Add implementation of ordindary DNS provider for query plain old DNS …

…records

.gitignore

@@ -1,6 +1,7 @@
-cmd/discover/discover
-.terraform/
-.terraform.tfstate.lock.info
-terraform.tfstate
-terraform.tfstate.backup
-terraform.tfvars
+*~
+*.bak
+terraform.*
+.terraform.*
+
+/discover
+/cmd/discover/discover

discover.go

@@ -13,6 +13,7 @@ import (
 	"github.com/hashicorp/go-discover/provider/aws"
 	"github.com/hashicorp/go-discover/provider/azure"
 	"github.com/hashicorp/go-discover/provider/digitalocean"
+	"github.com/hashicorp/go-discover/provider/dns"
 	"github.com/hashicorp/go-discover/provider/gce"
 	"github.com/hashicorp/go-discover/provider/linode"
 	"github.com/hashicorp/go-discover/provider/mdns"
@@ -49,6 +50,7 @@ var Providers = map[string]Provider{
 	"aws":          &aws.Provider{},
 	"azure":        &azure.Provider{},
 	"digitalocean": &digitalocean.Provider{},
+	"dns":          &dns.Provider{},
 	"gce":          &gce.Provider{},
 	"linode":       &linode.Provider{},
 	"mdns":         &mdns.Provider{},

go.mod

@@ -15,6 +15,7 @@ require (
 	github.com/hashicorp/vic v1.5.1-0.20190403131502-bbfe86ec9443
 	github.com/joyent/triton-go v0.0.0-20180628001255-830d2b111e62
 	github.com/linode/linodego v0.7.1
+	github.com/miekg/dns v1.0.14
 	github.com/mitchellh/go-homedir v1.1.0
 	github.com/nicolai86/scaleway-sdk v1.10.2-0.20180628010248-798f60e20bb2
 	github.com/packethost/packngo v0.1.1-0.20180711074735-b9cb5096f54c

provider/dns/dns_provider.go

@@ -0,0 +1,106 @@
+// Package dns provides node discovery via DNS.
+package dns
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net"
+	"strconv"
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+// Provider implements the Provider interface.
+type Provider struct{}
+
+// Help returns help information for the DNS package.
+func (p *Provider) Help() string {
+	return `DNS:
+
+    provider:          "dns"
+    query:             The DNS query to lookup.  Required.
+    server:            The DNS server to query.  Default "8.8.8.8" (Google DNS).
+    port:              The DNS port to use.      Default: "53" (standard DNS port).
+    timeout:           The mDNS lookup timeout.  Default "5s" (five seconds).
+`
+}
+
+// Addrs returns discovered addresses for the mDNS package.
+func (p *Provider) Addrs(args map[string]string, l *log.Logger) ([]string, error) {
+	var err error
+
+	// default to null logger
+	if l == nil {
+		l = log.New(ioutil.Discard, "", 0)
+	}
+
+	// validate and set service record
+	if args["query"] == "" {
+		return nil, fmt.Errorf("discover-dns: Query not provided." +
+			"  Please specify a valid dns query for the DNS lookup.")
+	}
+
+	var server string
+	// validate and set server
+	if args["server"] != "" {
+		server = args["server"]
+	} else {
+		server = "8.8.8.8"
+	}
+
+	var port int
+	// validate and set port
+	if args["port"] != "" {
+		if port, err = strconv.Atoi(args["port"]); err != nil {
+			return nil, fmt.Errorf("discover-dns: Failed to parse port: %s", err)
+		}
+	} else {
+		port = 53
+	}
+
+	var timeout time.Duration
+	// validate and set timeout
+	if args["timeout"] != "" {
+		if timeout, err = time.ParseDuration(args["timeout"]); err != nil {
+			return nil, fmt.Errorf("discover-dns: Failed to parse timeout: %s", err)
+		}
+	} else {
+		timeout = 5 * time.Second
+	}
+
+	var addrs []string
+
+	// lookup and return
+	m1 := new(dns.Msg)
+	m1.Id = dns.Id()
+	m1.RecursionDesired = true
+	m1.Question = make([]dns.Question, 1)
+	m1.Question[0] = dns.Question{args["query"], dns.TypeA, dns.ClassINET}
+
+	c := new(dns.Client)
+
+	laddr := net.UDPAddr{
+		IP:   net.ParseIP("[::1]"),
+		Port: 0,
+		Zone: "",
+	}
+	c.Dialer = &net.Dialer{
+		Timeout:   timeout,
+		LocalAddr: &laddr,
+	}
+	raddr := fmt.Sprintf("%s:%d", server, port)
+	in, _, err := c.Exchange(m1, raddr)
+	if err != nil {
+		return nil, fmt.Errorf("discover-mdns: Failed to process query: %s", err)
+	}
+
+	for _, answer := range in.Answer {
+		if t, ok := answer.(*dns.A); ok {
+			addrs = append(addrs, t.A.String())
+		}
+	}
+
+	return addrs, err
+}

