[router] Add Rerank Routing Logic in Regular Router (#10219)

sgl-router/tests/common/mock_worker.rs

@@ -81,6 +81,7 @@ impl MockWorker {
             .route("/generate", post(generate_handler))
             .route("/v1/chat/completions", post(chat_completions_handler))
             .route("/v1/completions", post(completions_handler))
+            .route("/v1/rerank", post(rerank_handler))
             .route("/v1/responses", post(responses_handler))
             .route("/flush_cache", post(flush_cache_handler))
             .route("/v1/models", get(v1_models_handler))
@@ -687,6 +688,56 @@ async fn v1_models_handler(State(config): State<Arc<RwLock<MockWorkerConfig>>>)
     .into_response()
 }
 
+async fn rerank_handler(
+    State(config): State<Arc<RwLock<MockWorkerConfig>>>,
+    Json(payload): Json<serde_json::Value>,
+) -> impl IntoResponse {
+    let config = config.read().await;
+
+    // Simulate response delay
+    if config.response_delay_ms > 0 {
+        tokio::time::sleep(tokio::time::Duration::from_millis(config.response_delay_ms)).await;
+    }
+
+    // Simulate failure rate
+    if rand::random::<f32>() < config.fail_rate {
+        return (StatusCode::INTERNAL_SERVER_ERROR, "Simulated failure").into_response();
+    }
+
+    // Extract documents from the request to create mock results
+    let empty_vec = vec![];
+    let documents = payload
+        .get("documents")
+        .and_then(|d| d.as_array())
+        .unwrap_or(&empty_vec);
+
+    // Create mock rerank results with scores based on document index
+    let mut mock_results = Vec::new();
+    for (i, doc) in documents.iter().enumerate() {
+        let score = 0.95 - (i as f32 * 0.1); // Decreasing scores
+        let result = serde_json::json!({
+            "score": score,
+            "document": doc.as_str().unwrap_or(""),
+            "index": i,
+            "meta_info": {
+                "confidence": if score > 0.9 { "high" } else { "medium" }
+            }
+        });
+        mock_results.push(result);
+    }
+
+    // Sort by score (highest first) to simulate proper ranking
+    mock_results.sort_by(|a, b| {
+        b["score"]
+            .as_f64()
+            .unwrap()
+            .partial_cmp(&a["score"].as_f64().unwrap())
+            .unwrap()
+    });
+
+    (StatusCode::OK, Json(mock_results)).into_response()
+}
+
 impl Default for MockWorkerConfig {
     fn default() -> Self {
         Self {