Mail attachments not passed into sandbox

[mcrha]

Coming from https://gitlab.gnome.org/GNOME/evolution/-/issues/3245

The xdp_portal_compose_email() does not convert provided attachment paths to their equivalents, which a sandboxed app could use and actually attach it. In fact it does not change the path at all. In case of Evolution, you use URI like:

mailto:?subject=&body=&attachment=/path/to/file

where the /path/to/file is in the host filesystem, not in the sandbox file system.

A simple reproducer follows. Note: it is executed on the host system (by nautilus), and it can start the corresponding app in the flatpak.

Change the /path/to/file to an actual file, which is available in the host system, but not in the sandbox.

/* gcc `pkg-config --cflags --libs gio-2.0 libportal` test.c -g -O2 -o test && ./test */

#include <gio/gio.h>
#include <libportal/portal.h>

static void
send_email_done (GObject *source_object,
		 GAsyncResult *result,
		 gpointer user_data)
{
	GError *local_error = NULL;

	if (!xdp_portal_compose_email_finish (XDP_PORTAL (source_object), result, &local_error)) {
		g_warning ("Failed to send mail: %s", local_error ? local_error->message : "unknown error");
		g_clear_error (&local_error);
	}

	g_main_loop_quit (user_data);
}

int main(void)
{
	const gchar *files[] = { "/path/to/file", NULL };
	const char * const addresses[] = { NULL };
	GMainLoop *main_loop;
	XdpPortal *portal;
	GError *local_error = NULL;

	portal = xdp_portal_initable_new (&local_error);
	if (!portal) {
		g_warning ("Failed to create portal: %s", local_error ? local_error->message : "unknown error");
		g_clear_error (&local_error);
		return 1;
	}

	main_loop = g_main_loop_new (NULL, FALSE);
	xdp_portal_compose_email (portal, NULL, addresses,
                              NULL, NULL, NULL, NULL, (const char * const *) files,
                              XDP_EMAIL_FLAG_NONE, NULL, send_email_done, main_loop);

	g_main_loop_run (main_loop);
	g_main_loop_unref (main_loop);
	g_object_unref (portal);

	return 0;
}