tar: fix name filter on windows

tar/sanitize_other_test.go

@@ -0,0 +1,7 @@
+//go:build !windows
+
+package tar
+
+func invalidFileNames() []string {
+	return nil // No special cases for this platform.
+}

tar/sanitize_test.go

@@ -5,9 +5,15 @@ import (
 )
 
 func TestValidatePlatformPath(t *testing.T) {
-	// Expect error if path contains null
-	if err := validatePlatformPath("foo\x00bar"); err == nil {
-		t.Fatal("expected error")
+	for _, name := range append(
+		invalidFileNames(),
+		"foo\x00bar", // Expect error if path contains null
+	) {
+		t.Run(name, func(t *testing.T) {
+			if err := validatePlatformPath(name); err == nil {
+				t.Fatal("expected error")
+			}
+		})
 	}
 
 	// No specification for a path component containing a "." component

tar/sanitize_windows.go

@@ -2,73 +2,75 @@ package tar
 
 import (
 	"fmt"
+	"os"
 	"path/filepath"
+	"slices"
 	"strings"
 )
 
-// https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
-var reservedNames = [...]string{"CON", "PRN", "AUX", "NUL", "COM1", "COM2", "COM3", "COM4", "COM5", "COM6", "COM7", "COM8", "COM9", "LPT1", "LPT2", "LPT3", "LPT4", "LPT5", "LPT6", "LPT7", "LPT8", "LPT9"}
+// NOTE: `/` is not included, it is already reserved as the standard path separator.
+const reservedRunes = `<>:"\|?*` + "\x00"
 
-const reservedCharsStr = `[<>:"\|?*]` + "\x00" // NOTE: `/` is not included as it is our standard path separator
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
+var reservedNames = [...]string{
+	"CON", "PRN", "AUX", "NUL", "COM1", "COM2",
+	"COM3", "COM4", "COM5", "COM6", "COM7", "COM8",
+	"COM9", "LPT1", "LPT2", "LPT3", "LPT4", "LPT5",
+	"LPT6", "LPT7", "LPT8", "LPT9",
+}
 
 func isNullDevice(path string) bool {
-	// This is a case insensitive comparison to NUL
-	if len(path) != 3 {
-		return false
-	}
-	if path[0]|0x20 != 'n' {
-		return false
-	}
-	if path[1]|0x20 != 'u' {
-		return false
-	}
-	if path[2]|0x20 != 'l' {
-		return false
-	}
-	return true
+	// "NUL" is standard but the device is case insensitive.
+	// Normalize to upper for the compare.
+	const nameLen = len(os.DevNull)
+	return len(path) == nameLen && strings.ToUpper(path) == os.DevNull
 }
 
-// validatePathComponent returns an error if the given path component is not allowed on the platform
-func validatePathComponent(c string) error {
-	// MSDN: Do not end a file or directory name with a space or a period
-	if strings.HasSuffix(c, ".") {
-		return fmt.Errorf("invalid platform path: path components cannot end with '.' : %q", c)
-	}
-	if strings.HasSuffix(c, " ") {
-		return fmt.Errorf("invalid platform path: path components cannot end with ' ' : %q", c)
-	}
-
-	if c == ".." {
-		return fmt.Errorf("invalid platform path: path component cannot be '..'")
+// validatePathComponent returns an error if the given path component is not allowed on the platform.
+func validatePathComponent(component string) error {
+	const invalidPathErr = "invalid platform path"
+	for _, suffix := range [...]string{
+		".", // MSDN: Do not end a file or directory
+		" ", // name with a space or a period.
+	} {
+		if strings.HasSuffix(component, suffix) {
+			return fmt.Errorf(
+				`%s: path components cannot end with '%s': "%s"`,
+				invalidPathErr, suffix, component,
+			)
+		}
 	}
-	// error on reserved characters
-	if strings.ContainsAny(c, reservedCharsStr) {
-		return fmt.Errorf("invalid platform path: path components cannot contain any of %s : %q", reservedCharsStr, c)
+	if strings.ContainsAny(component, reservedRunes) {
+		return fmt.Errorf(
+			`%s: path components cannot contain any of "%s": "%s"`,
+			invalidPathErr, reservedRunes, component,
+		)
 	}
-
-	// error on reserved names
-	for _, rn := range reservedNames {
-		if c == rn {
-			return fmt.Errorf("invalid platform path: path component is a reserved name: %s", c)
-		}
+	if slices.Contains(reservedNames[:], strings.ToUpper(component)) {
+		return fmt.Errorf(
+			`%s: path component is a reserved name: "%s"`,
+			invalidPathErr, component,
+		)
 	}
-
 	return nil
 }
 
-func validatePlatformPath(platformPath string) error {
-	// remove the volume name
-	p := platformPath[len(filepath.VolumeName(platformPath)):]
-
-	// convert to cleaned slash-path
-	p = filepath.ToSlash(p)
-	p = strings.Trim(p, "/")
-
-	// make sure all components of the path are valid
-	for _, e := range strings.Split(p, "/") {
-		if err := validatePathComponent(e); err != nil {
+func validatePlatformPath(nativePath string) error {
+	normalized := normalizeToGoPath(nativePath)
+	for component := range strings.SplitSeq(normalized, "/") {
+		if err := validatePathComponent(component); err != nil {
 			return err
 		}
 	}
 	return nil
 }
+
+func normalizeToGoPath(nativePath string) string {
+	var (
+		volumeName     = filepath.VolumeName(nativePath)
+		relativeNative = nativePath[len(volumeName):]
+		goPath         = filepath.ToSlash(relativeNative)
+		relativeGo     = strings.Trim(goPath, "/")
+	)
+	return relativeGo
+}

tar/sanitize_windows_test.go

@@ -0,0 +1,16 @@
+//go:build windows
+
+package tar
+
+func invalidFileNames() []string {
+	return []string{
+		"foo.",      // Cannot end in '.'.
+		"foo ",      // Cannot end in ' '.
+		"..",        // Cannot be parent dir name.
+		"CON",       // Cannot be device name.
+		"nul",       // Cannot be device name (case insensitive).
+		"AuX",       // Cannot be device name (case insensitive).
+		"foo?",      // Cannot use reserved character '?'.
+		`<\f|o:o*>`, // Cannot use reserved characters (multiple).
+	}
+}