https://rt.cpan.org/Public/Dist/Display.html?Queue=JSON-PP>
As for new features and requests to change common behaviors, please ask
the author of JSON::XS (Marc Lehmann, <schmorp[at]schmorp.de>) first,
by email (important!), to keep compatibility among JSON.pm backends.
Generally speaking, if you need something special for you, you are
advised to create a new module, maybe based on JSON::Tiny, which is
smaller and written in a much cleaner way than this module.
SEE ALSO
The json_pp(1) command line utility for quick experiments.
JSON::XS(3), Cpanel::JSON::XS(3), and JSON::Tiny(3) for faster
alternatives. JSON(3) and JSON::MaybeXS(3) for easy migration.
JSON::PP::Compat5005(3) and JSON::PP::Compat5006(3) for older perl
users.
RFC4627 (<http://www.ietf.org/rfc/rfc4627.txt>)
RFC7159 (<http://www.ietf.org/rfc/rfc7159.txt>)
RFC8259 (<http://www.ietf.org/rfc/rfc8259.txt>)
AUTHOR
Makamaka Hannyaharamitu, <makamaka[at]cpan.org>
CURRENT MAINTAINER
Kenichi Ishigaki, <ishigaki[at]cpan.org>
COPYRIGHT AND LICENSE
Copyright 2007-2016 by Makamaka Hannyaharamitu
Most of the documentation is taken from JSON::XS by Marc Lehmann
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.38.2 2023-11-28 JSON::PP(3pm)
perl 5.38.2 - Generated Sat Dec 7 14:37:56 CST 2024