Krzysztof Żuraw: Docker.py- python API for Docker

Assumptions

I need an application that gets a code from the user, executes it and gives output back. As many people before me said output from user cannot be trusted so I need to use some kind of container for user input. To do that I used Docker python API- docker.py. Using that and Flask I created Tdd-app-prototype. Under the hood, this application will work like this: user writes a code on a website, clicks submit. Then Docker creates a container based on python docker image and executes code. I take the output from the container and destroy it afterwards.

As we know what application should do, let's jump into the code.

Code

The first problem that I have is that I don't want to write a code provided by the user to a disk, then read it from the disk and it execute by Docker. I want to store it in memory - perfect case for StringIO. Code that does this looks as follows:

@app.route("/send_code",methods=['POST'])defexecute_code():data=request.form['source_code']code=io.StringIO(data)create_container(code)output=get_code_from_docker()returnoutput

Here beside specifying routes in Flask I take data from the form, cast it to StringIO and create a container from that code. Function that does that is below:

defcreate_container(code):cli.create_container(image='python:3',command=['python','-c',code.getvalue()],name='tdd_app_prototype',)

What is cli here? I can use docker.py with Docker from other than my own computer location so before I can use any of these functions I need to specify Client:

cli=Client(base_url='unix://var/run/docker.sock')

It tells docker.py to use my local Docker. Let's go back to create_container. I tell docker.py to use official python 3 images. Then I specify a command to run: python -c and my code from StringIO. If you want to run standalone python script you can use this:

defcreate_container(code):cli.create_container(image='python:3',command=['python','-c','my_code.py'],volumes=['/opt'],host_config=cli.create_host_config(binds={os.getcwd():{'bind':'/opt','mode':'rw',}}),name='tdd_app_prototype',working_dir='/opt')

volumes and host_config keywords are for telling Docker to mount volumes. It is the same as running docker run -v"$PWD":/opt. Finally I set up working_dir so I don't need to provide a full path to my_code.py. As we have a container created now it is time to start it:

defget_code_from_docker():cli.start('tdd_app_prototype')cli.wait('tdd_app_prototype')output=cli.logs('tdd_app_prototype')cli.remove_container('tdd_app_prototype',force=True)return"From docker: {}".format(output.strip())

I used here wait so I wait for the container to stop. Then I take output in form of lists and remove the container. Right now it looks as follows:

That's all for today! If you want to see full code grab it here. Do you know other ways of using docker.py? Please leave a comment.

Special thanks to Kasia for being editor for this post. Thank you.

Cover image by Gabriel Barathieu under CC BY-SA 2.0, via Wikimedia Commons