Feature.cpp

//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2012, 2013 Ripple Labs Inc.
 
    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.
 
    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================
 
#include <xrpl/basics/Slice.h>
#include <xrpl/basics/base_uint.h>
#include <xrpl/basics/contract.h>
#include <xrpl/beast/utility/instrumentation.h>
#include <xrpl/protocol/Feature.h>
#include <xrpl/protocol/digest.h>
 
#include <boost/container_hash/hash.hpp>
#include <boost/multi_index/hashed_index.hpp>
#include <boost/multi_index/indexed_by.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/multi_index/random_access_index.hpp>
#include <boost/multi_index/tag.hpp>
#include <boost/multi_index_container.hpp>
 
#include <atomic>
#include <cstddef>
#include <map>
#include <optional>
#include <string>
 
namespace ripple {
 
inline std::size_t
hash_value(ripple::uint256 const& feature)
{
    std::size_t seed = 0;
    using namespace boost;
    for (auto const& n : feature)
        hash_combine(seed, n);
    return seed;
}
 
namespace {
 
enum class Supported : bool { no = false, yes };
 
// *NOTE*
//
// Features, or Amendments as they are called elsewhere, are enabled on the
// network at some specific time based on Validator voting.  Features are
// enabled using run-time conditionals based on the state of the amendment.
// There is value in retaining that conditional code for some time after
// the amendment is enabled to make it simple to replay old transactions.
// However, once an amendment has been enabled for, say, more than two years
// then retaining that conditional code has less value since it is
// uncommon to replay such old transactions.
//
// Starting in January of 2020 Amendment conditionals from before January
// 2018 are being removed.  So replaying any ledger from before January
// 2018 needs to happen on an older version of the server code.  There's
// a log message in Application.cpp that warns about replaying old ledgers.
//
// At some point in the future someone may wish to remove amendment
// conditional code for amendments that were enabled after January 2018.
// When that happens then the log message in Application.cpp should be
// updated.
//
// Generally, amendments which introduce new features should be set as
// "VoteBehavior::DefaultNo" whereas in rare cases, amendments that fix
// critical bugs should be set as "VoteBehavior::DefaultYes", if off-chain
// consensus is reached amongst reviewers, validator operators, and other
// participants.
 
class FeatureCollections
{
    struct Feature
    {
        std::string name;
        uint256 feature;
 
        Feature() = delete;
        explicit Feature(std::string const& name_, uint256 const& feature_)
            : name(name_), feature(feature_)
        {
        }
 
        // These structs are used by the `features` multi_index_container to
        // provide access to the features collection by size_t index, string
        // name, and uint256 feature identifier
        struct byIndex
        {
        };
        struct byName
        {
        };
        struct byFeature
        {
        };
    };
 
    // Intermediate types to help with readability
    template <class tag, typename Type, Type Feature::*PtrToMember>
    using feature_hashed_unique = boost::multi_index::hashed_unique<
        boost::multi_index::tag<tag>,
        boost::multi_index::member<Feature, Type, PtrToMember>>;
 
    // Intermediate types to help with readability
    using feature_indexing = boost::multi_index::indexed_by<
        boost::multi_index::random_access<
            boost::multi_index::tag<Feature::byIndex>>,
        feature_hashed_unique<Feature::byFeature, uint256, &Feature::feature>,
        feature_hashed_unique<Feature::byName, std::string, &Feature::name>>;
 
    // This multi_index_container provides access to the features collection by
    // name, index, and uint256 feature identifier
    boost::multi_index::multi_index_container<Feature, feature_indexing>
        features;
    std::map<std::string, AmendmentSupport> all;
    std::map<std::string, VoteBehavior> supported;
    std::size_t upVotes = 0;
    std::size_t downVotes = 0;
    mutable std::atomic<bool> readOnly = false;
 
