implement separated mod for the Ban feature

src/ban.rs

@@ -0,0 +1,45 @@
+use chrono::{DateTime, Local};
+use librqbit::dht::Id20;
+use std::{collections::HashMap, time::Duration};
+
+pub struct Ban {
+    index: HashMap<Id20, DateTime<Local>>,
+    timeout: u64,
+}
+
+impl Ban {
+    pub fn init(timeout: u64, capacity: usize) -> Self {
+        Self {
+            index: HashMap::with_capacity(capacity),
+            timeout,
+        }
+    }
+
+    pub fn has(&self, key: &Id20) -> bool {
+        self.index.contains_key(key)
+    }
+
+    pub fn total(&self) -> usize {
+        self.index.len()
+    }
+
+    pub fn update(&mut self, time: DateTime<Local>) {
+        self.index.retain(|i, &mut expires| {
+            if time > expires {
+                log::debug!(
+                    "remove ban for `{}` by the timeout expiration ({expires})",
+                    i.as_string()
+                );
+                false
+            } else {
+                true
+            }
+        })
+    }
+
+    pub fn add(&mut self, key: Id20) -> DateTime<Local> {
+        let t = Local::now() + Duration::from_secs(self.index.len() as u64 * self.timeout);
+        assert!(self.index.insert(key, t).is_none());
+        t
+    }
+}