use crate::{Channel, DELIMITER_LINE, ERR_PREFIX, FLUSH_LINE, MAX_DATA_LEN, RESPONSE_END_LINE};use quick_error::quick_error;use std::io; quick_error! {    #[derive(Debug)]    pub enum Error {        Io(err: io::Error) {            display("An error occurred while writing")            from()            source(err)        }        DataLengthLimitExceeded(length_in_bytes: usize) {            display("Cannot encode more than {} bytes, got {}", MAX_DATA_LEN, length_in_bytes)        }        DataIsEmpty {            display("Empty lines are invalid")        }    }} pub fn response_end_to_write(mut out: impl io::Write) -> io::Result<usize> {    out.write_all(RESPONSE_END_LINE).map(|_| 4)} pub fn delim_to_write(mut out: impl io::Write) -> io::Result<usize> {    out.write_all(DELIMITER_LINE).map(|_| 4)} pub fn flush_to_write(mut out: impl io::Write) -> io::Result<usize> {    out.write_all(FLUSH_LINE).map(|_| 4)} pub fn error_to_write(data: &[u8], out: impl io::Write) -> Result<usize, Error> {    prefixed_data_to_write(ERR_PREFIX, data, out)} pub fn band_to_write(kind: Channel, data: &[u8], out: impl io::Write) -> Result<usize, Error> {    prefixed_data_to_write(&[kind as u8], data, out)} pub fn data_to_write(data: &[u8], out: impl io::Write) -> Result<usize, Error> {    prefixed_data_to_write(&[], data, out)} pub fn text_to_write(text: &[u8], out: impl io::Write) -> Result<usize, Error> {    prefixed_and_suffixed_data_to_write(&[], text, &[b'\n'], out)} fn prefixed_data_to_write(prefix: &[u8], data: &[u8], out: impl io::Write) -> Result<usize, Error> {    prefixed_and_suffixed_data_to_write(prefix, data, &[], out)} fn prefixed_and_suffixed_data_to_write(    prefix: &[u8],    data: &[u8],    suffix: &[u8],    mut out: impl io::Write,) -> Result<usize, Error> {    let data_len = prefix.len() + data.len() + suffix.len();    if data_len > MAX_DATA_LEN {        return Err(Error::DataLengthLimitExceeded(data_len));    }    if data.is_empty() {        return Err(Error::DataIsEmpty);    }     let data_len = data_len + 4;    let buf = u16_to_hex(data_len as u16);     out.write_all(&buf)?;    if !prefix.is_empty() {        out.write_all(prefix)?;    }    out.write_all(data)?;    if !suffix.is_empty() {        out.write_all(suffix)?;    }    Ok(data_len)} pub(crate) fn u16_to_hex(value: u16) -> [u8; 4] {    let mut buf = [0u8; 4];    hex::encode_to_slice((value as u16).to_be_bytes(), &mut buf).expect("two bytes to 4 hex chars never fails");    buf}