Clarify comments

llo/plugin_codecs.go

@@ -108,11 +108,12 @@ func (c protoObservationCodec) Decode(b types.Observation) (Observation, error)
 	if len(pbuf.StreamValues) > 0 {
 		streamValues = make(StreamValues, len(pbuf.StreamValues))
 		for id, enc := range pbuf.StreamValues {
-			// StreamValues shouldn't have explicit nils, but for safety we
-			// ought to handle it anyway
 			sv, err := UnmarshalProtoStreamValue(enc)
 			if err != nil {
-				return Observation{}, err
+				// Byzantine behavior makes this observation invalid; a
+				// well-behaved node should never encode invalid or nil values
+				// here
+				return Observation{}, fmt.Errorf("failed to decode observation; invalid stream value for stream ID: %d; %w", id, err)
 			}
 			streamValues[id] = sv
 		}

llo/plugin_outcome.go

@@ -291,19 +291,12 @@ func (p *Plugin) decodeObservations(aos []types.AttributedObservation, outctx oc
 			updateChannelDefinitionsByHash[channelHash] = defWithID
 		}
 
-		var missingObservations []llotypes.StreamID
 		for id, sv := range observation.StreamValues {
-			if sv != nil { // FIXME: nil checks don't work here. Test this and figure out what to do (also, are there other cases?)
-				streamObservations[id] = append(streamObservations[id], sv)
-			} else {
-				missingObservations = append(missingObservations, id)
-			}
+			// sv can never be nil here; validation is handled in the decoding
+			// of the observation
+			streamObservations[id] = append(streamObservations[id], sv)
 		}
 		if p.Config.VerboseLogging {
-			if len(missingObservations) > 0 {
-				sort.Slice(missingObservations, func(i, j int) bool { return missingObservations[i] < missingObservations[j] })
-				p.Logger.Debugw("Peer was missing observations", "streamIDs", missingObservations, "oracleID", ao.Observer, "stage", "Outcome", "seqNr", outctx.SeqNr)
-			}
 			p.Logger.Debugw("Got observations from peer", "stage", "Outcome", "sv", streamObservations, "oracleID", ao.Observer, "seqNr", outctx.SeqNr)
 		}
 	}

llo/plugin_outcome_test.go

@@ -616,4 +616,13 @@ func Test_Outcome_Methods(t *testing.T) {
 		require.Len(t, unreportable, 1)
 		assert.Equal(t, "ChannelID: 2; Reason: IsReportable=false; no validAfterSeconds entry yet, this must be a new channel", unreportable[0].Error())
 	})
+
+	t.Run("decodeObservations", func(t *testing.T) {
+		t.Run("with missing observations", func(t *testing.T) {
+			p := &Plugin{}
+			aos := []types.AttributedObservation{}
+			outctx := ocr3types.OutcomeContext{}
+			tsNS, prr, srv, rcv, ucv, so := p.decodeObservations(aos, outctx)
+		})
+	})
 }

llo/stream_value.go

@@ -32,6 +32,8 @@ var (
 
 func UnmarshalProtoStreamValue(enc *LLOStreamValue) (sv StreamValue, err error) {
 	if enc == nil {
+		// StreamValues shouldn't have explicit nils, but for safety we
+		// ought to handle it without panicking
 		return nil, ErrNilStreamValue
 	}
 	switch enc.Type {