autopilot/agent: split opening logic into own method

This commit takes the logic after the autopilot agent has decided that it
needs to open more channels, and moves it into a new method openChan.

autopilot/agent.go

@@ -1,6 +1,7 @@
 package autopilot
 
 import (
+	"fmt"
 	"net"
 	"sync"
 	"sync/atomic"
@@ -485,75 +486,85 @@ func (a *Agent) controller() {
 		log.Infof("Triggering attachment directive dispatch, "+
 			"total_funds=%v", a.totalBalance)
 
-		// We're to attempt an attachment so we'll obtain the set of
-		// nodes that we currently have channels with so we avoid
-		// duplicate edges.
-		connectedNodes := a.chanState.ConnectedNodes()
-		a.pendingMtx.Lock()
-		nodesToSkip := mergeNodeMaps(a.pendingOpens,
-			a.pendingConns, connectedNodes, a.failedNodes,
-		)
-		a.pendingMtx.Unlock()
-
-		// If we reach this point, then according to our heuristic we
-		// should modify our channel state to tend towards what it
-		// determines to the optimal state. So we'll call Select to get
-		// a fresh batch of attachment directives, passing in the
-		// amount of funds available for us to use.
-		chanCandidates, err := a.cfg.Heuristic.Select(
-			a.cfg.Self, a.cfg.Graph, availableFunds,
-			numChans, nodesToSkip,
-		)
+		err := a.openChans(availableFunds, numChans, totalChans)
 		if err != nil {
-			log.Errorf("Unable to select candidates for "+
-				"attachment: %v", err)
-			continue
+			log.Errorf("Unable to open channels: %v", err)
 		}
-
-		if len(chanCandidates) == 0 {
-			log.Infof("No eligible candidates to connect to")
-			continue
-		}
-
-		log.Infof("Attempting to execute channel attachment "+
-			"directives: %v", spew.Sdump(chanCandidates))
-
-		// Before proceeding, check to see if we have any slots
-		// available to open channels. If there are any, we will attempt
-		// to dispatch the retrieved directives since we can't be
-		// certain which ones may actually succeed. If too many
-		// connections succeed, we will they will be ignored and made
-		// available to future heuristic selections.
-		a.pendingMtx.Lock()
-		if uint16(len(a.pendingOpens)) >= a.cfg.Constraints.MaxPendingOpens {
-			a.pendingMtx.Unlock()
-			log.Debugf("Reached cap of %v pending "+
-				"channel opens, will retry "+
-				"after success/failure",
-				a.cfg.Constraints.MaxPendingOpens)
-			continue
-		}
-
-		// For each recommended attachment directive, we'll launch a
-		// new goroutine to attempt to carry out the directive. If any
-		// of these succeed, then we'll receive a new state update,
-		// taking us back to the top of our controller loop.
-		for _, chanCandidate := range chanCandidates {
-			// Skip candidates which we are already trying
-			// to establish a connection with.
-			nodeID := chanCandidate.NodeID
-			if _, ok := a.pendingConns[nodeID]; ok {
-				continue
-			}
-			a.pendingConns[nodeID] = struct{}{}
-
-			a.wg.Add(1)
-			go a.executeDirective(chanCandidate)
-		}
-		a.pendingMtx.Unlock()
 	}
 }
 
+// openChans queries the agent's heuristic for a set of channel candidates, and
+// attempts to open channels to them.
+func (a *Agent) openChans(availableFunds btcutil.Amount, numChans uint32,
+	totalChans []Channel) error {
+
+	// We're to attempt an attachment so we'll obtain the set of
+	// nodes that we currently have channels with so we avoid
+	// duplicate edges.
+	connectedNodes := a.chanState.ConnectedNodes()
+	a.pendingMtx.Lock()
+	nodesToSkip := mergeNodeMaps(a.pendingOpens,
+		a.pendingConns, connectedNodes, a.failedNodes,
+	)
+	a.pendingMtx.Unlock()
+
+	// If we reach this point, then according to our heuristic we
+	// should modify our channel state to tend towards what it
+	// determines to the optimal state. So we'll call Select to get
+	// a fresh batch of attachment directives, passing in the
+	// amount of funds available for us to use.
+	chanCandidates, err := a.cfg.Heuristic.Select(
+		a.cfg.Self, a.cfg.Graph, availableFunds,
+		numChans, nodesToSkip,
+	)
+	if err != nil {
+		return fmt.Errorf("Unable to select candidates for "+
+			"attachment: %v", err)
+	}
+
+	if len(chanCandidates) == 0 {
+		log.Infof("No eligible candidates to connect to")
+		return nil
+	}
+
+	log.Infof("Attempting to execute channel attachment "+
+		"directives: %v", spew.Sdump(chanCandidates))
+
+	// Before proceeding, check to see if we have any slots
+	// available to open channels. If there are any, we will attempt
+	// to dispatch the retrieved directives since we can't be
+	// certain which ones may actually succeed. If too many
+	// connections succeed, we will they will be ignored and made
+	// available to future heuristic selections.
+	a.pendingMtx.Lock()
+	defer a.pendingMtx.Unlock()
+	if uint16(len(a.pendingOpens)) >= a.cfg.Constraints.MaxPendingOpens {
+		log.Debugf("Reached cap of %v pending "+
+			"channel opens, will retry "+
+			"after success/failure",
+			a.cfg.Constraints.MaxPendingOpens)
+		return nil
+	}
+
+	// For each recommended attachment directive, we'll launch a
+	// new goroutine to attempt to carry out the directive. If any
+	// of these succeed, then we'll receive a new state update,
+	// taking us back to the top of our controller loop.
+	for _, chanCandidate := range chanCandidates {
+		// Skip candidates which we are already trying
+		// to establish a connection with.
+		nodeID := chanCandidate.NodeID
+		if _, ok := a.pendingConns[nodeID]; ok {
+			continue
+		}
+		a.pendingConns[nodeID] = struct{}{}
+
+		a.wg.Add(1)
+		go a.executeDirective(chanCandidate)
+	}
+	return nil
+}
+
 // executeDirective attempts to connect to the channel candidate specified by
 // the given attachment directive, and open a channel of the given size.
 //