netstack: Move the smolnetd source

netstack/src/port_set.rs

@@ -0,0 +1,62 @@
+use std::collections::btree_map::{BTreeMap, Entry};
+
+pub struct PortSet {
+    from: u16,
+    range: u16,
+    next: u16,
+    ports: BTreeMap<u16, usize>,
+}
+
+impl PortSet {
+    pub fn new(from: u16, to: u16) -> Option<PortSet> {
+        if from > to {
+            return None;
+        }
+        Some(PortSet {
+            from,
+            range: to - from + 1,
+            next: 0,
+            ports: BTreeMap::new(),
+        })
+    }
+
+    pub fn get_port(&mut self) -> Option<u16> {
+        if self.ports.len() >= self.range as usize {
+            return None;
+        }
+
+        let port = loop {
+            if let Entry::Vacant(entry) = self.ports.entry(self.next) {
+                entry.insert(1);
+                let port = self.from + self.next;
+                self.next = self.next.wrapping_add(1);
+                break port;
+            }
+            self.next = self.next.wrapping_add(1);
+        };
+
+        Some(port)
+    }
+
+    pub fn claim_port(&mut self, port: u16) -> bool {
+        if let Entry::Vacant(entry) = self.ports.entry(port) {
+            entry.insert(1);
+            true
+        } else {
+            false
+        }
+    }
+
+    pub fn acquire_port(&mut self, port: u16) {
+        *self.ports.entry(port).or_insert(0) += 1;
+    }
+
+    pub fn release_port(&mut self, port: u16) {
+        if let Entry::Occupied(mut entry) = self.ports.entry(port) {
+            *entry.get_mut() -= 1;
+            if *entry.get() == 0 {
+                entry.remove();
+            }
+        }
+    }
+}