Communications layer used for both the Oxen storage server and oxend
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// Copyright (c) 2019-2020, The Loki Project
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without modification, are
// permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of
// conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice, this list
// of conditions and the following disclaimer in the documentation and/or other
// materials provided with the distribution.
//
// 3. Neither the name of the copyright holder nor the names of its contributors may be
// used to endorse or promote products derived from this software without specific
// prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#pragma once
#include <vector>
#include <algorithm>
#include <functional>
#include <cstring>
#include <ostream>
#include <sstream>
#include <string_view>
#include <variant>
#include "bt_value.h"
namespace lokimq {
using namespace std::literals;
/** \file
* LokiMQ serialization for internal commands is very simple: we support two primitive types,
* strings and integers, and two container types, lists and dicts with string keys. On the wire
* these go in BitTorrent byte encoding as described in BEP-0003
* (https://www.bittorrent.org/beps/bep_0003.html#bencoding).
*
* On the C++ side, on input we allow strings, integral types, STL-like containers of these types,
* and STL-like containers of pairs with a string first value and any of these types as second
* value. We also accept std::variants of these.
*
* One minor deviation from BEP-0003 is that we don't support serializing values that don't fit in a
* 64-bit integer (BEP-0003 specifies arbitrary precision integers).
*
* On deserialization we can either deserialize into a special bt_value type supports everything
* (with arbitrary nesting), or we can fill a container of your given type (though this fails if the
* container isn't compatible with the deserialized data).
*
* There is also a stream deserialization that allows you to deserialize without needing heap
* allocations (as long as you know the precise data structure layout).
*/
/// Exception throw if deserialization fails
class bt_deserialize_invalid : public std::invalid_argument {
using std::invalid_argument::invalid_argument;
};
/// A more specific subclass that is thown if the serialization type is an initial mismatch: for
/// example, trying deserializing an int but the next thing in input is a list. This is not,
/// however, thrown if the type initially looks fine but, say, a nested serialization fails. This
/// error will only be thrown when the input stream has not been advanced (and so can be tried for a
/// different type).
class bt_deserialize_invalid_type : public bt_deserialize_invalid {
using bt_deserialize_invalid::bt_deserialize_invalid;
};
namespace detail {
/// Reads digits into an unsigned 64-bit int.
uint64_t extract_unsigned(std::string_view& s);
// (Provide non-constant lvalue and rvalue ref functions so that we only accept explicit
// string_views but not implicitly converted ones)
inline uint64_t extract_unsigned(std::string_view&& s) { return extract_unsigned(s); }
// Fallback base case; we only get here if none of the partial specializations below work
template <typename T, typename SFINAE = void>
struct bt_serialize { static_assert(!std::is_same_v<T, T>, "Cannot serialize T: unsupported type for bt serialization"); };
template <typename T, typename SFINAE = void>
struct bt_deserialize { static_assert(!std::is_same_v<T, T>, "Cannot deserialize T: unsupported type for bt deserialization"); };
/// Checks that we aren't at the end of a string view and throws if we are.
inline void bt_need_more(const std::string_view &s) {
if (s.empty())
throw bt_deserialize_invalid{"Unexpected end of string while deserializing"};
}
/// Deserializes a signed or unsigned 64-bit integer from a string. Sets the second bool to true
/// iff the value read was negative, false if positive; in either case the unsigned value is return
/// in .first. Throws an exception if the read value doesn't fit in a int64_t (if negative) or a
/// uint64_t (if positive). Removes consumed characters from the string_view.
