系统级I/O健壮性读程序

取自深入理解计算机系统第十一章

#include
#include
#include
#include
#include
#include
#include
#include
#include
/* rio with internal buf */
#define RIO_BUFSIZE 8192
typedef struct {
 int rio_fd;
int rio_cnt;
char *rio_bufptr;
char rio_buf[RIO_BUFSIZE];
} rio_t;

void rio_readinitb(rio_t *rp, int fd)
{
rp->rio_fd = fd;
rp->rio_cnt = 0;
rp->rio_bufptr = rp->rio_buf;
}
static ssize_t rio_read(rio_t *rp, char *usrbuf, size_t n)
{
int cnt;
while(rp->rio_cnt <= 0){
rp->rio_cnt = read(rp->rio_fd, rp->rio_buf, sizeof(rp->rio_buf));
if(rp->rio_cnt < 0 )
{
if(errno != EINTR)
return -1;
}
else if (rp->rio_cnt == 0) /* EOF */
return 0;
else
rp->rio_bufptr = rp->rio_buf;
}
cnt = n;
if(rp->rio_cnt < n)
cnt = rp->rio_cnt;
memcpy(usrbuf, rp->rio_bufptr, cnt);
rp->rio_bufptr += cnt;
rp->rio_cnt -= cnt;
return cnt;
}
ssize_t rio_readlineb(rio_t *rp, void *usrbuf, size_t maxlen)
{
int n, rc;
char c, *bufp = usrbuf;
for(n = 1; n < maxlen; n++)
{
if((rc = rio_read(rp, &c, 1)) == 1)
{
*bufp++ = c;
if(c == '\n')
 break;
}
else if(rc == 0)
{
if(n == 1)
return 0; /* EOF no data read */
else
break; /* EOF, some data was read */
}
else
return -1; /* error */
}
*bufp = 0;
return n;
}
ssize_t rio_readnb(rio_t *rp, void *usrbuf, size_t n)
{
size_t nleft = n;
ssize_t nread;
char *bufp = usrbuf;

while(nleft > 0)
{
if((nread = rio_read(rp, bufp, nleft)) < 0)
{
if(errno == EINTR)
nread = 0;
else
return -1;
}
else if(nread == 0)
break; /* EOF */
nleft -= nread;
bufp += nread;
}
return (n - nleft);
}
/* rio without internal buf */
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; /* EOF */
nleft -= nread;
bufp += nread;
}
return (n - nleft);
}
int main(int argc, char **argv)
{
int n;
rio_t rio;
char buf[100];
rio_readinitb(&rio, STDIN_FILENO);
while((n = rio_readlineb(&rio, buf, 100)) != 0)
write(STDOUT_FILENO, buf, n);
return 0;
}