metrics: add chain error counter

chain/chain.go

@@ -5,9 +5,17 @@ type Chainer interface {
 }
 
 type Chain struct {
+	name   string
 	groups []*NodeGroup
 }
 
+func NewChain(name string, groups ...*NodeGroup) *Chain {
+	return &Chain{
+		name:   name,
+		groups: groups,
+	}
+}
+
 func (c *Chain) AddNodeGroup(group *NodeGroup) {
 	c.groups = append(c.groups, group)
 }
@@ -17,7 +25,9 @@ func (c *Chain) Route(network, address string) (r *Route) {
 		return
 	}
 
-	r = &Route{}
+	r = &Route{
+		chain: c,
+	}
 	for _, group := range c.groups {
 		node := group.Next()
 		if node == nil {