Description: Predictable behaviour of client program.
 Better error recovery and exeption handling.
 .
 Ignore the SIGPIPE trigger.
 .
 Give priority to reading the device being snooped at,
 only then reading from standard input.
Author: Mats Erik Andersson <debian@gisladisker.se>
Forwarded: no
Last-Update: 2010-06-21
--- ttysnoop-0.12d.debian/ttysnoop.c
+++ ttysnoop-0.12d/ttysnoop.c
@@ -25,6 +25,7 @@
 #include <grp.h>
 #include <utmp.h>
 #include <errno.h>
+#include <signal.h>
 
 #include "config.h"
 #include "common.h"
@@ -33,6 +34,11 @@
 
 char buff[BUFF_SIZE];
 
+void message (void)
+{
+	printf ("\r\nBack at local tty.\r\n");
+}
+
 int main (int argc, char *argv[])
 {
 	fd_set readset;
@@ -40,24 +46,30 @@ int main (int argc, char *argv[])
 	int sockfd, fdmax, quit = 0, n;
 	char sockname[128];
 	
+	if (geteuid())
+		errorf("Insufficient privileges.\n");
+
 	if (argc < 2)
 		errorf ("Usage: ttysnoop <pty>\n");
 	
 	/* create the client socket */
 	
 	if ((sockfd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0)
-		errorf ("can't create client socket\n");
+		errorf ("Cannot create client socket.\n");
 	
-	sprintf (sockname, "%s/%s", SPOOLDIR, argv[1]);
+	snprintf (sockname, sizeof(sockname), "%s/%s", SPOOLDIR, argv[1]);
+	memset (&sock_addr, '\0', sizeof(sock_addr));
 	sock_addr.sun_family = AF_UNIX;
 	strncopy (sock_addr.sun_path, sockname);
+
 	if (connect(sockfd, (struct sockaddr *) &sock_addr, sizeof(sock_addr)) < 0)
-		errorf ("can't connect to server\n");
+		errorf ("Cannot connect to server. Is it really a valid socket?\n");
 	
 	/* put stdin into raw mode */
 	
 	stty_initstore ();
 	atexit (stty_orig);
+	atexit (message);
 	if (isatty(STDIN_FILENO))
 		stty_raw (STDIN_FILENO);
 
@@ -67,32 +79,52 @@ int main (int argc, char *argv[])
 	
 	/* do our thing */
 	
+	signal(SIGPIPE, SIG_IGN);
+	FD_ZERO (&readset);
+
 	while (!quit)
 	{
-		FD_ZERO (&readset);
+		int ret;
+
 		FD_SET (STDIN_FILENO, &readset);
 		FD_SET (sockfd, &readset);
 		
-		select (fdmax + 1, &readset, NULL, NULL, NULL);
-		
-		if (FD_ISSET(STDIN_FILENO, &readset))
-		{
-			n = read(STDIN_FILENO, buff, BUFF_SIZE);
+		if ( (ret = select (fdmax + 1, &readset, NULL, NULL, NULL)) < 0 ) {
+			if ( errno == EINTR )
+				continue;
 
-			if (write(sockfd, buff, n) < 0)
-				quit = 1;
+			break;	/* Cannot recover. */
 		}
 		
+		/* Give precedence to the end point where we snoop. */
 		if (FD_ISSET(sockfd, &readset))
 		{
-			if ((n = read(sockfd, buff, BUFF_SIZE)) < 1)
-				quit = 1;
+			if ((n = read(sockfd, buff, BUFF_SIZE)) <= 0) {
+				if ( (n < 0) && (errno == EINTR) )
+					continue;
+				if ( n == 0 )
+					break;	/* EOF on socket. */
 
+				quit = 1;	/* Will soon exit! */
+			}
 			if (n > 0)
 				write (STDOUT_FILENO, buff, n);
 		}
+		
+		if (FD_ISSET(STDIN_FILENO, &readset))
+		{
+			n = read(STDIN_FILENO, buff, BUFF_SIZE);
+			if ( n == 0 ) {
+				/* The observer has left. Close down! */
+				shutdown(sockfd, SHUT_WR);
+				FD_CLR(STDIN_FILENO, &readset);
+				quit = 1;
+			}
+
+			if ( ( n > 0 ) && ( write(sockfd, buff, n) < 0 ) )
+				quit = 1;	/* The terminal service has already closed down. */
+		}
 	}
 	
-	printf ("\r\nBack at local tty.\r\n");
 	return 0;
 }