Senthadev - Notes

How to decode a GET request which contains encoded (%xx quoted hex format) binary data. For example, following is a GET request:

http://mosms.senthadev.com/sendsms/?udh=%02q%00&ud=%00%0B%0A%B0%00%01%00%00%00%00%12%00%01

This was one of the hurdle that I faced while implementing a Django web application. In this request, parameters udh and ud contains encoded binary data.

Therefore, to retrieve the values, I used below code. But the return values were in ascii.

ud = request.GET.get('ud')
udh = request.GET.get('udh')
print('%r' % ud) # u'\x02q\x00'
print('%r' % udh) # u'\x00\x0b\n\ufffd\x00\x01\x00\x00\x00\x00\x12\x00\x01'

For example, I was expecting 027100 for ud, but I got u'\x02q\x00'. And this caused an error when I tried to convert the value back to binary using binascii.b2a_hex(ud). Django threw the following error:

UnicodeEncodeError: 'charmap' codec can't encode character u'\ufffd' in position 3: character maps to

This thrown for Django 1.4

How to solve this in a very limited time frame? And, I used following code:

import urllib, binascii
from django.http import HttpResponse

def submit():
    #collecting the GET params into dict
    data = dict(item.rsplit('=') for item in request.META['QUERY_STRING'].rsplit('&'))
    udh = str(binascii.b2a_hex(urllib.unquote(data['udh'])))
    ud = str(binascii.b2a_hex(urllib.unquote(data['ud'])))

    #now I have the ud and udh as proper hex string to be converted to binary data.
    #udh : 027100
    #ud : 000b0ab0000100000000120001