cleanup eon hw abstraction layer (#21396)

* cleanup eon hw

* handle none from getprop

selfdrive/hardware/eon/hardware.py

@@ -5,6 +5,7 @@ import re
 import serial
 import struct
 import subprocess
+from typing import List, Union
 
 from cereal import log
 from selfdrive.hardware.base import HardwareBase, ThermalConfig
@@ -14,7 +15,7 @@ NetworkStrength = log.DeviceState.NetworkStrength
 
 MODEM_PATH = "/dev/smd11"
 
-def service_call(call):
+def service_call(call: List[str]) -> Union[bytes, None]:
   try:
     ret = subprocess.check_output(["service", "call", *call], encoding='utf8').strip()
     if 'Parcel' not in ret:
@@ -24,31 +25,29 @@ def service_call(call):
     return None
 
 
-def parse_service_call_unpack(r, fmt):
+def parse_service_call_unpack(r, fmt) -> Union[bytes, None]:
   try:
     return struct.unpack(fmt, r)[0]
   except Exception:
     return None
 
 
-def parse_service_call_string(r):
+def parse_service_call_string(r: bytes) -> Union[str, None]:
   try:
     r = r[8:]  # Cut off length field
-    r = r.decode('utf_16_be')
+    r_str = r.decode('utf_16_be')
 
     # All pairs of two characters seem to be swapped. Not sure why
     result = ""
-    for a, b, in itertools.zip_longest(r[::2], r[1::2], fillvalue='\x00'):
-        result += b + a
+    for a, b, in itertools.zip_longest(r_str[::2], r_str[1::2], fillvalue='\x00'):
+      result += b + a
 
-    result = result.replace('\x00', '')
-
-    return result
+    return result.replace('\x00', '')
   except Exception:
     return None
 
 
-def parse_service_call_bytes(ret):
+def parse_service_call_bytes(ret: str) -> Union[bytes, None]:
   try:
     r = b""
     for hex_part in re.findall(r'[ (]([0-9a-f]{8})', ret):
@@ -58,8 +57,11 @@ def parse_service_call_bytes(ret):
     return None
 
 
-def getprop(key):
-  return subprocess.check_output(["getprop", key], encoding='utf8').strip()
+def getprop(key: str) -> Union[str, None]:
+  try:
+    return subprocess.check_output(["getprop", key], encoding='utf8').strip()
+  except subprocess.CalledProcessError:
+    return None
 
 
 class Android(HardwareBase):
@@ -134,9 +136,9 @@ class Android(HardwareBase):
 
   def get_network_info(self):
     msg = log.DeviceState.NetworkInfo.new_message()
-    msg.state = getprop("gsm.sim.state")
-    msg.technology = getprop("gsm.network.type")
-    msg.operator = getprop("gsm.sim.operator.numeric")
+    msg.state = getprop("gsm.sim.state") or ""
+    msg.technology = getprop("gsm.network.type") or ""
+    msg.operator = getprop("gsm.sim.operator.numeric") or ""
 
     try:
       modem = serial.Serial(MODEM_PATH, 115200, timeout=0.1)