add Hijacker interface to metrics middleware response writer. Fix #79

app/mgmt/metrics.go

@@ -1,7 +1,10 @@
 package mgmt
 
 import (
+	"bufio"
+	"errors"
 	"log"
+	"net"
 	"net/http"
 	"strconv"
 	"strings"
@@ -94,3 +97,12 @@ func (rw *responseWriter) WriteHeader(code int) {
 	rw.statusCode = code
 	rw.ResponseWriter.WriteHeader(code)
 }
+
+// Hijack delegate to the original writer if it implements http.Hijacker
+func (rw *responseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	h, ok := rw.ResponseWriter.(http.Hijacker)
+	if !ok {
+		return nil, nil, errors.New("hijack not supported")
+	}
+	return h.Hijack()
+}