Provide an API to configure the TempDirectory used by ASP.NET Core

ASP.NET Core currently uses an environment variable to drive the temp directory, falling back Path.GetTempPath(). See https://github.com/aspnet/AspNetCore/blob/56e2080ef7741dea9a5c24a8e0639b0921be2d22/src/Http/Http/src/Internal/BufferingHelper.cs#L18-L39.

This path is currently in use by FileBufferingReadStream and as of https://github.com/aspnet/AspNetCore/pull/9015 change, by FileBufferingWriteStream.

This is one of the few parts of the stack that is only configurable via environment variable. We should instead follow the regular pattern of having an option type (that can be configured via configuration) and use those in when constructing these streams and everywhere else ASP.NET Core may need to write to the temp directory.

[Tratcher]

We’re slowly trying to replace any APIs in the Internal namespace with fully internal or fully public types. It it’s needed by MVC and others then it needs to be in a public namespace.

[cjaliaga]

Hey @Tratcher, I could use your help here 😃

Since the code of the Func<string> factory would be the same one used in the callers, I was planning on adding this method to a place that can be shared easily. I thought about adding it to the current AspNetCoreTempDirectory class in Microsoft.AspNetCore.WebUtilities which seems OK for the EnableRewind in Microsoft.AspNetcore.Http with the file linked.

//Getting options in EnableRewind
var bufferingOptions = request.HttpContext.RequestServices.GetRequiredService<IOptions<HttpBufferingOptions>>().Value;
var fileStream = new FileBufferingReadStream(body, bufferThreshold, bufferLimit, AspNetCoreTempDirectory.TempDirectoryPathFactory(bufferingOptions.TempFileDirectory));

However I’m not sure, since currently it’s internal and in the Http group of projects, if I should refer to this class from the MVC formatters same way Microsoft.AspNetcore.Http is doing, add that factory in another place, just repeat the code in all the callers, or any other option that you may think about.

//Function defined in AspNetCoreTempDirectory
public static Func<string> TempDirectoryPathFactory(string path)
{
    return () =>
    {
        // Look for folders in the following order.
        var temp = path ?? Path.GetTempPath();

        if (!Directory.Exists(temp))
        {
            throw new DirectoryNotFoundException(temp);
        }

        return temp;
    };
}

Thanks!