How to shorten Connect timeout
Connect and BeginConnect methods take quite a long time to timeout, when you use incorrect server address. It usually takes almost 20 seconds for those methods to decide that connection is impossible. Setting SendTimeout/ReceiveTimeout doesn’t influence this in any way.
Not only Imap, Pop3, and Smtp classes suffer from this problem, it’s the same for regular Socket class.
There is a solution however, using BeginConnect and simply waiting for specified amount of time (AsyncWaitHandle.WaitOne) without calling EndConnect (which blocks):
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 | // C#using(Imap imap =new Imap()){ IAsyncResult result = imap.BeginConnectSSL("imap.example.com"); // 5 seconds timeout bool success = result.AsyncWaitHandle.WaitOne(5000, true); if (success == false) { throw new Exception("Failed to connect server."); } imap.EndConnect(result); //... imap.Close();} |
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 | ' VB.NETUsing imap As New Imap() Dim result As IAsyncResult = imap.BeginConnectSSL("imap.example.com") ' 5 seconds timeout Dim success As Boolean = result.AsyncWaitHandle.WaitOne(5000, True) If success = False Then Throw New Exception("Failed to connect server.") End If imap.EndConnect(result) '... imap.Close()End Using |