JSON::PP(3p) Perl Programmers Reference Guide JSON::PP(3p) #
JSON::PP(3p) Perl Programmers Reference Guide JSON::PP(3p)
NNAAMMEE #
JSON::PP - JSON::XS compatible pure-Perl module.
SSYYNNOOPPSSIISS #
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;
DDEESSCCRRIIPPTTIIOONN #
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.
FFUUNNCCTTIIOONNAALL IINNTTEERRFFAACCEE #
This section is taken from JSON::XS almost verbatim. "encode_json" and
"decode_json" are exported by default.
eennccooddee__jjssoonn $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.
ddeeccooddee__jjssoonn $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.
JJSSOONN::::PPPP::::iiss__bbooooll $is_boolean = JSON::PP::is_bool($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.
See MAPPING, below, for more information on how JSON values are mapped to
Perl.
OOBBJJEECCTT--OORRIIEENNTTEEDD IINNTTEERRFFAACCEE #
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.
nneeww $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 _d_i_s_a_b_l_e_d (with the
exception of "allow_nonref", which defaults to _e_n_a_b_l_e_d 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]}
aasscciiii $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 _E_N_C_O_D_I_N_G_/_C_O_D_E_S_E_T _F_L_A_G _N_O_T_E_S 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"]
llaattiinn11 $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 _E_N_C_O_D_I_N_G_/_C_O_D_E_S_E_T _F_L_A_G _N_O_T_E_S 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)
uuttff88 $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 _E_N_C_O_D_I_N_G_/_C_O_D_E_S_E_T _F_L_A_G _N_O_T_E_S 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);
pprreettttyy $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.
iinnddeenntt $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.
ssppaaccee__bbeeffoorree $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"}
ssppaaccee__aafftteerr $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"}
rreellaaxxeedd $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. _B_e _a_w_a_r_e _t_h_a_t _t_h_i_s _o_p_t_i_o_n _m_a_k_e_s _y_o_u _a_c_c_e_p_t _i_n_v_a_l_i_d
_J_S_O_N _t_e_x_t_s _a_s _i_f _t_h_e_y _w_e_r_e _v_a_l_i_d_!. 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 _s_e_p_a_r_a_t_e_s 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...
]
• 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... */
]
• 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...
]
• 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
]
ccaannoonniiccaall $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.
aallllooww__nnoonnrreeff $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...
aallllooww__uunnkknnoowwnn $json = $json->allow_unknown([$enable])
$enabled = $json->get_allow_unknown
If $enable is true (or missing), then "encode" will _n_o_t 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.
aallllooww__bblleesssseedd $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".
ccoonnvveerrtt__bblleesssseedd $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".
aallllooww__ttaaggss $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.
bboooolleeaann__vvaalluueess $json->boolean_values([$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.
ffiilltteerr__jjssoonn__oobbjjeecctt $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: _n_o_t
"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}');
ffiilltteerr__jjssoonn__ssiinnggllee__kkeeyy__oobbjjeecctt $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} }
}
sshhrriinnkk $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.
mmaaxx__ddeepptthh $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.
mmaaxx__ssiizzee $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.
eennccooddee $json_text = $json->encode($perl_scalar)
Converts the given Perl value or data structure to its JSON
representation. Croaks on error.
ddeeccooddee $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.
ddeeccooddee__pprreeffiixx ($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)
FFLLAAGGSS FFOORR JJSSOONN::::PPPP OONNLLYY #
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.
aallllooww__ssiinngglleeqquuoottee $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. _B_e _a_w_a_r_e _t_h_a_t _t_h_i_s
_o_p_t_i_o_n _m_a_k_e_s _y_o_u _a_c_c_e_p_t _i_n_v_a_l_i_d _J_S_O_N _t_e_x_t_s _a_s _i_f _t_h_e_y _w_e_r_e _v_a_l_i_d_!. 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'}|);
aallllooww__bbaarreekkeeyy $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. _B_e _a_w_a_r_e _t_h_a_t
_t_h_i_s _o_p_t_i_o_n _m_a_k_e_s _y_o_u _a_c_c_e_p_t _i_n_v_a_l_i_d _J_S_O_N _t_e_x_t_s _a_s _i_f _t_h_e_y _w_e_r_e _v_a_l_i_d_!. 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"}|);
aallllooww__bbiiggnnuumm $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.
lloooossee $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. _B_e _a_w_a_r_e _t_h_a_t _t_h_i_s _o_p_t_i_o_n _m_a_k_e_s _y_o_u
_a_c_c_e_p_t _i_n_v_a_l_i_d _J_S_O_N _t_e_x_t_s _a_s _i_f _t_h_e_y _w_e_r_e _v_a_l_i_d_!. 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"]|);
eessccaappee__ssllaasshh $json = $json->escape_slash([$enable]) $enabled = $json->get_escape_slash
If $enable is true (or missing), then "encode" will explicitly escape
_s_l_a_s_h (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.
