routing: disable FilteredChainView when AssumeChannelValid is active

In this commit, we disable attempting to determine when a channel has
been closed out on-chain whenever AssumeChannelValid is active. Since
the flag indicates that performing this operation is expensive, we do
this as a temporary optimization until we can include proofs of channels
being closed in the gossip protocol.

With this change, the only way for channels being removed from the graph
will be once they're considered zombies: which can happen when both
edges of a channel have their disabled bits set or when both edges
haven't had an update within the past two weeks.

routing/router.go

@@ -203,8 +203,7 @@ type Config struct {
 
 	// AssumeChannelValid toggles whether or not the router will check for
 	// spentness of channel outpoints. For neutrino, this saves long rescans
-	// from blocking initial usage of the wallet. This should only be
-	// enabled on testnet.
+	// from blocking initial usage of the daemon.
 	AssumeChannelValid bool
 }
 
@@ -396,26 +395,15 @@ func (r *ChannelRouter) Start() error {
 
 	log.Tracef("Channel Router starting")
 
-	// First, we'll start the chain view instance (if it isn't already
-	// started).
-	if err := r.cfg.ChainView.Start(); err != nil {
-		return err
-	}
-
-	// Once the instance is active, we'll fetch the channel we'll receive
-	// notifications over.
-	r.newBlocks = r.cfg.ChainView.FilteredBlocks()
-	r.staleBlocks = r.cfg.ChainView.DisconnectedBlocks()
-
 	bestHash, bestHeight, err := r.cfg.Chain.GetBestBlock()
 	if err != nil {
 		return err
 	}
 
+	// If the graph has never been pruned, or hasn't fully been created yet,
+	// then we don't treat this as an explicit error.
 	if _, _, err := r.cfg.Graph.PruneTip(); err != nil {
 		switch {
-		// If the graph has never been pruned, or hasn't fully been
-		// created yet, then we don't treat this as an explicit error.
 		case err == channeldb.ErrGraphNeverPruned:
 			fallthrough
 		case err == channeldb.ErrGraphNotFound:
@@ -433,6 +421,30 @@ func (r *ChannelRouter) Start() error {
 		}
 	}
 
+	// If AssumeChannelValid is present, then we won't rely on pruning
+	// channels from the graph based on their spentness, but whether they
+	// are considered zombies or not.
+	if r.cfg.AssumeChannelValid {
+		if err := r.pruneZombieChans(); err != nil {
+			return err
+		}
+
+		r.wg.Add(1)
+		go r.networkHandler()
+		return nil
+	}
+
+	// Otherwise, we'll use our filtered chain view to prune channels as
+	// soon as they are detected as spent on-chain.
+	if err := r.cfg.ChainView.Start(); err != nil {
+		return err
+	}
+
+	// Once the instance is active, we'll fetch the channel we'll receive
+	// notifications over.
+	r.newBlocks = r.cfg.ChainView.FilteredBlocks()
+	r.staleBlocks = r.cfg.ChainView.DisconnectedBlocks()
+
 	// Before we perform our manual block pruning, we'll construct and
 	// apply a fresh chain filter to the active FilteredChainView instance.
 	// We do this before, as otherwise we may miss on-chain events as the
@@ -480,10 +492,14 @@ func (r *ChannelRouter) Stop() error {
 		return nil
 	}
 
-	log.Infof("Channel Router shutting down")
+	log.Tracef("Channel Router shutting down")
 
-	if err := r.cfg.ChainView.Stop(); err != nil {
-		return err
+	// Our filtered chain view could've only been started if
+	// AssumeChannelValid isn't present.
+	if !r.cfg.AssumeChannelValid {
+		if err := r.cfg.ChainView.Stop(); err != nil {
+			return err
+		}
 	}
 
 	close(r.quit)
@@ -577,9 +593,9 @@ func (r *ChannelRouter) syncGraphWithChain() error {
 	log.Infof("Syncing channel graph from height=%v (hash=%v) to height=%v "+
 		"(hash=%v)", pruneHeight, pruneHash, bestHeight, bestHash)
 
-	// If we're not yet caught up, then we'll walk forward in the chain in
-	// the chain pruning the channel graph with each new block in the chain
-	// that hasn't yet been consumed by the channel graph.
+	// If we're not yet caught up, then we'll walk forward in the chain
+	// pruning the channel graph with each new block that hasn't yet been
+	// consumed by the channel graph.
 	var numChansClosed uint32
 	for nextHeight := pruneHeight + 1; nextHeight <= uint32(bestHeight); nextHeight++ {
 		// Using the next height, request a manual block pruning from