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Some old tmux versions can sometimes generate layout strings which have
the incorrect size for the top cell. Previously tmux didn't care but now
that panes can be partly hidden, the size matters and is checked more
strictly. So add some code to fix up the most common problem and a
sanity check to reject layouts with any other size problems. Reported by
Aleksandrs Ledovskis in GitHub issue 1930.

/* $OpenBSD: layout-custom.c,v 1.17 2019/10/14 09:16:48 nicm Exp $ */

/*
 * Copyright (c) 2010 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 <ctype.h>
#include <string.h>

#include "tmux.h"

static struct layout_cell	*layout_find_bottomright(struct layout_cell *);
static u_short			 layout_checksum(const char *);
static int			 layout_append(struct layout_cell *, char *,
				     size_t);
static struct layout_cell	*layout_construct(struct layout_cell *,
				     const char **);
static void			 layout_assign(struct window_pane **,
				     struct layout_cell *);

/* Find the bottom-right cell. */
static struct layout_cell *
layout_find_bottomright(struct layout_cell *lc)
{
	if (lc->type == LAYOUT_WINDOWPANE)
		return (lc);
	lc = TAILQ_LAST(&lc->cells, layout_cells);
	return (layout_find_bottomright(lc));
}

/* Calculate layout checksum. */
static u_short
layout_checksum(const char *layout)
{
	u_short	csum;

	csum = 0;
	for (; *layout != '\0'; layout++) {
		csum = (csum >> 1) + ((csum & 1) << 15);
		csum += *layout;
	}
	return (csum);
}

/* Dump layout as a string. */
char *
layout_dump(struct layout_cell *root)
{
	char	layout[8192], *out;

	*layout = '\0';
	if (layout_append(root, layout, sizeof layout) != 0)
		return (NULL);

	xasprintf(&out, "%04hx,%s", layout_checksum(layout), layout);
	return (out);
}

/* Append information for a single cell. */
static int
layout_append(struct layout_cell *lc, char *buf, size_t len)
{
	struct layout_cell     *lcchild;
	char			tmp[64];
	size_t			tmplen;
	const char	       *brackets = "][";

	if (len == 0)
		return (-1);

	if (lc->wp != NULL) {
		tmplen = xsnprintf(tmp, sizeof tmp, "%ux%u,%u,%u,%u",
		    lc->sx, lc->sy, lc->xoff, lc->yoff, lc->wp->id);
	} else {
		tmplen = xsnprintf(tmp, sizeof tmp, "%ux%u,%u,%u",
		    lc->sx, lc->sy, lc->xoff, lc->yoff);
	}
	if (tmplen > (sizeof tmp) - 1)
		return (-1);
	if (strlcat(buf, tmp, len) >= len)
		return (-1);

	switch (lc->type) {
	case LAYOUT_LEFTRIGHT:
		brackets = "}{";
		/* FALLTHROUGH */
	case LAYOUT_TOPBOTTOM:
		if (strlcat(buf, &brackets[1], len) >= len)
			return (-1);
		TAILQ_FOREACH(lcchild, &lc->cells, entry) {
			if (layout_append(lcchild, buf, len) != 0)
				return (-1);
			if (strlcat(buf, ",", len) >= len)
				return (-1);
		}
		buf[strlen(buf) - 1] = brackets[0];
		break;
	case LAYOUT_WINDOWPANE:
		break;
	}

	return (0);
}

/* Check layout sizes fit. */
static int
layout_check(struct layout_cell *lc)
{
	struct layout_cell	*lcchild;
	u_int			 n = 0;

	switch (lc->type) {
	case LAYOUT_WINDOWPANE:
		break;
	case LAYOUT_LEFTRIGHT:
		TAILQ_FOREACH(lcchild, &lc->cells, entry) {
			if (lcchild->sy != lc->sy)
				return (0);
			if (!layout_check(lcchild))
				return (0);
			n += lcchild->sx + 1;
		}
		if (n - 1 != lc->sx)
			return (0);
		break;
	case LAYOUT_TOPBOTTOM:
		TAILQ_FOREACH(lcchild, &lc->cells, entry) {
			if (lcchild->sx != lc->sx)
				return (0);
			if (!layout_check(lcchild))
				return (0);
			n += lcchild->sy + 1;
		}
		if (n - 1 != lc->sy)
			return (0);
		break;
	}
	return (1);
}

/* Parse a layout string and arrange window as layout. */
int
layout_parse(struct window *w, const char *layout)
{
	struct layout_cell	*lc, *lcchild;
	struct window_pane	*wp;
	u_int			 npanes, ncells, sx = 0, sy = 0;
	u_short			 csum;

	/* Check validity. */
	if (sscanf(layout, "%hx,", &csum) != 1)
		return (-1);
	layout += 5;
	if (csum != layout_checksum(layout))
		return (-1);

	/* Build the layout. */
	lc = layout_construct(NULL, &layout);
	if (lc == NULL)
		return (-1);
	if (*layout != '\0')
		goto fail;

