refactor(client): expose single latency measurement

Instead of exposing the time to establish a connection, the time to upload the
bytes and the time to download the bytes, expose a single time including all
three.

The rational here is, that differentiation of the three is flawed. E.g. when
does one stop the upload timer and start the download timer? When the last byte
is sent? When the last byte is flushed? When the first byte is received?

See libp2p/test-plans#184 (review)
for past discussion.

client.go

@@ -14,9 +14,7 @@ import (
 )
 
 type Result struct {
-	ConnectionEstablishedSeconds float64 `json:"connectionEstablishedSeconds"`
-	UploadSeconds                float64 `json:"uploadSeconds"`
-	DownloadSeconds              float64 `json:"downloadSeconds"`
+	Latency float64 `json:"latency"`
 }
 
 func RunClient(addr string, uploadBytes, downloadBytes uint64) error {
@@ -35,7 +33,6 @@ func RunClient(addr string, uploadBytes, downloadBytes uint64) error {
 	if err != nil {
 		return err
 	}
-	connectionEstablishmentTook := time.Since(start)
 	str, err := conn.OpenStream()
 	if err != nil {
 		return err
@@ -47,9 +44,7 @@ func RunClient(addr string, uploadBytes, downloadBytes uint64) error {
 	log.Printf("uploaded %s: %.2fs (%s/s)", formatBytes(uploadBytes), uploadTook.Seconds(), formatBytes(bandwidth(uploadBytes, uploadTook)))
 	log.Printf("downloaded %s: %.2fs (%s/s)", formatBytes(downloadBytes), downloadTook.Seconds(), formatBytes(bandwidth(downloadBytes, downloadTook)))
 	json, err := json.Marshal(Result{
-		ConnectionEstablishedSeconds: connectionEstablishmentTook.Seconds(),
-		UploadSeconds:                uploadTook.Seconds(),
-		DownloadSeconds:              downloadTook.Seconds(),
+		Latency: time.Since(start).Seconds(),
 	})
 	if err != nil {
 		return err