Internal Server Error when doing a POST with HttpClient in Windows Phone 8

Question

I am posting a string to a web server this way:

private async Task makeRequest(string url, string postData)
    {
        HttpClient client = null;
        HttpResponseMessage response = null;
        try
        {
            client = new HttpClient();
            response = await client.PostAsync(url, new StringContent(postData));

            response.EnsureSuccessStatusCode();
            Debug.WriteLine(response.StatusCode + " " + response.ReasonPhrase);
        }
        catch (HttpRequestException e)
        {
            Debug.WriteLine(e.Message);
        }
    }

But response.EnsureSuccessStatusCode(); throws a HttpRequestException. When I did a e.Message on the exception, it says : Response status code does not indicate success: 500 (Internal Server Error)..

What am I doing wrong that I get that error? And how do I correct it?

Answer 1

POSTing a StringContent will set the content type to text/plain. You might find the server doesn't like that. Try to find out what media type the server is expecting and set the Headers.ContentType of the StringContent instance.

Answer 2

Your best solution here, as a wise man said, in HTTP there is not magic.

Download Fiddler2, setup a proxy on the emulator to connect to it. Then run your code with HttpWebRequest save the header somewhere and then run it again with HttpClient.

Compare the two files carefully and fix whats needs to be fixed. Please note that even the smallest difference might matter.

Answer 3

If anyone is getting 500 (internal server error) when sending data with everything correct, using .net Standard, make sure ExpectContinue is set to false. Some APIs did not accept header Expect: 100-continue and send a 500 (internal server error) as response.

I lost a day because of this. I had to use Mockoon to see environment logs and what was being sent.

private TItemType AddItem<TItemType>(TItemType item)
{
    try
    {
        HttpClient httpClient = new HttpClient();
        httpClient.DefaultRequestHeaders.ExpectContinue = false; // <-- Make sure it is false.
        httpClient.Timeout = TimeSpan.FromSeconds(60);
        httpClient.DefaultRequestHeaders.Accept.Add(
            new MediaTypeWithQualityHeaderValue("application/json"));
                        
        var uri = new Uri("https://your.url/your/api");
        var content = new System.Net.Http.StringContent(
            JsonConvert.SerializeObject(item), Encoding.UTF8, "application/json");

        HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, uri);
        request.Content = content;

        HttpResponseMessage response = HttpClient.SendAsync(request).Result;
        if (response.StatusCode == HttpStatusCode.Created)
        {
            string responseContent = response.Content.ReadAsStringAsync().Result;
            return JsonConvert.DeserializeObject<TItemType>(responseContent);
        }

        return default;
    }
    catch (Exception)
    {
        throw;
    }
}

Answer 4

HTTP code 500 means that this is an error on your server. In plain words, the server threw an exception when trying to process this POST request.

So, this error has nothing to do with HttpClient or with your WP8 app.

Debug your server first and see what causes the exception, and if you're having problems there post another question.

Answer 5

I know it's been a while but I've stumbled upon this question looking for a way to send a POST request with a application/x-www-form-urlencoded content type.

Microsoft.Net.Http, as of version 2.2.28, includes the FormUrlEncodedContentclass which allows you to send such a request.

A code sample would look like this:

var client = new HttpClient();
var data = new Dictionary<String, String>
{
    { "firstname", "taj" },
    { "lastname", "burrow" }
};

var response = await client.PostAsync("http://mygreatapi.com", data);

For the curious ones, the constructor of FormUrlEncodedContent takes an IEnumerable<KeyValuePair<String, String>>