pprof middleware (#138)

Add pprof middleware, enabled by pprof directive.

middleware/pprof/pprof.go

@@ -0,0 +1,32 @@
+package pprof
+
+import (
+	"log"
+	"net/http"
+	_ "net/http/pprof"
+
+	"github.com/miekg/coredns/middleware"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+)
+
+const addr = "localhost:8053"
+
+type Handler struct {
+	Next middleware.Handler
+}
+
+// ServeDNS passes all other requests up the chain.
+func (h *Handler) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	return h.Next.ServeDNS(ctx, w, r)
+}
+
+func (h *Handler) Start() error {
+	go func() {
+		if err := http.ListenAndServe(addr, nil); err != nil {
+			log.Printf("[ERROR] Failed to start pprof handler: %s", err)
+		}
+	}()
+	return nil
+}