std::pair<uint64_t, bool> bt_deserialize_integer(std::string_view& s);
/// Integer specializations
template <typename T>
struct bt_serialize<T, std::enable_if_t<std::is_integral_v<T>>> {
static_assert(sizeof(T) <= sizeof(uint64_t), "Serialization of integers larger than uint64_t is not supported");
void operator()(std::ostream &os, const T &val) {
// Cast 1-byte types to a larger type to avoid iostream interpreting them as single characters
using output_type = std::conditional_t<(sizeof(T) > 1), T, std::conditional_t<std::is_signed_v<T>, int, unsigned>>;
os << 'i' << static_cast<output_type>(val) << 'e';
}
};
template <typename T>
struct bt_deserialize<T, std::enable_if_t<std::is_integral_v<T>>> {
void operator()(std::string_view& s, T &val) {
constexpr uint64_t umax = static_cast<uint64_t>(std::numeric_limits<T>::max());
constexpr int64_t smin = static_cast<int64_t>(std::numeric_limits<T>::min());
auto [magnitude, negative] = bt_deserialize_integer(s);
if (std::is_signed_v<T>) {
if (!negative) {
if (magnitude > umax)
throw bt_deserialize_invalid("Integer deserialization failed: found too-large value " + std::to_string(magnitude) + " > " + std::to_string(umax));
val = static_cast<T>(magnitude);
} else {
auto sval = -static_cast<int64_t>(magnitude);
if (!std::is_same_v<T, int64_t> && sval < smin)
throw bt_deserialize_invalid("Integer deserialization failed: found too-low value " + std::to_string(sval) + " < " + std::to_string(smin));
val = static_cast<T>(sval);
}
} else {
if (negative)
throw bt_deserialize_invalid("Integer deserialization failed: found negative value -" + std::to_string(magnitude) + " but type is unsigned");
if (!std::is_same_v<T, uint64_t> && magnitude > umax)
throw bt_deserialize_invalid("Integer deserialization failed: found too-large value " + std::to_string(magnitude) + " > " + std::to_string(umax));
val = static_cast<T>(magnitude);
}
}
};
extern template struct bt_deserialize<int64_t>;
extern template struct bt_deserialize<uint64_t>;
template <>
struct bt_serialize<std::string_view> {
void operator()(std::ostream &os, const std::string_view &val) { os << val.size(); os.put(':'); os.write(val.data(), val.size()); }
};
template <>
struct bt_deserialize<std::string_view> {
void operator()(std::string_view& s, std::string_view& val);
};
/// String specialization
template <>
struct bt_serialize<std::string> {
void operator()(std::ostream &os, const std::string &val) { bt_serialize<std::string_view>{}(os, val); }
};
template <>
struct bt_deserialize<std::string> {
void operator()(std::string_view& s, std::string& val) { std::string_view view; bt_deserialize<std::string_view>{}(s, view); val = {view.data(), view.size()}; }
};
/// char * and string literals -- we allow serialization for convenience, but not deserialization
template <>
struct bt_serialize<char *> {
void operator()(std::ostream &os, const char *str) { bt_serialize<std::string_view>{}(os, {str, std::strlen(str)}); }
};
template <size_t N>
struct bt_serialize<char[N]> {
void operator()(std::ostream &os, const char *str) { bt_serialize<std::string_view>{}(os, {str, N-1}); }
};
/// Partial dict validity; we don't check the second type for serializability, that will be handled
/// via the base case static_assert if invalid.
template <typename T, typename = void> struct is_bt_input_dict_container_impl : std::false_type {};
template <typename T>
struct is_bt_input_dict_container_impl<T, std::enable_if_t<
std::is_same_v<std::string, std::remove_cv_t<typename T::value_type::first_type>> ||
std::is_same_v<std::string_view, std::remove_cv_t<typename T::value_type::first_type>>,
std::void_t<typename T::const_iterator /* is const iterable */,
typename T::value_type::second_type /* has a second type */>>>
: std::true_type {};
/// Determines whether the type looks like something we can insert into (using `v.insert(v.end(), x)`)
template <typename T, typename = void> struct is_bt_insertable_impl : std::false_type {};
template <typename T>
struct is_bt_insertable_impl<T,
std::void_t<decltype(std::declval<T>().insert(std::declval<T>().end(), std::declval<typename T::value_type>()))>>
: std::true_type {};
template <typename T>
constexpr bool is_bt_insertable = is_bt_insertable_impl<T>::value;
/// Determines whether the given type looks like a compatible map (i.e. has std::string keys) that
/// we can insert into.
