Avoid calling GetTempFileName in BitmapDownload

Replace the Win32 GetTempFileName call with Path.GetRandomFileName
and CREATE_NEW in a retry loop to avoid IOException when the temp
folder contains 65k+ files. This follows the same pattern already
used by FileHelper.CreateAndOpenTemporaryFile elsewhere in WPF.

Fixes #259

Author: apoorvdarshan

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Imaging/BitmapDownload.cs

@@ -3,13 +3,11 @@
 
 using System.IO;
 using System.Collections;
-using System.ComponentModel;
 using System.Threading;
 using System.Windows.Threading;
 using MS.Internal;
 using System.Net;
 using System.Net.Cache;
-using System.Text;
 using MS.Win32;
 using Microsoft.Win32.SafeHandles;
 
@@ -112,47 +110,55 @@ Stream stream
             entry.inputStream = stream;
 
             string cacheFolder = MS.Win32.WinInet.InternetCacheFolder.LocalPath;
-            bool passed = false;
 
-            // Get the file path 
-            StringBuilder tmpFileName = new StringBuilder(NativeMethods.MAX_PATH);
-            MS.Win32.UnsafeNativeMethods.GetTempFileName(cacheFolder, "WPF", 0, tmpFileName);
-              
-            try
+            // Generate a temporary file using a random name instead of GetTempFileName,
+            // which fails when the folder contains too many temp files (65k limit).
+            // Retry with different random names if creation fails due to collision.
+            const int MaxRetries = 5;
+            SafeFileHandle fileHandle = null;
+            string pathToUse = null;
+
+            for (int retries = MaxRetries; retries > 0; retries--)
             {
-                string pathToUse = tmpFileName.ToString();
-                SafeFileHandle fileHandle = MS.Win32.UnsafeNativeMethods.CreateFile(
-                    pathToUse,
-                    dwDesiredAccess: NativeMethods.GENERIC_READ | NativeMethods.GENERIC_WRITE,
-                    dwShareMode: 0,
-                    lpSecurityAttributes: null,
-                    dwCreationDisposition: NativeMethods.CREATE_ALWAYS,
-                    dwFlagsAndAttributes: NativeMethods.FILE_ATTRIBUTE_TEMPORARY | NativeMethods.FILE_FLAG_DELETE_ON_CLOSE,
-                    hTemplateFile: IntPtr.Zero
-                    );
-
-                if (fileHandle.IsInvalid)
+                pathToUse = Path.Combine(cacheFolder, "WPF" + Path.GetRandomFileName());
+
+                try
                 {
-                    throw new Win32Exception();
+                    fileHandle = MS.Win32.UnsafeNativeMethods.CreateFile(
+                        pathToUse,
+                        dwDesiredAccess: NativeMethods.GENERIC_READ | NativeMethods.GENERIC_WRITE,
+                        dwShareMode: 0,
+                        lpSecurityAttributes: null,
+                        dwCreationDisposition: NativeMethods.CREATE_NEW,
+                        dwFlagsAndAttributes: NativeMethods.FILE_ATTRIBUTE_TEMPORARY | NativeMethods.FILE_FLAG_DELETE_ON_CLOSE,
+                        hTemplateFile: IntPtr.Zero
+                        );
+
+                    if (!fileHandle.IsInvalid)
+                    {
+                        break;
+                    }
+
+                    fileHandle.Dispose();
+                    fileHandle = null;
                 }
-                    
-                entry.outputStream = new FileStream(fileHandle, FileAccess.ReadWrite);
-                entry.streamPath = pathToUse;
-                passed = true;
-            }
-            catch(Exception e)
-            {
-                if (CriticalExceptions.IsCriticalException(e))
+                catch (Exception e)
                 {
-                    throw;
+                    if (CriticalExceptions.IsCriticalException(e))
+                    {
+                        throw;
+                    }
                 }
             }
 
-            if (!passed)
+            if (fileHandle == null || fileHandle.IsInvalid)
             {
                 throw new IOException(SR.Image_CannotCreateTempFile);
             }
 
+            entry.outputStream = new FileStream(fileHandle, FileAccess.ReadWrite);
+            entry.streamPath = pathToUse;
+
             entry.readBuffer  = new byte[READ_SIZE];
             entry.contentLength = -1;
             entry.contentType = string.Empty;

src/Microsoft.DotNet.Wpf/src/Shared/MS/Win32/NativeMethodsOther.cs

@@ -599,6 +599,7 @@ protected override bool ReleaseHandle()
         internal const int FILE_ATTRIBUTE_TEMPORARY = 0x00000100;
         internal const int FILE_FLAG_DELETE_ON_CLOSE = 0x04000000;
 
+        internal const int CREATE_NEW      = 1;
         internal const int CREATE_ALWAYS   = 2;
 
         internal const int PROCESS_ALL_ACCESS = (int)(STANDARD_RIGHTS_REQUIRED | SYNCHRONIZE | 0xFFF);

src/Microsoft.DotNet.Wpf/src/Shared/MS/Win32/UnsafeNativeMethodsOther.cs

@@ -14,20 +14,6 @@ namespace MS.Win32
 {
     internal partial class UnsafeNativeMethods
     {
-        [DllImport(ExternDll.Kernel32, CharSet = CharSet.Unicode, SetLastError = true, EntryPoint = "GetTempFileName")]
-        internal static extern uint _GetTempFileName(string tmpPath, string prefix, uint uniqueIdOrZero, StringBuilder tmpFileName);
-
-        internal static uint GetTempFileName(string tmpPath, string prefix, uint uniqueIdOrZero, StringBuilder tmpFileName)
-        {
-            uint result = _GetTempFileName(tmpPath, prefix, uniqueIdOrZero, tmpFileName);
-            if (result == 0)
-            {
-                throw new Win32Exception();
-            }
-
-            return result;
-        }
-
         [DllImport(ExternDll.Shell32, CharSet = CharSet.Auto, BestFitMapping = false, ThrowOnUnmappableChar = true)]
         internal static extern int ExtractIconEx(
                                         string szExeFileName,