Add metadata for IFormFile usage with minimal actions #35175
Description
Background and Motivation
As suggested in #34303 (comment), to support binding parameters of type IFormFile with minimal actions, some metadata to allow the form field name for the file would be needed to support names that can't be expressed with C# syntax within the parameter name.
Proposed API
namespace Microsoft.AspNetCore.Http.Metadata
{
+ public interface IFromFileMetadata
+ {
+ string? Name { get; }
+ }
}
namespace Microsoft.AspNetCore.Mvc
{
+ [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
+ public class FromFileAttribute : Attribute, IBindingSourceMetadata, IModelNameProvider, IFromFileMetadata
+ {
+ public FromFileAttribute();
+ public FromFileAttribute(string name);
+
+ public BindingSource BindingSource => BindingSource.FormFile;
+ public string? Name { get; set; }
+ }
}Usage Examples
app.MapPost("/upload", async ([FromFile("file-name")] IFormFile file) =>
{
using var stream = System.IO.File.OpenWrite("upload.txt");
await file.CopyToAsync(stream);
});Alternative Designs
A more explicit name, but having from and form next to each other looks a bit yuck.
namespace Microsoft.AspNetCore.Http.Metadata
{
+ public interface IFromFormFileMetadata
+ {
+ string? Name { get; }
+ }
}Putting FromFileAttribute in a different namespace so it's not coupled to MVC.
namespace Microsoft.AspNetCore.Http.Metadata
{
+ [AttributeUsage(AttributeTargets.Parameter, AllowMultiple = false)]
+ public class FromFileAttribute : Attribute, IFromFileMetadata
+ {
+ public FromFileAttribute();
+ public FromFileAttribute(string name);
+
+ public string? Name { get; set; }
+ }
}Risks
The other [From...] attributes live in the Microsoft.AspNetCore.Mvc namespace so adding another in the same place would make sense, but adding the concrete implementation for [FromFile(...)] to MVC wouldn't be right without also implementing it within model binding there too as a new feature to supplement the existing IFormFile support. Otherwise users of controllers might try and use it and it then not work as expected.