Add readme

Author: Jesper Jensen

README.md

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+P-REX
+=====
+The pushdown MPLS network checker
+
+
+P-Rex is a model checker based on pushdowns for exploring and verifying
+MPLS networks. P-Rex takes in the mpls network in one of two formats, either
+in a bespoke XML format, or as a juniper dump. It then puts it together with
+a query and generates a pushdown in such a way that reachability in the
+pushdown implies something about reachability in the source MPLS network.
+
+P-Rex is written in Python3, and only deals with the translation of
+xml/juniper -> (MPLS-model + query) -> Pushdown. The tool uses moped
+(Version 1), bundled with the application, to compute reachability in the
+pushdown. Moped can be found [here](http://www2.informatik.uni-stuttgart.de/fmi/szs/tools/moped/) and we want to
+thank the authors for making it available :).
+
+Structure
+---------
+The repository follows a simple structure. All code related to the core tool
+is located in the `prex` folder. The entrypoint of prex is `prex/main.py`.
+
+The `bin` folder containes the binaries we rely on, just moped. The `bin`
+folder should be in the `$PATH` of P-Rex in order for us to find it.
+
+`res` contains test data. `res/nestable` is a simple network, in the
+bespoke xml format, used extensively throughout testing and development
+of the tool, and has a myriad of fun edge cases to explore. It is also
+the network used in the majority of the test cases distributed with the
+tool, so you can glance some of them through there. `res/new_mpls_dump`
+is a dump of a real network, used to benchmark the tool in the
+whitepaper. It's in the juniper dump format.
+
+Lastly, the `test` folder includes a bunch of tests used during
+development. They are structure such that a linux machine should only
+have to run `./test/test_cli.sh` to run the full test suite and get
+a regression report. That also makes it a repository of examples.
+
+Running
+-------
+As said in structure, the tool needs moped to be in the path, luckily
+a compiled moped is located in `bin`. Due to P-Rex being bundled as a python
+module it's also necessary to include the project root in the `$PYTHONPATH`.
+The full command to run P-Rex on the nestable network with the query `<> .*
+<>` for `k = 1` in over-approximation mode becomes.
+
+    PATH="./bin/:$PATH" PYTHONPATH=. python3 prex/main.py xml res/nestable/topo.xml  res/nestable/routing.xml adv-query "<> .* <>" 1 compile run
+
+The juniper dump is run with, (beware this takes a while):
+
+    PATH="./bin/:$PATH" PYTHONPATH=. python3 prex/main.py juniper-xml res/new_mpls_dump/isis  res/new_mpls_dump/forwarding adv-query "<> .* <>" 1 compile run
+
+It should be possible to use the `--help` flag at any point to get help
+about the possible options.