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/walk.go

@@ -0,0 +1,96 @@
+package auto
+
+import (
+	"log"
+	"os"
+	"path"
+	"path/filepath"
+	"regexp"
+
+	"github.com/miekg/coredns/middleware/file"
+
+	"github.com/miekg/dns"
+)
+
+// Walk will recursively walk of the file under l.directory and adds the one that match l.re.
+func (z *Zones) Walk(l loader) error {
+
+	// TODO(miek): should add something so that we don't stomp on each other.
+
+	toDelete := make(map[string]bool)
+	for _, n := range z.Names() {
+		toDelete[n] = true
+	}
+
+	filepath.Walk(l.directory, func(path string, info os.FileInfo, err error) error {
+		if info.IsDir() {
+			return nil
+		}
+
+		match, origin := matches(l.re, info.Name(), l.template)
+		if !match {
+			return nil
+		}
+
+		if _, ok := z.Z[origin]; ok {
+			// we already have this zone
+			toDelete[origin] = false
+			return nil
+		}
+
+		reader, err := os.Open(path)
+		if err != nil {
+			log.Printf("[WARNING] Opening %s failed: %s", path, err)
+			return nil
+		}
+
+		zo, err := file.Parse(reader, origin, path)
+		if err != nil {
+			// Parse barfs warning by itself...
+			return nil
+		}
+
+		zo.NoReload = l.noReload
+		zo.TransferTo = l.transferTo
+
+		z.Insert(zo, origin)
+
+		zo.Notify()
+
+		log.Printf("[INFO] Inserting zone `%s' from: %s", origin, path)
+
+		toDelete[origin] = false
+
+		return nil
+	})
+
+	for origin, ok := range toDelete {
+		if !ok {
+			continue
+		}
+		z.Delete(origin)
+		log.Printf("[INFO] Deleting zone `%s'", origin)
+	}
+
+	return nil
+}
+
+// matches matches re to filename, if is is a match, the subexpression will be used to expand
+// template to an origin. When match is true that origin is returned. Origin is fully qualified.
+func matches(re *regexp.Regexp, filename, template string) (match bool, origin string) {
+	base := path.Base(filename)
+
+	matches := re.FindStringSubmatchIndex(base)
+	if matches == nil {
+		return false, ""
+	}
+
+	by := re.ExpandString(nil, template, base, matches)
+	if by == nil {
+		return false, ""
+	}
+
+	origin = dns.Fqdn(string(by))
+
+	return true, origin
+}