	/* Check this window will fit into the layout. */
	for (;;) {
		npanes = window_count_panes(w);
		ncells = layout_count_cells(lc);
		if (npanes > ncells)
			goto fail;
		if (npanes == ncells)
			break;

		/* Fewer panes than cells - close the bottom right. */
		lcchild = layout_find_bottomright(lc);
		layout_destroy_cell(w, lcchild, &lc);
	}

	/*
	 * It appears older versions of tmux were able to generate layouts with
	 * an incorrect top cell size - if it is larger than the top child then
	 * correct that (if this is still wrong the check code will catch it).
	 */
	switch (lc->type) {
	case LAYOUT_WINDOWPANE:
		break;
	case LAYOUT_LEFTRIGHT:
		TAILQ_FOREACH(lcchild, &lc->cells, entry) {
			sy = lcchild->sy + 1;
			sx += lcchild->sx + 1;
		}
		break;
	case LAYOUT_TOPBOTTOM:
		TAILQ_FOREACH(lcchild, &lc->cells, entry) {
			sx = lcchild->sx + 1;
			sy += lcchild->sy + 1;
		}
		break;
	}
	if (lc->sx != sx || lc->sy != sy) {
		log_debug("fix layout %u,%u to %u,%u", lc->sx, lc->sy, sx,sy);
		layout_print_cell(lc, __func__, 0);
		lc->sx = sx - 1; lc->sy = sy - 1;
	}

	/* Check the new layout. */
	if (!layout_check(lc))
		return (-1);

	/* Resize to the layout size. */
	window_resize(w, lc->sx, lc->sy);

	/* Destroy the old layout and swap to the new. */
	layout_free_cell(w->layout_root);
	w->layout_root = lc;

	/* Assign the panes into the cells. */
	wp = TAILQ_FIRST(&w->panes);
	layout_assign(&wp, lc);

	/* Update pane offsets and sizes. */
	layout_fix_offsets(w);
	layout_fix_panes(w);
	recalculate_sizes();

	layout_print_cell(lc, __func__, 0);

	notify_window("window-layout-changed", w);

	return (0);

fail:
	layout_free_cell(lc);
	return (-1);
}

/* Assign panes into cells. */
static void
layout_assign(struct window_pane **wp, struct layout_cell *lc)
{
	struct layout_cell	*lcchild;

	switch (lc->type) {
	case LAYOUT_WINDOWPANE:
		layout_make_leaf(lc, *wp);
		*wp = TAILQ_NEXT(*wp, entry);
		return;
	case LAYOUT_LEFTRIGHT:
	case LAYOUT_TOPBOTTOM:
		TAILQ_FOREACH(lcchild, &lc->cells, entry)
			layout_assign(wp, lcchild);
		return;
	}
}

/* Construct a cell from all or part of a layout tree. */
static struct layout_cell *
layout_construct(struct layout_cell *lcparent, const char **layout)
{
	struct layout_cell     *lc, *lcchild;
	u_int			sx, sy, xoff, yoff;
	const char	       *saved;

	if (!isdigit((u_char) **layout))
		return (NULL);
	if (sscanf(*layout, "%ux%u,%u,%u", &sx, &sy, &xoff, &yoff) != 4)
		return (NULL);

	while (isdigit((u_char) **layout))
		(*layout)++;
	if (**layout != 'x')
		return (NULL);
	(*layout)++;
	while (isdigit((u_char) **layout))
		(*layout)++;
	if (**layout != ',')
		return (NULL);
	(*layout)++;
	while (isdigit((u_char) **layout))
		(*layout)++;
	if (**layout != ',')
		return (NULL);
	(*layout)++;
	while (isdigit((u_char) **layout))
		(*layout)++;
	if (**layout == ',') {
		saved = *layout;
		(*layout)++;
		while (isdigit((u_char) **layout))
			(*layout)++;
		if (**layout == 'x')
			*layout = saved;
	}

	lc = layout_create_cell(lcparent);
	lc->sx = sx;
	lc->sy = sy;
	lc->xoff = xoff;
	lc->yoff = yoff;

	switch (**layout) {
	case ',':
	case '}':
	case ']':
	case '\0':
		return (lc);
	case '{':
		lc->type = LAYOUT_LEFTRIGHT;
		break;
	case '[':
		lc->type = LAYOUT_TOPBOTTOM;
		break;
	default:
		goto fail;
	}

	do {
		(*layout)++;
		lcchild = layout_construct(lc, layout);
		if (lcchild == NULL)
			goto fail;
		TAILQ_INSERT_TAIL(&lc->cells, lcchild, entry);
	} while (**layout == ',');

	switch (lc->type) {
	case LAYOUT_LEFTRIGHT:
		if (**layout != '}')
			goto fail;
		break;
	case LAYOUT_TOPBOTTOM:
		if (**layout != ']')
			goto fail;
		break;
	default:
		goto fail;
	}
	(*layout)++;

	return (lc);

fail:
	layout_free_cell(lc);
	return (NULL);
}