RequestHelper.Abort() throws exception

[cetonek]

Hi, I want to discard all requests that are made as soon as I leave given scene, so my code is:

    public class LadderRepository : MonoBehaviour {

        private string uri = "my uri";

        private readonly IList<RequestHelper> requests = new List<RequestHelper>();

        public IPromise<LadderResponse> FetchLadder() {
            var requestHelper = ComposeRequest(ladder);
            return RestClient.Get<LadderResponse>(requestHelper);
        }

        private RequestHelper ComposeRequest(string url) {
            var requestHelper = new RequestHelper {
                Uri = url,
                Timeout = 10
            };
            requests.Add(requestHelper);
            return requestHelper;
        }

        private void OnDestroy() {
            foreach (var requestHelper in requests) {
                requestHelper.Abort();
            }

            requests.Clear();
        }

    }

I get exception in editor when calling requestHelper.Abort() :

ArgumentNullException: Value cannot be null.
Parameter name: _unity_self
Proyecto26.RequestHelper.Abort () (at Assets/RestClient/Packages/Proyecto26.RestClient/Helpers/RequestHelperExtension.cs:129)
Script.LadderRepository.OnDestroy () (at Assets/Script/Ladder/LadderRepository.cs:30)

I have unity 2019.2.13f1 and RestClient version 2.6.0. My idea is I dont want to receive any callbacks from any requests after user leaves given scene, cant tell what this error means though.

[jdnichollsc]

Very odd because we're validating here https://github.com/proyecto26/RestClient/blob/master/src/Proyecto26.RestClient/Helpers/RequestHelperExtension.cs#L124

[cetonek]

Yeah that looks reasonable, in fact I added check even for !isDone, but it shouldnt change anything. Everytime I tried to access anything in the UnityWebRequest instance I got that exception

[jdnichollsc]

I'm not sure what validation to add here to fix the exception thrown by the UnityWebRequest instance 🤔

[wloczykij89]

I've the same problem when I check the download progress of a file that has already finished downloading. It looks like you're referring to UnityWebRequest object after it has been disposed by using block.

https://forum.unity.com/threads/argumentnullexception-appear-randomly-in-unitywebrequest.541629/#post-3856987

[jdnichollsc]

Please attach any reproducible demo to debug 🙂

[wloczykij89]

I really appreciate your work. It's a really good piece of code. Thanks man :) The following example downloads an image and after that checks progress and call Abort() with some delay. This actions cause errors. After download success UnityWebRequest was automatically disposed and can no longer be used.

using System;
using System.Collections;
using System.IO;
using Proyecto26;
using UnityEngine;
using UnityEngine.Networking;

public class DownloadTest : MonoBehaviour
{
    public static readonly string TestFilePath = "https://upload.wikimedia.org/wikipedia/commons/3/37/African_Bush_Elephant.jpg";
    private RequestHelper request;

    private void OnEnable()
    {
        Download(TestFilePath);
    }

    public void Download(string path)
    {
        string fileName = Path.GetFileName(path);
        string targetPath = Path.Combine(Application.persistentDataPath, fileName);

        var downloadHandler = new DownloadHandlerFile(targetPath);

        request = new RequestHelper
        {
            Uri = path,
            DownloadHandler = downloadHandler
        };

        RestClient.Get(request)
            .Then((ResponseHelper obj) =>
            {
                Debug.Log("Download success");

                StartCoroutine(DelayAbort(2));
            })
            .Catch((Exception error) =>
            {
                Debug.LogError("Download failed: " + error.Message);
            });
            
        StartCoroutine(CheckProgress());
    }

    public IEnumerator DelayAbort(float delay)
    {
        yield return new WaitForSeconds(delay);

        request.Abort();
    }

    private IEnumerator CheckProgress()
    {
        for(; ; )
        {
            var progress = request.DownloadProgress;

            yield return null;
        }
    }
}

[jdnichollsc]

I think you can't call Abort method from Then because the request has finished, also you can verify if the request is aborted using request.IsAborted

[wloczykij89]

The problem is not just about call Abort(). The above code is only a reproduction of @Ejstn's case. In his code in the OnDestroy method, all requests are aborted, both those completed and those that are still ongoing. For requests that were completed, the UnityWebRequest object was automatically Dispose() - using block calls Dispose() uppon leaving the block. In that case in RequestHelper checking if(Request != null) returns true but performing any operation on this object is forbidden and will throw ArgumentNullException (Request.isDone, Request.Abort() ...).

[jdnichollsc]

Thanks mate, let me check, also any pull request is welcome! <3