UDP network programming for Unix domain sockets

For UDP network programming of Unix domain sockets, the server side is as follows:

#include <stdio.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include <sys/socket.h>#include <sys/types.h>#include <sys/un.h>#define SA struct sockaddr#define PATHNAME "/tmp/unixudp"void err_sys(const char *errmsg);int main(void){    int sockfd;    struct sockaddr_un servaddr, cliaddr;    char buf[BUFSIZ];    ssize_t n;    socklen_t len = sizeof(cliaddr);    if ((sockfd = socket(AF_LOCAL, SOCK_DGRAM, 0)) == -1)        err_sys("socket");    bzero(&servaddr, sizeof(servaddr));    unlink(PATHNAME);    servaddr.sun_family = AF_LOCAL;    strncpy(servaddr.sun_path, PATHNAME, sizeof(servaddr.sun_path) - 1);    if (bind(sockfd, (SA *)&servaddr, sizeof(servaddr)) == -1)        err_sys("bind");    for(;;){        n = recvfrom(sockfd, buf, sizeof(buf), 0, (SA *)&cliaddr, &len);        if (n == -1)            err_sys("recvfrom");        else            printf("%s\n", buf);        if (sendto(sockfd, buf, n, 0, (SA *)&cliaddr, sizeof(cliaddr)) != n)            err_sys("sendto");    }    exit(0);}void err_sys(const char *errmsg){    perror(errmsg);    exit(1);}

Client Program:

#include <stdio.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include <sys/socket.h>#include <sys/types.h>#include <sys/un.h>#define SA struct sockaddr#define PATHNAME "/tmp/unixudp"void err_sys(const char *errmsg);int main(void){    int sockfd;    struct sockaddr_un servaddr, localaddr;    char buf[BUFSIZ], s[] = "hello china";    ssize_t n;    if ((sockfd = socket(AF_LOCAL, SOCK_DGRAM, 0)) == -1)        err_sys("socket");    bzero(&localaddr, sizeof(localaddr));    localaddr.sun_family = AF_LOCAL;    strncpy(localaddr.sun_path, tmpnam(NULL), sizeof(localaddr.sun_path) - 1);    if (bind(sockfd, (SA *)&localaddr, sizeof(localaddr)) == -1)        err_sys("bind");    bzero(&servaddr, sizeof(servaddr));    servaddr.sun_family = AF_LOCAL;    strncpy(servaddr.sun_path, PATHNAME, sizeof(servaddr.sun_path) - 1);    for(;;){        if (sendto(sockfd, s, strlen(s), 0, (SA *)&servaddr, sizeof(servaddr)) == -1)            err_sys("sendto");        if ((n = read(sockfd, buf, sizeof(buf))) == -1)            err_sys("read");        else             printf("%s\n", buf);        usleep((rand() % 10) * 10000);    }    exit(0);}void err_sys(const char *errmsg){    perror(errmsg);    exit(1);}

UDP network programming for Unix domain sockets