Merge 1b2a2d6 into 7bb3472

nats.go

@@ -1126,7 +1126,7 @@ func (nc *Conn) setupServerPool() error {
 
 	// Randomize if allowed to
 	if !nc.Opts.NoRandomize {
-		nc.shufflePool()
+		nc.shufflePool(0)
 	}
 
 	// Normally, if this one is set, Options.Servers should not be,
@@ -1223,14 +1223,16 @@ func (nc *Conn) addURLToPool(sURL string, implicit, saveTLSName bool) error {
 }
 
 // shufflePool swaps randomly elements in the server pool
-func (nc *Conn) shufflePool() {
-	if len(nc.srvPool) <= 1 {
+// The `offset` value indicates that the shuffling should start at
+// this offset and leave the elements from [0..offset) intact.
+func (nc *Conn) shufflePool(offset int) {
+	if len(nc.srvPool) <= offset+1 {
 		return
 	}
 	source := rand.NewSource(time.Now().UnixNano())
 	r := rand.New(source)
-	for i := range nc.srvPool {
-		j := r.Intn(i + 1)
+	for i := offset; i < len(nc.srvPool); i++ {
+		j := offset + r.Intn(i+1-offset)
 		nc.srvPool[i], nc.srvPool[j] = nc.srvPool[j], nc.srvPool[i]
 	}
 }
@@ -2431,8 +2433,14 @@ func (nc *Conn) processInfo(info string) error {
 		}
 		nc.addURLToPool(fmt.Sprintf("%s://%s", nc.connScheme(), curl), true, saveTLS)
 	}
-	if hasNew && !nc.initc && nc.Opts.DiscoveredServersCB != nil {
-		nc.ach.push(func() { nc.Opts.DiscoveredServersCB(nc) })
+	if hasNew {
+		// Randomize the pool if allowed but leave the first URL in place.
+		if !nc.Opts.NoRandomize {
+			nc.shufflePool(1)
+		}
+		if !nc.initc && nc.Opts.DiscoveredServersCB != nil {
+			nc.ach.push(func() { nc.Opts.DiscoveredServersCB(nc) })
+		}
 	}
 
 	return nil

nats_test.go

@@ -1118,28 +1118,32 @@ func TestAsyncINFO(t *testing.T) {
 	for _, srv := range c.srvPool {
 		urlsAfterPoolSetup = append(urlsAfterPoolSetup, srv.url.Host)
 	}
-	checkPoolOrderDidNotChange := func() {
+	checkNewURLsAddedRandomly := func() {
+		t.Helper()
+		var ok bool
 		for i := 0; i < len(urlsAfterPoolSetup); i++ {
 			if c.srvPool[i].url.Host != urlsAfterPoolSetup[i] {
-				stackFatalf(t, "Pool should have %q at index %q, has %q", urlsAfterPoolSetup[i], i, c.srvPool[i].url.Host)
+				ok = true
+				break
 			}
 		}
+		if !ok {
+			t.Fatalf("New URLs were not added randmonly: %q", c.Servers())
+		}
 	}
 	// Add new urls
-	newURLs := []string{
-		"localhost:6222",
-		"localhost:7222",
-		"localhost:8222\", \"localhost:9222",
-		"localhost:10222\", \"localhost:11222\", \"localhost:12222,",
-	}
-	for _, newURL := range newURLs {
-		info = []byte("INFO {\"connect_urls\":[\"" + newURL + "]}\r\n")
-		err = c.parse(info)
-		if err != nil || c.ps.state != OP_START {
-			t.Fatalf("Unexpected: %d : %v\n", c.ps.state, err)
-		}
-		// Check that pool order does not change up to the new addition(s).
-		checkPoolOrderDidNotChange()
+	newURLs := "\"impA:4222\", \"impB:4222\", \"impC:4222\", " +
+		"\"impD:4222\", \"impE:4222\", \"impF:4222\", \"impG:4222\", " +
+		"\"impH:4222\", \"impI:4222\", \"impJ:4222\""
+	info = []byte("INFO {\"connect_urls\":[" + newURLs + "]}\r\n")
+	err = c.parse(info)
+	if err != nil || c.ps.state != OP_START {
+		t.Fatalf("Unexpected: %d : %v\n", c.ps.state, err)
+	}
+	checkNewURLsAddedRandomly()
+	// Check that we have not moved the first URL
+	if u := c.srvPool[0].url.Host; u != urlsAfterPoolSetup[0] {
+		t.Fatalf("Expected first URL to be %q, got %q", urlsAfterPoolSetup[0], u)
 	}
 }