asp.net - HttpClient: Only one usage of each socket address (protocol/network address/port) is normally permitted

Question

using (var client = new HttpClient())
{
 client.BaseAddress = new Uri(Url);
 client.DefaultRequestHeaders.Accept.Clear();
 client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/xml"));

 using (var task = client.PostAsJsonAsync(Url, body))
 {
    if (task.Result.StatusCode != HttpStatusCode.OK)
       throw new Exception(task.Result.ReasonPhrase);
 }

}

Not Sure why we get the Only one usage of each socket address (protocol/network address/port) is normally permitted xx.xxx.xxx.xx:80 error

System.AggregateException: One or more errors occurred. ---> System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: Only one usage of each socket address (protocol/network address/port) is normally permitted xx.xx.xx.xx:80
at System.Net.Sockets.Socket.EndConnect(IAsyncResult asyncResult)
   at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception)
   --- End of inner exception stack trace ---
   at System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult, TransportContext& context)
   at System.Net.Http.HttpClientHandler.GetRequestStreamCallback(IAsyncResult ar)
   --- End of inner exception stack trace ---
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)

Answer 1

The error in question is WSAEADDRINUSE (10048):

Address already in use.
Typically, only one usage of each socket address (protocol/IP address/port) is permitted. This error occurs if an application attempts to bind a socket to an IP address/port that has already been used for an existing socket, or a socket that was not closed properly, or one that is still in the process of closing. For server applications that need to bind multiple sockets to the same port number, consider using setsockopt (SO_REUSEADDR). Client applications usually need not call bind at all—connect chooses an unused port automatically. When bind is called with a wildcard address (involving ADDR_ANY), a WSAEADDRINUSE error could be delayed until the specific address is committed. This could happen with a call to another function later, including connect, listen, WSAConnect, or WSAJoinLeaf.

Which means you either have multiple HttpClient objects trying to bind themselves to the same local IP/Port at the same time, or another app is using an IP/Port that an HttpClient is trying to also use.

More likely, you are probably posting HTTP requests too often, and maybe not fully consuming the responses, which would prevent ASP from pooling and reusing connections and thus encountering port exhaustion over time.