CODEWITHSUNDEEP
c#.net
sergio
sergio

Reputation: 71

WebRequest: The underlying connection was closed

My app has to download one certain file, here is the url. The app worked fine for years bur after a recent change on provider side I'm getting 'The underlying connection was closed: An unexpected error occurred on a send.'

I have read all related info in net but none of suggested fixes works for me.

Important note: the code works OK with Net Framework 4.6 but I need it to work with 3.5.

Any ideas?

Here is the code:

        var url = new Uri(@"http://www.ezv.admin.ch/pdf_linker.php?doc=edecReceiptResponse_stylesheet_v_3_0");

        var request = (HttpWebRequest)WebRequest.Create(url);
        request.KeepAlive = false;
        request.AllowAutoRedirect = true;
        request.UserAgent = "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36";
        request.ProtocolVersion = HttpVersion.Version10;

update: the stack:

System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Received an unexpected EOF or 0 bytes from the transport stream.
   at System.Net.FixedSizeReader.ReadPacket(Byte[] buffer, Int32 offset, Int32 count)
   at System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
   at System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size)
   at System.Net.PooledStream.Write(Byte[] buffer, Int32 offset, Int32 size)
   at System.Net.ConnectStream.WriteHeaders(Boolean async)

one more update: checked with Fiddler the app connecting to httpS and compared responses received with net 4.6 (works) with net 3.5 (fails):

Upvotes: 2

Views: 3202

Answers (1)

Eugene Komisarenko
Eugene Komisarenko

Reputation: 1543

As per conducted test here are the protocols supported by www.ezv.admin.ch.

Protocols
TLS 1.2 Yes
TLS 1.1 No
TLS 1.0 No
SSL 3   No
SSL 2   No

The server side upgrade has most likely upgraded the version of the security protocol to be exclusively TLS 1.2.

As per the following article .NET Framework 3.5 does not support this version and the only options you have is to upgrade your client libraries or patch them, see below.

.NET 3.5 or below. TLS 1.2 is not supported (*) and there is no workaround. Upgrade your application to more recent version of the framework.

Here is some more information of how to patch your client to add support.

P.P.S. As Christian Pop from Microsoft mentioned below, there is a recent patch available for .NET 3.5 which is enabling TLS1.2 support.

See:

KB3154518 – Reliability Rollup HR-1605 – NDP 2.0 SP2 – Win7 SP1/Win 2008 R2 SP1 KB3154519 – Reliability Rollup HR-1605 – NDP 2.0 SP2 – Win8 RTM/Win 2012 RTM KB3154520 – Reliability Rollup HR-1605 – NDP 2.0 SP2 – Win8.1RTM/Win 2012 R2 RTM KB3156421 -1605 HotFix Rollup through Windows Update for Windows 10.

Upvotes: 3

Related Questions