From f9da55e8a9d4fa6ca54984170fe647248185e266 Mon Sep 17 00:00:00 2001
From: Asim Aslam <asim@aslam.me>
Date: Mon, 7 Jan 2019 07:41:26 +0000
Subject: [PATCH] Add dns selector

---
 cmd/cmd.go          |   2 +
 selector/dns/dns.go | 100 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 102 insertions(+)
 create mode 100644 selector/dns/dns.go

diff --git a/cmd/cmd.go b/cmd/cmd.go
index 7d41b452..5793b48f 100644
--- a/cmd/cmd.go
+++ b/cmd/cmd.go
@@ -26,6 +26,7 @@ import (
 
 	// selectors
 	"github.com/micro/go-micro/selector"
+	"github.com/micro/go-micro/selector/dns"
 
 	// transports
 	"github.com/micro/go-micro/transport"
@@ -177,6 +178,7 @@ var (
 
 	DefaultSelectors = map[string]func(...selector.Option) selector.Selector{
 		"default": selector.NewSelector,
+		"dns":     dns.NewSelector,
 		"cache":   selector.NewSelector,
 	}
 
diff --git a/selector/dns/dns.go b/selector/dns/dns.go
new file mode 100644
index 00000000..05f493cc
--- /dev/null
+++ b/selector/dns/dns.go
@@ -0,0 +1,100 @@
+// Package dns provides a dns SRV selector
+package dns
+
+import (
+	"net"
+
+	"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) {
+	_, srv, err := net.LookupSRV(service, "tcp", d.domain)
+	if err != nil {
+		return nil, err
+	}
+
+	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}
+}