provider/dns/dns_provider_test.go

@@ -0,0 +1,151 @@
+package dns_test
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"testing"
+
+	"github.com/miekg/dns"
+
+	discover "github.com/hashicorp/go-discover"
+	provider "github.com/hashicorp/go-discover/provider/dns"
+)
+
+const (
+	testService = "test-service"
+)
+
+var (
+	testAddresses = []string{"127.0.0.1"}
+)
+
+func newTestServer() (*dns.Server, error) {
+	var rr []dns.RR
+
+	for _, testAddress := range testAddresses {
+		a, _ := dns.NewRR(fmt.Sprintf("tasks.%s. IN A %s", testService, testAddress))
+		rr = append(rr, a)
+	}
+
+	server := &dns.Server{Addr: ":5300", Net: "udp"}
+	go server.ListenAndServe()
+	dns.HandleFunc(fmt.Sprintf("tasks.%s.", testService), func(w dns.ResponseWriter, r *dns.Msg) {
+		m := new(dns.Msg)
+		m.SetReply(r)
+		m.Insert(rr)
+		w.WriteMsg(m)
+	})
+
+	return server, nil
+}
+
+func TestDiscover(t *testing.T) {
+	type testCases []struct {
+		desc  string
+		args  discover.Config
+		fail  bool
+		addrs int
+	}
+
+	cases := testCases{
+		{
+			"valid config - no addresses",
+			discover.Config{
+				"provider": "dns",
+				"query":    "tasks.fake-service",
+				"timeout":  "1s",
+				"v6":       "false",
+				"v4":       "false",
+			},
+			false,
+			0,
+		},
+		{
+			"valid config - one address",
+			discover.Config{
+				"provider": "dns",
+				"query":    "tasks.test-service",
+				"timeout":  "10s",
+				"v6":       "true",
+				"v4":       "true",
+			},
+			false,
+			1,
+		},
+		{
+			"invalid config - missing query option",
+			discover.Config{
+				"provider": "dns",
+				"query":    "",
+				"timeout":  "1s",
+				"v6":       "false",
+				"v4":       "false",
+			},
+			true,
+			0,
+		},
+		{
+			"invalid config - bad timeout option",
+			discover.Config{
+				"provider": "dns",
+				"query":    "tasks.fake-service",
+				"timeout":  "1z",
+				"v6":       "false",
+				"v4":       "false",
+			},
+			true,
+			0,
+		},
+		{
+			"invalid config - bad v6 option",
+			discover.Config{
+				"provider": "dns",
+				"service":  "tasks.fake-service",
+				"timeout":  "1s",
+				"v6":       "xxxx",
+				"v4":       "false",
+			},
+			true,
+			0,
+		},
+		{
+			"invalid config - bad v4 option",
+			discover.Config{
+				"provider": "dns",
+				"service":  "tasks.fake-service",
+				"timeout":  "1s",
+				"v6":       "false",
+				"v4":       "xxxx",
+			},
+			true,
+			0,
+		},
+	}
+
+	p := &provider.Provider{}
+	l := log.New(os.Stderr, "", log.LstdFlags)
+
+	svr, err := newTestServer()
+	if err != nil {
+		t.Fatalf("Failed to start test server: %s", err.Error())
+		return
+	}
+	defer svr.Shutdown()
+
+	for idx, tc := range cases {
+		addrs, err := p.Addrs(tc.args, l)
+
+		if !tc.fail && err != nil {
+			t.Fatalf("FAIL [%d/%d] %s -> %s",
+				idx, len(cases), tc.desc, err)
+		}
+
+		if len(addrs) != tc.addrs {
+			t.Fatalf("FAIL [%d/%d] %s -> wrong addr count: expected %d / got %d",
+				idx, len(cases), tc.desc, tc.addrs, len(addrs))
+		}
+
+		t.Logf("PASS [%d/%d] %s", idx, len(cases), tc.desc)
+	}
+}