edge-nal 0.6.0

Hosts a bunch of traits which are not yet available in the embedded-nal-async crate
Documentation 
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//! A trait for performing DNS lookups on embedded devices

use core::net::IpAddr;

/// This is the host address type to be returned by `gethostbyname`.
///
/// An IPv4 address type always looks for `A` records, while IPv6 address type
/// will look for `AAAA` records
#[derive(Clone, Debug, PartialEq)]
pub enum AddrType {
    /// Result is `A` record
    IPv4,
    /// Result is `AAAA` record
    IPv6,
    /// Result is either a `A` record, or a `AAAA` record
    Either,
}

/// This trait provides DNS resolution facility for embedded applications.
///
/// It does not handle every DNS record type, but is meant as an
/// embedded alternative to [`ToSocketAddrs`], and is as such meant to resolve
/// an ip address from a hostname, or a hostname from an ip address. This means
/// that it only deals in host address records `A` (IPv4) and `AAAA` (IPv6).
///
/// [`ToSocketAddrs`]:
/// https://doc.rust-lang.org/std/net/trait.ToSocketAddrs.html
pub trait Dns {
    /// The type returned when we have an error
    type Error: embedded_io_async::Error;

    /// Resolve the first ip address of a host, given its hostname and a desired
    /// address record type to look for
    async fn get_host_by_name(
        &self,
        host: &str,
        addr_type: AddrType,
    ) -> Result<IpAddr, Self::Error>;

    /// Resolve the hostname of a host, given its ip address.
    ///
    /// The hostname is stored at the beginning of `result`, the length is returned.
    ///
    /// If the buffer is too small to hold the domain name, an error should be returned.
    ///
    /// **Note**: A fully qualified domain name (FQDN), has a maximum length of
    /// 255 bytes according to [`rfc1035`]. Therefore, you can pass a 255-byte long
    /// buffer to guarantee it'll always be large enough.
    ///
    /// [`rfc1035`]: https://tools.ietf.org/html/rfc1035
    async fn get_host_by_address(
        &self,
        addr: IpAddr,
        result: &mut [u8],
    ) -> Result<usize, Self::Error>;
}

impl<T> Dns for &T
where
    T: Dns,
{
    type Error = T::Error;

    async fn get_host_by_name(
        &self,
        host: &str,
        addr_type: AddrType,
    ) -> Result<IpAddr, Self::Error> {
        T::get_host_by_name(self, host, addr_type).await
    }

    async fn get_host_by_address(
        &self,
        addr: IpAddr,
        result: &mut [u8],
    ) -> Result<usize, Self::Error> {
        T::get_host_by_address(self, addr, result).await
    }
}

impl<T> Dns for &mut T
where
    T: Dns,
{
    type Error = T::Error;

    async fn get_host_by_name(
        &self,
        host: &str,
        addr_type: AddrType,
    ) -> Result<IpAddr, Self::Error> {
        T::get_host_by_name(self, host, addr_type).await
    }

    async fn get_host_by_address(
        &self,
        addr: IpAddr,
        result: &mut [u8],
    ) -> Result<usize, Self::Error> {
        T::get_host_by_address(self, addr, result).await
    }
}