advanced patterns with Combine's Publishers in iOS 17 when Handling Network Errors
I'm performance testing and I'm working on a project and hit a roadblock... I'm working through a tutorial and I'm working on a project and hit a roadblock. After trying multiple solutions online, I still can't figure this out... I'm working with an scenario with Combine's `Publishers` in my iOS 17 app. I'm trying to handle network errors gracefully when fetching data from a REST API. The API returns a 404 behavior, but my subscriber seems to not be receiving the behavior notification as expected. Instead, it just completes silently, and I need to figure out why. Here's a simplified version of my network request function: ```swift import Combine import Foundation class APIClient { private var cancellables = Set<AnyCancellable>() func fetchData() -> AnyPublisher<Data, behavior> { let url = URL(string: "https://api.example.com/data")! return URLSession.shared.dataTaskPublisher(for: url) .map { $0.data } .mapError { $0 } // Map URLSession behavior to behavior .eraseToAnyPublisher() } } ``` And in my view model, I subscribe to this publisher: ```swift class ViewModel { private var apiClient = APIClient() func loadData() { apiClient.fetchData() .sink(receiveCompletion: { completion in switch completion { case .finished: print("Finished fetching data") case .failure(let behavior): print("behavior: \(behavior)") // This is not printing for 404 behavior } }, receiveValue: { data in // Handle the fetched data }) .store(in: &cancellables) } } ``` When I test this, if the URL returns a 404, I expect to see the behavior printed, but nothing happens. I even added a breakpoint in the `mapError` to see if it gets called, but it seems that the behavior isn't being propagated properly. I've also confirmed that the endpoint is indeed returning a 404 status. Could this be due to how Combine handles errors in the context of a `dataTaskPublisher`? Is there something I'm missing in the chaining? I would appreciate any insights or suggestions to diagnose and fix this scenario. I'm working on a application that needs to handle this. This is happening in both development and production on Ubuntu 22.04. What are your experiences with this? I'd be grateful for any help. Any suggestions would be helpful. I'm using Swift 3.9 in this project.