使用 HttpClient.GetAsync() 时如何确定 404 响应状态

Question

I am trying to determine the response returned by HttpClient 's GetAsync method in the case of 404 errors using C# and .NET 4.5.

At present I can only tell that an error has occurred rather than the error's status such as 404 or timeout.

Currently my code my code looks like this:

    static void Main(string[] args)
    {
        dotest("http://error.123");
        Console.ReadLine();
    }

    static async void dotest(string url)
    {
        HttpClient client = new HttpClient();

        HttpResponseMessage response = new HttpResponseMessage();

        try
        {
            response = await client.GetAsync(url);

            if (response.IsSuccessStatusCode)
            {
                Console.WriteLine(response.StatusCode.ToString());
            }
            else
            {
                // problems handling here
                string msg = response.IsSuccessStatusCode.ToString();

                throw new Exception(msg);
            }

        }
        catch (Exception e)
        {
            // .. and understanding the error here
            Console.WriteLine(  e.ToString()  );                
        }
    }

My problem is that I am unable to handle the exception and determine its status and other details of what went wrong.

How would I properly handle the exception and interpret what errors occurred?

Answer 1

You could simply check the StatusCode property of the response:

static async void dotest(string url)
{
    using (HttpClient client = new HttpClient())
    {
        HttpResponseMessage response = await client.GetAsync(url);

        if (response.IsSuccessStatusCode)
        {
            Console.WriteLine(response.StatusCode.ToString());
        }
        else
        {
            // problems handling here
            Console.WriteLine(
                "Error occurred, the status code is: {0}", 
                response.StatusCode
            );
        }
    }
}

Answer 2

The property response.StatusCode is a HttpStatusCode enum.

This is the code I use to get a friedly name

if (response != null)
{
    int numericStatusCode = (int)response.StatusCode;

    // like: 503 (ServiceUnavailable)
    string friendlyStatusCode = $"{ numericStatusCode } ({ response.StatusCode })";

    // ...

}

Or when only errors should be reported

if (response != null)
{
    int statusCode = (int)response.StatusCode;

    // 1xx-3xx are no real errors, while 3xx may indicate a miss configuration; 
    // 9xx are not common but sometimes used for internal purposes
    // so probably it is not wanted to show them to the user
    bool errorOccured = (statusCode >= 400);
    string friendlyStatusCode = "";

    if(errorOccured == true)
    {
        friendlyStatusCode = $"{ statusCode } ({ response.StatusCode })";
    }
    
    // ....
}