socket_wildcard.py

@@ -0,0 +1,45 @@
+import socket
+import struct
+
+# use with
+# iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 2000
+
+SO_ORIGINAL_DST = 80  # from linux/netfilter_ipv4.h
+
+def get_original_dst(conn):
+    """Return (ip, port) of the original destination before REDIRECT."""
+    # Get raw sockaddr_in (16 bytes)
+    odest = conn.getsockopt(socket.SOL_IP, SO_ORIGINAL_DST, 16)
+    port, raw_ip = struct.unpack_from('!2xH4s', odest)
+    ip = socket.inet_ntoa(raw_ip)
+    return ip, port
+
+def main():
+    HOST = '0.0.0.0'
+    PORT = 2000
+
+    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    s.bind((HOST, PORT))
+    s.listen(10)
+
+    print(f"Listening on {HOST}:{PORT}")
+
+    while True:
+        conn, addr = s.accept()
+        try:
+            orig_ip, orig_port = get_original_dst(conn)
+            print(f"Connection from {addr}, originally to {orig_ip}:{orig_port}")
+        except OSError as e:
+            print(f"Could not get original destination: {e}")
+
+        with conn:
+            while True:
+                data = conn.recv(1024)
+                if not data:
+                    break
+                conn.sendall(data)
+
+if __name__ == "__main__":
+    main()
+