Using Python SocketServer

Attending

Patrick Shriwise

Graduate student of Paul’s at UW-Madison.

Git Aside: First Steps with a Repository

Matthew Gidden will provide a short, live demo of cloning and updating a repository. Most of the content will cover similar examples from Software Carpentry workshops (1, 2).

Using Python’s SocketServer

Today’s presenation will be a brief demo of how to setup a local server, handling get and post requests using the server, and using the server to access classes or modules within python from the server instance. We will be using code from this repo.

###Python modules needed to follow along

• python-socketserver (for server)
• python-simplehttpserver (for request handler, ususally comes with python)
• python-gspread (for editing google sheets)
• python-cgi (a common interface for passing/parsing html data)

##Setting up the server

1. Import the needed modules

2. Create a request handler for this server

3. Create a new threaded server class

4. Starup the server

#1
import SimpleHTTPServer, SocketServer

#2
handler = SimpleHTTPServer.SimpleHTTPRequestHandler

#3
PORT=4000
httpd = SocketServer.ThreadingTCPServer(("", PORT), handler) # Can also use ForkingTCPServer

#4
print "serving at port", PORT
httpd.serve_forever()

Start the server by running python server.py in the terminal.

You can now access this server by navigating to http://localhost:4000, and what you’ll see is pretty standard server behavior. There will be a listing of all the files in your directory as well as some navigation options for moving through your file tree. By having this in our own python instance however, we can do more…

(Note: an easier way to get a simple file server like this from the cmd line is python -m SimpleHTTPServer <port_number>)

##Replacing the Request Handler

Rather than relying on a standard request handler, we can create our own for more control:

class Handler(SimpleHTTPServer.SimpleHTTPRequestHandler):

    def do_GET(self):
        self.send_response(200)     #  Send 200 OK
        self.end_headers()
        self.wfile.write("Hello Bucky!")

And give this to the server instance accordingly

httpd = SocketServer.ThreadingTCPServer(("", PORT), Handler)

So now when we visit our server, the browser will simply get an error response of “OK” and will display the text “Hello, Bucky!”. Pretty simple, but the effect is that we can now return any text we’d like from the python instance, including html. (see branch demo2 on at the repo) The takeaway is that you can now run a subset of processes locally within the python instance.

The Tie-in

So why might you want to use something like this?

• Relatively lightweight way to collaborate with others.
• Create a simple listening device on your machine (rather than polling).
• Another means of interaction with your machine from afar.

WARNING: If you plan on leaving a server like this running on a machine, it is important to take recommended saftey measures. (go here for more

Example: Dagmc Model Views

I’ve setup a very simple home server as an example of this. It’s purpose is to show slice views of models used for Monte Carly analysis using Dagmc.

Again, why is this useful?

Allows a user to view view slices of a model from afar without even having to build the dagmc stack (and more specifially the tool I’ve built to do this). The same system could be employed for programs that aren’t graphics-based through the passing back of files or output in the form of an html table.

To view the code used for this home server, see the home_version and home_version2 branches of the repo for this example.