1 files changed, 58 insertions, 0 deletions
diff --git a/src/System.Private.CoreLib/shared/System/IO/FileStream.Win32.cs b/src/System.Private.CoreLib/shared/System/IO/FileStream.Win32.cs
index 4b75ad6da..edcf8e546 100644
--- a/src/System.Private.CoreLib/shared/System/IO/FileStream.Win32.cs
+++ b/src/System.Private.CoreLib/shared/System/IO/FileStream.Win32.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Diagnostics;
 using Microsoft.Win32.SafeHandles;
 
 namespace System.IO
@@ -43,5 +44,62 @@ namespace System.IO
                     Interop.Kernel32.CreateFile(_path, fAccess, share, ref secAttrs, mode, flagsAndAttributes, IntPtr.Zero));
             }
         }
+
+        private static bool GetDefaultIsAsync(SafeFileHandle handle)
+        {
+            return handle.IsAsync ?? !IsHandleSynchronous(handle, ignoreInvalid: true) ?? DefaultIsAsync;
+        }
+
+        private static unsafe bool? IsHandleSynchronous(SafeFileHandle fileHandle, bool ignoreInvalid)
+        {
+            if (fileHandle.IsInvalid)
+                return null;
+
+            uint fileMode;
+
+            int status = Interop.NtDll.NtQueryInformationFile(
+                FileHandle: fileHandle,
+                IoStatusBlock: out Interop.NtDll.IO_STATUS_BLOCK ioStatus,
+                FileInformation: &fileMode,
+                Length: sizeof(uint),
+                FileInformationClass: Interop.NtDll.FileModeInformation);
+
+            switch (status)
+            {
+                case 0:
+                    // We we're successful
+                    break;
+                case Interop.NtDll.STATUS_INVALID_HANDLE:
+                    if (!ignoreInvalid)
+                    {
+                        throw Win32Marshal.GetExceptionForWin32Error(Interop.Errors.ERROR_INVALID_HANDLE);
+                    }
+                    else
+                    {
+                        return null;
+                    }
+                default:
+                    // Something else is preventing access
+                    Debug.Fail("Unable to get the file mode information, status was" + status.ToString());
+                    return null;
+            }
+
+            // If either of these two flags are set, the file handle is synchronous (not overlapped)
+            return (fileMode & (Interop.NtDll.FILE_SYNCHRONOUS_IO_ALERT | Interop.NtDll.FILE_SYNCHRONOUS_IO_NONALERT)) > 0;
+        }
+
+        private static void VerifyHandleIsSync(SafeFileHandle handle, int fileType, FileAccess access)
+        {
+            // As we can accurately check the handle type when we have access to NtQueryInformationFile we don't need to skip for
+            // any particular file handle type.
+
+            // If the handle was passed in without an explicit async setting, we already looked it up in GetDefaultIsAsync
+            if (!handle.IsAsync.HasValue)
+                return;
+
+            // If we can't check the handle, just assume it is ok.
+            if (!(IsHandleSynchronous(handle, ignoreInvalid: false) ?? true))
+                throw new ArgumentException(SR.Arg_HandleNotSync, nameof(handle));
+        }
     }
 }