http: check existence of codec when calling watermark callbacks

Signed-off-by: Anuraag Agrawal <anuraaga@gmail.com>

Author: anuraaga

changelogs/current.yaml

@@ -58,6 +58,9 @@ minor_behavior_changes:
 
 bug_fixes:
 # *Changes expected to improve the state of the world and are unlikely to have negative effects*
+- area: http
+  change: |
+    Fixed crash if a downstream watermark is hit by network filter writes before the HTTP codec is created.
 - area: tls
   change: |
     Fix on-demand TLS selector to enforce session resumption settings.

source/common/http/conn_manager_impl.h

@@ -109,10 +109,14 @@ class ConnectionManagerImpl : Logger::Loggable<Logger::Id::http>,
   void onEvent(Network::ConnectionEvent event) override;
   // Pass connection watermark events on to all the streams associated with that connection.
   void onAboveWriteBufferHighWatermark() override {
-    codec_->onUnderlyingConnectionAboveWriteBufferHighWatermark();
+    if (codec_) {
+      codec_->onUnderlyingConnectionAboveWriteBufferHighWatermark();
+    }
   }
   void onBelowWriteBufferLowWatermark() override {
-    codec_->onUnderlyingConnectionBelowWriteBufferLowWatermark();
+    if (codec_) {
+      codec_->onUnderlyingConnectionBelowWriteBufferLowWatermark();
+    }
   }
 
   TimeSource& timeSource() { return time_source_; }

test/common/http/conn_manager_impl_test_2.cc

@@ -1630,6 +1630,20 @@ TEST_F(HttpConnectionManagerImplTest, UnderlyingConnectionWatermarksUnwoundWithL
   doRemoteClose();
 }
 
+// Can happen if a network filter writes large payloads to downstream before the HTTP
+// filter gets data.
+TEST_F(HttpConnectionManagerImplTest, UnderlyingConnectionWatermarkLimitsNoCodec) {
+  // Not used in the test.
+  delete codec_;
+
+  server_transformation_ = HttpConnectionManagerProto::PASS_THROUGH;
+  setup();
+
+  // No-ops since no codec setup yet. Verify no crash.
+  conn_manager_->onAboveWriteBufferHighWatermark();
+  conn_manager_->onBelowWriteBufferLowWatermark();
+}
+
 TEST_F(HttpConnectionManagerImplTest, AlterFilterWatermarkLimits) {
   initial_buffer_limit_ = 100;
   setup();