From 0cc84b8cae70099b80eafd44afb9d624103a453a Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Fri, 10 Jul 2026 15:45:11 +0000
Subject: [PATCH] Do not make pty fds blocking again until all the data has
 been consumed or control mode clients can get stuck, GitHub issue 5356 from
 Ben Maurer.

---
 client.c  | 27 ++++++++++-----------------
 control.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 tmux.h    |  1 +
 3 files changed, 60 insertions(+), 17 deletions(-)

diff --git a/client.c b/client.c
index fcc49c395..b315f9083 100644
--- a/client.c
+++ b/client.c
@@ -240,9 +240,8 @@ client_main(struct event_base *base, int argc, char **argv, uint64_t flags,
 	pid_t			 ppid;
 	enum msgtype		 msg;
 	struct termios		 tio, saved_tio;
-	size_t			 size, linesize = 0;
-	ssize_t			 linelen;
-	char			*line = NULL, **caps = NULL, *cause;
+	size_t			 size;
+	char			**caps = NULL, *cause;
 	u_int			 ncaps = 0;
 	struct args_value	*values;
 
@@ -400,11 +399,6 @@ client_main(struct event_base *base, int argc, char **argv, uint64_t flags,
 		client_exec(client_execshell, client_execcmd);
 	}
 
-	/* Restore streams to blocking. */
-	setblocking(STDIN_FILENO, 1);
-	setblocking(STDOUT_FILENO, 1);
-	setblocking(STDERR_FILENO, 1);
-
 	/* Print the exit message, if any, and exit. */
 	if (client_attached) {
 		if (client_exitreason != CLIENT_EXIT_NONE)
@@ -419,15 +413,8 @@ client_main(struct event_base *base, int argc, char **argv, uint64_t flags,
 		else
 			printf("%%exit\n");
 		fflush(stdout);
-		if (client_flags & CLIENT_CONTROL_WAITEXIT) {
-			setvbuf(stdin, NULL, _IOLBF, 0);
-			for (;;) {
-				linelen = getline(&line, &linesize, stdin);
-				if (linelen <= 1)
-					break;
-			}
-			free(line);
-		}
+		if (client_flags & CLIENT_CONTROL_WAITEXIT)
+			control_wait_exit(STDIN_FILENO);
 		if (client_flags & CLIENT_CONTROLCONTROL) {
 			printf("\033\\");
 			fflush(stdout);
@@ -435,6 +422,12 @@ client_main(struct event_base *base, int argc, char **argv, uint64_t flags,
 		}
 	} else if (client_exitreason != CLIENT_EXIT_NONE)
 		fprintf(stderr, "%s\n", client_exit_message());
+
+	/* Restore the streams to blocking. */
+	setblocking(STDIN_FILENO, 1);
+	setblocking(STDOUT_FILENO, 1);
+	setblocking(STDERR_FILENO, 1);
+
 	return (client_exitval);
 }
 
diff --git a/control.c b/control.c
index c1cc79e25..a177c8b88 100644
--- a/control.c
+++ b/control.c
@@ -19,7 +19,9 @@
 
 #include <sys/types.h>
 
+#include <errno.h>
 #include <event.h>
+#include <poll.h>
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
@@ -486,6 +488,53 @@ control_all_done(struct client *c)
 	return (EVBUFFER_LENGTH(cs->write_event->output) == 0);
 }
 
+/*
+ * Wait for the terminal to send an empty line or close, used by a control
+ * client after printing %exit so a wrapping terminal (such as iTerm2) can
+ * finish reading.
+ */
+void
+control_wait_exit(int fd)
+{
+	struct pollfd	 pfd;
+	struct evbuffer	*evb;
+	char		*line;
+	int		 n;
+
+	evb = evbuffer_new();
+	if (evb == NULL)
+		fatalx("out of memory");
+
+	for (;;) {
+		line = evbuffer_readln(evb, NULL, EVBUFFER_EOL_LF);
+		if (line != NULL) {
+			if (*line == '\0') { /* empty line, stop */
+				free(line);
+				break;
+			}
+			free(line);
+			continue; /* drain buffered lines first */
+		}
+
+		memset(&pfd, 0, sizeof pfd);
+		pfd.fd = fd;
+		pfd.events = POLLIN;
+		if (poll(&pfd, 1, INFTIM) == -1) {
+			if (errno == EINTR)
+				continue;
+			break;
+		}
+
+		n = evbuffer_read(evb, fd, -1);
+		if (n == 0)
+			break;
+		if (n == -1 && errno != EAGAIN && errno != EINTR)
+			break;
+	}
+
+	evbuffer_free(evb);
+}
+
 /* Flush all blocks until output. */
 static void
 control_flush_all_blocks(struct client *c)
diff --git a/tmux.h b/tmux.h
index e698adf1b..b62e4ae23 100644
--- a/tmux.h
+++ b/tmux.h
@@ -3917,6 +3917,7 @@ void	control_discard(struct client *);
 void	control_start(struct client *);
 void	control_ready(struct client *);
 void	control_stop(struct client *);
+void	control_wait_exit(int);
 void	control_set_pane_on(struct client *, struct window_pane *);
 void	control_set_pane_off(struct client *, struct window_pane *);
 void	control_continue_pane(struct client *, struct window_pane *);