pprof middleware (#138)

Add pprof middleware, enabled by pprof directive.

middleware/health/README.md

@@ -19,3 +19,7 @@ will just return "OK", when CoreDNS is healthy.
 This middleware only needs to be enabled once.
 
 ## Examples
+
+~~~
+health localhost:8091
+~~~

middleware/metrics/handler.go

@@ -3,10 +3,10 @@ package metrics
 import (
 	"time"
 
-	"golang.org/x/net/context"
-
 	"github.com/miekg/coredns/middleware"
+
 	"github.com/miekg/dns"
+	"golang.org/x/net/context"
 )
 
 func (m Metrics) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {

middleware/pprof/README.md

@@ -0,0 +1,25 @@
+# pprof
+
+pprof publishes runtime profiling data at endpoints under /debug/pprof. You can visit /debug/pprof
+on your site for an index of the available endpoints. By default it will listen on localhost:8053.
+
+> This is a debugging tool. Certain requests (such as collecting execution traces) can be slow. If
+> you use pprof on a live site, consider restricting access or enabling it only temporarily.
+
+For more information, please see [Go's pprof
+documentation](https://golang.org/pkg/net/http/pprof/s://golang.org/pkg/net/http/pprof/) and read
+[Profiling Go Programs](https://blog.golang.org/profiling-go-programs).
+
+## Syntax
+
+~~~
+pprof
+~~~
+
+## Examples
+
+Enable pprof endpoints:
+
+~~~
+pprof
+~~~

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
+}