C# 从 web API 读取 JSON

Question

I am trying to read data from this API API Wykazu podatników VAT

Thru HttpWebRequest it's working:

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://wl-test.mf.gov.pl:9091/wykaz-podatnikow/api/search/nips/3245174504?date=2019-09-27");
    try
    {
        WebResponse response = request.GetResponse();
        using (Stream responseStream = response.GetResponseStream())
        {
            StreamReader reader = new StreamReader(responseStream, System.Text.Encoding.UTF8);
            Console.WriteLine(reader.ReadToEnd());
        }
    }
    catch (WebException ex)
    {
        WebResponse errorResponse = ex.Response;
        using (Stream responseStream = errorResponse.GetResponseStream())
        {
            StreamReader reader = new StreamReader(responseStream, System.Text.Encoding.GetEncoding("utf-8"));
            String errorText = reader.ReadToEnd();
            // log errorText
        }
        throw;
    }

But when I try it thru WebClient:

    var client = new WebClient();
    client.Headers.Add("nips", "3245174504");
    client.Headers.Add("date", "2019-09-27");
    var response = client.DownloadString("https://wl-test.mf.gov.pl:9091/wykaz-podatnikow/api/search/nips/");
    Console.WriteLine(response.ToString());

I got this error message:

Unhandled Exception: System.Net.WebException: An exception occurred during a WebClient request. ---> System.ArgumentException: The 'date' header must be modified using the appropriate property or method. Parameter name: name at System.Net.WebHeaderCollection.ThrowOnRestrictedHeader(String headerName) at System.Net.WebHeaderCollection.Add(String name, String value) at System.Net.HttpWebRequest.set_Headers(WebHeaderCollection value) at System.Net.WebClient.CopyHeadersTo(WebRequest request) at System.Net.WebClient.GetWebRequest(Uri address) at System.Net.WebClient.DownloadDataInternal(Uri address, WebRequest& request) --- End of inner exception stack trace --- at System.Net.WebClient.DownloadDataInternal(Uri address, WebRequest& request) at System.Net.WebClient.DownloadString(Uri address) at System.Net.WebClient.DownloadString(String address)

How should I format the second Date parameter?

Answer 1

I would recommend using the newer HTTPClient as it is specifically created for API calls -

    using (var x = new HttpClient())
    {
        var y = x.GetAsync("https://wl-test.mf.gov.pl:9091/wykaz-podatnikow/api/search/nips/3245174504?date=2019-09-27").Result;
        var json = y.Content.ReadAsStringAsync().Result;
    }

Just to add, please don't use.Result, instead use the async/await operators.

Answer 2

Are you mistaking request headers with Query Parameters? if so you might want the following instead:

https://wl-test.mf.gov.pl:9091/wykaz-podatnikow/api/search?nips=3245174504&date=2019-09-27