EmptyBodyBehavior.Allow should allow a missing Content-Type

[BieleckiLtd]

EmptyBodyBehavior.Allow allows a 0-length body, but does not work if the request does not have a Content-Type header. To make bodies truly optional, we need to expand the behavior of the switch to allow a missing Content-Type.

Original bug:

Describe the bug

This is either a bug or I'm using this new ASP.NET Core 5.0 feature wrong/API doc is not clear.

To Reproduce

1. Create new ASP.NET Core Web API from the default template, VS2019, target Framework = .NET 5.0 (Current)

2. Add below action at the end of the existing WeatherForecastController.cs:

[HttpPost("[action]")]
public async Task<IActionResult> MyAction([FromBody(EmptyBodyBehavior = EmptyBodyBehavior.Allow)] IEnumerable<int> elements = default)
{
    return Ok(elements);
}

3. I am using Postman, my application is available at port 44349.
4. I set Body as 'raw', body type JSON and body: [1,2]
5. I send POST request to https://localhost:44349/WeatherForecast/MyAction
6. SUCCESS, response is 200 body is [1,2]
7. I clear request body (still 'raw', JSON)
8. FAILURE, response is 415 Unsupported Media Type. I would expect 204 No Content
9. I change Body as 'none'
10. FAILURE, response is 415 Unsupported Media Type. I would expect 204 No Content

Exceptions (if any)

No exceptions, action is not being hit in point 8 and 10

Further technical details

• ASP.NET Core version 5.0
• dotnet --info
  .NET SDK (reflecting any global.json):
  Version: 5.0.301
  Commit: ef17233f86

Runtime Environment:
OS Name: Windows
OS Version: 10.0.18363
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\5.0.301\

Host (useful for support):
Version: 5.0.7
Commit: 556582d964

.NET SDKs installed:
2.1.602 [C:\Program Files\dotnet\sdk]
2.1.700 [C:\Program Files\dotnet\sdk]
2.1.801 [C:\Program Files\dotnet\sdk]
2.2.401 [C:\Program Files\dotnet\sdk]
5.0.301 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.All 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.16 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.16 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.16 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.7 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

• The IDE (VS / VS Code/ VS4Mac) VS2019 Pro (16.10.3)

Related

#30690

[rafikiassumani-msft]

@pranavkm any thoughts on this ?

[pranavkm]

EmptyBodyBehavior operates at the formatter level - once a formatter is picked, it decides to allow an empty body. Picking a formatter requires a Content-Type and the absence of one would produce a 415. Perhaps that's what's happening here.

[BieleckiLtd]

Is there any way to leverage this functionality then? If I was using HttpClient for example to call this action, I would have to newop dummy JsonContent for instance and attach with the body?

[BieleckiLtd]

Is there any way to leverage this functionality then? If I was using HttpClient for example to call this action, I would have to newop dummy JsonContent for instance and attach with the body?

As per this SO answer: Just add content-type in your request header. Without the content-type:application/json will appear 415 when body is empty.

[pranavkm]

A workaround until this is resolved might be to create a formatter that does not require a Content-Type. e.g.

[AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
public sealed class AllowEmptyBodyAttribute : Attribute
{

}

public class EmptyBodyFormatter : IInputFormatter
{
    public bool CanRead(InputFormatterContext context)
    {
        var endpoint = context.HttpContext.GetEndpoint();
        return endpoint?.Metadata.GetMetadata<AllowEmptyBodyAttribute>() is not null;
    }

    public Task<InputFormatterResult> ReadAsync(InputFormatterContext context)
    {
        return InputFormatterResult.NoValueAsync();
    }
}

[HttpPost]
[AllowEmptyBody]
public IActionResult Action(MyPoco? poco) { ... }

Note that this is using a different attribute to allow selection. MVC does not expose EmptyBodyBehavior via ModelMetadata, so we can't query that.