socket.c

socket.cc

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <fcntl.h>
#include <errno.h>

int main(int argc, char **argv)
{
    if (argc < 3) {
        printf("please input ip and port, for example ./main 120.12.34.56 80.\n");
        return -1;
    }

    
    char *ipaddr = argv[1];
    unsigned int port = atoi(argv[2]);

    int fd = 0;
    struct sockaddr_in  addr;
    fd_set fdr, fdw;
    struct timeval timeout;
    int err = 0;
    int errlen = sizeof(err);

    fd = socket(AF_INET,SOCK_STREAM,0);
    if (fd < 0) {
        fprintf(stderr, "create socket failed,error:%s.\n", strerror(errno));
        return -1;
    }

    bzero(&addr, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(port);
    inet_pton(AF_INET, ipaddr, &addr.sin_addr);

    /*设置套接字为非阻塞*/
    int flags = fcntl(fd, F_GETFL, 0);
    if (flags < 0) {
        fprintf(stderr, "Get flags error:%s\n", strerror(errno));
        close(fd);
        return -1;
    }
    flags |= O_NONBLOCK;
    if (fcntl(fd, F_SETFL, flags) < 0) {
        fprintf(stderr, "Set flags error:%s\n", strerror(errno));
        close(fd);
        return -1;
    }

    /*阻塞情况下linux系统默认超时时间为75s*/
    int rc = connect(fd, (struct sockaddr*)&addr, sizeof(addr));
    if (rc != 0) {
        if (errno == EINPROGRESS) {
            printf("Doing connection.\n");
            /*正在处理连接*/
            FD_ZERO(&fdr);
            FD_ZERO(&fdw);
            FD_SET(fd, &fdr);
            FD_SET(fd, &fdw);
            timeout.tv_sec = 10;
            timeout.tv_usec = 0;
            rc = select(fd + 1, &fdr, &fdw, NULL, &timeout);
            printf("rc is: %d\n", rc);
            /*select调用失败*/
            if (rc < 0) {
                fprintf(stderr, "connect error:%s\n", strerror(errno));
                close(fd);
                return -1;
            }
            
            /*连接超时*/
            if (rc == 0) {
                fprintf(stderr, "Connect timeout.\n");
                close(fd);
                return -1;
            }
            /*[1] 当连接成功建立时，描述符变成可写,rc=1*/
            if (rc == 1 && FD_ISSET(fd, &fdw)) {
                printf("Connect success\n");
                close(fd);
                return 0;
            }
            /*[2] 当连接建立遇到错误时，描述符变为即可读，也可写，rc=2 遇到这种情况，可调用getsockopt函数*/
            if (rc == 2) {
                if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &errlen) == -1) {
                    fprintf(stderr, "getsockopt(SO_ERROR): %s", strerror(errno));
                    close(fd);
                    return -1;

                }

                if (err) {
                    errno = err;
                    fprintf(stderr, "connect error:%s\n", strerror(errno));
                    close(fd);
                    return -1;

                }
            }

        } 
        fprintf(stderr, "connect failed, error:%s.\n", strerror(errno));
        return -1;
    } 
    return 0;
}