Turn millisecondsSince into millisecondsSinceOptional

... because we will have more cases of the NaN case, so share that
code path.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

Author: mtrmac

docker/body_reader.go

@@ -198,19 +198,20 @@ func (br *bodyReader) Read(p []byte) (int, error) {
 	}
 }
 
-// millisecondsSince is like time.Since(tm).Milliseconds, but it returns a floating-point value
-func millisecondsSince(tm time.Time) float64 {
+// millisecondsSinceOptional is like time.Since(tm).Milliseconds, but it returns a floating-point value.
+// If the input time is time.Time{}, it returns math.NaN()
+func millisecondsSinceOptional(tm time.Time) float64 {
+	if tm == (time.Time{}) {
+		return math.NaN()
+	}
 	return float64(time.Since(tm).Nanoseconds()) / 1_000_000.0
 }
 
 // errorIfNotReconnecting makes a heuristic decision whether we should reconnect after err at redactedURL; if so, it returns nil,
 // otherwise it returns an appropriate error to return to the caller (possibly augmented with data about the heuristic)
 func (br *bodyReader) errorIfNotReconnecting(originalErr error, redactedURL string) error {
-	totalTime := millisecondsSince(br.firstConnectionTime)
-	failureTime := math.NaN()
-	if (br.lastSuccessTime != time.Time{}) {
-		failureTime = millisecondsSince(br.lastSuccessTime)
-	}
+	totalTime := millisecondsSinceOptional(br.firstConnectionTime)
+	failureTime := millisecondsSinceOptional(br.lastSuccessTime)
 	logrus.Debugf("Reading blob body from %s failed (%#v), decision inputs: lastRetryOffset %d, offset %d, %.3f ms since first connection, %.3f ms since last progress",
 		redactedURL, originalErr, br.lastRetryOffset, br.offset, totalTime, failureTime)
 	progress := br.offset - br.lastRetryOffset