===== jesse

jesse (JSon Schema Erlang) is an implementation of a json schema validator for Erlang.

jesse implements [Draft 03] (http://tools.ietf.org/html/draft-zyp-json-schema-03) of the specification. It supports almost all core schema definitions except:

• format
• $ref

Quick start

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 json.
• 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 three
      formats: mochijson2, jiffy and jsx, 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">>}]}

(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">>}]}

• Since 0.4.0 it's possible to say jesse to collect errors, and not stop immediately when it finds an error in the given json:

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}]}

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}]}

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},
        {data_invalid,{[{<<"type">>,<<"string">>}]},wrong_type,2}]}

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},
        {data_invalid,{[{<<"type">>,<<"integer">>}]},
                      wrong_type,true}]}

we stil 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},
        {data_invalid,{[{<<"type">>,<<"string">>}]},wrong_type,2},
        {data_invalid,{[{<<"type">>,<<"integer">>}]},
                      wrong_type,true}]}

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 erlang docs: "re's matching algorithms are currently based on the PCRE library, but not all of the PCRE library is interfaced"

  But most of common cases should work fine.

Contributing

If you see something missing or incorrect, a pull request is most welcome!