Linux socket tcp

linux tcp客户端示例代码

    struct sockaddr_i n servaddr;
    int ret, flags;

    ble_agent_sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (ble_agent_sockfd == -1) {
        LOG_ERR("%s: socket creation failed...\n", __func__);
        return -1;
    }

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family      = AF_INET;
    servaddr.sin_port        = htons(LOCAL_SERVER_PORT);
    servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
    ret = connect(ble_agent_sockfd, (struct sockaddr*)&servaddr, sizeof(struct sockaddr));
    if (0 != ret) {
        LOG_ERR("%s: connect failed, %d\n", __func__, ret);
        return ret;
    }

    // set no-block mode
    flags = fcntl(ble_agent_sockfd, F_GETFL, 0);
    ret = fcntl(ble_agent_sockfd, F_SETFL, flags | O_NONBLOCK);
    if (0 != ret) {
        LOG_ERR("%s: fcntl() failed, %d\n", __func__, ret);
        return ret;
    }

错误：“bind() fail, Address already in use”

用netstat命令即可知道情况，可能是：

1. 已经有程序使用这个端口了；

2. 端口处于close_wait状态，参考https://web.archive.org/web/20170113135705/http://unix.derkeiler.com/Mailing-Lists/SunManagers/2006-01/msg00367.html，可能是因为连接已经FIN但应用程序没有响应并close掉fd；

3. 程序可能处于 time_wait 状态，可以等，或者用 SO_REUSEADDR（似乎不管用）；/proc/sys/net/ipv4/tcp_fin_timeout；或者设置SO_LINGER（似乎有效）：

struct linger sl;
sl.l_onoff = 1;      /* non-zero value enables linger option in kernel */
sl.l_linger = 0; /* timeout interval in seconds */
setsockopt(sockfd, SOL_SOCKET, SO_LINGER, &sl, sizeof(sl));

socket keepalive的opt设置

  setsockopt(_nSock, SOL_SOCKET, SO_KEEPALIVE, (void *)&keepAlive, sizeof(keepAlive));
  setsockopt(_nSock, SOL_TCP, TCP_KEEPIDLE, (void*)&keepIdle, sizeof(keepIdle));
  setsockopt(_nSock, SOL_TCP, TCP_KEEPINTVL, (void *)&keepInterval, sizeof(keepInterval));
  setsockopt(_nSock, SOL_TCP, TCP_KEEPCNT, (void *)&keepCount, sizeof(keepCount));
  int flags  = fcntl(_nSock,F_GETFL,0);
  logger->debug("SocketIO::connect flag:%d",flags);
  fcntl(_nSock,F_SETFL,flags&~O_NONBLOCK);

socket 指定网卡发包

#include <net/if.h>

struct ifreq ifr;
memset(&ifr, 0x00, sizeof(ifr));
strncpy(ifr.ifr_name, interface, strlen(interface));
setsockopt(_nSock, SOL_SOCKET, SO_BINDTODEVICE, (char *)&ifr, sizeof(ifr));

阻塞式socket设置超时时间

  {
    int ret = 0;
    struct timeval timeout;
    timeout.tv_sec = 5;
    timeout.tv_usec = 0;
    socklen_t len = sizeof(timeout);
    do {
      ret = setsockopt(_nSock, SOL_SOCKET, SO_SNDTIMEO, &timeout, len);
      CC_BREAK_IF(ret < 0);
      ret = setsockopt(_nSock, SOL_SOCKET, SO_RCVTIMEO, &timeout, len);
      CC_BREAK_IF(ret < 0);
    } while(0);
    if (ret < 0) {
        logger->error("Error when setsockopt: [%d]%s", errno, strerror(errno));
        return FALSE;
    }
  }