premiere-libtorrent/include/libtorrent/bencode.hpp

/*

Copyright (c) 2003-2018, Arvid Norberg
All rights reserved.

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modification, are permitted provided that the following conditions
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    * Redistributions of source code must retain the above copyright
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    * Redistributions in binary form must reproduce the above copyright
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      the documentation and/or other materials provided with the distribution.
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      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

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*/

#ifndef TORRENT_BENCODE_HPP_INCLUDED
#define TORRENT_BENCODE_HPP_INCLUDED

// OVERVIEW
//
// Bencoding is a common representation in bittorrent used for for dictionary,
// list, int and string hierarchies. It's used to encode .torrent files and
// some messages in the network protocol. libtorrent also uses it to store
// settings, resume data and other state between sessions.
//
// Strings in bencoded structures are not necessarily representing text.
// Strings are raw byte buffers of a certain length. If a string is meant to be
// interpreted as text, it is required to be UTF-8 encoded. See `BEP 3`_.
//
// There are two mechanisms to *decode* bencoded buffers in libtorrent.
//
// The most flexible one is `bdecode() bencode()`_, which returns a structure
// represented by entry. Once a buffer has been decoded with this function, it
// can be discarded. The entry does not contain any references back to it. This
// means that bdecode() copies all the data out of the buffer and into its own
// hierarchy. This makes this function expensive, which might matter if you're
// parsing large amounts of data.
//
// Another consideration is that `bdecode() bencode()`_ is a recursive parser.
// For this reason, in order to avoid DoS attacks by triggering a stack
// overflow, there is a recursion limit. This limit is a sanity check to make
// sure it doesn't run the risk of busting the stack.
//
// The second mechanism is the decode function for bdecode_node. This function
// builds a tree that points back into the original buffer. The returned
// bdecode_node will not be valid once the buffer it was parsed out of is
// discarded.
//
// Not only is this function more efficient because of less memory allocation
// and data copy, the parser is also not recursive, which means it probably
// performs a little bit better and can have a higher recursion limit on the
// structures it's parsing.

#include <string>
#include <iterator> // for distance

#include "libtorrent/config.hpp"
#include "libtorrent/entry.hpp"
#include "libtorrent/assert.hpp"
#include "libtorrent/io.hpp" // for write_string
#include "libtorrent/string_util.hpp" // for is_digit

namespace libtorrent {

#if TORRENT_ABI_VERSION == 1
	using invalid_encoding = system_error;
#endif

namespace detail {

		template <class OutIt, class In, typename Cond
			= typename std::enable_if<std::is_integral<In>::value>::type>
		int write_integer(OutIt& out, In data)
		{
			entry::integer_type const val = entry::integer_type(data);
			TORRENT_ASSERT(data == In(val));
			// the stack allocated buffer for keeping the
			// decimal representation of the number can
			// not hold number bigger than this:
			static_assert(sizeof(entry::integer_type) <= 8, "64 bit integers required");
			static_assert(sizeof(data) <= sizeof(entry::integer_type), "input data too big, see entry::integer_type");
			char buf[21];
			auto const str = integer_to_str(buf, val);
			for (char const c : str)
			{
				*out = c;
				++out;
			}
			return static_cast<int>(str.size());
		}

		template <class OutIt>
		void write_char(OutIt& out, char c)
		{
			*out = c;
			++out;
		}

		template <class InIt>
		std::string read_until(InIt& in, InIt end, char end_token, bool& err)
		{
			std::string ret;
			if (in == end)
			{
				err = true;
				return ret;
			}
			while (*in != end_token)
			{
				ret += *in;
				++in;
				if (in == end)
				{
					err = true;
					return ret;
				}
			}
			return ret;
		}

		template<class InIt>
		void read_string(InIt& in, InIt end, int len, std::string& str, bool& err)
		{
			TORRENT_ASSERT(len >= 0);
			for (int i = 0; i < len; ++i)
			{
				if (in == end)
				{
					err = true;
					return;
				}
				str += *in;
				++in;
			}
		}

