CODEWITHSUNDEEP
c#pythongzipzlib
Sergey Kucher
Sergey Kucher

Reputation: 4180

Compress in Python Decompress in C#

Problem

  1. Compressing long string 4k+ in python
  2. Decompress it in C#

What did I try to do:
1. Python

def deflate_and_base64_encode( string_val ):
    zlibbed_str = zlib.compress( string_val )
    compressed_string = zlibbed_str[2:-1]
    return base64.b64encode(compressed_string )

2. C#

public static string Inflate(string pythonZipped)
{
    byte[] gzBuffer = Convert.FromBase64String(pythonZipped);
    using (var ms = new MemoryStream())
    {
        ms.Write(gzBuffer, 0, gzBuffer.Length);
        var buffer = new byte[ms.Length];
        ms.Position = 0;
        using (var infS = new DeflateStream(ms,Ionic.Zlib.CompressionMode.Decompress, true))
        {
            infS.Read(buffer, 0, buffer.Length);
        }
        return Encoding.UTF8.GetString(buffer);
    }
}

But get some weird results for example:

Python.deflate_and_base64_encode('1'*1000)

Results in MzQcBaNgFAx3AABQpr8=

C#.Inflate("MzQcBaNgFAx3AABQpr8")

Results in 11111111111111 instead of 1000 ones

Can you explain what I am doing wrong or give me other way to acheive what I am tring to do?

Upvotes: 1

Views: 1384

Answers (2)

Bruce Jung
Bruce Jung

Reputation: 358

I had the same problem. I solved it.

"var buffer = new byte[ms.Length];" causes that problem.

The buffer size is too small.

Increase buffer size like this "var buffer = new byte[4096];" or "var buffer = new byte[ms.Length*1024];".

Upvotes: 1

Matt Cooper
Matt Cooper

Reputation: 937

The problem begins when 2 characters from the beginning and one from the end are chopped off. compressed_string = zlibbed_str[2:-1]

That line of code destroys header information in the first 2 characters, and even an immediate zlib.decompress can't make sense of what's left. (My guess: C#'s zlib implementation does its best to reconstruct what's left of the stream without a valid header. Python's, as you'll see below, is more strict.)

>>> import zlib
>>> z = zlib.compress('1'*1000)
>>> c = z[2:-1]
>>> zlib.decompress(z)
'1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111'
>>> zlib.decompress(c)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
zlib.error: Error -3 while decompressing data: incorrect header check

Upvotes: 1

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