PageIterator Not Following DeltaLink

[Freenex1911]

Describe the bug
The PageIterator is not following DeltaLink when I call IterateAsync() again.

To Reproduce
Run the following code and set a debug point at foreach and check the DeltaLink.

PageIterator<Message, DeltaGetResponse> pageIterator = null;
while (true)
{
	var messages = new List<Message>();

	if (pageIterator == null)
	{
		var response = await graphServiceClient.Users["..."].MailFolders["Inbox"].Messages.Delta.GetAsDeltaGetResponseAsync(x => x.Headers.Add("Prefer", "IdType=\"ImmutableId\""));
		pageIterator = PageIterator<Message, DeltaGetResponse>.CreatePageIterator(graphServiceClient, response, value =>
		{
			messages.Add(value);
			return true;
		});
	}

	await pageIterator.IterateAsync();

	foreach (var message in messages)
		await HandleMessage(message);

	await Task.Delay(10000);
}

Expected behavior
When I execute IterateAsync() again, I expect that it will follow DeltaLink to iterate over all pages again, as outlined in upgrade-to-v5.md.

Client version
5.36.0

Desktop:

• OS: Windows 11
• Browser: Firefox
• Version: 120.0

[andrueastman]

Thanks for raising this @Freenex1911

In the event that the page iterator encounters the deltaLink the paging will be paused as this means that the API has returned all the changes in the delta call. This therefore means that the client would need to wait for a bit for more changes to occur otherwise you may keep receiving a empty response(no changes since the last call) and another delta link.

Similar to the example captured in the documentation below, the paging state will not be complete, so you will need to call something like below to capture further changes after waiting for a time that is convenient for you.

await pageIterator.IterateAsync();

while (pageIterator.State != PagingState.Complete)// or while (pageIterator.State == PagingState.Delta)
{
    Console.WriteLine("Iteration paused for 5 seconds to wait for more changes...");
    await Task.Delay(5000);
    // Reset count
    await pageIterator.ResumeAsync();
}

https://learn.microsoft.com/en-us/graph/sdks/paging?tabs=csharp#stopping-and-resuming-the-iteration

[Freenex1911]

Thanks for the clarification, in upgrade-to-v5.md it states to use IterateAsync() instead of ResumeAsync(). Now everything works, thanks!

EDIT: I just realized that the Headers I set are not honored when using ResumeAsync().

[andrueastman]

Thanks for clarifying @Freenex1911

#2234 should make the documentation consistent.

With regards to the headers, the pageIterator will need to be initialized with the requestConfigurator parameter as below to propagate the Headers parameter as below.

pageIterator = PageIterator<Message, DeltaGetResponse>.CreatePageIterator(graphServiceClient, response, value =>
                                                                            {
                                                                                messages.Add(value);
                                                                                return true;
                                                                            }, 
                                                                            requestInformation =>
                                                                            {
                                                                                requestInformation.Headers.Add("Prefer", "IdType=\"ImmutableId\"");
                                                                                return requestInformation;
                                                                            });

[Freenex1911]

It works perfectly! However I find it kind of odd to specify the Headers twice in my code even tho the request serves the same purpose. Thanks anyway, as always!