Routing: public method to map (scope,prefix) to a cluster name (#403)

* Update connector.go

* Update CHANGELOG.md

* Create resolver.go

* Update resolver.go

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## v3.4.9 (unreleased)
  - clarifying message on success of scope drop, to wait before re-creating
  - modify the test cases using space as the delimiter between tags
+ - expose a method Resolve(scope,prefix) -> cluster
 
 ## v3.4.8 (2019-07-26)
  - Add transport parameter to yarpc connector and cli

connectors/routing/connector.go

@@ -49,9 +49,14 @@ func (rc *Connector) String() string {
 	return fmt.Sprintf("[Routing %s]", rc.config.String())
 }
 
+// Resolve returns the destination engine for the given scope and name-prefix.
+func (rc *Connector) Resolve(scope, namePrefix string) string {
+	return rc.config.getEngineName(scope, namePrefix)
+}
+
 // get connector by scope and namePrefix
 func (rc *Connector) getConnector(scope, namePrefix string) (dosa.Connector, error) {
-	connName := rc.config.getEngineName(scope, namePrefix)
+	connName := rc.Resolve(scope, namePrefix)
 	c, ok := rc.connectors[connName]
 	if !ok {
 		return nil, fmt.Errorf("can't find %q connector", connName)

connectors/routing/resolver.go

@@ -0,0 +1,7 @@
+package routing
+
+// Resolver is an object that knows about the map from (scope,prefix) to cluster.
+type Resolver interface {
+  // Resolve maps a (scope, prefix) to a cluster name.
+  Resolve(scope, namePrefix string) string
+}