Monthly Archives: April 2017

Cycle camera

I’ve started cycling to work regularly again, and got myself a helmet camera. This is one of those annoying areas where there are cheap items made in the far east, or very expensive items made by more recognised brands. There doesn’t seem to be anything in between.

So, I took a punt at the cheaper end, and here it is:

img_20170422_095710

As you can see, the only part of their fixing accessories I used were two velcro straps; the camera feels most stable and doesn’t un-balance me when it’s strapped tightly to the middle of my helmet.

So, what do the videos look like? Here’s a thrilling clip of my commute yesterday morning:

I had no idea I moved my head so much when cycling, but it’s not bad quality – certainly good enough to get a number plate in the unpleasant event of someone cutting me up or knocking me off. I might try it on the handlebars next.

Needless to say, the camera does not claim to have any night vision at this price, but on lit streets, it’s possible to make out registration numbers of most overtaking cars if you step through the footage frame by frame.

Configuring it involves a txt file which it writes to the SD card, but once you’ve set the date and time, there’s not much else to worry about. The battery doesn’t last very long, but it only takes a couple of hours to charge over USB, so not bad. The inbuilt microphone just picks up wind noise when any sort of motion is involved.

Obviously, the £40 cost of the camera is then bolstered by buying the biggest micro SD card you can afford. At 90MB per minute of footage, it soon fills up. The way it records in chunks (maximum 10 minutes each) is a bit silly, but there are plenty of tools on Linux to concatenate the chunks together again.

AquaMail

I’ve been a long-time user of K-9 mail on Android, but the combination of the dreaded doze (“syncing disabled”) bug and various bits of clunky UI persuaded me it was time to move on. AquaMail, on first impressions, is rather nice. It lets me set the Archive folder, and can Archive things in a couple of taps. It also has a better approach to folder management, not showing the entire list in most places, but rather the folders you’ve actually used. Well worth a few quid for the pro version.

screenshot_20170414-111751

URC e-mail fail

I don’t know exactly who my church has outsourced @urc.org.uk e-mail to, but whoever it is clearly hasn’t read RFC822 (“SMTP systems are expected to make every reasonable effort to accept mail directed to Postmaster from any other system on the Internet.”)…

fail

Rather difficult to complain about the original broken address I found…

Update: They did get back to me via Facebook eventually. Still not had an answer on why postmaster@ doesn’t work, though.

Proxy DHCP

Somebody should have thought of this, and it turns out that somebody did.

A couple of years ago, I wrote about setting up a network boot server on my home LAN. I said this meant “taking the job of doing DHCP away from the router and doing it myself on a Linux box”.

Reader, I was wrong.

Setting up my new connection from BT today, I really didn’t want to keep running DHCP separately on a Raspberry Pi. What I wanted was for the Pi to just talk to clients which wanted to do network boot, and leave the BT router to do DHCP for ordinary devices.

This exists, and it’s called proxy DHCP. dnsmasq on the Pi can handle it; this tutorial is the one I got working. Sadly proxy DHCP doesn’t seem to honour options, so I had to take the path prefix (option 210) and manually prepend it to all the paths in my boot config.

This is all back up and working now, and hopefully should prove useful and less disruptive for a few years yet to come.

Now that i have native IPv6 and DHCP is back on the router, the Pi ceases to be a single point of failure, though it’s been rock solid for nearly three years now.

VirtualBox does network boot, of course

VirtualBox does network boot, of course

IPv6 at home from BT

It works – 10/10 on test-ipv6.com; can’t really say fairer than that. I did however enjoy the comedy reverse DNS:

$ curl http://files.dnorth.net/ipquick.php   (05/04 19:19)
2a00:23c4:e81:3100:fdbc:e60a:226e:9903
broadband.bt.com

Oddly enough, broadband.bt.com doesn’t resolve forwards to every IPv6 address on their network, so why bother claiming the reverse?

IPv6 only IMAP server

Because why not.

I have an IPv6 only virtual machine hosted at Mythic Beasts. Sadly, I don’t have much time to play with it these days, so I’m retiring it next month. Meanwhile, I’ve got something working which I thought ought to be possible but failed at the last time I tried…

I participate in the minority sport of hosting my own e-mail. That means I run an IMAP server which mail clients can view and search messages using. For myself, I have native IPv6 on my home internet connection, but when I’m out and about, my mobile phone is still IPv4 only, and most of my relatives who I host mail for are v4 only too. Mythic and others have blogged at length on hosting websites behind their IPv4-to-IPv6 reverse proxy, but can it handle IMAP?

