POSTing large form data silently results in null-parameters

[alex-jitbit]

Describe the bug

I have a very simple ASP.NET 5 (Core) MVC app with this action method:

[HttpPost]
public IActionResult Send(string message, string secret)
{
    // ...
}

This method is called by external API that is POST'ing very(!) large data in the "message" form field. Like, 35-megabytes big.

This results in all parameters being "null". Silently. No exception is thrown. No log entry. Just have the "null" and good luck investigating ¯\_(ツ)_/¯

Smaller data works fine

THE FIX

This is obviously because of the size. Adding this attribute fixes the issue:

[RequestFormLimits(ValueLengthLimit = 50000000, MultipartBodyLengthLimit = 50000000)] //the fix
[HttpPost]
public IActionResult Send(string message, string secret)
{
    // ...
}

I'm not the only one with this problem: https://stackoverflow.com/questions/61295714/asp-net-core-3-1-argument-model-always-null-with-large-form-data-in-controller

Proposal

It would be nice if some kind of exception was thrown, so we know something's wrong. Like the "classic" ASP.NET always did - with the "request length" exception.

Further technical details

• ASP.NET Core version 5.0.5

[BrennanConroy]

Have you looked at the model state and seen if it is valid or has any errors?
Are there any errors in the logs?

[brunolins16]

@alex-jitbit , thanks for reporting this issue,.

To give you a little bit more detail, during the model binding the large file causes a BadHttpRequestException that derives from System.IO.IOException and all of them are wrapped in a ValueProviderException

aspnetcore/src/Mvc/Mvc.Core/src/ModelBinding/FormValueProviderFactory.cs

Line 50 in c68d3b7

catch (IOException ex)

Also, all ValueProviderException are handled and added to the ModelState.

aspnetcore/src/Mvc/Mvc.Core/src/ModelBinding/CompositeValueProvider.cs

Line 91 in c68d3b7

catch (ValueProviderException exception)

With that the expected error message Failed to read the request form. Request body too large. The max request body size is xxxxx bytes. is available in the ModelState and as recommended here (Model validation in ASP.NET Core) you should call ModelState.IsValid and react appropriately.

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