Recent blog entries for dan

core.async with aleph

(More sledge retrospective)

There was a point about three weeks ago when I thought I had a working audio player, then I tried using it on the phone and I got awkward screeches every thirty seconds through my stereo when I told it to play Ziggy Stardust. No, I’m not talking about David Bowie’s voice here, this was genuine “a dog ate my CD” style digital audio corruption. The problem seemed to appear only on Wifi: I could replicate it on my laptop, but it didn’t show up on localhost and it didn’t show up over an ssh tunnel: I suspect it was something related to buffering/backpressure, and facing the prospect of debugging Java code wth locks in it I punted and decided to try switching HTTP server instead.

Documentation on HTTP streaming from core.async channels with Aleph is kind of sparse, at least insofar as it is lacking a simple example of the kind of thing that should work. So here is my simple example of the kind of thing that worked for me: wrap the channel in a call to>source and make sure that the things received on it are byte-array

(defn transcode-handler [request pathname]
  {:status 200
   :headers {"content-type" "audio/ogg"
             "x-hello" "goodbye"}
   :body (manifold/->source (transcode-chan pathname))})

(from server.clj )

I’m sure there are other things you could put on the channel that would also work, but I don’t know what. java.nio.ByteBuffer doesn’t seem to be one of them, but I’m only going on git commit history and a very fuzzy recollection of what I was doing that day, it might be that I did something else wrong.

Syndicated 2014-12-16 07:34:29 from diary at Telent Netowrks

Using the HTML5 audio element in Om

A quick one: if you want to render the HTML5 audio element with Om and do stuff with the events it raises, you will find that the obvious answer is not the right one. Specifically, this doesn’t work

(dom/audio #js {:controls true
                :autoPlay true
		:ref "player"
                :src bits
		:onEnded #(do-something)

This might be because React has to be taught about each event that each element can trigger and it doesn’t know about this one, or it might be because (it is alleged that) event handling in React is done by placing a single event handler on the top-level component and then expecting events on subelements to bubble up. According to Stack Overflow, audio events don’t bubble

The workaround is to add the event listener explicitly in IDidMount, and to call addEventListener with its third parameter true, meaning that the event is captured by the parent before it even gets gets to the sub-element to be swallowed. Like this

Syndicated 2014-12-15 00:07:51 from diary at Telent Netowrks

clj-webdriver with recent Clojure/Firefox

At the time I write this, the latest release of clj-webdriver is 0.6.1. There are two separate problems with this version, at least as far as I can make out

1) some kind of bug which causes it to fail with the message No such var: clojure.core.cache/through. I haven’t tracked this to its root cause but am guessing that the [org.clojure/core.cache "0.5.0"] in clj-webdriver’s project.clj was too old a version for some other dependency I am pulling in. I added an explicit [org.clojure/core.cache “0.6.4”] in my project and that seems to have fixed it. See clj-webdriver issue 132

2) The version of Selenium it pulls in is 2.39, which is too old to work properly with even the vaguely recent version of firefox I’m using (33.1.1). Fixing this is again just a matter of adding the more recent versions of Selenium stuffz as explicit dependencies in project.clj

With those two changes clj-webdriver now seems pretty happy and I can start adding some basic smoke tests to Sledge so that I don’t have to manually test client-side behaviours whenever I change it

Done: use reference cursors instead of channels for enqueuing/dequeing tracks

Next up: use a channel for xhr search instead of quite so many callbacks

Forthcoming: more work on UI/UX. Add tabs to switch between search view and play queue, unify the different-for-no-good-reason “search” and “filters”.

