Fixes #42

Author: Galen Collins

pymodbus/constants.py

@@ -81,20 +81,28 @@ class Defaults(Singleton):
 
        Indicates if the slave datastore should use indexing at 0 or 1.
        Mor about this can be read in section 4.4 of the modbus specification.
+
+    .. attribute:: IgnoreMissingSlaves
+
+       In case a request is made to a missing slave, this defines if an error
+       should be returned or simply ignored. This is useful for the case of a
+       serial server emulater where a request to a non-existant slave on a bus
+       will never respond. The client in this case will simply timeout.
     '''
-    Port          = 502
-    Retries       = 3
-    RetryOnEmpty  = False
-    Timeout       = 3
-    Reconnects    = 0
-    TransactionId = 0
-    ProtocolId    = 0
-    UnitId        = 0x00
-    Baudrate      = 19200
-    Parity        = 'N'
-    Bytesize      = 8
-    Stopbits      = 1
-    ZeroMode      = False
+    Port                = 502
+    Retries             = 3
+    RetryOnEmpty        = False
+    Timeout             = 3
+    Reconnects          = 0
+    TransactionId       = 0
+    ProtocolId          = 0
+    UnitId              = 0x00
+    Baudrate            = 19200
+    Parity              = 'N'
+    Bytesize            = 8
+    Stopbits            = 1
+    ZeroMode            = False
+    IgnoreMissingSlaves = False
 
 
 class ModbusStatus(Singleton):

pymodbus/datastore/context.py

@@ -1,4 +1,4 @@
-from pymodbus.exceptions import ParameterException
+from pymodbus.exceptions import NoSuchSlaveException
 from pymodbus.interfaces import IModbusSlaveContext
 from pymodbus.datastore.store import ModbusSequentialDataBlock
 from pymodbus.constants import Defaults
@@ -129,7 +129,7 @@ def __setitem__(self, slave, context):
         if self.single: slave = Defaults.UnitId
         if 0xf7 >= slave >= 0x00:
             self.__slaves[slave] = context
-        else: raise ParameterException('slave index out of range')
+        else: raise NoSuchSlaveException('slave index[%d] out of range' % slave)
 
     def __delitem__(self, slave):
         ''' Wrapper used to access the slave context
@@ -138,7 +138,7 @@ def __delitem__(self, slave):
         '''
         if not self.single and (0xf7 >= slave >= 0x00):
             del self.__slaves[slave]
-        else: raise ParameterException('slave index out of range')
+        else: raise NoSuchSlaveException('slave index[%d] out of range' % slave)
 
     def __getitem__(self, slave):
         ''' Used to get access to a slave context
@@ -149,4 +149,4 @@ def __getitem__(self, slave):
         if self.single: slave = Defaults.UnitId
         if slave in self.__slaves:
             return self.__slaves.get(slave)
-        else: raise ParameterException("slave does not exist, or is out of range")
+        else: raise NoSuchSlaveException('slave index[%d] out of range' % slave)

pymodbus/exceptions.py

@@ -11,6 +11,7 @@ class ModbusException(Exception):
 
     def __init__(self, string):
         ''' Initialize the exception
+
         :param string: The message to append to the error
         '''
         self.string = string
@@ -24,6 +25,7 @@ class ModbusIOException(ModbusException):
 
     def __init__(self, string=""):
         ''' Initialize the exception
+
         :param string: The message to append to the error
         '''
         message = "[Input/Output] %s" % string
@@ -35,17 +37,32 @@ class ParameterException(ModbusException):
 
     def __init__(self, string=""):
         ''' Initialize the exception
+
         :param string: The message to append to the error
         '''
         message = "[Invalid Paramter] %s" % string
         ModbusException.__init__(self, message)
 
 
+class NoSuchSlaveException(ModbusException):
+    ''' Error resulting from making a request to a slave
+    that does not exist '''
+
+    def __init__(self, string=""):
+        ''' Initialize the exception
+
+        :param string: The message to append to the error
+        '''
+        message = "[No Such Slave] %s" % string
+        ModbusException.__init__(self, message)
+
+
 class NotImplementedException(ModbusException):
     ''' Error resulting from not implemented function '''
 
     def __init__(self, string=""):
         ''' Initialize the exception
+
         :param string: The message to append to the error
         '''
         message = "[Not Implemented] %s" % string
@@ -57,6 +74,7 @@ class ConnectionException(ModbusException):
 
     def __init__(self, string=""):
         ''' Initialize the exception
+
         :param string: The message to append to the error
         '''
         message = "[Connection] %s" % string
@@ -68,5 +86,5 @@ def __init__(self, string=""):
 __all__ = [
     "ModbusException", "ModbusIOException",
     "ParameterException", "NotImplementedException",
-    "ConnectionException",
+    "ConnectionException", "NoSuchSlaveException",
 ]

pymodbus/server/async.py

@@ -65,6 +65,11 @@ def _execute(self, request):
         try:
             context = self.factory.store[request.unit_id]
             response = request.execute(context)
+        except NoSuchSlaveException, ex:
+            _logger.debug("requested slave does not exist: %s; %s", ex, traceback.format_exc() )
+            if self.factory.ignore_missing_slaves:
+                return # the client will simply timeout waiting for a response
+            response = request.doException(merror.GatewayNoResponse)
         except Exception, ex:
             _logger.debug("Datastore unable to fulfill request: %s" % ex)
             response = request.doException(merror.SlaveFailure)
@@ -96,7 +101,7 @@ class ModbusServerFactory(ServerFactory):
 
     protocol = ModbusTcpProtocol
 
-    def __init__(self, store, framer=None, identity=None):
+    def __init__(self, store, framer=None, identity=None, **kwargs):
         ''' Overloaded initializer for the modbus factory
 
