|Subject:||Re: [lwip-users] Closing TCP connections|
|Date:||Sat, 02 Aug 2014 22:25:52 +0200|
|User-agent:||Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0|
Il 02/08/2014 20:52, Mark Lvov ha scritto:
This is one of the reason I wrote an "upper layer" to the raw functions to manage a tcp client connection.Hello, It seems, I still have some unanswered questions with regard to correct connection teardown. Let's consider the active close situation (we are closing the connection). We've just called tcp_closed and are waiting for the tcp_recv callback to be called with an empty pbuf. But, as I understand, if the remote side sends RST or does not send anything at all, the err handler will be called instead. The problem is, one does now know which particular connection (pcb) the callback is addressed to, because the callback function does not receive a pcb as an argument.
The idea is simple: create a struct to embed every information needed to manage a particular connection so I can pass it as the void *arg
that is also present in the error callback.
I think you can understand my idea just reading the struct I made:
STATE_NOT_CONNECTED = 0,
struct pbuf *pPbuf;
struct tcp_pcb *pPcb;
struct ip_addr tServerIpAddr;
the description field isn't necessary, I used it to debug in the simplest way my code.
Consider the scenario, when one needs to keep a connection open by reconnecting to the remote side whenever the connection is closed (either by the remote or the local side). It is all fine when the remote side closes the connection - we just receive a NULL pbuf, after that we can just call tcp_close on the "current" pcb, then immediately ask for the new pcb and reconnect. If, on the other hand, *we* want to close the connection (to reopen if afterwards), and call tcp_close, we might have the err callback called and then we won't really know if it means, that the current connection was terminated or some older connection, that maybe stuck in LAST_ACK finally timed out. Does this mean, that in such a situation, one has to keep only one err callback active at a time? It seems, the best course of action is to zero out the err callback on a pcb after calling on it tcp_close successfully (actually, its more like this: zero out the callback, then call tcp_close and if it fails reattach the callback, because we will have to wait a bit before calling tcp_close again). But then, once we call tcp_close, we have to start a timer (for, say, 5 seconds?) and if it runs out we consider the connection closed, remove all callbacks from that pcb and ask for the new one. Hopefully, I've managed to explain the problem I am facing. Sorry, that it took such a long message. Thanks, Mark On Fri, Aug 1, 2014 at 9:01 AM, Mark Lvov <address@hidden> wrote:Well, shame on me! I was actually using http://git.savannah.gnu.org/cgit/lwip.git/tree/doc/rawapi.txt?id=5b8b5d459e7dd890724515bbfad86c705234f9ec as a reference and it obviously lacks the details, that are present on the page you've linked. All my questions are answered by that page, thanks very much. Mark On Thu, Jul 31, 2014 at 10:01 PM, Sergio R. Caprile <address@hidden> wrote:Counter-proposal: Read the wiki, and if it is not clear enough, I will change it http://lwip.wikia.com/wiki/Raw/TCP Regards -- _______________________________________________ lwip-users mailing list address@hidden https://lists.nongnu.org/mailman/listinfo/lwip-users_______________________________________________ lwip-users mailing list address@hidden https://lists.nongnu.org/mailman/listinfo/lwip-users --- Questa e-mail è priva di virus e malware perché è attiva la protezione avast! Antivirus. http://www.avast.com
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