Progress bitshares#1604: Add dust check

Add dust check to limit order update logic, and test

Author: nathanielhourt

libraries/chain/market_evaluator.cpp

@@ -163,6 +163,17 @@ void_result limit_order_update_evaluator::do_evaluate(const limit_order_update_o
                     "Cannot deduct more from order than order contains");
    }
 
+   // Check dust
+   if (o.new_price || (o.delta_amount_to_sell && o.delta_amount_to_sell->amount < 0)) {
+      auto new_price = o.new_price? *o.new_price : _order->sell_price;
+      auto new_amount = _order->amount_for_sale();
+      if (o.delta_amount_to_sell)
+          new_amount += *o.delta_amount_to_sell;
+      auto new_amount_to_receive = new_amount * new_price;
+
+      FC_ASSERT(new_amount_to_receive.amount > 0, "Cannot update limit order: order becomes too small; cancel order instead");
+   }
+
    // Check expiration is in the future
    if (o.new_expiration)
       FC_ASSERT(*o.new_expiration >= d.head_block_time(),

tests/tests/operation_tests.cpp

@@ -172,6 +172,27 @@ BOOST_AUTO_TEST_CASE(limit_order_update_test)
    }
 }
 
+BOOST_AUTO_TEST_CASE(limit_order_update_dust_test)
+{
+   try {
+      ACTORS((nathan));
+      const auto& munee = create_user_issued_asset("MUNEE");
+
+      transfer(committee_account, nathan_id, asset(10000));
+      issue_uia(nathan, munee.amount(1000));
+
+      auto expiration = db.head_block_time() + 1000;
+      limit_order_id_type order_id = create_sell_order(nathan, asset(1000), munee.amount(100), expiration)->id;
+
+      GRAPHENE_REQUIRE_THROW(update_limit_order(order_id, {}, asset(-995)), fc::assert_exception);
+      GRAPHENE_REQUIRE_THROW(update_limit_order(order_id, price(asset(1000000), munee.amount(100))), fc::assert_exception);
+      GRAPHENE_REQUIRE_THROW(update_limit_order(order_id, price(asset(2000), munee.amount(100)), asset(-985)), fc::assert_exception);
+   } catch (fc::exception& e) {
+      edump((e.to_detail_string()));
+      throw;
+   }
+}
+
 BOOST_AUTO_TEST_CASE(limit_order_update_match_test)
 {
    try {