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"
@@ -485,6 +486,18 @@ func (a *Agent) controller() {
 		log.Infof("Triggering attachment directive dispatch, "+
 			"total_funds=%v", a.totalBalance)
 
+		err := a.openChans(availableFunds, numChans, totalChans)
+		if err != nil {
+			log.Errorf("Unable to open channels: %v", err)
+		}
+	}
+}
+
+// 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.
@@ -505,14 +518,13 @@ func (a *Agent) controller() {
 		numChans, nodesToSkip,
 	)
 	if err != nil {
-			log.Errorf("Unable to select candidates for "+
+		return fmt.Errorf("Unable to select candidates for "+
 			"attachment: %v", err)
-			continue
 	}
 
 	if len(chanCandidates) == 0 {
 		log.Infof("No eligible candidates to connect to")
-			continue
+		return nil
 	}
 
 	log.Infof("Attempting to execute channel attachment "+
@@ -525,13 +537,13 @@ func (a *Agent) controller() {
 	// 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 {
-			a.pendingMtx.Unlock()
 		log.Debugf("Reached cap of %v pending "+
 			"channel opens, will retry "+
 			"after success/failure",
 			a.cfg.Constraints.MaxPendingOpens)
-			continue
+		return nil
 	}
 
 	// For each recommended attachment directive, we'll launch a
@@ -550,8 +562,7 @@ func (a *Agent) controller() {
 		a.wg.Add(1)
 		go a.executeDirective(chanCandidate)
 	}
-		a.pendingMtx.Unlock()
+	return nil
-	}
 }
 
 // executeDirective attempts to connect to the channel candidate specified by