rpc: remove unused latency metric (#7810)

We have this one solitary metric from the go-metrics package.  In principle
this statistic could be useful, but the way we have it hooked up, nothing can
observe the value: We don't export it, we don't log it, and it does not auto
publish anywhere.

Given that this state of affairs has not changed since the metric was first
added in 2017 (c08618f), I think we can safely discard it. No one is now or has
ever gotten any data out of this metric.

go.mod

@@ -23,7 +23,6 @@ require (
 	github.com/oasisprotocol/curve25519-voi v0.0.0-20210609091139-0a56a4bca00b
 	github.com/ory/dockertest v3.3.5+incompatible
 	github.com/prometheus/client_golang v1.12.1
-	github.com/rcrowley/go-metrics v0.0.0-20200313005456-10cdbea86bc0
 	github.com/rs/cors v1.8.2
 	github.com/rs/zerolog v1.26.1
 	github.com/snikch/goodman v0.0.0-20171125024755-10e37e294daa

go.sum

@@ -865,8 +865,6 @@ github.com/quasilyte/gogrep v0.0.0-20220103110004-ffaa07af02e3/go.mod h1:wSEyW6O
 github.com/quasilyte/regex/syntax v0.0.0-20200407221936-30656e2c4a95 h1:L8QM9bvf68pVdQ3bCFZMDmnt9yqcMBro1pC7F+IPYMY=
 github.com/quasilyte/regex/syntax v0.0.0-20200407221936-30656e2c4a95/go.mod h1:rlzQ04UMyJXu/aOvhd8qT+hvDrFpiwqp8MRXDY9szc0=
 github.com/rcrowley/go-metrics v0.0.0-20181016184325-3113b8401b8a/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
-github.com/rcrowley/go-metrics v0.0.0-20200313005456-10cdbea86bc0 h1:MkV+77GLUNo5oJ0jf870itWm3D0Sjh7+Za9gazKc5LQ=
-github.com/rcrowley/go-metrics v0.0.0-20200313005456-10cdbea86bc0/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
 github.com/rogpeppe/fastuuid v0.0.0-20150106093220-6724a57986af/go.mod h1:XWv6SoW27p1b0cqNHllgS5HIMJraePCO15w5zCzIWYg=
 github.com/rogpeppe/fastuuid v1.2.0/go.mod h1:jVj6XXZzXRy/MSR5jhDC/2q6DgLz+nrA6LYCDYWNEvQ=
 github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=

rpc/jsonrpc/client/ws_client.go

@@ -11,7 +11,6 @@ import (
 	"time"
 
 	"github.com/gorilla/websocket"
-	metrics "github.com/rcrowley/go-metrics"
 
 	"github.com/tendermint/tendermint/libs/log"
 	rpctypes "github.com/tendermint/tendermint/rpc/jsonrpc/types"
@@ -66,10 +65,9 @@ type WSClient struct { // nolint: maligned
 
 	wg sync.WaitGroup
 
-	mtx            sync.RWMutex
-	sentLastPingAt time.Time
-	reconnecting   bool
-	nextReqID      int
+	mtx          sync.RWMutex
+	reconnecting bool
+	nextReqID    int
 	// sentIDs        map[types.JSONRPCIntID]bool // IDs of the requests currently in flight
 
 	// Time allowed to write a message to the server. 0 means block until operation succeeds.
@@ -80,10 +78,6 @@ type WSClient struct { // nolint: maligned
 
 	// Send pings to server with this period. Must be less than readWait. If 0, no pings will be sent.
 	pingPeriod time.Duration
-
-	// Time between sending a ping and receiving a pong. See
-	// https://godoc.org/github.com/rcrowley/go-metrics#Timer.
-	PingPongLatencyTimer metrics.Timer
 }
 
 // NewWS returns a new client with default options. The endpoint argument must
@@ -117,8 +111,6 @@ func NewWS(remoteAddr, endpoint string) (*WSClient, error) {
 
 		// sentIDs: make(map[types.JSONRPCIntID]bool),
 	}
-
-	c.PingPongLatencyTimer = metrics.NewTimer()
 	return c, nil
 }
 
@@ -165,7 +157,6 @@ func (c *WSClient) Start(ctx context.Context) error {
 func (c *WSClient) Stop() error {
 	// only close user-facing channels when we can't write to them
 	c.wg.Wait()
-	c.PingPongLatencyTimer.Stop()
 	close(c.ResponsesCh)
 	return nil
 }
@@ -386,9 +377,6 @@ func (c *WSClient) writeRoutine(ctx context.Context) {
 				c.reconnectAfter <- err
 				return
 			}
-			c.mtx.Lock()
-			c.sentLastPingAt = time.Now()
-			c.mtx.Unlock()
 		case <-c.readRoutineQuit:
 			return
 		case <-ctx.Done():
@@ -411,16 +399,6 @@ func (c *WSClient) readRoutine(ctx context.Context) {
 		c.wg.Done()
 	}()
 
-	c.conn.SetPongHandler(func(string) error {
-		// gather latency stats
-		c.mtx.RLock()
-		t := c.sentLastPingAt
-		c.mtx.RUnlock()
-		c.PingPongLatencyTimer.UpdateSince(t)
-
-		return nil
-	})
-
 	for {
 		// reset deadline for every message type (control or data)
 		if c.readWait > 0 {

rpc/jsonrpc/client/ws_client_test.go

@@ -11,20 +11,12 @@ import (
 
 	"github.com/fortytw2/leaktest"
 	"github.com/gorilla/websocket"
-	metrics "github.com/rcrowley/go-metrics"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	rpctypes "github.com/tendermint/tendermint/rpc/jsonrpc/types"
 )
 
-func init() {
-	// Disable go-metrics metrics in tests, since they start unsupervised
-	// goroutines that trip the leak tester. Calling Stop on the metric is not
-	// sufficient, as that does not wait for the goroutine.
-	metrics.UseNilMetrics = true
-}
-
 const wsCallTimeout = 5 * time.Second
 
 type myTestHandler struct {