[Boost-users] [Iostreams] Problem to chain gzip filter with home-made one

Subject: [Boost-users] [Iostreams] Problem to chain gzip filter with home-made one
From: Christophe hugon (chugon_at_[hidden])
Date: 2013-10-31 05:48:04

Hello everybody,

I meeting a execution issue while using the gzip filter of the 
Boost.Iostreams, 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;
     }