Tag: Web

Open PDFs at specific entry points in the browser

PDF files can be opened at specific points in a browser. It is possible to open them at a given page or at the beginning of a chapter. This is done by applying HTML attributes to the link URL.

Adobe has some documentation concerning start parameters for PDFs here and here.

Open via chapter name

Append the complete chapter name to your link URL.

Example: http://blog.dispatched.ch/sps/thesis.pdf#3.4%20Programmiersprache%20und%20Paradigmen

Note: Chapter names are to be encoded as is common practice in URLs. In this example blanks are encoded to %20.

Open a specific page

Append the attribute ‘page’ followed by the page number to your link URL.

Example: http://blog.dispatched.ch/sps/thesis.pdf#page=38

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Serving images dynamically with CherryPy (on Google AppEngine)

Google AppEngine(GAE) is great for hosting Python (or Java)  Web-Applications. They offer 1.3mio hits/d and 1GB up- and downstream/d for free. Considering that you will get access to Google infrastructure that let’s you crawl the web as fast as Google does itself, choosing GAE is a no-brainer for applications doing a lot of web-crawling, screen scraping or web-indexing. You can even do cron-jobs to get your job done periodically.

I won’t elaborate on how to get an account, download the SDK and get started, because Google hosts great tutorials for these itself. If you are already familiar with Python web development this will get you started in a matter of minutes.

I personally chose not to use the Google webapp framework, because I’m quite familiar with CherryPy. I fell in love with it, because it feels very sleek – very Zen-like. This comes to no surprise, because it was a deliberate design decision as can be read in The Zen of CherryPy.

Getting started with CherryPy on GAE is no trouble, either. GAE supports any Python framework that is WSGI-compliant. Those include Django, CherryPy, web.py and Pylons. Google doesn’t host these frameworks themselves, so all you have to do is copy the whole framework into your GAE project to get the import to work. That’s it. Same counts for any 3rd party module. Need BeautifulSoup? Just copy the py-file to your project. Easy as cake.

Now, if you want to serve images dynamically, you don’t have to store them on harddisk to link to them. Just save them in the Google Datastore and serve whenever needed.

Using the following snippet you will be able to dynamically serve images with URLs like this:

import cherrypy
from cherrypy import expose
import wsgiref.handlers
import DynamicImage

class Root:
  def index(self):
    return ""

class GetImage():
  """ GetImage provides a handler for dynamic images """

  def __init__(self):
      Mockup for getting some images. Datastore or live
      scraping could be done here
    # Note: DynamicImage is just a mockup.
    # There is no such module.
    dynamic_image = DynamicImage.DynamicImage()
    self.pictures = dynamic_image.getImages()

  def index(self, num=None):
      Provides the handler for urls:
    return self._convert_to_image(self.pictures[0][int(num)])

  def _convert_to_image(self, picture):
    cherrypy.response.headers['Content-Type'] = "image/jpg"
    return picture

# Root() doesn't do anything here. It normally serves your index page.
root = Root()

# Generate route http://app/img/
root.img = GetImage()

# Start CherryPy app in wsgi mode
app = cherrypy.tree.mount(root, "/")

One last note: Processes running longer than 15-30s will be cut off from GAE with the DeadlineExceededError exception. You can catch this exception and try to divide your workload into smaller pieces.

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Linux password reset via Webmin for endusers

Searching for a viable option for endusers to reset or change their passwords, I have come up empty. Maybe I just searched wrong.

Anyway, I normally don’t do any administration using web interfaces (such as Confixx, Plesk and the like), but I have come across Webmin, which is “a web-based interface for system administration for Unix. Using any modern web browser, you can setup user accounts, Apache, DNS, file sharing and much more.”

Webmin supports user administration. Any account can implement the role of “Change Passwords”. Unfortunately, this will enable this particular user to change any other users password. Lucky for me, Webmin is OSS and written in Perl. So a quick four line code change does exactly what I need.

This is how the Munin front-end looks after the patch. If you’re not root, you can only change your own password. End of line.

If you want to recreate this setup on your machine, you can download the patch here and apply it with

$ patch /usr/share/webmin/passwd/index.cgi > index.patch

Have fun.

See and download the full gallery on posterous

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