Reserve correct vector size for fee calculations:

* Using txnsExpected_, which is influenced by both the config
  and network behavior, can reserve far too much or far too
  little memory, wasting time and resources.
* Not an issue during normal operation, but a user could
  cause problems on their local node with extreme configuration
  settings.

src/ripple/app/misc/impl/TxQ.cpp

@@ -83,15 +83,20 @@ TxQ::FeeMetrics::update(Application& app,
     TxQ::Setup const& setup)
 {
     std::vector<uint64_t> feeLevels;
-    feeLevels.reserve(txnsExpected_);
-    for (auto const& tx : view.txs)
-    {
-        auto const baseFee = calculateBaseFee(view, *tx.first);
-        feeLevels.push_back(getFeeLevelPaid(*tx.first,
-            baseLevel, baseFee, setup));
-    }
+    auto const txBegin = view.txs.begin();
+    auto const txEnd = view.txs.end();
+    auto const size = std::distance(txBegin, txEnd);
+    feeLevels.reserve(size);
+    std::for_each(txBegin, txEnd,
+        [&](auto const& tx)
+        {
+            auto const baseFee = calculateBaseFee(view, *tx.first);
+            feeLevels.push_back(getFeeLevelPaid(*tx.first,
+                baseLevel, baseFee, setup));
+        }
+    );
     std::sort(feeLevels.begin(), feeLevels.end());
-    auto const size = feeLevels.size();
+    assert(size == feeLevels.size());
 
     JLOG(j_.debug()) << "Ledger " << view.info().seq <<
         " has " << size << " transactions. " <<

src/test/app/Regression_test.cpp

@@ -198,6 +198,32 @@ struct Regression_test : public beast::unit_test::suite
         }
     }
 
+    void testFeeEscalationExtremeConfig()
+    {
+        testcase("Fee escalation shouldn't allocate extreme memory");
+        using clock_type = std::chrono::steady_clock;
+        using namespace jtx;
+        using namespace std::chrono_literals;
+
+        Env env(*this, envconfig([](std::unique_ptr<Config> cfg)
+        {
+            auto& s = cfg->section("transaction_queue");
+            s.set("minimum_txn_in_ledger_standalone", "4294967295");
+            s.set("minimum_txn_in_ledger", "4294967295");
+            s.set("target_txn_in_ledger", "4294967295");
+            s.set("normal_consensus_increase_percent", "4294967295");
+
+            return cfg;
+        }));
+
+        env(noop(env.master));
+        // This test will probably fail if any breakpoints are encountered,
+        // but should pass on even the slowest machines.
+        auto const start = clock_type::now();
+        env.close();
+        BEAST_EXPECT(clock_type::now() - start < 1s);
+    }
+
     void testJsonInvalid()
     {
         using namespace jtx;
@@ -221,6 +247,7 @@ struct Regression_test : public beast::unit_test::suite
         testLowBalanceDestroy();
         testSecp256r1key();
         testFeeEscalationAutofill();
+        testFeeEscalationExtremeConfig();
         testJsonInvalid();
     }
 };