Unix-Linux编程实践教程-chapter13-udp

/*
 * dgram.c
 * support functions for datagram based programs
 */

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

#define HOSTLEN 256

int make_internet_address();

int make_dgram_server_socket(int portnum)
{
    struct sockaddr_in saddr;
    char hostname[HOSTLEN];
    int sock_id;

    sock_id = socket(PF_INET, SOCK_DGRAM, 0);
    if (sock_id == -1)
        return -1;

    gethostname(hostname, HOSTLEN);
    make_internet_address(hostname, portnum, &saddr);

    if (bind(sock_id, (struct sockaddr *)&saddr, sizeof(saddr)) != 0)
        return -1;

    return sock_id;
}

int make_dgram_client_socket()
{
    return socket(PF_INET, SOCK_DGRAM, 0);
}

int make_internet_address(char *hostname, int port, struct sockaddr_in *addrp)
{
    struct hostent * hp;

    bzero((void*)addrp, sizeof(struct sockaddr_in));
    hp = gethostbyname(hostname);
    if (hp == NULL)
        return -1;

    bcopy((void*)hp->h_addr, (void*)&addrp->sin_addr, hp->h_length);
    addrp->sin_port = htons(port);
    addrp->sin_family = AF_INET;
    return 0;
}

int get_internet_address(char *host, int len, int *portp, struct sockaddr_in *addrp)
{
    strncpy(host, inet_ntoa(addrp->sin_addr), len);
    *portp = ntohs(addrp->sin_port);
    return 0;
}