From db451b0a9ee9493f32e354d5934539c82a07cb0c Mon Sep 17 00:00:00 2001
From: Morten Brekkevold <morten.brekkevold@sikt.no>
Date: Thu, 4 Sep 2025 11:19:05 +0000
Subject: [PATCH 1/3] Add regression test for non-ascii community traps

A device that sends traps with non-ascii community values will cause
trap PDU processing to crash with a `UnicodeDecodeError`. community
values are defined as ASCII in the SNMP specs, but some devices do not
behave. netsnmp-cffi tries to be helpful to the client by automatically
making a Python string from the community, but if there's a misbehaving
device, this should not break everything.
---
 tests/test_trapsession.py | 40 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 tests/test_trapsession.py

diff --git a/tests/test_trapsession.py b/tests/test_trapsession.py
new file mode 100644
index 0000000..e7d7e0a
--- /dev/null
+++ b/tests/test_trapsession.py
@@ -0,0 +1,40 @@
+import pytest
+
+from netsnmpy.constants import SNMP_MSG_INFORM, SNMP_VERSION_2c
+from netsnmpy.netsnmp import ValueType, encode_variable, oid_to_c
+from netsnmpy.oids import OID
+from netsnmpy.trapsession import SNMPTrap, _ffi, _netsnmp
+
+_lib = _netsnmp.lib
+
+
+class TestSNMPTrap:
+    def test_given_trap_with_non_ascii_community_then_from_pdu_should_not_crash(
+        self, pdu_with_garbage_community, garbage_community
+    ):
+        trap = SNMPTrap.from_pdu(pdu_with_garbage_community)
+        assert isinstance(trap.community, bytes)
+        assert trap.community == garbage_community
+
+
+@pytest.fixture
+def pdu_with_garbage_community(garbage_community):
+    pdu = _lib.snmp_pdu_create(SNMP_MSG_INFORM)
+    pdu.version = SNMP_VERSION_2c
+
+    community_c = _ffi.new("char[]", garbage_community)
+    pdu.community = community_c
+
+    oid = oid_to_c(OID(".1.3.6.1.2.1.1.6.0"))
+    value_type = ValueType.OCTETSTRING
+    encoded_value = encode_variable(ValueType.OCTETSTRING, b"Milliways")
+    _lib.snmp_add_var(
+        pdu, oid, len(oid), value_type.value.encode("utf-8"), encoded_value
+    )
+
+    yield pdu
+
+
+@pytest.fixture
+def garbage_community():
+    yield b"foo\xcbbar"

From 3d3d089f342c98c0d81dcc4cd5fdae170773fc87 Mon Sep 17 00:00:00 2001
From: Morten Brekkevold <morten.brekkevold@sikt.no>
Date: Thu, 4 Sep 2025 11:20:07 +0000
Subject: [PATCH 2/3] Handle non-ascii community values gracefully

If the community value of an incoming trap cannot be parsed as ASCII,
we take care to just leave the raw bytes object for the client to
inspect for themselves.
---
 src/netsnmpy/trapsession.py | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/netsnmpy/trapsession.py b/src/netsnmpy/trapsession.py
index 4dc613f..2624329 100644
--- a/src/netsnmpy/trapsession.py
+++ b/src/netsnmpy/trapsession.py
@@ -4,7 +4,7 @@
 import platform
 from ipaddress import ip_address
 from socket import AF_INET, AF_INET6, inet_ntop
-from typing import Optional, Protocol
+from typing import Optional, Protocol, Union
 
 from netsnmpy import _netsnmp
 from netsnmpy.annotations import IPAddress
@@ -180,7 +180,7 @@ def __init__(
         generic_type: str,
         trap_oid: OID,
         uptime: int,
-        community: str,
+        community: Union[str, bytes],
         version: str,
         variables: VarBindList,
     ):
@@ -208,7 +208,14 @@ def from_pdu(cls, pdu: _ffi.CData) -> "SNMPTrap":
 
         source = cls.get_transport_addr(pdu)
         agent_addr = generic_type = trap_oid = uptime = None
-        community = _ffi.string(pdu.community).decode()
+        community = _ffi.string(pdu.community)
+        try:
+            community = community.decode("ascii")
+        except UnicodeDecodeError:
+            # SNMP communities are defined to be ASCII, but not every entity plays
+            # nice. If this is non-ascii, we'll keep the original bytestring as-is
+            # and leave it up to the client program to deal with it.
+            pass
 
         version = pdu.version
         if version == SNMP_VERSION_1:

From 7bc9d71e510a0406c12baa6768a21aa5e06c8183 Mon Sep 17 00:00:00 2001
From: Morten Brekkevold <morten.brekkevold@sikt.no>
Date: Thu, 4 Sep 2025 11:23:28 +0000
Subject: [PATCH 3/3] Add news fragment.

---
 changelog.d/9.fixed.md | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/9.fixed.md

diff --git a/changelog.d/9.fixed.md b/changelog.d/9.fixed.md
new file mode 100644
index 0000000..291e5c6
--- /dev/null
+++ b/changelog.d/9.fixed.md
@@ -0,0 +1 @@
+Handle non-ASCII trap message community values gracefully without crashing