From 5aff804d348175bd5f71057b395874e15282d4ab Mon Sep 17 00:00:00 2001
From: AdamMagued <adammagued@users.noreply.github.com>
Date: Fri, 2 Oct 2026 21:00:51 +0000
Subject: [PATCH] fix: enable IUTF8 input flag by default on darwin
 pseudo-terminals

Set the IUTF8 flag in termios iflag on darwin when opening a pseudo-terminal.
Without IUTF8, the Darwin terminal driver line discipline deletes single bytes
instead of whole UTF-8 characters when backspace/delete (0x7f) is sent, resulting
in mangled multibyte characters in canonical mode.

Fixes #138
---
 pty_darwin.go      |  7 +++++++
 pty_darwin_test.go | 29 +++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 pty_darwin_test.go

diff --git a/pty_darwin.go b/pty_darwin.go
index 91efb14..6e627bc 100644
--- a/pty_darwin.go
+++ b/pty_darwin.go
@@ -40,6 +40,13 @@ func open() (pty, tty *os.File, err error) {
 	if err != nil {
 		return nil, nil, err
 	}
+
+	var tios syscall.Termios
+	if err := ioctl(t, syscall.TIOCGETA, unsafe.Pointer(&tios)); err == nil {
+		tios.Iflag |= syscall.IUTF8
+		_ = ioctl(t, syscall.TIOCSETA, unsafe.Pointer(&tios))
+	}
+
 	return p, t, nil
 }
 
diff --git a/pty_darwin_test.go b/pty_darwin_test.go
new file mode 100644
index 0000000..2c636b9
--- /dev/null
+++ b/pty_darwin_test.go
@@ -0,0 +1,29 @@
+//go:build darwin
+// +build darwin
+
+package pty
+
+import (
+	"bufio"
+	"testing"
+)
+
+func TestDarwinIUTF8(t *testing.T) {
+	t.Parallel()
+
+	pty, tty := openClose(t)
+
+	// Write multibyte UTF-8 characters followed by Delete (0x7f) and a newline.
+	// With IUTF8 enabled, erasing deletes the entire multibyte character rather than only the final byte.
+	const input = "小明\x7f\n"
+	n, err := pty.WriteString(input)
+	noError(t, err, "Unexpected error writing input")
+	assert(t, len(input), n, "Unexpected count returned from WriteString")
+
+	r := bufio.NewReader(tty)
+	line, err := r.ReadString('\n')
+	noError(t, err, "Unexpected error reading from tty")
+
+	expected := "小\n"
+	assert(t, expected, line, "Expected multibyte character to be deleted cleanly")
+}