Add error handling to Cryomech PTC drivers and agent acq process (#767)

* Implement error handling in Cryomech drivers

* Handle ConnectionError in main acq process

* Handle connection error in init task

* Handle condition where socket returns None

This happens when we try to reset the connection, but can't establish anything
due to the device not accepting connections.

socs/agents/cryomech_cpa/agent.py

@@ -72,7 +72,11 @@ def init(self, session, params=None):
                            fake_errors=self.fake_errors)
 
             # Test connection and display identifying info
-            self.ptc.get_data()
+            try:
+                self.ptc.get_data()
+            except ConnectionError:
+                self.log.error("Could not establish connection to compressor.")
+                return False, "PTC agent initialization failed"
             print("PTC Model:", self.ptc.model)
             print("PTC Serial Number:", self.ptc.serial)
             print("Software Revision is:", self.ptc.software_revision)
@@ -141,7 +145,16 @@ def acq(self, session, params):
                 # Publish data, waiting 1/f_sample seconds in between calls.
                 pub_data = {'timestamp': time.time(),
                             'block_name': 'ptc_status'}
-                data_flag, data = self.ptc.get_data()
+                try:
+                    data_flag, data = self.ptc.get_data()
+                    if session.degraded:
+                        self.log.info("Connection re-established.")
+                        session.degraded = False
+                except ConnectionError:
+                    self.log.error("Failed to get data from compressor. Check network connection.")
+                    session.degraded = True
+                    time.sleep(1)
+                    continue
                 pub_data['data'] = data
                 # If there is an error in compressor output (data_flag = True),
                 # do not publish

socs/agents/cryomech_cpa/drivers.py

@@ -1,4 +1,5 @@
 import random
+import selectors
 import socket
 import struct
 
@@ -16,24 +17,95 @@
 
 class PTC:
     def __init__(self, ip_address, port=502, timeout=10, fake_errors=False):
-        self.ip_address = ip_address
-        self.port = int(port)
         self.fake_errors = fake_errors
 
         self.model = None
         self.serial = None
         self.software_revision = None
 
-        self.comm = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-        self.comm.connect((self.ip_address, self.port))  # connects to the PTC
-        self.comm.settimeout(timeout)
+        self.ip_address = ip_address
+        self.port = int(port)
+        self.timeout = timeout
+        self.comm = self._connect((self.ip_address, self.port))
+
+    def _connect(self, address):
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        sock.settimeout(self.timeout)
+        try:
+            sock.connect(address)
+        except TimeoutError:
+            print(f"Connection not established within {self.timeout}.")
+            return
+        except OSError as e:
+            print(f"Unable to connect. {e}")
+            return
+        except Exception as e:
+            print(f"Caught unexpected {type(e).__name__} while connecting:")
+            print(f"  {e}")
+            return
+        return sock
+
+    def reset(self):
+        print("Resetting the connection to the compressor.")
+        self.comm = self._connect((self.ip_address, self.port))
+
+    def _write(self, msg):
+        if self.comm is None:
+            print("Connection not established. Unable to send command.")
+            self.reset()
+            return
+
+        try:
+            self.comm.sendall(msg)
+            return
+        except (BrokenPipeError, ConnectionResetError) as e:
+            print(f"Connection error: {e}")
+            self.reset()
+        except TimeoutError as e:
+            print(f"Timeout error while writing: {e}")
+            self.reset()
+        except Exception as e:
+            print(f"Caught unexpected {type(e).__name__} during write:")
+            print(f"  {e}")
+            self.reset()
+
+        # Try a second time before giving up
+        try:
+            self.comm.sendall(msg)
+        except (BrokenPipeError, ConnectionResetError) as e:
+            print(f"Connection error: {e}")
+            raise ConnectionError
+        except TimeoutError as e:
+            print(f"Timeout error while writing: {e}")
+            raise ConnectionError
+        except AttributeError:
+            raise ConnectionError("Unable to reset connection.")
+        except Exception as e:
+            print(f"Caught unexpected {type(e).__name__} during write:")
+            print(f"  {e}")
+            raise ConnectionError
+
+    def _check_ready(self):
+        """Check socket is ready to read from."""
+        if self.comm is None:
+            raise ConnectionError("Connection not established, not ready to read.")
+
+        sel = selectors.DefaultSelector()
+        sel.register(self.comm, selectors.EVENT_READ)
+        if not sel.select(self.timeout):
+            raise ConnectionError
+
+    def _read(self):
+        self._check_ready()
+        data = self.comm.recv(1024)
+        return data
 
     def get_data(self):
         """
         Gets the raw data from the ptc and returns it in a usable format.
         """
-        self.comm.sendall(self.buildRegistersQuery())
-        data = self.comm.recv(1024)
+        self._write(self.buildRegistersQuery())
+        data = self._read()
         data_flag, brd = self.breakdownReplyData(data)
 
         return data_flag, brd