         If the identify structure is not passed in, the ModbusControlBlock
@@ -105,13 +110,14 @@ def __init__(self, store, framer=None, identity=None):
         :param store: The ModbusServerContext datastore
         :param framer: The framer strategy to use
         :param identity: An optional identify structure
-
+        :param ignore_missing_slaves: True to not send errors on a request to a missing slave
         '''
         self.decoder = ServerDecoder()
         self.framer = framer or ModbusSocketFramer
         self.store = store or ModbusServerContext()
         self.control = ModbusControlBlock()
         self.access = ModbusAccessControl()
+        self.ignore_missing_slaves = kwargs.get('ignore_missing_slaves', Defaults.IgnoreMissingSlaves)
 
         if isinstance(identity, ModbusDeviceIdentification):
             self.control.Identity.update(identity)
@@ -123,7 +129,7 @@ def __init__(self, store, framer=None, identity=None):
 class ModbusUdpProtocol(protocol.DatagramProtocol):
     ''' Implements a modbus udp server in twisted '''
 
-    def __init__(self, store, framer=None, identity=None):
+    def __init__(self, store, framer=None, identity=None, **kwargs):
         ''' Overloaded initializer for the modbus factory
 
         If the identify structure is not passed in, the ModbusControlBlock
@@ -132,13 +138,14 @@ def __init__(self, store, framer=None, identity=None):
         :param store: The ModbusServerContext datastore
         :param framer: The framer strategy to use
         :param identity: An optional identify structure
-
+        :param ignore_missing_slaves: True to not send errors on a request to a missing slave
         '''
         framer = framer or ModbusSocketFramer
         self.framer = framer(decoder=ServerDecoder())
         self.store = store or ModbusServerContext()
         self.control = ModbusControlBlock()
         self.access = ModbusAccessControl()
+        self.ignore_missing_slaves = kwargs.get('ignore_missing_slaves', Defaults.IgnoreMissingSlaves)
 
         if isinstance(identity, ModbusDeviceIdentification):
             self.control.Identity.update(identity)
@@ -163,6 +170,11 @@ def _execute(self, request, addr):
         try:
             context = self.store[request.unit_id]
             response = request.execute(context)
+        except NoSuchSlaveException, ex:
+            _logger.debug("requested slave does not exist: %s; %s", ex, traceback.format_exc() )
+            if self.ignore_missing_slaves:
+                return # the client will simply timeout waiting for a response
+            response = request.doException(merror.GatewayNoResponse)
         except Exception, ex:
             _logger.debug("Datastore unable to fulfill request: %s" % ex)
             response = request.doException(merror.SlaveFailure)
@@ -187,38 +199,40 @@ def _send(self, message, addr):
 #---------------------------------------------------------------------------#
 # Starting Factories
 #---------------------------------------------------------------------------#
-def StartTcpServer(context, identity=None, address=None, console=False):
+def StartTcpServer(context, identity=None, address=None, console=False, **kwargs):
     ''' Helper method to start the Modbus Async TCP server
 
     :param context: The server data context
     :param identify: The server identity to use (default empty)
     :param address: An optional (interface, port) to bind to.
     :param console: A flag indicating if you want the debug console
+    :param ignore_missing_slaves: True to not send errors on a request to a missing slave
     '''
     from twisted.internet import reactor
 
     address = address or ("", Defaults.Port)
     framer  = ModbusSocketFramer
-    factory = ModbusServerFactory(context, framer, identity)
+    factory = ModbusServerFactory(context, framer, identity, **kwargs)
     if console: InstallManagementConsole({'factory': factory})
 
     _logger.info("Starting Modbus TCP Server on %s:%s" % address)
     reactor.listenTCP(address[1], factory, interface=address[0])
     reactor.run()
 
 
-def StartUdpServer(context, identity=None, address=None):
+def StartUdpServer(context, identity=None, address=None, **kwargs):
     ''' Helper method to start the Modbus Async Udp server
 
     :param context: The server data context
     :param identify: The server identity to use (default empty)
     :param address: An optional (interface, port) to bind to.
+    :param ignore_missing_slaves: True to not send errors on a request to a missing slave
     '''
     from twisted.internet import reactor
 
     address = address or ("", Defaults.Port)
     framer  = ModbusSocketFramer
-    server  = ModbusUdpProtocol(context, framer, identity)
+    server  = ModbusUdpProtocol(context, framer, identity, **kwargs)
 
     _logger.info("Starting Modbus UDP Server on %s:%s" % address)
     reactor.listenUDP(address[1], server, interface=address[0])
@@ -235,6 +249,7 @@ def StartSerialServer(context, identity=None,
     :param port: The serial port to attach to
     :param baudrate: The baud rate to use for the serial device
     :param console: A flag indicating if you want the debug console
+    :param ignore_missing_slaves: True to not send errors on a request to a missing slave
     '''
     from twisted.internet import reactor
     from twisted.internet.serialport import SerialPort
@@ -244,7 +259,7 @@ def StartSerialServer(context, identity=None,
     console = kwargs.get('console', False)
 
     _logger.info("Starting Modbus Serial Server on %s" % port)
-    factory = ModbusServerFactory(context, framer, identity)
+    factory = ModbusServerFactory(context, framer, identity, **kwargs)
     if console: InstallManagementConsole({'factory': factory})
 
     protocol = factory.buildProtocol(None)