routing/chainview: make filter updates synchronous for neutrino

This commit fixes a possible race condition wherein a call to
FilterBlock after a call to UpdateFilter would result in the call to
FilterBlock not yet using the updated filter. We fix this by ensuring
the internal chain filter is updated by the time the call to
FilterBlock returns.

routing/chainview/btcd.go

@@ -361,6 +361,7 @@ func (b *BtcdFilteredChainView) chainFilterer() {
 type filterUpdate struct {
 	newUtxos     []wire.OutPoint
 	updateHeight uint32
+	done         chan struct{}
 }
 
 // UpdateFilter updates the UTXO filter which is to be consulted when creating

routing/chainview/neutrino.go

@@ -225,6 +225,10 @@ func (c *CfFilteredChainView) chainFilterer() {
 				log.Errorf("unable to update rescan: %v", err)
 			}
 
+			if update.done != nil {
+				close(update.done)
+			}
+
 		case <-c.quit:
 			return
 		}
@@ -253,11 +257,11 @@ func (c *CfFilteredChainView) FilterBlock(blockHash *chainhash.Hash) (*FilteredB
 	// If we don't have any items within our current chain filter, then we
 	// can exit early as we don't need to fetch the filter.
 	c.filterMtx.RLock()
-	numPoints := len(c.chainFilter)
-	c.filterMtx.RUnlock()
-	if numPoints == 0 {
+	if len(c.chainFilter) == 0 {
+		c.filterMtx.RUnlock()
 		return filteredBlock, nil
 	}
+	c.filterMtx.RUnlock()
 
 	// Next, using the block, hash, we'll fetch the compact filter for this
 	// block. We only require the regular filter as we're just looking for
@@ -338,17 +342,26 @@ func (c *CfFilteredChainView) FilterBlock(blockHash *chainhash.Hash) (*FilteredB
 //
 // NOTE: This is part of the FilteredChainView interface.
 func (c *CfFilteredChainView) UpdateFilter(ops []wire.OutPoint, updateHeight uint32) error {
-	select {
-
-	case c.filterUpdates <- filterUpdate{
+	doneChan := make(chan struct{})
+	update := filterUpdate{
 		newUtxos:     ops,
 		updateHeight: updateHeight,
-	}:
-		return nil
+		done:         doneChan,
+	}
 
+	select {
+	case c.filterUpdates <- update:
 	case <-c.quit:
 		return fmt.Errorf("chain filter shutting down")
 	}
+
+	select {
+	case <-doneChan:
+		return nil
+	case <-c.quit:
+		return fmt.Errorf("chain filter shutting down")
+	}
+
 }
 
 // FilteredBlocks returns the channel that filtered blocks are to be sent over.