Filter out from-self messages in GJKR

When we pre-process messages before executing GJKR protocol phase, we
now also remove the from-self message from the list.

gjkr/message_filter.go

@@ -59,15 +59,34 @@ func deduplicateBySender[T interface{ getSenderIndex() memberIndex }](
 	return result
 }
 
+// removeFromSelf filters out the from-self message from the provided message
+// list.
+func removeFromSelf[T interface{ getSenderIndex() memberIndex }](
+	selfMemberIndex memberIndex,
+	list []T,
+) []T {
+	result := make([]T, 0)
+
+	for _, msg := range list {
+		if msg.getSenderIndex() != selfMemberIndex {
+			result = append(result, msg)
+		}
+	}
+
+	return result
+}
+
 func (m *symmetricKeyGeneratingMember) preProcessMessages(
 	ephemeralPubKeyMessages []*ephemeralPublicKeyMessage,
 ) []*ephemeralPublicKeyMessage {
 	forThisSession := filterForSession(m.sessionID, ephemeralPubKeyMessages)
+	deduplicated := deduplicateBySender(forThisSession)
+	withoutSelf := removeFromSelf(m.memberIndex, deduplicated)
 
 	inactiveMembers := findInactive(m.group.groupSize, forThisSession)
 	for _, ia := range inactiveMembers {
 		m.group.markMemberAsInactive(ia)
 	}
 
-	return deduplicateBySender(forThisSession)
+	return withoutSelf
 }

gjkr/message_filter_test.go

@@ -7,19 +7,37 @@ import (
 )
 
 func TestFilterForSession(t *testing.T) {
-	msg0 := &ephemeralPublicKeyMessage{sessionID: "session-2", senderIndex: 1}
+	msg1 := &ephemeralPublicKeyMessage{sessionID: "session-2", senderIndex: 1}
+	msg2 := &ephemeralPublicKeyMessage{sessionID: "session-1", senderIndex: 1}
+	msg3 := &ephemeralPublicKeyMessage{sessionID: "session-1", senderIndex: 2}
+	msg4 := &ephemeralPublicKeyMessage{sessionID: "session-2", senderIndex: 3}
+
+	filtered := filterForSession("session-1", []*ephemeralPublicKeyMessage{
+		msg1, msg2, msg3, msg4,
+	})
+
+	testutils.AssertDeepEqual(
+		t,
+		"filtered messages",
+		[]*ephemeralPublicKeyMessage{msg2, msg3},
+		filtered,
+	)
+}
+
+func TestRemoveFromSelf(t *testing.T) {
 	msg1 := &ephemeralPublicKeyMessage{sessionID: "session-1", senderIndex: 1}
 	msg2 := &ephemeralPublicKeyMessage{sessionID: "session-1", senderIndex: 2}
-	msg3 := &ephemeralPublicKeyMessage{sessionID: "session-2", senderIndex: 3}
+	msg3 := &ephemeralPublicKeyMessage{sessionID: "session-1", senderIndex: 3}
+	msg4 := &ephemeralPublicKeyMessage{sessionID: "session-1", senderIndex: 4}
 
-	filtered := filterForSession("session-1", []*ephemeralPublicKeyMessage{
-		msg0, msg1, msg2, msg3,
+	filtered := removeFromSelf(memberIndex(2), []*ephemeralPublicKeyMessage{
+		msg1, msg2, msg3, msg4,
 	})
 
 	testutils.AssertDeepEqual(
 		t,
 		"filtered messages",
-		[]*ephemeralPublicKeyMessage{msg1, msg2},
+		[]*ephemeralPublicKeyMessage{msg1, msg3, msg4},
 		filtered,
 	)
 }