address comment

server/config.go

@@ -417,14 +417,17 @@ func parseConstraint(cfg *ConstraintConfig) (*Constraint, error) {
 	for _, label := range cfg.Labels {
 		kv := strings.Split(strings.ToLower(label), "=")
 		if len(kv) != 2 {
-			return nil, errors.Errorf("invalid constraint %q", label)
+			return nil, errors.Errorf("invalid label %q", label)
 		}
 		k, v := kv[0], kv[1]
-		if !validLabel.MatchString(k) || !validLabel.MatchString(v) {
-			return nil, errors.Errorf("invalid constraint %q, must match %s", label, validLabel)
+		if !validLabel.MatchString(k) {
+			return nil, errors.Errorf("invalid label key %q, must match %s", k, validLabel)
+		}
+		if !validLabel.MatchString(v) {
+			return nil, errors.Errorf("invalid label value %q, must match %s", k, validLabel)
 		}
 		if _, ok := labels[k]; ok {
-			return nil, errors.Errorf("duplicated constraint %q", label)
+			return nil, errors.Errorf("duplicated label %q", label)
 		}
 		labels[k] = v
 	}

server/constraints.go

@@ -118,7 +118,7 @@ func (stores storesByID) Less(i, j int) bool { return stores[i].GetId() < stores
 // Although we can use a more optimize algorithm, but it may be hard
 // to understand by most users.
 // So we decide to use a straight forward algorithm to match stores
-// and constraints one by one in order, and it works find in most
+// and constraints one by one in order, and it works fine in most
 // cases. However, if we add more complicated constraints in the
 // future, we may need to reconsider the algorithm.
 func (c *Constraints) Match(stores []*storeInfo) *MatchResult {