Will Angley

Wi-Fi doesn’t need holes in walls. But most Wi-Fi routers are still connected to the Internet through a wired connection to an ISP. This connection does.

Connecting to your ISP

The cable that your ISP uses to reach your home is a lot longer than cables inside your home. Even when it’s the same sort of cable, it uses different protocols that work better over long distances.

Installing Wi-Fi requires installing hardware that translates these protocols to home networking protocols: an optical network terminal (ONT) for fiber-optic networks, or a cable modem for cable Internet.

This hardware is usually installed close to where the cable to the ISP reaches your home, near an outside wall. This makes it easier for the ISP to fix when it breaks.

Connecting to your Wi-Fi router

But an exterior wall is a bad place for a Wi-Fi router. A computer on the other side of your home will be twice as far away as it would be if the Wi-Fi router was in the center of your home.

Wi-Fi is made of radio waves, so the inverse square law applies. Getting twice as far away means you have one fourth the signal strength.

Wi-Fi tries to make up for this by spending longer talking to far away devices, which leaves it less time to talk to every other device on your network. This is a common way to run into Wi-Fi performance problems, even when you think your Wi-Fi router should be good enough.

Putting the Wi-Fi router near the center of your home, and running an Ethernet cable between it and your ISP hardware, resolves this. It’s often the most impactful Wi-Fi upgrade you can make.

And you might save some money if you stop renting your ISP’s router, too.

Previously: Marking myself into a corner, part 1

I found unexpected paragraph breaks in a post I’d written in Markdown, and copy-pasted into WordPress, about a day after I published it.

Clicking Edit showed I had line breaks in the Markdown source where there were paragraph breaks in the published post. I recognized this as WordPress’s wpautop filter, which uses different rules to place paragraph breaks than Markdown. A quick search shows this was reported upstream and closed as infeasible: jetpack#1965

I worked around it by deleting the line breaks.

Can I fix this with a plugin?

I tried dealing with this by using a plugin, Toggle wpautop, but found that wasn’t the right thing either; Jetpack Markdown relies on having wpautop active.

This is the second time I’ve encountered this; the first time was in 2019, when I was looking at moving from Hugo to WordPress. I felt overwhelmed and gave up on the project then.

This time, I looked back at the Jetpack issue, and saw there’s a workaround: calling wpautop( $content, false ); will do the right thing for Markdown posts. I haven’t found a plugin that implements this, but I might be able to patch it in to the one I’ve found…

First published September 18, 2020; Upgrading OpenWRT added January 4, 2021.

Why?

I wanted to get to my WiFi router from the Internet, but didn’t want it serving the Internet. Putting it on a VPN is a good way to do this, and Tailscale makes VPNs easy enough to run and use that there’s no good reason not to.

When?

This past weekend. I’d just gotten back to Brooklyn and installed OpenWRT 19.07, which included a new enough kernel to support Wireguard.

This was possible before – Tailscale’s been shipping ARM builds for a while, and OpenWRT’s been shipping 19.07 for a while too – but I didn’t try it before now.

How?

I get out a MacBook Pro that I’ve already set up Tailscale on, and read through the Tailscale docs for setting up Tailscale with static binaries to know how the install is supposed to flow.

It probably won’t be possible to follow them exactly, because OpenWRT is different, so I start playing around.

Installing Tailscale on the router

I look up my router’s hardware specs, then find the tarball for my router in Tailscale’s stable track, and download it to my machine:

% curl -O https://pkgs.tailscale.com/stable/tailscale_1.0.5_arm.tgz
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 11.9M  100 11.9M    0     0  3433k      0  0:00:03  0:00:03 --:--:-- 3433k
%
Code language: plaintext (plaintext)

I’m not sure how much free RAM and flash I have on my router, but I know I haven’t installed anything else, and guess that 11.9M is relatively small enough that I don’t need to worry about it.

