IF: Implement message propagation

libraries/hotstuff/include/eosio/hotstuff/qc_chain.hpp

@@ -93,6 +93,12 @@ namespace eosio::hotstuff {
       bool                                quorum_met = false; // not serialized across network
    };
 
+   struct seen_votes {
+      fc::sha256                                     proposal_id; // id of proposal being voted on
+      uint64_t                                       height;      // height of the proposal (for GC)
+      std::set<fc::crypto::blslib::bls_public_key>   finalizers;  // finalizers that have voted on the proposal
+   };
+
    // Concurrency note: qc_chain is a single-threaded and lock-free decision engine.
    //                   All thread synchronization, if any, is external.
    class qc_chain {
@@ -118,6 +124,10 @@ namespace eosio::hotstuff {
       void on_hs_vote_msg(const uint32_t connection_id, const hs_vote_message& msg);
       void on_hs_proposal_msg(const uint32_t connection_id, const hs_proposal_message& msg);
       void on_hs_new_view_msg(const uint32_t connection_id, const hs_new_view_message& msg);
+
+      // NOTE: The hotstuff New Block message is not ever propagated (multi-hop) by this method.
+      //       Unit tests do not use network topology emulation for this message.
+      //       The live network does not actually dispatch this message to the wire; this is a local callback.
       void on_hs_new_block_msg(const uint32_t connection_id, const hs_new_block_message& msg);
 
    private:
@@ -240,6 +250,27 @@ namespace eosio::hotstuff {
 
       proposal_store_type _proposal_store;  //internal proposals store
 #endif
+
+      // Possible optimization: merge _proposal_store and _seen_votes_store.
+      // Store a struct { set<name> seen_votes; hs_proposal_message p; } in the (now single) multi-index.
+      struct by_seen_votes_proposal_id{};
+      struct by_seen_votes_proposal_height{};
+      typedef multi_index_container<
+         seen_votes,
+         indexed_by<
+            hashed_unique<
+               tag<by_seen_votes_proposal_id>,
+               BOOST_MULTI_INDEX_MEMBER(seen_votes,fc::sha256,proposal_id)
+               >,
+            ordered_non_unique<
+               tag<by_seen_votes_proposal_height>,
+               BOOST_MULTI_INDEX_MEMBER(seen_votes,uint64_t,height)
+               >
+            >
+         > seen_votes_store_type;
+
+      // given a height, store a map of proposal IDs at that height and the seen votes for it
+      seen_votes_store_type _seen_votes_store;
    };
 
 } /// eosio::hotstuff

libraries/hotstuff/qc_chain.cpp

@@ -382,6 +382,9 @@ namespace eosio::hotstuff {
       //update internal state
       update(proposal);
 
+      //propagate this proposal since it was new to us
+      send_hs_proposal_msg(connection_id, proposal);
+
       for (auto &msg : msgs) {
          send_hs_vote_msg( std::nullopt, msg );
       }
@@ -401,23 +404,45 @@ namespace eosio::hotstuff {
 
       bool am_leader = am_i_leader();
 
-      if (!am_leader)
-         return;
-      fc_tlog(_logger, " === Process vote from ${finalizer_key} : current bitset ${value}" ,
-              ("finalizer_key", vote.finalizer_key)("value", _current_qc.get_active_finalizers_string()));
-      // only leader need to take action on votes
-      if (vote.proposal_id != _current_qc.get_proposal_id()) {
-         send_hs_message_warning(connection_id, hs_message_warning::discarded); // example; to be tuned to actual need
-         return;
-      }
+      if (am_leader) {
+         if (vote.proposal_id != _current_qc.get_proposal_id()) {
+            send_hs_message_warning(connection_id, hs_message_warning::discarded); // example; to be tuned to actual need
+            return;
+         }
+       }
 
       const hs_proposal_message *p = get_proposal( vote.proposal_id );
       if (p == nullptr) {
-         fc_elog(_logger, " *** ${id} couldn't find proposal, vote : ${vote}", ("id",_id)("vote", vote));
+         if (am_leader)
+            fc_elog(_logger, " *** ${id} couldn't find proposal, vote : ${vote}", ("id",_id)("vote", vote));
          send_hs_message_warning(connection_id, hs_message_warning::discarded); // example; to be tuned to actual need
          return;
       }
 
