From 1ce12ba19589c12a3d7af06d42c3b0fb78df649a Mon Sep 17 00:00:00 2001
From: Ivan Kozlovic <ivan@synadia.com>
Date: Mon, 8 May 2023 09:06:16 -0600
Subject: [PATCH] Fixed issue with route s2_auto when compression is actually
 off

This is a fix for PR https://github.com/nats-io/nats-server/pull/4001.
If a server has an s2_auto configuration, the compression level
needs to be updated based on the RTT, however, this should not
happen if a particular route is actually not using compression,
either because it is a connection to an older server or the other
side has explicitly configure compression to be "off".

Extended a test that would have caught this issue.

Signed-off-by: Ivan Kozlovic <ivan@synadia.com>
---
 server/client.go      | 12 ++++++------
 server/routes_test.go | 15 +++++++++++++++
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/server/client.go b/server/client.go
index fc552c83c8..4f1049de6f 100644
--- a/server/client.go
+++ b/server/client.go
@@ -2389,12 +2389,12 @@ func (c *client) processPong() {
 	c.rtt = computeRTT(c.rttStart)
 	srv := c.srv
 	reorderGWs := c.kind == GATEWAY && c.gw.outbound
-	// For routes, check if we have compression auto and if we should change
-	// the compression level. However, exclude the route if compression is
-	// "not supported", which indicates that this is a route to an older server.
-	if c.kind == ROUTER && c.route.compression != CompressionNotSupported {
-		if opts := srv.getOpts(); opts.Cluster.Compression.Mode == CompressionS2Auto {
-			if cm := selectS2AutoModeBasedOnRTT(c.rtt, opts.Cluster.Compression.RTTThresholds); cm != c.route.compression {
+	// If compression is currently active for a route connection, if the
+	// compression configuration is s2_auto, check if we should change
+	// the compression level.
+	if c.kind == ROUTER && needsCompression(c.route.compression) {
+		if co := &(srv.getOpts().Cluster.Compression); co.Mode == CompressionS2Auto {
+			if cm := selectS2AutoModeBasedOnRTT(c.rtt, co.RTTThresholds); cm != c.route.compression {
 				c.route.compression = cm
 				c.out.cw = s2.NewWriter(nil, s2WriterOptions(cm)...)
 			}
diff --git a/server/routes_test.go b/server/routes_test.go
index 9fa3018b1c..04ddda68f4 100644
--- a/server/routes_test.go
+++ b/server/routes_test.go
@@ -3637,6 +3637,9 @@ func TestRouteCompressionAuto(t *testing.T) {
 		checkFor(t, 2*time.Second, 15*time.Millisecond, func() error {
 			s2.mu.RLock()
 			defer s2.mu.RUnlock()
+			if n := s2.numRoutes(); n != 4 {
+				return fmt.Errorf("Cluster not formed properly, got %v routes", n)
+			}
 			var err error
 			s2.forEachRoute(func(r *client) {
 				if err != nil {
@@ -3694,6 +3697,18 @@ func TestRouteCompressionAuto(t *testing.T) {
 	time.Sleep(100 * time.Millisecond)
 	np.updateRTT(25 * time.Millisecond)
 	checkComp(CompressionS2Fast)
+
+	// Now disable compression on s1
+	reloadUpdateConfig(t, s1, conf1, fmt.Sprintf(tmpl, "A", "10s", "off", _EMPTY_))
+	// Wait a bit to make sure we don't check for cluster too soon since
+	// we expect a disconnect.
+	time.Sleep(100 * time.Millisecond)
+	checkClusterFormed(t, s1, s2)
+	// Now change the RTT values in the proxy.
+	np.updateRTT(1 * time.Millisecond)
+	// Now check that s2 also shows as "off". Wait for some ping intervals.
+	time.Sleep(200 * time.Millisecond)
+	checkComp(CompressionOff)
 }
 
 func TestRoutePings(t *testing.T) {