modbus service and entity

Dockerfile

@@ -1,13 +1,13 @@
 ARG img_user=ghcr.io/driplineorg
 ARG img_repo=dripline-python
-#ARG img_tag=develop-dev
-ARG img_tag=receiver-test
+ARG img_tag=v5.0.0-dev
 
 FROM ${img_user}/${img_repo}:${img_tag}
 
 COPY . /usr/local/src_dragonfly
 
 WORKDIR /usr/local/src_dragonfly
+RUN pip install pymodbus
 RUN pip install docker
 RUN pip install .
 

dripline/extensions/__init__.py

@@ -8,5 +8,7 @@
 # Modules in this directory
 
 from .add_auth_spec import *
+from .ethernet_modbus_service import *
+#from .asteval_endpoint import *
 from .thermo_fisher_endpoint import *
 from .ethernet_thermo_fisher_service import *

dripline/extensions/ethernet_modbus_service.py

@@ -0,0 +1,101 @@
+try:
+    import pymodbus
+    from pymodbus.client import ModbusTcpClient
+    from pymodbus.payload import BinaryPayloadDecoder
+except ImportError:
+    pass
+
+import scarab
+
+from dripline.core import calibrate, Entity, Service, ThrowReply
+
+import logging
+logger = logging.getLogger(__name__)
+
+__all__ = []
+
+
+__all__.append('EthernetModbusService')
+class EthernetModbusService(Service):
+    '''
+    Service for connectivity to ModbusTCP instruments built on pymodbus library.
+    '''
+    def __init__(self,
+                 ip_address,
+                 **kwargs
+                 ):
+        '''
+        Args:
+            ip_address (str): properly formatted ip address of Modbus device
+
+        '''
+        if not 'pymodbus' in globals():
+            raise ImportError('pymodbus not found, required for EthernetModbusService class')
+
+        Service.__init__(self, **kwargs)
+
+        self.ip = ip_address
+        self.client = ModbusTcpClient(self.ip)
+        self._reconnect()
+
+    def _reconnect(self):
+        '''
+        Minimal connection method.
+        TODO: Expand to call on failed read/write, and add sophistication.
+        '''
+        if self.client.connected:
+            self.client.close()
+
+        if self.client.connect():
+            logger.debug('Connected to Alicat Device.')
+        else:
+            raise ThrowReply('resource_error_connection','Failed to Connect to Alicat Device')
+
+    def read_register(self, register):
+        '''
+        Currently only register read type #4, read_input_registers, is implemented.
+        Expand as desired according to other calls in https://pymodbus.readthedocs.io/en/latest/source/client.html#modbus-calls
+        '''
+        logger.debug('Reading register {}'.format(register))
+        try:
+            result = self.client.read_holding_registers(register, count=1)
+        except Exception as e:
+            logger.debug(f'read_holding_registers failed: {e}. Attempting reconnect.')
+            self._reconnect()
+            result = self.client.read_holding_registers(register, count=1)
+
+        logger.debug('Device returned {}'.format(result.registers))
+        return result.registers
+
+    def write_register(self, register, value):
+        logger.debug('writing {} to register {}'.format(value, register))
+        try:
+            response = self.client.write_register(register, value)
+        except Exception as e:
+            logger.debug(f'write_registers failed: {e}. Attempting reconnect.')
+            self._reconnect()
+            response = self.client.write_register(register, value)
+
+        logger.debug('device respond with {} '.format(response))
+        return value
+
+
+__all__.append('ModbusEntity')
+class ModbusEntity(Entity):
+    '''
+    Generic entity for Modbus read and write.
+    TODO: Add additional read-only or write-only versions
+    '''
+    def __init__(self,
+                 register,
+                 **kwargs):
+        self.register = register
+        Entity.__init__(self, **kwargs)
+
+    @calibrate()
+    def on_get(self):
+        result = self.service.read_register(self.register)
+        return result[0] 
+
+    def on_set(self, value):
+        return self.service.write_register(self.register, value)