struct input_seekable_device_tag :
	boost::iostreams::device_tag,
	boost::iostreams::input_seekable
{};

class PhysfsReadDevice
{
public:
	typedef char        char_type;
	typedef input_seekable_device_tag  category;

	PhysfsReadDevice(const std::string& fname)
	{
		handle = PHYSFS_openRead(fname.c_str());

		cout << "Opening file " << fname << endl;

		if(!handle)
			throw std::runtime_error(physfs::getLastError());
	}

	std::streamsize read(char* s, std::streamsize n)
        {
		// Read up to n characters from the input 
		// sequence into the buffer s, returning   
		// the number of characters read, or -1 
		// to indicate end-of-sequence.

		PHYSFS_sint64 bytesread = PHYSFS_read(handle,s,1,static_cast<PHYSFS_uint32>(n));

		if(bytesread < 0)
		{
			throw std::runtime_error(physfs::getLastError());
		}
		else if(bytesread == 0)
		{
			if(PHYSFS_eof(handle))
				return -1;
		}

		return static_cast<std::streamsize>(bytesread);
        }

	std::streampos seek(boost::iostreams::stream_offset off, std::ios_base::seekdir way) 
	{
		// Advances the read/write head by off characters, 
		// returning the new position, where the offset is 
		// calculated from:
		//  - the start of the sequence if way == ios_base::beg
		//  - the current position if way == ios_base::cur
		//  - the end of the sequence if way == ios_base::end

		PHYSFS_uint64 seekAmt;
		PHYSFS_sint64 currentPos;

		cout << "Seeking... offset=" << off << endl;

		if(way == ios_base::beg)
		{
			cout << "From beginning..." << endl;
			seekAmt = (off > 0) ? static_cast<PHYSFS_uint64>(off) : 0;
		}
		else if(way == ios_base::cur)
		{
			cout << "From current..." << endl;
			currentPos = PHYSFS_tell(handle);
			if(currentPos < 0)
				throw std::runtime_error(physfs::getLastError());

			currentPos += static_cast<PHYSFS_sint64>(off);

			seekAmt = (currentPos > 0) ? static_cast<PHYSFS_uint64>(currentPos) : 0;
		}
		else if(way == ios_base::end)
		{
			cout << "From end..." << endl;
			currentPos = PHYSFS_fileLength(handle);
			if(currentPos < 0) // file length could not be determined... what to do...
				throw std::runtime_error("Could not determine file size, possibly streamed");

			currentPos += static_cast<PHYSFS_sint64>(off);

			seekAmt = (currentPos > 0) ? static_cast<PHYSFS_uint64>(currentPos) : 0;
		}
		else
			throw std::runtime_error("Invalid seek direction");

		if(!PHYSFS_seek(handle, static_cast<PHYSFS_uint64>(seekAmt)))
			throw std::runtime_error(physfs::getLastError());

		currentPos = PHYSFS_tell(handle);
		if(currentPos < 0)
			throw std::runtime_error(physfs::getLastError());

		cout << "New position: " << currentPos << endl;

		return std::streampos(static_cast<PHYSFS_uint32>(currentPos));
	}

private:
	PHYSFS_File* handle;
};

boost::iostreams::stream<PhysfsReadDevice> ifile("somefile.txt");

boost::iostreams::stream_buffer<PhysfsReadDevice> ifilebuf("somefile.txt");
std::istream ifile(&ifilebuf);