jesse

jesse (JSON Schema Erlang) is an implementation of a JSON Schema validator for Erlang, though it can work just as well as a CLI tool.

jesse implements the following specifications:

Install from git or https://hex.pm/packages/jesse .

For convenience, available as a Docker image too: docker run --rm -it -v $PWD:$PWD -w $PWD ysoftwareab/jesse ....

And whalebrew package: brew install whalebrew && sudo whalebrew install ysoftwareab/jesse; jesse ...

Erlang API Docs

Automatically generated docs are available https://dev.erldocs.com/github.com/for-get/jesse/ .

Please keep in mind that the public API is the jesse.erl module alone.

Command-Line Interface

You can either build the bin/jesse executable yourself (just type make), or you can use a Docker image a call it with docker run ysoftwareab/jesse.

You can fire up jesse from the CLI, with

bin/jesse [path_to_json_schema] path_to_json_schema -- path_to_json_instance [path_to_json_instance]

You can also output the result in JSON format, with --json, and beautify it e.g. with python

bin/jesse [path_to_json_schema] path_to_json_schema --json -- path_to_json_instance [path_to_json_instance] | python -m json.tool

You can pass multiple JSON schemas which should be loaded into jesse in-memory storage, but JSON instances will be validated against the last JSON schema passed.

Erlang Interface

There are two ways of using jesse:

to use jesse internal in-memory storage to keep all your schema definitions In this case jesse will look up a schema definition in its own storage, and then validate given a JSON instance.
it is also possible to provide jesse with schema definitions when jesse is called.

Examples

NOTE: jesse doesn't have any parsing functionality. It currently works with four
      formats: mochijson2, jiffy, jsx and Erlang 17+ maps, so JSON needs to be
      parsed in advance, or you can specify a callback which jesse will use to
      parse JSON.

      In examples below and in jesse test suite jiffy parser is used.

Use jesse's internal in-memory storage:

(parse JSON in advance)

1> Schema = jiffy:decode(<<"{\"items\": {\"type\": \"integer\"}}">>).
{[{<<"items">>,{[{<<"type">>,<<"integer">>}]}}]}
2> jesse:add_schema("some_key", Schema).
ok
3> Json1 = jiffy:decode(<<"[1, 2, 3]">>).
[1,2,3]
4> jesse:validate("some_key", Json1).
{ok,[1,2,3]}
5> Json2 = jiffy:decode(<<"[1, \"x\"]">>).
[1,<<"x">>]
6> jesse:validate("some_key", Json2).
{error,[{data_invalid,{[{<<"type">>,<<"integer">>}]},
                      wrong_type,<<"x">>,
                      [1]}]}

The [1] in the error is the path in the original value to <<"x">> where the validation failed. See Validation errors below for the full error format.

(using a callback)

1> jesse:add_schema("some_key",
1>                  <<"{\"uniqueItems\": true}">>,
1>                  [{parser_fun, fun jiffy:decode/1}]).
ok
2> jesse:validate("some_key",
2>                <<"[1, 2]">>,
2>                [{parser_fun, fun jiffy:decode/1}]).
{ok,[1, 2]}
3> jesse:validate("some_key",
3>                <<"[{\"foo\": \"bar\"}, {\"foo\": \"bar\"}] ">>,
3>                [{parser_fun, fun jiffy:decode/1}]).
{error,[{data_invalid,{[{<<"uniqueItems">>,true}]},
                      {not_unique,{[{<<"foo">>,<<"bar">>}]}},
                      [{[{<<"foo">>,<<"bar">>}]},{[{<<"foo">>,<<"bar">>}]}],
                      []}]}

Call jesse with schema definition in place (do not use internal storage)

(parse JSON in advance)

