common: add a UTF-8 check helper

tar/common/utf8.go

@@ -0,0 +1,21 @@
+package common
+
+// IsValidUtf8String checks for in valid UTF-8 characters
+func IsValidUtf8String(s string) bool {
+	for _, r := range s {
+		if int(r) == 0xfffd {
+			return false
+		}
+	}
+	return true
+}
+
+// IsValidUtf8Btyes checks for in valid UTF-8 characters
+func IsValidUtf8Btyes(b []byte) bool {
+	for _, r := range string(b) {
+		if int(r) == 0xfffd {
+			return false
+		}
+	}
+	return true
+}