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.

middleware/auto/watcher_test.go

@@ -0,0 +1,48 @@
+package auto
+
+import (
+	"io/ioutil"
+	"log"
+	"os"
+	"path"
+	"regexp"
+	"testing"
+)
+
+func TestWatcher(t *testing.T) {
+	log.SetOutput(ioutil.Discard)
+
+	tempdir, err := createFiles()
+	if err != nil {
+		if tempdir != "" {
+			os.RemoveAll(tempdir)
+		}
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tempdir)
+
+	ldr := loader{
+		directory: tempdir,
+		re:        regexp.MustCompile(`db\.(.*)`),
+		template:  `${1}`,
+	}
+
+	z := &Zones{}
+
+	z.Walk(ldr)
+
+	// example.org and example.com should exist
+	if x := len(z.Z["example.org."].All()); x != 4 {
+		t.Fatalf("expected 4 RRs, got %d", x)
+	}
+	if x := len(z.Z["example.com."].All()); x != 4 {
+		t.Fatalf("expected 4 RRs, got %d", x)
+	}
+
+	// Now remove one file, rescan and see if it's gone.
+	if err := os.Remove(path.Join(tempdir, "db.example.com")); err != nil {
+		t.Fatal(err)
+	}
+
+	z.Walk(ldr)
+}