Add optional parameter to DtlsSocket: client_timeout (seconds)

If client_timeout is specified, clients that have not communicated
within the time frame will be dropped.

dtls/wrapper.py

@@ -72,13 +72,26 @@ class DtlsSocket(object):
 
     class _ClientSession(object):
 
-        def __init__(self, host, port, handshake_done=False):
+        def __init__(self, host, port, handshake_done=False, timeout=None):
             self.host = host
             self.port = int(port)
             self.handshake_done = handshake_done
+            self.timeout = timeout
+            self.updateTimestamp()
 
         def getAddr(self):
             return self.host, self.port
+        
+        def updateTimestamp(self):
+            if self.timeout != None:
+                self.last_update = time.time()
+
+        def expired(self):
+            if self.timeout == None:
+                return False
+            else:
+                return (time.time() - self.last_update) > self.timeout
+        
 
     def __init__(self,
                  sock=None,
@@ -95,7 +108,8 @@ class DtlsSocket(object):
                  sigalgs=None,
                  user_mtu=None,
                  server_key_exchange_curve=None,
-                 server_cert_options=ssl.SSL_BUILD_CHAIN_FLAG_NONE):
+                 server_cert_options=ssl.SSL_BUILD_CHAIN_FLAG_NONE,
+                 client_timeout=None):
 
         if server_cert_options is None:
             server_cert_options = ssl.SSL_BUILD_CHAIN_FLAG_NONE
@@ -108,6 +122,7 @@ class DtlsSocket(object):
         self._user_mtu = user_mtu
         self._server_key_exchange_curve = server_key_exchange_curve
         self._server_cert_options = server_cert_options
+        self._client_timeout = client_timeout
 
         # Default socket creation
         _sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
@@ -205,6 +220,7 @@ class DtlsSocket(object):
                     else:
                         buf = self._clientRead(conn, bufsize)
                         if buf:
+                            self._clients[conn].updateTimestamp()
                             if conn in self._clients:
                                 return buf, self._clients[conn].getAddr()
                             else:
@@ -220,6 +236,10 @@ class DtlsSocket(object):
                     ret = conn.handle_timeout()
                     _logger.debug('Retransmission triggered for %s: %d' % (str(self._clients[conn].getAddr()), ret))
 
+                if self._clients[conn].expired() == True:
+                    _logger.debug('Found expired session')
+                    self._clientDrop(conn)
+
         except Exception as e:
             raise e