input: consume only the actual length of an escape sequence

Instead of assuming that the entire contents of the keybuffer are an
escape sequence (even if this is far longer than any escape sequence
can be), remove from the keybuffer only those integers that actually
constituted a sequence, valid or invalid.

This fixes https://savannah.gnu.org/bugs/?48659.

src/winio.c

@@ -763,15 +763,17 @@ int parse_kbinput(WINDOW *win)
  * keypad values, into their corresponding key values.  These sequences
  * are generated when the keypad doesn't support the needed keys.
  * Assume that Escape has already been read in. */
-int convert_sequence(const int *seq, size_t length)
+int convert_sequence(const int *seq, size_t length, int *consumed)
 {
 	if (length > 1) {
+		*consumed = 2;
 		switch (seq[0]) {
 			case 'O':
 				switch (seq[1]) {
 					case '1':
 						if (length > 4  && seq[2] == ';') {
 
+		*consumed = 5;
 		switch (seq[3]) {
 			case '2':
 				switch (seq[4]) {
@@ -808,7 +810,8 @@ int convert_sequence(const int *seq, size_t length)
 						}
 						break;
 					case '2':
-						if (length >= 3) {
+						if (length > 2) {
+							*consumed = 3;
 							switch (seq[2]) {
 								case 'P': /* Esc O 2 P == F13 on xterm. */
 									return KEY_F(13);
@@ -822,7 +825,8 @@ int convert_sequence(const int *seq, size_t length)
 						}
 						break;
 					case '5':
-						if (length >= 3) {
+						if (length > 2) {
+							*consumed = 3;
 							switch (seq[2]) {
 								case 'A': /* Esc O 5 A == Ctrl-Up on Haiku. */
 									return CONTROL_UP;
@@ -834,6 +838,7 @@ int convert_sequence(const int *seq, size_t length)
 									return CONTROL_LEFT;
 							}
 						}
+						break;
 					case 'A': /* Esc O A == Up on VT100/VT320/xterm. */
 					case 'B': /* Esc O B == Down on VT100/VT320/xterm. */
 					case 'C': /* Esc O C == Right on VT100/VT320/xterm. */
@@ -933,9 +938,12 @@ int convert_sequence(const int *seq, size_t length)
 				}
 				break;
 			case '[':
+				if (seq[1] < '9')
+					*consumed = 3;
 				switch (seq[1]) {
 					case '1':
 						if (length > 3 && seq[3] == '~') {
+							*consumed = 4;
 							switch (seq[2]) {
 								case '1': /* Esc [ 1 1 ~ == F1 on rxvt/Eterm. */
 									return KEY_F(1);
@@ -957,6 +965,7 @@ int convert_sequence(const int *seq, size_t length)
 							}
 						} else if (length > 4 && seq[2] == ';') {
 
+		*consumed = 5;
 		switch (seq[3]) {
 			case '2':
 				switch (seq[4]) {
@@ -1033,12 +1042,15 @@ int convert_sequence(const int *seq, size_t length)
 #endif
 		}
 
-						} else if (length > 2 && seq[2] == '~')
+						} else if (length > 2 && seq[2] == '~') {
+							*consumed = 3;
 							/* Esc [ 1 ~ == Home on VT320/Linux console. */
 							return KEY_HOME;
+						}
 						break;
 					case '2':
 						if (length > 3 && seq[3] == '~') {
+							*consumed = 4;
 							switch (seq[2]) {
 								case '0': /* Esc [ 2 0 ~ == F9 on VT220/VT320/
 										   * Linux console/xterm/rxvt/Eterm. */
@@ -1146,6 +1158,7 @@ int convert_sequence(const int *seq, size_t length)
 						return KEY_F(2);
 					case 'O':
 						if (length > 2) {
+							*consumed = 3;
 							switch (seq[2]) {
 								case 'P': /* Esc [ O P == F1 on xterm. */
 									return KEY_F(1);
@@ -1191,6 +1204,7 @@ int convert_sequence(const int *seq, size_t length)
 						return arrow_from_abcd(seq[1]);
 					case '[':
 						if (length > 2) {
+							*consumed = 3;
 							switch (seq[2]) {
 								case 'A': /* Esc [ [ A == F1 on Linux console. */
 									return KEY_F(1);
@@ -1236,15 +1250,20 @@ int arrow_from_abcd(int kbinput)
  * isn't empty, and that the initial escape has already been read in. */
 int parse_escape_sequence(WINDOW *win, int kbinput)
 {
-	int retval, *sequence, length;
+	int retval, *sequence, length, consumed;
 
-	/* Put back the non-escape character, get the complete escape
-	 * sequence, translate the sequence into its corresponding key
-	 * value, and save that as the result. */
+	/* Put back the non-escape code, then grab at most five integers
+	 * (the longest possible escape sequence) from the keybuffer and
+	 * translate the sequence into its corresponding keycode. */
 	unget_input(kbinput);
-	length = key_buffer_len;
+	length = (key_buffer_len < 5 ? key_buffer_len : 5);
 	sequence = get_input(NULL, length);
-	retval = convert_sequence(sequence, length);
+	retval = convert_sequence(sequence, length, &consumed);
+
+	/* If not all grabbed integers were consumed, put the leftovers back. */
+	for (int i = length - 1; i >= consumed; i--)
+		unget_input(sequence[i]);
+
 	free(sequence);
 
 	/* If we got an unrecognized escape sequence, notify the user. */