diff --git a/crates/shadowsocks-service/src/config.rs b/crates/shadowsocks-service/src/config.rs
index 3bc451e2..7a97860e 100644
--- a/crates/shadowsocks-service/src/config.rs
+++ b/crates/shadowsocks-service/src/config.rs
@@ -1338,30 +1338,24 @@ impl LocalConfig {
 
         match self.protocol {
             #[cfg(feature = "local-dns")]
-            ProtocolType::Dns => {
-                if self.local_dns_addr.is_none() || self.remote_dns_addr.is_none() {
-                    let err = Error::new(
-                        ErrorKind::MissingField,
-                        "missing `local_dns_addr` or `remote_dns_addr` in configuration",
-                        None,
-                    );
-                    return Err(err);
-                }
+            ProtocolType::Dns if self.local_dns_addr.is_none() || self.remote_dns_addr.is_none() => {
+                let err = Error::new(
+                    ErrorKind::MissingField,
+                    "missing `local_dns_addr` or `remote_dns_addr` in configuration",
+                    None,
+                );
+                return Err(err);
             }
             #[cfg(feature = "local-tunnel")]
-            ProtocolType::Tunnel => {
-                if self.forward_addr.is_none() {
-                    let err = Error::new(ErrorKind::MissingField, "missing `forward_addr` in configuration", None);
-                    return Err(err);
-                }
+            ProtocolType::Tunnel if self.forward_addr.is_none() => {
+                let err = Error::new(ErrorKind::MissingField, "missing `forward_addr` in configuration", None);
+                return Err(err);
             }
 
             #[cfg(feature = "local-http")]
-            ProtocolType::Http => {
-                if !self.mode.enable_tcp() {
-                    let err = Error::new(ErrorKind::Invalid, "TCP mode have to be enabled for http", None);
-                    return Err(err);
-                }
+            ProtocolType::Http if !self.mode.enable_tcp() => {
+                let err = Error::new(ErrorKind::Invalid, "TCP mode have to be enabled for http", None);
+                return Err(err);
             }
 
             _ => {}
diff --git a/crates/shadowsocks-service/src/local/dns/dns_resolver.rs b/crates/shadowsocks-service/src/local/dns/dns_resolver.rs
index 20d12750..48e5a373 100644
--- a/crates/shadowsocks-service/src/local/dns/dns_resolver.rs
+++ b/crates/shadowsocks-service/src/local/dns/dns_resolver.rs
@@ -76,7 +76,7 @@ impl DnsResolver {
                     {
                         Ok(msg) => return Ok(msg),
                         Err(err) => {
-                            last_err = io::Error::new(io::ErrorKind::Other, err);
+                            last_err = io::Error::other(err);
                         }
                     }
                 }
@@ -85,7 +85,7 @@ impl DnsResolver {
                     match self.client_cache.lookup_local(ns, msg, &self.connect_opts, false).await {
                         Ok(msg) => return Ok(msg),
                         Err(err) => {
-                            last_err = io::Error::new(io::ErrorKind::Other, err);
+                            last_err = io::Error::other(err);
                         }
                     }
                 }
@@ -98,7 +98,7 @@ impl DnsResolver {
                 .client_cache
                 .lookup_unix_stream(path, msg)
                 .await
-                .map_err(|err| io::Error::new(io::ErrorKind::Other, err)),
+                .map_err(io::Error::other),
         }
     }
 }
diff --git a/crates/shadowsocks-service/src/local/dns/server.rs b/crates/shadowsocks-service/src/local/dns/server.rs
index 11f66cda..eb932da6 100644
--- a/crates/shadowsocks-service/src/local/dns/server.rs
+++ b/crates/shadowsocks-service/src/local/dns/server.rs
@@ -321,7 +321,7 @@ impl DnsTcpServer {
                 Ok(m) => m,
                 Err(err) => {
                     error!("dns tcp {} parse message failed, error: {}", peer_addr, err);
-                    return Err(io::Error::new(io::ErrorKind::Other, err));
+                    return Err(io::Error::other(err));
                 }
             };
 
@@ -329,13 +329,13 @@ impl DnsTcpServer {
                 Ok(m) => m,
                 Err(err) => {
                     error!("dns tcp {} lookup error: {}", peer_addr, err);
-                    return Err(io::Error::new(io::ErrorKind::Other, err));
+                    return Err(io::Error::other(err));
                 }
             };
 
             let mut buf = match respond_message.to_vec() {
                 Ok(buf) => buf,
-                Err(err) => return Err(io::Error::new(io::ErrorKind::Other, err)),
+                Err(err) => return Err(io::Error::other(err)),
             };
             let length = buf.len();
             buf.resize(length + 2, 0);
@@ -485,7 +485,7 @@ impl DnsUdpServer {
 
         let buf = match respond_message.to_vec() {
             Ok(buf) => buf,
-            Err(err) => return Err(io::Error::new(io::ErrorKind::Other, err)),
+            Err(err) => return Err(io::Error::other(err)),
         };
         listener.send_to(&buf, peer_addr).await?;
 
