transmission/libtransmission/benc.h

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// This file Copyright © 2022 Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0), GPLv3 (SPDX: GPL-3.0),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.
#pragma once
#include <array>
#include <cerrno>
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#include <cstddef> // size_t
#include <cstdint> // int64_t
#include <cstdlib>
#include <optional>
#include <string_view>
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#include <utility> // make_pair
#include "error.h"
namespace transmission::benc
{
namespace impl
{
std::optional<int64_t> ParseInt(std::string_view* benc);
std::optional<std::string_view> ParseString(std::string_view* benc);
} // namespace impl
struct Handler
{
class Context
{
public:
Context(char const* stream_begin_in, tr_error** error_in)
: error{ error_in }
, stream_begin_{ stream_begin_in }
{
}
[[nodiscard]] std::pair<long, long> tokenSpan() const
{
return std::make_pair(token_begin_ - stream_begin_, token_end_ - stream_begin_);
}
[[nodiscard]] auto raw() const
{
return std::string_view{ token_begin_, size_t(token_end_ - token_begin_) };
}
void setTokenSpan(char const* a, size_t len)
{
token_begin_ = a;
token_end_ = token_begin_ + len;
}
tr_error** error = nullptr;
private:
char const* token_begin_ = nullptr;
char const* token_end_ = nullptr;
char const* const stream_begin_;
};
virtual ~Handler() = default;
virtual bool Int64(int64_t, Context const& context) = 0;
virtual bool String(std::string_view, Context const& context) = 0;
virtual bool StartDict(Context const& context) = 0;
virtual bool Key(std::string_view, Context const& context) = 0;
virtual bool EndDict(Context const& context) = 0;
virtual bool StartArray(Context const& context) = 0;
virtual bool EndArray(Context const& context) = 0;
};
template<std::size_t MaxDepth>
struct BasicHandler : public Handler
{
bool Int64(int64_t /*value*/, Context const& /*context*/) override
{
return true;
}
bool String(std::string_view /*value*/, Context const& /*context*/) override
{
return true;
}
bool StartDict(Context const& /*context*/) override
{
push();
return true;
}
bool Key(std::string_view key, Context const& /*context*/) override
{
keys_[depth_] = key;
return true;
}
bool EndDict(Context const& /*context*/) override
{
pop();
return true;
}
bool StartArray(Context const& /*context*/) override
{
push();
return true;
}
bool EndArray(Context const& /*context*/) override
{
pop();
return true;
}
auto key(size_t i) const
{
return keys_[i];
}
auto depth() const
{
return depth_;
}
auto currentKey() const
{
return key(depth());
}
private:
void push()
{
++depth_;
keys_[depth_] = {};
}
void pop()
{
--depth_;
}
size_t depth_ = 0;
std::array<std::string_view, MaxDepth> keys_;
};
template<std::size_t MaxDepth>
struct ParserStack
{
enum class ParentType
{
Array,
Dict
};
struct Node
{
ParentType parent_type;
size_t n_children_walked;
};
std::array<Node, MaxDepth> stack;
std::size_t depth = 0;
void clear()
{
depth = 0;
}
void tokenWalked()
{
++stack[depth].n_children_walked;
}
Node& current()
{
return stack[depth];
}
Node& current() const
{
return stack[depth];
}
[[nodiscard]] bool expectingDictKey() const
{
return depth > 0 && stack[depth].parent_type == ParentType::Dict && (stack[depth].n_children_walked % 2) == 0;
}
std::optional<ParentType> parentType() const
{
if (depth == 0)
{
return {};
}
return stack[depth].parent_type;
}
std::optional<ParentType> pop(tr_error** error)
{
if (depth == 0)
{
tr_error_set(error, EILSEQ, "Cannot pop empty stack");
return {};
}
if (stack[depth].parent_type == ParentType::Dict && ((stack[depth].n_children_walked % 2) != 0))
{
tr_error_set(error, EILSEQ, "Premature end-of-dict found. Malformed benc?");
return {};
}
auto const ret = stack[depth].parent_type;
--depth;
return ret;
}
bool push(ParentType parent_type, tr_error** error)
{
if (depth + 1 >= std::size(stack))
{
tr_error_set(error, E2BIG, "Max stack depth reached; unable to continue parsing");
return false;
}
++depth;
current() = { parent_type, 0 };
return true;
}
};
template<size_t MaxDepth>
bool parse(
std::string_view benc,
ParserStack<MaxDepth>& stack,
Handler& handler,
char const** setme_end = nullptr,
tr_error** error = nullptr)
{
stack.clear();
auto const* const stream_begin = std::data(benc);
auto context = Handler::Context(stream_begin, error);
int err = 0;
for (;;)
{
if (std::empty(benc))
{
err = EILSEQ;
}
if (err != 0)
{
break;
}
auto const* const front = std::data(benc);
switch (benc.front())
{
case 'i': // int
if (auto const value = impl::ParseInt(&benc); !value)
{
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tr_error_set(error, err, "Malformed benc? Unable to parse integer");
err = EILSEQ;
}
else
{
context.setTokenSpan(front, std::data(benc) - front);
if (!handler.Int64(*value, context))
{
err = ECANCELED;
}
else
{
stack.tokenWalked();
}
}
break;
case 'l': // list
case 'd': // dict
{
bool ok = benc.front() == 'l' ? stack.push(ParserStack<MaxDepth>::ParentType::Array, error) :
stack.push(ParserStack<MaxDepth>::ParentType::Dict, error);
if (!ok)
{
err = EILSEQ;
break;
}
context.setTokenSpan(front, 1);
ok = benc.front() == 'l' ? handler.StartArray(context) : handler.StartDict(context);
if (!ok)
{
err = ECANCELED;
break;
}
benc.remove_prefix(1);
break;
}
case 'e': // end of list or dict
benc.remove_prefix(1);
if (auto const parent_type = stack.pop(error); !parent_type)
{
err = EILSEQ;
}
else
{
stack.tokenWalked();
context.setTokenSpan(front, 1);
if (auto const ok = *parent_type == ParserStack<MaxDepth>::ParentType::Array ? handler.EndArray(context) :
handler.EndDict(context);
!ok)
{
err = ECANCELED;
}
}
break;
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9': // string
if (auto const sv = impl::ParseString(&benc); !sv)
{
err = EILSEQ;
tr_error_set(error, err, "Malformed benc? Unable to parse string");
}
else
{
context.setTokenSpan(front, std::data(benc) - front);
if (bool const ok = stack.expectingDictKey() ? handler.Key(*sv, context) : handler.String(*sv, context); !ok)
{
err = ECANCELED;
}
else
{
stack.tokenWalked();
}
}
break;
default: // invalid bencoded text... march past it
benc.remove_prefix(1);
break;
}
if (stack.depth == 0)
{
break;
}
}
if (err != 0)
{
errno = err;
return false;
}
if (stack.depth != 0)
{
err = EILSEQ;
tr_error_set(error, err, "premature end-of-data reached");
errno = err;
return false;
}
if (stack.stack[0].n_children_walked == 0)
{
err = EILSEQ;
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tr_error_set(error, err, "no bencoded data to parse");
errno = err;
return false;
}
if (setme_end != nullptr)
{
*setme_end = std::data(benc);
}
return true;
}
} // namespace transmission::benc