Socket Connectivity

[JCst]

Just start using&nbsp;&nbsp;Visual C++.<br>I detect socket connectivity with Host using 'Select' before sending a data from client (act as Middleware) Client-M-Host, <br>&nbsp;&nbsp;&nbsp;<br>&nbsp;&nbsp;&nbsp;&nbsp;FD_ZERO( &f_set );<br>&nbsp;&nbsp;&nbsp;&nbsp;FD_SET( sock, &f_set );<br>&nbsp;&nbsp;&nbsp;&nbsp;if( (res = select( sock + 1, NULL, &f_set,&nbsp;&nbsp;&nbsp;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;NULL, &timeout )) != 1 ) <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return 1;&nbsp;&nbsp;&nbsp;// Socket Closed <br>&nbsp;&nbsp;&nbsp;&nbsp;return 0;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Socket still Connect<br><br>but the result is not good; it can't detect although remote host already closed the socket. Is there any other way to detect connectivity beetwen M-Host?<br>Without send the data first <br><br>Thanks

 

[palbano]

Dear JCst,<br><br>In your code:<br>FD_SET( sock, &f_set );<br><br>where did you get the variable 'sock' and how did you initialize it?<br><br>-pete

 

[JCst]

Thanks for replying me,<br>I init the variable sock like below :<br>&nbsp;&nbsp;Socket Sock;<br><br>&nbsp;&nbsp;sock = socket( AF_INET, SOCK_STREAM, 0 );<br>&nbsp;&nbsp;if (sock == INVALID_SOCKET) {<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*retErrVal = SGetLastError();<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return( 0 );<br>&nbsp;&nbsp;}<br><br>&nbsp;&nbsp;memset( &addr, 0, sizeof( addr ));<br>&nbsp;&nbsp;addr.sin_family = AF_INET;<br>&nbsp;&nbsp;addr.sin_port = htons( (unsigned short) port );<br>&nbsp;&nbsp;addr.sin_addr.s_addr = inet_addr( IPAddress );<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;res = connect( sock, (struct sockaddr *) &addr, <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sizeof( addr ) );<br>&nbsp;&nbsp;if (res == SOCKET_ERROR) {<br>&nbsp;&nbsp;&nbsp;&nbsp;*retErrVal = SGetLastError();<br>&nbsp;&nbsp;&nbsp;&nbsp;closesocket( sock );<br>&nbsp;&nbsp;&nbsp;&nbsp;return( 0 );<br>&nbsp;&nbsp;}<br>&nbsp;&nbsp;....&nbsp;&nbsp;<br>&nbsp;&nbsp;&nbsp;timeout.tv_sec = 0;<br>&nbsp;&nbsp;&nbsp;timeout.tv_usec = 1;<br>&nbsp;&nbsp;&nbsp;FD_ZERO( &f_set );<br>&nbsp;&nbsp;&nbsp;FD_SET( sock, &f_set );<br>&nbsp;&nbsp;&nbsp;if( (res = select( sock + 1, NULL, &f_set,&nbsp;&nbsp;&nbsp;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;NULL, &timeout )) != 1 ) <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return 1;&nbsp;&nbsp;&nbsp;// Socket Closed <br>&nbsp;&nbsp;&nbsp;return 0;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Socket still Connect<br><br>sorry, I write down not the complete version , it'll be long. <br><br>But do I use the correct statement :<br>&nbsp;&nbsp;* 'select' the socket for the write_set<br><br>on purpose to simulate 'ping' socket just like ping an address without send any data to the client/server<br><br>Thanks a lot

 

[palbano]

Dear JCst,<br><br>In this code:<br><br>if( (res = select( sock + 1, NULL, &f_set,&nbsp;&nbsp;&nbsp;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;NULL, &timeout )) != 1 ) <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return 1;&nbsp;&nbsp;&nbsp;// Socket Closed <br>&nbsp;&nbsp;&nbsp;return 0;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Socket still Connect<br><br><br>select() can return the number of sockets that are ready to read or write or it can return SOCKET_ERROR. So you should be checking for that and when found use WSAGetLastError() to find out the specific error that is occuring.<br><br>-pete

 

[AmiTavory]

<br>Hello,<br><br>Here is a tentative suggestion: it seems to me you did not add the socket to the &quot;exception&quot; fds (it is NULL in your code). Perhaps you could change that, and chek, via FD_ISSET the &quot;exception&quot; fds?<br><br>All the Best,<br><br>Ami Tavory <br>

 

[JCst]

Thanks Pete (Palbano) <br>Thanks Ami Tavory<br><br>I'll try your suggestion first.<br><br>By the way, anyone know Socket programming books or any link that provide a lot of stuffs about socket programming.<br><br>PS I'm not a single 'fighter' know, I've tek-tips.