Provided by: libjson-schema-modern-perl_0.569-1_all 
NAME
JSON::Schema::Modern - Validate data against a schema
VERSION
version 0.569
SYNOPSIS
use JSON::Schema::Modern;
$js = JSON::Schema::Modern->new(
specification_version => 'draft2020-12',
output_format => 'flag',
... # other options
);
$result = $js->evaluate($instance_data, $schema_data);
DESCRIPTION
This module aims to be a fully-compliant JSON Schema <https://json-schema.org/> evaluator
and validator, targeting the currently-latest Draft 2020-12 <https://json-
schema.org/specification-links.html#2020-12> version of the specification.
CONFIGURATION OPTIONS
These values are all passed as arguments to the constructor.
specification_version
Indicates which version of the JSON Schema specification is used during evaluation. When
not set, this value is derived from the $schema keyword in the schema used in evaluation,
or defaults to the latest version (currently "draft2020-12").
The use of this option is HIGHLY encouraged to ensure continued correct operation of your
schema. The current default value will not stay the same over time.
May be one of:
• "draft2020-12" or "2020-12" <https://json-schema.org/specification-
links.html#2020-12>, corresponding to metaschema
"https://json-schema.org/draft/2020-12/schema"
• "draft2019-09" or "2019-09" <https://json-schema.org/specification-
links.html#2019-09-formerly-known-as-draft-8>, corresponding to metaschema
"https://json-schema.org/draft/2019-09/schema"
• "draft7" or 7 <https://json-schema.org/specification-links.html#draft-7>,
corresponding to metaschema "http://json-schema.org/draft-07/schema#"
Note that you can also use a $schema keyword in the schema itself, to specify a different
metaschema or specification version.
output_format
One of: "flag", "basic", "strict_basic", "detailed", "verbose", "terse". Defaults to
"basic". "strict_basic" can only be used with "specification_version = draft2019-09".
Passed to "output_format" in JSON::Schema::Modern::Result.
short_circuit
When true, evaluation will return early in any execution path as soon as the outcome can
be determined, rather than continuing to find all errors or annotations. Be aware that
this can result in invalid results in the presence of keywords that depend on annotations,
namely "unevaluatedItems" and "unevaluatedProperties".
Defaults to true when "output_format" is "flag", and false otherwise.
max_traversal_depth
The maximum number of levels deep a schema traversal may go, before evaluation is halted.
This is to protect against accidental infinite recursion, such as from two subschemas that
each reference each other, or badly-written schemas that could be optimized. Defaults to
50.
validate_formats
When true, the "format" keyword will be treated as an assertion, not merely an annotation.
Defaults to false.
format_validations
An optional hashref that allows overriding the validation method for formats, or adding
new ones. Overrides to existing formats (see "Format Validation") must be specified in
the form of "{ $format_name => $format_sub }", where the format sub is a subref that takes
one argument and returns a boolean result. New formats must be specified in the form of "{
$format_name => { type => $type, sub => $format_sub } }", where the type indicates which
of the core JSON Schema types (null, object, array, boolean, string, number, or integer)
the instance value must be for the format validation to be considered.
validate_content_schemas
When true, the "contentMediaType" and "contentSchema" keywords are not treated as pure
annotations: "contentEncoding" (when present) is used to decode the applied data payload
and then "contentMediaType" will be used as the media-type for decoding to produce the
data payload which is then applied to the schema in "contentSchema" for validation. (Note
that treating these keywords as anything beyond simple annotations is contrary to the
specification, therefore this option defaults to false.)
See "add_media_type" and "add_encoding" for adding additional type support.
Technically only draft7 allows this and drafts 2019-09 and 2020-12 prohibit ever returning
the subschema evaluation results together with their parent schema's, so shhh. I'm trying
to get this fixed for the next draft.
collect_annotations
When true, annotations are collected from keywords that produce them, when validation
succeeds. These annotations are available in the returned result (see
JSON::Schema::Modern::Result). Defaults to false.
scalarref_booleans
When true, any type that is expected to be a boolean in the instance data may also be
expressed as the scalar references "\0" or "\1" (which are serialized as booleans by JSON
backends). Defaults to false.
strict
When true, unrecognized keywords are disallowed in schemas (they will cause an immediate
abort in "traverse" or "evaluate").
METHODS
evaluate_json_string
$result = $js->evaluate_json_string($data_as_json_string, $schema);
$result = $js->evaluate_json_string($data_as_json_string, $schema, { collect_annotations => 1});
Evaluates the provided instance data against the known schema document.
