diff options
| -rw-r--r-- | src/Makefile.am | 2 | ||||
| -rw-r--r-- | src/txrequest.cpp | 606 | ||||
| -rw-r--r-- | src/txrequest.h | 197 | ||||
| -rw-r--r-- | src/uint256.cpp | 1 | ||||
| -rw-r--r-- | src/uint256.h | 1 |
5 files changed, 807 insertions, 0 deletions
diff --git a/src/Makefile.am b/src/Makefile.am index aa63b5f516..e29063889b 100644 --- a/src/Makefile.am +++ b/src/Makefile.am @@ -215,6 +215,7 @@ BITCOIN_CORE_H = \ timedata.h \ torcontrol.h \ txdb.h \ + txrequest.h \ txmempool.h \ undo.h \ util/asmap.h \ @@ -327,6 +328,7 @@ libbitcoin_server_a_SOURCES = \ timedata.cpp \ torcontrol.cpp \ txdb.cpp \ + txrequest.cpp \ txmempool.cpp \ validation.cpp \ validationinterface.cpp \ diff --git a/src/txrequest.cpp b/src/txrequest.cpp new file mode 100644 index 0000000000..bb64a00847 --- /dev/null +++ b/src/txrequest.cpp @@ -0,0 +1,606 @@ +// Copyright (c) 2020 The Bitcoin Core developers +// Distributed under the MIT software license, see the accompanying +// file COPYING or http://www.opensource.org/licenses/mit-license.php. + +#include <txrequest.h> + +#include <crypto/siphash.h> +#include <net.h> +#include <primitives/transaction.h> +#include <random.h> +#include <uint256.h> +#include <util/memory.h> + +#include <boost/multi_index_container.hpp> +#include <boost/multi_index/ordered_index.hpp> + +#include <chrono> +#include <unordered_map> +#include <utility> + +#include <assert.h> + +namespace { + +/** The various states a (txhash,peer) pair can be in. + * + * Note that CANDIDATE is split up into 3 substates (DELAYED, BEST, READY), allowing more efficient implementation. + * Also note that the sorting order of ByTxHashView relies on the specific order of values in this enum. + * + * Expected behaviour is: + * - When first announced by a peer, the state is CANDIDATE_DELAYED until reqtime is reached. + * - Announcements that have reached their reqtime but not been requested will be either CANDIDATE_READY or + * CANDIDATE_BEST. Neither of those has an expiration time; they remain in that state until they're requested or + * no longer needed. CANDIDATE_READY announcements are promoted to CANDIDATE_BEST when they're the best one left. + * - When requested, an announcement will be in state REQUESTED until expiry is reached. + * - If expiry is reached, or the peer replies to the request (either with NOTFOUND or the tx), the state becomes + * COMPLETED. + */ +enum class State : uint8_t { + /** A CANDIDATE announcement whose reqtime is in the future. */ + CANDIDATE_DELAYED, + /** A CANDIDATE announcement that's not CANDIDATE_DELAYED or CANDIDATE_BEST. */ + CANDIDATE_READY, + /** The best CANDIDATE for a given txhash; only if there is no REQUESTED announcement already for that txhash. + * The CANDIDATE_BEST is the highest-priority announcement among all CANDIDATE_READY (and _BEST) ones for that + * txhash. */ + CANDIDATE_BEST, + /** A REQUESTED announcement. */ + REQUESTED, + /** A COMPLETED announcement. */ + COMPLETED, +}; + +//! Type alias for sequence numbers. +using SequenceNumber = uint64_t; + +/** An announcement. This is the data we track for each txid or wtxid that is announced to us by each peer. */ +struct Announcement { + /** Txid or wtxid that was announced. */ + const uint256 m_txhash; + /** For CANDIDATE_{DELAYED,BEST,READY} the reqtime; for REQUESTED the expiry. */ + std::chrono::microseconds m_time; + /** What peer the request was from. */ + const NodeId m_peer; + /** What sequence number this announcement has. */ + const SequenceNumber m_sequence : 59; + /** Whether the request is preferred. */ + const bool m_preferred : 1; + /** Whether this is a wtxid request. */ + const bool m_is_wtxid : 1; + + /** What state this announcement is in. */ + State m_state : 3; + + /** Whether this announcement is selected. There can be at most 1 selected peer per txhash. */ + bool IsSelected() const + { + return m_state == State::CANDIDATE_BEST || m_state == State::REQUESTED; + } + + /** Whether this announcement is waiting for a certain time to pass. */ + bool IsWaiting() const + { + return m_state == State::REQUESTED || m_state == State::CANDIDATE_DELAYED; + } + + /** Whether this announcement can feasibly be selected if the current IsSelected() one disappears. */ + bool IsSelectable() const + { + return m_state == State::CANDIDATE_READY || m_state == State::CANDIDATE_BEST; + } + + /** Construct a new announcement from scratch, initially in CANDIDATE_DELAYED state. */ + Announcement(const GenTxid& gtxid, NodeId peer, bool preferred, std::chrono::microseconds reqtime, + SequenceNumber sequence) : + m_txhash(gtxid.GetHash()), m_time(reqtime), m_peer(peer), m_sequence(sequence), m_preferred(preferred), + m_is_wtxid(gtxid.IsWtxid()), m_state(State::CANDIDATE_DELAYED) {} +}; + +//! Type alias for priorities. +using Priority = uint64_t; + +/** A functor with embedded salt that computes priority of an announcement. + * + * Higher priorities are selected first. + */ +class PriorityComputer { + const uint64_t m_k0, m_k1; +public: + explicit PriorityComputer(bool deterministic) : + m_k0{deterministic ? 