[hackers] [st][PATCH v2] st: fix C1 bytes (0x80-0x9F) shown as garbage in UTF-8 mode

From: nyxvoid <nyxvoid00_AT_gmail.com>
Date: Mon, 16 Mar 2026 09:42:55 +0545

From: amritxyz <amrit44404_AT_proton.me>

Raw C1 bytes are not valid UTF-8. utf8decode() returns U+FFFD for
them which gets drawn on screen as a replacement character.

Fix this by skipping C1 bytes in twrite() before utf8decode() sees
them. The ESC_STR guard lets them through when inside a STR sequence
so they can still act as sequence terminators.

Also add an early return in tputc() as a safety net for any direct
callers, and call strhandle() when a C1 byte terminates a STR
sequence so OSC sequences are not silently lost.

Tested: printf '\x8f' now produces no output.

---
 st.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/st.c b/st.c
index 6f40e35..d0bf933 100644
--- a/st.c
+++ b/st.c
_AT_@ -2396,6 +2396,9 @@ tputc(Rune u)
 	Glyph *gp;
 
 	control = ISCONTROL(u);
+	/* in UTF-8 mode, ignore C1 control characters early */
+	if (IS_SET(MODE_UTF8) && ISCONTROLC1(u) && !(term.esc & ESC_STR))
+		return;
 	if (u < 127 || !IS_SET(MODE_UTF8)) {
 		c[0] = u;
 		width = len = 1;
_AT_@ -2455,8 +2458,11 @@ check_control_code:
 	 */
 	if (control) {
 		/* in UTF-8 mode ignore handling C1 control characters */
-		if (IS_SET(MODE_UTF8) && ISCONTROLC1(u))
+		if (IS_SET(MODE_UTF8) && ISCONTROLC1(u)) {
+			if (term.esc & ESC_STR_END)
+				strhandle();
 			return;
+		}
 		tcontrolcode(u);
 		/*
 		 * control codes are not shown ever
_AT_@ -2546,6 +2552,11 @@ twrite(const char *buf, int buflen, int show_ctrl)
 
 	for (n = 0; n < buflen; n += charsize) {
 		if (IS_SET(MODE_UTF8)) {
+			/* skip C1 bytes before utf8decode() mangles them */
+			if (ISCONTROLC1(buf[n] & 0xFF) && !(term.esc & ESC_STR)) {
+				charsize = 1;
+				continue;
+			}
 			/* process a complete utf8 char */
 			charsize = utf8decode(buf + n, &u, buflen - n);
 			if (charsize == 0)
-- 
2.53.0

Received on Mon Mar 16 2026 - 04:57:55 CET