Merge pull request #7 from furio/patch-1

Fixes #6 fix panic when request body length less than 0

Author: penglongli

Diff for: ginmetrics/middleware.go

@@ -114,7 +114,10 @@ func (m *Monitor) ginMetricHandle(ctx *gin.Context, start time.Time) {
 	_ = m.GetMetric(metricURIRequestTotal).Inc([]string{ctx.FullPath(), r.Method, strconv.Itoa(w.Status())})
 
 	// set request body size
-	_ = m.GetMetric(metricRequestBody).Add(nil, float64(r.ContentLength))
+	// since r.ContentLength can be negative (in some occasions) guard the operation
+	if r.ContentLength >= 0 {
+		_ = m.GetMetric(metricRequestBody).Add(nil, float64(r.ContentLength))
+	}
 
 	// set slow request
 	latency := time.Since(start)