add serverEntry struct and methods

src/async_resolver/server_entry.rs

@@ -0,0 +1,32 @@
+use crate::async_resolver::server_info::ServerInfo;
+
+/// Struct that holds the state of a single server for a request.
+pub struct ServerEntry {
+    info: ServerInfo,
+    retransmissions: u32,
+}
+
+impl ServerEntry {
+    pub fn new(info: ServerInfo) -> ServerEntry {
+        ServerEntry {
+            info,
+            retransmissions: 0,
+        }
+    }
+
+    pub fn get_info(&self) -> &ServerInfo {
+        &self.info
+    }
+
+    pub fn get_retransmissions(&self) -> u32 {
+        self.retransmissions
+    }
+
+    pub fn increment_retransmissions(&mut self) {
+        self.retransmissions += 1;
+    }
+
+    pub fn reset_retransmissions(&mut self) {
+        self.retransmissions = 0;
+    }
+}