Latestversionserver

Christian Jacobsen
http://christian.lyderjacobsen.org/
http://www.absolutepanic.org/

A Python/WSGI based webservice that reports the latest version of a configurable set of files.

License

The server is distributed under a BSD-style license.

Files

• latestversionserver.py
  The WSGI application.

• latestversion.wsgi
  An example of how to configure and run the webservice for use with mod_wsgi

Use and Configuration

To use the latest version server you need a wsgi compatible webserver. You have a number of choices including wsgiref.simple_server and mod_wsgi. This documentation will show you how to set up the latestversionserver using these two wsgi servers.

wsgiref.simple_server

wsgiref is a standard python module as of Python 2.5. You can use this server to test and experiment with the server. An example of how to configure the server can be seen at the bottom of the latestversionserver.py file and more help can be found in the relevant Python documentation. An example is also given below:

import os
import re
from wsgiref.simple_server import make_server

from latestversionserver import latestversion_server

def test_server(environ, start_response):
    config = dict(
      base     = os.path.join(os.getcwd(), 'test'),
  # url where version info should be served using the json format
  # (optional)
  json_path = '/downloads.json',
  # base URL of the file server
  # (only required if json_path is used)
  base_url = 'http://localhost:8000',
      paths = [
          ('mac',    # url (relative)
           'mac',    # fs path (relative to base)
           cmp,      # compare function
           re.compile('Application-mac-[0-9]{8}\.[0-9]{4}\.zip'))])
    environ['latestversion.config'] = config
    return latestversion_server(environ, start_response)

httpd = make_server('', 8000, test_server)
httpd.serve_forever()

mod_wsgi

Serving using mod_wsgi is not too different from with wsgiref.simple_server. An example can be found in latestversion.wsgi.

Configuration

The configuration of the webservice happens by passing a dictionary to the application using the environ variable. The dictionary should be set to the key latestversion.config in the environ dictionary. See the two example files for an example of how to do this. The dictionary contains two items. The key base contains the base path in which files are found. This path is used in conjunction with the information stored in the tuples contained in the dictionary's paths key. Thus, paths should contain a list of tuples. Each tuple contains four items, the first describing the (relative) URL at which this tuple describes; the second describes the path (relative to base) where the files reside; the third is a comparison function (sorting in ascending order, see the Python documentation on [how to define a comparison function][com] or the [sorting tutorial][sortingtutorial]); and finally the fourth item which is a regular expression defining the files in the directory (specified as the second item) which have filenames that should be considered for inclusion in finding the latest version.

  config = dict(
      base  = os.path.join(os.getcwd(), 'test'),
      paths = [
          ('mac',    # url (relative)
           'mac',    # fs path (relative to base)
           cmp,      # compare function
           re.compile('Application-mac-[0-9]{8}\.[0-9]{4}\.zip')),
          ('win',
           'win',
           cmp,
           re.compile('Application-win-[0-9]{8}\.[0-9]{4}\.zip'))])

Using the webservice

The webservice exposes the URLs which you have defined in the configuration at a location relative to where you have attached your webservice. For example, if your webservice is running on http://download.amazingapp.com/latest then, if you have configured your webservice as in the configuration example above, you can see the latest Mac and Windows files at:

• http://download.amazingapp.com/latest/mac
• http://download.amazingapp.com/latest/win

If you are running the latestversionserver.py file directly to test the server, the following URLs are the ones you want to use:

• http://localhost:8000/mac
• http://localhost:8000/win

Visiting these URLs returns a single line, the name of the latest file according to the service. It is also possible to get more results than just the most recent. This is done by appending a number to the URL, which indicates the maximum number of results desired. For example, to display the five last versions one would use the following URL:

• http://download.amazingapp.com/latest/mac/5

or if running the test server:

• http://localhost:8000/mac/5

Visiting this URL shows the 5 most recent files, one on each line, sorted in ascending order. That is, the oldest one first, and the latest one last.

Special Cases

The webservice behaviour is as follows in these special cases:

• A filesystem path is referenced but it does not exist

  500 Server Error

  This can, for example, happen when there is a configuration entry for a partciular path, but the path is not a directory or the directory does not exist.

• There are no files in a configured directory

  200 OK but with no data, to indicate no latest version was found

• The user references a URL which has not been configured

  404 File Not Found

  URLs that have not been configured do not exist and return a 404.