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", "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 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 draft7 allows 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 "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.

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)
• "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);
  $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 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);
  $js->add_schema($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 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 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).

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).

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. 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>)