Hello Peter,
On 08/11/2016 03:23 AM, Peter Wu wrote:
Avoid closing cfd if it is -1. Initialize buf1_avail, etc. to avoid
uninitialized memory access in the event that accept() fails. Remove
redundant setting of nfds. Fix tabs with spaces.
Do not try to read/write from/to file descriptors once an existing
connection is overwritten, the select() states are stale now.
Avoid writing zero bytes from the buffer and then closing the fd.
Thanks for these clean-ups! Patch applied.
Cheers,
Michael
Signed-off-by: Peter Wu <peter@xxxxxxxxxxxxx>
---
man2/select_tut.2 | 38 ++++++++++++++++++--------------------
1 file changed, 18 insertions(+), 20 deletions(-)
diff --git a/man2/select_tut.2 b/man2/select_tut.2
index 25dd3c6..7e4f41d 100644
--- a/man2/select_tut.2
+++ b/man2/select_tut.2
@@ -594,7 +594,6 @@ connect_socket(int connect_port, char *address)
cfd = socket(AF_INET, SOCK_STREAM, 0);
if (cfd == \-1) {
perror("socket");
- close(cfd);
return \-1;
}
@@ -641,8 +640,8 @@ main(int argc, char *argv[])
int h;
int fd1 = \-1, fd2 = \-1;
char buf1[BUF_SIZE], buf2[BUF_SIZE];
- int buf1_avail, buf1_written;
- int buf2_avail, buf2_written;
+ int buf1_avail = 0, buf1_written = 0;
+ int buf2_avail = 0, buf2_written = 0;
if (argc != 4) {
fprintf(stderr, "Usage\\n\\tfwd <listen\-port> "
@@ -660,7 +659,7 @@ main(int argc, char *argv[])
for (;;) {
int ready, nfds = 0;
- ssize_t nbytes;
+ ssize_t nbytes;
fd_set readfds, writefds, exceptfds;
FD_ZERO(&readfds);
@@ -668,22 +667,18 @@ main(int argc, char *argv[])
FD_ZERO(&exceptfds);
FD_SET(h, &readfds);
nfds = max(nfds, h);
- if (fd1 > 0 && buf1_avail < BUF_SIZE) {
+
+ if (fd1 > 0 && buf1_avail < BUF_SIZE)
FD_SET(fd1, &readfds);
- nfds = max(nfds, fd1);
- }
- if (fd2 > 0 && buf2_avail < BUF_SIZE) {
+ /* Note: nfds is updated below, when fd1 is added to exceptfds. */
+ if (fd2 > 0 && buf2_avail < BUF_SIZE)
FD_SET(fd2, &readfds);
- nfds = max(nfds, fd2);
- }
- if (fd1 > 0 && buf2_avail \- buf2_written > 0) {
+
+ if (fd1 > 0 && buf2_avail \- buf2_written > 0)
FD_SET(fd1, &writefds);
- nfds = max(nfds, fd1);
- }
- if (fd2 > 0 && buf1_avail \- buf1_written > 0) {
+ if (fd2 > 0 && buf1_avail \- buf1_written > 0)
FD_SET(fd2, &writefds);
- nfds = max(nfds, fd2);
- }
+
if (fd1 > 0) {
FD_SET(fd1, &exceptfds);
nfds = max(nfds, fd1);
@@ -706,9 +701,9 @@ main(int argc, char *argv[])
if (FD_ISSET(h, &readfds)) {
socklen_t addrlen;
struct sockaddr_in client_addr;
- int fd;
+ int fd;
- addrlen = sizeof(client_addr);
+ addrlen = sizeof(client_addr);
memset(&client_addr, 0, addrlen);
fd = accept(h, (struct sockaddr *) &client_addr, &addrlen);
if (fd == \-1) {
@@ -725,6 +720,9 @@ main(int argc, char *argv[])
else
printf("connect from %s\\n",
inet_ntoa(client_addr.sin_addr));
+
+ /* Skip any events on the old, closed file descriptors. */
+ continue;
}
}
@@ -764,7 +762,7 @@ main(int argc, char *argv[])
else
buf2_avail += nbytes;
}
- if (fd1 > 0 && FD_ISSET(fd1, &writefds)) {
+ if (fd1 > 0 && FD_ISSET(fd1, &writefds) && buf2_avail > 0) {
nbytes = write(fd1, buf2 + buf2_written,
buf2_avail \- buf2_written);
if (nbytes < 1)
@@ -772,7 +770,7 @@ main(int argc, char *argv[])
else
buf2_written += nbytes;
}
- if (fd2 > 0 && FD_ISSET(fd2, &writefds)) {
+ if (fd2 > 0 && FD_ISSET(fd2, &writefds) && buf1_avail > 0) {
nbytes = write(fd2, buf1 + buf1_written,
buf1_avail \- buf1_written);
if (nbytes < 1)
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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