    // These helper functions provide access to the features collection by name,
    // index, and uint256 feature identifier, so the details of
    // multi_index_container can be hidden
    Feature const&
    getByIndex(size_t i) const
    {
        if (i >= features.size())
            LogicError("Invalid FeatureBitset index");
        const auto& sequence = features.get<Feature::byIndex>();
        return sequence[i];
    }
    size_t
    getIndex(Feature const& feature) const
    {
        const auto& sequence = features.get<Feature::byIndex>();
        auto const it_to = sequence.iterator_to(feature);
        return it_to - sequence.begin();
    }
    Feature const*
    getByFeature(uint256 const& feature) const
    {
        const auto& feature_index = features.get<Feature::byFeature>();
        auto const feature_it = feature_index.find(feature);
        return feature_it == feature_index.end() ? nullptr : &*feature_it;
    }
    Feature const*
    getByName(std::string const& name) const
    {
        const auto& name_index = features.get<Feature::byName>();
        auto const name_it = name_index.find(name);
        return name_it == name_index.end() ? nullptr : &*name_it;
    }
 
public:
    FeatureCollections();
 
    std::optional<uint256>
    getRegisteredFeature(std::string const& name) const;
 
    uint256
    registerFeature(
        std::string const& name,
        Supported support,
        VoteBehavior vote);
 
    bool
    registrationIsDone();
 
    std::size_t
    featureToBitsetIndex(uint256 const& f) const;
 
    uint256 const&
    bitsetIndexToFeature(size_t i) const;
 
    std::string
    featureToName(uint256 const& f) const;
 
    std::map<std::string, AmendmentSupport> const&
    allAmendments() const
    {
        return all;
    }
 
    std::map<std::string, VoteBehavior> const&
    supportedAmendments() const
    {
        return supported;
    }
 
    std::size_t
    numDownVotedAmendments() const
    {
        return downVotes;
    }
 
    std::size_t
    numUpVotedAmendments() const
    {
        return upVotes;
    }
};
 
//------------------------------------------------------------------------------
 
FeatureCollections::FeatureCollections()
{
    features.reserve(ripple::detail::numFeatures);
}
 
std::optional<uint256>
FeatureCollections::getRegisteredFeature(std::string const& name) const
{
    XRPL_ASSERT(
        readOnly.load(),
        "ripple::FeatureCollections::getRegisteredFeature : startup completed");
    Feature const* feature = getByName(name);
    if (feature)
        return feature->feature;
    return std::nullopt;
}
 
void
check(bool condition, const char* logicErrorMessage)
{
    if (!condition)
        LogicError(logicErrorMessage);
}
 
uint256
FeatureCollections::registerFeature(
    std::string const& name,
    Supported support,
    VoteBehavior vote)
{
    check(!readOnly, "Attempting to register a feature after startup.");
    check(
        support == Supported::yes || vote == VoteBehavior::DefaultNo,
        "Invalid feature parameters. Must be supported to be up-voted.");
    Feature const* i = getByName(name);
    if (!i)
    {
        check(
            features.size() < detail::numFeatures,
            "More features defined than allocated.");
 
        auto const f = sha512Half(Slice(name.data(), name.size()));
 
        features.emplace_back(name, f);
 
        auto const getAmendmentSupport = [=]() {
            if (vote == VoteBehavior::Obsolete)
                return AmendmentSupport::Retired;
            return support == Supported::yes ? AmendmentSupport::Supported
                                             : AmendmentSupport::Unsupported;
        };
        all.emplace(name, getAmendmentSupport());
 
        if (support == Supported::yes)
        {
            supported.emplace(name, vote);
 
            if (vote == VoteBehavior::DefaultYes)
                ++upVotes;
            else
                ++downVotes;
        }
        check(
            upVotes + downVotes == supported.size(),
            "Feature counting logic broke");
        check(
            supported.size() <= features.size(),
            "More supported features than defined features");
        check(
            features.size() == all.size(),
            "The 'all' features list is populated incorrectly");
        return f;
    }
    else
        // Each feature should only be registered once
        LogicError("Duplicate feature registration");
}
 
bool
FeatureCollections::registrationIsDone()
{
    readOnly = true;
    return true;
}
 
size_t
FeatureCollections::featureToBitsetIndex(uint256 const& f) const
{
    XRPL_ASSERT(
        readOnly.load(),
        "ripple::FeatureCollections::featureToBitsetIndex : startup completed");
 
