Simulate a slow network connection on Mac OS X

January 14th, 2014 12:28 – by Torsten Trautwein

Testing how a website, app, service, etc. reacts to a slow and/or unstable network connection is pretty straightforward on OS X. This is very useful to especially simulate mobile connections which sometimes have a low bandwidth, high latency, or drop network packages altogether.

To make your connection sloppy, you can utilize ipfw pipes which is provided by Mac OS X 10.9 Mavericks. Open up your favorite Terminal app and use the following commands:

Show all existing rules

sudo ipfw list

Configure pipe to add some latency

sudo ipfw pipe 1 config delay 200ms

Configure pipe to have a limited bandwidth

sudo ipfw pipe 1 config bw 30KByte/s

Configure pipe to randomly lose half of the packets

sudo ipfw pipe 1 config plr 0.5

You can also set multiple options for a pipe

sudo ipfw pipe 1 config delay 500ms bw 100KByte/s plr 0.2

Use the configured pipe for all IP traffic

sudo ipfw add 1 pipe 1 ip from any to any

Remove the pipe and its configuration to reset everything you set up

sudo ipfw pipe 1 delete
sudo ipfw delete 1

How to subscribe to a Google Group without a Google account

October 31st, 2013 08:22 – by Torsten Trautwein

A few weeks ago, I switched my email accounts from Google Apps to FastMail – which, by the way, was as easy and straightforward as it gets.

I'm subscribed to some mailing lists on Google Groups and so I wanted to receive these mails without using my Google account. Here's how to do it:

  1. Go to the about page of the group you want to join, e.g.!aboutgroup/rubyonrails-core.
  2. Have a look at the Group email. In this example, that would be
  3. Append +subscribe to the address and send an email with the subject subscribe. Here, we would send that email to
  4. You'll receive a mail from the group asking you to confirm your subscription. Just hit reply and send the email without modifying the subject field.

That's it! You'll receive a confirmation shortly after.

Ruby Gem for Pen Editor

October 18th, 2013 15:09 – by Torsten Trautwein

While on the search for a nice wysiwyg editor with markdown support written in JavaScript, I came across Pen which I found very nice because of its unobtrusiveness.

Since I wanted to use it in Rails and couldn't find any Ruby Gem for it, I decided to write and publish my very first Gem loosely following Zurb's Yetify Your Rails blog post.

It's licensed under MIT and available on Github and via RubyGems.

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Torsten Trautwein
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