Dio options.contentType vs header "Content-Type"

Question

I was trying to make a call to a REST service using the Dio plugin, but kept getting HTTP 400 response code. I thought I was doing everything right by setting the content type and response type options to JSON:

Response response = await Dio().get(
    'https://api.example.com/v1/products/$productId',
    queryParameters: {},
    options: Options(
        contentType: ContentType.json,
        responseType: ResponseType.json,
        headers: {'Authorization': 'Bearer $MY_API_KEY'}
    ),
);

However, it turns out that I needed to add a Content-Type header as well:

headers: {'Authorization': 'Bearer $MY_API_KEY'}, 'Content-Type': 'application/json' };

So now I'm confused - what exactly does the contentType option do? I thought it was analogous to setting the Content-Type header manually?

Solution

I've tried this locally using dio: ^3.0.10 and it seems that ContentType.json is an invalid value for contentType.

Digging through the documentation for dio, Headers.jsonContentType should be used.