//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012-2020 OpenVPN Inc.
//
//    This program is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Affero General Public License Version 3
//    as published by the Free Software Foundation.
//
//    This program is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//    GNU Affero General Public License for more details.
//
//    You should have received a copy of the GNU Affero General Public License
//    along with this program in the COPYING file.
//    If not, see <http://www.gnu.org/licenses/>.

// This is a "stub" compression object.  It acts like a compressor
// in the sense that it plays along with compression framing in
// the OpenVPN protocol, but it always sends packets with NO_COMPRESS
// or NO_COMPRESS_SWAP compression status.  While it's not designed
// to receive compressed packets, it will try to handle received LZO
// packets, but it will never send compressed packets.

#ifndef OPENVPN_COMPRESS_COMPSTUB_H
#define OPENVPN_COMPRESS_COMPSTUB_H

#ifndef NO_LZO
#include <openvpn/compress/lzoselect.hpp>
#endif

namespace openvpn {

  class CompressStub : public Compress
  {
  public:
    CompressStub(const Frame::Ptr& frame, const SessionStats::Ptr& stats, const bool support_swap_arg)
      : Compress(frame, stats),
	support_swap(support_swap_arg)
#ifndef NO_LZO
        ,lzo(frame, stats, false, true)
#endif
    {
      OPENVPN_LOG_COMPRESS("Comp-stub init swap=" << support_swap_arg);
    }

    virtual const char *name() const { return "stub"; }

    virtual void compress(BufferAllocated& buf, const bool hint)
    {
      // skip null packets
      if (!buf.size())
	return;

      // indicate that we didn't compress
      if (support_swap)
	do_swap(buf, NO_COMPRESS_SWAP);
      else
	buf.push_front(NO_COMPRESS);
    }

    virtual void decompress(BufferAllocated& buf)
    {
      // skip null packets
      if (!buf.size())
	return;

      const unsigned char c = buf.pop_front();
      switch (c)
	{
	case NO_COMPRESS_SWAP:
	  do_unswap(buf);
	case NO_COMPRESS:
	  break;
#ifndef NO_LZO
	// special mode to support older servers that ignore
	// compression handshake -- this will handle receiving
	// compressed packets even if we didn't ask for them
	case CompressLZO::LZO_COMPRESS:
	  OPENVPN_LOG_COMPRESS_VERBOSE("CompressStub: handled unsolicited LZO packet");
	  lzo.decompress_work(buf);
	  break;
#endif
	default: 
	  OPENVPN_LOG_COMPRESS_VERBOSE("CompressStub: unable to handle op=" << int(c));
	  error(buf);
	}
    }

  private:
    const bool support_swap;
#ifndef NO_LZO
    CompressLZO lzo;
#endif
  };

  // Compression stub using V2 protocol
  class CompressStubV2 : public Compress
  {
  public:
    CompressStubV2(const Frame::Ptr& frame, const SessionStats::Ptr& stats)
      : Compress(frame, stats)
    {
      OPENVPN_LOG_COMPRESS("Comp-stubV2 init");
    }

    virtual const char *name() const { return "stubv2"; }

    virtual void compress(BufferAllocated& buf, const bool hint)
    {
      // skip null packets
      if (!buf.size())
	return;

      // indicate that we didn't compress
      v2_push(buf, OVPN_COMPv2_NONE);
    }

    virtual void decompress(BufferAllocated& buf)
    {
      // skip null packets
      if (!buf.size())
	return;

      const int cop = v2_pull(buf);
      if (cop)
	{
	  OPENVPN_LOG_COMPRESS_VERBOSE("CompressStubV2: unable to handle op=" << c);
	  error(buf);
	}
    }
  };

} // namespace openvpn

#endif // OPENVPN_COMPRESS_COMPSTUB_H