NAME
JSON - JSON (JavaScript Object Notation) encoder/decoder
SYNOPSIS
use JSON; # imports encode_json, decode_json, to_json and from_json.
# simple and fast interfaces (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->new->allow_nonref;
$json_text = $json->encode( $perl_scalar );
$perl_scalar = $json->decode( $json_text );
$pretty_printed = $json->pretty->encode( $perl_scalar ); # pretty-printing
VERSION
2.93
DESCRIPTION
This module is a thin wrapper for JSON::XS-compatible modules with
a few additional features. All the backend modules convert a Perl
data structure to a JSON text as of RFC4627 (which we know is
obsolete but we still stick to; see below for an option to support
part of RFC7159) and vice versa. This module uses JSON::XS by
default, and when JSON::XS is not available, this module falls
back on JSON::PP, which is in the Perl core since 5.14. If
JSON::PP is not available either, this module then falls back on
JSON::backportPP (which is actually JSON::PP in a different .pm
file) bundled in the same distribution as this module. You can
also explicitly specify to use Cpanel::JSON::XS, a fork of
JSON::XS by Reini Urban.
All these backend modules have slight incompatibilities between
them, including extra features that other modules don't support,
but as long as you use only common features (most important ones
are described below), migration from backend to backend should be
reasonably easy. For details, see each backend module you use.
CHOOSING BACKEND
This module respects an environmental variable called
"PERL_JSON_BACKEND" when it decides a backend module to use. If
this environmental variable is not set, it tries to load JSON::XS,
and if JSON::XS is not available, it falls back on JSON::PP, and
then JSON::backportPP if JSON::PP is not available either.
If you always don't want it to fall back on pure perl modules, set
the variable like this ("export" may be "setenv", "set" and the
likes, depending on your environment):
> export PERL_JSON_BACKEND=JSON::XS
If you prefer Cpanel::JSON::XS to JSON::XS, then:
> export PERL_JSON_BACKEND=Cpanel::JSON::XS,JSON::XS,JSON::PP
You may also want to set this variable at the top of your test
files, in order not to be bothered with incompatibilities between
backends (you need to wrap this in "BEGIN", and set before
actually "use"-ing JSON module, as it decides its backend as soon
as it's loaded):
BEGIN { $ENV{PERL_JSON_BACKEND}='JSON::backportPP'; }
use JSON;
USING OPTIONAL FEATURES
There are a few options you can set when you "use" this module:
-support_by_pp
BEGIN { $ENV{PERL_JSON_BACKEND} = 'JSON::XS' }
use JSON -support_by_pp;
my $json = JSON->new;
# escape_slash is for JSON::PP only.
$json->allow_nonref->escape_slash->encode("/");
With this option, this module loads its pure perl backend
along with its XS backend (if available), and lets the XS
backend to watch if you set a flag only JSON::PP supports.
When you do, the internal JSON::XS object is replaced with a
newly created JSON::PP object with the setting copied from the
XS object, so that you can use JSON::PP flags (and its slower
"decode"/"encode" methods) from then on. In other words, this
is not something that allows you to hook JSON::XS to change
its behavior while keeping its speed. JSON::XS and JSON::PP
objects are quite different (JSON::XS object is a blessed
scalar reference, while JSON::PP object is a blessed hash
reference), and can't share their internals.
To avoid needless overhead (by copying settings), you are
advised not to use this option and just to use JSON::PP
explicitly when you need JSON::PP features.
-convert_blessed_universally
use JSON -convert_blessed_universally;
my $json = JSON->new->allow_nonref->convert_blessed;
my $object = bless {foo => 'bar'}, 'Foo';
$json->encode($object); # => {"foo":"bar"}
JSON::XS-compatible backend modules don't encode blessed
objects by default (except for their boolean values, which are
typically blessed JSON::PP::Boolean objects). If you need to
encode a data structure that may contain objects, you usually
need to look into the structure and replace objects with
alternative non-blessed values, or enable "convert_blessed"
and provide a "TO_JSON" method for each object's (base) class
that may be found in the structure, in order to let the
methods replace the objects with whatever scalar values the
methods return.
