Provided by: libjson-schema-modern-perl_0.605-1_all 
NAME
JSON::Schema::Modern - Validate data against a schema using a JSON Schema
VERSION
version 0.605
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. This value is
overridden by the value determined from the $schema keyword in the schema used in evaluation (when
present), or defaults to the latest version (currently "draft2020-12").
The use of the $schema keyword in your schema 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#"
• "draft6" or 6 <https://json-schema.org/specification-links.html#draft-6>, corresponding to metaschema
"http://json-schema.org/draft-06/schema#"
• "draft4" or 4 <https://json-schema.org/specification-links.html#draft-4>, corresponding to metaschema
"http://json-schema.org/draft-04/schema#"
output_format
One of: "flag", "basic", "strict_basic", "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. This option is safe to use in all
circumstances, even in the presence of "unevaluatedItems" and "unevaluatedProperties" keywords: the
validation result will not change; only some errors will be omitted from the result.
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
true when specification_version is draft4, draft6 or draft7, and false for all other versions, but this
may change in the future.
Note that the use of a format that does not have a defined handler will not be interpreted as an error in
this mode; instead, the undefined format will simply be ignored. If you instead want this to be treated
as an evaluation error, you must define a custom schema dialect that uses the format-assertion vocabulary
(available in specification version "draft2020-12") and reference it in your schema with the $schema
keyword.
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 draft4, draft6 and draft7 allow this and drafts 2019-09 and 2020-12 prohibit ever
returning the subschema evaluation results together with their parent schema's results, 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). Not operational
when "specification_version" is "draft4", "draft6" or "draft7".
Defaults to false.
scalarref_booleans
When true, any value 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.
stringy_numbers
When true, any value that is expected to be a number or integer in the instance data may also be
expressed as a string. This applies only to the following keywords:
• "type" (where both "string" and "number" (and possibly "integer") are considered valid)
• "const" and "enum" (where the string "1" will match with ""const": 1")
• "uniqueItems" (where strings and numbers are compared numerically to each other, if either or both
are numeric)
• "multipleOf"
• "maximum"
• "exclusiveMaximum"
• "minimum"
• "exclusiveMinimum"
• "format" (for formats defined to validate numbers)
This allows you to write a schema like this (which validates a string representing an integer):
type: string
pattern: ^[0-9]$
multipleOf: 4
minimum: 16
maximum: 256
Such keywords are only applied if the value looks like a number, and do not generate a failure otherwise.
Values are determined to be numbers via "looks_like_number" in perlapi. This option is only intended to
be used for evaluating data from sources that can only be strings, such as the extracted value of an HTTP
header or query parameter.
Defaults to false.
strict
When true, unrecognized keywords are disallowed in schemas (they will cause an immediate abort in
"traverse" or "evaluate").
Defaults to false.
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", "stringy_numbers", "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", "stringy_numbers", "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)
• "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);
$result = $js->validate_schema($schema, $config_override);
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
$ref)
• "initial_schema_uri": adjusts the absolute keyword location as of the start of evaluation
• "metaschema_uri": use the indicated URI as the metaschema
You can pass a series of callback subs to this method corresponding to keywords, which is useful for
extracting data from within schemas and skipping properties that may look like keywords but actually are
not (for example "{"const": {"$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);
$js->add_schema($schema);
Introduces the (unblessed, nested) Perl data structure representing a JSON Schema to the implementation,
registering it under the indicated URI if provided, and all identifiers found within the document will be
resolved against this URI (if provided) and added as well. '' will be used if no other identifier can be
found within.
You MUST call "add_schema" or "add_document" (below) 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.
If you add multiple schemas (either with this method, or implicitly via "evaluate") with no root
identifier (either provided explicitly in the method call, or via an $id keyword at the schema root), all
such previous schemas are removed from memory and can no longer be referenced.
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_document
$js->add_document($uri => $document);
$js->add_document($document);
Introduces the JSON::Schema::Modern::Document (or subclass) object, representing a JSON Schema, to the
implementation, registering it under the indicated URI if provided (and all known identifiers within the
document will be added as well, resolved against the provided URI).
If you add multiple documents (either with this method, or implicitly via "evaluate") with no root
identifier (either provided explicitly in the method call, or via an $id keyword at the schema root), all
such previous schemas are removed from memory and can no longer be referenced.
