Entries posted in September 2015

All about sharing files easily

Sunday, 13 September 2015

Although I've been writing a bit recently about file-storage, this post is about something much more simple: Just making a random file or two available on an ad-hoc basis.

In the past I used to have my email and website(s) hosted on the same machine, and that machine was well connected. Making a file visible just involved running ~/bin/publish, which used scp to write a file beneath an apache document-root.

These days I use "my computer", "my work computer", and "my work laptop", amongst other hosts. The SSH-keys required to access my personal boxes are not necessarily available on all of these hosts. Add in firewall constraints and suddenly there isn't an obvious way for me to say "Publish this file online, and show me the root".

I asked on twitter but nothing useful jumped out. So I ended up writing a simple server, via sinatra which would allow:

  • Login via the site, and a browser. The login-form looks sexy via bootstrap.
  • Upload via a web-form, once logged in. The upload-form looks sexy via bootstrap.
  • Or, entirely seperately, with HTTP-basic-auth and a HTTP POST (i.e. curl)

This worked, and was even secure-enough, given that I run SSL if you import my CA file.

But using basic auth felt like cheating, and I've been learning more Go recently, and I figured I should start taking it more seriously, so I created a small repository of learning-programs. The learning programs started out simply, but I did wire up a simple TOTP authenticator.

Having TOTP available made me rethink things - suddenly even if you're not using SSL having an eavesdropper doesn't compromise future uploads.

I'd also spent a few hours working out how to make extensible commands in go, the kind of thing that lets you run:

cmd sub-command1 arg1 arg2
cmd sub-command2 arg1 .. argN

The solution I came up with wasn't perfect, but did work, and allow the seperation of different sub-command logic.

So suddenly I have the ability to run "subcommands", and the ability to authenticate against a time-based secret. What is next? Well the hard part with golang is that there are so many things to choose from - I went with gorilla/mux as my HTTP-router, then I spend several hours filling in the blanks.

The upshot is now that I have a TOTP-protected file upload site:

publishr init    - Generates the secret
publishr secret  - Shows you the secret for import to your authenticator
publishr serve   - Starts the HTTP daemon

Other than a lack of comments, and test-cases, it is complete. And stand-alone. Uploads get dropped into ./public, and short-links are generated for free.

If you want to take a peak the code is here:

The only annoyance is the handling of dependencies - which need to be "go got ..". I guess I need to look at godep or similar, for my next learning project.

I guess there's a minor gain in making this service available via golang. I've gained protection against replay attacks, assuming non-SSL environment, and I've simplified deployment. The downside is I can no longer login over the web, and I must use curl, or similar, to upload. Acceptible tradeoff.



The Jessie 8.2 point-release broke for me

Monday, 7 September 2015

I have about 18 personal hosts, all running the Jessie release of Debian GNU/Linux. To keep up with security updates I use unattended-upgrades.

The intention is that every day, via cron, the system will look for updates and apply them. Although I mostly expect it to handle security updates I also have it configured such that point-releases will be applied by magic too.

Unfortunately this weekend, with the 8.2 release, things broke in a significant way - The cron deamon was left in a broken state, such that all cronjobs failed to execute.

I was amazed that nobody had reported a bug, as several people on twitter had the same experience as me, but today I read through a lot of bug-reports and discovered that #783683 is to blame:

  • Old-cron runs.
  • Scheduled unattended-upgrades runs.
  • This causes cron to restart.
  • When cron restarts the jobs it was running are killed.
  • The system is in a broken state.

The solution:

# dpkg --configure -a
# apt-get upgrade

I guess the good news is I spotted it promptly, with the benefit of hindsight the bug report does warn of this as being a concern, but I guess there wasn't a great solution.

Anyway I hope others see this, or otherwise spot the problem themselves.


In unrelated news the seaweedfs file-store I previously introduced is looking more and more attractive to me.

I reported a documentation-related bug which was promptly handled, even though it turned out I was wrong, and I contributed CIDR support to whitelisting hosts which was merged in well.

I've got a two-node "cluster" setup at the moment, and will be expanding that shortly.

I've been doing a lot of little toy-projects in Go recently. This weekend I was mostly playing with the nats.io message-bus, and tying it together with sinatra.

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