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Merged
ilyam8 merged 3 commits into from
Oct 12, 2026
Merged

fix: answer a request only with a Response or a Report #49

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ce1b522
test: pin a request sent back unchanged as its own answer
ilyam8 Oct 11, 2026
7414f50
fix: answer a request only with a Response or a Report
ilyam8 Oct 11, 2026
cab4fb9
test: pin a discovery request sent back unchanged
ilyam8 Oct 11, 2026
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25 changes: 15 additions & 10 deletions engine.go
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Original file line number Diff line number Diff line change
Expand Up @@ -400,30 +400,35 @@ func (e *exchange) unauthenticatedReport(resp []byte, cursor int, reply *SnmpPac
// answers reports whether reply answers the request, and with which error. An
// SNMPv3 request is answered only by an SNMPv3 reply with the msgID of its
// current or an earlier attempt, and an SNMPv3 reply answers no other request
// (RFC 3412 section 7.2 step 10). A Report then answers with its kind's error,
// none for a resync Report; another reply with the request ID of the current
// or an earlier attempt. Known bugs: nothing else of the reply is compared
// with the request (its PDU type, the SNMPv1 and SNMPv2c versions, the
// (RFC 3412 section 7.2 step 10). A Report that reportKindOf maps then answers
// with its kind's error, none for a resync Report; any other reply only as a
// Response (GetResponse), with the request ID of the current or an earlier
// attempt: a request sent back unchanged carries the client's own IDs and
// digest, and other PDUs answer no request. Known bugs: nothing else of the
// reply is compared with the request (the SNMPv1 and SNMPv2c versions, the
// security model, level and context of RFC 3412 section 7.2 step 12 b, nor,
// for a request without authentication, the user and engine ID); an empty
// reply without an error status answers before its request ID is checked;
// request ID 0 answers any request.
// Response without an error status answers before its request ID is checked;
// a Response with request ID 0 answers any request.
func (e *exchange) answers(reply *SnmpPacket, earlier []sentIDs) (bool, error) {
if reply.Version == Version3 || e.packet.Version == Version3 {
if reply.Version != e.packet.Version || !e.sentWithMsgID(reply.MsgID, earlier) {
return false, nil
}
}
if reply.Error == NoError && len(reply.Variables) < 1 {
e.x.Logger.Print("Empty result: the reply answers the request")
return true, nil
}
if kind, ok := reportKindOf(reply); ok {
if kind.resync {
return true, nil
}
return true, kind.err
}
if reply.PDUType != GetResponse {
return false, nil
}
if reply.Error == NoError && len(reply.Variables) < 1 {
e.x.Logger.Print("Empty result: the reply answers the request")
return true, nil
}
return e.sentWithRequestID(reply.RequestID, earlier) || reply.RequestID == 0, nil
}

Expand Down
10 changes: 5 additions & 5 deletions engine_requests_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -298,7 +298,6 @@ func engineScenarios() map[string]engineScenario {
}
return []agentReply{{data: b}}
},
knownBug: "a reply with request ID 0 is accepted for any request, even a v1 Trap",
},
"answer/empty": {agent: answerWith(nil)},
"answer/empty-wrong-id": {
Expand All @@ -308,12 +307,13 @@ func engineScenarios() map[string]engineScenario {
"answer/empty-with-error-status-wrong-id": {agent: answerWith(func(p *SnmpPacket) { p.RequestID += 100; p.Error = GenErr })},
"answer/error-status": {agent: answerWith(func(p *SnmpPacket) { p.Error, p.ErrorIndex = NoSuchName, 1 }, SnmpPDU{Name: engineOID, Type: Null})},
"answer/not-a-response": {
agent: answerWith(func(p *SnmpPacket) { p.PDUType = GetRequest }, sysDescr),
knownBug: "the reply's PDU type is not checked",
agent: answerWith(func(p *SnmpPacket) { p.PDUType = GetRequest }, sysDescr),
},
"answer/reflected-request": {
agent: func(_ int, req []byte) []agentReply { return []agentReply{{data: bytes.Clone(req)}} },
},
"answer/report": {
agent: answerWith(func(p *SnmpPacket) { p.PDUType = Report }, sysDescr),
knownBug: "the reply's PDU type is not checked",
agent: answerWith(func(p *SnmpPacket) { p.PDUType = Report }, sysDescr),
},
"answer/unknown-pdu-type": {
agent: answerRaw(func(r []byte) []byte {
Expand Down
9 changes: 8 additions & 1 deletion engine_v3_agent_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -75,7 +75,10 @@ type agentAnswer struct {
raw func(*v3Message) // edits the encoded answer, after edit
encode func(v3Message) []byte // encodes the answer after raw, instead of v3Message.bytes
drop bool // no answer
why string
// reflect sends the request back unchanged instead of an answer, as a
// loop or an on-path sender does.
reflect bool
why string
}

