Rio包

// 读写网络套接字时，由于内部缓冲约束和较长的网络延迟会引起read和write返回不足值。
// Rio包可以解决上述问题进行健壮地读和写

#include <unistd.h>
#include <stdio.h>
#include <errno.h>

ssize_t rio_readn(int fd, void *usrbuf, size_t n)
{
    size_t nleft = n;
    ssize_t nread;
    char *bufp = usrbuf;

    while (nleft > 0)
    {
        if ((nread = read(fd, bufp, nleft)) < 0)
        {
            if (errno == EINTR)
            {
                nread = 0;
            }
            else
            {
                return -1;
            }
        }
        else if (nread == 0)
        {
            break;
        }

        nleft -= nread;
        bufp += nread;
    }

    return (n-nleft);
}

ssize_t rio_writen(int fd, void *usrbuf, size_t n)
{
    size_t nleft = n;
    ssize_t nwritten;
    char *bufp = usrbuf;

    while (nleft > 0)
    {
        if ((nwritten = write(fd, bufp, nleft)) <= 0)
        {
            if (errno == EINTR)
            {
                nwritten = 0;
            }
            else
            {
                return -1;
            }
        }

        nleft -= nwritten;
        bufp += nwritten;
    }

    return n;
}