Boost Iostreams, chaining gzip filter with home-made one

Question

I meeting a execution issue while using the gzip filter of the Boost Iostreams library, combined with a buffered home-made one. I would like to know what is wrong in my way to do it.

Firstly, my filter is a general DualFilter. It uses an buffer (of 16 bytes) before the transformation and the put/return. The categories of my filter is closable and dual_use. You can find code details in the end of this mail.

My problem is ([a/b] means for the separates case with the letter a and b): If I take the 6 possibilities for write and read:

1) io::filtering_[i/o]stream stm;
2) stm.push(io::gzip_[de/]compressor());
3) stm.push(my_[Unt/T]ransFilter);

at the moment to use the stm.[get/put] to read/write

1)-2)     works perfectly
1)-3)     works perfectly
1)-3)-2) works perfectly
1)-2)-3) Stay stuck (obviously it is the one I really need)

In fact in the last case, the gzip filter give this infinite loop to the put of the TransFilter :

31 -117 8 0 0 0 0 0 0 31 -117 8 0 0...

A similar case occur with the bzip filter (even if it is a bit longer loop).

What do I do wrong ? Somebody can help me ?

Thanks in advance

Christophe

PS: here a simplified implementation of my filter

template<typename Source>
int get(Source& src)
{
  //at the very beginning or if the buffer are fully returned
  if (fcurrent_pos == fblkLength)
    {
      fcurrent_pos =0;
      FillThem (src); //fill&transform the buffers with the right number of src.get()
      fc=CheckNSolveBufferIsEnd (src); //eventually prepare read the suffix of the file
    }

  //The effective return
  if (fcurrent_pos < fUntrans.size ())
    return (int)fUntrans[fcurrent_pos++];
  else
    return fc;
}

template<typename Sink>
bool put(Sink& dest, int c)
{
  if (c==EOF || c ==boost::iostreams::WOULD_BLOCK)
    return false;

  if (fUntrans.size () < fblkLength - 1)
    {
      fUntrans.AddData((char*)(&c),1);
      return true;
    }
  fUntrans.AddData((char*)(&c),1);

  fenc->TransformThis (fUntrans, fTrans, fKey);


  for (int i=0; i<fblkLength; i++)
    {
      if (!boost::iostreams::put(dest, (int)fTrans[i]))
        return false;
    }

  return true;
}

template<typename Sink>
bool close (Sink &dest, BOOST_IOS::openmode m)
{
  if (fFlushed)
    return true;

  PrepareSuffix ();

  for (int i=0; i< fblkLength*2; //suffix length
       i++)
    {
      if (!boost::iostreams::put(dest, (int)fTrans[i]))
        return false;
    }
  return true;
}

Boost Iostreams, chaining gzip filter with home-made one

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