Exception "Detected nextLink loop. Nextlink value: " thrown when Making Delta-Requests with the PageIterator

[Danny4021]

Hello,

I'm trying to upgrade the MS Graph SDK from 4.x to 5.11 and encountered the following problem:
I've previously used NextPageRequests to access the next page of a delta request I made but since this features was removed in 5.x I'm trying to use the PageIterator to make Delta-Requests.
I'm creating the PageIterator like this:

DeltaResponse deltaRequest = await  _graphClient
					.Users[mailAddress]
					.MailFolders[folderId]
					.Messages
					.Delta
					.GetAsync();
			
PageIterator<Message, DeltaResponse> iterator = PageIterator<Message, DeltaResponse>.CreatePageIterator(_graphClient, deltaRequest, message => callback.Invoke(message));

When I then call await iterator.IterateAsync() it works the first time without any problems.
Note that I currently don't have any mails in the folder I'm listening to. I'm simply trying to check for changes every x-seconds.
Since the iterator couldn't find any changes, the API returned a DeltaLink and the NextLink is set to string.Empty as seen in the class PageIterator.cs:

Deltalink = deltalink.ToString();
State = PagingState.Delta;
Nextlink = string.Empty;

When I then try to call ResumeAsync() OR IteratorAsync() once more, I get this error message:
Detected nextLink loop. Nextlink value:

I debugged the code to find the code that throws this exception and found this inside the PageIterator.cs class:

// Detect nextLink loop
if (Nextlink.Equals(ExtractNextLinkFromParsable(_currentPage)))
{
    throw new ServiceException($"Detected nextLink loop. Nextlink value: {Nextlink}");
}

Since I don't have any new changes inside the watched folder, the next request made also returns a DeltaLink instead of a NextLink.
But since there is no NextLink inside the the AdditionalData inside of the _currentPage, the method ExtractNextLinkFromParsable returns an empty string, as seen here:

// the next link property may not be defined in the response schema so we also check its presence in the additional data bag
return parsableCollection.AdditionalData.TryGetValue(CoreConstants.OdataInstanceAnnotations.NextLink,out var nextLink) ? nextLink.ToString() : string.Empty;

But this is a problem, because the PageIterator assigned the NextLink to string.Empty in the last request and now this request returns a string.Empty as well, so the PageIterator thinks that I am inside a NextLink loop and throws an exception.
So now my question:
Am I doing something wrong? Am I not supposed to use the PageIterator like this? Is there any better way to check for changes with a Delta-Request? I've tried to follow this microsoft turorial for delta-requests: https://learn.microsoft.com/en-us/graph/delta-query-users?tabs=http
But the QueryParameters don't have a SkipToken or DeltaToken anymore and since the PageIterator has a Delta State I thought I should be able to use it instead.

Thanks in advance

[Danny4021]

Hey,

I just wanted to ask if there is anything new regarding this issue?
Do I need to provide further info? If there's something not clear just point it out and I'll try to explain it.

Thanks

[Nemeczek]

It is the same in Python SDK. I think currently SkipToken and DeltaToken are not supported at all. And the worst part is that you can't pass arbitrary headers to QueryParameters. Then I could easily do the paging and delta by myself.