If you need to serialise data structures that may contain
arbitrary objects, it's probably better to use other
serialisers (such as Sereal or Storable for example), but if
you do want to use this module for that purpose,
"-convert_blessed_universally" option may help, which tweaks
"encode" method of the backend to install "UNIVERSAL::TO_JSON"
method (locally) before encoding, so that all the objects that
don't have their own "TO_JSON" method can fall back on the
method in the "UNIVERSAL" namespace. Note that you still need
to enable "convert_blessed" flag to actually encode objects in
a data structure, and "UNIVERSAL::TO_JSON" method installed by
this option only converts blessed hash/array references into
their unblessed clone (including private keys/values that are
not supposed to be exposed). Other blessed references will be
converted into null.
This feature is experimental and may be removed in the future.
-no_export
When you don't want to import functional interfaces from a
module, you usually supply "()" to its "use" statement.
use JSON (); # no functional interfaces
If you don't want to import functional interfaces, but you
also want to use any of the above options, add "-no_export" to
the option list.
# no functional interfaces, while JSON::PP support is enabled.
use JSON -support_by_pp, -no_export;
FUNCTIONAL INTERFACE
This section is taken from JSON::XS. "encode_json" and
"decode_json" are exported by default.
This module also exports "to_json" and "from_json" for backward
compatibility. These are slower, and may expect/generate different
stuff from what "encode_json" and "decode_json" do, depending on
their options. It's better just to use Object-Oriented interfaces
than using these two functions.
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:
$json_text = JSON->new->utf8->encode($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:
$perl_scalar = JSON->new->utf8->decode($json_text)
Except being faster.
to_json
$json_text = to_json($perl_scalar[, $optional_hashref])
Converts the given Perl data structure to a Unicode string by
default. Croaks on error.
Basically, this function call is functionally identical to:
$json_text = JSON->new->encode($perl_scalar)
Except being slower.
You can pass an optional hash reference to modify its behavior,
but that may change what "to_json" expects/generates (see
"ENCODING/CODESET FLAG NOTES" for details).
$json_text = to_json($perl_scalar, {utf8 => 1, pretty => 1})
# => JSON->new->utf8(1)->pretty(1)->encode($perl_scalar)
from_json
$perl_scalar = from_json($json_text[, $optional_hashref])
The opposite of "to_json": expects a Unicode string and tries to
parse it, returning the resulting reference. Croaks on error.
Basically, this function call is functionally identical to:
$perl_scalar = JSON->new->decode($json_text)
You can pass an optional hash reference to modify its behavior,
but that may change what "from_json" expects/generates (see
"ENCODING/CODESET FLAG NOTES" for details).
$perl_scalar = from_json($json_text, {utf8 => 1})
# => JSON->new->utf8(1)->decode($json_text)
JSON::is_bool
$is_boolean = JSON::is_bool($scalar)
Returns true if the passed scalar represents either JSON::true or
JSON::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.
COMMON 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->new
Creates a new JSON::XS-compatible backend object that can be used
to de/encode JSON strings. All boolean flags described below are
by default *disabled*.
The mutators for flags all return the backend object again and
thus calls can be chained:
my $json = JSON->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->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->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;
$jsontext = encode "UTF-16BE", JSON->new->encode ($object);
Example, decode UTF-32LE-encoded JSON:
use Encode;
$object = JSON->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.
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:
* list items can have an end-comma
JSON *separates* array elements and key-value pairs with
commas. This can be annoying if you write JSON texts manually
and want to be able to quickly append elements, so this
extension accepts comma at the end of such items not just
between them:
[
1,
2, <- this comma not normally allowed
]
{
"k1": "v1",
"k2": "v2", <- this comma not normally allowed
}
* shell-style '#'-comments
Whenever JSON allows whitespace, shell-style comments are
additionally allowed. They are terminated by the first
carriage-return or line-feed character, after which more
white-space and comments are allowed.
[
1, # this comment not allowed in JSON
# neither this one...
]
canonical
$json = $json->canonical([$enable])
$enabled = $json->get_canonical
If $enable is true (or missing), then the "encode" method will
output JSON objects by sorting their keys. This is adding a
comparatively high overhead.
If $enable is false, then the "encode" method will output
key-value pairs in the order Perl stores them (which will likely
change between runs of the same script, 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
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 with enabled
"allow_nonref", resulting in an invalid JSON text:
JSON->new->allow_nonref->encode ("Hello, World!")
=> "Hello, World!"
allow_unknown
$json = $json->allow_unknown ([$enable])
$enabled = $json->get_allow_unknown
If $enable is true (or missing), then "encode" will *not* throw an
exception when it encounters values it cannot represent in JSON
(for example, filehandles) but instead will encode a JSON "null"
value. Note that blessed objects are not included here and are
handled separately by c<allow_nonref>.
