client/selector: query across multiple domains (micro#1725)

* client/selector: query across multiple domains

* client/selector: check for nil services

* config/cmd: fix merge bug

client/selector/default.go

@@ -46,17 +46,28 @@ func (c *registrySelector) Select(service string, opts ...SelectOption) (Next, e
 		opt(&sopts)
 	}
 
-	// get the service
-	// try the cache first
-	// if that fails go directly to the registry
-	services, err := c.rc.GetService(service)
-	if err != nil {
-		if err == registry.ErrNotFound {
-			return nil, ErrNotFound
-		}
+	// get the service. Because the service could be running in the current or the default domain,
+	// we call both. For example, go.micro.service.foo could be running in the services current domain,
+	// however the runtime (go.micro.runtime) will always be run in the default domain.
+	services, err := c.rc.GetService(service, registry.GetDomain(c.so.Domain))
+	if err != nil && err != registry.ErrNotFound {
 		return nil, err
 	}
 
+	if c.so.Domain != registry.DefaultDomain {
+		srvs, err := c.rc.GetService(service, registry.GetDomain(registry.DefaultDomain))
+		if err != nil && err != registry.ErrNotFound {
+			return nil, err
+		}
+		if err == nil {
+			services = append(services, srvs...)
+		}
+	}
+
+	if services == nil {
+		return nil, ErrNoneAvailable
+	}
+
 	// apply the filters
 	for _, filter := range sopts.Filters {
 		services = filter(services)

client/selector/options.go

@@ -10,6 +10,9 @@ type Options struct {
 	Registry registry.Registry
 	Strategy Strategy
 
+	// Domain to lookup services from within the registry
+	Domain string
+
 	// Other options for implementations of the interface
 	// can be stored in a context
 	Context context.Context
@@ -37,6 +40,13 @@ func Registry(r registry.Registry) Option {
 	}
 }
 
+// Domain sets the domain used by the selector
+func Domain(d string) Option {
+	return func(o *Options) {
+		o.Domain = d
+	}
+}
+
 // SetStrategy sets the default strategy for the selector
 func SetStrategy(fn Strategy) Option {
 	return func(o *Options) {