storagenode/nodestats: fix issue on 32 bit platforms (#2841)

* storagenode/nodestats: fix issue on 32 bit platforms

time.Duration is an int64, so casting it down to an int
can cause it to become negative, causing a panic.

Change-Id: I33da7c29ddd59be60d8deec944a25f4a025902c7

* storagenode/nodestats: fix lint issue in test

Change-Id: Ie68598d724d2cae0dc959d4877098a08f4eb9af7

storagenode/nodestats/cache.go

@@ -146,7 +146,7 @@ func (cache *Cache) sleep(ctx context.Context) error {
 		return nil
 	}
 
-	jitter := time.Duration(rand.Intn(int(cache.maxSleep)))
+	jitter := time.Duration(rand.Int63n(int64(cache.maxSleep)))
 	if !sync2.Sleep(ctx, jitter) {
 		return ctx.Err()
 	}

storagenode/nodestats/cache_test.go

@@ -0,0 +1,18 @@
+// Copyright (C) 2019 Storj Labs, Inc.
+// See LICENSE for copying information.
+
+package nodestats
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestCacheSleep32bitBug(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Millisecond)
+	defer cancel()
+
+	// Ensure that a large maxSleep doesn't roll over to negative values on 32 bit systems.
+	_ = (&Cache{maxSleep: 1 << 32}).sleep(ctx)
+}