fix: keep writing previous speedtest result (#15484)

when object speedtest is running keep writing
previous speedtest result back to client until
we have a new result - this avoids sending back
blank entries in between the speedtest when it
is running in 'autotune' mode.

cmd/admin-handlers.go

@@ -1272,14 +1272,24 @@ func (a adminAPIHandlers) ObjectSpeedTestHandler(w http.ResponseWriter, r *http.
 		storageClass:     storageClass,
 		bucketName:       customBucket,
 	})
+	var prevResult madmin.SpeedTestResult
 	for {
 		select {
 		case <-ctx.Done():
 			return
 		case <-keepAliveTicker.C:
-			// Write a blank entry to prevent client from disconnecting
+			// if previous result is set keep writing the
-			if err := enc.Encode(madmin.SpeedTestResult{}); err != nil {
+			// previous result back to the client
-				return
+			if prevResult.Version != "" {
+				if err := enc.Encode(prevResult); err != nil {
+					return
+				}
+			} else {
+				// first result is not yet obtained, keep writing
+				// empty entry to prevent client from disconnecting.
+				if err := enc.Encode(madmin.SpeedTestResult{}); err != nil {
+					return
+				}
 			}
 			w.(http.Flusher).Flush()
 		case result, ok := <-ch:
@@ -1289,6 +1299,7 @@ func (a adminAPIHandlers) ObjectSpeedTestHandler(w http.ResponseWriter, r *http.
 			if err := enc.Encode(result); err != nil {
 				return
 			}
+			prevResult = result
 			w.(http.Flusher).Flush()
 		}
 	}