		template<class OutIt>
		int bencode_recursive(OutIt& out, const entry& e)
		{
			int ret = 0;
			switch(e.type())
			{
			case entry::int_t:
				write_char(out, 'i');
				ret += write_integer(out, e.integer());
				write_char(out, 'e');
				ret += 2;
				break;
			case entry::string_t:
				ret += write_integer(out, e.string().length());
				write_char(out, ':');
				ret += write_string(e.string(), out);
				ret += 1;
				break;
			case entry::list_t:
				write_char(out, 'l');
				for (auto const& i : e.list())
					ret += bencode_recursive(out, i);
				write_char(out, 'e');
				ret += 2;
				break;
			case entry::dictionary_t:
				write_char(out, 'd');
				for (auto const& i : e.dict())
				{
					// write key
					ret += write_integer(out, i.first.length());
					write_char(out, ':');
					ret += write_string(i.first, out);
					// write value
					ret += bencode_recursive(out, i.second);
					ret += 1;
				}
				write_char(out, 'e');
				ret += 2;
				break;
			case entry::preformatted_t:
				std::copy(e.preformatted().begin(), e.preformatted().end(), out);
				ret += static_cast<int>(e.preformatted().size());
				break;
			case entry::undefined_t:

				// empty string
				write_char(out, '0');
				write_char(out, ':');

				ret += 2;
				break;
			}
			return ret;
		}

		template<class InIt>
		void bdecode_recursive(InIt& in, InIt end, entry& ret, bool& err, int depth)
		{
			if (depth >= 100)
			{
				err = true;
				return;
			}

			if (in == end)
			{
				err = true;
#if TORRENT_USE_ASSERTS
				ret.m_type_queried = false;
#endif
				return;
			}
			switch (*in)
			{

			// ----------------------------------------------
			// integer
			case 'i':
				{
				++in; // 'i'
				std::string const val = read_until(in, end, 'e', err);
				if (err) return;
				TORRENT_ASSERT(*in == 'e');
				++in; // 'e'
				ret = entry(entry::int_t);
				char* end_pointer;
				ret.integer() = std::strtoll(val.c_str(), &end_pointer, 10);
#if TORRENT_USE_ASSERTS
				ret.m_type_queried = false;
#endif
				if (end_pointer == val.c_str())
				{
					err = true;
					return;
				}
				}
				break;

			// ----------------------------------------------
			// list
			case 'l':
				ret = entry(entry::list_t);
				++in; // 'l'
				while (*in != 'e')
				{
					ret.list().emplace_back();
					entry& e = ret.list().back();
					bdecode_recursive(in, end, e, err, depth + 1);
					if (err)
					{
#if TORRENT_USE_ASSERTS
						ret.m_type_queried = false;
#endif
						return;
					}
					if (in == end)
					{
						err = true;
#if TORRENT_USE_ASSERTS
						ret.m_type_queried = false;
#endif
						return;
					}
				}
#if TORRENT_USE_ASSERTS
				ret.m_type_queried = false;
#endif
				TORRENT_ASSERT(*in == 'e');
				++in; // 'e'
				break;

			// ----------------------------------------------
			// dictionary
			case 'd':
				ret = entry(entry::dictionary_t);
				++in; // 'd'
				while (*in != 'e')
				{
					entry key;
					bdecode_recursive(in, end, key, err, depth + 1);
					if (err || key.type() != entry::string_t)
					{
#if TORRENT_USE_ASSERTS
						ret.m_type_queried = false;
#endif
						return;
					}
					entry& e = ret[key.string()];
					bdecode_recursive(in, end, e, err, depth + 1);
					if (err)
					{
#if TORRENT_USE_ASSERTS
						ret.m_type_queried = false;
#endif
						return;
					}
					if (in == end)
					{
						err = true;
#if TORRENT_USE_ASSERTS
						ret.m_type_queried = false;
#endif
						return;
					}
				}
#if TORRENT_USE_ASSERTS
				ret.m_type_queried = false;
#endif
				TORRENT_ASSERT(*in == 'e');
				++in; // 'e'
				break;

