Cannot access a closed file when using FileStream.CopyToAsync?

Question

I have the following method,

    public Task SaveFileContentsAsync(string filePath, Stream stream)
    {
        using (var fileStream = new FileStream(filePath, FileMode.Create))
        {
            return stream.CopyToAsync(fileStream);
        }
    }

This method simply saving the stream into disk. When I call this method with HttpPostedFileBase.InputStream I am getting,

Exception Details: System.ObjectDisposedException: Cannot access a closed file.


[ObjectDisposedException: Cannot access a closed file.]
   System.IO.__Error.FileNotOpen() +57
   System.IO.FileStream.Write(Byte[] array, Int32 offset, Int32 count) +10549618
   System.IO.Stream.<BeginWriteInternal>b__11(Object param0) +59
   System.Threading.Tasks.Task`1.InnerInvoke() +3132781
   System.Threading.Tasks.Task.Execute() +45
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52
   System.IO.Stream.EndWrite(IAsyncResult asyncResult) +85
   System.IO.FileStream.EndWrite(IAsyncResult asyncResult) +24
   System.IO.Stream.<BeginEndWriteAsync>b__17(Stream stream, IAsyncResult asyncResult) +24
   System.Threading.Tasks.FromAsyncTrimPromise`1.Complete(TInstance thisRef, Func`3 endMethod, IAsyncResult asyncResult, Boolean requiresSynchronization) +44
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52
   System.IO.<CopyToAsyncInternal>d__2.MoveNext() +253
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52
   System.Runtime.CompilerServices.TaskAwaiter.GetResult() +21
   S.Web.Controllers.<Add>d__15.MoveNext() in c:\Users\A\Source\Test\STest\S.Web\Controllers\ProductController.cs:66
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52
   System.Web.Mvc.Async.TaskAsyncActionDescriptor.EndExecute(IAsyncResult asyncResult) +84
   System.Web.Mvc.Async.<>c__DisplayClass37.<BeginInvokeAsynchronousActionMethod>b__36(IAsyncResult asyncResult) +17
   System.Web.Mvc.Async.WrappedAsyncResult`1.CallEndDelegate(IAsyncResult asyncResult) +10
   System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +48
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult) +32
   System.Web.Mvc.Async.AsyncInvocationWithFilters.<InvokeActionMethodFilterAsynchronouslyRecursive>b__3f() +50
   System.Web.Mvc.Async.<>c__DisplayClass48.<InvokeActionMethodFilterAsynchronouslyRecursive>b__41() +225
   System.Web.Mvc.Async.<>c__DisplayClass33.<BeginInvokeActionMethodWithFilters>b__32(IAsyncResult asyncResult) +10
   System.Web.Mvc.Async.WrappedAsyncResult`1.CallEndDelegate(IAsyncResult asyncResult) +10
   System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +48
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult) +34
   System.Web.Mvc.Async.<>c__DisplayClass2b.<BeginInvokeAction>b__1c() +26
   System.Web.Mvc.Async.<>c__DisplayClass21.<BeginInvokeAction>b__1e(IAsyncResult asyncResult) +100
   System.Web.Mvc.Async.WrappedAsyncResult`1.CallEndDelegate(IAsyncResult asyncResult) +10
   System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +48
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +27
   System.Web.Mvc.Controller.<BeginExecuteCore>b__1d(IAsyncResult asyncResult, ExecuteCoreState innerState) +13
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +36
   System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +53
   System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +39
   System.Web.Mvc.Controller.<BeginExecute>b__15(IAsyncResult asyncResult, Controller controller) +12
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +28
   System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +53
   System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +29
   System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.EndExecute(IAsyncResult asyncResult) +10
   System.Web.Mvc.MvcHandler.<BeginProcessRequest>b__5(IAsyncResult asyncResult, ProcessRequestState innerState) +21
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +36
   System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +53
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +31
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +9
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +9514812
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

Answer 1

It is because the stream is disposed on the very next line. The call is asynchronous.. and therefore drops to the Dispose call at the end of the using block.

await the Task returned from CopyToAsync so that the fileStream instance is still available to it as its doing what it needs to do:

public async Task SaveFileContentsAsync(string filePath, Stream stream)
{
    using (var fileStream = new FileStream(filePath, FileMode.Create))
    {
        await stream.CopyToAsync(fileStream);
    }
}