Workaround for dnsmasq problem

[yichya]

openwrt/openwrt#14975 involves a change to dnsmasq configuration path (/tmp/dnsmasq.d -> /tmp/dnsmasq.cfg01411c.d) which breaks DNS configurations for luci-app-xray. Add this to Custom Configurations as a workaround:

return function(config) {
    const fs = require("fs");
    const uci = require("uci");
    const cursor = uci.cursor();
    const first = cursor.get_first("dhcp", "dnsmasq");

    fs.mkdir("/tmp/dnsmasq.d");
    fs.symlink("/tmp/dnsmasq.d/xray.conf", `/tmp/dnsmasq.${first}.d/xray.conf`);   
}

[yichya]

Caution: if you're using OpenWrt with ujail enabled, the workaround above won't work and may even make dnsmasq unable to start at all. Manually edit /etc/init.d/dnsmasq to add /tmp/dnsmasq.d to jail mount before applying workaround above:

diff --git a/package/network/services/dnsmasq/files/dnsmasq.init b/package/network/services/dnsmasq/files/dnsmasq.init
index b864ea9069..7a535f576d 100755
--- a/package/network/services/dnsmasq/files/dnsmasq.init
+++ b/package/network/services/dnsmasq/files/dnsmasq.init
@@ -1253,7 +1253,7 @@ dnsmasq_start()
 
        procd_add_jail dnsmasq ubus log
        procd_add_jail_mount $CONFIGFILE $DHCPBOGUSHOSTNAMEFILE $DHCPSCRIPT $DHCPSCRIPT_DEPENDS
-       procd_add_jail_mount $EXTRA_MOUNT $RFC6761FILE $TRUSTANCHORSFILE
+       procd_add_jail_mount $EXTRA_MOUNT $RFC6761FILE $TRUSTANCHORSFILE /tmp/dnsmasq.d
        procd_add_jail_mount $dnsmasqconffile $dnsmasqconfdir $resolvdir $user_dhcpscript
        procd_add_jail_mount /etc/passwd /etc/group /etc/TZ /etc/hosts /etc/ethers
        procd_add_jail_mount_rw /var/run/dnsmasq/ $leasefile

A better solution for this problem will be included in version 3.5 of this project (which is not planned before, but seems necessary now).

[yichya]

#430 includes an option to set dnsmasq integration mode in preview app.

If luci-app-xray works correctly, don't change this option. Only try "Per Instance" mode if:

• You're encountering problems related to dnsmasq: add filter-rr and cache-rr options openwrt/openwrt#14975
  • Select "Default instance"
• You're using other DNS services like AdGuard Home and it somewhat conflicts with luci-app-xray
  • Select none to disable any dnsmasq integrations
  • Make sure your DNS services are working correctly
  • Use 127.0.0.1:5300 (this is still provided by luci-app-xray) as an upstream server for your DNS services
  • You may not be able to associate domain names in manual transparent proxy under this circumstance (because of being unable to exempt Rebind Protection). Use some public blackholes (for example NYIIX RTBH) to avoid that.
• You're really setting up multiple dnsmasq instances and only some of them needs luci-app-xray