template <typename T, typename = void> struct is_bt_output_dict_container_impl : std::false_type {};
template <typename T>
struct is_bt_output_dict_container_impl<T, std::enable_if_t<
std::is_same_v<std::string, std::remove_cv_t<typename T::value_type::first_type>> && is_bt_insertable<T>,
std::void_t<typename T::value_type::second_type /* has a second type */>>>
: std::true_type {};
template <typename T>
constexpr bool is_bt_output_dict_container = is_bt_output_dict_container_impl<T>::value;
template <typename T>
constexpr bool is_bt_input_dict_container = is_bt_output_dict_container_impl<T>::value;
// Sanity checks:
static_assert(is_bt_input_dict_container<bt_dict>);
static_assert(is_bt_output_dict_container<bt_dict>);
/// Specialization for a dict-like container (such as an unordered_map). We accept anything for a
/// dict that is const iterable over something that looks like a pair with std::string for first
/// value type. The value (i.e. second element of the pair) also must be serializable.
template <typename T>
struct bt_serialize<T, std::enable_if_t<is_bt_input_dict_container<T>>> {
using second_type = typename T::value_type::second_type;
using ref_pair = std::reference_wrapper<const typename T::value_type>;
void operator()(std::ostream &os, const T &dict) {
os << 'd';
std::vector<ref_pair> pairs;
pairs.reserve(dict.size());
for (const auto &pair : dict)
pairs.emplace(pairs.end(), pair);
std::sort(pairs.begin(), pairs.end(), [](ref_pair a, ref_pair b) { return a.get().first < b.get().first; });
for (auto &ref : pairs) {
bt_serialize<std::string>{}(os, ref.get().first);
bt_serialize<second_type>{}(os, ref.get().second);
}
os << 'e';
}
};
template <typename T>
struct bt_deserialize<T, std::enable_if_t<is_bt_output_dict_container<T>>> {
using second_type = typename T::value_type::second_type;
void operator()(std::string_view& s, T& dict) {
// Smallest dict is 2 bytes "de", for an empty dict.
if (s.size() < 2) throw bt_deserialize_invalid("Deserialization failed: end of string found where dict expected");
if (s[0] != 'd') throw bt_deserialize_invalid_type("Deserialization failed: expected 'd', found '"s + s[0] + "'"s);
s.remove_prefix(1);
dict.clear();
bt_deserialize<std::string> key_deserializer;
bt_deserialize<second_type> val_deserializer;
while (!s.empty() && s[0] != 'e') {
std::string key;
second_type val;
key_deserializer(s, key);
val_deserializer(s, val);
dict.insert(dict.end(), typename T::value_type{std::move(key), std::move(val)});
}
if (s.empty())
throw bt_deserialize_invalid("Deserialization failed: encountered end of string before dict was finished");
s.remove_prefix(1); // Consume the 'e'
}
};
/// Accept anything that looks iterable; value serialization validity isn't checked here (it fails
/// via the base case static assert).
template <typename T, typename = void> struct is_bt_input_list_container_impl : std::false_type {};
template <typename T>
struct is_bt_input_list_container_impl<T, std::enable_if_t<
!std::is_same_v<T, std::string> && !std::is_same_v<T, std::string_view> && !is_bt_input_dict_container<T>,
std::void_t<typename T::const_iterator, typename T::value_type>>>
: std::true_type {};
template <typename T, typename = void> struct is_bt_output_list_container_impl : std::false_type {};
template <typename T>
struct is_bt_output_list_container_impl<T, std::enable_if_t<
!std::is_same_v<T, std::string> && !is_bt_output_dict_container<T> && is_bt_insertable<T>>>
: std::true_type {};
template <typename T>
constexpr bool is_bt_output_list_container = is_bt_output_list_container_impl<T>::value;
template <typename T>
constexpr bool is_bt_input_list_container = is_bt_input_list_container_impl<T>::value;
// Sanity checks:
static_assert(is_bt_input_list_container<bt_list>);
static_assert(is_bt_output_list_container<bt_list>);
/// List specialization
template <typename T>
struct bt_serialize<T, std::enable_if_t<is_bt_input_list_container<T>>> {
void operator()(std::ostream& os, const T& list) {
os << 'l';
for (const auto &v : list)
bt_serialize<std::remove_cv_t<typename T::value_type>>{}(os, v);
os << 'e';
}
};
template <typename T>
struct bt_deserialize<T, std::enable_if_t<is_bt_output_list_container<T>>> {
using value_type = typename T::value_type;
void operator()(std::string_view& s, T& list) {
// Smallest list is 2 bytes "le", for an empty list.
