Merge pull request #371 from micro/dns

Add dns selector

cmd/cmd.go

@@ -26,6 +26,7 @@ import (
 
 	// selectors
 	"github.com/micro/go-micro/selector"
+	"github.com/micro/go-micro/selector/dns"
 	"github.com/micro/go-micro/selector/static"
 
 	// transports
@@ -178,6 +179,7 @@ var (
 
 	DefaultSelectors = map[string]func(...selector.Option) selector.Selector{
 		"default": selector.NewSelector,
+		"dns":     dns.NewSelector,
 		"cache":   selector.NewSelector,
 		"static": static.NewSelector,
 	}

selector/dns/dns.go

@@ -0,0 +1,128 @@
+// Package dns provides a dns SRV selector
+package dns
+
+import (
+	"net"
+	"strconv"
+
+	"github.com/micro/go-micro/registry"
+	"github.com/micro/go-micro/selector"
+)
+
+type dnsSelector struct {
+	options selector.Options
+	domain  string
+}
+
+var (
+	DefaultDomain = "local"
+)
+
+func (d *dnsSelector) Init(opts ...selector.Option) error {
+	for _, o := range opts {
+		o(&d.options)
+	}
+	return nil
+}
+
+func (d *dnsSelector) Options() selector.Options {
+	return d.options
+}
+
+func (d *dnsSelector) Select(service string, opts ...selector.SelectOption) (selector.Next, error) {
+	var srv []*net.SRV
+
+	// check if its host:port
+	host, port, err := net.SplitHostPort(service)
+	// not host:port
+	if err != nil {
+		// lookup the SRV record
+		_, srvs, err := net.LookupSRV(service, "tcp", d.domain)
+		if err != nil {
+			return nil, err
+		}
+		// set SRV records
+		srv = srvs
+		// got host:port
+	} else {
+		p, _ := strconv.Atoi(port)
+
+		// lookup the A record
+		ips, err := net.LookupHost(host)
+		if err != nil {
+			return nil, err
+		}
+
+		// create SRV records
+		for _, ip := range ips {
+			srv = append(srv, &net.SRV{
+				Target: ip,
+				Port:   uint16(p),
+			})
+		}
+	}
+
+	var nodes []*registry.Node
+	for _, node := range srv {
+		nodes = append(nodes, &registry.Node{
+			Id:      node.Target,
+			Address: node.Target,
+			Port:    int(node.Port),
+		})
+	}
+
+	services := []*registry.Service{
+		&registry.Service{
+			Name:  service,
+			Nodes: nodes,
+		},
+	}
+
+	sopts := selector.SelectOptions{
+		Strategy: d.options.Strategy,
+	}
+
+	for _, opt := range opts {
+		opt(&sopts)
+	}
+
+	// apply the filters
+	for _, filter := range sopts.Filters {
+		services = filter(services)
+	}
+
+	// if there's nothing left, return
+	if len(services) == 0 {
+		return nil, selector.ErrNoneAvailable
+	}
+
+	return sopts.Strategy(services), nil
+}
+
+func (d *dnsSelector) Mark(service string, node *registry.Node, err error) {
+	return
+}
+
+func (d *dnsSelector) Reset(service string) {
+	return
+}
+
+func (d *dnsSelector) Close() error {
+	return nil
+}
+
+func (d *dnsSelector) String() string {
+	return "dns"
+}
+
+func NewSelector(opts ...selector.Option) selector.Selector {
+	options := selector.Options{
+		Strategy: selector.Random,
+	}
+
+	for _, o := range opts {
+		o(&options)
+	}
+
+	return &dnsSelector{options: options, domain: DefaultDomain}
+}