@@ -877,14 +877,14 @@ impl DnsClient {
                 self.client_cache
                     .lookup_remote(&self.context, server.server_config(), remote_addr, message, false)
                     .await
-                    .map_err(|err| io::Error::new(io::ErrorKind::Other, err))
+                    .map_err(io::Error::other)
             }
             Mode::UdpOnly => {
                 let server = self.balancer.best_udp_server();
                 self.client_cache
                     .lookup_remote(&self.context, server.server_config(), remote_addr, message, true)
                     .await
-                    .map_err(|err| io::Error::new(io::ErrorKind::Other, err))
+                    .map_err(io::Error::other)
             }
             Mode::TcpAndUdp => {
                 // Query TCP & UDP simultaneously
@@ -916,11 +916,11 @@ impl DnsClient {
                 match future::select(tcp_fut, udp_fut).await {
                     Either::Left((res, next)) => match res {
                         Ok(o) => Ok(o),
-                        Err(..) => next.await.map_err(|err| io::Error::new(io::ErrorKind::Other, err)),
+                        Err(..) => next.await.map_err(io::Error::other),
                     },
                     Either::Right((res, next)) => match res {
                         Ok(o) => Ok(o),
-                        Err(..) => next.await.map_err(|err| io::Error::new(io::ErrorKind::Other, err)),
+                        Err(..) => next.await.map_err(io::Error::other),
                     },
                 }
             }
@@ -968,13 +968,9 @@ impl DnsClient {
 
                 match future::select(udp_query, tcp_query).await {
                     Either::Left((Ok(m), ..)) => Ok(m),
-                    Either::Left((Err(..), next)) => {
-                        next.await.map_err(|err| io::Error::new(io::ErrorKind::Other, err))
-                    }
+                    Either::Left((Err(..), next)) => next.await.map_err(io::Error::other),
                     Either::Right((Ok(m), ..)) => Ok(m),
-                    Either::Right((Err(..), next)) => {
-                        next.await.map_err(|err| io::Error::new(io::ErrorKind::Other, err))
-                    }
+                    Either::Right((Err(..), next)) => next.await.map_err(io::Error::other),
                 }
             }
             #[cfg(unix)]
@@ -982,7 +978,7 @@ impl DnsClient {
                 .client_cache
                 .lookup_unix_stream(path, message)
                 .await
-                .map_err(|err| io::Error::new(io::ErrorKind::Other, err)),
+                .map_err(io::Error::other),
         }
     }
 }
diff --git a/crates/shadowsocks-service/src/server/tcprelay.rs b/crates/shadowsocks-service/src/server/tcprelay.rs
index ee542530..fbb29fbe 100644
--- a/crates/shadowsocks-service/src/server/tcprelay.rs
+++ b/crates/shadowsocks-service/src/server/tcprelay.rs
@@ -40,6 +40,8 @@ impl<'a> TcpDialer for ServerTcpDialer<'a> {
 }
 
 /// Unified outbound stream: either direct or through the outbound proxy chain.
+// Not boxed: one instance per connection, boxing would add an allocation on the hot path
+#[allow(clippy::large_enum_variant)]
 enum RemoteStream {
     Direct(OutboundTcpStream),
     Proxied(OutboundProxyStream),
diff --git a/crates/shadowsocks/src/dns_resolver/hickory_dns_resolver.rs b/crates/shadowsocks/src/dns_resolver/hickory_dns_resolver.rs
index be7a04fe..2f8852e4 100644
--- a/crates/shadowsocks/src/dns_resolver/hickory_dns_resolver.rs
+++ b/crates/shadowsocks/src/dns_resolver/hickory_dns_resolver.rs
@@ -161,7 +161,7 @@ pub async fn create_resolver(
                 Ok(resolver) => Ok(resolver),
                 Err(err) => {
                     error!("initialize DNS resolver with config failed, error: {}", err);
-                    Err(io::Error::new(io::ErrorKind::Other, err))
+                    Err(io::Error::other(err))
                 }
             }
         }
@@ -186,13 +186,13 @@ pub async fn create_resolver(
                         Ok(resolver) => Ok(resolver),
                         Err(err) => {
                             error!("initialize DNS resolver with config failed, error: {}", err);
-                            Err(io::Error::new(io::ErrorKind::Other, err))
+                            Err(io::Error::other(err))
                         }
                     }
                 }
                 Err(err) => {
                     error!("initialize DNS resolver with system-config failed, error: {}", err);
-                    Err(io::Error::new(io::ErrorKind::Other, err))
+                    Err(io::Error::other(err))
                 }
             }
         }