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Up to now, tmux sees \033\033[OA as M-Up and since we turned on
xterm-keys by default, generates \033[1;3A instead of
\033\033[OA. Unfortunately this confuses vi, which doesn't understand
xterm keys and now sees Escape+Up pressed within escape-time as Escape
followed by A.

The issue doesn't happen in xterm itself because it gets the keys from X
and can distinguish between a genuine M-Up and Escape+Up.

Because xterm can, tmux can too: xterm will give us \033[1;3A (that is,
kUP3) for a real M-Up and \033\033OA for Escape+Up - in fact, we can be
sure any \033 preceding an xterm key is a real Escape key press because
Meta would be part of the xterm key instead of a separate \033.

So change tmux to recognise both sequences as M-Up for its own purposes,
but generate the xterm version of M-Up only if it originally received
the xterm version from the terminal.

This means we will return to sending \033\033OA instead of the xterm key
for terminals that do not support xterm keys themselves, but there is no
practical way around this because they do not allow us to distinguish
between Escape+Up and M-Up. xterm style escape sequences are now the de
facto standard for these keys in any case.

Problem reported by jsing@ and subsequently by Cecile Tonglet in GitHub
issue 907.

/* $OpenBSD: xterm-keys.c,v 1.22 2017/05/07 21:25:59 nicm Exp $ */

/*
 * Copyright (c) 2009 Nicholas Marriott <nicholas.marriott@gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
 * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>

#include <string.h>

#include "tmux.h"

/*
 * xterm-style function keys append one of the following values before the last
 * character:
 *
 * 2 Shift
 * 3 Alt
 * 4 Shift + Alt
 * 5 Ctrl
 * 6 Shift + Ctrl
 * 7 Alt + Ctrl
 * 8 Shift + Alt + Ctrl
 *
 * Rather than parsing them, just match against a table.
 *
 * There are three forms for F1-F4 (\\033O_P and \\033O1;_P and \\033[1;_P).
 * We accept any but always output the latter (it comes first in the table).
 */

static int	xterm_keys_match(const char *, const char *, size_t, size_t *,
		    key_code *);
static int	xterm_keys_modifiers(const char *, size_t, size_t *,
		    key_code *);

struct xterm_keys_entry {
	key_code	 key;
	const char	*template;
};

static const struct xterm_keys_entry xterm_keys_table[] = {
	{ KEYC_F1,	"\033[1;_P" },
	{ KEYC_F1,	"\033O1;_P" },
	{ KEYC_F1,	"\033O_P" },
	{ KEYC_F2,	"\033[1;_Q" },
	{ KEYC_F2,	"\033O1;_Q" },
	{ KEYC_F2,	"\033O_Q" },
	{ KEYC_F3,	"\033[1;_R" },
	{ KEYC_F3,	"\033O1;_R" },
	{ KEYC_F3,	"\033O_R" },
	{ KEYC_F4,	"\033[1;_S" },
	{ KEYC_F4,	"\033O1;_S" },
	{ KEYC_F4,	"\033O_S" },
	{ KEYC_F5,	"\033[15;_~" },
	{ KEYC_F6,	"\033[17;_~" },
	{ KEYC_F7,	"\033[18;_~" },
	{ KEYC_F8,	"\033[19;_~" },
	{ KEYC_F9,	"\033[20;_~" },
	{ KEYC_F10,	"\033[21;_~" },
	{ KEYC_F11,	"\033[23;_~" },
	{ KEYC_F12,	"\033[24;_~" },
	{ KEYC_UP,	"\033[1;_A" },
	{ KEYC_DOWN,	"\033[1;_B" },
	{ KEYC_RIGHT,	"\033[1;_C" },
	{ KEYC_LEFT,	"\033[1;_D" },
	{ KEYC_HOME,	"\033[1;_H" },
	{ KEYC_END,	"\033[1;_F" },
	{ KEYC_PPAGE,	"\033[5;_~" },
	{ KEYC_NPAGE,	"\033[6;_~" },
	{ KEYC_IC,	"\033[2;_~" },
	{ KEYC_DC,	"\033[3;_~" },

