[Router] Add a rust-based router (#1790)

rust/src/router.rs

@@ -0,0 +1,88 @@
+// src/router.rs
+
+use std::fmt::Debug;
+
+/// Generic Router trait that can be implemented with different policies
+pub trait Router: Send + Sync + Debug {
+    /// Select a worker URL based on the implementation's policy
+    /// Returns None if no worker is available
+    fn select(&self) -> Option<String>;
+
+    // get first worker
+    fn get_first(&self) -> Option<String>;
+}
+
+// Round Robin Router
+#[derive(Debug)]
+pub struct RoundRobinRouter {
+    worker_urls: Vec<String>,
+    current_index: std::sync::atomic::AtomicUsize, // AtomicUsize is a thread-safe integer
+}
+
+impl RoundRobinRouter {
+    pub fn new(worker_urls: Vec<String>) -> Self {
+        Self {
+            worker_urls,
+            current_index: std::sync::atomic::AtomicUsize::new(0),
+        }
+    }
+}
+
+impl Router for RoundRobinRouter {
+    fn select(&self) -> Option<String> {
+        if self.worker_urls.is_empty() {
+            return None;
+        }
+        // Use relaxed because operation order doesn't matter in round robin
+        let index = self.current_index.fetch_add(1, std::sync::atomic::Ordering::Relaxed) 
+            % self.worker_urls.len();
+        Some(self.worker_urls[index].clone())
+    }
+
+    fn get_first(&self) -> Option<String> {
+        if self.worker_urls.is_empty() {
+            return None;
+        }
+        Some(self.worker_urls[0].clone())
+    }
+}
+
+// Random Router
+#[derive(Debug)]
+pub struct RandomRouter {
+    worker_urls: Vec<String>,
+}
+
+impl RandomRouter {
+    pub fn new(worker_urls: Vec<String>) -> Self {
+        Self { worker_urls }
+    }
+}
+
+impl Router for RandomRouter {
+    fn select(&self) -> Option<String> {
+        use rand::seq::SliceRandom;
+        
+        if self.worker_urls.is_empty() {
+            return None;
+        }
+        
+        self.worker_urls.choose(&mut rand::thread_rng()).cloned()
+    }
+
+    fn get_first(&self) -> Option<String> {
+        if self.worker_urls.is_empty() {
+            return None;
+        }
+        Some(self.worker_urls[0].clone())
+    }
+}
+
+// create a router based on routing policy
+pub fn create_router(worker_urls: Vec<String>, policy: String) -> Box<dyn Router> {
+    match policy.to_lowercase().as_str() {
+        "random" => Box::new(RandomRouter::new(worker_urls)),
+        "round_robin" => Box::new(RoundRobinRouter::new(worker_urls)),
+        _ => panic!("Unknown routing policy: {}. The available policies are 'random' and 'round_robin'", policy),
+    }
+}