So I copy the tarball over:

% scp tailscale_1.0.5_arm.tgz root@192.168.1.1:/tmp
Code language: plaintext (plaintext)

then SSH to the router and try to unpack the tarball:

# cd /tmp
# tar xvf tailscale_1.0.5_arm.tgz
tar: invalid tar magic
# 
Code language: plaintext (plaintext)

and it doesn’t work. OpenWRT uses busybox tar, so I fumble around for a bit (xkcd.com/1168 applies) and eventually figure out:

# tar x -zvf tailscale_1.0.5_arm.tgz
Code language: plaintext (plaintext)

Then I try running the binaries to make sure they’re actually the right ones 😛 :

# cd tailscale_1.0.5_arm
# ./tailscale version
1.0.5-g31b5dec0a
# ./tailscaled --help
<...>
Code language: plaintext (plaintext)

Looks it. Then I try to start tailscaled for real to figure out its dependencies.

# ./tailscaled
logtail started
Program starting: v1.0.5-g31b5dec0a, Go 1.14.4-ts56db765: []string{"/usr/sbin/tailscaled"}
LogID: 025f6648f94bcd1d40b0ee005ac472e123f7aeb2813874a71a7ba121da3d1827
logpolicy: using system state directory "/var/lib/tailscale"
2.6M/14.9M Starting userspace wireguard engine with tun device "tailscale0"
2.9M/16.6M Linux kernel version: 4.14.195
2.9M/16.8M is CONFIG_TUN enabled in your kernel? `modprobe tun` failed with:
2.9M/16.8M CreateTUN: can't create TUN device; /dev/net/tun does not exist
2.9M/16.8M wgengine.New: can't create TUN device; /dev/net/tun does not exist
flushing log.
logger closing down
logtail: dialed "log.tailscale.io:443" in 415ms
logtail: upload: log upload of 659 bytes compressed failed: Post "https://log.tailscale.io/c/tailnode.log.tailscale.io/0055d7ffaa6c80ecda7fef05574c36d025a42ead7d7409fce3b7218f84628e4a": x509: certificate signed by unknown authority
logtail: backoff: 12 msec
logtail: dialed "log.tailscale.io:443" in 413ms
logtail: upload: log upload of 659 bytes compressed failed: Post "https://log.tailscale.io/c/tailnode.log.tailscale.io/0055d7ffaa6c80ecda7fef05574c36d025a42ead7d7409fce3b7218f84628e4a": context canceled
#
Code language: plaintext (plaintext)

There are many lines of error messages but really two errors:

• `modprobe tun` failed means that Tailscale asked the kernel for a TUN device and got back “huh?”
• x509: certificate signed by unknown authority means that Tailscale tried to make a TLS connection but couldn’t figure out who was on the other end. When this happens with professional software (like Tailscale) it usually means no certificates are installed at all.

Both of these are pretty standard things to get from a package manager, but everyone calls them different names. I poke around OpenWRT’s packages and determine I probably need kmod-tun and ca-bundle, so I install them and try again.

# opkg update
# opkg install ca-bundle kmod-tun
Code language: plaintext (plaintext)

After this, tailscaled is able to start:

# ./tailscaled
<...>
Code language: HTML, XML (xml)

so I copy it to Flash.

# cp tailscale tailscaled /usr/sbin
Code language: plaintext (plaintext)

Running as a service

Tailscale comes with a simple systemd unit file. OpenWRT can’t use this directly, since it uses procd instead. I read the procd docs and, after about an hour of trial and error, port enough of it to get things working:

#!/bin/sh /etc/rc.common

# Copyright 2020 Google LLC.
# SPDX-License-Identifier: Apache-2.0

USE_PROCD=1
START=80

start_service() {
  procd_open_instance 
  procd_set_param command /usr/sbin/tailscaled

  # Set the port to listen on for incoming VPN packets.
  # Remote nodes will automatically be informed about the new port number,
  # but you might want to configure this in order to set external firewall
  # settings.
  procd_append_param command --port 41641

  # OpenWRT /var is a symlink to /tmp, so write persistent state elsewhere.
  procd_append_param command --state /etc/tailscale/tailscaled.state

  procd_set_param respawn
  procd_set_param stdout 1
  procd_set_param stderr 1

  procd_close_instance
}

stop_service() {
  /usr/sbin/tailscaled --cleanup
}
Code language: Bash (bash)

Also available as a GitHub Gist.

