You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: cache.rs
    path of file: ./repos/salvo/crates/core/src/conn/acme
    
    the code of the file until where you have to start completion: /*! Ways to cache account data and certificates.
A default implementation for `AsRef<Path>` (`Sting`, `OsString`, `PathBuf`, ...)
allows the use of a local directory as cache.
Note that the fi
    
    async fn read_key(&self, directory_name: &str, domains: &[String]) -> Result<Option<Vec<u8>>, Self::Error> {
        let mut path = self.as_ref().to_path_buf();
        path.push(format!(
            "{}{}-{}",
            KEY_PEM_PREFIX,
            directory_name,
            file_hash_part(domains)
        ));
        match read(path).await {
            Ok(data) => Ok(Some(data)),
            Err(e) => match e.kind() {
                ErrorKind::NotFound => Ok(None),
                _ => Err(e),
            },
        }
    }