Okhttp header 中文异常解决方案

private fun getValidUA(userAgent: String?): String {
        if (userAgent.isNullOrEmpty()) return ""
        val sb = StringBuilder()
        var i = 0
        val length = userAgent.length
        while (i < length) {
            val c = userAgent[i]
            if (c <= '\u001f' || c >= '\u007f') {//检测为不合法字符，就转为unicode 编码
                sb.append(String.format("\\u%04x", c.code))
            } else {
                sb.append(c)
            }
            i++
        }
        return sb.toString()
    }