Turn off domain sniffing

leaf/src/app/dispatcher.rs

@@ -80,8 +80,10 @@ impl Dispatcher {
     where
         T: 'static + AsyncRead + AsyncWrite + Unpin + Send + Sync,
     {
-        let mut lhs: Box<dyn ProxyStream> =
-            if !sess.destination.is_domain() && sess.destination.port() == 443 {
+        let mut lhs: Box<dyn ProxyStream> = if *option::DOMAIN_SNIFFING
+            && !sess.destination.is_domain()
+            && sess.destination.port() == 443
+        {
             let mut lhs = sniff::SniffingStream::new(lhs);
             match lhs.sniff().await {
                 Ok(res) => {

leaf/src/option/mod.rs

@@ -97,6 +97,10 @@ lazy_static! {
         get_env_var_or("LOG_NO_COLOR", false)
     };
 
+    pub static ref DOMAIN_SNIFFING: bool = {
+        get_env_var_or("DOMAIN_SNIFFING", false)
+    };
+
     /// Uplink timeout after downlink EOF.
     pub static ref TCP_UPLINK_TIMEOUT: u64 = {
         get_env_var_or("TCP_UPLINK_TIMEOUT", 10)