1> Schema = jiffy:decode(<<"{\"pattern\": \"^a*$\"}">>).
{[{<<"pattern">>,<<"^a*$">>}]}
2> Json1 = jiffy:decode(<<"\"aaa\"">>).
<<"aaa">>
3> jesse:validate_with_schema(Schema, Json1).
{ok,<<"aaa">>}
4> Json2 = jiffy:decode(<<"\"abc\"">>).
<<"abc">>
5> jesse:validate_with_schema(Schema, Json2).
{error,[{data_invalid,{[{<<"pattern">>,<<"^a*$">>}]},
                      no_match,
                      <<"abc">>,[]}]}

(using a callback)

1> Schema = <<"{\"patternProperties\": {\"f.*o\": {\"type\": \"integer\"}}}">>.
<<"{\"patternProperties\": {\"f.*o\": {\"type\": \"integer\"}}}">>
2> jesse:validate_with_schema(Schema,
2>                            <<"{\"foo\": 1, \"foooooo\" : 2}">>,
2>                            [{parser_fun, fun jiffy:decode/1}]).
{ok,{[{<<"foo">>,1},{<<"foooooo">>,2}]}}
3> jesse:validate_with_schema(Schema,
3>                            <<"{\"foo\": \"bar\", \"fooooo\": 2}">>,
3>                            [{parser_fun, fun jiffy:decode/1}]).
{error,[{data_invalid,{[{<<"type">>,<<"integer">>}]},
                      wrong_type,<<"bar">>,
                      [<<"foo">>]}]}

Since 0.4.0 it's possible to instruct jesse to collect errors, and not stop immediately when it finds an error in the given JSON instance:

1> Schema = <<"{\"properties\": {\"a\": {\"type\": \"integer\"}, \"b\": {\"type\": \"string\"}, \"c\": {\"type\": \"boolean\"}}}">>.
<<"{\"properties\": {\"a\": {\"type\": \"integer\"}, \"b\": {\"type\": \"string\"}, \"c\": {\"type\": \"boolean\"}}}">>
2> jesse:validate_with_schema(Schema,
2>                            <<"{\"a\": 1, \"b\": \"b\", \"c\": true}">>,
2>                            [{parser_fun, fun jiffy:decode/1}]).
{ok,{[{<<"a">>,1},{<<"b">>,<<"b">>},{<<"c">>,true}]}}

now let's change the value of the field "b" to an integer

3> jesse:validate_with_schema(Schema,
3>                            <<"{\"a\": 1, \"b\": 2, \"c\": true}">>,
3>                            [{parser_fun, fun jiffy:decode/1}]).
{error,[{data_invalid,{[{<<"type">>,<<"string">>}]},
                      wrong_type,2,
                      [<<"b">>]}]}

works as expected, but let's change the value of the field "c" as well

4> jesse:validate_with_schema(Schema,
4>                            <<"{\"a\": 1, \"b\": 2, \"c\": 3}">>,
4>                            [{parser_fun, fun jiffy:decode/1}]).
{error,[{data_invalid,{[{<<"type">>,<<"string">>}]},
                      wrong_type,2,
                      [<<"b">>]}]}

still works as expected, jesse stops validating as soon as finds an error.

Let's use the allowed_errors option, and set it to 1

5> jesse:validate_with_schema(Schema,
5>                            <<"{\"a\": 1, \"b\": 2, \"c\": 3}">>,
5>                            [{parser_fun, fun jiffy:decode/1},
5>                             {allowed_errors, 1}]).
{error,[{data_invalid,{[{<<"type">>,<<"boolean">>}]},
                      wrong_type,3,
                      [<<"c">>]},
        {data_invalid,{[{<<"type">>,<<"string">>}]},
                      wrong_type,2,
                      [<<"b">>]}]}

now we got a list of two errors.

Let's now change the value of the field "a" to a boolean

6> jesse:validate_with_schema(Schema,
6>                            <<"{\"a\": true, \"b\": 2, \"c\": 3}">>,
6>                            [{parser_fun, fun jiffy:decode/1},
6>                             {allowed_errors, 1}]).
{error,[{data_invalid,{[{<<"type">>,<<"string">>}]},
                      wrong_type,2,
                      [<<"b">>]},
        {data_invalid,{[{<<"type">>,<<"integer">>}]},
                      wrong_type,true,
                      [<<"a">>]}]}

we still got only two errors.