0 : GetRand(0xFFFFFFFFFFFFFFFF)}, + m_k1{deterministic ? 0 : GetRand(0xFFFFFFFFFFFFFFFF)} {} + + Priority operator()(const uint256& txhash, NodeId peer, bool preferred) const + { + uint64_t low_bits = CSipHasher(m_k0, m_k1).Write(txhash.begin(), txhash.size()).Write(peer).Finalize() >> 1; + return low_bits | uint64_t{preferred} << 63; + } + + Priority operator()(const Announcement& ann) const + { + return operator()(ann.m_txhash, ann.m_peer, ann.m_preferred); + } +}; + +// Definitions for the 3 indexes used in the main data structure. +// +// Each index has a By* type to identify it, a By*View data type to represent the view of announcement it is sorted +// by, and an By*ViewExtractor type to convert an announcement into the By*View type. +// See https://www.boost.org/doc/libs/1_58_0/libs/multi_index/doc/reference/key_extraction.html#key_extractors +// for more information about the key extraction concept. + +// The ByPeer index is sorted by (peer, state == CANDIDATE_BEST, txhash) +// +// Uses: +// * Looking up existing announcements by peer/txhash, by checking both (peer, false, txhash) and +// (peer, true, txhash). +// * Finding all CANDIDATE_BEST announcements for a given peer in GetRequestable. +struct ByPeer {}; +using ByPeerView = std::tuple<NodeId, bool, const uint256&>; +struct ByPeerViewExtractor +{ + using result_type = ByPeerView; + result_type operator()(const Announcement& ann) const + { + return ByPeerView{ann.m_peer, ann.m_state == State::CANDIDATE_BEST, ann.m_txhash}; + } +}; + +// The ByTxHash index is sorted by (txhash, state, priority). +// +// Note: priority == 0 whenever state != CANDIDATE_READY. +// +// Uses: +// * Deleting all announcements with a given txhash in ForgetTxHash. +// * Finding the best CANDIDATE_READY to convert to CANDIDATE_BEST, when no other CANDIDATE_READY or REQUESTED +// announcement exists for that txhash. +// * Determining when no more non-COMPLETED announcements for a given txhash exist, so the COMPLETED ones can be +// deleted. +struct ByTxHash {}; +using ByTxHashView = std::tuple<const uint256&, State, Priority>; +class ByTxHashViewExtractor { + const PriorityComputer& m_computer; +public: + ByTxHashViewExtractor(const PriorityComputer& computer) : m_computer(computer) {} + using result_type = ByTxHashView; + result_type operator()(const Announcement& ann) const + { + const Priority prio = (ann.m_state == State::CANDIDATE_READY) ? m_computer(ann) : 0; + return ByTxHashView{ann.m_txhash, ann.m_state, prio}; + } +}; + +enum class WaitState { + //! Used for announcements that need efficient testing of "is their timestamp in the future?". + FUTURE_EVENT, + //! Used for announcements whose timestamp is not relevant. + NO_EVENT, + //! Used for announcements that need efficient testing of "is their timestamp in the past?". + PAST_EVENT, +}; + +WaitState GetWaitState(const Announcement& ann) +{ + if (ann.IsWaiting()) return WaitState::FUTURE_EVENT; + if (ann.IsSelectable()) return WaitState::PAST_EVENT; + return WaitState::NO_EVENT; +} + +// The ByTime index is sorted by (wait_state, time). +// +// All announcements with a timestamp in the future can be found by iterating the index forward from the beginning. +// All announcements with a timestamp in the past can be found by iterating the index backwards from the end. +// +// Uses: +// * Finding CANDIDATE_DELAYED announcements whose reqtime has passed, and REQUESTED announcements whose expiry has +// passed. +// * Finding CANDIDATE_READY/BEST announcements whose reqtime is in the future (when the clock time went backwards). +struct ByTime {}; +using ByTimeView = std::pair<WaitState, std::chrono::microseconds>; +struct ByTimeViewExtractor +{ + using result_type = ByTimeView; + result_type operator()(const Announcement& ann) const + { + return ByTimeView{GetWaitState(ann), ann.m_time}; + } +}; + +/** Data type for the main data structure (Announcement objects with ByPeer/ByTxHash/ByTime indexes). */ +using Index = boost::multi_index_container< + Announcement, + boost::multi_index::indexed_by< + boost::multi_index::ordered_unique<boost::multi_index::tag<ByPeer>, ByPeerViewExtractor>, + boost::multi_index::ordered_non_unique<boost::multi_index::tag<ByTxHash>, ByTxHashViewExtractor>, + boost::multi_index::ordered_non_unique<boost::multi_index::tag<ByTime>, ByTimeViewExtractor> + > +>; + +/** Helper type to simplify syntax of iterator types. */ +template<typename Tag> +using Iter = typename Index::index<Tag>::type::iterator; + +/** Per-peer statistics object. */ +struct PeerInfo { + size_t m_total = 0; //!< Total number of announcements for this peer. + size_t m_completed = 0; //!< Number of COMPLETED announcements for this peer. + size_t m_requested = 0; //!