I needed a way to strip EXIF data from JPEGs in Python. All of the methods I found relied on external C/C++ libraries or shell execs which, unfortunately, meant I could not use ‘em — I can’t install external libraries or exec in my environment.

Luckily I found an easy to understand description of the EXIF spec and used it to make this python script:

import struct
def stripExif(image):
	# http://www.media.mit.edu/pia/Research/deepview/exif.html
	# Read the jpeg blocks, remove APP1 (FFE1..)
 
	begin_exif = image.find(b'\xff\xe1')
	if begin_exif >= 0:
		# JPEG header (FFD8) and anything between FFD8 and FFE1
		# needs to be preserved.
		ret = image[0:begin_exif]
 
		# Two bytes after FFE1 is the size of APP1.
		exif_size = struct.unpack('>H', image[begin_exif+2:begin_exif+4])[0]
 
		# Skip exif_size bytes plus 2 bytes (for the size itself).
		ret += image[begin_exif+exif_size+2:]
 
		# All done.
		return ret
 
	# No EXIF. Just return it.
	return image

It’s easy to use:

f = open('foo.jpg')
image = f.read()
f.close()

outputImage = stripExif(image)
f = open('output.jpg', 'w')
f.write(outputImage)
f.close()

Sure hope this is useful for someone out there. I spent a lot of time searching and coming up empty.

This may be old news for people more familiar with perl internals.

dpk@dpk1:~$ perl -version | head -2

This is perl, v5.8.8 built for i486-linux-gnu-thread-multi
dpk@dpk1:~$ cat test1.pl
#!/usr/bin/perl

use strict;

my $x = 0;
while ($x < 100)
{
  &doit();
  $x++;
}

sub doit() {
  my $foo = 'foobar'; my $x = 0; my $y = 0;
  while ($x < 1000000)
  {
    if ($foo eq 'foofoo')
    {
      $y++;
    }
    $x++;
  }
}
dpk@dpk1:~$ perl -d:DProf test1.pl;dprofpp
Total Elapsed Time = 52.07938 Seconds
  User+System Time = 52.07938 Seconds
Exclusive Times
%Time ExclSec CumulS #Calls sec/call Csec/c  Name
 99.9   52.07 52.070    100   0.5207 0.5207  main::doit
 0.00       - -0.000      1        -      -  strict::bits
 0.00       - -0.000      1        -      -  strict::import
 0.00       - -0.000      1        -      -  main::BEGIN

And then:

dpk@dpk1:~$ cat test2.pl
#!/usr/bin/perl

use strict;

my $x = 0;
while ($x < 100)
{
  &doit();
  $x++;
}

sub doit() {
  my $foo = 'foobar'; my $x = 0; my $y = 0;
  while ($x < 1000000)
  {
    if ('foofoo' eq $foo)
    {
      $y++;
    }
    $x++;
  }
}
Total Elapsed Time = 51.31948 Seconds
  User+System Time = 51.30948 Seconds
Exclusive Times
%Time ExclSec CumulS #Calls sec/call Csec/c  Name
 100.   51.31 51.310    100   0.5131 0.5131  main::doit
 0.00       - -0.000      1        -      -  strict::bits
 0.00       - -0.000      1        -      -  strict::import
 0.00       - -0.000      1        -      -  main::BEGIN

I’ve repeated this little test multiple times, with different several different inputs, but the result is always the same. if ('string' eq $variable) is faster than if ($variable eq 'string')

There are sites out there (in the tired “Rick Roll” category) that make it hard to close a tab, by adding hooks that allow for dozens or hundreds of alert dialog boxes to appear, preventing the tab from closing. One is http://www.internetisseriousbusiness.com. Don’t go to this site, unless you want to see the bug in action.

I posted a bug on bugzilla, after doing a search. I didn’t see any, but as there are hundreds of thousands of other bugs on there, I didn’t want to spend hours hunting down an exact match, so I just went ahead with it. Turns out I should have searched for “rick roll,” rather than something more specific such as “javascript alert exit loop” or similar. Ah, well, such is the folly of search engines.

So, it got merged in to another bug that’s over 7 years old. Surprisingly, it has only gathered 60 votes in that incredible period of time. I’m asking you, the loyal dpk dot net reader, to use one of your 10000 votes on this bug, and to help raise awareness of this issue, so that it might be squashed.

Looking at the code, it seems like it might involve simply adding another button to the alert dialog box, that would just kill the tab’s javascript context. But, I don’t really know how to do all that. It kinda looks like there’s different alert box code for each “platform.” I dunno. I’m no mozilla pro.

The pdf extension library shipped with PHP-4.4.7 doesn’t work, and it’s a known “non-bug”. I’m not sure why they still ship the broken library. I installed the PECL version, via pear (my first time trying that), and that was pretty painless. It created a pdf.so and put it in some long /usr/local/lib path. So I figured, now I can just load it with:

dl("/usr/local/lib/php/extensions/no-debug-non-zts-20020429/pdf.so");

right? Wrong:

Warning: dl(): Unable to load dynamic library './/usr/local/lib/php/extensions/no-debug-non-zts-20020429/pdf.so' - Cannot open ".//usr/local/lib/php/extensions/no-debug-non-zts-20020429/pdf.so" in /root/test.php on line 7

I have “./” as my extension_dir in php.ini. For some reason, the code for dl doesn’t recognize that I’m specifying a full path, though. The fix, according to posters on http://www.php.net/dl, is to prepend a sufficient number of ../’s to the path before calling dl() !

The resulting code (with helpful dpk-comments) is:
<?php
// This is required, and is astounding.
$dotdots = preg_replace ('//([^/]+)/', '../', dirname(__FILE__));
$dlpath = $dotdots . '/usr/local/lib/php/extensions/no-debug-non-zts-20020429/pdf.so';
dl($dlpath);
// My brain still hurts.
$p = PDF_new();
?>