Zlib compression in boost::iostreams not compatible with zlib.NET

Question

Hello,

I want to send compressed data between my C# to a C++ application in ZLIB format. In C++, I use the zlib_compressor/zlib_decompressor available in boost::iostreams. In C#, I am currently using the ZOutputStream available in the zlib.NET library. First of all, when I compress the same data using both libraries, the results look different:

1. boost::iostreams::zlib_compressor:

63 61 60 60 F8 00 C4 C1 25 45 99 79 E9 23 87 04 00

1. zlib.NET (zlib.ZOutputStream):

78 9C 63 61 60 60 F8 00 C4 C1 25 45 99 79 E9 23 87 04 00 4F 31 63 8D

(Note the 78 9C pattern that is present in zlib.NET, but not in boost).

Furthermore, when I decompress data in boost that I compressed in zlib.NET, I am not able to read from the stream suggesting something is wrong. It does work when I try to decompress data compressed in boost.

Does anybody know what is going wrong?

Thank you,

Johan

Answer 1

I haven't figured out why zlib.NET is not compatible with Boost iostreams, but I did find a solution: I am now using DotNetZip (http://dotnetzip.codeplex.com/) and that works fine.

Answer 2

It's because the boost::iostreams::zlib_compressor code is producing raw deflated data, whereas the zlib.NET is adding a header and footer so that the data is in the compress format.

For evidence, consider this log of a Tcl session:

% set s {78 9C 63 61 60 60 F8 00 C4 C1 25 45 99 79 E9 23 87 04 00 4F 31 63 8D}
78 9C 63 61 60 60 F8 00 C4 C1 25 45 99 79 E9 23 87 04 00 4F 31 63 8D
% set b [binary format H* [join $s ""]];string length $b
23
% zlib decompress $b
ðStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringString
% zlib inflate $b
data error
% set s {63 61 60 60 F8 00 C4 C1 25 45 99 79 E9 23 87 04 00}
63 61 60 60 F8 00 C4 C1 25 45 99 79 E9 23 87 04 00
% set b [binary format H* [join $s ""]];string length $b
17
% zlib decompress $b
data error
% zlib inflate $b
ðStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringStringString

(The zlib decompress command expands data in “compress” format, the zlib inflate command expands data in “raw deflated” format.)