mitzi

Hello,

I need to implement TCP client(s) in thread(s) with reconnect feature (if connection is closed with error then client tries to reconnect) which should run in service. I created server and client demo app to test this concept but I met following issues and I'm really not able to find out what's wrong in my implementation.

1.  When I run server, start it and start internal client (client implemented the same exe) server throws "error:00000000:lib(0):func(0):reason(0), State: before SSL initialization, connection closed unexpectedly" in OnSslHandshakeDone and disconnects client. When I start (the same) client as standalone exe, it works.
2. When I run and start server, then run and start standalone client and then kill server app (to simulate connection error) client starts to reconnect and when server is started again TWO client connections are established (!?) from client application. The second one is correct and the first one is some ghost or whatever.
3. Sometimes while client tries to reconnect after text is received from server or sent to server, first connection attempt causes various exceptions and client thread is terminated.

Can you please inspect my code in attachment? Test self-signed certificate for SSL is included (SSC.pfx).

Thanks in advance

ICSTCP.ZIP

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It's a pitty. It could be perfect for webhook implementation.

ICS v8.63

Hi,

Is TSimpleWebSrv able to process POST request with some data (JSON) in body?

GET works as expected but POST returns (to Postman) 404 and OnSimpWebSrvReq event is not triggered.

Thanks

Of course I did. But when i set TimeoutConnect either to 5 or 5000 OnTimeout event was triggered after 3-4 seconds after Connect was called regardless of TimeoutConnect value. So I'm a little confused.

Thanks, that's it. And timeout is defined in seconds or milliseconds?

hm, i'm trying, but despite the fact I have BUILTIN_TIMEOUT defined, property TimeoutConnect has no effect 😞

What is scale? Seconds or milliseconds?

Well but this is what I ask for. How did you (or others) solve this scenario? Your suggestion is ping. Well, when ping is successful it tells me nothing about my TCP server, if it is running and listening or not. Other suggestion is to abort connection attempt with timer. But it creates new problem with socket reusing. So what?

It seems there's no useful advice. I will try to make my own port scan via WinSock.Select with timeout set to 5 secs (as I did in my post above for Delphi Socket component) before TWSocket.Connect. Disadvantage is when server is on, then i will do two connection attempts. First by port scan and second with real client connect.  Another one is that this is blocking attempt. 😞

Anyone has better solution?

If client connect attempt to primary server fails, it needs immediately to connect to another one. If socket is in use even after timer 'breaks' connection attempt by Abort, then next immediate attempt will fail too due to socket is in use, won't it?

Your suggestions are no usable. ICMP is security issue and it is no allowed in our environment. Also it only checks IP address accessibility. Not TCP server itself. Other suggestions does not allow the socket to be immediately reused for new connection attempt. 

Do you really think my request is so stupid?

No I don't have this intent. I found ICS very usable, but this is, in my opinion, key property ICS should have.

I just wanted to point that this timeout is possible to be set. You wrote it is not possible by design. It seems it is not true.

So my question is whether it is possible to implement this timeout setting to ICS?

Consider this situation. I have primary TCP server and backup TCP server. Clients are connected to primary one. If this primary server goes down for any reason, then client loses connection and tries to reconnect. But it can take 20 secs now than it finds server is really inaccessible and then connects to backup server. This reconnection should be as short as possible. Mostly if client is not able to connect within 5 secs server can be considered as inaccessible and then connection to another backup server is processed. But 20 secs is really too long.

Your recommendations how to solve this problem when connection timeout cannot be set?

If ICS uses WinSock.Select for connection then timeout can be set via latest parameter.

Look at following code sample. I modified method from Delphi System.Win.ScktComp.pas and it does exactly what I want. Sets timeout for connection attempt to 5 secs. Originally it took 20 secs too. But I can't use these components :(.

procedure TCustomWinSocket.DoOpen;
var
  v: integer;
  WrSet   : TFDSet;
  TimeVal : TTimeVal;
begin
  DoSetASyncStyles;
  Event(Self, seConnecting);

  v:=1;
  IOCtlSocket(FSocket,FIONBIO,v);
  try
    CheckSocketResult(Winapi.WinSock.connect(FSocket, FAddr, SizeOf(FAddr)),'connect');
    TimeVal.tv_sec:=5;
    TimeVal.tv_usec:=0;
    FD_ZERO(WrSet);
    FD_SET(FSocket,WrSet);
    if Select(0,nil,@WrSet,nil,@TimeVal)<>1 then
      CheckSocketResult(1,'select');
  finally
    v:=0;
    IOCtlSocket(FSocket,FIONBIO,v);
  end;

  FLookupState := lsIdle;
  if not (asConnect in FAsyncStyles) then
  begin
    FConnected := FSocket <> INVALID_SOCKET;
    Event(Self, seConnect);
  end;
end;

Couldn't be something like this implemented to ICS?

Another question: Is there some timeout for connection attempt? When TWSocket tries to connect to server and server does not exist (non-existing ip address or non-listening server) it takes 20 secs than OnSessionClosed is triggered. Can this timeout be changed/set?

Thanks for your support

Is it possible to use TSslWSocketThrdClient descendant instead of TSslWSocket on client side? I tried and it worked except one thing. OnSessionClosed is triggered only once and then never again. 

Well. Maybe we dont understand each other. How can I recognize that tcp client is connected to server? On client side? There’s no property except State. 

I'm talking about client states, not server.

Sequence is taken from TSslWSocket.OnChangeState event.