113 lines
4.4 KiB
C
113 lines
4.4 KiB
C
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/*
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* BLT Memory Util for parsing DNS packets.
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* This software is unlikely to become part of BLT main but is provided under the BLT license (GPL 3).
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* Copyright (C) 2023 Brett Terpstra
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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#ifndef INSANE_DNS_UTIL_H
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#define INSANE_DNS_UTIL_H
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#include <insane_dns/constants.h>
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namespace blt
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{
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/**
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* Basic parser for processing strings of bytes received from UDP sockets. This class provides a simple interface for efficiently copying the
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* big endian bytes from the network into the little endian bytes required by x86 processors. The class also provides basic safety guarantees
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* in that the program will halt execution if reading the bytes would overflow the internal buffer.
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*/
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class byte_reader
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{
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private:
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unsigned char* _data;
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const size_t _size;
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mutable size_t _current_byte = DNS_HEADER_END;
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public:
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explicit byte_reader(unsigned char* data, size_t size): _data(data), _size(size)
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{}
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/**
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* Read the next byte in the data stream then increment the internal counter by 1
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* @return the next byte in the array
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*/
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inline unsigned char& next() const
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{
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BLT_ASSERT(_current_byte < _size);
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return _data[_current_byte++];
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}
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/**
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* Reads data into the provided template parameter, reordering the byte into the correct little endian format
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* @tparam T type to read (deduction is automatic)
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* @param t variable reference to read into
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*/
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template<typename T>
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inline void to(T& t) const
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{
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BLT_ASSERT(_current_byte + sizeof(T) <= _size);
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// I hate little endian. I hate dealing with converting between endianness
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// it is very easy to do it very slowly
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// So I made BLT provide a simple interface to convert between bytes dependent on the platform
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// for small integral types (16, 32, and 64) it will compile to 3 instructions using compiler intrinsics.
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// Larger POD types are supported but will use std::reverse and therefore be slow.
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blt::mem::fromBytes(&_data[_current_byte], t);
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skip(sizeof(T));
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}
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/**
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* Copy from the internal data buffer, advancing the internal stream, into the provided unsigned char array. *No reordering is done*
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* @param out character array to write to
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* @param size number of bytes to copy
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*/
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inline void copy(unsigned char*& out, size_t size) const
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{
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BLT_ASSERT(_current_byte + size < _size);
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std::memcpy(out, &_data[_current_byte], size);
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skip(size);
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}
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/**
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* Skip bytes in the data stream, useful for skipping sections of the DNS packet we may not care about.
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* @param s number of bytes to skip.
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*/
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inline void skip(size_t s = 1) const
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{
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_current_byte += s;
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}
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/**
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* @return 1 past the last byte we wrote to, otherwise known as the next byte we will be writing to.
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*/
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inline size_t last() const
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{
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return _current_byte;
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}
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/**
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* @return a pointer to a location in the internal buffer starting at last()
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*/
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inline unsigned char* from()
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{
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BLT_ASSERT(_current_byte < _size);
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return &_data[_current_byte];
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}
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};
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}
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#endif //INSANE_DNS_UTIL_H
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