$ nc -vv proxy.mythic-beasts.com 993                                 (01/04 17:06)
DNS fwd/rev mismatch: proxy.mythic-beasts.com != rproxy46-hex-a.mythic-beasts.com
DNS fwd/rev mismatch: proxy.mythic-beasts.com != rproxy46-sov-a.mythic-beasts.com
proxy.mythic-beasts.com [46.235.225.189] 993 (imaps) open

The fact that they’ve got it listening on the standard port for IMAP over SSL is encouraging. Let’s give it a go…

Prerequisites

In addition to your IPv6 only VM, you’ll need a domain and you’ll need to point some DNS. The examples below assume you’ve CNAMEd imap6.example.com to proxy.mythic-beasts.com.

Part 1: Install and configure Dovecot

Couldn’t be easier if we’re using Debian:

# apt-get install dovecot-imapd

Configuring Dovecot to properly store mail is beyond the scope of this article, so we’ll just do some minimal setup.

Part 2: SSL

It’s 2017, and SSL certificates are free. So let’s get some.

# apt-get install dehydrated apache2 dehydrated-apache2

The Apache server is only necessary because I’m taking the path of least resistance to getting SSL certificates from letsencrypt, which involves them verifying control over the domains using HTTP based challenges. You could set up Mythic’s DNS API to eliminate the need for this.

Once you’ve done this, edit /etc/dehydrated/domains.txt to include your domain (e.g. imap6.example.com) and add /etc/dehydrated/conf.d/config.sh containing CONTACT_EMAIL=”you@example.com”.

Having done this, you can run “dehydrated -c”. I’d recommend not running it as root, which means fixing the directory permissions when it falls over the first time. All that sorted, we should now have a directory /var/lib/dehydrated/certs/imap6.example.com/. That means we can go ahead and edit /etc/dovecot/conf.d/11-ssl.conf to read:

ssl = required
ssl_cert = </var/lib/dehydrated/certs/imap6.example.com/fullchain.pem
ssl_key = </var/lib/dehydrated/certs/imap6.example.com/privkey.pem

While you’re there, you should set port=0 on the non-SSL IMAP listener in 10-master.conf, to stop it listening on non-SSL ports.

All that sorted, we can restart Dovecot:

# service dovecot restart

And now we can jump over to a client machine and try it out:

$ ncat --ssl -v imap6.example.com 993
Ncat: Version 6.47 ( http://nmap.org/ncat )
Ncat: SSL connection to 2a00:1098:0:82:1000:3b:1:1:993.
Ncat: SHA-1 fingerprint: 2FB3 9166 A7B7 6552 6215 963C 43D0 824E A02F 9FB3
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN] Dovecot ready.

Assuming all is well, you’ll see the OK response from Dovecot, and when you hit Ctrl-C, you’ll get a line logged in /var/log/syslog on the server complaining about how your client hung up.

At this point, you should be able to try it with a real mail client, e.g. Thunderbird. And you’ll notice that everything in the garden is lovely, except that the logs show all connections coming from Mythic’s proxy, rather than their true source IPs.

Part 3: Proper IP addresses in the logs

Mythic’s proxy supports the PROXY protocol to enable this, but does Dovecot? As it turns out, they added support in 2.2.19, but Debian stable has 2.2.13. Backports to the rescue:

# apt-get install -t jessie-backports dovecot-imapd

Now we need to turn on PROXY support for imap6.example.com using the Mythic control panel. Having done that, I was very impressed with Dovecot – the logging in /var/log/syslog walked me through fixing each mistake I made, starting with needing to configure Dovecot for PROXY:

Edit /etc/dovecot/conf.d/10-master.conf and add haproxy = yes to the imaps listener. The defaults are sensibly secure: to avoid clients spoofing IP addresses, you must provide a whitelist of clients allowed to speak to listeners with haproxy support turned on. That means setting haproxy_trusted_networks in the same file. You can find the necessary IPv6 addresses to space-separate on this page.

Having done that and restarted Dovecot, I moved my laptop over to my guest wifi network (where there is no IPv6), and restarted Thunderbird…

$ grep dovecot /var/log/syslog
Apr  1 17:17:55 test-box dovecot: imap-login: Login: user=<david>, method=PLAIN, rip=192.0.2.1, lip=93.93.129.174, mpid=1234, TLS, session=<...>

Result! The IP quoted as “rip” (remote IP) is the IPv4 one I’m running Thunderbird on. Interestingly, Dovecot has chosen to log the IPv4 of Mythic’s proxy as the local IP (lip).