if (s.size() < 2) throw bt_deserialize_invalid("Deserialization failed: end of string found where list expected");
if (s[0] != 'l') throw bt_deserialize_invalid_type("Deserialization failed: expected 'l', found '"s + s[0] + "'"s);
s.remove_prefix(1);
list.clear();
bt_deserialize<value_type> deserializer;
while (!s.empty() && s[0] != 'e') {
value_type v;
deserializer(s, v);
list.insert(list.end(), std::move(v));
}
if (s.empty())
throw bt_deserialize_invalid("Deserialization failed: encountered end of string before list was finished");
s.remove_prefix(1); // Consume the 'e'
}
};
/// variant visitor; serializes whatever is contained
class bt_serialize_visitor {
std::ostream &os;
public:
using result_type = void;
bt_serialize_visitor(std::ostream &os) : os{os} {}
template <typename T> void operator()(const T &val) const {
bt_serialize<T>{}(os, val);
}
};
template <typename T>
constexpr bool is_bt_deserializable = std::is_same_v<T, std::string> || std::is_integral_v<T> ||
is_bt_output_dict_container<T> || is_bt_output_list_container<T>;
// General template and base case; this base will only actually be invoked when Ts... is empty,
// which means we reached the end without finding any variant type capable of holding the value.
template <typename SFINAE, typename Variant, typename... Ts>
struct bt_deserialize_try_variant_impl {
void operator()(std::string_view&, Variant&) {
throw bt_deserialize_invalid("Deserialization failed: could not deserialize value into any variant type");
}
};
template <typename... Ts, typename Variant>
void bt_deserialize_try_variant(std::string_view& s, Variant& variant) {
bt_deserialize_try_variant_impl<void, Variant, Ts...>{}(s, variant);
}
template <typename Variant, typename T, typename... Ts>
struct bt_deserialize_try_variant_impl<std::enable_if_t<is_bt_deserializable<T>>, Variant, T, Ts...> {
void operator()(std::string_view& s, Variant& variant) {
if ( is_bt_output_list_container<T> ? s[0] == 'l' :
is_bt_output_dict_container<T> ? s[0] == 'd' :
std::is_integral_v<T> ? s[0] == 'i' :
std::is_same_v<T, std::string> ? s[0] >= '0' && s[0] <= '9' :
false) {
T val;
bt_deserialize<T>{}(s, val);
variant = std::move(val);
} else {
bt_deserialize_try_variant<Ts...>(s, variant);
}
}
};
template <typename Variant, typename T, typename... Ts>
struct bt_deserialize_try_variant_impl<std::enable_if_t<!is_bt_deserializable<T>>, Variant, T, Ts...> {
void operator()(std::string_view& s, Variant& variant) {
// Unsupported deserialization type, skip it
bt_deserialize_try_variant<Ts...>(s, variant);
}
};
// Serialization of a variant; all variant types must be bt-serializable.
template <typename... Ts>
struct bt_serialize<std::variant<Ts...>, std::void_t<bt_serialize<Ts>...>> {
void operator()(std::ostream &os, const std::variant<Ts...>& val) {
std::visit(bt_serialize_visitor{os}, val);
}
};
// Deserialization to a variant; at least one variant type must be bt-deserializble.
