In MC65, SIM card is already inserted. Any web site can be browsed.
In my application, there is sending email feature using Rebex. Sometimes, it cannot send email. So I tried to browse IE and I'm beware if 3G connection signal appears, sending works properly.
Around connection signal on Screen, there is "H" symbol. What is it?
For my case, it's not good to switch 3G connection by browsing IE. how to handle it.
Does the Rebex Mail throw any exception when it's unable to send email? Error message might help to diagnose the problem.
Is it possible to create a SMTP communication log file and include part of it with error message? Following code shows how to do it:
Dim mailMessage As New MailMessage()
'todo: set mail message properties
Dim smtp As New Smtp
smtp.LogWriter = new Rebex.FileLogWriter("\temp\log.txt", Rebex.LogLevel.Debug)
smtp.Connect("smtp.example.org")
smtp.Send(mailMessage)
Edit:
The 'H' symbol could mean HSDPA - high speed data transfer over 3G network.
Is it possible, that connection is dropped and IExplorer re-establishes connection automatically. In such case you may try to 'dial' connection manually. The How to establish a GPRS connection for FTP use on .NET CF post shows how.
Related
I am using Vb.Net and VS 2013, based on my research it isn't possible to detect whether the client is still connected or not unless the client sends a KEEP ALIVE command to my server or sends a string indicating that that client will be disconnected before it disconnects itself, due to this I wanted to know if it is possible to detect if a client disconnects itself from my server? I mean if the client willingly disconnects it self from the server?
This is a follow up question to this wherein I am asking if it is possible to detect currently connected clients to my server
Edit: I've added that it is also possible by telling the client to send a string of command indicating that it will disconnect itself before the client actually disconnects itself.
I think you should do a few tutorials on the subject :
https://msdn.microsoft.com/en-us/library/vstudio/ms172757(v=vs.100).aspx
and have a look at the documentation :
https://msdn.microsoft.com/en-us/library/vstudio/system.net.sockets.socket(v=vs.100).aspx?cs-save-lang=1&cs-lang=vb#code-snippet-2
https://msdn.microsoft.com/en-us/library/vstudio/1011kecd(v=vs.100).aspx
You can check the current state of the socket via Poll although i would recommend switching to an OOP approach
'Creates the Socket for sending data over TCP.
Dim s As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
' Connects to host using IPEndPoint.
s.Connect(EPhost)
If Not s.Connected Then
strRetPage = "Unable to connect to host"
End If
' Use the SelectWrite enumeration to obtain Socket status.
If s.Poll(- 1, SelectMode.SelectWrite) Then
Console.WriteLine("This Socket is writable.")
Else
If s.Poll(- 1, SelectMode.SelectRead) Then
Console.WriteLine(("This Socket is readable. "))
Else
If s.Poll(- 1, SelectMode.SelectError) Then
Console.WriteLine("This Socket has an error.")
End If
End If
End If
If SelectMode.SelectError is True your client/server has either disconnected or timed out.
I have an application that needs to stream data up to a server over a particular port. When the application starts it performs a number of checks, for network connectivity, a reachable host, among others. I'd like it to also check the port to ensure it's able to receive data.
I have this code:
Private Function CheckPort(ByVal Host As String) As Boolean
Dim IPs() As IPAddress = Dns.GetHostAddresses(Host)
Dim s As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
s.Connect(IPs(0), <port # removed>)
If s.Poll(-1, SelectMode.SelectWrite) Then
Return True
End If
Return False
End Function
The code works well, but I'm concerned that by performing the check I might be inadvertently preventing subsequent messages from the application from reaching the port. Will performing this check interfere with the actual data I want to send to the host? Should I close the socket with s.close() before returning the function?
I mainly agree with CodeCaster's response.
If you say the server is buggy, it is also probable that a few minutes after you check the port connection, the connection is broken or even closed by the server.
If you still want to do it as a means to reduce risk of making the user write some message that later cannot be sent, this would be a good approach to follow. An alternative is that you can save the data as draft locally or somewhere else for sending it later when the server is available.
