middleware/auto: add (#333)

Add auto-load middleware that automatically picks up zones.

Every X seconds it will scan for new zones.
Add tests and documentation.

Make 'make test' use -race.

test/auto_test.go

@@ -0,0 +1,88 @@
+package test
+
+import (
+	"io/ioutil"
+	"log"
+	"os"
+	"path"
+	"testing"
+	"time"
+
+	"github.com/miekg/coredns/middleware/proxy"
+	"github.com/miekg/coredns/middleware/test"
+	"github.com/miekg/coredns/request"
+
+	"github.com/miekg/dns"
+)
+
+func TestAuto(t *testing.T) {
+	tmpdir, err := ioutil.TempDir(os.TempDir(), "coredns")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	corefile := `org:0 {
+		auto {
+			directory ` + tmpdir + ` db\.(.*) {1} 1
+		}
+	}
+`
+
+	i, err := CoreDNSServer(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+
+	udp, _ := CoreDNSServerPorts(i, 0)
+	if udp == "" {
+		t.Fatalf("Could not get UDP listening port")
+	}
+	defer i.Stop()
+
+	log.SetOutput(ioutil.Discard)
+
+	p := proxy.New([]string{udp})
+	state := request.Request{W: &test.ResponseWriter{}, Req: new(dns.Msg)}
+
+	resp, err := p.Lookup(state, "www.example.org.", dns.TypeA)
+	if err != nil {
+		t.Fatal("Expected to receive reply, but didn't")
+	}
+	if resp.Rcode != dns.RcodeServerFailure {
+		t.Fatalf("Expected reply to be a SERVFAIL, got %d", resp.Rcode)
+	}
+
+	// Write db.example.org to get example.org.
+	if err = ioutil.WriteFile(path.Join(tmpdir, "db.example.org"), []byte(zoneContent), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	time.Sleep(1100 * time.Millisecond) // wait for it to be picked up
+	resp, err = p.Lookup(state, "www.example.org.", dns.TypeA)
+	if err != nil {
+		t.Fatal("Expected to receive reply, but didn't")
+	}
+	if len(resp.Answer) != 1 {
+		t.Fatalf("Expected 1 RR in the answer section, got %d", len(resp.Answer))
+	}
+
+	// Remove db.example.org again.
+	os.Remove(path.Join(tmpdir, "db.example.org"))
+
+	time.Sleep(1100 * time.Millisecond) // wait for it to be picked up
+	resp, err = p.Lookup(state, "www.example.org.", dns.TypeA)
+	if err != nil {
+		t.Fatal("Expected to receive reply, but didn't")
+	}
+	if resp.Rcode != dns.RcodeServerFailure {
+		t.Fatalf("Expected reply to be a SERVFAIL, got %d", resp.Rcode)
+	}
+}
+
+const zoneContent = `; testzone
+@	IN	SOA	sns.dns.icann.org. noc.dns.icann.org. 2016082534 7200 3600 1209600 3600
+		NS	a.iana-servers.net.
+		NS	b.iana-servers.net.
+
+www IN A 127.0.0.1
+`