# Elixir JSON Schema validator
[](https://travis-ci.org/jonasschmidt/ex_json_schema) [](https://coveralls.io/github/jonasschmidt/ex_json_schema?branch=travis-elixir-version) [](https://hex.pm/packages/ex_json_schema) [](LICENSE)
A JSON Schema validator with full support for the draft 4 specification and zero dependencies. Passes the official [JSON Schema Test Suite](https://github.com/json-schema/JSON-Schema-Test-Suite).
## Installation
Add the project to your Mix dependencies in `mix.exs`:
```elixir
defp deps do
[{:ex_json_schema, "~> 0.5.4"}]
end
```
Update your dependencies with:
```shell
$ mix deps.get
```
### Loading remote schemata
If you have remote schemata that need to be fetched at runtime, you have to register a function that takes a URL and returns a `Map` of the parsed JSON. So in your Mix configuration in `config/config.exs` you should have something like this:
```elixir
config :ex_json_schema,
:remote_schema_resolver,
fn url -> HTTPoison.get!(url).body |> Poison.decode! end
```
Alternatively, you can specify a module and function name for situations where using anonymous functions is not possible (i.e. working with Erlang releases):
```elixir
config :ex_json_schema,
:remote_schema_resolver,
{MyModule, :my_resolver}
```
You do not have to do that for the official draft 4 meta-schema found at http://json-schema.org/draft-04/schema# though. That schema is bundled with the project and will work out of the box without any network calls.
### Resolving a schema
In this step the schema is validated against its meta-schema (the draft 4 schema definition) and `$ref`s are being resolved (making sure that the reference points to an existing fragment). You should only resolve a schema once to avoid the overhead of resolving it in every validation call.
```elixir
iex> schema = %{
"type" => "object",
"properties" => %{
"foo" => %{
"type" => "string"
}
}
} |> ExJsonSchema.Schema.resolve
```
Note that `Map` keys are expected to be strings, since in practice that data will always come from some JSON parser.
## Usage
If you're only interested in whether a piece of data is valid according to the schema:
```elixir
iex> ExJsonSchema.Validator.valid?(schema, %{"foo" => "bar"})
true
iex> ExJsonSchema.Validator.valid?(schema, %{"foo" => 1})
false
```
Or in case you want to have detailed validation errors:
```elixir
iex> ExJsonSchema.Validator.validate(schema, %{"foo" => "bar"})
:ok
iex> ExJsonSchema.Validator.validate(schema, %{"foo" => 1})
{:error, [{"Type mismatch. Expected String but got Integer.", "#/foo"}]}
```
Errors are tuples of a message and the path to the element not matching the schema. The path is following the same conventions used in JSON Schema for referencing JSON elements.
## Format support
The validator supports all the formats specified by draft 4 (`date-time`, `email`, `hostname`, `ipv4`, `ipv6`), with the exception of the `uri` format which has confusing/broken requirements in the official test suite (see https://github.com/json-schema/JSON-Schema-Test-Suite/issues/77).
## License
Released under the [MIT license](LICENSE).
## TODO
* Add some source code documentation
* Enable providing JSON for known schemata at resolve time