< Number of REQUESTED announcements for this peer. +}; + +} // namespace + +/** Actual implementation for TxRequestTracker's data structure. */ +class TxRequestTracker::Impl { + //! The current sequence number. Increases for every announcement. This is used to sort txhashes returned by + //! GetRequestable in announcement order. + SequenceNumber m_current_sequence{0}; + + //! This tracker's priority computer. + const PriorityComputer m_computer; + + //! This tracker's main data structure. + Index m_index; + + //! Map with this tracker's per-peer statistics. + std::unordered_map<NodeId, PeerInfo> m_peerinfo; + + //! Wrapper around Index::...::erase that keeps m_peerinfo up to date. + template<typename Tag> + Iter<Tag> Erase(Iter<Tag> it) + { + auto peerit = m_peerinfo.find(it->m_peer); + peerit->second.m_completed -= it->m_state == State::COMPLETED; + peerit->second.m_requested -= it->m_state == State::REQUESTED; + if (--peerit->second.m_total == 0) m_peerinfo.erase(peerit); + return m_index.get<Tag>().erase(it); + } + + //! Wrapper around Index::...::modify that keeps m_peerinfo up to date. + template<typename Tag, typename Modifier> + void Modify(Iter<Tag> it, Modifier modifier) + { + auto peerit = m_peerinfo.find(it->m_peer); + peerit->second.m_completed -= it->m_state == State::COMPLETED; + peerit->second.m_requested -= it->m_state == State::REQUESTED; + m_index.get<Tag>().modify(it, std::move(modifier)); + peerit->second.m_completed += it->m_state == State::COMPLETED; + peerit->second.m_requested += it->m_state == State::REQUESTED; + } + + //! Convert a CANDIDATE_DELAYED announcement into a CANDIDATE_READY. If this makes it the new best + //! CANDIDATE_READY (and no REQUESTED exists) and better than the CANDIDATE_BEST (if any), it becomes the new + //! CANDIDATE_BEST. + void PromoteCandidateReady(Iter<ByTxHash> it) + { + assert(it != m_index.get<ByTxHash>().end()); + assert(it->m_state == State::CANDIDATE_DELAYED); + // Convert CANDIDATE_DELAYED to CANDIDATE_READY first. + Modify<ByTxHash>(it, [](Announcement& ann){ ann.m_state = State::CANDIDATE_READY; }); + // The following code relies on the fact that the ByTxHash is sorted by txhash, and then by state (first + // _DELAYED, then _READY, then _BEST/REQUESTED). Within the _READY announcements, the best one (highest + // priority) comes last. Thus, if an existing _BEST exists for the same txhash that this announcement may + // be preferred over, it must immediately follow the newly created _READY. + auto it_next = std::next(it); + if (it_next == m_index.get<ByTxHash>().end() || it_next->m_txhash != it->m_txhash || + it_next->m_state == State::COMPLETED) { + // This is the new best CANDIDATE_READY, and there is no IsSelected() announcement for this txhash + // already. + Modify<ByTxHash>(it, [](Announcement& ann){ ann.m_state = State::CANDIDATE_BEST; }); + } else if (it_next->m_state == State::CANDIDATE_BEST) { + Priority priority_old = m_computer(*it_next); + Priority priority_new = m_computer(*it); + if (priority_new > priority_old) { + // There is a CANDIDATE_BEST announcement already, but this one is better. + Modify<ByTxHash>(it_next, [](Announcement& ann){ ann.m_state = State::CANDIDATE_READY; }); + Modify<ByTxHash>(it, [](Announcement& ann){ ann.m_state = State::CANDIDATE_BEST; }); + } + } + } + + //! Change the state of an announcement to something non-IsSelected(). If it was IsSelected(), the next best + //! announcement will be marked CANDIDATE_BEST. + void ChangeAndReselect(Iter<ByTxHash> it, State new_state) + { + assert(new_state == State::COMPLETED || new_state == State::CANDIDATE_DELAYED); + assert(it != m_index.get<ByTxHash>().end()); + if (it->IsSelected() && it != m_index.get<ByTxHash>().begin()) { + auto it_prev = std::prev(it); + // The next best CANDIDATE_READY, if any, immediately precedes the REQUESTED or CANDIDATE_BEST + // announcement in the ByTxHash index. + if (it_prev->m_txhash == it->m_txhash && it_prev->m_state == State::CANDIDATE_READY) { + // If one such CANDIDATE_READY exists (for this txhash), convert it to CANDIDATE_BEST. + Modify<ByTxHash>(it_prev, [](Announcement& ann){ ann.m_state = State::CANDIDATE_BEST; }); + } + } + Modify<ByTxHash>(it, [new_state](Announcement& ann){ ann.m_state = new_state; }); + } + + //! Check if 'it' is the only announcement for a given txhash that isn't COMPLETED. + bool IsOnlyNonCompleted(Iter<ByTxHash> it) + { + assert(it != m_index.get<ByTxHash>().end()); + assert(it->m_state != State::COMPLETED); // Not allowed to call this on COMPLETED announcements. + + // This announcement has a predecessor that belongs to the same txhash. Due to ordering, and the + // fact that 'it' is not COMPLETED, its predecessor cannot be COMPLETED here. + if (it != m_index.get<ByTxHash>().begin() && std::prev(it)->m_txhash == it->m_txhash) return false; + + // This announcement has a successor that belongs to the same txhash, and is not COMPLETED. + if (std::next(it) != m_index.get<ByTxHash>().end() && std::next(it)->m_txhash == it->m_txhash && + std::next(it)->m_state != State::COMPLETED) return false; + + return true; + } + + /** Convert any announcement to a COMPLETED one. If there are no non-COMPLETED announcements left for this + * txhash, they are deleted. If this was a REQUESTED announcement, and there are other CANDIDATEs left, the + * best one is made CANDIDATE_BEST. Returns whether the announcement still exists. */ + bool MakeCompleted(Iter<ByTxHash> it) + { + assert(it != m_index.get<ByTxHash>().end()); + + // Nothing to be done if it's already COMPLETED. + if (it->m_state == State::COMPLETED) return true; + + if (IsOnlyNonCompleted(it)) { + // This is the last non-COMPLETED announcement for this txhash. Delete all. + uint256 txhash = it->m_txhash; + do { + it = Erase<ByTxHash>(it); + } while (it != m_index.get<ByTxHash>().end() && it->m_txhash == txhash); + return false; + } + + // Mark the announcement COMPLETED, and select the next best announcement (the first CANDIDATE_READY) if + // needed. + ChangeAndReselect(it, State::COMPLETED); + + return true; + } + + //! Make the data structure consistent with a given point in time: + //! - REQUESTED annoucements with expiry <= now are turned into COMPLETED. + //! - CANDIDATE_DELAYED announcements with reqtime <= now are turned into CANDIDATE_{READY,BEST}. + //! - CANDIDATE_{READY,BEST} announcements with reqtime > now are turned into CANDIDATE_DELAYED. + void SetTimePoint(std::chrono::microseconds now) + { + // Iterate over all CANDIDATE_DELAYED and REQUESTED from old to new, as long as they're in the past, + // and convert them to CANDIDATE_READY and COMPLETED respectively. + while (!m_index.empty()) { + auto it = m_index.get<ByTime>().begin(); + if (it->m_state == State::CANDIDATE_DELAYED && it->m_time <= now) { + PromoteCandidateReady(m_index.project<ByTxHash>(it)); + } else if (it->m_state == State::REQUESTED && it->m_time <= now) { + MakeCompleted(m_index.project<ByTxHash>(it)); + } else { + break; + } + } + + while (!m_index.empty()) { + // If time went backwards, we may need to demote CANDIDATE_BEST and CANDIDATE_READY announcements back + // to CANDIDATE_DELAYED. This is an unusual edge case, and unlikely to matter in production. However, + // it makes it much easier to specify and test TxRequestTracker::Impl's behaviour. + auto it = std::prev(m_index.get<ByTime>().end()); + if (it->IsSelectable() && it->m_time > now) { + ChangeAndReselect(m_index.project<ByTxHash>(it), State::CANDIDATE_DELAYED); + } else { + break; + } + } + } + +public: + Impl(bool deterministic) : + m_computer(deterministic), + // Explicitly initialize m_index as we need to pass a reference to m_computer to ByTxHashViewExtractor. + m_index(boost::make_tuple( + boost::make_tuple(ByPeerViewExtractor(), std::less<ByPeerView>()), + boost::make_tuple(ByTxHashViewExtractor(m_computer), std::less<ByTxHashView>()), + boost::make_tuple(ByTimeViewExtractor(), std::less<ByTimeView>()) + )) {} + + // Disable copying and assigning (a default copy won't work due the stateful ByTxHashViewExtractor). + Impl(const Impl&) = delete; + Impl& operator=(const Impl&) = delete; + + void DisconnectedPeer(NodeId peer) + { + auto& index = m_index.get<ByPeer>(); + auto it = index.lower_bound(ByPeerView{peer, false, uint256::ZERO}); + while (it != index.end() && it->m_peer == peer) { + // Check what to continue with after this iteration. 'it' will be deleted in what follows, so we need to + // decide what to continue with afterwards. There are a number of cases to consider: + // - std::next(it) is end() or belongs to a different peer. In that case, this is the last iteration + // of the loop (denote this by setting it_next to end()). + // - 'it' is not the only non-COMPLETED announcement for its txhash. This means it will be deleted, but + // no other Announcement objects will be modified. Continue with std::next(it) if it belongs to the + // same peer, but decide this ahead of time (as 'it' may change position in what follows). + // - 'it' is the only non-COMPLETED announcement for its txhash. This means it will be deleted along + // with all other announcements for the same txhash - which may include std::next(it). However, other + // than 'it', no announcements for the same peer can be affected (due to (peer, txhash) uniqueness). + // In other words, the situation where std::next(it) is deleted can only occur if std::next(it) + // belongs to a different peer but the same txhash as 'it'. This is covered by the first bulletpoint + // already, and we'll have set it_next to end(). + auto it_next = (std::next(it) == index.end() || std::next(it)->m_peer != peer) ? index.end() : + std::next(it); + // If the announcement isn't already COMPLETED, first make it COMPLETED (which will mark other + // CANDIDATEs as CANDIDATE_BEST, or delete all of a txhash's announcements if no