XmlNamespaceManager corruption

[andersjonsson]

When testing things on our servers I got this exception:

System.InvalidOperationException: Operations that change non-concurrent collections must have exclusive access. A concurrent update was performed on this collection and corrupted its state. The collection's state is no longer correct.
   at System.Collections.Generic.Dictionary<TKey,TValue>.FindValue(TKey key)
   at System.Collections.Generic.Dictionary<TKey,TValue>.TryGetValue(TKey key, TValue& value)
   at System.Xml.XmlNamespaceManager.LookupNamespaceDecl(String prefix)
   at System.Xml.XmlNamespaceManager.LookupNamespace(String prefix)
   at System.Xml.XmlNamespaceManager.LookupPrefix(String uri)
   at SoapCore.Namespaces.AddNamespaceIfNotAlreadyPresentAndGetPrefix(XmlNamespaceManager xmlNamespaceManager, String preferredPrefix, String uri)
   at SoapCore.Namespaces.AddDefaultNamespaces(XmlNamespaceManager xmlNamespaceManager)
   at SoapCore.SoapEndpointMiddleware<T>.GetXmlNamespaceManager()
   at SoapCore.SoapEndpointMiddleware<T>.ProcessMeta(HttpContext httpContext)
   at SoapCore.SoapEndpointMiddleware<T>.Invoke(HttpContext httpContext, IServiceProvider serviceProvider)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at legaonline.apiws.Startup.<>c.<<Configure>b__4_0>d.MoveNext() in Startup.cs:line 112
--- End of stack trace from previous location ---
   at StackExchange.Exceptional.ExceptionalMiddleware.Invoke(HttpContext context)

I see that this kind of error has been encountered before and that a PR has been merged #693 but obviously it can still happen, if multiple people access the endpoint before the XmlNamespaceManager has been fully populated

[JonRobidus]

And when this happens the current middleware is corrupt and every Soap endpoint call throws an error.
That is what we have seen in our project :(
Not something you should accept... I think...

XmlNamespaceManager is not threadsafe. So do not change the same instance in different requests.

Caching XmlNamespaceManager's in the middleware (=singleton!) and mutating it within a request causes these thread safety issues.

[JonRobidus]

My workaround:

/// <summary>
/// Fixes a thread safety issue in SoapCore. 
/// SoapCore can mutate XmlNamespaceManager instances over multiple request when the first call is not finisched yet. This can lead to corrupted SoapCoreMiddleware.
/// This cause errors for all subsequent requests to the same endpoint. 
/// See issue: https://github.com/DigDes/SoapCore/issues/743
/// </summary>
public class AlwaysAwaitFirstCallToSoapEndpointMiddleware(RequestDelegate next)
{
    private bool hasFirstRequestCompleted;
    private readonly SemaphoreSlim semaphore = new(1, 1);

    public async Task InvokeAsync(HttpContext context)
    {
        if (context.Request.Path.ToString().Contains("/SOAP/"))
        {
            if (!hasFirstRequestCompleted)
            {
                await semaphore.WaitAsync();
                try
                {
                    if (!hasFirstRequestCompleted)
                    {
                        await next(context);
                        hasFirstRequestCompleted = true;
                        return;
                    }
                }
                finally
                {
                    semaphore.Release();
                }
            }
        }
        await next(context);
    }
}

[JonRobidus]

See PR #1146
for the fix of this issue.