封装一些函数使得通用

在使用时为了使得方法更加通用对代码进行优化

/* include sock_ntop */
char *
sock_ntop(const struct sockaddr *sa, socklen_t salen)
{
    char        portstr[8];
    static char str[128];       /* Unix domain is largest */

    switch (sa->sa_family) {
    case AF_INET: {
        struct sockaddr_in  *sin = (struct sockaddr_in *) sa;

        if (inet_ntop(AF_INET, &sin->sin_addr, str, sizeof(str)) == NULL)
            return(NULL);
        if (ntohs(sin->sin_port) != 0) {
            snprintf(portstr, sizeof(portstr), ":%d", ntohs(sin->sin_port));
            strcat(str, portstr);
        }
        return(str);
    }
/* end sock_ntop */
#ifdef  IPV6
    case AF_INET6: {
        struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *) sa;

        str[0] = '[';
        if (inet_ntop(AF_INET6, &sin6->sin6_addr, str + 1, sizeof(str) - 1) == NULL)
            return(NULL);
        if (ntohs(sin6->sin6_port) != 0) {
            snprintf(portstr, sizeof(portstr), "]:%d", ntohs(sin6->sin6_port));
            strcat(str, portstr);
            return(str);
        }
        return (str + 1);
    }
#endif
#ifdef  AF_UNIX
    case AF_UNIX: {
        struct sockaddr_un  *unp = (struct sockaddr_un *) sa;

            /* OK to have no pathname bound to the socket: happens on
               every connect() unless client calls bind() first. */
        if (unp->sun_path[0] == 0)
            strcpy(str, "(no pathname bound)");
        else
            snprintf(str, sizeof(str), "%s", unp->sun_path);
        return(str);
    }
#endif
#ifdef  HAVE_SOCKADDR_DL_STRUCT
    case AF_LINK: {
        struct sockaddr_dl  *sdl = (struct sockaddr_dl *) sa;

        if (sdl->sdl_nlen > 0)
            snprintf(str, sizeof(str), "%*s (index %d)",
                     sdl->sdl_nlen, &sdl->sdl_data[0], sdl->sdl_index);
        else
            snprintf(str, sizeof(str), "AF_LINK, index=%d", sdl->sdl_index);
        return(str);
    }
#endif
    default:
        snprintf(str, sizeof(str), "sock_ntop: unknown AF_xxx: %d, len %d",
                 sa->sa_family, salen);
        return(str);
    }
    return (NULL);
}
char *
Sock_ntop(const struct sockaddr *sa, socklen_t salen)
{
    char    *ptr;

    if ( (ptr = sock_ntop(sa, salen)) == NULL)
        err_sys("sock_ntop error"); /* inet_ntop() sets errno */
    return(ptr);
}

类似的我们还是可将其他的函数变得通用一些，字节流套接字上的read和write函数所表现的行为不同于通常的文件I/O。字节流套接字上调用read或write输入或输出的字节数可能比请求的数量少，然而这不是出错的状态。这个现象的原因在于内核中用于套接字的缓冲区可能已达到了极限。此时所需的事调用者再次调用read或write函数，以输入或输出剩余的字节。

#include "unp.h"
ssize_t readn(int filedes, void *buff, size_t nbytes);
ssize_t written(int filedes, const void *buff, size_t nbytes);
ssize_t readline(int filedes, void *buff, size_t maxlen);

ssize_t                     /* Read "n" bytes from a descriptor. */
readn(int fd, void *vptr, size_t n)
{
    size_t  nleft;
    ssize_t nread;
    char    *ptr;

    ptr = vptr;
    nleft = n;
    while (nleft > 0) {
        if ( (nread = read(fd, ptr, nleft)) < 0) {
            if (errno == EINTR)
                nread = 0;      /* and call read() again */
            else
                return(-1);
        } else if (nread == 0)
            break;              /* EOF */

        nleft -= nread;
        ptr   += nread;
    }
    return(n - nleft);      /* return >= 0 */
}
/* end readn */

ssize_t
Readn(int fd, void *ptr, size_t nbytes)
{
    ssize_t     n;

    if ( (n = readn(fd, ptr, nbytes)) < 0)
        err_sys("readn error");
    return(n);
}

ssize_t                     /* Write "n" bytes to a descriptor. */
writen(int fd, const void *vptr, size_t n)
{
    size_t      nleft;
    ssize_t     nwritten;
    const char  *ptr;

    ptr = vptr;
    nleft = n;
    while (nleft > 0) {
        if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
            if (nwritten < 0 && errno == EINTR)
                nwritten = 0;       /* and call write() again */
            else
                return(-1);         /* error */
        }

        nleft -= nwritten;
        ptr   += nwritten;
    }
    return(n);
}
/* end writen */

void
Writen(int fd, void *ptr, size_t nbytes)
{
    if (writen(fd, ptr, nbytes) != nbytes)
        err_sys("writen error");
}

static ssize_t
my_read(int fd, char *ptr)
{

    if (read_cnt <= 0) {
again:
        if ( (read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) {
            if (errno == EINTR)
                goto again;
            return(-1);
        } else if (read_cnt == 0)
            return(0);
        read_ptr = read_buf;
    }

    read_cnt--;
    *ptr = *read_ptr++;
    return(1);
}

ssize_t
readline(int fd, void *vptr, size_t maxlen)
{
    ssize_t n, rc;
    char    c, *ptr;

    ptr = vptr;
    for (n = 1; n < maxlen; n++) {
        if ( (rc = my_read(fd, &c)) == 1) {
            *ptr++ = c;
            if (c == '\n')
                break;  /* newline is stored, like fgets() */
        } else if (rc == 0) {
            *ptr = 0;
            return(n - 1);  /* EOF, n - 1 bytes were read */
        } else
            return(-1);     /* error, errno set by read() */
    }

    *ptr = 0;   /* null terminate like fgets() */
    return(n);
}

ssize_t
readlinebuf(void **vptrptr)
{
    if (read_cnt)
        *vptrptr = read_ptr;
    return(read_cnt);
}
/* end readline */

ssize_t
Readline(int fd, void *ptr, size_t maxlen)
{
    ssize_t     n;

    if ( (n = readline(fd, ptr, maxlen)) < 0)
        err_sys("readline error");
    return(n);
}