[ECOS] RE : I lose sockets

["Goldschmidt Simon" <sgoldschmidt@de.pepperl-fuchs.com>]

 Hi Roger,

>> You have the basic TCP server structure wrong. You should create one
listen'ing socket and then keep it for
>> ever, repeatadly doing accept() on it as each client connects. ie you
don't need a listening socket per
>> connection.


>Now I've made the following structure (simplistic)

>socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); bind(hmiParameter->IPsocket,
(struct sockaddr *) &local, sizeof(local));
listen(hmiParameter->IPsocket, SOMAXCONN);
>
>Connect: accept(hmiParameter->IPsocket, (struct sockaddr
*)&client_addr,
>&x))
>while(true) {
>	select(hmiParameter->client + 1, &in_fds, 0, 0, &tv);
>	if(read(hmiParameter->client, buf, sizeof(buf)-1) <= 0) {
>		goto Connect;
>	}
>}
>
>( remark: close(hmiParameter->IPsocket) will never be called )

TCP state machine needs the client to close a connection first, before
the server closes it.
Otherwise sockets must stay in a half-open state for 3 minutes. If you
ensure the client closes the connection first, this code would make sure
you don't loose sockets:

int listen_sock=-1;
int client_sock=-1;
...
listen(listen_sock, ..);
...
while(true)
{
   client_sock = accept(listen_sock ,...);
   // now, the actual connection:
   recv(client_sock, ..);
   send(client_sock, ..);
   ... // some more communication...
   
   // and if the client finally wants to disconnect:
   close(client_sock);
}

Closing a connection from the server side first won't fail, but you
'loose' sockets (for some minutes) because they stay in TIME_WAIT state.

Hope this is an answer to your problem.

Simon.

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