New CoAPClient creator method using a standard socket

In some scenarios it's useful to have control over advanced socket
configuration. These advanced settings are available in the socket2
crate. To create CoAPClient using sockets with these advanced
settings, we need a creator method capable of using standard-socket-
compatible socket instance that can be explicitly configured by the
API user.

Cargo.toml

@@ -38,5 +38,6 @@ dtls = ["dep:webrtc-dtls", "dep:webrtc-util", "dep:rustls", "dep:rustls-pemfile"
 
 [dev-dependencies]
 quickcheck = "0.8.2"
-
+socket2 = "0.5"
+tokio-test = "0.4.4"
 

src/client.rs

@@ -391,13 +391,8 @@ impl UdpCoAPClient {
         bind_addr: A,
         peer_addr: B,
     ) -> IoResult<Self> {
-        let peer_addr = lookup_host(peer_addr).await?.next().ok_or(Error::new(
-            ErrorKind::InvalidInput,
-            "could not get socket address",
-        ))?;
         let socket = UdpSocket::bind(bind_addr).await?;
-        let transport = UdpTransport { socket, peer_addr };
-        return Ok(UdpCoAPClient::from_transport(transport));
+        Self::new_with_tokio_socket(socket, peer_addr).await
     }
 
     pub async fn new_udp<A: ToSocketAddrs>(addr: A) -> IoResult<Self> {
@@ -410,6 +405,45 @@ impl UdpCoAPClient {
             SocketAddr::V6(_) => Self::new_with_specific_source(":::0", sock_addr).await?,
         })
     }
+
+    /// Create a client with a `std::net` socket
+    ///
+    /// Using a standard socket is useful to get advanced features from socket2 crate
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # tokio_test::block_on(async {
+    ///   use socket2::{Socket, Domain, Type};
+    ///   use coap::UdpCoAPClient;
+    ///
+    ///   let socket = Socket::new(Domain::IPV6, Type::DGRAM, None).expect("Standard socket creation failed");
+    ///   socket.set_multicast_hops_v6(16).expect("Setting multicast hops failed");
+    ///   let client = UdpCoAPClient::new_with_std_socket(socket.into(), "[::1]:5683").await.expect("Client creation failed");
+    /// # })
+    /// ```
+    pub async fn new_with_std_socket<A: ToSocketAddrs>(
+        socket: std::net::UdpSocket,
+        peer_addr: A,
+    ) -> IoResult<Self> {
+        socket.set_nonblocking(true)?;
+        let socket = UdpSocket::from_std(socket)?;
+        Self::new_with_tokio_socket(socket, peer_addr).await
+    }
+
+    async fn new_with_tokio_socket<A: ToSocketAddrs>(
+        socket: UdpSocket,
+        peer_addr: A,
+    ) -> IoResult<Self> {
+        let peer_addr = lookup_host(peer_addr).await?.next().ok_or(Error::new(
+            ErrorKind::InvalidInput,
+            "could not get socket address",
+        ))?;
+
+        let transport = UdpTransport { socket, peer_addr };
+        Ok(UdpCoAPClient::from_transport(transport))
+    }
+
     /// Send a request to all CoAP devices.
     /// - IPv4 AllCoAP multicast address is '224.0.1.187'
     /// - IPv6 AllCoAp multicast addresses are 'ff0?::fd'