[sgl-router] improvement to avoid hang (#4482)

Co-authored-by: Yineng Zhang <me@zhyncs.com>
Co-authored-by: Byron Hsu <byronhsu1230@gmail.com>

sgl-router/src/server.rs

 use crate::router::PolicyConfig;
 use crate::router::Router;
-use actix_web::{get, post, web, App, HttpRequest, HttpResponse, HttpServer, Responder};
+use actix_web::{
+    error, get, post, web, App, Error, HttpRequest, HttpResponse, HttpServer, Responder,
+};
 use bytes::Bytes;
 use env_logger::Builder;
+use futures_util::StreamExt;
 use log::{info, LevelFilter};
 use std::collections::HashMap;
 use std::io::Write;
+use std::time::Duration;
 
 #[derive(Debug)]
 pub struct AppState {
@@ -25,6 +29,22 @@ impl AppState {
     }
 }
 
+async fn sink_handler(_req: HttpRequest, mut payload: web::Payload) -> Result<HttpResponse, Error> {
+    // Drain the payload
+    while let Some(chunk) = payload.next().await {
+        if let Err(err) = chunk {
+            println!("Error while draining payload: {:?}", err);
+            break;
+        }
+    }
+    Ok(HttpResponse::NotFound().finish())
+}
+
+// Custom error handler for JSON payload errors.
+fn json_error_handler(_err: error::JsonPayloadError, _req: &HttpRequest) -> Error {
+    error::ErrorPayloadTooLarge("Payload too large")
+}
+
 #[get("/health")]
 async fn health(req: HttpRequest, data: web::Data<AppState>) -> impl Responder {
     data.router
@@ -162,6 +182,7 @@ pub async fn startup(config: ServerConfig) -> std::io::Result<()> {
     );
 
     let client = reqwest::Client::builder()
+        .pool_idle_timeout(Some(Duration::from_secs(50)))
         .build()
         .expect("Failed to create HTTP client");
 
@@ -180,7 +201,11 @@ pub async fn startup(config: ServerConfig) -> std::io::Result<()> {
     HttpServer::new(move || {
         App::new()
             .app_data(app_state.clone())
-            .app_data(web::JsonConfig::default().limit(config.max_payload_size))
+            .app_data(
+                web::JsonConfig::default()
+                    .limit(config.max_payload_size)
+                    .error_handler(json_error_handler),
+            )
             .app_data(web::PayloadConfig::default().limit(config.max_payload_size))
             .service(generate)
             .service(v1_chat_completions)
@@ -192,6 +217,8 @@ pub async fn startup(config: ServerConfig) -> std::io::Result<()> {
             .service(get_server_info)
             .service(add_worker)
             .service(remove_worker)
+            // Default handler for unmatched routes.
+            .default_service(web::route().to(sink_handler))
     })
     .bind((config.host, config.port))?
     .run()