The branch/commit policy from hereon in is

  • it is a bug if master doesn’t pass regression tests on my machine
  • but there could be any kind of rubbish on branches
  • but I firmly subscribe to the Kanban notion of limiting work-in-progress, so will be striving to keep each of these branches short-lived or to declare them moribund at the earliest opportunity

Note that the tests currently depend on having a music collection containing at least four tracks by Queen. This is not ideal and I will fix it some day but in the meantime you’ll just have to work around it somehow. Maybe try leaving a USB stick in the car for two weeks or something

Syndicated 2014-12-14 23:06:29 from diary at Telent Netowrks

ANN Sledge (We're lost in music)

As a person with a large ripped CD collection at home
I want to find and listen to that music from work/on my phone
So that I don’t have to talk to the people around me

Sledge is a program that you can run on a computer with

  • some music you want to listen to
  • a JVM
  • some means of exposing a TCP server port to the internet
  • libav / ffmpeg

It indexes all the music in the directories you tell it to look in, and then it serves a web page with a search box and some buttons on it, which you can access on a device (computer/phone/tablet/etc) that

  • can access the internet
  • has a web browser that supports the HTML5 AUDIO element and likes Ogg files (most of them, these days)

It’s also the first useful[*] thing I’ve written using Clojure and Clojurescript and Om . Get it at – no jar file download yet, so you’ll need leiningen to build it

[*] defined as: I’m using it.

Standing on the shoulders of github

The heavy lifting was mostly done by others. In addition to the above-mentioned, it uses

  • as a Lucene interface
  • for streaming the transcoded audio
  • to wrap JAudioTagger

Future plans

It’s reached MVP, as far as I’m concerned: aside from a couple of bugs it meets my use case. But I do have more planned for it as time permits:

  • UI makeover, make it easier to discover music I’d forgotten I have
  • Make the initial media scan much much faster (currently does about 2000 files a minute on my machine) and/or show the progress as it scans
  • some tools for reporting on duplicate files
  • something to deal with correcting/adding tags to media files that have bad or no metadata
  • transcode to formats other than Ogg Vorbis, maybe, if there are people who wnt to use it with browsers that don’t support Ogg

A long long time ago

Previously: “I started looking at all the UPNP/DLNA stuff once for a “copious spare time” project, but I couldn’t help thinking that for most common uses it was surely way over-engineered”. In the four years (and two days) since my opinions haven’t changed but my tools have.

Syndicated 2014-12-08 07:16:18 from diary at Telent Netowrks

If you can see this, it worked

For values of “this” which you don’t care about and can’t see, but my hacky homebrew blogging engine now watches a bare git repo using inotify and runs a checkout/refreshes its content when it sees changes. I’m not sure it wouldn’t have been simpler just to make it die and then use a, y’know, shell script or something to run a git pull before restarting the server, but I did it this way because ZERO DOWNTIME.

Anyway. You don’t see and can’t care, or possibly vice versa. But the previous Heath Robinson stuff with git hooks wasn’t working now that the bare git repo is owned by someone other than the uid that runs the http daemon, so a different Heath was called for.

Syndicated 2014-02-13 22:50:59 from diary at Telent Netowrks

Keeping secrets in public with puppet

I recently stumbled across dotgpg , which is in essence some scripts to make it easy to securely keep secret files in a public git repo, which are protected by means of having been encrypted (usually for multiple recipients). It comes with capistrano glue for decrypting them again and sending them to your production servers, but it doesn’t quite fit my masterless use case where everything happens on the same box and there isn’t the same notion of a ‘target system’

But it set me to thinking: what if there was some kind of gpg agent that let you type in your key once and used it for multiple decryptions (turns out there is) and what if you then wrote some custom puppet function, let’s call it decrypt, so you could then say

  file {'/etc/wpa_supplicant.conf':

and everything would Just Work. Well, turns out I did and you can and (as far as I can tell) it does. The custom function is as simple as creating the file puppet/parser/functions/decrypt.rb inside /etc/puppet (or wherever) containing

module Puppet::Parser::Functions
  newfunction(:decrypt, :type=>:rvalue) do |args|
    filename = args[0]
    `/usr/bin/gpg --use-agent --decrypt #{filename}`

and now at the expense of a slightly more convoluted puppet invocation

$ sudo  make -C/etc/puppet/ GNUPGHOME=$HOME/.gnupg GPG_AGENT_INFO=$GPG_AGENT_INFO

I can put my wpa network configuration (and my jabber passwords, and smtp client passwords, and some other stuff I can’t right now remember what it is but am sure exists) alongside my all my other configuration instead of either having to do something silly with git submodules or rebuilding it by hand. Am now furiously trying to memorise my passphrase.

