WebException (Status: Protocol Error)

Question

I am calling a url in C# using WebClient class. Following is the code: -

    public string SendWebRequest(string requestUrl)
    {
        using (var client = new WebClient())
        {
            string responseText = client.DownloadString(requestUrl);
            return responseText;
        } 
    }

This code fails with following Exception details: -

System.Net.WebException: The remote server returned an error: (1201).
   at System.Net.WebClient.DownloadDataInternal(Uri address, WebRequest& request)
   at System.Net.WebClient.DownloadString(Uri address)
   at System.Net.WebClient.DownloadString(String address)

Exception Status: ProtocolError

URL hit the server properly. Actions expected (update database) on server happen properly. Server sends response properly. WebClient is not processing the response.

I also tried using HttpWebRequest class without success.

Initially, similar issue was there while request. It was resolved when I modified my app.config with following: -

    <settings>
        <httpWebRequest useUnsafeHeaderParsing = "true"/>
    </settings>

I cannot post URL on this forum and anyway it is not accessible outside network.

If I copy same URL in browser address bar, it just works fine and returns expected response.

What could be the problem with windows application then?

Edit 1

I implemented suggestions from answer. I also implemented suggestion in accepted answer for this question. Now, my function looks as follows: -

    public string SendWebRequest(string requestUrl)
    {
        using (var client = new WebClient())
        {
            client.Headers.Add("Accept", "text/plain");
            client.Headers.Add("Accept-Language", "en-US");
            client.Headers.Add("User-Agent", "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)");
            client.Headers["Content-Type"] = "text/plain;charset=UTF-8";
            string responseText = client.DownloadString(requestUrl);
            return responseText;
        } 
    }

It still does not solve the problem. Response is now blank string ("") instead of "Success". This is not fault from server which is confirmed.

If I remove configuration in app.config, it throws other exception.

System.Net.WebException: The server committed a protocol violation. Section=ResponseStatusLine
   at System.Net.WebClient.DownloadDataInternal(Uri address, WebRequest& request)
   at System.Net.WebClient.DownloadString(Uri address)
   at System.Net.WebClient.DownloadString(String address)

Solution 1

Your server is returning HTTP 1201 which is not a standard status code.

WebClient will fail with an exception when facing a non-successful status code (or an unrecognized one, in your case).

I encorauge you to use the new HttpClient class if you can:

public async Task<string> SendWebRequest(string requestUrl)
{
    using (HttpClient client = new HttpClient())
    using (HttpResponseMessage response = await client.GetAsync(requestUrl))
         return await response.Content.ReadAsStringAsync();
}

If you have to do it synchronously:

public string SendWebRequest(string requestUrl)
{
    using (HttpClient client = new HttpClient())
    using (HttpResponseMessage response = client.GetAsync(requestUrl).GetAwaiter().GetResult())
         return response.Content.ReadAsStringAsync().GetAwaiter().GetResult();
}

Solution 2

Try changing the headers of your webclient. It seems that your response is not compatible with the header types. I would suggest that you add an Accept header to your client client.Headers.Add("Accept", "application/json"); assuming that you are waiting for Json.

Comments

[Matias Cicero]

You need to send the appropiate request headers (Accept for instance), and any other header that the server may need (such as User-Agent)

[Amit Joshi]

problem is not on server. problem is on client side when it receives response, it is not able to parse it IMO.

[TheDude]

Possible duplicate of Bad Request 400 - protocol error on a valid url - Webclient

[Sameh Awad]

if you are returning plain text, then try client.Headers.Add("Accept", "text/plain");

[Sameh Awad]

@A_J Can u check it with Fiddler, may be the problem is with your Http Response. If you can post here the response that Fiddler sees may be it would be helpful.

[Amit Joshi]

I am not sure what exactly from Fiddler you are asking. See if following is helpful; otherwise let me know. **RESPONSE BYTES (by Content-Type) -------------- ~headers~: 101 ~???????~: 10 **

[Amit Joshi]

Response Header from Fiddler: -HTTP/1.1 1201 Server: Apache-Coyote/1.1 Content-Length: 10 Date: Tue, 27 Sep 2016 11:10:23 GMT SUCCESS

[Amit Joshi]

Response Auth: No Proxy-Authenticate Header is present. No WWW-Authenticate Header is present.

[Sameh Awad]

@A_J Ok If you are just returning SUCCESS then why is your Content-Length:10 and not Content-Length:7. Also check the Content-Type in the response header on Fiddler whether it is has a charset sent with it. Something like Content-Type: text/plain; charset=UTF-8

[Amit Joshi]

I am doing this synchronously. I get following exception: - An unhandled exception of type 'System.ArgumentOutOfRangeException' occurred in mscorlib.dll on line HttpResponseMessage response = client.GetAsync(requestUrl).GetAwaiter().GetResult()

[Matias Cicero]

@A_J Looks like an issue on the server, not the client. Client code is fine.

[Sreerag G]

It's bad practice to dispose HttpClient please fix @MatiasCicero