iinnddeenntt__lleennggtthh $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.
ssoorrtt__bbyy $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
IINNCCRREEMMEENNTTAALL PPAARRSSIINNGG #
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.
iinnccrr__ppaarrssee $json->incr_parse( [$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 _o_n_e 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]");
iinnccrr__tteexxtt $lvalue_string = $json->incr_text
This method returns the currently stored JSON fragment as an lvalue, that
is, you can manipulate it. This _o_n_l_y works when a preceding call to
"incr_parse" in _s_c_a_l_a_r _c_o_n_t_e_x_t 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 _w_i_l_l 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).
iinnccrr__sskkiipp $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.
iinnccrr__rreesseett $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.
MMAAPPPPIINNGG #
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 _p_e_r_l refers to the Perl interpreter, while uppercase _P_e_r_l
refers to the abstract Perl language itself.
JJSSOONN -->> PPEERRLL #
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 ("# _t_e_x_t")
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 ("(_t_a_g)_v_a_l_u_e").
Another nonstandard extension to the JSON syntax, enabled with the
"allow_tags" setting, are tagged values. In this implementation, the
_t_a_g must be a perl package/class name encoded as a JSON string, and
the _v_a_l_u_e must be a JSON array encoding optional constructor
arguments.
See "OBJECT SERIALISATION", below, for details.
PPEERRLL -->> JJSSOONN #
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 _c_a_n_o_n_i_c_a_l flag and/or _s_o_r_t___b_y 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.
OOBBJJEECCTT SSEERRIIAALLIISSAATTIIOONN #
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.
_S_E_R_I_A_L_I_S_A_T_I_O_N #
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) = @_;
$uri->as_string
}
3. "allow_bignum" is enabled and the object is a "Math::BigInt" or
"Math::BigFloat".
The object will be serialised as a JSON number value.
4. "allow_blessed" is enabled.
The object will be serialised as a JSON null value.
5. none of the above
If none of the settings are enabled or the respective methods are
missing, "JSON::PP" throws an exception.
_D_E_S_E_R_I_A_L_I_S_A_T_I_O_N #
For deserialisation there are only two cases to consider: either
nonstandard tagging was used, in which case "allow_tags" decides, or
objects cannot be automatically be deserialised, in which case you can
use postprocessing or the "filter_json_object" or
"filter_json_single_key_object" callbacks to get some real objects our of
your JSON.
This section only considers the tagged value case: a tagged JSON object
is encountered during decoding and "allow_tags" is disabled, a parse
error will result (as if tagged values were not part of the grammar).
If "allow_tags" is enabled, "JSON::PP" will look up the "THAW" method of
the package/classname used during serialisation (it will not attempt to
load the package as a Perl module). If there is no such method, the
decoding will fail with an error.
Otherwise, the "THAW" method is invoked with the classname as first
argument, the constant string "JSON" as second argument, and all the
values from the JSON array (the values originally returned by the
"FREEZE" method) as remaining arguments.
The method must then return the object. While technically you can return
any Perl scalar, you might have to enable the "allow_nonref" setting to
make that work in all cases, so better return an actual blessed
reference.
As an example, let's implement a "THAW" function that regenerates the
"My::Object" from the "FREEZE" example earlier:
sub My::Object::THAW {
my ($class, $serialiser, $type, $id) = @_;
$class->new (type => $type, id => $id)
}
EENNCCOODDIINNGG//CCOODDEESSEETT FFLLAAGG NNOOTTEESS #
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 _e_n_c_o_d_e_s 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 _a_n_d 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-_e_n_c_o_d_e_d 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
_c_o_d_e_s_e_t 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.
BBUUGGSS #
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.
SSEEEE AALLSSOO #
The _j_s_o_n___p_p command line utility for quick experiments.
JSON::XS, Cpanel::JSON::XS, and JSON::Tiny for faster alternatives. JSON
and JSON::MaybeXS for easy migration.
JSON::PP::Compat5005 and JSON::PP::Compat5006 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>)
AAUUTTHHOORR #
Makamaka Hannyaharamitu, <makamaka[at]cpan.org>
CCUURRRREENNTT MMAAIINNTTAAIINNEERR #
Kenichi Ishigaki, <ishigaki[at]cpan.org>
CCOOPPYYRRIIGGHHTT AANNDD LLIICCEENNSSEE #
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 v5.36.3 2023-02-15 JSON::PP(3p)