The data is in the form of a JSON-encoded string (in accordance with RFC8259
<https://datatracker.ietf.org/doc/html/rfc8259>). The string is expected to be UTF-8
encoded.
The schema must be in one of these forms:
• a Perl data structure, such as what is returned from a JSON decode operation,
• a JSON::Schema::Modern::Document object,
• or a URI string indicating the location where such a schema is located.
Optionally, a hashref can be passed as a third parameter which allows changing the values
of the "short_circuit", "collect_annotations", "scalarref_booleans", "strict",
"validate_formats", and/or "validate_content_schemas" settings for just this evaluation
call.
You can also pass use these keys to alter behaviour (these are generally only used by
custom validation applications that contain embedded JSON Schemas):
• "data_path": adjusts the effective path of the data instance as of the start of
evaluation
• "traversed_schema_path": adjusts the accumulated path as of the start of evaluation
(or last $id or $ref)
• "initial_schema_uri": adjusts the recorded absolute keyword location as of the start
of evaluation
• "effective_base_uri": locations in errors and annotations are resolved against this
URI
The return value is a JSON::Schema::Modern::Result object, which can also be used as a
boolean.
evaluate
$result = $js->evaluate($instance_data, $schema);
$result = $js->evaluate($instance_data, $schema, { short_circuit => 0 });
Evaluates the provided instance data against the known schema document.
The data is in the form of an unblessed nested Perl data structure representing any type
that JSON allows: null, boolean, string, number, object, array. (See "TYPES" below.)
The schema must be in one of these forms:
• a Perl data structure, such as what is returned from a JSON decode operation,
• a JSON::Schema::Modern::Document object,
• or a URI string indicating the location where such a schema is located.
Optionally, a hashref can be passed as a third parameter which allows changing the values
of the "short_circuit", "collect_annotations", "scalarref_booleans", "strict",
"validate_formats", and/or "validate_content_schemas" settings for just this evaluation
call.
You can also pass use these keys to alter behaviour (these are generally only used by
custom validation applications that contain embedded JSON Schemas):
• "data_path": adjusts the effective path of the data instance as of the start of
evaluation
• "traversed_schema_path": adjusts the accumulated path as of the start of evaluation
(or last $id or $ref)
• "initial_schema_uri": adjusts the recorded absolute keyword location as of the start
of evaluation
• "effective_base_uri": locations in errors and annotations are resolved against this
URI
You can pass a series of callback subs to this method corresponding to keywords, which is
useful for identifying various data that are not exposed by annotations. This feature is
highly experimental and may change in the future.
For example, to find the locations where all $ref keywords are applied successfully:
my @used_ref_at;
$js->evaluate($data, $schema_or_uri, {
callbacks => {
'$ref' => sub ($data, $schema, $state) {
push @used_ref_at, $state->{data_path};
}
},
});
The return value is a JSON::Schema::Modern::Result object, which can also be used as a
boolean. Callbacks are not compatible with "short_circuit" mode.
validate_schema
$result = $js->validate_schema($schema);
Evaluates the provided schema as instance data against its metaschema. Accepts $schema and
$config_override parameters in the same form as "evaluate".
traverse
$result = $js->traverse($schema);
$result = $js->traverse($schema, { initial_schema_uri => 'http://example.com' });
Traverses the provided schema without evaluating it against any instance data. Returns the
internal state object accumulated during the traversal, including any identifiers found
therein, and any errors found during parsing. For internal purposes only.
Optionally, a hashref can be passed as a second parameter which alters some behaviour
(these are generally only used by custom validation applications that contain embedded
JSON Schemas):
• "traversed_schema_path": adjusts the accumulated path as of the start of evaluation
(or last $id or $ref)
• "initial_schema_uri": adjusts the recorded absolute keyword location as of the start
of evaluation
• "metaschema_uri": use the indicated URI as the metaschema
You can pass a series of callback subs to this method corresponding to keywords, which is
useful for extracting data from within schemas and skipping properties that may look like
keywords but actually are not (for example "{"const":{"$ref": "this is not actually a
$ref"}}"). This feature is highly experimental and is highly likely to change in the
future.
