snmp: Better sensor support to resolve previous issues (#113624)

Co-authored-by: Christian Kühnel <christian.kuehnel@gmail.com>
Co-authored-by: jan iversen <jancasacondor@gmail.com>

homeassistant/components/snmp/sensor.py

@@ -4,7 +4,9 @@ from __future__ import annotations
 
 from datetime import timedelta
 import logging
+from struct import unpack
 
+from pyasn1.codec.ber import decoder
 from pysnmp.error import PySnmpError
 import pysnmp.hlapi.asyncio as hlapi
 from pysnmp.hlapi.asyncio import (
@@ -18,6 +20,8 @@ from pysnmp.hlapi.asyncio import (
     UsmUserData,
     getCmd,
 )
+from pysnmp.proto.rfc1902 import Opaque
+from pysnmp.proto.rfc1905 import NoSuchObject
 import voluptuous as vol
 
 from homeassistant.components.sensor import CONF_STATE_CLASS, PLATFORM_SCHEMA
@@ -165,7 +169,10 @@ async def async_setup_platform(
     errindication, _, _, _ = get_result
 
     if errindication and not accept_errors:
-        _LOGGER.error("Please check the details in the configuration file")
+        _LOGGER.error(
+            "Please check the details in the configuration file: %s",
+            errindication,
+        )
         return
 
     name = config.get(CONF_NAME, Template(DEFAULT_NAME, hass))
@@ -248,10 +255,44 @@ class SnmpData:
             _LOGGER.error(
                 "SNMP error: %s at %s",
                 errstatus.prettyPrint(),
-                errindex and restable[-1][int(errindex) - 1] or "?",
+                restable[-1][int(errindex) - 1] if errindex else "?",
             )
         elif (errindication or errstatus) and self._accept_errors:
             self.value = self._default_value
         else:
             for resrow in restable:
-                self.value = resrow[-1].prettyPrint()
+                self.value = self._decode_value(resrow[-1])
+
+    def _decode_value(self, value):
+        """Decode the different results we could get into strings."""
+
+        _LOGGER.debug(
+            "SNMP OID %s received type=%s and data %s",
+            self._baseoid,
+            type(value),
+            bytes(value),
+        )
+        if isinstance(value, NoSuchObject):
+            _LOGGER.error(
+                "SNMP error for OID %s: No Such Object currently exists at this OID",
+                self._baseoid,
+            )
+            return self._default_value
+
+        if isinstance(value, Opaque):
+            # Float data type is not supported by the pyasn1 library,
+            # so we need to decode this type ourselves based on:
+            # https://tools.ietf.org/html/draft-perkins-opaque-01
+            if bytes(value).startswith(b"\x9f\x78"):
+                return str(unpack("!f", bytes(value)[3:])[0])
+            # Otherwise Opaque types should be asn1 encoded
+            try:
+                decoded_value, _ = decoder.decode(bytes(value))
+                return str(decoded_value)
+            # pylint: disable=broad-except
+            except Exception as decode_exception:
+                _LOGGER.error(
+                    "SNMP error in decoding opaque type: %s", decode_exception
+                )
+                return self._default_value
+        return str(value)