non-COMPLETED ones are + // left). + if (MakeCompleted(m_index.project<ByTxHash>(it))) { + // Then actually delete the announcement (unless it was already deleted by MakeCompleted). + Erase<ByPeer>(it); + } + it = it_next; + } + } + + void ForgetTxHash(const uint256& txhash) + { + auto it = m_index.get<ByTxHash>().lower_bound(ByTxHashView{txhash, State::CANDIDATE_DELAYED, 0}); + while (it != m_index.get<ByTxHash>().end() && it->m_txhash == txhash) { + it = Erase<ByTxHash>(it); + } + } + + void ReceivedInv(NodeId peer, const GenTxid& gtxid, bool preferred, + std::chrono::microseconds reqtime) + { + // Bail out if we already have a CANDIDATE_BEST announcement for this (txhash, peer) combination. The case + // where there is a non-CANDIDATE_BEST announcement already will be caught by the uniqueness property of the + // ByPeer index when we try to emplace the new object below. + if (m_index.get<ByPeer>().count(ByPeerView{peer, true, gtxid.GetHash()})) return; + + // Try creating the announcement with CANDIDATE_DELAYED state (which will fail due to the uniqueness + // of the ByPeer index if a non-CANDIDATE_BEST announcement already exists with the same txhash and peer). + // Bail out in that case. + auto ret = m_index.get<ByPeer>().emplace(gtxid, peer, preferred, reqtime, m_current_sequence); + if (!ret.second) return; + + // Update accounting metadata. + ++m_peerinfo[peer].m_total; + ++m_current_sequence; + } + + //! Find the GenTxids to request now from peer. + std::vector<GenTxid> GetRequestable(NodeId peer, std::chrono::microseconds now) + { + // Move time. + SetTimePoint(now); + + // Find all CANDIDATE_BEST announcements for this peer. + std::vector<const Announcement*> selected; + auto it_peer = m_index.get<ByPeer>().lower_bound(ByPeerView{peer, true, uint256::ZERO}); + while (it_peer != m_index.get<ByPeer>().end() && it_peer->m_peer == peer && + it_peer->m_state == State::CANDIDATE_BEST) { + selected.emplace_back(&*it_peer); + ++it_peer; + } + + // Sort by sequence number. + std::sort(selected.begin(), selected.end(), [](const Announcement* a, const Announcement* b) { + return a->m_sequence < b->m_sequence; + }); + + // Convert to GenTxid and return. + std::vector<GenTxid> ret; + ret.reserve(selected.size()); + std::transform(selected.begin(), selected.end(), std::back_inserter(ret), [](const Announcement* ann) { + return GenTxid{ann->m_is_wtxid, ann->m_txhash}; + }); + return ret; + } + + void RequestedTx(NodeId peer, const uint256& txhash, std::chrono::microseconds expiry) + { + auto it = m_index.get<ByPeer>().find(ByPeerView{peer, true, txhash}); + if (it == m_index.get<ByPeer>().end()) { + // There is no CANDIDATE_BEST announcement, look for a _READY or _DELAYED instead. If the caller only + // ever invokes RequestedTx with the values returned by GetRequestable, and no other non-const functions + // other than ForgetTxHash and GetRequestable in between, this branch will never execute (as txhashes + // returned by GetRequestable always correspond to CANDIDATE_BEST announcements). + + it = m_index.get<ByPeer>().find(ByPeerView{peer, false, txhash}); + if (it == m_index.get<ByPeer>().end() || (it->m_state != State::CANDIDATE_DELAYED && + it->m_state != State::CANDIDATE_READY)) { + // There is no CANDIDATE announcement tracked for this peer, so we have nothing to do. Either this + // txhash wasn't tracked at all (and the caller should have called ReceivedInv), or it was already + // requested and/or completed for other reasons and this is just a superfluous RequestedTx call. + return; + } + + // Look for an existing CANDIDATE_BEST or REQUESTED with the same txhash. We only need to do this if the + // found announcement had a different state than CANDIDATE_BEST. If it did, invariants guarantee that no + // other CANDIDATE_BEST or REQUESTED can exist. + auto it_old = m_index.get<ByTxHash>().lower_bound(ByTxHashView{txhash, State::CANDIDATE_BEST, 0}); + if (it_old != m_index.get<ByTxHash>().end() && it_old->m_txhash == txhash) { + if (it_old->m_state == State::CANDIDATE_BEST) { + // The data structure's invariants require that there can be at most one CANDIDATE_BEST or one + // REQUESTED announcement per txhash (but not both simultaneously), so we have to convert any + // existing CANDIDATE_BEST to another CANDIDATE_* when constructing another REQUESTED. + // It doesn't matter whether we pick CANDIDATE_READY or _DELAYED here, as SetTimePoint() + // will correct it at GetRequestable() time. If time only goes forward, it will always be + // _READY, so pick that to avoid extra work in SetTimePoint(). + Modify<ByTxHash>(it_old, [](Announcement& ann) { ann.m_state = State::CANDIDATE_READY; }); + } else if (it_old->m_state == State::REQUESTED) { + // As we're no longer waiting for a response to the previous REQUESTED announcement, convert it + // to COMPLETED. This also helps guaranteeing progress. + Modify<ByTxHash>(it_old, [](Announcement& ann) { ann.m_state = State::COMPLETED; }); + } + } + } + + Modify<ByPeer>(it, [expiry](Announcement& ann) { + ann.m_state = State::REQUESTED; + ann.m_time = expiry; + }); + } + + void ReceivedResponse(NodeId peer, const uint256& txhash) + { + // We need to search the ByPeer index for both (peer, false, txhash) and (peer, true, txhash). + auto it = m_index.get<ByPeer>().find(ByPeerView{peer, false, txhash}); + if (it == m_index.get<ByPeer>().end()) { + it = m_index.get<ByPeer>().find(ByPeerView{peer, true, txhash}); + } + if (it != m_index.get<ByPeer>().end()) MakeCompleted(m_index.project<ByTxHash>(it)); + } + + size_t CountInFlight(NodeId peer) const + { + auto it = m_peerinfo.find(peer); + if (it != m_peerinfo.end()) return it->second.m_requested; + return 0; + } + + size_t CountCandidates(NodeId peer) const + { + auto it = m_peerinfo.find(peer); + if (it != m_peerinfo.end()) return it->second.m_total - it->second.m_requested - it->second.m_completed; + return 0; + } + + size_t Count(NodeId peer) const + { + auto it = m_peerinfo.find(peer); + if (it != m_peerinfo.end()) return it->second.m_total; + return 0; + } + + //! Count how many announcements are being tracked in total across all peers and transactions. + size_t Size() const { return m_index.size(); } +}; + +TxRequestTracker::TxRequestTracker(bool deterministic) : + m_impl{MakeUnique<TxRequestTracker::Impl>(deterministic)} {} + +TxRequestTracker::~TxRequestTracker() = default; + +void TxRequestTracker::ForgetTxHash(const uint256& txhash) { m_impl->ForgetTxHash(txhash); } +void TxRequestTracker::DisconnectedPeer(NodeId peer) { m_impl->DisconnectedPeer(peer); } +size_t TxRequestTracker::CountInFlight(NodeId peer) const { return m_impl->CountInFlight(peer); } +size_t TxRequestTracker::CountCandidates(NodeId peer) const { return m_impl->CountCandidates(peer); } +size_t TxRequestTracker::Count(NodeId peer) const { return m_impl->Count(peer); } +size_t TxRequestTracker::Size() const { return m_impl->Size(); } + +void TxRequestTracker::ReceivedInv(NodeId peer, const GenTxid& gtxid, bool preferred, + std::chrono::microseconds reqtime) +{ + m_impl->ReceivedInv(peer, gtxid, preferred, reqtime); +} + +void TxRequestTracker::RequestedTx(NodeId peer, const uint256& txhash, std::chrono::microseconds expiry) +{ + m_impl->RequestedTx(peer, txhash, expiry); +} + +void TxRequestTracker::ReceivedResponse(NodeId peer, const uint256& txhash) +{ + m_impl->ReceivedResponse(peer, txhash); +} + +std::vector<GenTxid> TxRequestTracker::GetRequestable(NodeId peer, std::chrono::microseconds now) +{ + return m_impl->GetRequestable(peer, now); +} diff --git a/src/txrequest.h b/src/txrequest.h new file mode 100644 index 0000000000..e24390b6aa --- /dev/null +++ b/src/txrequest.h @@ -0,0 +1,197 @@ +// Copyright (c) 2020 The Bitcoin Core developers +// Distributed under the MIT software license, see the accompanying +// file COPYING or http://www.opensource.org/licenses/mit-license.php. + +#ifndef BITCOIN_TXREQUEST_H +#define BITCOIN_TXREQUEST_H + +#include <primitives/transaction.h> +#include <net.h> // For NodeId +#include <uint256.h> + +#include <chrono> +#include <vector> + +#include <stdint.h> + +/** Data structure to keep track of, and schedule, transaction downloads from peers. + * + * === Specification === + * + * We keep track of which peers have announced which transactions, and use that to determine which requests + * should go to which peer, when, and in what order. + * + * The following information is tracked per peer/tx combination ("announcement"): + * - Which peer announced it (through their NodeId) + * - The txid or wtxid of the transaction (collectively called "txhash" in what follows) + * - Whether it was a tx or wtx announcement (see BIP339). + * - What the earliest permitted time is that that transaction can be requested from that peer (called "reqtime"). + * - Whether it's from a "preferred" peer or not. Which announcements get this flag is determined by the caller, but + * this is designed for outbound peers, or other peers that we have a higher level of trust in. Even when the + * peers' preferredness changes, the preferred flag of existing announcements from that peer won't change. + * - Whether or not the transaction was requested already, and if so, when it times out (called "expiry"). + * - Whether or not the transaction request failed already (timed out, or invalid transaction or NOTFOUND was + * received). + * + * Transaction requests are then assigned to peers, following these rules: + * + * - No transaction is requested as long as another request for the same txhash is outstanding (it needs to fail + * first by passing expiry, or a NOTFOUND or invalid transaction has to be received for it). + * + * Rationale: to avoid wasting bandwidth on multiple copies of the same transaction. Note that this only works + * per txhash, so if the same transaction is announced both through