Ways to refer to locahost in Chromium

The filter rules preventing websites from portscanning the local machine have recently been tightened in Brave. It turns out there are a surprising number of ways to refer to the local machine in Chromium.

localhost and friends

127.0.0.1 is the first address that comes to mind when thinking of the local machine. localhost is typically aliased to that address (via /etc/hosts), though that convention is not mandatory. The IPv6 equivalent is [::1].

0.0.0.0

0.0.0.0 is not a routable address, but that's what's used to tell a service to bind (listen) on all network interfaces. In Chromium, it resolves to the local machine, just like 127.0.0.1. The IPv6 equivalent is [::].

DNS-based

Of course, another way to encode these numerical URLs is to create A / AAAA records for them under a domain you control. I've done this under my personal domain:

For these to work, you'll need to:

  • Make sure you can connect to IPv6-only hosts, for example by connecting to an appropriate VPN if needed.
  • Put nameserver 8.8.8.8 in /etc/resolv.conf since you need a DNS server that will not filter these localhost domains. (For example, Unbound will do that if you use private-address: 127.0.0.0/8 in the server config.)
  • Go into chrome://settings/security and disable Always use secure connections to make sure the OS resolver is used.
  • Turn off the chrome://flags/#block-insecure-private-network-requests flag since that security feature (CORS-RFC1918) is designed to protect against these kinds of requests.

127.0.0.0/8 subnet

Technically, the entire 127.0.0.0/8 subnet can used to refer to the local machine. However, it's not a reliable way to portscan a machine from a web browser because it only catches the services that listen on all interfaces (i.e. 0.0.0.0).

For example, on my machine, if I nmap 127.0.0.1, I get:

PORT     STATE SERVICE   VERSION
22/tcp   open  ssh       OpenSSH 8.2p1
25/tcp   open  smtp      Postfix smtpd

whereas if I nmap 127.0.1.25, I only get:

PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 8.2p1

That's because I've got the following in /etc/postfix/main.cf:

inet_interfaces = loopback-only

which I assume is explicitly binding 127.0.0.1.

Nevertheless, it would be good to get that fixed in Brave too.

Using a Streamzap remote control with MythTV on Debian Bullseye

After upgrading my MythTV machine to Debian Bullseye and MythTV 31, my Streamzap remote control stopped working correctly: the up and down buttons were working, but the OK button wasn't.

Here's the complete solution that made it work with the built-in kernel support (i.e. without LIRC).

Button re-mapping

Since some of the buttons were working, but not others, I figured that the buttons were probably not mapped to the right keys.

Inspired by these old v4l-utils-based instructions, I made my own custom keymap by by copying the original keymap:

cp /lib/udev/rc_keymaps/streamzap.toml /etc/rc_keymaps/

and then modifying it to adapt it to what MythTV needs. This is what I ended up with:

[[protocols]]
name = "streamzap"
protocol = "rc-5-sz"
[protocols.scancodes]
0x28c0 = "KEY_0"
0x28c1 = "KEY_1"
0x28c2 = "KEY_2"
0x28c3 = "KEY_3"
0x28c4 = "KEY_4"
0x28c5 = "KEY_5"
0x28c6 = "KEY_6"
0x28c7 = "KEY_7"
0x28c8 = "KEY_8"
0x28c9 = "KEY_9"
0x28ca = "KEY_ESC"
0x28cb = "KEY_MUTE"
0x28cc = "KEY_UP"
0x28cd = "KEY_RIGHTBRACE"
0x28ce = "KEY_DOWN"
0x28cf = "KEY_LEFTBRACE"
0x28d0 = "KEY_UP"
0x28d1 = "KEY_LEFT"
0x28d2 = "KEY_ENTER"
0x28d3 = "KEY_RIGHT"
0x28d4 = "KEY_DOWN"
0x28d5 = "KEY_M"
0x28d6 = "KEY_ESC"
0x28d7 = "KEY_L"
0x28d8 = "KEY_P"
0x28d9 = "KEY_ESC"
0x28da = "KEY_BACK"
0x28db = "KEY_FORWARD"
0x28dc = "KEY_R"
0x28dd = "KEY_PAGEUP"
0x28de = "KEY_PAGEDOWN"
0x28e0 = "KEY_D"
0x28e1 = "KEY_I"
0x28e2 = "KEY_END"
0x28e3 = "KEY_A"

Note that the keycodes can be found in the kernel source code.

With my own keymap in place at /etc/rc_keymaps/streamzap.toml, I changed /etc/rc_maps.cfg to have the kernel driver automatically use it:

--- a/rc_maps.cfg
+++ b/rc_maps.cfg
@@ -126,7 +126,7 @@
 *      rc-real-audio-220-32-keys real_audio_220_32_keys.toml
 *      rc-reddo                 reddo.toml
 *      rc-snapstream-firefly    snapstream_firefly.toml
-*      rc-streamzap             streamzap.toml
+*      rc-streamzap             /etc/rc_keymaps/streamzap.toml
 *      rc-su3000                su3000.toml
 *      rc-tango                 tango.toml
 *      rc-tanix-tx3mini         tanix_tx3mini.toml

Button repeat delay

To adjust the delay before button presses are repeated, I followed these old out-of-date instructions on the MythTV wiki and put the following in /etc/udev/rules.d/streamzap.rules:

ACTION=="add", ATTRS{idVendor}=="0e9c", ATTRS{idProduct}=="0000", RUN+="/usr/bin/ir-keytable -s rc0 -D 1000 -P 250"

Note that the -d option has been replaced with -s in the latest version of ir-keytable.

To check that the Streamzap is indeed detected as rc0 on your system, use this command:

$ ir-keytable 
Found /sys/class/rc/rc0/ with:
    Name: Streamzap PC Remote Infrared Receiver (0e9c:0000)
    Driver: streamzap
    Default keymap: rc-streamzap
...

Make sure you don't pass the -c to ir-keytable or else it will clear the keymap set via /etc/rc_maps.cfg, removing all of the button mappings.