[PrivateSend] Fallback to less participants if possible, fix too long…

… timeouts on server side (#2616)

* Fallback to less participants on timeouts if possible

* Only bump nTimeLastSuccessfulStep when state is changed

* Consistency: always set state first before relaying smth to clients

src/privatesend-server.cpp

@@ -244,7 +244,6 @@ void CPrivateSendServer::ProcessMessage(CNode* pfrom, const std::string& strComm
             RelayStatus(STATUS_ACCEPTED, connman);
         } else {
             PushStatus(pfrom, STATUS_REJECTED, nMessageID, connman);
-            SetNull();
         }
 
     } else if (strCommand == NetMsgType::DSSIGNFINALTX) {
@@ -332,8 +331,8 @@ void CPrivateSendServer::CreateFinalTransaction(CConnman& connman)
     LogPrint("privatesend", "CPrivateSendServer::CreateFinalTransaction -- finalMutableTransaction=%s", txNew.ToString());
 
     // request signatures from clients
-    RelayFinalTransaction(finalMutableTransaction, connman);
     SetState(POOL_STATE_SIGNING);
+    RelayFinalTransaction(finalMutableTransaction, connman);
 }
 
 void CPrivateSendServer::CommitFinalTransaction(CConnman& connman)
@@ -484,7 +483,7 @@ void CPrivateSendServer::ChargeRandomFees(CConnman& connman)
 
         CValidationState state;
         if (!AcceptToMemoryPool(mempool, state, txCollateral, false, NULL, false, maxTxFee)) {
-            // should never really happen
+            // Can happen if this collateral belongs to some misbehaving participant we punished earlier
             LogPrintf("CPrivateSendServer::ChargeRandomFees -- ERROR: AcceptToMemoryPool failed!\n");
         } else {
             connman.RelayTransaction(*txCollateral);
@@ -498,18 +497,40 @@ void CPrivateSendServer::ChargeRandomFees(CConnman& connman)
 void CPrivateSendServer::CheckTimeout(CConnman& connman)
 {
     if (!fMasternodeMode) return;
+    if (nState == POOL_STATE_IDLE) return;
 
     CheckQueue();
 
     int nTimeout = (nState == POOL_STATE_SIGNING) ? PRIVATESEND_SIGNING_TIMEOUT : PRIVATESEND_QUEUE_TIMEOUT;
     bool fTimeout = GetTime() - nTimeLastSuccessfulStep >= nTimeout;
 
-    if (nState != POOL_STATE_IDLE && fTimeout) {
-        LogPrint("privatesend", "CPrivateSendServer::CheckTimeout -- %s timed out (%ds) -- resetting\n",
-            (nState == POOL_STATE_SIGNING) ? "Signing" : "Session", nTimeout);
+    // Too early to do anything
+    if (!fTimeout) return;
+
+    // See if we have at least min number of participants, if so - we can still do smth
+    if (nState == POOL_STATE_QUEUE && vecSessionCollaterals.size() >= CPrivateSend::GetMinPoolParticipants()) {
+        LogPrint("privatesend", "CPrivateSendServer::CheckTimeout -- Queue for %d participants timed out (%ds) -- falling back to %d participants\n",
+            nSessionMaxParticipants, nTimeout, vecSessionCollaterals.size());
+        nSessionMaxParticipants = vecSessionCollaterals.size();
+        return;
+    }
+
+    if (nState == POOL_STATE_ACCEPTING_ENTRIES && GetEntriesCount() >= CPrivateSend::GetMinPoolParticipants()) {
+        LogPrint("privatesend", "CPrivateSendServer::CheckTimeout -- Accepting entries for %d participants timed out (%ds) -- falling back to %d participants\n",
+            nSessionMaxParticipants, nTimeout, GetEntriesCount());
+        // Punish misbehaving participants
         ChargeFees(connman);
-        SetNull();
+        // Try to complete this session ignoring the misbehaving ones
+        nSessionMaxParticipants = GetEntriesCount();
+        CheckPool(connman);
+        return;
     }
+
+    // All other cases
+    LogPrint("privatesend", "CPrivateSendServer::CheckTimeout -- %s timed out (%ds) -- resetting\n",
+        (nState == POOL_STATE_SIGNING) ? "Signing" : "Session", nTimeout);
+    ChargeFees(connman);
+    SetNull();
 }
 
 /*
@@ -617,7 +638,6 @@ bool CPrivateSendServer::AddEntry(const CPrivateSendEntry& entryNew, PoolMessage
 
     LogPrint("privatesend", "CPrivateSendServer::AddEntry -- adding entry %d of %d required\n", GetEntriesCount(), nSessionMaxParticipants);
     nMessageIDRet = MSG_ENTRIES_ADDED;
-    nTimeLastSuccessfulStep = GetTime();
 
     return true;
 }
@@ -726,7 +746,6 @@ bool CPrivateSendServer::CreateNewSession(const CPrivateSendAccept& dsa, PoolMes
     nSessionMaxParticipants = CPrivateSend::GetMinPoolParticipants() + GetRandInt(CPrivateSend::GetMaxPoolParticipants() - CPrivateSend::GetMinPoolParticipants() + 1);
 
     SetState(POOL_STATE_QUEUE);
-    nTimeLastSuccessfulStep = GetTime();
 
     if (!fUnitTest) {
         //broadcast that I'm accepting entries, only if it's the first entry through
@@ -769,7 +788,6 @@ bool CPrivateSendServer::AddUserToExistingSession(const CPrivateSendAccept& dsa,
     // count new user as accepted to an existing session
 
     nMessageIDRet = MSG_NOERR;
-    nTimeLastSuccessfulStep = GetTime();
     vecSessionCollaterals.push_back(MakeTransactionRef(dsa.txCollateral));
 
     LogPrintf("CPrivateSendServer::AddUserToExistingSession -- new user accepted, nSessionID: %d  nSessionDenom: %d (%s)  vecSessionCollaterals.size(): %d  nSessionMaxParticipants: %d\n",
@@ -876,6 +894,7 @@ void CPrivateSendServer::SetState(PoolState nStateNew)
     }
 
     LogPrintf("CPrivateSendServer::SetState -- nState: %d, nStateNew: %d\n", nState, nStateNew);
+    nTimeLastSuccessfulStep = GetTime();
     nState = nStateNew;
 }