txid and wtxid, we have no means + * to prevent fetching both (the caller can however mitigate this by delaying one, see further). + * + * - The same transaction is never requested twice from the same peer, unless the announcement was forgotten in + * between, and re-announced. Announcements are forgotten only: + * - If a peer goes offline, all its announcements are forgotten. + * - If a transaction has been successfully received, or is otherwise no longer needed, the caller can call + * ForgetTxHash, which removes all announcements across all peers with the specified txhash. + * - If for a given txhash only already-failed announcements remain, they are all forgotten. + * + * Rationale: giving a peer multiple chances to announce a transaction would allow them to bias requests in their + * favor, worsening transaction censoring attacks. The flip side is that as long as an attacker manages + * to prevent us from receiving a transaction, failed announcements (including those from honest peers) + * will linger longer, increasing memory usage somewhat. The impact of this is limited by imposing a + * cap on the number of tracked announcements per peer. As failed requests in response to announcements + * from honest peers should be rare, this almost solely hinders attackers. + * Transaction censoring attacks can be done by announcing transactions quickly while not answering + * requests for them. See https://allquantor.at/blockchainbib/pdf/miller2015topology.pdf for more + * information. + * + * - Transactions are not requested from a peer until its reqtime has passed. + * + * Rationale: enable the calling code to define a delay for less-than-ideal peers, so that (presumed) better + * peers have a chance to give their announcement first. + * + * - If multiple viable candidate peers exist according to the above rules, pick a peer as follows: + * + * - If any preferred peers are available, non-preferred peers are not considered for what follows. + * + * Rationale: preferred peers are more trusted by us, so are less likely to be under attacker control. + * + * - Pick a uniformly random peer among the candidates. + * + * Rationale: random assignments are hard to influence for attackers. + * + * Together these rules strike a balance between being fast in non-adverserial conditions and minimizing + * susceptibility to censorship attacks. An attacker that races the network: + * - Will be unsuccessful if all preferred connections are honest (and there is at least one preferred connection). + * - If there are P preferred connections of which Ph>=1 are honest, the attacker can delay us from learning + * about a transaction by k expiration periods, where k ~ 1 + NHG(N=P-1,K=P-Ph-1,r=1), which has mean + * P/(Ph+1) (where NHG stands for Negative Hypergeometric distribution). The "1 +" is due to the fact that the + * attacker can be the first to announce through a preferred connection in this scenario, which very likely means + * they get the first request. + * - If all P preferred connections are to the attacker, and there are NP non-preferred connections of which NPh>=1 + * are honest, where we assume that the attacker can disconnect and reconnect those connections, the distribution + * becomes k ~ P + NB(p=1-NPh/NP,r=1) (where NB stands for Negative Binomial distribution), which has mean + * P-1+NP/NPh. + * + * Complexity: + * - Memory usage is proportional to the total number of tracked announcements (Size()) plus the number of + * peers with a nonzero number of tracked announcements. + * - CPU usage is generally logarithmic in the total number of tracked announcements, plus the number of + * announcements affected by an operation (amortized O(1) per announcement). + */ +class TxRequestTracker { + // Avoid littering this header file with implementation details. + class Impl; + const std::unique_ptr<Impl> m_impl; + +public: + //! Construct a TxRequestTracker. + explicit TxRequestTracker(bool deterministic = false); + ~TxRequestTracker(); + + // Conceptually, the data structure consists of a collection of "announcements", one for each peer/txhash + // combination: + // + // - CANDIDATE announcements represent transactions that were announced by a peer, and that become available for + // download after their reqtime has passed. + // + // - REQUESTED announcements represent transactions that have been requested, and which we're awaiting a + // response for from that peer. Their expiry value determines when the request times out. + // + // - COMPLETED announcements represent transactions that have been requested from a peer, and a NOTFOUND or a + // transaction was received in response (valid or not), or they timed out. They're only kept around to + // prevent requesting them again. If only COMPLETED announcements for a given txhash remain (so no CANDIDATE + // or REQUESTED ones), all of them are deleted (this is an invariant, and maintained by all