How to post a compressed string and decompress the string in Django?

Question

I make a server use django and I wanna post a compressed string then decompress the string in django. My OS is Ubuntu14.04 and my python's version is 2.7.6. My django response function like these:

# coding=utf-8

import json
from django.http import HttpResponse
import zlib

def first_page(request):
    result = {
        "title": u"bye"
    }
    try:
        param = request.POST["content"]
        a = param.encode("utf-8")
        param = zlib.decompress(a)
        result["result"] = param
    except Exception, e:
        print "error in line 21"
        print e
    result = json.dumps(result)
    response = HttpResponse(result, content_type="application/json")
    return response

Then I write a test case to test the function,the function's url is "music_main_page", my test code like these:

# coding=utf-8

__author__ = 'lizhihao'


import zlib
import httplib
import urllib

httpClient = None
try:
    a = "hello world! what are you doing!"
    a = zlib.compress(a)
    params = urllib.urlencode(
        {
            "content": a
        }
    )
    headers = {
        "Content-type": "application/x-www-form-urlencoded",
        "Accept": "text/plain"
    }
    httpClient = httplib.HTTPConnection("localhost", 8000, timeout=30)
    httpClient.request("POST", "/music_main_page", params, headers)
    response = httpClient.getresponse()
    print response.read()
except Exception, e:
    print e
finally:
    if httpClient:
        httpClient.close()

The program throw an exception:Error -2 while preparing to decompress data: inconsistent stream state,how to fix the bug?

Anton Strogonoff · Accepted Answer · 2015-07-31 19:29:23Z

1

I bet it has something to do with encoding. Try converting the unicode string you obtain from request.POST["content"] into a byte string before decompression (do .encode('latin-1') instead of .encode('utf-8'), in other words).

This fixed it for me. I was too lazy to reproduce your bug on a full Django project though, I used this to put your string through approximate request parsing stages:

>>> zlib.decompress(
...     bytes_to_text(
...         urlparse.parse_qsl(
...             urllib.urlencode({"content":
...                 zlib.compress("hello world! what are you doing!")
...             })
...         )[0][1].decode('iso-8859-1'), 'utf-8'
...     ).encode('utf-8')
... )

(Where bytes_to_text is this one.)

What do you get if you use browser form instead of a script?

In any case though, perhaps you shouldn’t send compressed data in POSTed form contents. It’s intended for clear unicode text, which is what’s screwing things up from what I can see.

Instead you could just send compressed bytes as-is, and use request.body to read the data and then decompress. Or, even better, set things up so that your server-side gzip compression works.

edited Jul 31, 2015 at 19:29

answered Jul 31, 2015 at 19:13

Anton Strogonoff

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2 Comments

Karl Doenitz Over a year ago

I just use this function bytes_to_text(), then I can decompress the string.

Anton Strogonoff Over a year ago

I shouldn’t need to call bytes_to_text() because it’s done by Django when you access request.POST["content"]… I only put it there to illustrate what processing form parameters go through when submitted.

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