introduce EmptyReadRequest for status_endpoint (#12653)

Co-authored-by: Daniel Nephin <dnephin@hashicorp.com>

agent/consul/stats_fetcher.go

@@ -5,11 +5,12 @@ import (
 	"net"
 	"sync"
 
-	"github.com/hashicorp/consul/agent/pool"
-	"github.com/hashicorp/consul/agent/structs"
 	"github.com/hashicorp/go-hclog"
 	"github.com/hashicorp/raft"
 	autopilot "github.com/hashicorp/raft-autopilot"
+
+	"github.com/hashicorp/consul/agent/pool"
+	"github.com/hashicorp/consul/agent/structs"
 )
 
 // StatsFetcher has two functions for autopilot. First, lets us fetch all the
@@ -42,7 +43,7 @@ func NewStatsFetcher(logger hclog.Logger, pool *pool.ConnPool, datacenter string
 // RPC to each server, so we let it finish and then clean up the in-flight
 // tracking.
 func (f *StatsFetcher) fetch(server *autopilot.Server, replyCh chan *autopilot.ServerStats) {
-	var args struct{}
+	var args EmptyReadRequest
 	var reply structs.RaftStats
 
 	// defer some cleanup to notify everything else that the fetching is no longer occurring

agent/consul/status_endpoint.go

@@ -13,7 +13,7 @@ type Status struct {
 }
 
 // Ping is used to just check for connectivity
-func (s *Status) Ping(args struct{}, reply *struct{}) error {
+func (s *Status) Ping(args EmptyReadRequest, reply *struct{}) error {
 	return nil
 }
 
@@ -55,8 +55,16 @@ func (s *Status) Peers(args *structs.DCSpecificRequest, reply *[]string) error {
 	return nil
 }
 
-// Used by Autopilot to query the raft stats of the local server.
+// EmptyReadRequest implements the interface used by middleware.RequestRecorder
-func (s *Status) RaftStats(args struct{}, reply *structs.RaftStats) error {
+// to communicate properties of requests.
+type EmptyReadRequest struct{}
+
+func (e EmptyReadRequest) IsRead() bool {
+	return true
+}
+
+// RaftStats is used by Autopilot to query the raft stats of the local server.
+func (s *Status) RaftStats(args EmptyReadRequest, reply *structs.RaftStats) error {
 	stats := s.server.raft.Stats()
 
 	var err error