If $enable is false (the default), then "encode" will throw an
exception when it encounters anything it cannot encode as JSON.
This option does not affect "decode" in any way, and it is
recommended to leave it off unless you know your communications
partner.
allow_blessed
$json = $json->allow_blessed([$enable])
$enabled = $json->get_allow_blessed
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".
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 (i.e. a copy of
that scalar to avoid aliasing) is inserted into the deserialised
data structure. If it returns an empty list (NOTE: *not* "undef",
which is a valid scalar), the original deserialised hash will be
inserted. This setting can slow down decoding considerably.
When $coderef is omitted or undefined, any existing callback will
be removed and "decode" will not change the deserialised hash in
any way.
Example, convert all JSON objects into the integer 5:
my $js = JSON->new->filter_json_object (sub { 5 });
# returns [5]
$js->decode ('[{}]'); # the given subroutine takes a hash reference.
# throw an exception because allow_nonref is not enabled
# so a lone 5 is not allowed.
$js->decode ('{"a":1, "b":2}');
filter_json_single_key_object
$json = $json->filter_json_single_key_object($key [=> $coderef])
Works remotely similar to "filter_json_object", but is only called
for JSON objects having a single key named $key.
This $coderef is called before the one specified via
"filter_json_object", if any. It gets passed the single value in
the JSON object. If it returns a single value, it will be inserted
into the data structure. If it returns nothing (not even "undef"
but the empty list), the callback from "filter_json_object" will
be called next, as if no single-key callback were specified.
If $coderef is omitted or undefined, the corresponding callback
will be disabled. There can only ever be one callback for a given
key.
As this callback gets called less often then the
"filter_json_object" one, decoding speed will not usually suffer
as much. Therefore, single-key objects make excellent targets to
serialise Perl objects into, especially as single-key JSON objects
are as close to the type-tagged value concept as JSON gets (it's
basically an ID/VALUE tuple). Of course, JSON does not support
this in any way, so you need to make sure your data never looks
like a serialised Perl hash.
Typical names for the single object key are "__class_whatever__",
or "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or
even things like "__class_md5sum(classname)__", to reduce the risk
of clashing with real hashes.
Example, decode JSON objects of the form "{ "__widget__" => <id>
}" into the corresponding $WIDGET{<id>} object:
# return whatever is in $WIDGET{5}:
JSON
->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} }
}
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.
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).
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->new->decode_prefix ("[1] the tail")
=> ([1], 3)
ADDITIONAL METHODS
The following methods are for this module only.
backend
$backend = $json->backend
Since 2.92, "backend" method returns an abstract backend module
used currently, which should be JSON::Backend::XS (which inherits
JSON::XS or Cpanel::JSON::XS), or JSON::Backend::PP (which
inherits JSON::PP), not to monkey-patch the actual backend module
globally.
If you need to know what is used actually, use "isa", instead of
string comparison.
is_xs
$boolean = $json->is_xs
Returns true if the backend inherits JSON::XS or Cpanel::JSON::XS.
is_pp
$boolean = $json->is_pp
Returns true if the backend inherits JSON::PP.
property
$settings = $json->property()
Returns a reference to a hash that holds all the common flag
settings.
$json = $json->property('utf8' => 1)
$value = $json->property('utf8') # 1
You can use this to get/set a value of a particular flag.
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).
This module will only attempt to parse the JSON text once it is
sure it has enough text to get a decisive result, using a very
simple but truly incremental parser. This means that it sometimes
won't stop as early as the full parser, for example, it doesn't
detect 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->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 the backend modules map 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 preserver
object key ordering itself).
array
A JSON array becomes a reference to an array in Perl.
string
A JSON string becomes a string scalar in Perl - Unicode
codepoints in JSON are represented by the same codepoints in
the Perl string, so no manual decoding is necessary.
number
A JSON number becomes either an integer, numeric (floating
point) or string scalar in perl, depending on its range and
any fractional parts. On the Perl level, there is no
difference between those as Perl handles all the conversion
details, but an integer may take slightly less memory and
might represent more values exactly than floating point
numbers.
If the number consists of digits only, this module 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, this module only
guarantees precision up to but not including the least
significant bit.
true, false
These JSON atoms become "JSON::true" and "JSON::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::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.
