Box Conversion: Cancel conversion during html_destroy

If dom_to_box is still in progress when we destroy an HTML
content, we need to cancel the conversion otherwise we will
end up with a scheduled callback into infinity.

Signed-off-by: Daniel Silverstone <dsilvers@digital-scurf.org>

content/handlers/html/box.h

@@ -359,7 +359,8 @@ bool box_vscrollbar_present(const struct box *box);
 bool box_hscrollbar_present(const struct box *box);
 
 nserror dom_to_box(struct dom_node *n, struct html_content *c,
-		box_construct_complete_cb cb);
+		   box_construct_complete_cb cb, void **box_conversion_context);
+nserror cancel_dom_to_box(void *box_conversion_context);
 
 bool box_normalise_block(
 		struct box *block,

content/handlers/html/box_construct.c

@@ -163,10 +163,12 @@ static const struct element_entry element_table[] = {
  * \return    netsurf error code indicating status of call
  */
 
-nserror dom_to_box(dom_node *n, html_content *c, box_construct_complete_cb cb)
+nserror dom_to_box(dom_node *n, html_content *c, box_construct_complete_cb cb, void **box_conversion_context)
 {
 	struct box_construct_ctx *ctx;
 
+	assert(box_conversion_context != NULL);
+
 	if (c->bctx == NULL) {
 		/* create a context allocation for this box tree */
 		c->bctx = talloc_zero(0, int);
@@ -186,9 +188,28 @@ nserror dom_to_box(dom_node *n, html_content *c, box_construct_complete_cb cb)
 	ctx->cb = cb;
 	ctx->bctx = c->bctx;
 
+	*box_conversion_context = ctx;
+
 	return guit->misc->schedule(0, (void *)convert_xml_to_box, ctx);
 }
 
+nserror cancel_dom_to_box(void *box_conversion_context)
+{
+	struct box_construct_ctx *ctx = box_conversion_context;
+	nserror err;
+
+	err = guit->misc->schedule(-1, (void *)convert_xml_to_box, ctx);
+	if (err != NSERROR_OK) {
+		return err;
+	}
+
+	dom_node_unref(ctx->n);
+	free(ctx);
+
+	return NSERROR_OK;
+}
+
+
 /* mapping from CSS display to box type
  * this table must be in sync with libcss' css_display enum */
 static const box_type box_map[] = {

content/handlers/html/html.c

@@ -115,6 +115,8 @@ static void html_box_convert_done(html_content *c, bool success)
 
 	NSLOG(netsurf, INFO, "Done XML to box (%p)", c);
 
+	c->box_conversion_context = NULL;
+
 	/* Clean up and report error if unsuccessful or aborted */
 	if ((success == false) || (c->aborted)) {
 		html_object_free_objects(c);
@@ -656,7 +658,7 @@ void html_finish_conversion(html_content *htmlc)
 
 	html_get_dimensions(htmlc);
 
-	error = dom_to_box(html, htmlc, html_box_convert_done);
+	error = dom_to_box(html, htmlc, html_box_convert_done, &htmlc->box_conversion_context);
 	if (error != NSERROR_OK) {
 		NSLOG(netsurf, INFO, "box conversion failed");
 		dom_node_unref(html);
@@ -1710,6 +1712,13 @@ static void html_destroy(struct content *c)
 
 	NSLOG(netsurf, INFO, "content %p", c);
 
+	/* If we're still converting a layout, cancel it */
+	if (html->box_conversion_context != NULL) {
+		if (cancel_dom_to_box(html->box_conversion_context) != NSERROR_OK) {
+			NSLOG(netsurf, CRITICAL, "WARNING, Unable to cancel conversion context, browser may crash");
+		}
+	}
+
 	/* Destroy forms */
 	for (f = html->forms; f != NULL; f = g) {
 		g = f->prev;

content/handlers/html/html_internal.h

@@ -138,6 +138,10 @@ typedef struct html_content {
 
 	/** A talloc context purely for the render box tree */
 	int *bctx;
+	/** A context pointer for the box conversion, NULL if no conversion
+	 * is in progress.
+	 */
+	void *box_conversion_context;
 	/** Box tree, or NULL. */
 	struct box *layout;
 	/** Document background colour. */