* @retval #WEBRTC_ERROR_INVALID_OPERATION Invalid operation
* @retval #WEBRTC_ERROR_INVALID_STATE Invalid state
* @pre @a channel should be opened before calling this function.
+ * @post webrtc_data_channel_error_cb() will be invoked if this function fails.
* @see webrtc_data_channel_open_cb()
* @see webrtc_data_channel_send_bytes()
*/
* @retval #WEBRTC_ERROR_INVALID_OPERATION Invalid operation
* @retval #WEBRTC_ERROR_INVALID_STATE Invalid state
* @pre @a channel should be opened before calling this function.
+ * @post webrtc_data_channel_error_cb() will be invoked if this function fails.
* @see webrtc_data_channel_open_cb()
* @see webrtc_data_channel_send_string()
*/