Better temp file cleanup on Windows.

internal/fs/file_windows.go

@@ -1,10 +1,41 @@
 package fs
 
 import (
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
+	"syscall"
+	"strconv"
+	"sync"
+	"time"
+)
+
+// Random number state.
+// We generate random temporary file names so that there's a good
+// chance the file doesn't exist yet - keeps the number of tries in
+// TempFile to a minimum.
+var rand uint32
+var randmu sync.Mutex
+
+func reseed() uint32 {
+	return uint32(time.Now().UnixNano() + int64(os.Getpid()))
+}
+
+func nextRandom() string {
+	randmu.Lock()
+	r := rand
+	if r == 0 {
+		r = reseed()
+	}
+	r = r*1664525 + 1013904223 // constants from Numerical Recipes
+	rand = r
+	randmu.Unlock()
+	return strconv.Itoa(int(1e9 + r%1e9))[1:]
+}
+
+const (
+	FILE_ATTRIBUTE_TEMPORARY  = 0x00000100
+	FILE_FLAG_DELETE_ON_CLOSE = 0x04000000
 )
 
 // fixpath returns an absolute path on windows, so restic can open long file
@@ -32,7 +63,25 @@ func fixpath(name string) string {
 
 // TempFile creates a temporary file.
 func TempFile(dir, prefix string) (f *os.File, err error) {
-	return ioutil.TempFile(dir, prefix)
+	if dir == "" {
+		dir = os.TempDir()
+	}
+
+	access := uint32(syscall.GENERIC_READ | syscall.GENERIC_WRITE)
+	creation := uint32(syscall.CREATE_NEW)
+	flags := uint32(FILE_ATTRIBUTE_TEMPORARY | FILE_FLAG_DELETE_ON_CLOSE)
+	
+	for i := 0; i < 10000; i++ {
+		path := filepath.Join(dir, prefix+nextRandom())
+
+		h, err := syscall.CreateFile(syscall.StringToUTF16Ptr(path), access, 0, nil, creation, flags, 0)
+		if err == nil {
+			return os.NewFile(uintptr(h), path), nil
+		}
+	}
+	
+	// Proper error handling is still to do
+	return nil, os.ErrExist
 }
 
 // Chmod changes the mode of the named file to mode.