Retrofit for android @Multipart remove default headers

Question

Making a @Multipart request adds these default headers (Content-Transfer-Encoding, Content-Type) for each part, is there any way to remove them?

//REQUEST BODY
--25d35373-d2c3-46a3-969f-f5a1fd5f781a 
Content-Disposition: form-data; name="client_id"
Content-Transfer-Encoding: binary <-- remove this one
Content-Type: application/json; charset=UTF-8 <-- remove this one
Content-Length: 34
"40ccfee680a844780a41fbe23ea89934"
//

NOTE: I do not have access to the server so there is no way I will be able to make the server accept these headers.

Answer 1

You can build multipart body by your self in this way (kotlin code but same idea may be expressed with java):

val mpart = MultipartBody.Builder()
            .addFormDataPart("param", paramValue)
            .addPart(null, someRequestBody).build() // <-- (*) see explanation below

//thus, service method should looks like this:
@POST("upload/endpoint")
fun upload(@Body parts: MultipartBody)

(*) - this is the addPart(headers: Headers, reqBody: RequestBody) method, when you pass null to headers arg this removes all headers except Content-Length: