First things first: I copied code from https://github.com/hubdotcom/marlon-tools and https://github.com/amoffat/focus to build a custom DNS server facilitating my needs.

focus-dns.py helps you keep focused by applying schedulable firewall rules to distracting websites. An example firewall rule looks like this:

def domain_reddit_com(dt):
    return dt.hour == 21 # allow from 9-10pm

Starting

Now start Focus:

sudo FOCUS_ROOT="$HOME/Github/focus-dns" python focus_dns.py --server=1.1.1.1 --backup-server=8.8.8.8

where FOCUS_ROOT is where the focus_blacklist.py will be created.

Personally I like to keep my hosts and focus_blacklist.py file in the same directory as the focus-dns.py file.

Filtering Domains

Firewall rules involving schedules and timeframes can get complicated fast. For this reason, the scheduling specification is pure Python, so you can make your filtering rules as simple or as complex as you want.

The default filter rules is created on first startup in $FOCUS_ROOT/focus_blacklist.py:

def domain_news_ycombinator_com(dt):
    # return dt.hour % 2 # every other hour
    return False

def domain_reddit_com(dt):
    # return dt.hour in (12, 21) # at noon-1pm, or from 9-10pm
    return False

def domain_facebook_com(dt):
    return False

def default(domain, dt):
    # do something with regular expressions here?
    return True

You can test it with dig command.

> dig @127.0.0.1 facebook.com +short
127.0.0.1
> dig @127.0.0.1 news.ycombinator.com +short
127.0.0.1
> dig @127.0.0.1 reddit.com +short
127.0.0.1

The format is simple; Just define a function named like the domain you want to block, preceeded by "domain_". Have it take a single datetime object and have it return True or False. In the body, you can write whatever logic makes the most sense for you. Maybe you want to write your own Pomodoro routine, or maybe you want to scrape your google calendar for exam dates, and block certain websites on those dates.

For sites without their own scheduler function, the default() function is called.

There's no need to restart Focus if you redefine your schedules.

It is also

A simple DNS proxy server, support wilcard hosts, IPv6, cache.

Instructions:

1. Edit /etc/hosts, add:
127.0.0.1 *.local
-2404:6800:8005::62 *.blogspot.com

2. startup dnsproxy (here using Google DNS server as delegating server):
$ sudo python FOCUS_ROOT="$HOME/focus/" focus-dns.py -s 8.8.8.8

3. Then set system dns server as 127.0.0.1, you can verify it by dig:
$ dig test.local
The result should contain 127.0.0.1.

Usage:

focus-dns.py [options]

Options:
  -h, --help            show this help message and exit
  -f <file>, --hosts-file=<file>
                        specify hosts file, default /etc/hosts
  -H HOST, --host=HOST  specify the address to listen on
  -p PORT, --port=PORT  specify the port to listen on
  -s SERVER, --server=SERVER
                        specify the delegating dns server
  -C, --no-cache        disable dns cache

How it works

focus-dns.py is, at its core, a DNS server. By making it your primary nameserver, it receives all DNS lookup requests. Based on the domain name being requested, it either responds with a "fail ip" address (blocked), or passes the request on to your other nameservers (not blocked). In both cases, Focus adjusts the TTL of each DNS response so that the service requesting the DNS lookup will do minimal caching on the IP, allowing Focus's filtering rules to be more immediate.

FAQ

• Q: I started Focus, but it's not blacklisting the site I picked.

• A: Your browser may be caching that site's ip. Give it a few minutes.

• Q: Why do I need to start Focus with sudo?

• A: Focus needs to listen on a privileged port as a DNS server.

• Q: How do I stop Focus?

• A: Press Ctrl-c, just like you would terminate any running bash process.

TODO

[ ] Add commandline option to pass blacklist python file. [ ] Add another threaded application server like flask to show motivational quotes while opening the procrastinating sites.