			// ----------------------------------------------
			// string
			default:
				static_assert(sizeof(*in) == 1, "Input iterator to 8 bit data required");
				if (is_digit(char(*in)))
				{
					std::string len_s = read_until(in, end, ':', err);
					if (err)
					{
#if TORRENT_USE_ASSERTS
						ret.m_type_queried = false;
#endif
						return;
					}
					TORRENT_ASSERT(*in == ':');
					++in; // ':'
					int len = atoi(len_s.c_str());
					ret = entry(entry::string_t);
					read_string(in, end, len, ret.string(), err);
					if (err)
					{
#if TORRENT_USE_ASSERTS
						ret.m_type_queried = false;
#endif
						return;
					}
				}
				else
				{
					err = true;
#if TORRENT_USE_ASSERTS
					ret.m_type_queried = false;
#endif
					return;
				}
#if TORRENT_USE_ASSERTS
				ret.m_type_queried = false;
#endif
			}
		}
	}

	// These functions will encode data to bencoded or decode bencoded data.
	//
	// If possible, ``bdecode()`` producing a bdecode_node should be preferred
	// over this function.
	//
	// The entry_ class is the internal representation of the bencoded data
	// and it can be used to retrieve information, an entry_ can also be build by
	// the program and given to ``bencode()`` to encode it into the ``OutIt``
	// iterator.
	//
	// The ``OutIt`` and ``InIt`` are iterators
	// (InputIterator_ and OutputIterator_ respectively). They
	// are templates and are usually instantiated as ostream_iterator_,
	// back_insert_iterator_ or istream_iterator_. These
	// functions will assume that the iterator refers to a character
	// (``char``). So, if you want to encode entry ``e`` into a buffer
	// in memory, you can do it like this::
	//
	//	std::vector<char> buffer;
	//	bencode(std::back_inserter(buf), e);
	//
	// .. _InputIterator: http://www.sgi.com/tech/stl/InputIterator.html
	// .. _OutputIterator: http://www.sgi.com/tech/stl/OutputIterator.html
	// .. _ostream_iterator: http://www.sgi.com/tech/stl/ostream_iterator.html
	// .. _back_insert_iterator: http://www.sgi.com/tech/stl/back_insert_iterator.html
	// .. _istream_iterator: http://www.sgi.com/tech/stl/istream_iterator.html
	//
	// If you want to decode a torrent file from a buffer in memory, you can do it like this::
	//
	//	std::vector<char> buffer;
	//	// ...
	//	entry e = bdecode(buf.begin(), buf.end());
	//
	// Or, if you have a raw char buffer::
	//
	//	const char* buf;
	//	// ...
	//	entry e = bdecode(buf, buf + data_size);
	//
	// Now we just need to know how to retrieve information from the entry.
	//
	// If ``bdecode()`` encounters invalid encoded data in the range given to it
	// it will return a default constructed ``entry`` object.
	template<class OutIt> int bencode(OutIt out, const entry& e)
	{
		return detail::bencode_recursive(out, e);
	}
	template<class InIt> entry bdecode(InIt start, InIt end)
	{
		entry e;
		bool err = false;
		detail::bdecode_recursive(start, end, e, err, 0);
		TORRENT_ASSERT(e.m_type_queried == false);
		if (err) return entry();
		return e;
	}
	template<class InIt> entry bdecode(InIt start, InIt end
		, typename std::iterator_traits<InIt>::difference_type& len)
	{
		entry e;
		bool err = false;
		InIt s = start;
		detail::bdecode_recursive(start, end, e, err, 0);
		len = std::distance(s, start);
		TORRENT_ASSERT(len >= 0);
		if (err) return entry();
		return e;
	}
}

#endif // TORRENT_BENCODE_HPP_INCLUDED