For example, to find the resolved targets of all $ref keywords in a schema document:
my @refs;
JSON::Schema::Modern->new->traverse($schema, {
callbacks => {
'$ref' => sub ($schema, $state) {
push @refs, Mojo::URL->new($schema->{'$ref'})
->to_abs(JSON::Schema::Modern::Utilities::canonical_uri($state));
}
},
});
add_schema
$js->add_schema($uri => $schema);
$js->add_schema($uri => $document);
$js->add_schema($schema);
$js->add_schema($document);
Introduces the (unblessed, nested) Perl data structure or JSON::Schema::Modern::Document
object, representing a JSON Schema, to the implementation, registering it under the
indicated URI if provided (and if not, '' will be used if no other identifier can be found
within).
You MUST call "add_schema" for any external resources that a schema may reference via $ref
before calling "evaluate", other than the standard metaschemas which are loaded from a
local cache as needed.
Returns "undef" if the resource could not be found; if there were errors in the document,
will die with these errors; otherwise returns the JSON::Schema::Modern::Document that
contains the added schema.
add_format_validation
$js->add_format_validation(no_nines => { type => 'number', sub => sub ($value) { $value =~ m/^[0-8]$$/ });
Adds support for a custom format. The data type that this format applies to must be
supplied; all values of any other type will automatically be deemed to be valid, and will
not be passed to the subref.
add_vocabulary
$js->add_vocabulary('My::Custom::Vocabulary::Class');
Makes a custom vocabulary class available to metaschemas that make use of this vocabulary.
as described in the specification at "Meta-Schemas and Vocabularies" <https://json-
schema.org/draft/2020-12/json-schema-core.html#rfc.section.8.1>.
The class must compose the JSON::Schema::Modern::Vocabulary role and implement the
vocabulary and keywords methods.
add_media_type
$js->add_media_type('application/furble' => sub ($content_ref) {
return ...; # data representing the deserialized text for Content-Type: application/furble
});
Takes a media-type name and a subref which takes a single scalar reference, which is
expected to be a reference to a string, which might contain wide characters (i.e. not
octets), especially when used in conjunction with "get_encoding" below. Must return a
reference to a value of any type (which is then dereferenced for the "contentSchema"
keyword).
These media types are already known:
• "application/json" - see RFC 4627 <https://datatracker.ietf.org/doc/html/rfc4627>
• "application/schema+json" - see proposed definition <https://json-
schema.org/draft/2020-12/json-schema-core.html#name-application-schemajson>
• "application/schema-instance+json" - see proposed definition <https://json-
schema.org/draft/2020-12/json-schema-core.html#name-application-schema-instance>
• "application/octet-stream" - passes strings through unchanged
• "application/x-www-form-urlencoded"
• "application/x-ndjson" - see <https://github.com/ndjson/ndjson-spec>
• "text/*" - passes strings through unchanged
get_media_type
Fetches a decoder sub for the indicated media type. Lookups are performed without case
sensitivity.
You can use it thusly:
$js->add_media_type('application/furble' => sub { ... }); # as above
my $decoder = $self->get_media_type('application/furble') or die 'cannot find media type decoder';
my $content_ref = $decoder->(\$content_string);
add_encoding
$js->add_encoding('bloop' => sub ($content_ref) {
return \ ...; # data representing the deserialized content for Content-Transfer-Encoding: bloop
});
Takes an encoding name and a subref which takes a single scalar reference, which is
expected to be a reference to a string, which SHOULD be a 7-bit or 8-bit string. Result
values MUST be a scalar-reference to a string (which is then dereferenced for the
"contentMediaType" keyword).
Encodings handled natively are:
• "identity" - passes strings through unchanged
• "base64" - see RFC 4648 X4 <https://datatracker.ietf.org/doc/html/rfc4648#section-4>
• "base64url" - see RFC 4648 X5
<https://datatracker.ietf.org/doc/html/rfc4648#section-5>
See also "encode" in HTTP::Message.
get_encoding
Fetches a decoder sub for the indicated encoding. Incoming values MUST be a reference to
an octet string. Result values will be a scalar-reference to a string, which might be
passed to a media_type decoder (see above).
You can use it thusly:
my $decoder = $self->get_encoding('base64') or die 'cannot find encoding decoder';
my $content_ref = $decoder->(\$content_string);
get
my $schema = $js->get($uri);
my ($schema, $canonical_uri) = $js->get($uri);
Fetches the Perl data structure representing the JSON Schema at the indicated URI. When
called in list context, the canonical URI of that location is also returned, as a
Mojo::URL. Returns "undef" if the schema with that URI has not been loaded (or cached).
