Troubleshooting iOS app's inability to read HttpResponseMessage from ASP.NET Web API

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1

I’m working on an iOS app that uses an ASP.NET Web API. The API controllers have filters that generate HttpResponseMessage responses. Everything works fine when there are no errors, but when something goes wrong in the filter (like an invalid token), the iOS app can’t get the HttpResponseMessage.

I’ve tested it with Fiddler and a REST client, and I can see the HttpResponseMessage from both the action and the filters when they fail. But the iOS app gets a nil response if the filter fails.

Here’s a simplified version of our iOS code:

let task = session.dataTask(with: request) { data, response, error in
    guard error == nil, let data = data else {
        handleError()
        return
    }
    
    do {
        if let json = try JSONSerialization.jsonObject(with: data) as? [String: Any] {
            print("Response: \(json)")
            handleSuccess(json)
        } else {
            handleInvalidJSON()
        }
    } catch {
        handleJSONError()
    }
}
task.resume()

Any ideas why this might be happening? The iOS team is stuck and I’m not an iOS expert. Could it be a problem with how we’re handling the response?

2

As someone who’s worked extensively with cross-platform apps, I can say this issue often stems from how different platforms handle HTTP responses. In your case, it sounds like the iOS app might be silently failing when it encounters non-200 status codes.

One approach that’s worked well for me is to implement a custom error handling middleware on the server-side. This can standardize error responses across your API, making them easier to parse on the client side. For example, you could wrap all your error responses in a consistent JSON format, regardless of where they originate (filter, action, etc.).

On the iOS side, I’d suggest implementing a more robust networking layer. Something like Alamofire can simplify request handling and provide better error management out of the box. It’s saved me countless hours of debugging similar issues.

Remember, thorough logging on both ends is crucial for tracking down these kinds of problems. Good luck with your troubleshooting!

3

I’ve encountered a similar issue before. The problem might be in how the iOS app is handling HTTP status codes. When the filter fails, it’s likely sending a non-200 status code, which some HTTP clients treat differently.

Try modifying your iOS code to check the response status code before attempting to parse the JSON. Something like:

let task = session.dataTask(with: request) { data, response, error in
    guard let httpResponse = response as? HTTPURLResponse else {
        handleError("Invalid response")
        return
    }

    if httpResponse.statusCode >= 400 {
        handleError("Server error: \(httpResponse.statusCode)")
        return
    }

    // Rest of your existing code here
}

This way, you can properly handle and log error responses from your API, including those generated by filters. It’s also good practice to check status codes in general for more robust error handling.

4

hey mate, i had similar probs. try checkin the response headers? sometimes the error info’s there instead of the body. also, make sure ur app’s not ignorin certain status codes. might be worth loggin the raw response data to see whats actually comin back from the server. good luck!