HttpRequest.Form throws an undocumented System.InvalidOperationException

[Grauenwolf]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

After upgrading from ASP.NET Core 3.x to ASP.NET Core 6, we found that HttpRequest.Form throws an undocumented System.InvalidOperationException with the message "Incorrect Content-Type: image/png".

System.InvalidOperationException: Incorrect Content-Type: image/png
   at Microsoft.AspNetCore.Http.Features.FormFeature.ReadForm()
   at Microsoft.AspNetCore.Http.DefaultHttpRequest.get_Form()

This seems to only affect image files. Using the same code to read CSV files continues to work.

Expected Behavior

Form object is returned.

Steps To Reproduce

No response

Exceptions (if any)

System.InvalidOperationException

.NET Version

7.0.304

Anything else?

• https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.http.httprequest.form
• https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.http.features.formfeature.readform

[Grauenwolf]

Looking at the code, there are two paths it can go down. One throws...

            throw new InvalidOperationException("This request does not have a Content-Type header. Forms are available from requests with bodies like POSTs and a form Content-Type of either application/x-www-form-urlencoded or multipart/form-data.");

the other throws...

throw new InvalidOperationException("Incorrect Content-Type: " + _request.ContentType);

~\src\Http\Http\src\Features\FormFeature.cs

Neither is complete, as really we want both the current request type and the desired request type.

[Tratcher]

Code links:

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

Lines 102 to 104 in d07f4d4

	if (!HasFormContentType)
	{
	throw new InvalidOperationException("This request does not have a Content-Type header. Forms are available from requests with bodies like POSTs and a form Content-Type of either application/x-www-form-urlencoded or multipart/form-data.");

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

Lines 134 to 136 in d07f4d4

	if (!HasFormContentType)
	{
	throw new InvalidOperationException("Incorrect Content-Type: " + _request.ContentType);

Yes, both code paths check the same condition and should return the same exception type and message. And yes we should add this exception to the doc comments, as well as OperationCancelledException (ReadFormAsync), InvalidDataException, and IOException