readn、readline与writen

因为TCP是基于流的传输，会产生粘包现象，为解决这个问题，重新封装了read和write函数，以后要用可以直接调用。

/**
 * readn - 读取固定字节数
 * @fd: 文件描述符
 * @buf: 接收缓冲区
 * @count: 要读取的字节数
 * 成功返回count，失败返回-1，读到EOF返回<count
 */
ssize_t readn(int fd, void *buf, size_t count)
{
size_t nleft = count;
ssize_t nread;
char *bufp = (char*)buf;


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


bufp += nread;
nleft -= nread;
}


return count;
}

/**
 * readline - 按行读取数据
 * @sockfd: 套接字
 * @buf: 接收缓冲区
 * @maxline: 每行最大长度
 * 成功返回>=0，失败返回-1
 */
ssize_t readline(int sockfd, void *buf, size_t maxline)
{
int ret;
int nread;
char *bufp = buf;
int nleft = maxline;
while (1)
{
ret = recv_peek(sockfd, bufp, nleft);
if (ret < 0)
return ret;
else if (ret == 0)
return ret;


nread = ret;
int i;
for (i=0; i<nread; i++)
{
if (bufp[i] == '\n')
{
ret = readn(sockfd, bufp, i+1);
if (ret != i+1)
exit(EXIT_FAILURE);


return ret;
}
}


if (nread > nleft)
exit(EXIT_FAILURE);


nleft -= nread;
ret = readn(sockfd, bufp, nread);
if (ret != nread)
exit(EXIT_FAILURE);


bufp += nread;
}


return -1;
}

/**
 * writen - 发送固定字节数
 * @fd: 文件描述符
 * @buf: 发送缓冲区
 * @count: 要读取的字节数
 * 成功返回count，失败返回-1
 */
ssize_t writen(int fd, const void *buf, size_t count)
{
size_t nleft = count;
ssize_t nwritten;
char *bufp = (char*)buf;


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


bufp += nwritten;
nleft -= nwritten;
}


return count;
}