Support keyed fetches of expvar information

http/service.go

@@ -1456,10 +1456,14 @@ func (s *Service) handleExpvar(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusUnauthorized)
 		return
 	}
+	key := keyParam(r)
 
 	fmt.Fprintf(w, "{\n")
 	first := true
 	expvar.Do(func(kv expvar.KeyValue) {
+		if key != "" && key != kv.Key {
+			return
+		}
 		if !first {
 			fmt.Fprintf(w, ",\n")
 		}
@@ -1764,6 +1768,11 @@ func isRedirect(req *http.Request) (bool, error) {
 	return queryParam(req, "redirect")
 }
 
+func keyParam(req *http.Request) string {
+	q := req.URL.Query()
+	return strings.TrimSpace(q.Get("key"))
+}
+
 // timeoutParam returns the value, if any, set for timeout. If not set, it
 // returns the value passed in as a default.
 func timeoutParam(req *http.Request, def time.Duration) (time.Duration, error) {

system_test/cluster_test.go

@@ -1768,3 +1768,17 @@ func Test_MultiNodeClusterNoReapReadOnlyZero(t *testing.T) {
 		t.Fatalf("didn't time out waiting for node to be removed")
 	}
 }
+
+func mustGetExpvar(n *Node) string {
+	j, err := n.Expvar()
+	if err != nil {
+		panic(err.Error())
+	}
+	return j
+}
+
+func mustGetExpvarKey(n *Node, k string) string {
+	j, err := n.ExpvarKey(k)
+	if err != nil {
+		panic(err.Error())
+	}

system_test/helpers.go

@@ -313,7 +313,12 @@ func (n *Node) Liveness() (bool, error) {
 
 // Expvar returns the expvar output for node.
 func (n *Node) Expvar() (string, error) {
-	v, _ := url.Parse("http://" + n.APIAddr + "/debug/vars")
+	return n.ExpvarKey("")
+}
+
+// ExpvarKey returns the expvar output, for a given key, for a node.
+func (n *Node) ExpvarKey(k string) (string, error) {
+	v, _ := url.Parse("http://" + n.APIAddr + "/debug/vars?key=" + k)
 
 	resp, err := http.Get(v.String())
 	if err != nil {