    Feature const* feature = getByFeature(f);
    if (!feature)
        LogicError("Invalid Feature ID");
 
    return getIndex(*feature);
}
 
uint256 const&
FeatureCollections::bitsetIndexToFeature(size_t i) const
{
    XRPL_ASSERT(
        readOnly.load(),
        "ripple::FeatureCollections::bitsetIndexToFeature : startup completed");
    Feature const& feature = getByIndex(i);
    return feature.feature;
}
 
std::string
FeatureCollections::featureToName(uint256 const& f) const
{
    XRPL_ASSERT(
        readOnly.load(),
        "ripple::FeatureCollections::featureToName : startup completed");
    Feature const* feature = getByFeature(f);
    return feature ? feature->name : to_string(f);
}
 
static FeatureCollections featureCollections;
 
}  // namespace
 
std::map<std::string, AmendmentSupport> const&
allAmendments()
{
    return featureCollections.allAmendments();
}
 
std::map<std::string, VoteBehavior> const&
detail::supportedAmendments()
{
    return featureCollections.supportedAmendments();
}
 
std::size_t
detail::numDownVotedAmendments()
{
    return featureCollections.numDownVotedAmendments();
}
 
std::size_t
detail::numUpVotedAmendments()
{
    return featureCollections.numUpVotedAmendments();
}
 
//------------------------------------------------------------------------------
 
std::optional<uint256>
getRegisteredFeature(std::string const& name)
{
    return featureCollections.getRegisteredFeature(name);
}
 
uint256
registerFeature(std::string const& name, Supported support, VoteBehavior vote)
{
    return featureCollections.registerFeature(name, support, vote);
}
 
// Retired features are in the ledger and have no code controlled by the
// feature. They need to be supported, but do not need to be voted on.
uint256
retireFeature(std::string const& name)
{
    return registerFeature(name, Supported::yes, VoteBehavior::Obsolete);
}
 
bool
registrationIsDone()
{
    return featureCollections.registrationIsDone();
}
 
size_t
featureToBitsetIndex(uint256 const& f)
{
    return featureCollections.featureToBitsetIndex(f);
}
 
uint256
bitsetIndexToFeature(size_t i)
{
    return featureCollections.bitsetIndexToFeature(i);
}
 
std::string
featureToName(uint256 const& f)
{
    return featureCollections.featureToName(f);
}
 
// All known amendments must be registered either here or below with the
// "retired" amendments
 
#pragma push_macro("XRPL_FEATURE")
#undef XRPL_FEATURE
#pragma push_macro("XRPL_FIX")
#undef XRPL_FIX
#pragma push_macro("XRPL_RETIRE")
#undef XRPL_RETIRE
 
#define XRPL_FEATURE(name, supported, vote) \
    uint256 const feature##name = registerFeature(#name, supported, vote);
#define XRPL_FIX(name, supported, vote) \
    uint256 const fix##name = registerFeature("fix" #name, supported, vote);
#define XRPL_RETIRE(name)                                                     \
    [[deprecated("The referenced amendment has been retired"), maybe_unused]] \
    uint256 const retired##name = retireFeature(#name);
 
#include <xrpl/protocol/detail/features.macro>
 
#undef XRPL_RETIRE
#pragma pop_macro("XRPL_RETIRE")
#undef XRPL_FIX
#pragma pop_macro("XRPL_FIX")
#undef XRPL_FEATURE
#pragma pop_macro("XRPL_FEATURE")
 
// All of the features should now be registered, since variables in a cpp file
// are initialized from top to bottom.
//
// Use initialization of one final static variable to set
// featureCollections::readOnly.
[[maybe_unused]] static const bool readOnlySet =
    featureCollections.registrationIsDone();
 
}  // namespace ripple