Save file extension with retrofit and coroutine

Extension.kt

Call<ResponseBody>.saveFile(fileNameWithExt: String, action: (file: File?) -> Unit) {
        GlobalScope.launch {
            try {
                cacheDir.listFiles { _, name -> name.contains("${fileType}.pdf") }?.lastOrNull {
                    action(it)
                    true
                }?:
                withContext(Dispatchers.IO) {
                    val response = this@saveFile.execute()
                    val buffer = response.body()?.byteStream()
                    var file: File? = null
                    if (buffer != null) {
                        file = File.createTempFile(fileNameWithExt, null, baseContext?.cacheDir)
                        if (file != null) {
                            buffer.copyStreamToFile(file)
                        }
                    }
                    action(file)
                }
            } catch (e: Exception) {
                Log.e("error", e.message ?: "")
            }
        }
    }

    private fun InputStream.copyStreamToFile(outputFile: File) {
        this.use { input ->
            val outputStream = FileOutputStream(outputFile)
            outputStream.use { output ->
                val buffer = ByteArray(4 * 1024)
                while (true) {
                    val byteCount = input.read(buffer)
                    if (byteCount < 0) break
                    output.write(buffer, 0, byteCount)
                }
                output.flush()
            }

        }
    }