const (
Expand Down Expand Up @@ -178,6 +181,10 @@ func (a *fakeV3Agent) handle(n int, data []byte) []agentReply {
a.tr.addf("agent: drops #%d (%s)", n, ans.why)
return nil
}
if ans.reflect {
a.tr.addf("agent: reflects #%d unchanged (%s)", n, ans.why)
return []agentReply{{data: bytes.Clone(data)}}
}

out := a.answer(req, ans)
a.tr.addf("agent: answers #%d with %s at %s (%s)", n, describeAnswerPDU(out), describeFlags(out.MsgFlags), ans.why)
Expand Down
23 changes: 21 additions & 2 deletions engine_v3_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -997,6 +997,25 @@ func v3Scenarios() map[string]v3Scenario {
"answer/other-version/noauth": {
user: "codec-noauth", script: onRequest(2, agentAnswer{why: "SNMPv2c GetResponse", edit: asV2c}),
},
// A request sent back unchanged carries the client's own msgID,
// request ID and, when authenticated, its own digest and ciphertext.
"answer/reflected-request/noauth": {
user: "codec-noauth", script: onRequest(2, agentAnswer{reflect: true, why: "the request sent back"}),
},
"answer/reflected-request/discovery": {
user: "codec-md5", script: onRequest(1, agentAnswer{reflect: true, why: "the discovery request sent back"}),
},
"answer/reflected-request/md5": {
user: "codec-md5", script: onRequest(2, agentAnswer{reflect: true, why: "the request sent back"}),
},
"answer/reflected-request/md5-set": {
user: "codec-md5", script: onRequest(2, agentAnswer{reflect: true, why: "the request sent back"}),
run: func(x *GoSNMP, _ *fakeV3Agent) (*SnmpPacket, error) { return setEngineOID(x) },
},
"answer/reflected-request/sha-aes-set": {
user: "codec-sha-aes", script: onRequest(2, agentAnswer{reflect: true, why: "the request sent back"}),
run: func(x *GoSNMP, _ *fakeV3Agent) (*SnmpPacket, error) { return setEngineOID(x) },
},
// An SNMPv2c message whose body reads as a scoped PDU, with the
// request's request ID, does not answer an SNMPv3 request.
"answer/other-version/noauth-scoped-body": {
Expand Down Expand Up @@ -1033,19 +1052,19 @@ func v3Scenarios() map[string]v3Scenario {
}),
knownBug: "a reply with another security model is accepted, then returned together with the model mismatch error",
},
// A Report carries one varbind (RFC 3412 section 7.1 step 3 d): one with
// two is read past.
"answer/report-two-varbinds": {
user: "codec-noauth", script: onRequest(2, agentAnswer{
report: usmStatsNotInTimeWindows, why: "Report with two varbinds",
edit: func(p *SnmpPacket) { p.Variables = append(p.Variables, sysDescr) },
}),
knownBug: "a Report with more than one varbind is returned as a successful reply",
},
"answer/report-two-varbinds-error-oid": {
user: "codec-noauth", script: onRequest(2, agentAnswer{
report: usmStatsUnknownUserNames, why: "Report with two varbinds",
edit: func(p *SnmpPacket) { p.Variables = append(p.Variables, sysDescr) },
}),
knownBug: "a Report with more than one varbind is returned as a successful reply",
},

// Reports after the engine is known: whether their engine
Expand Down
110 changes: 98 additions & 12 deletions testdata/engine/requests.golden
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Original file line number Diff line number Diff line change
Expand Up @@ -267,10 +267,28 @@
0s hook OnSent
0s read from 127.0.0.2:161: 2c "public" GetRequest id=1001 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"]
0s hook OnRecv
0s hook OnFinish
0s result: packet 2c "public" GetRequest id=1001 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"], no error
0s client after: retries=2 next request id=1002
0s known bug: the reply's PDU type is not checked
1s read from 127.0.0.2:161: deadline
1s hook OnRetry
1s deadline +1s
1s hook PreSend
1s write #2: 2c "public" GetRequest id=1002 [.1.3.6.1.2.1.1.1.0]
1s agent answers #2 after 0s
1s hook OnSent
1s read from 127.0.0.2:161: 2c "public" GetRequest id=1002 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"]
1s hook OnRecv
2s read from 127.0.0.2:161: deadline
2s hook OnRetry
2s deadline +1s
2s hook PreSend
2s write #3: 2c "public" GetRequest id=1003 [.1.3.6.1.2.1.1.1.0]
2s agent answers #3 after 0s
2s hook OnSent
2s read from 127.0.0.2:161: 2c "public" GetRequest id=1003 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"]
2s hook OnRecv
3s read from 127.0.0.2:161: deadline
3s hook OnRetry
3s result: packet nil, error "request timeout (after 2 retries)" *errors.errorString
3s client after: retries=2 next request id=1004

