Dynamize trusted validator list and quorum (RIPD-1220):

Instead of specifying a static list of trusted validators in the config
or validators file, the configuration can now include trusted validator
list publisher keys.

The trusted validator list and quorum are now reset each consensus
round using the latest validator lists and the list of recent
validations seen. The minimum validation quorum is now only
configurable via the command line.

src/ripple/app/ledger/impl/LedgerMaster.cpp

@@ -33,6 +33,7 @@
 #include <ripple/app/misc/Transaction.h>
 #include <ripple/app/misc/TxQ.h>
 #include <ripple/app/misc/Validations.h>
+#include <ripple/app/misc/ValidatorList.h>
 #include <ripple/app/paths/PathRequests.h>
 #include <ripple/basics/contract.h>
 #include <ripple/basics/Log.h>
@@ -53,9 +54,6 @@ namespace ripple {
 
 using namespace std::chrono_literals;
 
-// 150/256ths of validations of previous ledger
-#define MIN_VALIDATION_RATIO    150
-
 // Don't catch up more than 100 ledgers (cannot exceed 256)
 #define MAX_LEDGER_GAP          100
 
@@ -73,8 +71,6 @@ LedgerMaster::LedgerMaster (Application& app, Stopwatch& stopwatch,
     , mHeldTransactions (uint256 ())
     , mLedgerCleaner (detail::make_LedgerCleaner (
         app, *this, app_.journal("LedgerCleaner")))
-    , mMinValidations (0)
-    , mStrictValCount (false)
     , mLastValidateSeq (0)
     , mAdvanceThread (false)
     , mAdvanceWork (false)
@@ -115,13 +111,6 @@ LedgerMaster::isCompatible (
     beast::Journal::Stream s,
     char const* reason)
 {
-    if (mStrictValCount)
-    {
-        // If we're only using validation count, then we can't
-        // reject a ledger even if it's incompatible
-        return true;
-    }
-
     auto validLedger = getValidatedLedger();
 
     if (validLedger &&
@@ -217,7 +206,7 @@ LedgerMaster::setValidLedger(
 
     NetClock::time_point signTime;
 
-    if (! times.empty () && times.size() >= mMinValidations)
+    if (! times.empty () && times.size() >= app_.validators ().quorum ())
     {
         // Calculate the sample median
         std::sort (times.begin (), times.end ());
@@ -702,7 +691,7 @@ LedgerMaster::failedSave(std::uint32_t seq, uint256 const& hash)
 void
 LedgerMaster::checkAccept (uint256 const& hash, std::uint32_t seq)
 {
-    int valCount = 0;
+    std::size_t valCount = 0;
 
     if (seq != 0)
     {
@@ -713,18 +702,11 @@ LedgerMaster::checkAccept (uint256 const& hash, std::uint32_t seq)
         valCount =
             app_.getValidations().getTrustedValidationCount (hash);
 
-        if (valCount >= mMinValidations)
+        if (valCount >= app_.validators ().quorum ())
         {
             ScopedLockType ml (m_mutex);
             if (seq > mLastValidLedger.second)
                 mLastValidLedger = std::make_pair (hash, seq);
-
-            if (!mStrictValCount && (mMinValidations < (valCount/2 + 1)))
-            {
-                mMinValidations = (valCount/2 + 1);
-                JLOG (m_journal.info())
-                    << "Raising minimum validations to " << mMinValidations;
-            }
         }
 
         if (seq == mValidLedgerSeq)
@@ -742,7 +724,7 @@ LedgerMaster::checkAccept (uint256 const& hash, std::uint32_t seq)
         if ((seq != 0) && (getValidLedgerIndex() == 0))
         {
             // Set peers sane early if we can
-            if (valCount >= mMinValidations)
+            if (valCount >= app_.validators ().quorum ())
                 app_.overlay().checkSanity (seq);
         }
 
@@ -757,30 +739,14 @@ LedgerMaster::checkAccept (uint256 const& hash, std::uint32_t seq)
 }
 
 /**
-    * Determines how many validations are needed to fully-validated a ledger
+    * Determines how many validations are needed to fully validate a ledger
     *
     * @return Number of validations needed
     */
-int
+std::size_t
 LedgerMaster::getNeededValidations ()
 {
-    if (standalone_)
-        return 0;
-
-    int minVal = mMinValidations;
-
-    if (mLastValidateHash.isNonZero ())
-    {
-        int val = app_.getValidations ().getTrustedValidationCount (
-            mLastValidateHash);
-        val *= MIN_VALIDATION_RATIO;
-        val /= 256;
-
-        if (val > minVal)
-            minVal = val;
-    }
-
-    return minVal;
+    return standalone_ ? 0 : app_.validators().quorum ();
 }
 
 void
@@ -904,7 +870,7 @@ LedgerMaster::consensusBuilt(
                 ledgerSeq_ = seq;
         }
 
-        int valCount_;
+        std::size_t valCount_;
         LedgerIndex ledgerSeq_;
     };
 
@@ -916,7 +882,7 @@ LedgerMaster::consensusBuilt(
         vs.mergeValidation (v->getFieldU32 (sfLedgerSequence));
     }
 
-    auto neededValidations = getNeededValidations ();
+    auto const neededValidations = getNeededValidations ();
     auto maxSeq = mValidLedgerSeq.load();
     auto maxLedger = ledger->info().hash;
 
@@ -1313,21 +1279,6 @@ LedgerMaster::getPublishedLedger ()
     return mPubLedger;
 }
 
-int
-LedgerMaster::getMinValidations ()
-{
-    return mMinValidations;
-}
-
-void
-LedgerMaster::setMinValidations (int v, bool strict)
-{
-    JLOG (m_journal.info()) << "Validation quorum: " << v
-        << (strict ? " strict" : "");
-    mMinValidations = v;
-    mStrictValCount = strict;
-}
-
 std::string
 LedgerMaster::getCompleteLedgers ()
 {