/*
* BLT Memory Util for parsing DNS packets.
* This software is unlikely to become part of BLT main but is provided under the BLT license (GPL 3).
* Copyright (C) 2023 Brett Terpstra
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see .
*/
#ifndef INSANE_DNS_UTIL_H
#define INSANE_DNS_UTIL_H
#include
namespace blt
{
/**
* Basic parser for processing strings of bytes received from UDP sockets. This class provides a simple interface for efficiently copying the
* big endian bytes from the network into the little endian bytes required by x86 processors. The class also provides basic safety guarantees
* in that the program will halt execution if reading the bytes would overflow the internal buffer.
*/
class byte_reader
{
private:
unsigned char* _data;
const size_t _size;
mutable size_t _current_byte = DNS_HEADER_END;
public:
explicit byte_reader(unsigned char* data, size_t size): _data(data), _size(size)
{}
/**
* Read the next byte in the data stream then increment the internal counter by 1
* @return the next byte in the array
*/
inline unsigned char& next() const
{
BLT_ASSERT(_current_byte < _size);
return _data[_current_byte++];
}
/**
* Reads data into the provided template parameter, reordering the byte into the correct little endian format
* @tparam T type to read (deduction is automatic)
* @param t variable reference to read into
*/
template
inline void to(T& t) const
{
BLT_ASSERT(_current_byte + sizeof(T) <= _size);
// I hate little endian. I hate dealing with converting between endianness
// it is very easy to do it very slowly
// So I made BLT provide a simple interface to convert between bytes dependent on the platform
// for small integral types (16, 32, and 64) it will compile to 3 instructions using compiler intrinsics.
// Larger POD types are supported but will use std::reverse and therefore be slow.
blt::mem::fromBytes(&_data[_current_byte], t);
skip(sizeof(T));
}
/**
* Copy from the internal data buffer, advancing the internal stream, into the provided unsigned char array. *No reordering is done*
* @param out character array to write to
* @param size number of bytes to copy
*/
inline void copy(unsigned char*& out, size_t size) const
{
BLT_ASSERT(_current_byte + size < _size);
std::memcpy(out, &_data[_current_byte], size);
skip(size);
}
/**
* Skip bytes in the data stream, useful for skipping sections of the DNS packet we may not care about.
* @param s number of bytes to skip.
*/
inline void skip(size_t s = 1) const
{
_current_byte += s;
}
/**
* @return 1 past the last byte we wrote to, otherwise known as the next byte we will be writing to.
*/
inline size_t last() const
{
return _current_byte;
}
/**
* @return a pointer to a location in the internal buffer starting at last()
*/
inline unsigned char* from()
{
BLT_ASSERT(_current_byte < _size);
return &_data[_current_byte];
}
};
}
#endif //INSANE_DNS_UTIL_H