Fix index out of bounds in tty implementation.

The previous implementation revolved around runes instead of bytes, which caused
weird behavior when converting between the two. For example, peekRune would read
the byte 0xff from a buffer, convert it to a rune, then return it. As rune is an
alias of int32, 0xff was 0-padded to int32(255), which is the hex code point for
?. However, peekRune also returned the length of the byte (1). When calling
utf8.EncodeRune, we only allocated 1 byte, but tried the write the 2-byte
character ?.

tl;dr: I apparently didn't understand runes when I wrote this.

PiperOrigin-RevId: 241789081
Change-Id: I14c788af4d9754973137801500ef6af7ab8a8727

1 files changed, 12 insertions, 8 deletions

diff --git a/pkg/abi/linux/tty.go b/pkg/abi/linux/tty.go
index e6f7c5b2a..bff882d89 100644
--- a/pkg/abi/linux/tty.go
+++ b/pkg/abi/linux/tty.go
@@ -14,10 +14,6 @@
 
 package linux
 
-import (
-	"unicode/utf8"
-)
-
 const (
 	// NumControlCharacters is the number of control characters in Termios.
 	NumControlCharacters = 19
@@ -104,11 +100,19 @@ func (t *KernelTermios) FromTermios(term Termios) {
 }
 
 // IsTerminating returns whether c is a line terminating character.
-func (t *KernelTermios) IsTerminating(c rune) bool {
+func (t *KernelTermios) IsTerminating(cBytes []byte) bool {
+	// All terminating characters are 1 byte.
+	if len(cBytes) != 1 {
+		return false
+	}
+	c := cBytes[0]
+
+	// Is this the user-set EOF character?
 	if t.IsEOF(c) {
 		return true
 	}
-	switch byte(c) {
+
+	switch c {
 	case disabledChar:
 		return false
 	case '\n', t.ControlCharacters[VEOL]:
@@ -120,8 +124,8 @@ func (t *KernelTermios) IsTerminating(c rune) bool {
 }
 
 // IsEOF returns whether c is the EOF character.
-func (t *KernelTermios) IsEOF(c rune) bool {
-	return utf8.RuneLen(c) == 1 && byte(c) == t.ControlCharacters[VEOF] && t.ControlCharacters[VEOF] != disabledChar
+func (t *KernelTermios) IsEOF(c byte) bool {
+	return c == t.ControlCharacters[VEOF] && t.ControlCharacters[VEOF] != disabledChar
 }
 
 // Input flags.