add: timestamp getter and constructor

src/async_resolver/state_block.rs

@@ -1,4 +1,43 @@
+use tokio::time::Instant;
+
 /// This struct represent the state of information of a pending request.
+/// 
+/// [RFC 1035](https://datatracker.ietf.org/doc/html/rfc1035#section-7.1)
+/// 
+/// Since a resolver must be able to multiplex multiple requests if it is to
+/// perform its function efficiently, each pending request is usually
+/// represented in some block of state information.
+/// 
+/// The key algorithm uses the state information of the request to select the next name server address to
+/// query
 pub struct StateBlock {
-    timestamp: u64,
+    /// A timestamp indicating the time the request began.
+    /// 
+    /// The timestamp is used to decide whether RRs in the database
+    /// can be used or are out of date. This timestamp uses the
+    /// absolute time format.
+    timestamp: Instant,
+}
+
+impl StateBlock {
+    /// Creates a new StateBlock for a request.
+    /// 
+    /// # Arguments
+    /// * `timestamp` - A Instant that represents the time the request began.
+    /// 
+    /// # Example
+    /// ```
+    /// let state_block = StateBlock::new(Instant::now());
+    /// ```
+    pub fn new() -> StateBlock {
+        StateBlock {
+            timestamp: Instant::now(),
+        }
+    }
+
+    /// Returns a reference to the `timestamp` of the request.
+    pub fn get_timestamp(&self) -> &Instant {
+        return &self.timestamp;
+    }
+
 }