Better error checking would be nice, so that it doesn’t overwrite a perfectly good config file with an empty one if the gpg stars aren’t all aligned, but that is left as an exercise for next time.

Syndicated 2014-02-10 18:26:14 from diary at Telent Netowrks

MuDDLe, a faster simpler maildir downloader

One of the services running on my old Bytemark VM was the Dovecot IMAP server. When I started thinking about configuring it on the replacement box I realised that I don’t actually need IMAP these days, so, er, why bother? So I didn’t. But what I do need is a way of getting the Maildir on that machine onto other machines, and everything I looked at to do this job (other than rsync) was fearsomely complicated because it also catered for a zillion other file formats and/or transports. Or because it wanted to sync in both directions, which I don’t really care about that much.

So, muddle

In essence, what it does is this: connect to the remote host, find list of files in cur/ and new/, compare with similar list on local host, create tar stream of differences, transfer it, unpack each transferred file into tmp/ and atomically rename into cur/ when done.

This adds up to one transfer of file names and a second transfer of all the file contents. Each of these is one-way and distinctly non-chatty, so it should have reasonably good network performance characteristics and you can use ssh compression if your network bête noire is bandwidth itself and not just latency.

It might not be as simple as possible, but at the same time it might also be simpler. For example, and as alluded to above, the download is one-way only, so it won’t e.g. update the server to mark messages as read. If you care about that stuff, this is not for you.

(Why not rsync? It can’t detect that a rename from new/foo to cur/foo:2, is a rename, so treats the latter as a new file. Which is a teensy bit suboptimal)

Syndicated 2014-02-02 23:27:24 from diary at Telent Netowrks

Debian, runit, chruby, bundler

Pretty much ever since I wrote it the software that powers this blog – a Ruby Sinatra app called “My Way” – has been running on a Bytemark VM inside a tmux session, and every time I’ve rebooted the server I’ve not only had to restart it by hand but first to remember how to restart it by hand.

I’m in the process of migrating the said VM to one of Bytemark’s new BigV VMs (New! Shiny! More RAM! Marginally Cheaper!) and taking the opportunity to clean it up a bit first. After reading Steve Kemp’s article on runit I decided to give that a go. This is notes-to-myself on what I’ve found so far

:; cat /etc/sv/my-way/run 
exec 2>&1
cd /home/my-way/my-way
. /usr/local/share/chruby/
chruby ruby-2.0.0 
export LANG=en_GB.UTF-8
exec chpst -u my-way -v bundle exec ruby -I lib bin/my-way.rb

:; sudo update-service --add /etc/sv/my-way
Service my-way added.

This is the script that starts the blog server, and the installation procedure thereof

Worthy of note:

  1. per convention, the run scripts (and attendant files) live in directories /etc/sv/someservicename, and these directories are are then symlinked into /etc/service by update-service
  2. chruby doesn’t run in sh, so we run this script under bash
  3. it redirects stderr to stdout so the svlog process (see below) can see it
  4. it runs as root up until the chpst invocation, so the ruby that you specify needs to be in /opt/rubies and not in /home/yourusualuser/.rubies. If you ran ruby-install under sudo it will have put it in the right place.
  5. runing bundle install with the --deployment flag when installing the ruby project will have sidestepped a whole class of “can’t find your gems” issues. So do that.

Next up is

:; cat /etc/sv/my-way/log/run 
exec svlogd /var/log/my-way

This is the script that makes sure logs go somewhere. Specifically, they go to the file /var/log/my-way/current, which svlog is able (though as far as I know not yet configured) to rotate according to some defined criteria, and without needing to restart the server. The log files are owned by root, but maybe that’s changeable using chpst again.