It’s my first time working with procd, so I’m pretty happy with how it turned out.

Gists have awkwardly long URLs, so I make a redirect to it that will let me download it with a short URL and upload it to my router easily:

% curl -LO https://willangley.org/tailscale-procd
% less tailscale-procd
% scp tailscale-procd root@192.168.1.1:/tmp
Code language: plaintext (plaintext)

I SSH to the router, install the init script, and run it to start tailscaled.

# cp /tmp/tailscale-procd /etc/init.d/tailscale
# chmod +x /etc/init.d/tailscale
# /etc/init.d/tailscale start
Code language: plaintext (plaintext)

Log in to Tailscale

Once tailscaled is running, I run

# tailscale up
Code language: plaintext (plaintext)

to get a login link, and click it to log in.

After logging in, I go to the Tailscale admin console and look for my router’s hostname; since I’ve never changed it, it’s OpenWRT.

I copy its IP address and make sure I can ping it from the machine I’m working from. (This would fail if the machine wasn’t on Tailscale, or was on a different Tailscale network.)

% ping 100.114.61.77
PING 100.114.61.77 (100.114.61.77): 56 data bytes
64 bytes from 100.114.61.77: icmp_seq=0 ttl=64 time=43.378 ms
64 bytes from 100.114.61.77: icmp_seq=1 ttl=64 time=7.895 ms
64 bytes from 100.114.61.77: icmp_seq=2 ttl=64 time=7.046 ms
64 bytes from 100.114.61.77: icmp_seq=3 ttl=64 time=5.387 ms
^C
--- 100.114.61.77 ping statistics ---
4 packets transmitted, 4 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 5.387/15.926/43.378/15.875 ms
Code language: plaintext (plaintext)

Once I confirm the connection works, I disable key expiry for the router to avoid it falling off of my network.

Surviving reboot

Now that I know it’s working, I enable the Tailscale service so it launches on every boot.

# /etc/init.d/tailscale enable
Code language: plaintext (plaintext)

And check to make sure it has succeeded:

# ls /etc/rc.d/*tailscale
/etc/rc.d/S80tailscale
Code language: plaintext (plaintext)

This took me several tries to get right, because I forgot to add the START=80 variable to my init script; without it, OpenWRT didn’t know where to link it into the startup order.

But now that it’s there, I’m good to go! At least until the next sysupgrade. If we don’t do anything all of this will get wiped away.

Upgrading OpenWRT

Added January 4, 2021

Yes! It is, in fact, possible to upgrade in-place with Tailscale. Keeping Tailscale around solves half of this, and only needs to be set up one time.

Providing its dependencies in an upgrade image solves the other half. This needs to be done for each upgrade, because of how OpenWRT works.

Keeping Tailscale around

Reading the CLI upgrade docs shows there’s a config directory, /lib/upgrade/keep.d/, that holds lists of files to keep through sysupgrades. The format isn’t documented, but it looks a lot like “one file or directory a line,” and I create /lib/upgrade/keep.d/tailscale with all of the files above:

/etc/init.d/tailscale
/etc/rc.d/*tailscale
/etc/tailscale/
/lib/upgrade/keep.d/tailscale
/usr/sbin/tailscale
/usr/sbin/tailscaled

OpenWRT doesn’t use globs in any of the files in the base image, but they seem to work; testing with sysupgrade -l shows that all the files above are now included in the backup.

Building an OpenWRT image with our dependencies

To make the packages we need available after an upgrade, I’ll make a custom image with those packages using Image Builder. This is much quicker than building from source, O(45 seconds) with a fast network connection. I like fast when I can get it.

Both Image Builder and the targets it contains are specific to your WiFi router. I’m, once again, only going to show what I did for mine.

