Move selector to client/selector

client/selector/selector.go

@@ -0,0 +1,42 @@
+// Package selector is a way to pick a list of service nodes
+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 {
+	Init(opts ...Option) error
+	Options() Options
+	// 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
+	// Name of the selector
+	String() string
+}
+
+// Next is a function that returns the next node
+// based on the selector's strategy
+type Next func() (*registry.Node, error)
+
+// Filter is used to filter a service during the selection process
+type Filter func([]*registry.Service) []*registry.Service
+
+// Strategy is a selection strategy e.g random, round robin
+type Strategy func([]*registry.Service) Next
+
+var (
+	DefaultSelector = NewSelector()
+
+	ErrNotFound      = errors.New("not found")
+	ErrNoneAvailable = errors.New("none available")
+)