JSON::Schema::Modern - Validate data against a schema
version 0.582
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);
This module aims to be a fully-compliant JSON Schema evaluator and validator, targeting the currently-latest Draft 2020-12 version of the specification.
These values are all passed as arguments to the constructor.
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).
$schema
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, corresponding to metaschema https://json-schema.org/draft/2020-12/schema
2020-12
https://json-schema.org/draft/2020-12/schema
draft2019-09 or 2019-09, corresponding to metaschema https://json-schema.org/draft/2019-09/schema
draft2019-09
2019-09
https://json-schema.org/draft/2019-09/schema
draft7 or 7, corresponding to metaschema http://json-schema.org/draft-07/schema#
draft7
7
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.
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.
flag
basic
strict_basic
detailed
verbose
terse
specification_version = draft2019-09
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.
unevaluatedItems
unevaluatedProperties
Defaults to true when output_format is flag, and false otherwise.
output_format
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.
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.
format
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.
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.
{ $format_name => $format_sub }
{ $format_name => { type => $type, sub => $format_sub } }
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.)
contentMediaType
contentSchema
contentEncoding
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.
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.
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).
\0
\1
Defaults to false.
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)
type
string
number
integer
const and enum (where the string "1" will match with "const": 1)
const
enum
"1"
"const": 1
uniqueItems (where strings and numbers are compared numerically to each other, if either or both are numeric)
uniqueItems
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.
When true, unrecognized keywords are disallowed in schemas (they will cause an immediate abort in "traverse" or "evaluate").
$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). 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
data_path
traversed_schema_path: adjusts the accumulated path as of the start of evaluation (or last $id or $ref)
traversed_schema_path
$id
$ref
initial_schema_uri: adjusts the recorded absolute keyword location as of the start of evaluation
initial_schema_uri
effective_base_uri: locations in errors and annotations are resolved against this URI
effective_base_uri
The return value is a JSON::Schema::Modern::Result object, which can also be used as a boolean.
$result = $js->evaluate($instance_data, $schema); $result = $js->evaluate($instance_data, $schema, { short_circuit => 0 });
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.)
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.
$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".
$config_override
$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):
metaschema_uri: use the indicated URI as the metaschema
metaschema_uri
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 $ref"}}). This feature is highly experimental and is highly likely to change in the future.
{"const": {"$ref": "this is not actually a $ref"}}
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)); } }, });
$js->add_schema($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.
add_schema
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.
undef
$js->add_format_validation(all_lc => sub ($value) { lc($value) eq $value });
or
$js->add_format_validation(no_nines => { type => 'number', sub => sub ($value) { $value =~ m/^[0-8]$$/ });
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.
$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".
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.
_traverse_keyword_<keyword name>
_eval_keyword_<keyword name>
$js->add_media_type('application/furble' => sub ($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
application/json
application/schema+json - see proposed definition
application/schema+json
application/schema-instance+json - see proposed definition
application/schema-instance+json
application/octet-stream - passes strings through unchanged
application/octet-stream
application/x-www-form-urlencoded
application/x-ndjson - see https://github.com/ndjson/ndjson-spec
application/x-ndjson
text/* - passes strings through unchanged
text/*
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);
$js->add_encoding('bloop' => sub ($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
identity
base64 - see RFC 4648 §4
base64
base64url - see RFC 4648 §5
base64url
See also "encode" in HTTP::Message.
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).
my $decoder = $self->get_encoding('base64') or die 'cannot find encoding decoder'; my $content_ref = $decoder->(\$content_string);
my $schema = $js->get($uri); my ($schema, $canonical_uri) = $js->get($uri);
Fetches the Perl data structure representing the JSON Schema at 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).
my $document = $js->get_document($uri_reference);
Fetches the JSON::Schema::Modern::Document object that contains the provided identifier (uri or uri-reference). undef if the schema with that URI has not been loaded (or cached).
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.
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
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)
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.
pattern
patternProperties
(In particular, see vulnerability "CVE-2023-47038-Write-past-buffer-end-via-illegal-user-defined-Unicode-property" in perl5363delta, which is closed in Perl releases 5.34.3, 5.36.3 and 5.38.1.)
json-schema-eval
https://json-schema.org
RFC8259: The JavaScript Object Notation (JSON) Data Interchange Format
RFC3986: Uniform Resource Identifier (URI): Generic Syntax
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: 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
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.
irc.perl.org
irc.libera.chat
You can also find me on the JSON Schema Slack server and OpenAPI Slack server, which are also great resources for finding help.
Karen Etheridge <ether@cpan.org>
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.
To install JSON::Schema::Modern, copy and paste the appropriate command in to your terminal.
cpanm
cpanm JSON::Schema::Modern
CPAN shell
perl -MCPAN -e shell install JSON::Schema::Modern
For more information on module installation, please visit the detailed CPAN module installation guide.