# Elixir JSON Schema validator

[![Build Status](]( [![Coverage Status](]( [![](]( [![](](LICENSE)

A JSON Schema validator with full support for the draft 4 specification and zero dependencies. Passes the official [JSON Schema Test Suite](

## Installation

Add the project to your Mix dependencies in `mix.exs`:

defp deps do
  [{:nex_json_schema, "~> 0.5.4"}]

Update your dependencies with:

$ 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:

config :nex_json_schema,
  fn url -> HTTPoison.get!(url).body |> Jason.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):

config :ex_json_schema,
  {MyModule, :my_resolver}

You do not have to do that for the official draft 4 meta-schema found at 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.

iex> schema = %{
  "type" => "object",
  "properties" => %{
    "foo" => %{
      "type" => "string"
} |> NExJsonSchema.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:

iex> NExJsonSchema.Validator.valid?(schema, %{"foo" => "bar"})

iex> NExJsonSchema.Validator.valid?(schema, %{"foo" => 1})

Or in case you want to have detailed validation errors:

iex> NExJsonSchema.Validator.validate(schema, %{"foo" => "bar"})

iex> NExJsonSchema.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

## License

Released under the [MIT license](LICENSE).


* Add some source code documentation
* Enable providing JSON for known schemata at resolve time