	{ '!',          "\033[27;_;33~" },
	{ '#',		"\033[27;_;35~" },
	{ '(',		"\033[27;_;40~" },
	{ ')',		"\033[27;_;41~" },
	{ '+',		"\033[27;_;43~" },
	{ ',',		"\033[27;_;44~" },
	{ '-',		"\033[27;_;45~" },
	{ '.',		"\033[27;_;46~" },
	{ '0',		"\033[27;_;48~" },
	{ '1',		"\033[27;_;49~" },
	{ '2',		"\033[27;_;50~" },
	{ '3',		"\033[27;_;51~" },
	{ '4',		"\033[27;_;52~" },
	{ '5',		"\033[27;_;53~" },
	{ '6',		"\033[27;_;54~" },
	{ '7',		"\033[27;_;55~" },
	{ '8',		"\033[27;_;56~" },
	{ '9',		"\033[27;_;57~" },
	{ ':',		"\033[27;_;58~" },
	{ ';',		"\033[27;_;59~" },
	{ '<',		"\033[27;_;60~" },
	{ '=',		"\033[27;_;61~" },
	{ '>',		"\033[27;_;62~" },
	{ '?',		"\033[27;_;63~" },
	{ '\'',		"\033[27;_;39~" },
	{ '\r',		"\033[27;_;13~" },
	{ '\t',		"\033[27;_;9~" },
};

/*
 * Match key against buffer, treating _ as a wildcard. Return -1 for no match,
 * 0 for match, 1 if the end of the buffer is reached (need more data).
 */
static int
xterm_keys_match(const char *template, const char *buf, size_t len,
    size_t *size, key_code *modifiers)
{
	size_t	pos;
	int	retval;

	*modifiers = 0;

	if (len == 0)
		return (0);

	pos = 0;
	do {
		if (*template == '_') {
			retval = xterm_keys_modifiers(buf, len, &pos,
			    modifiers);
			if (retval != 0)
				return (retval);
			continue;
		}
		if (buf[pos] != *template)
			return (-1);
		pos++;
	} while (*++template != '\0' && pos != len);

	if (*template != '\0')	/* partial */
		return (1);

	*size = pos;
	return (0);
}

/* Find modifiers from buffer. */
static int
xterm_keys_modifiers(const char *buf, size_t len, size_t *pos,
    key_code *modifiers)
{
	u_int	flags;

	if (len - *pos < 2)
		return (1);

	if (buf[*pos] < '0' || buf[*pos] > '9')
		return (-1);
	flags = buf[(*pos)++] - '0';
	if (buf[*pos] >= '0' && buf[*pos] <= '9')
		flags = (flags * 10) + (buf[(*pos)++] - '0');
	flags -= 1;

	*modifiers = 0;
	if (flags & 1)
		*modifiers |= KEYC_SHIFT;
	if (flags & 2)
		*modifiers |= KEYC_ESCAPE;
	if (flags & 4)
		*modifiers |= KEYC_CTRL;
	if (flags & 8)
		*modifiers |= KEYC_ESCAPE;
	return (0);
}

/*
 * Lookup key from a buffer against the table. Returns 0 for found (and the
 * key), -1 for not found, 1 for partial match.
 */
int
xterm_keys_find(const char *buf, size_t len, size_t *size, key_code *key)
{
	const struct xterm_keys_entry	*entry;
	u_int				 i;
	int				 matched;
	key_code			 modifiers;

	for (i = 0; i < nitems(xterm_keys_table); i++) {
		entry = &xterm_keys_table[i];

		matched = xterm_keys_match(entry->template, buf, len, size,
		    &modifiers);
		if (matched == -1)
			continue;
		if (matched == 0)
			*key = (entry->key|modifiers|KEYC_XTERM);
		return (matched);
	}
	return (-1);
}

/* Lookup a key number from the table. */
char *
xterm_keys_lookup(key_code key)
{
	const struct xterm_keys_entry	*entry;
	u_int				 i;
	key_code			 modifiers;
	char				*out;

	modifiers = 1;
	if (key & KEYC_SHIFT)
		modifiers += 1;
	if (key & KEYC_ESCAPE)
		modifiers += 2;
	if (key & KEYC_CTRL)
		modifiers += 4;

	/*
	 * If the key has no modifiers, return NULL and let it fall through to
	 * the normal lookup.
	 */
	if (modifiers == 1)
		return (NULL);

	/*
	 * If this has the escape modifier, but was not originally an xterm
	 * key, it may be a genuine escape + key. So don't pass it through as
	 * an xterm key or programs like vi may be confused.
	 */
	if ((key & (KEYC_ESCAPE|KEYC_XTERM)) == KEYC_ESCAPE)
		return (NULL);

	/* Otherwise, find the key in the table. */
	key &= KEYC_MASK_KEY;
	for (i = 0; i < nitems(xterm_keys_table); i++) {
		entry = &xterm_keys_table[i];
		if (key == entry->key)
			break;
	}
	if (i == nitems(xterm_keys_table))
		return (NULL);

	/* Copy the template and replace the modifier. */
	out = xstrdup(entry->template);
	out[strcspn(out, "_")] = '0' + modifiers;
	return (out);
}