Feature.cpp

#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 xrpl {
 
inline std::size_t
hash_value(xrpl::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");
        auto const& sequence = features.get<Feature::byIndex>();
        return sequence[i];
    }
    size_t
    getIndex(Feature const& feature) const
    {
        auto const& 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
    {
        auto const& 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
    {
        auto const& 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(xrpl::detail::numFeatures);
}
 
std::optional<uint256>
FeatureCollections::getRegisteredFeature(std::string const& name) const
{
    XRPL_ASSERT(
        readOnly.load(), "xrpl::FeatureCollections::getRegisteredFeature : startup completed");
    Feature const* feature = getByName(name);
    if (feature)
        return feature->feature;
    return std::nullopt;
}
 
void
check(bool condition, char const* 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(), "xrpl::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(), "xrpl::FeatureCollections::bitsetIndexToFeature : startup completed");
    Feature const& feature = getByIndex(i);
    return feature.feature;
}
 
std::string
FeatureCollections::featureToName(uint256 const& f) const
{
    XRPL_ASSERT(readOnly.load(), "xrpl::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_FEATURE")
#undef XRPL_RETIRE_FEATURE
#pragma push_macro("XRPL_RETIRE_FIX")
#undef XRPL_RETIRE_FIX
 
#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);
 
// clang-format off
#define XRPL_RETIRE_FEATURE(name)                                       \
    [[deprecated("The referenced feature amendment has been retired")]] \
    [[maybe_unused]]                                                    \
    uint256 const retiredFeature##name = retireFeature(#name);
 
#define XRPL_RETIRE_FIX(name)                                           \
    [[deprecated("The referenced fix amendment has been retired")]]     \
    [[maybe_unused]]                                                    \
    uint256 const retiredFix##name = retireFeature("fix" #name);
// clang-format on
 
#include <xrpl/protocol/detail/features.macro>
 
#undef XRPL_RETIRE_FEATURE
#pragma pop_macro("XRPL_RETIRE_FEATURE")
#undef XRPL_RETIRE_FIX
#pragma pop_macro("XRPL_RETIRE_FIX")
#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 bool const readOnlySet = featureCollections.registrationIsDone();
 
}  // namespace xrpl