Add DC selector example

examples/client/dc_selector/dc_selector.go

@@ -0,0 +1,117 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"sync"
+	"time"
+
+	"github.com/micro/go-micro/client"
+	"github.com/micro/go-micro/cmd"
+	example "github.com/micro/go-micro/examples/server/proto/example"
+	"github.com/micro/go-micro/registry"
+	"golang.org/x/net/context"
+)
+
+// Built in random hashed node selector
+type dcSelector struct {
+	opts registry.SelectorOptions
+}
+
+var (
+	datacenter = "local"
+)
+
+func init() {
+	rand.Seed(time.Now().Unix())
+}
+
+func (n *dcSelector) Select(service string, opts ...registry.SelectOption) (registry.SelectNext, error) {
+	services, err := n.opts.Registry.GetService(service)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(services) == 0 {
+		return nil, registry.ErrNotFound
+	}
+
+	var nodes []*registry.Node
+
+	// Filter the nodes for datacenter
+	for _, service := range services {
+		for _, node := range service.Nodes {
+			if node.Metadata["datacenter"] == datacenter {
+				nodes = append(nodes, node)
+			}
+		}
+	}
+
+	if len(nodes) == 0 {
+		return nil, registry.ErrNotFound
+	}
+
+	var i int
+	var mtx sync.Mutex
+
+	return func() (*registry.Node, error) {
+		mtx.Lock()
+		defer mtx.Unlock()
+		i++
+		return nodes[i%len(nodes)], nil
+	}, nil
+}
+
+func (n *dcSelector) Mark(service string, node *registry.Node, err error) {
+	return
+}
+
+func (n *dcSelector) Reset(service string) {
+	return
+}
+
+func (n *dcSelector) Close() error {
+	return nil
+}
+
+// Return a new first node selector
+func DCSelector(opts ...registry.SelectorOption) registry.Selector {
+	var sopts registry.SelectorOptions
+	for _, opt := range opts {
+		opt(&sopts)
+	}
+	if sopts.Registry == nil {
+		sopts.Registry = registry.DefaultRegistry
+	}
+	return &dcSelector{sopts}
+}
+
+func call(i int) {
+	// Create new request to service go.micro.srv.example, method Example.Call
+	req := client.NewRequest("go.micro.srv.example", "Example.Call", &example.Request{
+		Name: "John",
+	})
+
+	rsp := &example.Response{}
+
+	// Call service
+	if err := client.Call(context.Background(), req, rsp); err != nil {
+		fmt.Println("call err: ", err, rsp)
+		return
+	}
+
+	fmt.Println("Call:", i, "rsp:", rsp.Msg)
+}
+
+func main() {
+	cmd.Init()
+
+	client.DefaultClient = client.NewClient(
+		client.Selector(DCSelector()),
+	)
+
+	fmt.Println("\n--- Call example ---\n")
+	for i := 0; i < 10; i++ {
+		call(i)
+	}
+}