template <typename... Ts>
struct bt_deserialize<std::variant<Ts...>, std::enable_if_t<(is_bt_deserializable<Ts> || ...)>> {
void operator()(std::string_view& s, std::variant<Ts...>& val) {
bt_deserialize_try_variant<Ts...>(s, val);
}
};
template <>
struct bt_serialize<bt_value> : bt_serialize<bt_variant> {};
template <>
struct bt_deserialize<bt_value> {
void operator()(std::string_view& s, bt_value& val);
};
template <typename T>
struct bt_stream_serializer {
const T &val;
explicit bt_stream_serializer(const T &val) : val{val} {}
operator std::string() const {
std::ostringstream oss;
oss << *this;
return oss.str();
}
};
template <typename T>
std::ostream &operator<<(std::ostream &os, const bt_stream_serializer<T> &s) {
bt_serialize<T>{}(os, s.val);
return os;
}
} // namespace detail
/// Returns a wrapper around a value reference that can serialize the value directly to an output
/// stream. This class is intended to be used inline (i.e. without being stored) as in:
///
/// std::list<int> my_list{{1,2,3}};
/// std::cout << bt_serializer(my_list);
///
/// While it is possible to store the returned object and use it, such as:
///
/// auto encoded = bt_serializer(42);
/// std::cout << encoded;
///
/// this approach is not generally recommended: the returned object stores a reference to the
/// passed-in type, which may not survive. If doing this note that it is the caller's
/// responsibility to ensure the serializer is not used past the end of the lifetime of the value
/// being serialized.
///
/// Also note that serializing directly to an output stream is more efficient as no intermediate
/// string containing the entire serialization has to be constructed.
///
template <typename T>
detail::bt_stream_serializer<T> bt_serializer(const T &val) { return detail::bt_stream_serializer<T>{val}; }
/// Serializes the given value into a std::string.
///
/// int number = 42;
/// std::string encoded = bt_serialize(number);
/// // Equivalent:
/// //auto encoded = (std::string) bt_serialize(number);
///
/// This takes any serializable type: integral types, strings, lists of serializable types, and
/// string->value maps of serializable types.
template <typename T>
std::string bt_serialize(const T &val) { return bt_serializer(val); }
/// Deserializes the given string view directly into `val`. Usage:
///
/// std::string encoded = "i42e";
/// int value;
/// bt_deserialize(encoded, value); // Sets value to 42
///
template <typename T, std::enable_if_t<!std::is_const_v<T>, int> = 0>
void bt_deserialize(std::string_view s, T& val) {
return detail::bt_deserialize<T>{}(s, val);
}
/// Deserializes the given string_view into a `T`, which is returned.
///
/// std::string encoded = "li1ei2ei3ee"; // bt-encoded list of ints: [1,2,3]
/// auto mylist = bt_deserialize<std::list<int>>(encoded);
///
template <typename T>
T bt_deserialize(std::string_view s) {
T val;
bt_deserialize(s, val);
return val;
}
/// Deserializes the given value into a generic `bt_value` type (wrapped std::variant) which is
/// capable of holding all possible BT-encoded values (including recursion).
///
/// Example:
///
/// std::string encoded = "i42e";
/// auto val = bt_get(encoded);
/// int v = get_int<int>(val); // fails unless the encoded value was actually an integer that
/// // fits into an `int`
///
inline bt_value bt_get(std::string_view s) {
return bt_deserialize<bt_value>(s);
}
/// Helper functions to extract a value of some integral type from a bt_value which contains either
/// a int64_t or uint64_t. Does range checking, throwing std::overflow_error if the stored value is
/// outside the range of the target type.
///
/// Example:
///
/// std::string encoded = "i123456789e";
/// auto val = bt_get(encoded);
/// auto v = get_int<uint32_t>(val); // throws if the decoded value doesn't fit in a uint32_t
template <typename IntType, std::enable_if_t<std::is_integral_v<IntType>, int> = 0>
IntType get_int(const bt_value &v) {
if (std::holds_alternative<uint64_t>(v)) {
uint64_t value = std::get<uint64_t>(v);
if constexpr (!std::is_same_v<IntType, uint64_t>)
if (value > static_cast<uint64_t>(std::numeric_limits<IntType>::max()))
throw std::overflow_error("Unable to extract integer value: stored value is too large for the requested type");
return static_cast<IntType>(value);
}
int64_t value = std::get<int64_t>(v);
if constexpr (!std::is_same_v<IntType, int64_t>)
if (value > static_cast<int64_t>(std::numeric_limits<IntType>::max())
|| value < static_cast<int64_t>(std::numeric_limits<IntType>::min()))
throw std::overflow_error("Unable to extract integer value: stored value is outside the range of the requested type");
return static_cast<IntType>(value);
}
/// Class that allows you to walk through a bt-encoded list in memory without copying or allocating
/// memory. It accesses existing memory directly and so the caller must ensure that the referenced
/// memory stays valid for the lifetime of the bt_list_consumer object.