Let's try using 'infinity' as the argument for the allowed_errors option

7> jesse:validate_with_schema(Schema,
7>                            <<"{\"a\": true, \"b\": 2, \"c\": 3}">>,
7>                            [{parser_fun, fun jiffy:decode/1},
7>                             {allowed_errors, infinity}]).
{error,[{data_invalid,{[{<<"type">>,<<"boolean">>}]},
                      wrong_type,3,
                      [<<"c">>]},
        {data_invalid,{[{<<"type">>,<<"string">>}]},
                      wrong_type,2,
                      [<<"b">>]},
        {data_invalid,{[{<<"type">>,<<"integer">>}]},
                      wrong_type,true,
                      [<<"a">>]}]}

Maps example

8> jesse:validate_with_schema(Schema,
8>                            <<"{\"a\": 1, \"b\": 2, \"c\": true}">>,
8>                            [{parser_fun, fun(Bin) -> jiffy:decode(Bin, [return_maps]) end}]).
{error,[{data_invalid,#{<<"type">> => <<"string">>},
                      wrong_type,2,
                      [<<"b">>]}]}
9> jesse:validate_with_schema(Schema,
9>                            <<"{\"a\": 1, \"b\": \"val\", \"c\": true}">>,
9>                            [{parser_fun, fun(Bin) -> jiffy:decode(Bin, [return_maps]) end}]).
{ok, #{<<"a">> => 1, <<"b">> => <<"val">>, <<"c">> => true}}

jesse currently supports JSON Schema draft3, draft4 and draft6. To decide which validator to use jesse tries to read $schema property from the given schema, and checks if it's a supported one, otherwise it will return an error. If $schema property isn't provided in the given schema, jesse will use the default validator (currently the validator for draft3).

To specify which validator to use by default (if there's no schema property in the given schema), one should use 'default_schema_ver' option when call jesse:validate/3 or jesse:validate_with_schema/3, the value should be a binary consisting a schema path, i.e. <<"http://json-schema.org/draft-03/schema#">>.

Validation errors

The validation functions jesse:validate/2 and jesse:validate_with_schema/2,3 return {ok, Value} on success and {error, ListOfErrors} on failure. An error is either data_invalid or schema_invalid.

A data_invalid error is a tuple on the form {data_invalid, Schema, ErrorType, Value, Path} where

Schema is the part of the schema where validation failed
ErrorType is the type of error, usually an atom such as wrong_type, not_in_range or no_match
Value is The part of the value where failed validation against Schema
Path is a path to where validation failed within the original value. The path is a list of property names and zero-based array indices referencing the properties and array items within a JSON document; e.g. in the JSON document {"foo": [42, 43, 44]}, the path [<<"foo">>, 0] refers to the value 42. An empty list refers to the whole JSON document.

A schema_invalid error is a tuple on the form {schema_invalid, Schema, ErrorType} where

Schema is the part of the schema which is invalid
ErrorType is an atom such as missing_id_field or a tuple such as {wrong_type_dependency, Dependency}.

Caveats

pattern and patternProperty attributes:

jesse uses standard erlang module re for regexp matching, therefore there could be some incompatible regular expressions in schemas you define.

From the erlang docs:

The matching algorithms of the library are based on the PCRE library, but not all of the PCRE library is interfaced and some parts of the library go beyond what PCRE offers.

Most common cases should work fine. Note that jesse provides an application environment setting, re_options (default: [unicode, ucp]), for customizing its use of the re module. ucp provides the widest compatibility for matching unicode code points beyond ISO Latin-1 in character classes like \w, \s, and \d, but hurts performance. If maximum compatibility is not required and performance is a significant concern, set re_options to [unicode] instead. See notes on the ucp option at re:compile/2 for more details.
internal references (id attribute) are NOT supported

http://json-schema.org/latest/json-schema-core.html#rfc.section.8.2.1