Initial Form-binding support

[brunolins16]

General design:

• No inference ([FromForm] required)
• IFormCollection is supported and the source will be inferred
  • FromFromAttribute.Name not supported
• No changes to the current array support
  • Only arrays (T[]) where T supports TryParse
  • Support string[] and StringValues
• Inferred Accepts metadata (application/x-www-form-urlencoded / multipart/form-data)
  • multipart/form-data only when also include IFromFile or IFormFileCollection

Examples

app.MapPost("/form-collection", (IFormCollection form) => form["name"]);
app.MapPost("/form-collection", ([FromForm]IFormCollection form) => form["name"]);
app.MapPost("/string", ([FromForm] string name) => name);
app.MapPost("/string-array", ([FromForm] string[] names) => names);
app.MapPost("/string-values", ([FromForm] StringValues names) => names);
app.MapPost("/array-of-T", ([FromForm] int[] ids) => ids);
app.MapPost("/array-of-customT", ([FromForm] CustomType[] ids) => ids);

public class CustomType
{
    public static bool TryParse([NotNullWhen(true)] string? s, IFormatProvider? provider, [MaybeNullWhen(false)] out CustomType result)
    {
        result = new CustomType();
        return true;
    }
}

Contributes to #39430

[davidfowl]

@brunolins16 any reason this is a draft?

[brunolins16]

@brunolins16 any reason this is a draft?

Nope. I was waiting before I have all checks green to make it ready for review. 😬

[brunolins16]

Please take a look 🙏@BrennanConroy @captainsafia @halter73

[BrennanConroy]

Do we care if someone accesses the same form data from multiple parameters? I assume it would just work because we are just reading indexes from an already created collection.

[BrennanConroy]

I'm not very familiar with how forms work, but is there any way to have this code path run and register just "multipart/form-data", then have one of the other paths run which would normally add "application/x-www-form-urlencoded" as well, but now they won't because we set ReadForm below.

[brunolins16]

I am not sure if I get your question correctly but, while might be possible send file using application/x-www-form-urlencoded (i am not very familiar 🤷‍♂️ ) . The FormFeature only read files from a multipart/form-data request.

aspnetcore/src/Http/Http/src/Features/FormFeature.cs

Line 171 in 8dc4325

else if (HasMultipartFormContentType(contentType))

My approach here is to keep not adding duplicated metadata, however, since we don't know the parameter ordering and we process them sequentially, in case we found a IFormFile or IFormFileCollection an additional is added, for the first parameter only, with multipart/form-data and since the last metadata is the most relevant it should basically this one been used, make sense?

[brunolins16]

Do we care if someone accesses the same form data from multiple parameters? I assume it would just work because we are just reading indexes from an already created collection.

It just works. if I am not wrong, we are calling Form.ReadAsync once and just accessing the created collection as you mentioned. It is a weird scenario, but I don't think we need to add restrictions. Multiples IFormFileCollection are supported already.

[captainsafia]

Nit: make this a constant?

[davidfowl]

@brunolins16 where's the issue for this PR?

[brunolins16]

@davidfowl #39430. I decided no close it because we need to investigate the complex types support but I should have updated the description to include what we have already.

[ghost]

Hi @brunolins16. It looks like you just commented on a closed PR. The team will most probably miss it. If you'd like to bring something important up to their attention, consider filing a new issue and add enough details to build context.