class bt_list_consumer {
protected:
std::string_view data;
bt_list_consumer() = default;
public:
bt_list_consumer(std::string_view data_);
/// Copy constructor. Making a copy copies the current position so can be used for multipass
/// iteration through a list.
bt_list_consumer(const bt_list_consumer&) = default;
bt_list_consumer& operator=(const bt_list_consumer&) = default;
/// Returns true if the next value indicates the end of the list
bool is_finished() const { return data.front() == 'e'; }
/// Returns true if the next element looks like an encoded string
bool is_string() const { return data.front() >= '0' && data.front() <= '9'; }
/// Returns true if the next element looks like an encoded integer
bool is_integer() const { return data.front() == 'i'; }
/// Returns true if the next element looks like an encoded negative integer
bool is_negative_integer() const { return is_integer() && data.size() >= 2 && data[1] == '-'; }
/// Returns true if the next element looks like an encoded list
bool is_list() const { return data.front() == 'l'; }
/// Returns true if the next element looks like an encoded dict
bool is_dict() const { return data.front() == 'd'; }
/// Attempt to parse the next value as a string (and advance just past it). Throws if the next
/// value is not a string.
std::string consume_string();
std::string_view consume_string_view();
/// Attempts to parse the next value as an integer (and advance just past it). Throws if the
/// next value is not an integer.
template <typename IntType>
IntType consume_integer() {
if (!is_integer()) throw bt_deserialize_invalid_type{"next value is not an integer"};
std::string_view next{data};
IntType ret;
detail::bt_deserialize<IntType>{}(next, ret);
data = next;
return ret;
}
/// Consumes a list, return it as a list-like type. This typically requires dynamic allocation,
/// but only has to parse the data once. Compare with consume_list_data() which allows
/// alloc-free traversal, but requires parsing twice (if the contents are to be used).
template <typename T = bt_list>
T consume_list() {
T list;
consume_list(list);
return list;
}
/// Same as above, but takes a pre-existing list-like data type.
template <typename T>
void consume_list(T& list) {
if (!is_list()) throw bt_deserialize_invalid_type{"next bt value is not a list"};
std::string_view n{data};
detail::bt_deserialize<T>{}(n, list);
data = n;
}
/// Consumes a dict, return it as a dict-like type. This typically requires dynamic allocation,
/// but only has to parse the data once. Compare with consume_dict_data() which allows
/// alloc-free traversal, but requires parsing twice (if the contents are to be used).
template <typename T = bt_dict>
T consume_dict() {
T dict;
consume_dict(dict);
return dict;
}
/// Same as above, but takes a pre-existing dict-like data type.
template <typename T>
void consume_dict(T& dict) {
if (!is_dict()) throw bt_deserialize_invalid_type{"next bt value is not a dict"};
std::string_view n{data};
detail::bt_deserialize<T>{}(n, dict);
data = n;
}
/// Consumes a value without returning it.
void skip_value();
/// Attempts to parse the next value as a list and returns the string_view that contains the
/// entire thing. This is recursive into both lists and dicts and likely to be quite
/// inefficient for large, nested structures (unless the values only need to be skipped but
/// aren't separately needed). This, however, does not require dynamic memory allocation.
std::string_view consume_list_data();
/// Attempts to parse the next value as a dict and returns the string_view that contains the
/// entire thing. This is recursive into both lists and dicts and likely to be quite
/// inefficient for large, nested structures (unless the values only need to be skipped but
/// aren't separately needed). This, however, does not require dynamic memory allocation.
std::string_view consume_dict_data();
};
/// Class that allows you to walk through key-value pairs of a bt-encoded dict in memory without
/// copying or allocating memory. It accesses existing memory directly and so the caller must
/// ensure that the referenced memory stays valid for the lifetime of the bt_dict_consumer object.
class bt_dict_consumer : private bt_list_consumer {
std::string_view key_;
/// Consume the key if not already consumed and there is a key present (rather than 'e').
