c# catch empty Json / 404 error

Question

I have the following code for accessing a Api which returns a Json value. Now it's possible that i try to access the api but nothing is being returned, aka the given ID its trying to search doesnt exist. This ofcourse returns a 404 but i do not know how to handle this error so the code continious on going, now it breaks the program and crashes.

public RootObject GetApi(string url)
        {

            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);

            try{
                WebResponse response = request.GetResponse();
                using (Stream responseStream = response.GetResponseStream()){
                    StreamReader reader = new StreamReader(responseStream, Encoding.UTF8);
                    var jsonReader = new JsonTextReader(reader);
                    var serializer = new JsonSerializer();
                    return serializer.Deserialize<RootObject>(jsonReader);
                }
            }

            catch (WebException ex){
                WebResponse errorResponse = ex.Response;
                using (Stream responseStream = errorResponse.GetResponseStream()){
                    StreamReader reader = new StreamReader(responseStream, Encoding.GetEncoding("utf-8"));
                    String errorText = reader.ReadToEnd();
                    // log errorText
                }
                throw;
            }
        }

This is the button click event where the Url of the api is given.

 private void button1_Click(object sender, EventArgs e)
        {
            result_rTBox.Text = "";
            api_Handler api_Handler = new api_Handler();

            string spidyApi_itemSearch = "http://www.gw2spidy.com/api/v0.9/json/item-search/";
            string Gw2Api_allListings = "https://api.guildwars2.com/v2/commerce/listings/";


            string userInput_itemName = userSearchInput_tBox.Text;
            string spidyApi_searchIdByName = spidyApi_itemSearch + userInput_itemName;

            if (!string.IsNullOrWhiteSpace(userSearchInput_tBox.Text)){
                var spidyApi_searchIdByName_result = api_Handler.GetApi(spidyApi_searchIdByName);
                var Gw2Api_isItemIdinListing_result = api_Handler.GetApi(Gw2Api_allListings + spidyApi_searchIdByName_result.results[0].data_id);

                //result_rTBox.Text = Gw2Api_isItemIdinListing_result.results[0].data_id.ToString();
            }
}

First i access the api with string "spidApi_itemSearch" and after that I have and ID that i need to check if exists in the api Gw2Api_allListings. If it doesnt exist, which will happen quite often, it returns nothing with a 404 error. How do i get around of making the code continue even if it returns nothing?

EDIT: code that i have now, still crashes on the break.

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);

            try
            {
                var requesting = WebRequest.Create(url);
                using (var response = request.GetResponse())
                {
                    using (var responseStream = response.GetResponseStream())
                    {
                        StreamReader reader = new StreamReader(responseStream, Encoding.UTF8);
                        var jsonReader = new JsonTextReader(reader);
                        var serializer = new JsonSerializer();
                        return serializer.Deserialize<RootObject>(jsonReader);
                    }
                }
            }
            catch (WebException ex)
            {
                if (ex.Status == WebExceptionStatus.ProtocolError &&
                    ex.Response != null)
                {
                    var resp = (HttpWebResponse)ex.Response;
                    if (resp.StatusCode == HttpStatusCode.NotFound){

                    }

                }
                throw;
            }
        }

JunaidKirkire · Accepted Answer · 2015-04-03 12:25:27Z

1

Use the HttpStatusCode Enumeration, specifically HttpStatusCode.NotFound

Instead of WebResponse, try using HttpWebResponse

HttpWebResponse errorResponse = we.Response as HttpWebResponse;
if (errorResponse.StatusCode == HttpStatusCode.NotFound) {
  // handle the error here
}

Where we is a WebException

answered Apr 3, 2015 at 12:25

JunaidKirkire

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7 Comments

Rien Over a year ago

I dont fully understand how to implement this. Do i have to replace the try catch with this if statement?

JunaidKirkire Over a year ago

@KrijnvanderBurg Yes. You need to cast we.Response as an HttpWebResponse first.

Rien Over a year ago

i have edited my post with the new code, its still breaking on the throw as i do not know what to return as value, since there is nothing to return.

JunaidKirkire Over a year ago

@KrijnvanderBurg you must send an empty RootObject as return value. And let the code which invokes the GetApi handle it. Remove the throw as I don't see any such use for it. You are better of handling the exception yourself.

JunaidKirkire Over a year ago

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