On Mac

I’ve already set up my Mac with the keys to verify OpenWRT images, so I:

• download Image Builder there
• verify it (not shown)
• then transfer it to an Ubuntu VM I’m already running under Multipass for WordPress development

% curl -LO https://downloads.openwrt.org/releases/19.07.5/targets/ipq806x/generic/openwrt-imagebuilder-19.07.5-ipq806x-generic.Linux-x86_64.tar.xz
% # verify image (snipped)
% multipass transfer openwrt-imagebuilder-19.07.5-ipq806x-generic.Linux-x86_64.tar.xz primary:
Code language: PHP (php)

On Linux

• install Image Builder’s prerequisites
• unpack Image Builder
• figure out my WiFi router’s profile with make info
• build an image with the packages we’ll need for the install (and LuCI, it’s not included by default)
• print out where it wound up

$ sudo apt install build-essential libncurses5-dev libncursesw5-dev 
zlib1g-dev gawk git gettext libssl-dev xsltproc wget unzip python
$ tar xvf openwrt-imagebuilder-19.07.5-ipq806x-generic.Linux-x86_64.tar.xz
$ cd openwrt-imagebuilder-19.07.5-ipq806x-generic.Linux-x86_64/
$ make info
$ export LUCI_PACKAGES="uhttpd uhttpd-mod-ubus libiwinfo-lua luci-base luci-app-firewall luci-mod-admin-full luci-theme-bootstrap"
$ make image PROFILE=netgear_r7800 PACKAGES="ca-bundle kmod-tun $LUCI_PACKAGES"
$ cd bin/targets/ipq806x/generic/
$ realpath openwrt-19.07.5-ipq806x-generic-netgear_r7800-squashfs-sysupgrade.bin
/home/ubuntu/openwrt-imagebuilder-19.07.5-ipq806x-generic.Linux-x86_64/bin/targets/ipq806x/generic/openwrt-19.07.5-ipq806x-generic-netgear_r7800-squashfs-sysupgrade.bin
Code language: JavaScript (javascript)

On Mac

Finally, I copy the built image back to my Mac.

% multipass transfer primary:/home/ubuntu/openwrt-imagebuilder-19.07.5-ipq806x-generic.Linux-x86_64/bin/targets/ipq806x/generic/openwrt-19.07.5-ipq806x-generic-netgear_r7800-squashfs-sysupgrade.bin .
Code language: JavaScript (javascript)

Flashing the custom image

Flashing a custom image works the same way as prebuilt ones. In fact, there’s no difference in the UI. If you’ve worked with both you’ll need to take care to not install a prebuilt image by mistake and break Tailscale.

I upload the image to my router with LuCI, make sure it looks like it’s the right size (it should be slightly larger than the image from the Downloads page for my router; when it was smaller, it meant I’d forgotten LuCI), and that the SHA256 sum does not appear on the Downloads page for my router (which would verify I’m about to break Tailscale.)

I leave the option to keep settings and retain the current configuration selected, and click Continue.

A few minutes later my WiFi router comes back up and Tailscale does too .

Repeat

I’ll need to repeat building a custom OpenWRT image with our dependencies and flashing the custom image for each future OpenWRT upgrade.

Future Work

Updated January 4, 2021

There’s an open Tailscale issue, tailscale/tailscale#724, to package Tailscale for OpenWRT. If this happens soon, there won’t be much to do here 🙂

If it takes longer, I’ll probably try to get OpenWRT to not wipe this away with a sysupgrade – I think this’ll involve some combination of editing /etc/sysupgrade.conf and using sysupgrade -k on future upgrades.

It’s possible to bake Tailscale into the image with the FILES= argument to Image Builder, supplying a Tailscale pre-authenticated key to establish the connection. This should be O(hours) to do as a one off, and I might try this for a future OpenWRT upgrade.

Google Cloud Build makes these sorts of builds easy to automate, and I could probably do so with O(days) work. But this still seems like overkill unless I wind up with a fleet of these somehow.

Appendix

I broke my router’s firmware once doing this.

It wasn’t even a step that I needed to do; I was trying to figure out how much space I’d consumed with packages, and ran a command from a snippet in a Google search that was supposed to remove unused packages without clicking it to read the rest of the page.

The snippet looked reasonable, but if I’d clicked in, I would have seen the command I was about to run was going to remove the WiFi drivers.

But as I said, I didn’t, and wound up needing to rummage for a USB-to-Ethernet adapter and Ethernet cable to reinstall my firmware.

