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