check if the linked device is a member of the closed group

SignalServiceKit/src/Contacts/Threads/TSGroupThread.h

@@ -38,6 +38,7 @@ extern NSString *const TSGroupThread_NotificationKey_UniqueId;
 
 - (BOOL)isLocalUserInGroup;
 - (BOOL)isLocalUserInGroupWithTransaction:(YapDatabaseReadTransaction *)transaction;
+- (BOOL)isUserInGroup:(NSString *)hexEncodedPublicKey transaction:(YapDatabaseReadWriteTransaction *)transaction;
 
 // all group threads containing recipient as a member
 + (NSArray<TSGroupThread *> *)groupThreadsWithRecipientId:(NSString *)recipientId

SignalServiceKit/src/Contacts/Threads/TSGroupThread.m

@@ -204,6 +204,13 @@ NSString *const TSGroupThread_NotificationKey_UniqueId = @"TSGroupThread_Notific
     return [linkedDeviceHexEncodedPublicKeys intersectsSet:[NSSet setWithArray:self.groupModel.groupMemberIds]];
 }
 
+- (BOOL)isUserInGroup:(NSString *)hexEncodedPublicKey transaction:(YapDatabaseReadWriteTransaction *)transaction
+{
+    if (hexEncodedPublicKey == nil) { return NO; }
+    NSSet<NSString *> *linkedDeviceHexEncodedPublicKeys = [LKDatabaseUtilities getLinkedDeviceHexEncodedPublicKeysFor:hexEncodedPublicKey in:transaction];
+    return [linkedDeviceHexEncodedPublicKeys intersectsSet:[NSSet setWithArray:self.groupModel.groupMemberIds]];
+}
+
 - (NSString *)name
 {
     // TODO sometimes groupName is set to the empty string. I'm hesitent to change

SignalServiceKit/src/Messages/OWSMessageManager.m

@@ -1360,7 +1360,7 @@ NS_ASSUME_NONNULL_BEGIN
     }
 
     // Ensure sender is in the group.
-    if (![gThread.groupModel.groupMemberIds containsObject:envelope.source]) {
+    if (![gThread isUserInGroup:envelope.source transaction:transaction]) {
         OWSLogWarn(@"Ignoring 'Request Group Info' message for non-member of group. %@ not in %@",
             envelope.source,
             gThread.groupModel.groupMemberIds);