converters.md

Converters

Converter are used to apply transformation to a request or response body, for example transforming a Dart object to a Map<String, dynamic>

Both converter and errorConverter are called before request and response interceptors.

final chopper = new ChopperClient(
   converter: JsonConverter(),
   errorConverter: JsonConverter()
);

{% hint style="info" %} errorConverter is called only on error response (statusCode < 200 || statusCode >= 300) {% endhint %}

JSON

Chopper integrate a JsonConverter that take care of encoding data to JSON and decoding JSON string. It will also apply the correct header to the request (application/json).

However, if content type header is overrided using@Post(headers: {'content-type': '...'})The converter won't add json header and won't apply json.encode if content type is not JSON.

{% hint style="danger" %} JsonConverter won't convert a Dart object into a Map<String, dynamic> or a List, but it will convert the Map<String, dynamic> into a JSON string. {% endhint %}

Custom converter

You can implement a converter by implementing the Converter class.

class MyConverter implements Converter {
  @override
  Response<BodyType> convertResponse<BodyType, InnerType>(Response res) {
   return res;
  }

  @override
  Request convertRequest(Request req) {
    return req;
  }
}

BodyTypeis the expected type of your response (ex: String or CustomObject)

In the case of BodyType is a List or BuildList, InnerType will be the type of the generic (ex: convertResponse<List<CustomObject>, CustomObject>(response) )

Factory Converter

In case you want to apply a converter to a single endpoint, you can use a FactoryConverter

@ChopperApi(baseUrl: "/todos")
abstract class TodosListService extends ChopperService {

  @FactoryConverter(
      request: FormUrlEncodedConverter.requestFactory,
      response: convertResponse,
  )
  @Post(path: '/')
  Future<Response> post(@Field() String foo, @Field() int bar);

}

Response<T> convertResponse<T>(Response res) =>
    JsonConverter().convertResponse(res);