Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Configuration/System/Configuration/FileUtil.cs

@@ -0,0 +1,47 @@
+//------------------------------------------------------------------------------
+// <copyright file="FileUtil.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//------------------------------------------------------------------------------
+
+namespace System.Configuration {
+    using System;
+    using System.IO;
+    using Microsoft.Win32;
+    using System.Runtime.InteropServices;
+
+    static internal class FileUtil {
+        const int HRESULT_WIN32_FILE_NOT_FOUND = unchecked((int)0x80070002);
+        const int HRESULT_WIN32_PATH_NOT_FOUND = unchecked((int)0x80070003);
+
+        //
+        // Use to avoid the perf hit of a Demand when the Demand is not necessary for security.
+        // 
+        // If trueOnError is set, then return true if we cannot confirm that the file does NOT exist.
+        //
+        internal static bool FileExists(string filename, bool trueOnError) {
+            UnsafeNativeMethods.WIN32_FILE_ATTRIBUTE_DATA data;
+            bool ok = UnsafeNativeMethods.GetFileAttributesEx(filename, UnsafeNativeMethods.GetFileExInfoStandard, out data);
+            if (ok) {
+                // The path exists. Return true if it is a file, false if a directory.
+                return (data.fileAttributes & (int) FileAttributes.Directory) != (int) FileAttributes.Directory;
+            }
+            else {
+                if (!trueOnError) {
+                    return false;
+                }
+                else {
+                    // Return true if we cannot confirm that the file does NOT exist.
+                    int hr = Marshal.GetHRForLastWin32Error();
+                    if (hr == HRESULT_WIN32_FILE_NOT_FOUND || hr == HRESULT_WIN32_PATH_NOT_FOUND) {
+                        return false;
+                    }
+                    else {
+                        return true;
+                    }
+                }
+            }
+        }
+    }
+}
+