diff --git a/kernel/libs/aster-bigtcp/src/errors.rs b/kernel/libs/aster-bigtcp/src/errors.rs
index 8e221c26c..a20890334 100644
--- a/kernel/libs/aster-bigtcp/src/errors.rs
+++ b/kernel/libs/aster-bigtcp/src/errors.rs
@@ -12,6 +12,9 @@ pub enum BindError {
 pub mod tcp {
     pub use smoltcp::socket::tcp::{RecvError, SendError};
 
+    /// An error returned by [`TcpListener::new_listen`].
+    ///
+    /// [`TcpListener::new_listen`]: crate::socket::TcpListener::new_listen
     #[derive(Debug, PartialEq, Eq, Clone, Copy)]
     pub enum ListenError {
         InvalidState,
@@ -29,6 +32,9 @@ pub mod tcp {
         }
     }
 
+    /// An error returned by [`TcpConnection::new_connect`].
+    ///
+    /// [`TcpConnection::new_connect`]: crate::socket::TcpConnection::new_connect
     #[derive(Debug, PartialEq, Eq, Clone, Copy)]
     pub enum ConnectError {
         InvalidState,
@@ -50,13 +56,23 @@ pub mod tcp {
 pub mod udp {
     pub use smoltcp::socket::udp::RecvError;
 
-    /// An error returned by [`BoundTcpSocket::recv`].
+    /// An error returned by [`UdpSocket::send`].
     ///
-    /// [`BoundTcpSocket::recv`]: crate::socket::BoundTcpSocket::recv
+    /// [`UdpSocket::send`]: crate::socket::UdpSocket::send
     #[derive(Debug, PartialEq, Eq, Clone, Copy)]
     pub enum SendError {
-        TooLarge,
         Unaddressable,
         BufferFull,
+        /// The packet is too large.
+        TooLarge,
+    }
+
+    impl From<smoltcp::socket::udp::SendError> for SendError {
+        fn from(value: smoltcp::socket::udp::SendError) -> Self {
+            match value {
+                smoltcp::socket::udp::SendError::Unaddressable => Self::Unaddressable,
+                smoltcp::socket::udp::SendError::BufferFull => Self::BufferFull,
+            }
+        }
     }
 }
diff --git a/kernel/libs/aster-bigtcp/src/socket/bound.rs b/kernel/libs/aster-bigtcp/src/socket/bound.rs
index eeb2b88ba..b9838ba3a 100644
--- a/kernel/libs/aster-bigtcp/src/socket/bound.rs
+++ b/kernel/libs/aster-bigtcp/src/socket/bound.rs
@@ -23,7 +23,10 @@ use super::{
     RawTcpSocket, RawUdpSocket, TcpStateCheck,
 };
 use crate::{
-    errors::tcp::{ConnectError, ListenError},
+    errors::{
+        tcp::{ConnectError, ListenError},
+        udp::SendError,
+    },
     ext::Ext,
     iface::{BindPortConfig, BoundPort, Iface},
     socket_table::{ConnectionKey, ListenerKey},
@@ -31,7 +34,7 @@ use crate::{
 
 pub struct Socket<T: Inner<E>, E: Ext>(Takeable<Arc<SocketBg<T, E>>>);
 
-/// [`TcpConnectionInner`] or [`UdpSocketInner`].
+/// [`TcpConnectionInner`], [`TcpListenerInner`], or [`UdpSocketInner`].
 pub trait Inner<E: Ext> {
     type Observer: SocketEventObserver;
 
@@ -59,7 +62,7 @@ pub struct SocketBg<T: Inner<E>, E: Ext> {
     next_poll_at_ms: AtomicU64,
 }
 
-/// States needed by [`TcpConnectionBg`] but not [`UdpSocketBg`].
+/// States needed by [`TcpConnectionBg`].
 pub struct TcpConnectionInner<E: Ext> {
     socket: SpinLock<RawTcpSocketExt<E>, LocalIrqDisabled>,
     is_dead: AtomicBool,
@@ -204,6 +207,7 @@ pub struct TcpBacklog<E: Ext> {
     connected: Vec<TcpConnection<E>>,
 }
 
+/// States needed by [`TcpListenerBg`].
 pub struct TcpListenerInner<E: Ext> {
     backlog: SpinLock<TcpBacklog<E>, LocalIrqDisabled>,
     listener_key: ListenerKey,
@@ -242,7 +246,7 @@ impl<E: Ext> Inner<E> for TcpListenerInner<E> {
     }
 }
 
-/// States needed by [`UdpSocketBg`] but not [`TcpConnectionBg`].
+/// States needed by [`UdpSocketBg`].
 type UdpSocketInner = SpinLock<Box<RawUdpSocket>, LocalIrqDisabled>;
 
 impl<E: Ext> Inner<E> for UdpSocketInner {
@@ -631,14 +635,10 @@ impl<E: Ext> UdpSocket<E> {
         size: usize,
         meta: impl Into<UdpMetadata>,
         f: F,
-    ) -> Result<R, crate::errors::udp::SendError>
+    ) -> Result<R, SendError>
     where
         F: FnOnce(&mut [u8]) -> R,
     {
-        use smoltcp::socket::udp::SendError as SendErrorInner;
-
-        use crate::errors::udp::SendError;
-
         let mut socket = self.0.inner.lock();
 
         if size > socket.packet_send_capacity() {
@@ -647,8 +647,7 @@ impl<E: Ext> UdpSocket<E> {
 
         let buffer = match socket.send(size, meta) {
             Ok(data) => data,
-            Err(SendErrorInner::Unaddressable) => return Err(SendError::Unaddressable),
-            Err(SendErrorInner::BufferFull) => return Err(SendError::BufferFull),
+            Err(err) => return Err(err.into()),
         };
         let result = f(buffer);
         self.0.update_next_poll_at_ms(PollAt::Now);