LWIP 1.3.2 建立一个TCP服务端，客户端非正常断开问题。

发布于 2013-10-30 19:30:12 浏览：8643 订阅该版

4 个回答

jlb555 2013-11-01

这家伙很懒，什么也没写！

问题已解决：
首先感谢好好微笑，在搜狐博文中的work栏中的一文（LWIP中使用keep_alive），解决了我在处理TCP非正常断线困惑了已久的问题，由衷感谢！现转载一下，一是为了记录一下，在下次遇见同样问题时可参考处理，二是帮助其他同仁，以免遇见类似情况。
链接来自：http://haohaoweixiao.blog.sohu.com/161392118.html

>Please finish lwIP TCP workshop  before trying this one
>
>Keepalive is an important feature in TCP connection to make sure we don't lose the link. For more info regarding keepalive in TCP, please visit Wikipedia.
>
>Use the codes in  lwIP TCP workshop to create a TCP echo server first
>In lwipopts.h, add "#define LWIP_TCP_KEEPALIVE 1"
>In tcp.h, modify the timing parameters according to your application. We chose the following for shorter time.
>TCPKEEPINTVL_DEFAULT to 3000UL (default was 7200000UL)
>TCP_KEEPCNT_DEFAULT to 1000UL (default was 75000UL) 
>TCP_KEEPCNT_DEDAULT to 3U (default was 9U) 
>Bring lwip_socket definition from sockets.c to sockets.h so that we can use it in the TCP thread
>Add the follow lines after lwip_socket:
>struct lwip_socket *sock=get_socket(lSocket);
>struct netconn* myconn = sock->conn;
>myconn->pcb.tcp->so_options |= SOF_KEEPALIVE;
>Due to a bug in lwIP, the following patch is necessary until next release of lwIP, refer to [https://savannah.nongnu.org/bugs/?25629](https://savannah.nongnu.org/bugs/?25629):
>In src/core/tcp_out.c:tcp_keepalive(), locate the following lines
>tcphdr->ackno = htonl(pcb->rcv_nxt); 
>TCPH_FLAGS_SET(tcphdr, 0); 
>tcphdr->wnd = htons(pcb->rcv_ann_wnd); 
>tcphdr->urgp = 0;
>Replace with:
>tcphdr->ackno = htonl(pcb->rcv_nxt); 
>TCPH_FLAGS_SET(tcphdr, TCP_ACK); 
>tcphdr->wnd = htons(pcb->rcv_ann_wnd + 1); 
>tcphdr->urgp = 0;
>Add a call to tcp_tmr() every 250ms
>Build and run
>Telnet to it
>To verify keepalive,  run Wireshark. If you don't type anything for 3 seconds (defined by TCPKEEPINTVL_DEFAULT), keepalive packet be sent out once a second (defined by TCP_KEEPCNT_DEFAULT) will by lwIP, and the PC will ACK the keepalive packet.
>If you remove the ethernet cable, thus the lwIP will not receive the ACK from the PC. After 3 tries (defined by TCP_KEEPCNT_DEDAULT), lwIP will close the connection
>Find out how to upgrade to the latest lwIP

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