LIMITATIONS
Types
Perl is a more loosely-typed language than JSON. This module delves into a value's
internal representation in an attempt to derive the true "intended" type of the value.
However, if a value is used in another context (for example, a numeric value is
concatenated into a string, or a numeric string is used in an arithmetic operation),
additional flags can be added onto the variable causing it to resemble the other type.
This should not be an issue if data validation is occurring immediately after decoding a
JSON payload, or if the JSON string itself is passed to this module. If you are still
having difficulties, make sure you are using Perl's fastest and most trusted and reliable
JSON decoder, Cpanel::JSON::XS (or its proxy, useful for fatpacking, JSON::MaybeXS).
Other JSON decoders are known to produce data with incorrect data types.
For more information, see "MAPPING" in Cpanel::JSON::XS.
Format Validation
By default (and unless you specify a custom metaschema with the $schema keyword or
"metaschema" in JSON::Schema::Modern::Document), formats are treated only as annotations,
not assertions. When "validate_formats" is true, strings are also checked against the
format as specified in the schema. At present the following formats are supported (use of
any other formats than these will always evaluate as true, but remember you can always
supply custom format handlers; see "format_validations" above):
• "date-time"
• "date"
• "time"
• "duration"
• "email"
• "idn-email"
• "hostname"
• "idn-hostname"
• "ipv4"
• "ipv6"
• "uri"
• "uri-reference"
• "iri"
• "uuid"
• "json-pointer"
• "relative-json-pointer"
• "regex"
A few optional prerequisites are needed for some of these (if the prerequisite is missing,
validation will always succeed):
• "date-time", "date", and "time" require Time::Moment, DateTime::Format::RFC3339
• "email" and "idn-email" require Email::Address::XS version 1.04 (or higher)
• "hostname" and "idn-hostname" require Data::Validate::Domain
• "idn-hostname" requires Net::IDN::Encode
Specification Compliance
This implementation is now fully specification-compliant (for versions draft7,
draft2019-09, draft2020-12), but until version 1.000 is released, it is still deemed to be
missing some optional but quite useful features, such as:
• loading schema documents from disk
• loading schema documents from the network
• loading schema documents from a local web application (e.g. Mojolicious)
• additional output formats beyond "flag", "basic", and "terse"
(<https://json-schema.org/draft/2020-12/json-schema-core.html#rfc.section.12>)
SECURITY CONSIDERATIONS
The "pattern" and "patternProperties" keywords evaluate regular expressions from the
schema, the "regex" format validator evaluates regular expressions from the data, and some
keywords in the Validation vocabulary perform floating point operations on potentially-
very large numbers. No effort is taken (at this time) to sanitize the regular expressions
for embedded code or detect potentially pathological constructs that may pose a security
risk, either via denial of service or by allowing exposure to the internals of your
application. DO NOT USE SCHEMAS FROM UNTRUSTED SOURCES.
SEE ALSO
• json-schema-eval
• <https://json-schema.org>
• RFC8259: The JavaScript Object Notation (JSON) Data Interchange Format
<https://datatracker.ietf.org/doc/html/rfc8259>
• RFC3986: Uniform Resource Identifier (URI): Generic Syntax
<https://datatracker.ietf.org/doc/html/rfc3986>
• Test::JSON::Schema::Acceptance: contains the official JSON Schema test suite
• JSON::Schema::Tiny: a more stripped-down implementation of the specification, with
fewer dependencies and faster evaluation
• <https://json-schema.org/draft/2020-12/release-notes.html>
• <https://json-schema.org/draft/2019-09/release-notes.html>
• <https://json-schema.org/draft-07/json-schema-release-notes.html>
• Understanding JSON Schema <https://json-schema.org/understanding-json-schema>:
tutorial-focused documentation
SUPPORT
Bugs may be submitted through
<https://github.com/karenetheridge/JSON-Schema-Modern/issues>.
I am also usually active on irc, as 'ether' at "irc.perl.org" and "irc.libera.chat".
You can also find me on the JSON Schema Slack server <https://json-schema.slack.com> and
OpenAPI Slack server <https://open-api.slack.com>, which are also great resources for
finding help.
AUTHOR
Karen Etheridge <ether@cpan.org>
COPYRIGHT AND LICENCE
This software is copyright (c) 2020 by Karen Etheridge.
This is free software; you can redistribute it and/or modify it under the same terms as
the Perl 5 programming language system itself.