Web API 415: Unsupported Media Type

Question

How can I support two content types for an endpoint

• application/x-www-form-urlencoded
• application/json

Answer 1

Hi @Nithin ,

Web API 415: Unsupported Media Type

In Asp.Net Core API application, if not add the binding source attributes like [FromBody] or [FromForm] (refer to the above code), on the Post method when bind the complex object, it will find the action parameter value from the request body(the Content-Type: application/json), if you transfer the parameter value from the request Form (application/x-www-form-urlencoded), it will show the 415 error.

How can I support two content types for an endpoint

• application/x-www-form-urlencoded
• application/json

To let one endpoint to support two content types, you can try to use custom model binding. In the custom model binder method, you can check the request content type, then based on the content type to get the parameter value from the request Form or request body, then create the object instance and return to the API method.

For example, create an asp.net 6 API application:

1. Create a Student class:
2. Add the API controller as below:
3. Add the custom model binder: [Note] need to install the Newtonsoft.Json package.
4. Register the custom model binder in the program.cs file. [Note] We need to allow Synchronous IO to get the value from the request body.

You can view the source code, it contains all above code: 219796-sourcecode.txt

Then the result as below:

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Answer 2

• To use application/x-www-form-urlencoded, [ApiController]
  [Route("[controller]")]
  public class ToDosController : ControllerBase
  {
  [HttpPost]
  public IActionResult Post([FromForm] ToDo toDo)
  {
  return Ok();
  }
  } public record class ToDo(int Id, string Title);

cURL,

   curl --location --request POST 'http://localhost:5000/Todos' \  
   \--header 'Content-Type: application/x-www-form-urlencoded' \  
   \--data-urlencode 'id=1' \  
   \--data-urlencode 'title=ToDo 1'  

• To use application/json, [ApiController]
  [Route("[controller]")]
  public class ToDosController : ControllerBase
  {
  [HttpPost]
  public IActionResult Post(ToDo toDo) // you can be explicit if you want to, something like Post([FromBody] ToDo toDo), default is application/json
  {
  return Ok();
  }
  } public record class ToDo(int Id, string Title);

cURL

   curl --location --request POST 'http://localhost:5000/Todos' \  
   \--header 'Content-Type: application/json' \  
   \--data-raw '{  
       "id": 1,  
       "title": "ToDo 1"  
   }'  

Answer 3

if you use:

public IActionResult Post([FromBody] ToDo toDo)     

you are telling the binder to use an input formatter. the builtin are text and json InputFormatters. You can optionally add additional formatters like Xml via .AddXmlSerializerFormatters()

there currently isn't a form url encoded input formatter.

if you use:

public IActionResult Post([FromForm] ToDo toDo)     

then the binder uses a media formatter (much slower) to access the form data

if you use:

public IActionResult Post(ToDo toDo)     
 

the binder will look at the content-type and pick either FromForm or FromBody processing

Answer 4

Hi @Nithin ,

In Postman , the multipart/form-data request type allows you to specify a content type for each individual part.

By default, the content type of each part is not visible. You need to enable this by clicking the three dots and enabling Content Type.

Below is an example , you can refer to it.

Values Controller:

    [Route("api/[controller]")]  
    [ApiController]  
    public class ValuesController : ControllerBase  
    {  
        [HttpPost]  
        public IActionResult Post([FromForm] ToDo toDo)  
        {  
            return Ok();  
        }        
    }  

result:

---

If the answer is helpful, please click "Accept Answer" and upvote it.

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Regards,
Qing Guo