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//! DNS resolver configuration

use std::io;
use std::net::SocketAddr;
use std::time::Duration;

/// Configures the behavior of DNS requests
#[derive(Clone, Debug)]
pub struct DnsConfig {
    /// List of name servers; must not be empty
    pub name_servers: Vec<SocketAddr>,
    /// List of search domains
    pub search: Vec<String>,

    /// Minimum number of dots in a name to trigger an initial absolute query
    pub n_dots: u32,
    /// Duration before retrying or failing an unanswered request
    pub timeout: Duration,
    /// Number of attempts made before returning an error
    pub attempts: u32,

    /// Whether to rotate through available nameservers
    pub rotate: bool,
    /// If `true`, perform `AAAA` queries first and return IPv4 addresses
    /// as IPv4-mapped IPv6 addresses.
    pub use_inet6: bool,
}

/// Returns the default system configuration for DNS requests.
pub fn default_config() -> io::Result<DnsConfig> {
    default_config_impl()
}

#[cfg(unix)]
fn default_config_impl() -> io::Result<DnsConfig> {
    use resolv_conf::load;
    load()
}

#[cfg(windows)]
fn default_config_impl() -> io::Result<DnsConfig> {
    // TODO: Get a list of nameservers from Windows API.
    // For now, return an IO error.
    Err(io::Error::new(io::ErrorKind::Other, "Nameserver list not available on Windows"))
}