Sometimes it’s useful to test your web application for situations where internet connections are less than stellar. It turns out that Mac OS X has a builtin utility called ipfw than, among other things, can do just this.
I first saw this technique from Joe Miller’s post on the subject. I packaged up the settings he mentioned into a little shell script:
| #!/bin/bash | |
| set -e | |
| USAGE="Usage: $0 [ip_address | reset]" | |
| if [ "$#" == "0" ]; then | |
| echo "$USAGE" | |
| exit 1 | |
| fi | |
| ip=$1 | |
| if [ "$ip" = "reset" ]; then | |
| printf 'Resetting... ' | |
| sudo ipfw list | grep 'pipe' | awk '{print $1}' | while read name; do sudo ipfw delete $name ; done | |
| echo 'Done' | |
| else | |
| echo "Creating rules to simulate latency to $ip... " | |
| # Create 2 pipes and assigned traffic to and from our webserver to each: | |
| sudo ipfw add pipe 1 ip from any to $ip | |
| sudo ipfw add pipe 2 ip from $ip to any | |
| # Configure the pipes we just created: | |
| sudo ipfw pipe 1 config delay 250ms bw 1Mbit/s plr 0.1 | |
| sudo ipfw pipe 2 config delay 250ms bw 1Mbit/s plr 0.1 | |
| echo "Done" | |
| fi |
You can drop that somewhere in your $PATH and chmod +x to make it executable. You can call it whatever you want, but I called mine “hinder”. After that, it’s simply a matter of using it:
$ hinder www.google.com
Now when you visit google.com, you should see some marked slowness. To reset, just run:
$ hinder reset
Google is now fast again.
The script works by adding 250ms delay to both directions of network traffic. It also adds a packet-loss percentage of 10%. You can play with these numbers to get even more latency simulation. Enjoy!