Error Handling

Because the callbacks’ HTTPResponse parameter can be null in cases where there was an error on client side (request aborting, timeouts or non-reachable server), as a best practice a HTTPRequest’s callback should look like this:

private void OnRequestFinished(HTTPRequest req, HTTPResponse resp)
{
    switch (req.State)
    {
        // The request finished without any problem.
        case HTTPRequestStates.Finished:
            if (resp.IsSuccess)
            {
                // Everything went as expected!
            }
            else
            {
                Debug.LogWarning(string.Format("Request finished Successfully, but the server sent an error. Status Code: {0}-{1} Message: {2}",
                                                resp.StatusCode,
                                                resp.Message,
                                                resp.DataAsText));
            }
            break;

        // The request finished with an unexpected error. The request's Exception property may contain more info about the error.
        case HTTPRequestStates.Error:
            Debug.LogError("Request Finished with Error! " + (req.Exception != null ? (req.Exception.Message + "\n" + req.Exception.StackTrace) : "No Exception"));
            break;

        // The request aborted, initiated by the user.
        case HTTPRequestStates.Aborted:
            Debug.LogWarning("Request Aborted!");
            break;

        // Connecting to the server is timed out.
        case HTTPRequestStates.ConnectionTimedOut:
            Debug.LogError("Connection Timed Out!");
            break;

        // The request didn't finished in the given time.
        case HTTPRequestStates.TimedOut:
            Debug.LogError("Processing the request Timed Out!");
            break;
    }
}

A request may fail even before reaching the server so it’s wise to check its State first. But even if the request reach the server it can fail if the request is badly constructed or incomplete (status code of 4xxx), or because the server had an issue (status code of 5xxx). So in the Finshed case we still have to check the HTTPResponse’s StatusCode for those codes, or just simple test against the IsSuccess property. IsSuccess is just a shortened way to check whether the status code is in a valid range:

public bool IsSuccess { get { return (this.StatusCode >= 200 && this.StatusCode < 300) || this.StatusCode == 304; } }