访问daytime服务

#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <unistd.h>
#include <assert.h>
#include <string.h>
#include <arpa/inet.h>


int main(int argc, char *argv[])
{
    // 命令hostname获取本地计算机名
    char* host = "localhost.localdomain";
    struct hostent* hostinfo = gethostbyname(host);

#if 1
    struct in_addr addr;
    addr.s_addr = inet_addr("10.12.129.189");

    // 16, AF_INET6 IPV6 16字节
    // 4, AF_INET   IPV4 4字节
    hostinfo = gethostbyaddr(&addr, 4, AF_INET);
#else
    hostinfo = gethostbyname(host);
#endif

    assert(hostinfo);
    struct servent* servinfo = getservbyname("daytime", "tcp");
    assert(servinfo);
    printf("daytime port is %d\n", ntohs(servinfo->s_port));

    struct sockaddr_in address = { 0 };
    address.sin_family = AF_INET;
    address.sin_port = servinfo->s_port;
    address.sin_addr = *(struct in_addr*)*hostinfo->h_addr_list;

    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    int result = connect(sockfd, (struct sockaddr*)&address, sizeof(address));
    assert(result != -1);

    char buffer[128] = { 0 };
    result = read(sockfd, buffer, sizeof(buffer));
    assert(result > 0);
    buffer[result] = '\0';
    printf("the day tiem is: %s", buffer);
    close(sockfd);
    return 0;
}