[PYTHON] The diagrams were interesting so I tried wrapping them with flask

What is diagrams

It is software that can draw an architecture diagram with python.

https://diagrams.mingrammer.com

A few days ago, my motivation was that I wanted to do something like the following about my eyes.

<img src='http://localhost:8080/?
with Diagram("Grouped Workers", show=False, direction="TB"):
    ELB("lb") >> [EC2("worker1"),
                  EC2("worker2"),
                  EC2("worker3"),
                  EC2("worker4"),
                  EC2("worker5")] >> RDS("events")

For the time being, I will finally make it

I wrestled for about 10 hours and created it. The complete source code is the following repository.

https://github.com/tamuto/diagrams-server

Compile Python code

First and foremost, the question is how to compile the Python source code passed in the URL? is. It's okay to get it from query_string, but you have to format it and then compile it. I used yapf as a library.

PROBLEM TO BE SOLVED: To have no line feed code in query_string in the first place.

I was planning to have them describe it, including the import statement, as it is posted in examples. However, the query_string is attached like ``` ... import EC2from ...` ````, and even if it is formatted, it cannot be separated (obviously).

Change arguments using AST

Here, we were able to implement the expected behavior. It is rewritten using NodeTransformer, compiled and executed by exec. I got an error saying that there was no lineno on the way, but I solved it safely with `ast.fix_missing_location`. (I think I did ...)

Forcibly requesting an icon ...

If you output with svg, an icon request will be generated separately. I forcibly processed it with Flask's route. (Because it is running in docker, it should be allowed !?)

Other issues

I tried my best to make it, but I think there are various problems.

• The received Python code will be executed as it is, so it is useless if it is published on the Internet. I couldn't judge whether it was okay in a limited way because it was running in docker. (If you hit something, there should be a security hole)
• When I tried using a sample other than the one described above, I got a Syntax Error. I have not investigated the details.
• If you specify / png in the URL, it will be created in that file format, but the characters will be garbled ... (When running with docker. There is no problem with running with python server.py at the time of development)
• The output image files will be stored in the / work folder. It has not been deleted.

Normally, it should be written as an issue ...

For some reason, I rushed to release it with a time trial feeling. After this, I would like to sit down and respond.