:; sudo sv  status my-way
down: my-way: 94s, normally up; run: log: (pid 13620) 48806s
:; sudo sv  start my-way
ok: run: my-way: (pid 28343) 0s
:; sudo sv  status my-way
run: my-way: (pid 28343) 8s; run: log: (pid 13620) 48818s
:; pkill ruby
:; sudo sv  status my-way
run: my-way: (pid 28379) 31s; run: log: (pid 13620) 48949s
:; sudo sv  stop my-way
ok: down: my-way: 0s, normally up

And here’s how I start and stop it and stuff. Note that it magically restarted after I ran pkill ruby.

If you can read this, it works.

Syndicated 2014-01-19 11:18:31 from diary at Telent Netowrks

Using the HP IP Console Viewer app on Linux

Another success criterion in my current story to get the Machine That Does Everything out of the living room is being able to do things like kernel upgrades without having to go to where it is and plug in a keyboard and screen, and to that end I bidded for and – somewhat unexpectedly – won an HP 1×1×8 IP KVM switch on Ebay.

  1. It appears to be actually made by someone called Avocent, though Avocent seem to change their products in non-trivial ways for different badge engineers
  2. Along with the switch itself, you need an “Interface Adaptor” for each connected server. This is a thingy that has an RJ45 at one end and a set of keyboard/video/mouse connectors at the other, and should cost around £7 or £8
  3. Although you can plug in a keyboard and mouse – and it works just like a local KVM if you do – you will need to connect to the serial port to configure the network settings, there seems to be no way of doing it from a connected keyboard.
  4. Although some variants of these things run web servers on ports 80 and 443 which let you download java applets to connect to the servers plugged into them, mine doesn’t. I know not why.
    Starting Nmap 6.00 ( ) at 2014-01-08 22:48 GMT
    Nmap scan report for kvm.lan (
    Host is up (0.011s latency).
    Not shown: 997 closed ports
    2068/tcp open  advocentkvm
    3211/tcp open  avsecuremgmt
    8192/tcp open  sophos
    MAC Address: 00:02:99:03:62:5C (Apex)
    None of those responds to HTTP or HTTPS requests
  5. So you need to download the software yourself. HP love to rearrange their web site, judging from the number of dead links in the google seearch results, but as of the time I write this you can get it from here and if that link is out of date when you read this you may find the file you need by googling for SP50317.tar
  6. Having downloaded it, you must untar it and run the setup.bin shell script. Do this with LOCALE=C or it doesn’t work
  7. On a 64 bit platform it may complain about missing libraries that you thought you had. This is because it’s 32 bit. Users of the Universal Operating System (a.k.a Debian) can grab the necessary with
    $ sudo apt-get install  libxext6:i386 libxtst6:i386 
  8. Once you’re through the setup process, you can start the actual viewer which is called IPViewer. The warning strings: '/lib/': No such file it emits is non-fatal and as far as I can tell entirely ignorable.
  9. Its keystroke handling is a bit screwy: I found that it has some kind of ‘double echo’ problem on the console, so each key I press emits a character once when I press it and again when I release.
    loaclhost login: ddaann
    There is an autohiding menu at the middle of the top of the screen - mouse around near the titlebar to see if you can find it. From this menu I selected Tools →Session Options, and then the ‘General’ tab. This pops up a dialog box in wich there is a checkbox ‘Keyboard Pass-through’. Selecting this option fixed the ddoouubbllee kkeeyyss problem for me. It’s not all peachy yet, though, because neither Right Arrow nor DEL seem to do anything in Pass-through mode, and the latter of those is key (sorry) to entering the system BIOS Setup interface.
  10. The IPViewer.lax file has some interesting-looking settings, including the path to the JVM it wants (I tried with my system OpenJDK 1.7.0_25 and it kind of worked but the keyboard didn’t work at all) and the jvm max memory size. More as I find it.

Syndicated 2014-01-08 22:40:29 from diary at Telent Netowrks

How to avoid using Outlook for Mac (mostly)

New Year’s Resolution number 2 (number 1 is domestic) is, taking inspiration from Neil Gaiman, to spend less time on Twitter and more time on long-form – or at least, paragraphs-long-forms – of writing. So to ease myself in gently, here’s a plug for DavMail

It might be overstating the case slightly to claim that one of the worst things about working at $JOB is that everyone has to use Outlook, but it’s certainly not one of the better things. So, having a spot of time between Christmas and the New Year to improve my working environment, I started looking for other ways to address the Exchange server.