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. This module can
optionally sort the hash keys (determined by the *canonical*
flag), so the same data structure will serialise to the same
JSON text (given same settings and version of the same
backend), but this incurs a runtime overhead and is only
rarely useful, e.g. when you want to compare some JSON text
against another for equality.
array references
Perl array references become JSON arrays.
other references
Other unblessed references are generally not allowed and will
cause an exception to be thrown, except for references to the
integers 0 and 1, which get turned into "false" and "true"
atoms in JSON. You can also use "JSON::false" and "JSON::true"
to improve readability.
encode_json [\0,JSON::true] # yields [false,true]
JSON::true, JSON::false, JSON::null
These special values become JSON true and JSON false values,
respectively. You can also use "\1" and "\0" directly if you
want.
blessed objects
Blessed objects are not directly representable in JSON, but
"JSON::XS" 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: this module will encode
undefined scalars as JSON "null" values, scalars that have
last been used in a string context before encoding as JSON
strings, and anything else as number value:
# dump as number
encode_json [2] # yields [2]
encode_json [-3.0e17] # yields [-3e+17]
my $value = 5; encode_json [$value] # yields [5]
# used as string, so dump as string
print $value;
encode_json [$value] # yields ["5"]
# undef becomes null
encode_json [undef] # yields [null]
You can force the type to be a string by stringifying it:
my $x = 3.1; # some variable containing a number
"$x"; # stringified
$x .= ""; # another, more awkward way to stringify
print $x; # perl does it for you, too, quite often
You can force the type to be a number by numifying it:
my $x = "3"; # some variable containing a string
$x += 0; # numify it, ensuring it will be dumped as a number
$x *= 1; # same thing, the choice is yours.
You can not currently force the type in other, less obscure,
ways. Tell me if you need this capability (but don't forget to
explain why it's needed :).
Note that numerical precision has the same meaning as under
Perl (so binary to decimal conversion follows the same rules
as in Perl, which can differ to other languages). Also, your
perl interpreter might expose extensions to the floating point
numbers of your platform, such as infinities or NaN's - these
cannot be represented in JSON, and it is an error to pass
those in.
OBJECT SERIALISATION
As for Perl objects, this module only supports a pure JSON
representation (without the ability to deserialise the object
automatically again).
SERIALISATION
What happens when this module encounters a Perl object depends on
the "allow_blessed" and "convert_blessed" settings, which are used
in this order:
1. "convert_blessed" is enabled and the object has a "TO_JSON"
method.
In this case, the "TO_JSON" method of the object is invoked in
scalar context. It must return a single scalar that can be
directly encoded into JSON. This scalar replaces the object in
the JSON text.
For example, the following "TO_JSON" method will convert all
URI objects to JSON strings when serialised. The fact that
these values originally were URI objects is lost.
sub URI::TO_JSON {
my ($uri) = @_;
$uri->as_string
}
2. "allow_blessed" is enabled.
The object will be serialised as a JSON null value.
3. none of the above
If none of the settings are enabled or the respective methods
are missing, this module throws an exception.
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.
BACKWARD INCOMPATIBILITY
Since version 2.90, stringification (and string comparison) for
"JSON::true" and "JSON::false" has not been overloaded. It
shouldn't matter as long as you treat them as boolean values, but
a code that expects they are stringified as "true" or "false"
doesn't work as you have expected any more.
if (JSON::true eq 'true') { # now fails
print "The result is $JSON::true now."; # => The result is 1 now.
And now these boolean values don't inherit JSON::Boolean, either.
When you need to test a value is a JSON boolean value or not, use
"JSON::is_bool" function, instead of testing the value inherits a
particular boolean class or not.
BUGS
Please report bugs on backend selection and additional features
this module provides to RT or GitHub issues for this module:
https://rt.cpan.org/Public/Dist/Display.html?Queue=JSON
https://github.com/makamaka/JSON/issues
Please report bugs and feature requests on decoding/encoding and
boolean behaviors to the author of the backend module you are
using.
SEE ALSO
JSON::XS, Cpanel::JSON::XS, JSON::PP for backends.
JSON::MaybeXS, an alternative that prefers Cpanel::JSON::XS.
"RFC4627"(<
http://www.ietf.org/rfc/rfc4627.txt>)
AUTHOR
Makamaka Hannyaharamitu, <makamaka[at]cpan.org>
JSON::XS was written by Marc Lehmann <schmorp[at]schmorp.de>
The release of this new version owes to the courtesy of Marc
Lehmann.
COPYRIGHT AND LICENSE
Copyright 2005-2013 by Makamaka Hannyaharamitu
This library is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
