When script(1) reads EOF from input it starts spinning on zero-byte

reads eating 100% CPU. Fix this by skipping select on STDIN after
reading EOF -- permanently if STDIN is not terminal and for one second
if it is.

Also after reading EOF from STDIN we have to pass it to the program
being scripted. The previous approach was to write zero bytes into the
pseudo-terminal. This does not work because zero-byte write does not
have any effect on read. Fix this by sending VEOF instead.

Submitted by:	Ronald Klop <ronald-freebsd8@klop.yi.org>
Discussed with:	kib, Chris Torek <chris.torek@gmail.com>
Approved by:	kib
MFC after:	1 week

2 files changed, 29 insertions, 12 deletions

diff --git a/usr.bin/script/script.1 b/usr.bin/script/script.1
index 3aa03e5..cd3f800 100644
--- a/usr.bin/script/script.1
+++ b/usr.bin/script/script.1
@@ -166,3 +166,12 @@ The slave terminal mode is checked
 for ECHO mode to check when to avoid manual echo logging.
 This does not
 work when in a raw mode where the program being run is doing manual echo.
+.Pp
+If the
+.Nm
+reads zero bytes from the terminal it switches to a mode when it probes read
+only once a second until it gets some data.
+This prevents the
+.Nm
+spinning on zero-byte reads, but might cause a 1-second delay in
+processing of the user input.
diff --git a/usr.bin/script/script.c b/usr.bin/script/script.c
index ad99721..ea5a1f6 100644
--- a/usr.bin/script/script.c
+++ b/usr.bin/script/script.c
@@ -86,6 +86,7 @@ main(int argc, char *argv[])
 	char ibuf[BUFSIZ];
 	fd_set rfd;
 	int flushtime = 30;
+	int readstdin;
 
 	aflg = kflg = 0;
 	while ((ch = getopt(argc, argv, "aqkt:")) != -1)
@@ -155,19 +156,21 @@ main(int argc, char *argv[])
 		doshell(argv);
 	close(slave);
 
-	if (flushtime > 0)
-		tvp = &tv;
-	else
-		tvp = NULL;
-
-	start = time(0);
-	FD_ZERO(&rfd);
+	start = tvec = time(0);
+	readstdin = 1;
 	for (;;) {
+		FD_ZERO(&rfd);
 		FD_SET(master, &rfd);
-		FD_SET(STDIN_FILENO, &rfd);
-		if (flushtime > 0) {
-			tv.tv_sec = flushtime;
+		if (readstdin)
+			FD_SET(STDIN_FILENO, &rfd);
+		if ((!readstdin && ttyflg) || flushtime > 0) {
+			tv.tv_sec = !readstdin && ttyflg ? 1 :
+			    flushtime - (tvec - start);
 			tv.tv_usec = 0;
+			tvp = &tv;
+			readstdin = 1;
+		} else {
+			tvp = NULL;
 		}
 		n = select(master + 1, &rfd, 0, 0, tvp);
 		if (n < 0 && errno != EINTR)
@@ -176,8 +179,13 @@ main(int argc, char *argv[])
 			cc = read(STDIN_FILENO, ibuf, BUFSIZ);
 			if (cc < 0)
 				break;
-			if (cc == 0)
-				(void)write(master, ibuf, 0);
+			if (cc == 0) {
+				if (tcgetattr(master, &stt) == 0 &&
+				    (stt.c_lflag & ICANON) != 0) {
+					(void)write(master, &stt.c_cc[VEOF], 1);
+				}
+				readstdin = 0;
+			}
 			if (cc > 0) {
 				(void)write(master, ibuf, cc);
 				if (kflg && tcgetattr(master, &stt) >= 0 &&