If there were errors in the document, will die with these errors; otherwise returns the
JSON::Schema::Modern::Document object.
add_format_validation
$js->add_format_validation(all_lc => sub ($value) { lc($value) eq $value });
or
$js->add_format_validation(no_nines => { type => 'number', sub => sub ($value) { $value =~ m/^[0-8]+$/ });
$js->add_format_validation(8bits => { type => 'string', sub => sub ($value) { $value =~ m/^[\x00-\xFF]+$/ });
Adds support for a custom format. If not supplied, the data type(s) that this format applies to defaults
to string; all values of any other type will automatically be deemed to be valid, and will not be passed
to the subref.
Additionally, you can redefine the definition for any core format (see "Format Validation"), but the data
type(s) supported by that format may not be changed.
Be careful to not mutate the type of the value while checking it -- for example, if it is a string, do
not apply arithmetic operators to it -- or subsequent type checks on this value may fail.
See <https://spec.openapis.org/registry/format/> for a registry of known and useful formats; for
compatibility reasons, avoid defining a format listed here with different semantics.
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, as well as "_traverse_keyword_<keyword name>" methods for each keyword.
"_eval_keyword_<keyword name>" methods are optional; when not provided, evaluation will always return a
true result.
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 §4 <https://datatracker.ietf.org/doc/html/rfc4648#section-4>
• "base64url" - see RFC 4648 §5 <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 represented by the indicated identifier (uri or uri-reference). 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).
Note that the data so returned may not be a JSON Schema, if the document encapsulating this location is a
subclass of JSON::Schema::Modern::Document (for example JSON::Schema::Modern::Document::OpenAPI, which
contains addressable locations of various semantic types).
get_document
my $document = $js->get_document($uri_reference);
Fetches the JSON::Schema::Modern::Document object (or subclass) that contains the provided identifier
(uri or uri-reference). "undef" if the schema with that URI has not been loaded (or cached).
CACHING
Very large documents, particularly those used by OpenAPI::Modern, may take a noticeable time to be loaded
and parsed. You can reduce the impact to your preforking application by loading all necessary documents
at startup, and impact can be further reduced by saving objects to cache and then reloading them (perhaps
by using a timestamp or checksum to determine if a fresh reload is needed).
Custom format validations, media types or encodings are not serialized, as they are represented by
subroutine references, and will need to be manually added after thawing.
sub get_evaluator (...) {
my $serialized_file = Path::Tiny::path($filename);
my $schema_file = Path::Tiny::path($schema_filename);
my $js;
if ($serialized_file->stat->mtime < $schema_file->stat->mtime)) {
$js = JSON::Schema::Modern->new;
$js->add_schema(decode_json($schema_file->slurp_raw)); # your application schema
my $frozen = Sereal::Encoder->new({ freeze_callbacks => 1 })->encode($js);
$serialized_file->spew_raw($frozen);
}
else {
my $frozen = $serialized_file->slurp_raw;
$js = Sereal::Decoder->new->decode($frozen);
}
# add custom format validations, media types and encodings here
$js->add_media_type(...);
return $js;
}
See also "CACHING" in OpenAPI::Modern.
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. 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 having difficulties, make sure you are using Perl's fastest
and most trusted and reliable JSON decoder, Cpanel::JSON::XS. Other JSON decoders are known to produce
data with incorrect data types, and data from other sources may also be problematic.
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 draft4, draft6, 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.
(In particular, see vulnerability
"CVE-2023-47038-Write-past-buffer-end-via-illegal-user-defined-Unicode-property" in perl5363delta, which
was fixed in Perl releases 5.34.3, 5.36.3 and 5.38.1.)
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>
• <https://json-schema.org/draft-06#draft-06-release-notes>
• <https://json-schema.org/draft-04/draft-zyp-json-schema-04>
• Understanding JSON Schema <https://json-schema.org/understanding-json-schema>: tutorial-focused
documentation
• OpenAPI::Modern: a parser and evaluator for OpenAPI v3.1 documents
• Mojolicious::Plugin::OpenAPI::Modern: a Mojolicious plugin providing OpenAPI functionality
• Test::Mojo::Role::OpenAPI::Modern: test your Mojolicious application's OpenAPI compliance
AVAILABILITY
This distribution and executable is available on modern Debian versions (via "apt-get") as the
"libjson-schema-modern-perl" package.
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.
perl v5.40.1 2025-03-15 JSON::Schema::Modern(3pm)