new filter: remove redundant offer updates (closes #330) (#331)

* 1 - dedupeRedundantUpdatesFilter.go and always add to submitFilters list

* 2 - fix filterOps: when we keep op and new op is nil we need a second subcase for offers vs ops

Author: nikhilsaraf

cmd/trade.go

@@ -387,6 +387,9 @@ func makeBot(
 		}
 		submitFilters = append(submitFilters, filter)
 	}
+	// always add the dedupeRedundantUpdatesFilter as the second-last filter
+	dedupeRedundantUpdatesFilter := plugins.MakeFilterDedupeRedundantUpdates(assetBase, assetQuote)
+	submitFilters = append(submitFilters, dedupeRedundantUpdatesFilter)
 	// exchange constraints filter is last so we catch any modifications made by previous filters. this ensures that the exchange is
 	// less likely to reject our updates
 	submitFilters = append(submitFilters,

plugins/dedupeRedundantUpdatesFilter.go

@@ -0,0 +1,52 @@
+package plugins
+
+import (
+	"fmt"
+
+	hProtocol "github.com/stellar/go/protocols/horizon"
+	"github.com/stellar/go/txnbuild"
+)
+
+type dedupeRedundantUpdatesFilter struct {
+	name       string
+	baseAsset  hProtocol.Asset
+	quoteAsset hProtocol.Asset
+}
+
+// MakeFilterDedupeRedundantUpdates makes a submit filter that dedupes offer updates that would result in the same offer being placed on the orderbook
+func MakeFilterDedupeRedundantUpdates(baseAsset hProtocol.Asset, quoteAsset hProtocol.Asset) SubmitFilter {
+	return &dedupeRedundantUpdatesFilter{
+		name:       "dedupeRedundantUpdatesFilter",
+		baseAsset:  baseAsset,
+		quoteAsset: quoteAsset,
+	}
+}
+
+var _ SubmitFilter = &dedupeRedundantUpdatesFilter{}
+
+func (f *dedupeRedundantUpdatesFilter) Apply(ops []txnbuild.Operation, sellingOffers []hProtocol.Offer, buyingOffers []hProtocol.Offer) ([]txnbuild.Operation, error) {
+	offersMap := map[int64]hProtocol.Offer{}
+	for _, offer := range append(sellingOffers, buyingOffers...) {
+		offersMap[offer.ID] = offer
+	}
+
+	innerFn := func(op *txnbuild.ManageSellOffer) (*txnbuild.ManageSellOffer, bool, error) {
+		existingOffer, hasOffer := offersMap[op.OfferID]
+		isDupe := hasOffer && existingOffer.Amount == op.Amount && existingOffer.Price == op.Price
+
+		if isDupe {
+			// do not return an op because this is spawned from an offer (hasOffer = true) and we do not want to drop the offer nor do we want to create
+			// a new operation to delete the offer and re-update the offer to the same values, so the returned Operation is nil with keep = false
+			return nil, false, nil
+		}
+
+		// this an actual update of either the offer or a new operation, we dont want to make any changes to that so we return the original op with keep = true
+		return op, true, nil
+	}
+	ops, e := filterOps(f.name, f.baseAsset, f.quoteAsset, sellingOffers, buyingOffers, ops, innerFn)
+	if e != nil {
+		return nil, fmt.Errorf("could not apply filter: %s", e)
+	}
+
+	return ops, nil
+}

plugins/submitFilter.go

@@ -19,7 +19,7 @@ type SubmitFilter interface {
 	) ([]txnbuild.Operation, error)
 }
 
-type filterFn func(op *txnbuild.ManageSellOffer) (*txnbuild.ManageSellOffer, bool, error)
+type filterFn func(op *txnbuild.ManageSellOffer) (newOp *txnbuild.ManageSellOffer, keep bool, e error)
 
 type filterCounter struct {
 	idx         int
@@ -306,8 +306,13 @@ func runInnerFilterFn(
 			return newOp, nil, opCounter, &filterCounter{kept: 1}, nil
 		}
 	} else if isNewOpNil {
-		// newOp will never be nil for an original offer since we will return the original non-nil offer
-		return nil, nil, opCounter, &filterCounter{dropped: 1}, nil
+		if originalOfferAsOp != nil {
+			// if newOp is nil for an original offer it means we want to keep that offer.
+			return nil, nil, offerCounter, &filterCounter{kept: 1}, nil
+		} else {
+			// if newOp is nil and it is not an original offer it means we want to drop the operation.
+			return nil, nil, opCounter, &filterCounter{dropped: 1}, nil
+		}
 	} else {
 		// newOp can be a transformed op to change the op to an effectively "dropped" state
 		// prepend this so we always have delete commands at the beginning of the operation list