Advanced Debugging

A guide to using Wireshark when debugging complex use such as chained-connections or version specific issues. To test more complex issues, we may wish to use pyenv or Docker in our development environment.

Testing Supported Python Versions via pyenv

Let’s use pyenv to install Python versions under active development. Since development versions are pulled from a VCS, we wish to force install to get the latest commit before testing. The dependency plumbum needs to be installed as well (add [dev] for plumbum development dependencies). All together now!

versions=( 3.7-dev 3.8-dev 3.9-dev 3.10-dev 3.11-dev )
for ver in ${versions[@]}; do
    pyenv install --force ${ver}
    pyenv global ${ver}
    pyenv exec pip install --upgrade pip setuptools wheel plumbum[dev]
    site="$(pyenv exec python -c 'import site; print(site.getsitepackages()[0])')"
    printf "${PWD}\n" > "${site}/rpyc.pth"
done

Each venv contains a .pth file that appends rpyc to sys.path.

PYENV_VERSION=3.11-dev pyenv exec python ./bin/rpyc_classic.py --host 127.0.0.1
PYENV_VERSION=3.10-dev pyenv exec python -c "import rpyc; conn = rpyc.utils.classic.connect('127.0.0.1'); conn.modules.sys.stderr.write('hello world\n')"

Testing Supported Python Versions via Docker

Testing RPyC often requires that you use specific Python versions. Docker will make your life easier when testing RPyC locally, especially when performing packet captures of RPyC communication across Python versions. The current settings will use bind mounts to simplify synchronization of RPyC source code within the containers. So, remember to checkout the commit you desire the containers to use on your host!

If desired, individual containers can be specified started

docker-compose -f ./docker/docker-compose.yml create
docker-compose -f ./docker/docker-compose.yml start rpyc-python-3.7
docker-compose -f ./docker/docker-compose.yml start rpyc-python-3.10

The registry server can be started like so

docker exec rpyc-3.8 /opt/rpyc/bin/rpyc_registry.py

The containers can then be used to test to your hearts desire

docker exec rpyc-3.7 /opt/rpyc/bin/rpyc_classic.py --host 0.0.0.0 &
docker exec -it rpyc-3.10 python -c "import rpyc;conn = rpyc.utils.classic.connect('rpyc-3.7'); conn.modules.sys.stderr.write('hello world\n')"

Tips and Tricks

Display filtering for Wireshark

tcp.port == 18878 || tcp.port == 18879
(tcp.port == 18878 || tcp.port == 18879) && tcp.segment_data contains "rpyc.core.service.SlaveService"

Running the chained-connection unit test

cd tests
python  -m unittest test_get_id_pack.Test_get_id_pack.test_chained_connect

After stopping Wireshark, export specified packets, and open the PCAP. If not already configured, add a custom display column:

Title,        Type,   Fields,     Field Occurrence
Stream Index, Custom, tcp.stream, 0

The stream index column makes it easier to decide which TCP stream to follow. Following a TCP provides a more human readable overview of requests and replies that can be printed as a PDF.