From c6b51cea923e0c4e92636998a776ada42511b6e5 Mon Sep 17 00:00:00 2001
From: Nicholas Marriott <nicholas.marriott@gmail.com>
Date: Wed, 27 Apr 2022 11:34:08 +0100
Subject: [PATCH] If a mouse position was above the maximum supported by the
 normal mouse protocol (223), tmux was allowing it to wrap around. However,
 since tmux was not correctly handling this on input, other programs also do
 not handle it correctly, and the alternative SGR mouse mode is now
 widespread, this seems unnecessary, so remove this feature. Also define some
 constants to make it clearer what the numbers mean. Mostly from Leonid S Usov
 in GitHub issue 3165.

---
 input-keys.c | 31 +++++++++++++++++++++++--------
 tmux.h       |  6 ++++++
 tty-keys.c   | 16 ++++++----------
 3 files changed, 35 insertions(+), 18 deletions(-)

diff --git a/input-keys.c b/input-keys.c
index feb62f6d..ebf61333 100644
--- a/input-keys.c
+++ b/input-keys.c
@@ -606,19 +606,34 @@ input_key_get_mouse(struct screen *s, struct mouse_event *m, u_int x, u_int y,
 		len = xsnprintf(buf, sizeof buf, "\033[<%u;%u;%u%c",
 		    m->sgr_b, x + 1, y + 1, m->sgr_type);
 	} else if (s->mode & MODE_MOUSE_UTF8) {
-		if (m->b > 0x7ff - 32 || x > 0x7ff - 33 || y > 0x7ff - 33)
+		if (m->b > MOUSE_PARAM_UTF8_MAX - MOUSE_PARAM_BTN_OFF ||
+		    x > MOUSE_PARAM_UTF8_MAX - MOUSE_PARAM_POS_OFF ||
+		    y > MOUSE_PARAM_UTF8_MAX - MOUSE_PARAM_POS_OFF)
 			return (0);
 		len = xsnprintf(buf, sizeof buf, "\033[M");
-		len += input_key_split2(m->b + 32, &buf[len]);
-		len += input_key_split2(x + 33, &buf[len]);
-		len += input_key_split2(y + 33, &buf[len]);
+		len += input_key_split2(m->b + MOUSE_PARAM_BTN_OFF, &buf[len]);
+		len += input_key_split2(x + MOUSE_PARAM_POS_OFF, &buf[len]);
+		len += input_key_split2(y + MOUSE_PARAM_POS_OFF, &buf[len]);
 	} else {
-		if (m->b > 223)
+		if (m->b + MOUSE_PARAM_BTN_OFF > MOUSE_PARAM_MAX)
 			return (0);
+
 		len = xsnprintf(buf, sizeof buf, "\033[M");
-		buf[len++] = m->b + 32;
-		buf[len++] = x + 33;
-		buf[len++] = y + 33;
+		buf[len++] = m->b + MOUSE_PARAM_BTN_OFF;
+
+		/*
+		 * The incoming x and y may be out of the range which can be
+		 * supported by the "normal" mouse protocol. Clamp the
+		 * coordinates to the supported range.
+		 */
+		if (x + MOUSE_PARAM_POS_OFF > MOUSE_PARAM_MAX)
+			buf[len++] = MOUSE_PARAM_MAX;
+		else
+			buf[len++] = x + MOUSE_PARAM_POS_OFF;
+		if (y + MOUSE_PARAM_POS_OFF > MOUSE_PARAM_MAX)
+			buf[len++] = MOUSE_PARAM_MAX;
+		else
+			buf[len++] = y + MOUSE_PARAM_POS_OFF;
 	}
 
 	*rbuf = buf;
diff --git a/tmux.h b/tmux.h
index a893bdb2..53084b8b 100644
--- a/tmux.h
+++ b/tmux.h
@@ -581,6 +581,12 @@ enum tty_code_code {
 #define MOTION_MOUSE_MODES (MODE_MOUSE_BUTTON|MODE_MOUSE_ALL)
 #define CURSOR_MODES (MODE_CURSOR|MODE_CURSOR_BLINKING|MODE_CURSOR_VERY_VISIBLE)
 
+/* Mouse protocol constants. */
+#define MOUSE_PARAM_MAX 0xff
+#define MOUSE_PARAM_UTF8_MAX 0x7ff
+#define MOUSE_PARAM_BTN_OFF 0x20
+#define MOUSE_PARAM_POS_OFF 0x21
+
 /* A single UTF-8 character. */
 typedef u_int utf8_char;
 
diff --git a/tty-keys.c b/tty-keys.c
index 8538e74b..64dd91bb 100644
--- a/tty-keys.c
+++ b/tty-keys.c
@@ -1061,17 +1061,13 @@ tty_keys_mouse(struct tty *tty, const char *buf, size_t len, size_t *size,
 		log_debug("%s: mouse input: %.*s", c->name, (int)*size, buf);
 
 		/* Check and return the mouse input. */
-		if (b < 32)
+		if (b < MOUSE_PARAM_BTN_OFF ||
+		    x < MOUSE_PARAM_POS_OFF ||
+		    y < MOUSE_PARAM_POS_OFF)
 			return (-1);
-		b -= 32;
-		if (x >= 33)
-			x -= 33;
-		else
-			x = 256 - x;
-		if (y >= 33)
-			y -= 33;
-		else
-			y = 256 - y;
+		b -= MOUSE_PARAM_BTN_OFF;
+		x -= MOUSE_PARAM_POS_OFF;
+		y -= MOUSE_PARAM_POS_OFF;
 	} else if (buf[2] == '<') {
 		/* Read the three inputs. */
 		*size = 3;