On 10/12/2020 2:02 PM, Ken Brown via Cygwin-patches wrote:
It looks to me like there's been a bug in the MSG_WAITALL support for
AF_INET and AF_LOCAL sockets ever since that support was first
introduced 13 years ago in commit 023a2fa7. If I'm right, MSG_WAITALL
has never worked.
This patch fixes it. I'll push it in a few days if no one sees
anything wrong with it.
In a followup email I'll show how I tested it.
Attached are slight variants of the server/client programs from Section 57.2 of
Kerrisk's book, "The Linux Programming Interface". The only essential
difference is that I've changed the server program to (a) use a small buffer
(size 10 instead of 100) and (b) use 'recv' with the MSG_WAITALL flag instead of
'read'. The 'recv' call shouldn't return until it reads 10 bytes.
To test, run waitall_sv in one terminal and waitall_cl in a second. Type
something in the second terminal (followed by RET), and it should be echoed in
the first. But because of the MSG_WAITALL flag, the echoing shouldn't occur
until 10 bytes have been written. For example, if I type "abcd<RET>" in the
second terminal and then do it again, I should see the following:
# Terminal 2:
$ ./waitall_cl
abcd
abcd
# Terminal 1:
$ ./waitall_sv
abcd
abcd
Here the echoing in Terminal 1 shouldn't occur until I've typed both "abcd"
lines in Terminal 2.
[Note that there is a newline character after each "abcd", so "abcd<RET>" is 5
bytes long, and the two lines together are 10 bytes long.]
Before I apply my patch, each line typed in Terminal 2 is immediately echoed in
Terminal 1. After I apply the patch, the echoing doesn't occur until I've typed
both lines.
Ken
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/un.h>
#include <sys/socket.h>
#define SV_SOCK_PATH "/tmp/waitall"
#define BUF_SIZE 10
#define BACKLOG 5
int
main ()
{
struct sockaddr_un addr;
int sfd, cfd;
ssize_t nread;
char buf[BUF_SIZE];
if ((sfd = socket (AF_UNIX, SOCK_STREAM, 0)) < 0)
{
perror ("socket");
exit (1);
}
if (remove (SV_SOCK_PATH) < 0 && errno != ENOENT)
{
perror ("remove");
exit (1);
}
memset (&addr, 0, sizeof (struct sockaddr_un));
addr.sun_family = AF_UNIX;
strncpy (addr.sun_path, SV_SOCK_PATH, sizeof (addr.sun_path) - 1);
if (bind (sfd, (struct sockaddr *) &addr, sizeof (struct sockaddr_un)) < 0)
{
perror ("bind");
exit (1);
}
if (listen (sfd, BACKLOG) < 0)
{
perror ("listen");
exit (1);
}
while (1)
{
cfd = accept (sfd, NULL, NULL);
if (cfd < 0)
{
perror ("accept");
exit (1);
}
/* Transfer data from connected socket to stdout until EOF. */
while ((nread = recv (cfd, buf, BUF_SIZE, MSG_WAITALL)) > 0)
if (write (STDOUT_FILENO, buf, nread) != nread)
{
perror ("partial/failed write");
exit (1);
}
if (nread < 0)
{
perror ("read");
exit (1);
}
if (close (cfd) < 0)
{
perror ("close");
exit (1);
}
}
}
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/un.h>
#include <sys/socket.h>
#define SV_SOCK_PATH "/tmp/waitall"
#define BUF_SIZE 100
int
main ()
{
struct sockaddr_un addr;
int sfd;
ssize_t nread;
char buf[BUF_SIZE];
if ((sfd = socket (AF_UNIX, SOCK_STREAM, 0)) < 0)
{
perror ("socket");
exit (1);
}
memset (&addr, 0, sizeof(struct sockaddr_un));
addr.sun_family = AF_UNIX;
strncpy (addr.sun_path, SV_SOCK_PATH, sizeof(addr.sun_path) - 1);
if (connect (sfd, (struct sockaddr *) &addr,
sizeof (struct sockaddr_un)) < 0)
{
perror ("connect");
exit (1);
}
/* Copy stdin to socket. */
while ((nread = read (STDIN_FILENO, buf, BUF_SIZE)) > 0)
if (write (sfd, buf, nread) != nread)
{
perror ("partial/failed write");
exit (1);
}
if (nread < 0)
{
perror ("read");
exit (1);
}
}
