Learning Objectives:

1. Learn to use and write async functions
2. Increase understanding of internet architecture

The CS40 wardialing lab creates a simple script to scan all computers on the North Korean internet for web servers. You should complete the lab in order to get background on this assignment. (There is nothing to turn in for the lab, though, so you can gloss over the implementation details if you'd like.) The final code takes about an hour to run because it scans all ip addresses sequentially, without concurrency.

In this homework, we will use python's async functions to build a script that can scan arbitrary sections of the internet much faster. For example, the following command scans all North Korean ip addresses in only 30 seconds:

$ time python3 wardial.py 175.45.176.0/22
INFO:root:server at http://175.45.178.161
INFO:root:server at http://175.45.176.71
INFO:root:server at http://175.45.176.91
INFO:root:server at http://175.45.176.77
INFO:root:server at http://175.45.176.83
INFO:root:server at http://175.45.176.85
total ips found = 6

real    0m32.930s
user    0m1.006s
sys 0m0.067s

Scanning all ip addresses that belong to the Claremont Colleges takes about 20 minutes:

$ time python3 wardial.py 134.173.32.22/16 --timeout=1
INFO:root:server at http://134.173.238.250
INFO:root:server at http://134.173.53.33
INFO:root:server at http://134.173.53.35
...
INFO:root:server at http://134.173.114.161
INFO:root:server at http://134.173.69.195
INFO:root:server at http://134.173.254.189
total ips found = 71

real    18m7.277s
user    16m12.539s
sys     0m3.050s

The --timeout parameter adjusts how long the program should wait for a response from a server. There is also a parameter --max_connections which controls the number of servers to attempt to connect to simultaneously. (On most machines, non-root users cannot have more than about 1000 simultaneous web connections.) Tuning either of these parameters can improve the scanning performance.

State of the art scanning tools are able to scan all 4 billion internet addresses in under an hour. Getting that level of performance requires carefully tuning many other network configuration parameters as well.

Update the README.md file so that the test case badges point to your repo. Completing each of the tasks below should cause the badges to change from red to green.

Task 1:

The wardial function currently contains failing doctests, as seen by the command:

$ python3 -m doctest wardial.py

Find the FIXME (Task 1) comment inside the wardial function, and follow the instructions to make the doctests pass. Note that the doctests can take up to an hour to run, and it is okay to move onto task 2 without waiting for the doctests to finish.

Task 2:

Unfortunately, the code is still extremely slow. Even though we have functions labeled async and we are awaiting them, we are not doing it correctly, and the web requests are not happening concurrently.

Find the FIXME (Task 2) comment inside the _wardial_async function, and follow the instructions to enable concurrency.

Once the test cases pass and the badges turn green, submit your github url to sakai.