/// Throws exception if what should be a key isn't a string, or if the key consumes the entire
/// data (i.e. requires that it be followed by something). Returns true if the key was consumed
/// (either now or previously and cached).
bool consume_key();
/// Clears the cached key and returns it. Must have already called consume_key directly or
/// indirectly via one of the `is_{...}` methods.
std::string_view flush_key() {
std::string_view k;
k.swap(key_);
return k;
}
public:
bt_dict_consumer(std::string_view data_);
/// Copy constructor. Making a copy copies the current position so can be used for multipass
/// iteration through a list.
bt_dict_consumer(const bt_dict_consumer&) = default;
bt_dict_consumer& operator=(const bt_dict_consumer&) = default;
/// Returns true if the next value indicates the end of the dict
bool is_finished() { return !consume_key() && data.front() == 'e'; }
/// Operator bool is an alias for `!is_finished()`
operator bool() { return !is_finished(); }
/// Returns true if the next value looks like an encoded string
bool is_string() { return consume_key() && data.front() >= '0' && data.front() <= '9'; }
/// Returns true if the next element looks like an encoded integer
bool is_integer() { return consume_key() && data.front() == 'i'; }
/// Returns true if the next element looks like an encoded negative integer
bool is_negative_integer() { return is_integer() && data.size() >= 2 && data[1] == '-'; }
/// Returns true if the next element looks like an encoded list
bool is_list() { return consume_key() && data.front() == 'l'; }
/// Returns true if the next element looks like an encoded dict
bool is_dict() { return consume_key() && data.front() == 'd'; }
/// Returns the key of the next pair. This does not have to be called; it is also returned by
/// all of the other consume_* methods. The value is cached whether called here or by some
/// other method; accessing it multiple times simple accesses the cache until the next value is
/// consumed.
std::string_view key() {
if (!consume_key())
throw bt_deserialize_invalid{"Cannot access next key: at the end of the dict"};
return key_;
}
/// Attempt to parse the next value as a string->string pair (and advance just past it). Throws
/// if the next value is not a string.
std::pair<std::string_view, std::string_view> next_string();
/// Attempts to parse the next value as an string->integer pair (and advance just past it).
/// Throws if the next value is not an integer.
template <typename IntType>
std::pair<std::string_view, IntType> next_integer() {
if (!is_integer()) throw bt_deserialize_invalid_type{"next bt dict value is not an integer"};
std::pair<std::string_view, IntType> ret;
ret.second = bt_list_consumer::consume_integer<IntType>();
ret.first = flush_key();
return ret;
}
/// Consumes a string->list pair, return it as a list-like type. This typically requires
/// dynamic allocation, but only has to parse the data once. Compare with consume_list_data()
/// which allows alloc-free traversal, but requires parsing twice (if the contents are to be
/// used).
template <typename T = bt_list>
std::pair<std::string_view, T> next_list() {
std::pair<std::string_view, T> pair;
pair.first = consume_list(pair.second);
return pair;
}
/// Same as above, but takes a pre-existing list-like data type. Returns the key.
template <typename T>
std::string_view next_list(T& list) {
if (!is_list()) throw bt_deserialize_invalid_type{"next bt value is not a list"};
bt_list_consumer::consume_list(list);
return flush_key();
}
/// Consumes a string->dict pair, return it as a dict-like type. This typically requires
/// dynamic allocation, but only has to parse the data once. Compare with consume_dict_data()
/// which allows alloc-free traversal, but requires parsing twice (if the contents are to be
/// used).
template <typename T = bt_dict>
std::pair<std::string_view, T> next_dict() {
std::pair<std::string_view, T> pair;