I cannot set a content-type of a form-data field

[MarinF00]

Package

dio

Version

5.4.0

Operating-System

Android

Output of flutter doctor -v

No response

Dart Version

No response

Steps to Reproduce

  formData.fields.add(MapEntry(
      'data',
      jsonEncode(bpData.toJson())
  ));

Expected Result

  formData.fields.add(MapEntry(
      'data',
      {value: jsonEncode(bpData.toJson(),
     contentType: 'application/json'}

)
));

Actual Result

Could not resolve parameter [0] in public org.springframework.http.ResponseEntity<?> com.bp.api.controllers.PdfController.generatePdf(com.bp.api.models.dtos.Pdf,org.springframework.web.multipart.MultipartFile,org.springframework.web.multipart.MultipartFile,org.springframework.web.multipart.MultipartFile,org.springframework.web.multipart.MultipartFile,org.springframework.web.multipart.MultipartFile,java.util.List<org.springframework.web.multipart.MultipartFile>): Content-Type 'application/octet-stream' is not supported
api-bp | 2023-12-11T14:58:50.733Z WARN 55 --- [nio-8080-exec-5] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.web.HttpMediaTypeNotSupportedException: Content-Type 'application/octet-stream' is not supported]
api-bp | 2023-12-11T14:58:50.734Z DEBUG 55 --- [nio-8080-exec-5] o.s.web.servlet.DispatcherServlet : Completed 415 UNSUPPORTED_MEDIA_TYPE

[AlexV525]

Only MultipartFile contains content-type. What is your purpose?

[MarinF00]

I am trying to pass json object and I need to give it a content-type as you can see in the example but its not possible.
content-file should be supported if the data is just text. Right now there is no way to set application-json type when trying to pass json object.

[AlexV525]

Won't MultipartFile.fromBytes work?

[MarinF00]

It won't.

[AlexV525]

Why? MultipartFile.fromBytes(utf8.encode(jsonEncode(json)), contentType: MediaType('application', 'json')) should work for your case.