Move to a selector package

selector/selector.go

@@ -0,0 +1,93 @@
+/*
+The Selector package provides a way to algorithmically filter and return
+nodes required by the client or any other system. Selector's implemented
+by Micro build on the registry but it's of optional use. One could
+provide a static Selector that has a fixed pool.
+
+	func (r *randomSelector) Select(service string, opts ...SelectOption) (Next, error) {
+		var sopts SelectOptions
+		for _, opt := range opts {
+			opt(&sopts)
+		}
+
+		// get the service
+		services, err := r.so.Registry.GetService(service)
+		if err != nil {
+			return nil, err
+		}
+
+		// apply the filters
+		for _, filter := range sopts.Filters {
+			services = filter(services)
+		}
+
+		// if there's nothing left, return
+		if len(services) == 0 {
+			return nil, ErrNotFound
+		}
+
+		var nodes []*registry.Node
+
+		for _, service := range services {
+			for _, node := range service.Nodes {
+				nodes = append(nodes, node)
+			}
+		}
+
+		if len(nodes) == 0 {
+			return nil, ErrNotFound
+		}
+
+		return func() (*registry.Node, error) {
+			i := rand.Int()
+			j := i % len(services)
+
+			if len(services[j].Nodes) == 0 {
+				return nil, ErrNotFound
+			}
+
+			k := i % len(services[j].Nodes)
+			return services[j].Nodes[k], nil
+		}, nil
+	}
+
+
+*/
+package selector
+
+import (
+	"errors"
+	"github.com/micro/go-micro/registry"
+)
+
+// Selector builds on the registry as a mechanism to pick nodes
+// and mark their status. This allows host pools and other things
+// to be built using various algorithms.
+type Selector interface {
+	// Select returns a function which should return the next node
+	Select(service string, opts ...SelectOption) (Next, error)
+	// Mark sets the success/error against a node
+	Mark(service string, node *registry.Node, err error)
+	// Reset returns state back to zero for a service
+	Reset(service string)
+	// Close renders the selector unusable
+	Close() error
+}
+
+// Next is a function that returns the next node
+// based on the selector's algorithm
+type Next func() (*registry.Node, error)
+
+// SelectFilter is used to filter a service during the selection process
+type SelectFilter func([]*registry.Service) []*registry.Service
+
+var (
+	DefaultSelector = newRandomSelector()
+
+	ErrNotFound      = errors.New("not found")
+	ErrNoneAvailable = errors.New("none available")
+)
+
+func NewSelector(opts ...Option) Selector {
+	return newRandomSelector(opts...)
+}