nrg_codec.h

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/*
  LibNRG - Networking for Real-time Games
  
  Copyright (C) 2012-2014 Alex Baines <alex@abaines.me.uk>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/
#ifndef NRG_CODEC_H
#define NRG_CODEC_H
#include "nrg_core.h"
#include "nrg_varint.h"
#include <string>
#include <type_traits>

namespace nrg {

namespace detail {

using namespace std;

template<class T>
class has_encode_decode {
    template<class C, C> struct S {};
    template<class X> static true_type check(S<size_t (X::*)(Packet&) const, &X::encode>*,
                                             S<size_t (X::*)(Packet&), &X::decode>*);
    template<class X> static false_type check(...);
public:
    static const bool value = decltype(check<T>(0, 0))::value;
};

}

using std::enable_if;
using detail::has_encode_decode;

template<class T, class E = void>
struct Codec {
    size_t encode(Packet& p, const T& data){
        p.write(data);
        return sizeof(data);
    }
    
    size_t decode(Packet& p, T& data){
        if(p.remaining() >= sizeof(data)){
            p.read(data);
            return sizeof(data);
        } else {
            return 0;
        }
    }
};

template<class T>
struct Codec<T, typename enable_if<has_encode_decode<T>::value>::type> {
    size_t encode(Packet& p, const T& data){
        return data.encode(p);
    }
    
    size_t decode(Packet& p, T& data){
        return data.decode(p);
    }
};

template<size_t len>
struct Codec<char[len]> {

    size_t encode(Packet& p, const char (&data)[len]){
        p.writeArray(data, len);
        return len;
    }
    
    size_t decode(Packet& p, char (&data)[len]){
        if(p.remaining() >= len){
            p.readArray(&data, len);
            return len;
        } else {
            return 0;
        }
    }
};

template<>
struct Codec<std::string> {

    size_t encode(Packet& p, const std::string& str){
        size_t ret = UVarint(str.length()).encode(p);
        p.writeArray(str.c_str(), str.length());
        return ret + str.length();
    }
    
    size_t decode(Packet& p, std::string& str){
        if(!p.remaining()) return 0;
                
        UVarint v;
        size_t read_bytes = 0;
        
        if((read_bytes = v.decode(p)) == 0) return 0;
        if(p.remaining() < v.get()) return 0;
        
        str = std::string(reinterpret_cast<const char*>(p.getPointer()), v.get());
        
        p.seek(v.get(), SEEK_CUR);
        return read_bytes + v.get();
    }
};

}

#endif