Prevent duplicate member UUIDs in groups.

Fixes #10702

libsignal/service/src/main/java/org/whispersystems/signalservice/api/groupsv2/DecryptedGroupUtil.java

@@ -20,6 +20,7 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.Iterator;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Set;
 import java.util.UUID;
@@ -295,7 +296,20 @@ public final class DecryptedGroupUtil {
   }
 
   private static void applyAddMemberAction(DecryptedGroup.Builder builder, List<DecryptedMember> newMembersList) {
-    builder.addAllMembers(newMembersList);
+    if (newMembersList.isEmpty()) return;
+
+    LinkedHashMap<ByteString, DecryptedMember> members = new LinkedHashMap<>();
+
+    for (DecryptedMember member : builder.getMembersList()) {
+      members.put(member.getUuid(), member);
+    }
+
+    for (DecryptedMember member : newMembersList) {
+      members.put(member.getUuid(), member);
+    }
+
+    builder.clearMembers();
+    builder.addAllMembers(members.values());
 
     removePendingAndRequestingMembersNowInGroup(builder);
   }

libsignal/service/src/test/java/org/whispersystems/signalservice/api/groupsv2/DecryptedGroupUtil_apply_Test.java

@@ -82,6 +82,54 @@ public final class DecryptedGroupUtil_apply_Test {
                  newGroup);
   }
 
+  @Test
+  public void apply_new_member_already_in_the_group() throws NotAbleToApplyGroupV2ChangeException {
+    DecryptedMember member1 = member(UUID.randomUUID());
+    DecryptedMember member2 = member(UUID.randomUUID());
+
+    DecryptedGroup newGroup = DecryptedGroupUtil.apply(DecryptedGroup.newBuilder()
+                                                                     .setRevision(10)
+                                                                     .addMembers(member1)
+                                                                     .addMembers(member2)
+                                                                     .build(),
+                                                       DecryptedGroupChange.newBuilder()
+                                                                           .setRevision(11)
+                                                                           .addNewMembers(member2)
+                                                                           .build());
+
+    assertEquals(DecryptedGroup.newBuilder()
+                               .setRevision(11)
+                               .addMembers(member1)
+                               .addMembers(member2)
+                               .build(),
+                 newGroup);
+  }
+
+  @Test
+  public void apply_new_member_already_in_the_group_by_uuid() throws NotAbleToApplyGroupV2ChangeException {
+    DecryptedMember member1     = member(UUID.randomUUID());
+    UUID            member2Uuid = UUID.randomUUID();
+    DecryptedMember member2a    = member(member2Uuid, newProfileKey());
+    DecryptedMember member2b    = member(member2Uuid, newProfileKey());
+
+    DecryptedGroup newGroup = DecryptedGroupUtil.apply(DecryptedGroup.newBuilder()
+                                                                     .setRevision(10)
+                                                                     .addMembers(member1)
+                                                                     .addMembers(member2a)
+                                                                     .build(),
+                                                       DecryptedGroupChange.newBuilder()
+                                                                           .setRevision(11)
+                                                                           .addNewMembers(member2b)
+                                                                           .build());
+
+    assertEquals(DecryptedGroup.newBuilder()
+                               .setRevision(11)
+                               .addMembers(member1)
+                               .addMembers(member2b)
+                               .build(),
+                 newGroup);
+  }
+
   @Test
   public void apply_remove_member() throws NotAbleToApplyGroupV2ChangeException {
     DecryptedMember member1 = member(UUID.randomUUID());