Sunday, November 16, 2008

Hacks: Replace yum's downloader with Axel

/!\ This is an ugly hack, use it at your own risk, 
I am not responsible for any breakage

P/S, your sysadmin might not gonna like this


Disclaimer aside, I really love Python.

So, I'm behind such a bad network which keep timing out, and downloading stuff using yum in this network is a real PITA. And so, I had enough of it and decided to hack around.

Axel is a CLI download accelerator thats lightweight and pretty fast. I've been using it quite frequently to get a bit more speed for my downloads. I think, why not just replace this urllib2 grabber with axel, so, I did. (I am such an evil guy)

After a few hours looking through yum code to find what to modify, I ended up with this



# file: /usr/lib/python2.5/site-packages/urlgrabber/customgrabber.py

import grabber
import os

class AxelGrabber(grabber.URLGrabber):
def urlgrab(self, url, filename=None, **kwargs):
"""grab the file at and make a local copy at
If filename is none, the basename of the url is used.
urlgrab returns the filename of the local file, which may be
different from the passed-in filename if copy_local == 0.
"""

opts = self.opts.derive(**kwargs)
(url,parts) = opts.urlparser.parse(url, opts)
(scheme, host, path, parm, query, frag) = parts


def retryfunc(opts, url, filename):
if os.environ.has_key('http_proxy'):
os.environ['HTTP_PROXY'] = os.environ['http_proxy']
os.system('/usr/bin/axel -a -o %s %s' % (filename,url))
return filename

return self._retry(opts, retryfunc, url, filename)


Make sure you put the file above at its path unless you are sure what you are doing. To make it usable with yum, some modification is needed in one of yum's source file.

Edit
/usr/lib/python2.5/site-packages/yum/yumRepo.py

change
from urlgrabber.grabber import URLGrabber

to
from urlgrabber.customgrabber import AxelGrabber as URLGrabber


and you are good to go. Do it at YOUR own risk remember.
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