Whether the default content-type should be implied?

[AlexV525]

This should be addressed before the diox 5.0.0 stable release.

Previously in dio, the content-type will be implied to

• application/json; charset=utf-8 by default.
  This makes many applications behave normally without extra configurations, even without tweaking the BaseOptions.

However, this is not following any standard or specification, leading users that follow the specification confused and maintainers hard to fix related issues.

We should carefully discuss these:

1. Whether the diox should continue to imply the content-type in the future.
2. Whether the BaseOptions.setRequestContentTypeWhenNoPayload should be removed.

cc @cfug/devs

In dio

• https://github.com/flutterchina/dio/blob/9040bde4a07ffe4e201e4ec014242a16eb69d926/dio/lib/src/options.dart#L289-L297
• https://github.com/flutterchina/dio/blob/9040bde4a07ffe4e201e4ec014242a16eb69d926/dio/lib/src/options.dart#L614-L616

In diox

• diox/dio/lib/src/options.dart

  Lines 306 to 319 in 580b08d

  	final headers = caseInsensitiveKeyMap(baseOpt.headers);
  	if (this.headers != null) {
  	headers.addAll(this.headers!);
  	}
  	if (this.contentType != null) {
  	headers[Headers.contentTypeHeader] = this.contentType;
  	}
  	// Imply the default content type if capable.
  	// This is a historical issue that dio used to imply the json type, it'll be
  	// too breaking to let user apply a base content type at the moment.
  	if (data != null || baseOpt.setRequestContentTypeWhenNoPayload) {
  	headers[Headers.contentTypeHeader] ??= Headers.jsonContentType;
  	}
  	final String? contentType = headers[Headers.contentTypeHeader];

• diox/dio/lib/src/options.dart

  Lines 663 to 665 in 580b08d

  	if (!contentTypeInHeader) {
  	this.contentType = contentType;
  	}

• diox/dio/lib/src/transformer.dart

  Lines 79 to 83 in 2b7aa3b

  	} else if (data is Map) {
  	options.contentType =
  	options.contentType ?? Headers.formUrlEncodedContentType;
  	return Transformer.urlEncodeMap(data);
  	}

[kuhnroyal]

I am not sure, the Transformer encodes the JSON by default if the content type is set, right?

[AlexV525]

the Transformer encodes the JSON by default if the content type is set, right?

Partially correct, see this:

diox/dio/lib/src/transformer.dart

Lines 77 to 78 in dd6e39b

	if (Transformer.isJsonMimeType(options.contentType)) {
	return json.encode(options.data);

[AlexV525]

I think we have the conclusion at present, we'll make no content type implied by default.