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Submitting a MiniZinc Coursera assignment

Date: 2020-09-27

I’m taking a Basic Modeling for Discrete Optimization course through Coursera, and the first assignment is due today. It was a challenge to run MiniZinc and also submit the assignment.

To summarize the problems:

• Gecode and MiniZinc would not easily build from source.
  • It looks like bison generates a parser.tab.cpp that references a parser.tab.hpp, but these projects have build rules to rename the file to have a .hh extension.
  • I couldn’t figure out an easy fix.
  • Fix: Use the binary AppImage.
• The assignment came with a submit.py file for Coursera that didn’t work with Python >= 3.8.
  • Error: AttributeError: module 'time' has no attribute 'clock'
  • I could submit by running it with Python 3.7, but the submission didn’t pass Coursera checks.
    • Error: Check your output statement and make sure it meets the requirements of the assignment.
  • Fix: Submit from the MiniZinc IDE.
• MiniZinc IDE failed to submit due to an old OpenSSL 1.0 dependency.
  • Error: qt.network.ssl: QSslSocket: cannot resolve SSL_library_init
  • Error: Error creating SSL context (error:140A90C4:SSL routines:func(169):reason(196))
  • Fix: Build a shared OpenSSL 1.0.2 library.

Installing MiniZinc

MiniZinc couldn’t build from source, so I installed the binary AppImage. Since it’s untrusted, I set it up to run as separate user named grencez-for-games, which was created in a previous article. The username does make some sense as MiniZinc will be solving puzzles.

Installation was fairly straightforward. I placed the AppImage in an Applications directory, and the installation step just creates some symlinks to it.

sudo -u grencez-for-games -- bash
cd ~/
mkdir -p Applications
wget -P Applications/ https://github.com/MiniZinc/MiniZincIDE/releases/download/2.4.3/MiniZincIDE-2.4.3-x86_64.AppImage
chmod u=rwx,go= Applications/MiniZincIDE-2.4.3-x86_64.AppImage
mkdir -p bin
BIN_LOCATION=$HOME/bin ./Applications/MiniZincIDE-2.4.3-x86_64.AppImage install

To quickly run minizinc as my normal user, I made a script /home/grencez/bin/minizinc:

#!/bin/sh

exec sudo -u grencez-for-games -- /home/grencez-for-games/bin/minizinc "$@"

Running MiniZincIDE with OpenSSL 1.0.2 library

I built the shared library for OpenSSL in /home/grencez-for-games/local/opt/openssl-1.0.2/:

sudo -u grencez-for-games -- bash
# Download and put in ~/local/opt/.
wget -O - https://ftp.openssl.org/source/old/1.0.2/openssl-1.0.2.tar.gz |
tar -x -z -f - -C ~/local/opt/

cd ~/local/opt/openssl-1.0.2/
make clean
# Configure to build shared libraries.
./config shared
make

Now we can invoke MiniZincIDE with LD_LIBRARY_PATH set so it finds the OpenSSL shared library. Here is my /home/grencez/bin/MiniZincIDE script:

#!/bin/sh

role=grencez-for-games

exec sudo -u "$role" \
  LD_LIBRARY_PATH="/home/$role/local/opt/openssl-1.0.2" \
  -- "/home/$role/bin/MiniZincIDE" "$@"

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