FIX: Django, uwsgi, Apache, ProxyPass, host is localhost and using ProxyPreserveHost

I just spent some time trying to figure out how to set our Django application.

Our setup is:
  Apache (handles HTTPS and client certificates) is front-end proxy to uwsgi
  uwsgi is used to run Django application in the backend.

The problem we faced is that our redirects were broken as links build by django used 'localhost' instead of name of the virtual host. After looking through solutions, and finding some of the issues like:

• Redirect is broken when HTTP_X_FORWARDED_HOST contains multiple hosts
• django.http.get_host() breaks reverse proxying on apache

I looked into django handling of get_host() and tried to understand what's happening.

Long story short, Apache passed HOST header as 'localhost', this led to search of apache documentation, as I was thinking that I reset headers using 

   RequestHeader set X-FORWARDED-PROTOCOL ssl

   RequestHeader set X-FORWARDED-SSL on

   RequestHeader set X-FORWARDED-HOST *hostname*

   RequestHeader set HTTP_HOST *hostname*

   RequestHeader set HOST *hostname*

but apparently, apache does not pass these through the proxy... so... drumroll, saving grace is:

   ProxyPreserveHost on

and side note, ProxyPreserveHost needs to be on the VirtualHost level or higher.

I hope this short post will save you some time :)

MacOSX & Chrome: How to make scrollbars ALWAYS visible in your web application

If you are, like me, annoyed that overflow: scroll does not display scrollbars on all MacOSX computers in chrome; you can actually force Chrome to behave by just adding this to your CSS:


::-webkit-scrollbar {
    -webkit-appearance: none;
    width: 7px;
}
::-webkit-scrollbar-thumb {
    border-radius: 4px;
    background-color: rgba(192,192,192,.3);
    -webkit-box-shadow: 0 0 1px rgba(255,255,255,.5);
}

How to calculate MD5 and SHA1 fingerprints using web browser?

Downloads and fingerprints

MD5 and SHA1 fingerprints often listed next to the large files one can downloads from files are there to ensure that data downloaded is the same as the data on the server. It is a good policy to always check if downloaded file has the same fingerprint as the one provided from the trusted source.

How to perform MD5 or SHA1 check using web browser?

While you can download the command line tools (shasum and md5sum) or use GUI tools to calculate MD5 and SHA1 checksum, it seems that today's browsers should be suited to let you do that calculation without resorting to specialized applications. One such tools that does not require you to download software, but lets you check MD5 and SHA1 sums right from the browser is Checksum MD5 and SHA1 calculator. This handy tool let you pick one or more files, and without uploading them anywhere check them right from the comfort of your device. It works with most of the modern browsers (IE10+, Chrome, Firefox, Safari) and it even works with your mobile devices if you ever need to do that sort of calculation (for example for .apk you just downloaded).

Dropbox (Error code -36)

Today, I was faced with Dropbox 'Error 36' on MacOS.
So, let's start from beginning... Dropbox has file name limitations, and those limitations are a bit different than operating system limitations (MacOSX).
I am convinced that there are good reasons for these, as they have special meaning on the command line level or would look really weird in the browser.

Let's start with the issues:
- Issue 1: File names can not start or end with blank character
- Issue 2: File names should not contain slashes

Where issue 2 is easy to spot, finder does not make it easy to spot issue 1. Thus I have created a short script that fixes blank characters in file names.

You can download dropbox_fix_script.pl. You need to navigate to the folder you are trying to copy, unzip and run this script from terminal.

Before you run this script, make sure to backup your data.

If there are enough interested readers, I may wrap this into application that you can drop a folder on.

--- script content is:
#!/usr/bin/env perl
#
sub fix()
{
    my @list = `find .` ;
    chomp(@list);
    for my $file (@list)
    {
    print "." ;
    my $base = `basename "$file"` ;
    my $dir = `dirname "$file"` ;
    chomp($base);
    chomp($dir);
        if( ($base =~ /\s+$/) || ($base =~ /^\s+/) || ($base =~ /\// )
        {
      print "match $file\n" ;
          $base =~ s/\s+$//mig ;
          $base =~ s/^\s+//mig ;
          $base =~ s/\//_/mig ;
    print "\n" ;
          return ( $file, "$dir/$base");
        }
    }
    return undef;
}

while( 1 )
{
    my ($file, $new_file) = &fix();
    if( defined( $file ) )
    {
        print "rename '$file' '$new_file'\n" ;
        if( -f $new_file )
        {
            print "file already exists $new_file -- fix $file \n" ;
            exit ;
        }
        if( -d $new_file )
        {
            print "dir already exists $new_file -- fix $file \n" ;
            exit ;
        }
        rename $file , $new_file ;
    }
    else
    {
        last;
    }

}

DNA reverse complement

Just published simple DNA reverse complement tool. It features reverse sequence generation, complementary RNA and DNA generation and of course reverse complement for both DNA and RNA. Check it out.

Click-o-mania and cyclick-o-mania in pure HTML

Last time I wrote click-o-mania clone was in summer of 1999. I wrote it in an MIT Athena cluster one summer day with the idea that it would help me with, than fresh Java skills.

Now the time has come, and I wanted to work on my GWT skills - thus - new HTML only, Flash-free, Java-free version of Click-o-mania and cyclick-o-mania are available. This simple games are written in using GWT/Java and compiled and tested on Mac and Windows, in variety of browsers and also adapted to work on iPhone. If they work well on Android, I would be interested to hear.

I hope you will enjoy these games as much as I enjoyed writing them.

Punnett Square at Bugaco.com

I just started writing Punnett Square calculator. It seems to be a nice tool for understanding inheritance relationships. Check it out at: http://www.bugaco.com/calculators/punnett_square.php