ExecuteTaskAsync null response is causing an unhandled exception

I'm testing using my app offline by switching off my server. If I call ExecuteTaskAsync I'm getting an unhandled exception since the server is unavailable and the response is null.

The error arises in RestClient.Async.cs,

var async = ExecuteAsync(request, (response, _) =>
{
....
});

Would it make sense to handle the case where response is null e.g.

else if (response == null)
{
taskCompletionSource.TrySetException(new NullReferenceException());
}

or is there a better way this should be handled ?

[haacked]

Yeah, but we should probably throw a more descriptive exception. Not sure which one we do.

I had the same question, I was thinking of throwing a TimeoutException instead of a NullException, since if
the response is null, there’s a good chance the request has timed out.

From: Phil Haack <notifications@github.commailto:notifications@github.com>
Reply-To: restsharp/RestSharp <reply@reply.github.commailto:reply@reply.github.com>
Date: Wednesday 13 November 2013 22:12
To: restsharp/RestSharp <RestSharp@noreply.github.commailto:RestSharp@noreply.github.com>
Cc: Ciaran Byrne <ciaran.byrne@clickahead.iemailto:ciaran.byrne@clickahead.ie>
Subject: Re: [RestSharp] ExecuteTaskAsync null response is causing an unhandled exception (#466)

Yeah, but we should probably throw a more descriptive exception. Not sure which one we do.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/466#issuecomment-28439260.

[haacked]

TimeoutException sounds good. Perhaps have the NullRef as an inner exception.

Sounds great Phil !

On 13 Nov 2013, at 22:45, "Phil Haack" <notifications@github.commailto:notifications@github.com> wrote:

TimeoutException sounds good. Perhaps have the NullRef as an inner exception.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/466#issuecomment-28441913.

[sidristij]

but why response is null?? response.Data should be null, with Error -> TimeOutError

Using my windows phone app online then offline, response is null. And I find BeginGetRequestStream does not fire its callback.

[ekrapfl]

Is anyone working on a fix for this? We are using RestSharp for MonoTouch, and we have experienced some trouble if we lose an internet connection on the device and still try to call ExecuteTaskAsync. Some sort of a null check here would be really helpful.

[haacked]

Nobody is working on this that I know of. I'm trying to find a new person to take over RestSharp. Care to submit a PR?

[chriseldredge]

Using 104.4.0, I ran into a similar issue when an SSL handshake fails (certificate not trusted), my callback is invoked and result is null. I was able to access the underlying exception as follows:

var tcs = new TaskCompletionSource<IRestResponse<T>>();

Action<IRestResponse<T>, RestRequestAsyncHandle> callback = (r, h) =>
{
    if (r != null)
    {
        tcs.SetResult(r);
        return;
    }

    try
    {
        // typically throws some exception:
        h.WebRequest.GetResponse();

        // typically not reached, added as fallback:
        throw new IOException("Unknown Error");
    }
    catch (Exception ex)
    {
        tcs.SetException(ex);
    }
};

var asyncHandle = Client.ExecuteAsync(request, callback);

// snip

It seems response is null because RestClient.Async:152 soft casts the response to RestResponse<T> which ends up null when an error response is produced.

It would be nice if RestRequestAsyncHandle provided access to the underlying exception thrown so we don't have to jump through hoops to find it.

[alexeyzimarev]

This seems to be fixed by that PR.