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/setup.go

@@ -0,0 +1,150 @@
+package auto
+
+import (
+	"log"
+	"os"
+	"path"
+	"regexp"
+	"strconv"
+	"time"
+
+	"github.com/miekg/coredns/core/dnsserver"
+	"github.com/miekg/coredns/middleware"
+	"github.com/miekg/coredns/middleware/file"
+
+	"github.com/mholt/caddy"
+)
+
+func init() {
+	caddy.RegisterPlugin("auto", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	a, err := autoParse(c)
+	if err != nil {
+		return middleware.Error("auto", err)
+	}
+
+	walkChan := make(chan bool)
+
+	c.OnStartup(func() error {
+		err := a.Zones.Walk(a.loader)
+		if err != nil {
+			return err
+		}
+
+		go func() {
+			ticker := time.NewTicker(a.loader.duration)
+			for {
+				select {
+				case <-walkChan:
+					return
+				case <-ticker.C:
+					a.Zones.Walk(a.loader)
+				}
+			}
+		}()
+		return nil
+	})
+
+	c.OnShutdown(func() error {
+		close(walkChan)
+		return nil
+	})
+
+	dnsserver.GetConfig(c).AddMiddleware(func(next middleware.Handler) middleware.Handler {
+		a.Next = next
+		return a
+	})
+
+	return nil
+}
+
+func autoParse(c *caddy.Controller) (Auto, error) {
+	var a = Auto{
+		loader: loader{template: "${1}", re: regexp.MustCompile(`db\.(.*)`), duration: time.Duration(60 * time.Second)},
+		Zones:  &Zones{},
+	}
+
+	config := dnsserver.GetConfig(c)
+
+	for c.Next() {
+		if c.Val() == "auto" {
+			// auto [ZONES...]
+			a.Zones.origins = make([]string, len(c.ServerBlockKeys))
+			copy(a.Zones.origins, c.ServerBlockKeys)
+
+			args := c.RemainingArgs()
+			if len(args) > 0 {
+				a.Zones.origins = args
+			}
+			for i := range a.Zones.origins {
+				a.Zones.origins[i] = middleware.Host(a.Zones.origins[i]).Normalize()
+			}
+
+			for c.NextBlock() {
+				switch c.Val() {
+				case "directory": // directory DIR [REGEXP [TEMPLATE] [DURATION]]
+					if !c.NextArg() {
+						return a, c.ArgErr()
+					}
+					a.loader.directory = c.Val()
+					if !path.IsAbs(a.loader.directory) && config.Root != "" {
+						a.loader.directory = path.Join(config.Root, a.loader.directory)
+					}
+					_, err := os.Stat(a.loader.directory)
+					if err != nil {
+						if os.IsNotExist(err) {
+							log.Printf("[WARNING] Directory does not exist: %s", a.loader.directory)
+						} else {
+							return a, c.Errf("Unable to access root path '%s': %v", a.loader.directory, err)
+						}
+					}
+
+					// regexp
+					if c.NextArg() {
+						a.loader.re, err = regexp.Compile(c.Val())
+						if err != nil {
+							return a, err
+						}
+						if a.loader.re.NumSubexp() == 0 {
+							return a, c.Errf("Need at least one sub expression")
+						}
+					}
+
+					// template
+					if c.NextArg() {
+						a.loader.template = rewriteToExpand(c.Val())
+					}
+
+					// template
+					if c.NextArg() {
+						i, err := strconv.Atoi(c.Val())
+						if err != nil {
+							return a, err
+						}
+						if i < 1 {
+							i = 1
+						}
+						a.loader.duration = time.Duration(i) * time.Second
+					}
+
+				case "no_reload":
+					a.loader.noReload = true
+
+				default:
+					t, _, e := file.TransferParse(c, false)
+					if e != nil {
+						return a, e
+					}
+					a.loader.transferTo = t
+				}
+			}
+
+		}
+	}
+	return a, nil
+}