operations below). + // + // The operations below manipulate the data structure. + + /** Adds a new CANDIDATE announcement. + * + * Does nothing if one already exists for that (txhash, peer) combination (whether it's CANDIDATE, REQUESTED, or + * COMPLETED). Note that the txid/wtxid property is ignored for determining uniqueness, so if an announcement + * is added for a wtxid H, while one for txid H from the same peer already exists, it will be ignored. This is + * harmless as the txhashes being equal implies it is a non-segwit transaction, so it doesn't matter how it is + * fetched. The new announcement is given the specified preferred and reqtime values, and takes its is_wtxid + * from the specified gtxid. + */ + void ReceivedInv(NodeId peer, const GenTxid& gtxid, bool preferred, + std::chrono::microseconds reqtime); + + /** Deletes all announcements for a given peer. + * + * It should be called when a peer goes offline. + */ + void DisconnectedPeer(NodeId peer); + + /** Deletes all announcements for a given txhash (both txid and wtxid ones). + * + * This should be called when a transaction is no longer needed. The caller should ensure that new announcements + * for the same txhash will not trigger new ReceivedInv calls, at least in the short term after this call. + */ + void ForgetTxHash(const uint256& txhash); + + /** Find the txids to request now from peer. + * + * It does the following: + * - Convert all REQUESTED announcements (for all txhashes/peers) with (expiry <= now) to COMPLETED ones. + * - Requestable announcements are selected: CANDIDATE announcements from the specified peer with + * (reqtime <= now) for which no existing REQUESTED announcement with the same txhash from a different peer + * exists, and for which the specified peer is the best choice among all (reqtime <= now) CANDIDATE + * announcements with the same txhash (subject to preferredness rules, and tiebreaking using a deterministic + * salted hash of peer and txhash). + * - The selected announcements are converted to GenTxids using their is_wtxid flag, and returned in + * announcement order (even if multiple were added at the same time, or when the clock went backwards while + * they were being added). This is done to minimize disruption from dependent transactions being requested + * out of order: if multiple dependent transactions are announced simultaneously by one peer, and end up + * being requested from them, the requests will happen in announcement order. + */ + std::vector<GenTxid> GetRequestable(NodeId peer, std::chrono::microseconds now); + + /** Marks a transaction as requested, with a specified expiry. + * + * If no CANDIDATE announcement for the provided peer and txhash exists, this call has no effect. Otherwise: + * - That announcement is converted to REQUESTED. + * - If any other REQUESTED announcement for the same txhash already existed, it means an unexpected request + * was made (GetRequestable will never advise doing so). In this case it is converted to COMPLETED, as we're + * no longer waiting for a response to it. + */ + void RequestedTx(NodeId peer, const uint256& txhash, std::chrono::microseconds expiry); + + /** Converts a CANDIDATE or REQUESTED announcement to a COMPLETED one. If no such announcement exists for the + * provided peer and txhash, nothing happens. + * + * It should be called whenever a transaction or NOTFOUND was received from a peer. When the transaction is + * not needed entirely anymore, ForgetTxhash should be called instead of, or in addition to, this call. + */ + void ReceivedResponse(NodeId peer, const uint256& txhash); + + // The operations below inspect the data structure. + + /** Count how many REQUESTED announcements a peer has. */ + size_t CountInFlight(NodeId peer) const; + + /** Count how many CANDIDATE announcements a peer has. */ + size_t CountCandidates(NodeId peer) const; + + /** Count how many announcements a peer has (REQUESTED, CANDIDATE, and COMPLETED combined). */ + size_t Count(NodeId peer) const; + + /** Count how many announcements are being tracked in total across all peers and transaction hashes. */ + size_t Size() const; +}; + +#endif // BITCOIN_TXREQUEST_H diff --git a/src/uint256.cpp b/src/uint256.cpp index d074df2f20..f358b62903 100644 --- a/src/uint256.cpp +++ b/src/uint256.cpp @@ -80,4 +80,5 @@ template std::string base_blob<256>::ToString() const; template void base_blob<256>::SetHex(const char*); template void base_blob<256>::SetHex(const std::string&); +const uint256 uint256::ZERO(0); const uint256 uint256::ONE(1); diff --git a/src/uint256.h b/src/uint256.h index c55cb31456..ceae70707e 100644 --- a/src/uint256.h +++ b/src/uint256.h @@ -126,6 +126,7 @@ public: constexpr uint256() {} constexpr explicit uint256(uint8_t v) : base_blob<256>(v) {} explicit uint256(const std::vector<unsigned char>& vch) : base_blob<256>(vch) {} + static const uint256 ZERO; static const uint256 ONE; }; |