fix: skip parsing of unrecognized FDv2 stream events

Author: beekld

libs/internal/include/launchdarkly/fdv2_protocol_handler.hpp

@@ -95,6 +95,13 @@ class FDv2ProtocolHandler {
      */
     void Reset();
 
+    /**
+     * @return true if event_type is one that the protocol handler recognizes
+     * and may dispatch on. Events outside this set are spec-defined as
+     * "unrecognized data that can be safely ignored".
+     */
+    static bool IsKnownEvent(std::string_view event_type);
+
     FDv2ProtocolHandler() = default;
 
    private:

libs/internal/src/fdv2_protocol_handler.cpp

@@ -14,6 +14,12 @@ static char const* const kGoodbye = "goodbye";
 
 using Error = FDv2ProtocolHandler::Error;
 
+bool FDv2ProtocolHandler::IsKnownEvent(std::string_view event_type) {
+    return event_type == kServerIntent || event_type == kPutObject ||
+           event_type == kDeleteObject || event_type == kPayloadTransferred ||
+           event_type == kError || event_type == kGoodbye;
+}
+
 FDv2ProtocolHandler::Result FDv2ProtocolHandler::HandleEvent(
     std::string_view event_type,
     boost::json::value const& data) {

libs/server-sdk/tests/fdv2_streaming_synchronizer_test.cpp

@@ -574,6 +574,26 @@ TEST(FDv2StreamingSynchronizerTest, ServerErrorEventReturnsInterrupted) {
               std::string::npos);
 }
 
+TEST(FDv2StreamingSynchronizerTest, UnknownEventWithGarbageBodyIsIgnored) {
+    auto logger = MakeNullLogger();
+    IoContextRunner runner;
+
+    FDv2StreamingSynchronizer synchronizer(
+        runner.context().get_executor(), logger,
+        MakeEndpoints("http://localhost"), MakeHttpProperties(), std::nullopt,
+        1s);
+    FDv2StreamingSynchronizerTestPeer::MarkStarted(synchronizer);
+
+    auto mock_client = std::make_shared<MockSseClient>();
+    FDv2StreamingSynchronizerTestPeer::SetSseClient(synchronizer, mock_client);
+
+    sse::Event unknown_with_garbage("whatever", "not json");
+    FDv2StreamingSynchronizerTestPeer::OnEvent(synchronizer,
+                                               unknown_with_garbage);
+
+    EXPECT_EQ(mock_client->restart_count_, 0);
+}
+
 TEST(FDv2StreamingSynchronizerTest, MalformedJsonEventReturnsInterrupted) {
     auto logger = MakeNullLogger();
     IoContextRunner runner;