[Boost-users] Problem with iostreams and zlib

Subject: [Boost-users] Problem with iostreams and zlib
From: Alfred Kohl (alfred.kohl_at_[hidden])
Date: 2008-09-09 09:00:04

Hi!

the gzip_decompressor sometimes fails with Z_BUF_ERROR wrapped in zlib_error().
I'm using boost-1.36.0 and zlib-1.2.3, both statically linked.
Stream setup is as follows:

        std::ifstream filein("testfile");

        boost::iostreams::filtering_streambuf<boost::iostreams::input>	strbuf;
        strbuf.push(boost::iostreams::gzip_decompressor());
        strbuf.push(filein);

        std::istream	input(&strbuf);

        do
        {
                char  buf[4096];
                input.read(&buf, 4096);
        } while (input.gcount() > 0);

For one particular file, read() will fail after reading about 2 MB (of 3 MB total file size). The file decompresses fine with external tools and contains mainly zeros.

The error happens in (boost/iostreams/filter/zlib.hpp):

bool zlib_decompressor_impl<Alloc>::filter
    ( const char*& src_begin, const char* src_end,
      char*& dest_begin, char* dest_end, bool /* flush */ )
{
    before(src_begin, src_end, dest_begin, dest_end);
    int result = inflate(zlib::sync_flush);
    after(src_begin, dest_begin, false);
    zlib_error::check(result);                   // <---
    return result != zlib::stream_end;
}

src_begin and src_end both point to the same location! I'm not an expert with zlib but this looks wrong to me...

Re-compressing the file with an external tool does not help.
Any ideas?

Cheers,
Alfred.
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