+      // if not leader, check message propagation and quit
+      if (! am_leader) {
+         seen_votes_store_type::nth_index<0>::type::iterator itr = _seen_votes_store.get<by_seen_votes_proposal_id>().find( p->proposal_id );
+         bool propagate = false;
+         if (itr == _seen_votes_store.get<by_seen_votes_proposal_id>().end()) {
+            seen_votes sv = { p->proposal_id, p->get_height(), { vote.finalizer_key } };
+            _seen_votes_store.insert(sv);
+            propagate = true;
+         } else {
+            _seen_votes_store.get<by_seen_votes_proposal_id>().modify(itr, [&](seen_votes& sv) {
+               if (sv.finalizers.count(vote.finalizer_key) == 0) {
+                  sv.finalizers.insert(vote.finalizer_key);
+                  propagate = true;
+               }
+            });
+         }
+         if (propagate)
+            send_hs_vote_msg(connection_id, vote);
+         return;
+      }
+
+      fc_tlog(_logger, " === Process vote from ${finalizer_key} : current bitset ${value}" ,
+              ("finalizer_key", vote.finalizer_key)("value", _current_qc.get_active_finalizers_string()));
+
       bool quorum_met = _current_qc.is_quorum_met(); //check if quorum already met
 
       // If quorum is already met, we don't need to do anything else. Otherwise, we aggregate the signature.
@@ -490,6 +515,11 @@ namespace eosio::hotstuff {
       auto increment_version = fc::make_scoped_exit([this]() { ++_state_version; });
       if (!update_high_qc(quorum_certificate{msg.high_qc, 21})) { // TODO: use active schedule size
          increment_version.cancel();
+      } else {
+         // Always propagate a view that's newer than ours.
+         // If it's not newer, then we have already propagated ours.
+         // If the recipient doesn't think ours is newer, it has already propagated its own, and so on.
+         send_hs_new_view_msg(connection_id, msg);
       }
    }
 
@@ -662,7 +692,12 @@ namespace eosio::hotstuff {
          _b_leaf = _high_qc.get_proposal_id();
 
          fc_tlog(_logger, " === ${id} _b_leaf updated (update_high_qc) : ${proposal_id}", ("proposal_id", _high_qc.get_proposal_id())("id", _id));
-         return true;
+
+         // avoid looping message propagation when receiving a new-view message with a high_qc.get_proposal_id().empty().
+         // not sure if high_qc.get_proposal_id().empty() + _high_qc.get_proposal_id().empty() is something that actually ever happens in the real world.
+         // not sure if high_qc.get_proposal_id().empty() should be tested and always rejected (return false + no _high_qc / _b_leaf update).
+         // if this returns false, we won't update the get_finality_status information, but I don't think we care about that at all.
+         return !high_qc.get_proposal_id().empty();
       } else {
          const hs_proposal_message *old_high_qc_prop = get_proposal( _high_qc.get_proposal_id() );
          const hs_proposal_message *new_high_qc_prop = get_proposal( high_qc.get_proposal_id() );
@@ -952,6 +987,9 @@ namespace eosio::hotstuff {
    void qc_chain::gc_proposals(uint64_t cutoff){
       //fc_tlog(_logger, " === garbage collection on old data");
 
+      auto& seen_votes_index = _seen_votes_store.get<by_seen_votes_proposal_height>();
+      seen_votes_index.erase(seen_votes_index.begin(), seen_votes_index.upper_bound(cutoff));
+
 #ifdef QC_CHAIN_SIMPLE_PROPOSAL_STORE
       ps_height_iterator psh_it = _proposal_stores_by_height.begin();
       while (psh_it != _proposal_stores_by_height.end()) {