diff --git a/chat.py b/chat.py
index 9701021..ce0f332 100644
--- a/chat.py
+++ b/chat.py
@@ -1,60 +1,87 @@
 import socket
 import threading
 import protocol
+import sys
 
 LOCAL_PORT = 9000
-TIMEOUT = 2
+TIMEOUT = 2   # 秒
+
 
 class StopWaitChat:
     def __init__(self, local_port, peer_addr):
-        self.sock = socket.socket(
-            socket.AF_INET6,
-            socket.SOCK_DGRAM
-        )
+        # IPv6 UDP socket
+        self.sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
+
+        # 绑定本地 IPv6 任意地址
         self.sock.bind(("::", local_port))
+
+        # 设置 socket 超时（用于停等协议）
         self.sock.settimeout(TIMEOUT)
 
         self.peer_addr = peer_addr
+
+        # 停等协议序号
         self.send_seq = 0
         self.recv_seq = 0
 
     def sender(self):
+        """
+        发送线程（停等协议）
+        """
         while True:
-            msg = input(">> ").encode()
+            try:
+                msg = input(">> ").encode()
+            except EOFError:
+                break
+
             pkt = protocol.make_packet(
                 self.send_seq,
                 protocol.TYPE_DATA,
                 msg
             )
 
+            # 停等：一直发，直到收到正确 ACK
             while True:
                 self.sock.sendto(pkt, self.peer_addr)
+
                 try:
                     data, _ = self.sock.recvfrom(1024)
                     seq, ptype, _ = protocol.parse_packet(data)
+
                     if ptype == protocol.TYPE_ACK and seq == self.send_seq:
+                        # 正确 ACK
                         self.send_seq ^= 1
                         break
+
                 except socket.timeout:
                     print("[timeout] retransmit")
 
     def receiver(self):
+        """
+        接收线程（必须捕获 timeout）
+        """
         while True:
-            data, addr = self.sock.recvfrom(1024)
+            try:
+                data, addr = self.sock.recvfrom(1024)
+            except socket.timeout:
+                continue
+
             seq, ptype, payload = protocol.parse_packet(data)
 
             if ptype == protocol.TYPE_DATA:
                 if seq == self.recv_seq:
                     print("\npeer:", payload.decode())
                     self.recv_seq ^= 1
+
+                # 无论是否重复，都返回 ACK
                 ack = protocol.make_packet(seq, protocol.TYPE_ACK)
                 self.sock.sendto(ack, addr)
 
-if __name__ == "__main__":
-    import sys
+
+def main():
     if len(sys.argv) != 3:
-        print("用法: python3 chat.py <对方IPv6地址> <对方端口>")
-        exit(1)
+        print("用法: python3 chat.py <对方IPv6地址或域名> <对方端口>")
+        sys.exit(1)
 
     peer_ip = sys.argv[1]
     peer_port = int(sys.argv[2])
@@ -64,5 +91,16 @@ if __name__ == "__main__":
         (peer_ip, peer_port)
     )
 
-    threading.Thread(target=chat.receiver, daemon=True).start()
+    # 启动接收线程
+    recv_thread = threading.Thread(
+        target=chat.receiver,
+        daemon=True
+    )
+    recv_thread.start()
+
+    # 主线程负责发送
     chat.sender()
+
+
+if __name__ == "__main__":
+    main()