== requests/answer/other-community
0s client: 2c timeout=1s retries=2 exponential=false
Expand Down Expand Up @@ -456,6 +474,38 @@
3s result: packet nil, error "request timeout (after 2 retries)" *errors.errorString
3s client after: retries=2 next request id=1004

== requests/answer/reflected-request
0s client: 2c timeout=1s retries=2 exponential=false
0s deadline +1s
0s hook PreSend
0s write #1: 2c "public" GetRequest id=1001 [.1.3.6.1.2.1.1.1.0]
0s agent answers #1 after 0s
0s hook OnSent
0s read from 127.0.0.2:161: 2c "public" GetRequest id=1001 [.1.3.6.1.2.1.1.1.0]
0s hook OnRecv
1s read from 127.0.0.2:161: deadline
1s hook OnRetry
1s deadline +1s
1s hook PreSend
1s write #2: 2c "public" GetRequest id=1002 [.1.3.6.1.2.1.1.1.0]
1s agent answers #2 after 0s
1s hook OnSent
1s read from 127.0.0.2:161: 2c "public" GetRequest id=1002 [.1.3.6.1.2.1.1.1.0]
1s hook OnRecv
2s read from 127.0.0.2:161: deadline
2s hook OnRetry
2s deadline +1s
2s hook PreSend
2s write #3: 2c "public" GetRequest id=1003 [.1.3.6.1.2.1.1.1.0]
2s agent answers #3 after 0s
2s hook OnSent
2s read from 127.0.0.2:161: 2c "public" GetRequest id=1003 [.1.3.6.1.2.1.1.1.0]
2s hook OnRecv
3s read from 127.0.0.2:161: deadline
3s hook OnRetry
3s result: packet nil, error "request timeout (after 2 retries)" *errors.errorString
3s client after: retries=2 next request id=1004

== requests/answer/report
0s client: 2c timeout=1s retries=2 exponential=false
0s deadline +1s
Expand All @@ -465,10 +515,28 @@
0s hook OnSent
0s read from 127.0.0.2:161: 2c "public" Report id=1001 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"]
0s hook OnRecv
0s hook OnFinish
0s result: packet 2c "public" Report id=1001 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"], no error
0s client after: retries=2 next request id=1002
0s known bug: the reply's PDU type is not checked
1s read from 127.0.0.2:161: deadline
1s hook OnRetry
1s deadline +1s
1s hook PreSend
1s write #2: 2c "public" GetRequest id=1002 [.1.3.6.1.2.1.1.1.0]
1s agent answers #2 after 0s
1s hook OnSent
1s read from 127.0.0.2:161: 2c "public" Report id=1002 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"]
1s hook OnRecv
2s read from 127.0.0.2:161: deadline
2s hook OnRetry
2s deadline +1s
2s hook PreSend
2s write #3: 2c "public" GetRequest id=1003 [.1.3.6.1.2.1.1.1.0]
2s agent answers #3 after 0s
2s hook OnSent
2s read from 127.0.0.2:161: 2c "public" Report id=1003 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"]
2s hook OnRecv
3s read from 127.0.0.2:161: deadline
3s hook OnRetry
3s result: packet nil, error "request timeout (after 2 retries)" *errors.errorString
3s client after: retries=2 next request id=1004

== requests/answer/second-attempt
0s client: 2c timeout=1s retries=2 exponential=false
Expand Down Expand Up @@ -570,10 +638,28 @@
0s hook OnSent
0s read from 127.0.0.2:161: 1 "public" Trap id=0 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"]
0s hook OnRecv
0s hook OnFinish
0s result: packet 1 "public" Trap id=0 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"], no error
0s client after: retries=2 next request id=1002
0s known bug: a reply with request ID 0 is accepted for any request, even a v1 Trap
1s read from 127.0.0.2:161: deadline
1s hook OnRetry
1s deadline +1s
1s hook PreSend
1s write #2: 2c "public" GetRequest id=1002 [.1.3.6.1.2.1.1.1.0]
1s agent answers #2 after 0s
1s hook OnSent
1s read from 127.0.0.2:161: 1 "public" Trap id=0 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"]
1s hook OnRecv
2s read from 127.0.0.2:161: deadline
2s hook OnRetry
2s deadline +1s
2s hook PreSend
2s write #3: 2c "public" GetRequest id=1003 [.1.3.6.1.2.1.1.1.0]
2s agent answers #3 after 0s
2s hook OnSent
2s read from 127.0.0.2:161: 1 "public" Trap id=0 [.1.3.6.1.2.1.1.1.0=OctetString:"codec agent"]
2s hook OnRecv
3s read from 127.0.0.2:161: deadline
3s hook OnRetry
3s result: packet nil, error "request timeout (after 2 retries)" *errors.errorString
3s client after: retries=2 next request id=1004

== requests/answer/wrong-id
0s client: 2c timeout=1s retries=2 exponential=false
Expand Down
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