Inferring FromBody.AllowEmptyBehavior = Allow based nullability information #39754
Description
Current design
Today, MVC infer optionality for parameters/properties based on nullability or if they have default value for all Binding Sources, eg.:
#nullable enable
public IActionResult Post([FromBody] string? name);
public IActionResult Get([FromQuery] string? name);
public IActionResult Post([FromForm] string? name);
#nullable restoreOr
#nullable disable
public IActionResult Post([FromBody] string name = null) ;
public IActionResult Get([FromQuery] string name = null);
public IActionResult Post([FromForm] string name = null);
#nullable restoreAll examples above will allow the null value for the parameter name, however, when the binding From Body (inferred or not) the current default behavior is fail when the Content-Length == 0.
{
"type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
"title": "One or more validation errors occurred.",
"status": 400,
"traceId": "00-1a27854a7f1211e53fbc64e054801c11-a79404ee342e26ff-00",
"errors": {
"": [
"A non-empty request body is required."
]
}
}Currently, are available 2 options to override this behavior and any of those available options are based on the Nullability information and need to be explicitly specified by the user.
Globally:
builder.Services.Configure<MvcOptions>(options =>
{
options.AllowEmptyInputInBodyModelBinding = true;
});Scoped:
public IActionResult Post([FromBody(EmptyBodyBehavior = EmptyBodyBehavior.Allow)] string? name);Proposed Change
As part of the idea to bring Minimal APIs enhancements to MVC the proposal is applying the same default behavior and allow empty input body (Content-Length = 0) when the parameter/property is nullable or has the default value.
The suggestion is to always allow empty input (Content-Length = 0) when a [FromBody] parameter/property sets a default value or is nullable without allowing or requiring configuration.
After this change the following scenarios will allow an empty input:
#nullable disable
public IActionResult Action([FromBody] string value);
public IActionResult Action([FromBody] string value = null);
#nullable restore#nullable enable
public IActionResult Action([FromBody] string? value);
public IActionResult Action([FromBody] string? value = null);
#nullable restoreUsage Examples
If the users are affected by this change and they would like a different behavior, the simplest way to avoid it is to define the action parameter/property correctly based on the optionality, as the examples listed below.
Required parameter in a disabled nullable context
Before
#nullable disable
public IActionResult Action([FromBody] string value);
public IActionResult Action([FromBody] string value = null);
#nullable restoreAfter
#nullable disable
public IActionResult Action([FromBody][Required] string value);
#nullable restoreRequired parameter in an enabled nullable context
Before
#nullable enable
public IActionResult Action([FromBody] string? value);
public IActionResult Action([FromBody] string? value = null);
#nullable restoreAfter
#nullable enable
public IActionResult Action([FromBody] string value);
#nullable restore