Now, going to your code:
You are opening a connection inside function CheckPort so when the function finishes you will lose any reference to s, the open socket. In C, you would have a leak of resources; in Java, a garbage collector will take care of the Socket and close it. I don't know how it is in VB but I'd close that socket before leaving the function. In any case it's a healthy practice.
Additionally, when you have data ready to send you won't be able to do it on the same connection if you lose the reference (s) to the open socket or you close the socket (unless VB has any trick that I don't know). You will have to open a new connection to send data. Don't worry, you will be able to do it even if you made the check before. The server will see it as just a different connection, maybe from a different source port (or could be the same if you closed the connection before, that depends on the OS).
Checking a port before connecting to it is as useful as verifying file existence before opening it: not at all.
The file can be deleted in between checking and opening, and your socket can be closed for a variety of reasons.
Just connect and write to it, it'll throw an appropriate exception when it won't work.
We have (Multiple)Clients-(One)Server architecture for poker desktop game. We are using callback Notifications using callback Channels.
But sometimes because of internet connection drops, that particualr client gets disconected from server and that particular's client's WCF channel is also gone to faluted state and his callback Channel which lies in server is also faluted.
Scenario :
That client is playing game, while internet connection drops, that game is stopped, still his game window remains open and when his/her internet connection gets back that client is dropped out from Server, but that player's game window still opens and that player can't do anything as his/her WCF channel is dropped out.
We want to close that particular client's window while he/she is dropped out from server and throwing 'CommunicationObjectAbortedException ' exception.
We can't use previous WCF channel's callback channel as it's in faluted state.
So we have tried to create new callbackChannel in server while dropping using below code :
OperationContext.Current.GetCallbackChannel();
but here Current is showing "NULL" as that player's WCF channel is aborted, so it's throwing an error that "Object reference not set to an instance of object".
So is there any solution to use aborted WCF channel's callback Channel or recover that WCF channel without reinitializing them or to call that client using new channel?
I'd try following:
On server side, when trying to communicate using faulted / aborted chanel - you'll failed.
Catch this failure, and remove its callback from the list (I suppose you manage some callback list).
On client side - when chanel Faulted / ... handled - try to re-open new chanel to server. When this new chenel will be open, on server side place this new callback back to the "valid callbacks" list.
I have fully working duplex messaging solution for Silverlight application. Now I would like to add one feature to it. When user leaves the application I want to notify the server about that by sending the last message before exit.
I have tried to send duplex message during Application Exit event, but DuplexServiceClient is already in CommunicationState.Faulted state.
I've also tried to establish new connection and send the message. Everything seemed to be okay on the client side, but no message has been send at all. I checked that twice by using Fiddler.
App.Current.Exit += (s, e) =>
{
var dsc = new DuplexServiceClient(_binding, new EndpointAddress("../Services/MyService.svc"));
dsc.SendToServiceAsync(new UserLeave());
};
Crucial thing is, that I need to notify the server immediately after user leaves the application, so timeouts or similar workarounds are not good enough for me in this situation.
Does anybody have a working solution?
I found similar topic here in SO. Aliostad's answer made me think about this once more. You can never be sure you will get the signal from client that he's leaving. So I ended up with timeout solution.
Is it necessary to close the connection of a tcplistener or tcpclient after every message received, or is it possible to close it at a later time while it continues to receive data? Is there any major security issue with leaving it open and listening? I know trojans tend to open a listener and leave it open, will my program be detected as such? Its just a simple chat program....
Thanks for the help!
This is in vb.net.
It depends what the protocol is. If the protocol expects a new connection for each message, then you should close it. (This is like HTTP 1.0.)
If the protocol allows multiple messages to be sent down the same connection, then it's entirely reasonable to leave it open. (This is like HTTP 1.1 and most native database connections.)
I wouldn't expect your connection to be treated with undue suspicion just for keeping open.