Try to detect and remove stale sockets when dtach -A is used. Be

paranoid about this, and only remove the specified file if connect says
the connection was refused and stat says the file is a socket.

Also dtach -A now only tries to create the socket if the connection was
refused or the socket did not exist, instead of on any random error as
before.

attach.c

@@ -60,6 +60,18 @@ connect_socket(char *name)
 	if (connect(s, (struct sockaddr*)&sockun, sizeof(sockun)) < 0)
 	{
 		close(s);
+
+		/* ECONNREFUSED is also returned for regular files, so make
+		** sure we are trying to connect to a socket. */
+		if (errno == ECONNREFUSED)
+		{
+			struct stat st;
+
+			if (stat(name, &st) < 0)
+				return -1;
+			else if (!S_ISSOCK(st.st_mode) || S_ISREG(st.st_mode))
+				errno = ENOTSOCK;
+		}
 		return -1;
 	}
 	return s;

dtach.h

@@ -73,6 +73,14 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 
+#ifndef S_ISREG
+#define S_ISREG(m) (((m) & S_IFMT) == S_IFREG)
+#endif
+
+#ifndef S_ISSOCK
+#define S_ISSOCK(m) (((m) & S_IFMT) == S_IFSOCK)
+#endif
+
 extern char *progname, *sockname;
 extern int detach_char, no_suspend, redraw_method;
 extern struct termios orig_term;

main.c

@@ -256,8 +256,13 @@ main(int argc, char **argv)
 		** socket. */
 		if (attach_main(1) != 0)
 		{
+			if (errno == ECONNREFUSED || errno == ENOENT)
+			{
+				if (errno == ECONNREFUSED)
+					unlink(sockname);
 				if (master_main(argv, 1) != 0)
 					return 1;
+			}
 			return attach_main(0);
 		}
 	}