In August, I emailed my priest, Fr. Mark Burke, to ask for help living with my parents during COVID. We talked, and he included a prayer:

You can grow in your faith if you ask God for the grace to see your parents as He does. Ask for the grace to listen to them better. Let your faith be manifest in your charity. God gently will work through you, even if you’re unaware.

that I prayed, and later realized applied to more than my parents. I’ve come to see it as a statement of my values in life, and often the nearest I have to an answer to “what does it mean for me to be Catholic here?”

It’s largely about listening.

I spoke too soon. Shortly after thinking I’d be happy in the Gutenberg editor for everything, I found that it pushed me towards not writing complicated documents effectively – it’s hard to move sentences that cross paragraph boundaries around, and hard to set information aside when it doesn’t work well – and started writing in Markdown again.

Preparing to publish one of these stories, I turned on server-side Markdown:

1. install the Classic Editor plugin
2. enable Markdown in Jetpack
3. create a post in the Classic Editor.

since it’s closer to the Markdown dialects I’m familiar with than Jetpack’s Markdown block. I did some quick tests, and found that footnotes work¹, but syntax highlighting and math don’t:

And then I remembered that I’d only gotten them working with syntax highlighting and MathML Gutenberg blocks. Oops.

What was I supposed to do?

Markdown code blocks output classes compatible with SyntaxHighlighter Evolved, which seems instructive: it looks like I’m meant to handle this in JavaScript.

I can’t, though, because I’m using AMP. This is by design: it’s how AMP is cacheable on third-party servers, and how it defends against XSS. I don’t get enough traffic for caching to matter but I do like having baked-in XSS defense, especially if I want to turn on comments later, and I’m hoping not to turn off AMP.

Instead, if I want to use these with server-side Markdown and AMP, I’ll need to either:

• use alternatives to native Markdown syntax to embed these in posts, like:
  • GitHub Gists
  • Carbon images of code
  • LaTeX in Jetpack
• render these in JavaScript on the server side. this is seldom done in WordPress, but Wikipedia has been doing this at scale with Mathoid for some time now
• or glue together Markdown and the server-side logic I’m already using

I don’t like the way LaTeX in Jetpack renders to images – they’re blurry on the monitor I use most often for this – and I don’t want to upgrade my server in order to run Node, so I started exploring what it would take to render math here. With any luck this will be a superset of the work needed to get syntax highlighting working, too, and I’ll be able to do both quickly once I’ve done one.

Inline math is hard

The normal way of denoting math is $...$ for inline math, and $$
...
$$ for display math.

Double dollar signs are uncommon, so it’s pretty safe to use regexes to match them.

It’s just my $0.02, but I want to type single dollar signs often enough I wouldn’t want them to introduce a math context every time I use them. There are a couple ways of dealing with this:

• Wrap them in inline code, following Yihui Xie
• Tighten up the parser, since Marked, Pandoc and Rmarkdown don’t have this problem.

I think I’d rather tighten up the parser, since I’m already using Marked to preview Markdown on the Mac. Marked is closed source, so I can’t be sure what it does. But Pandoc is open-source, and instructive: it uses careful rules to restrict where single dollar signs introduce math contexts, and parser combinators to implement them (source).

A sketch of getting inline math working

1. Dust off my local development environment, since it tends to bitrot.
2. Set up a core functionality plugin for my site. Right now I’ve got this logic scattered throughout a Genesis child theme and a bunch of two or three line plugins.
3. Port the CommonMark Math extension from Haskell to PHP. A straight port is possible, since PHP has parser combinator libraries nowadays like Parsica.
4. Write a filter that replaces $...$ with <span class="math inline">...</span> and $$...$$ with <span class="math display">...</span>
5. Write a filter that conditionally replaces <span class="math ..."> with the corresponding <amp-mathml> tags when AMP is enabled
6. Wire them together in an AMP Custom Sanitizer

It seems simple enough. But I haven’t actually done any step after the first before, and recognize there are ways things could go wrong at each, or all, of the levels². And I’ll likely need to ask for help along the way if I pick this up; it’ll be the most PHP I’ve written in a decade.

So I might as well write this down and go looking for help before things go wrong rather than after 😛