ca: Add CARoots.Active method

Which will be used in the next commit.

agent/consul/state/connect_ca.go

@@ -252,18 +252,8 @@ func caRootsTxn(tx ReadTxn, ws memdb.WatchSet) (uint64, structs.CARoots, error)
 func (s *Store) CARootActive(ws memdb.WatchSet) (uint64, *structs.CARoot, error) {
 	// Get all the roots since there should never be that many and just
 	// do the filtering in this method.
-	var result *structs.CARoot
 	idx, roots, err := s.CARoots(ws)
-	if err == nil {
-		for _, r := range roots {
-			if r.Active {
-				result = r
-				break
-			}
-		}
-	}
-
-	return idx, result, err
+	return idx, roots.Active(), err
 }
 
 // CARootSetCAS sets the current CA root state using a check-and-set operation.

agent/structs/connect_ca.go

@@ -145,6 +145,20 @@ func (c *CARoot) Clone() *CARoot {
 // CARoots is a list of CARoot structures.
 type CARoots []*CARoot
 
+// Active returns the single CARoot that is marked as active, or nil if there
+// is no active root (ex: when they are no roots).
+func (c CARoots) Active() *CARoot {
+	if c == nil {
+		return nil
+	}
+	for _, r := range c {
+		if r.Active {
+			return r
+		}
+	}
+	return nil
+}
+
 // CASignRequest is the request for signing a service certificate.
 type CASignRequest struct {
 	// Datacenter is the target for this request.