C# HttpClient An existing connection was forcibly closed by the remote host

user_1265205 0
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I'm working on an integration with Alternative Payments using their hosted page integration. Their C# SDK does not have this integration available at the moment, but as you can see it's pretty simple and I made a small class to send the post request and get the JSON response.

I tested the json object I'm sending on PostMan and cURL and both work, also the authentication header, so I think they are not the problem. Here is the constructor of my class:

public AlternativePaymentsCli(string apiSecretKey)
{
    this._apiSecretKey = apiSecretKey;

    _httpClient = new HttpClient();
    _httpClient.DefaultRequestHeaders.Accept
        .Add(new MediaTypeWithQualityHeaderValue("application/json"));

    var authInfo = _apiSecretKey;
    authInfo = Convert.ToBase64String(System.Text.ASCIIEncoding.ASCII.GetBytes(string.Format("{0}:", _apiSecretKey)));

    // The two line below because I saw in an answer on stackoverflow.
    _httpClient.DefaultRequestHeaders.Add("Connection", "Keep-Alive"); 
    _httpClient.DefaultRequestHeaders.Add("Keep-Alive", "3600");

    _httpClient.DefaultRequestHeaders.UserAgent.ParseAdd("Anything.com custom client v1.0");
    _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", authInfo);

}

And the method where I'm posting the data:

public string CreateHostedPageTransaction(HostedPageRequest req) 
{
    var settings = new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore };

    // I send this same json content on PostMan and it works. The json is not the problem
    var content = new StringContent(JsonConvert.SerializeObject(req, settings), Encoding.UTF8, "application/json");
    var response = _httpClient.PostAsync(this._baseUrl + "/transactions/hosted", content).Result;
    var responseText = response.Content.ReadAsStringAsync().GetAwaiter().GetResult();

    if (response.IsSuccessStatusCode)
        return responseText;

    return "";
}

Then I get this error: An existing connection was forcibly closed by the remote host, at the PostAsync line. This is the error details:

[SocketException (0x2746): An existing connection was forcibly closed by the remote host]
   System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult) +8192811
   System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult) +47

[IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.]
   System.Net.TlsStream.EndWrite(IAsyncResult asyncResult) +294
   System.Net.ConnectStream.WriteHeadersCallback(IAsyncResult ar) +149

[WebException: The underlying connection was closed: An unexpected error occurred on a send.]
   System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult, TransportContext& context) +324
   System.Net.Http.HttpClientHandler.GetRequestStreamCallback(IAsyncResult ar) +137

[HttpRequestException: An error occurred while sending the request.]

I'm using C# 4.5, Asp.Net MVC. I've been reading answers for the same error and none of them solved my issue so far. What am I missing in this code?

Thanks for any help

dotnet-httpclient asp.net json c#
5 Answers

If you are using .Net 4.0 then SecurityProtocolType.Tls11 and SecurityProtocolType.Tls2 are not defined so instead you can use the hard coded value below.

ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;

user_26864380

It is possible to solve the issue without any changes in the code, as described in this excellent answer to a similar question:

Retarget the web project to .Net 4.6+, then update web.config as the following:

<system.web>
  <compilation targetFramework="4.6" /> 
  <httpRuntime targetFramework="4.6" /> 
</system.web>
user_14266850

This worked for me, the first line ensures the protocols ssl3 and TLS1.2, and the second line ignores any potential certificate errors (ignore and continue - like expired certs.): 

ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls12;
ServicePointManager.ServerCertificateValidationCallback +=  (sender, certificate, chain, sslPolicyErrors) => true;
user_129554840

For me this error was caused by forgetting to configure the proxy server. Using the following code to construct the HttpClient solved it for my .NET 4.7.2 application:

var httpClientHandler = new HttpClientHandler { Proxy = WebRequest.GetSystemWebProxy() };
var httpClient = new HttpClient(httpClientHandler);

Hope this helps someone.

user_3059090
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