Step 1 was to install DavMail

DavMail is a POP/IMAP/SMTP/Caldav/Carddav/LDAP exchange gateway allowing users to use any mail/calendar client (e.g. Thunderbird with Lightning or Apple iCal) with an Exchange server, even from the internet or behind a firewall through Outlook Web Access.

This bit went smoothly.

(Step 1.1 was to Paypal the DavMail author a small amount of cash: this is already making my work environment so much nicer)

Step 2: install and configure offlineimap. It would be neat if using offlineimap didn’t require one to learn Python (folder filtering syntax, I am looking at you) but I told it my ‘remote’ server was reachable at localhost:1143 and cargo culted some stuff to drop all the boring folders full of crap, and off it went (very slowly) downloading my mail. This is approximately how my .offlineimaprc looks:

accounts = Exchange

[Account Exchange]
localrepository = Local
remoterepository = Remote
status_backend = sqlite

autorefresh = 1 
# minutes between refreshes
quick = 30
# partial refreshes between full ones

[Repository Local]
type = Maildir
localfolders = ~/SB-Mail

[Repository Remote]
folderfilter = lambda folder: folder not in ['Trash','Drafts', 'Junk'] and not"INBOX/20\d\d$", folder) and not"^Trash/", folder)
type = IMAP
remotehost = localhost
remoteport = 1143
remoteuser = mydomain\myusername
remotepass = mypassword

mydomain, myusername and mypassword are placeholders: make the obvious substitutions.

Step 3: Gnus. Point it at the local folder that offlineimap is talking to, and tell it to use davmail via smtpmail for sending outgoing messages:

(setq gnus-select-method '(nnmaildir "sb"
                           (get-new-mail nil)
                           (target-prefix "")
                           (directory "~/SB-Mail/")))

(setq user-mail-address "")
(setq smtpmail-smtp-server "localhost")
(setq smtpmail-smtp-service 1025)
(setq smtpmail-auth-credentials "~/.authinfo")

.authinfo looks like this

machine localhost login mydomain\myusername password mypassword port 1025
Again, replace my* with actual values

Step 4: Oh but, dear Lord, this thing could not find an uglier way to render HTML email, what’s up with that? Turns out this is because the Emacs app in Homebrew wasn’t built with libxml support. Turns out this is because the bundled libxml in MacOS Lion (other Bloodthirtsy Yet Cuddly Big Cats are available) is missing the file that pkg-config needs so that any app that might want to build against it can find it. So:

Step 3.9: Building your own Mac Emacs is surprisingly easy – just follow the instructions in nextstep/INSTALL – but unless you take steps to make libxml show up, the resulting app will suffer the same problem as Homebrew’s binary. So:

Step 3.8 Install the homebrew libxml package, and (2) add the .pc file it provides to PKG_CONFIG_PATH, because – as it doesn’t want to clash with the broken builtin libxml – it installs into some obscure out-of-the-way place that nobody will ever find it. “I eventually had to go down to the Cellar”. “Yes, Mr Dent, that’s the display department”.

$ pkg-config --cflags libxml-2.0
Package libxml-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `libxml-2.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libxml-2.0' found
$ PKG_CONFIG_PATH=/opt/boxen/homebrew/opt/libxml2/lib/pkgconfig/  pkg-config --cflags libxml-2.0

Your Pathnames May Vary. You get the idea. When is Macos Shaved Yak planned for release?

But after all that, it Just Works. Mostly. Sometimes it complains that files go missing, but I think that’s because I’m still checking mail occasionally (so causing them to be marked as read) in Outlook and this makes them jump from new/ to cur/. And I haven’t yet figured out how to deal with calendaring or contacts, but the former is a minor annoyance and the latter is probably just a matter of finding a way to make Gnus talk LDAP to the LDAP proxy in DavMail

Anyway, Happy New Year. Mine will be.

Syndicated 2014-01-06 07:51:17 from diary at Telent Netowrks

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