Allow ConnectFunc to reject connections by returning nullptr (#42387)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/42387

Changelog: [Internal]

Documents that it's legal for a Page's connection function to return null, and adds new logic to `InspectorPackagerConnection` (NOTE: to the C++ implementation *only*) to handle this case without crashing.

The legacy RN CDP backend (`ConnectionDemux`) has a case similar to this that causes crashes depending on the timing of connection requests.

Reviewed By: cortinico

Differential Revision: D52905490

fbshipit-source-id: 2102adc859d1509647a31f92737a1e164781fadf

packages/react-native/ReactCommon/jsinspector-modern/InspectorInterfaces.h

@@ -93,7 +93,15 @@ class JSINSPECTOR_EXPORT IInspector : public IDestructible {
 
   virtual ~IInspector() = 0;
 
-  /// addPage is called by the VM to add a page to the list of debuggable pages.
+  /**
+   * Add a page to the list of inspectable pages.
+   * Callers are responsible for calling removePage when the page is no longer
+   * expecting connections.
+   * \param connectFunc a function that will be called to establish a
+   * connection. \c connectFunc may return nullptr to reject the connection
+   * (e.g. if the page is in the process of shutting down).
+   * \returns the ID assigned to the new page.
+   */
   virtual int addPage(
       const std::string& title,
       const std::string& vm,
@@ -107,8 +115,12 @@ class JSINSPECTOR_EXPORT IInspector : public IDestructible {
   /// getPages is called by the client to list all debuggable pages.
   virtual std::vector<InspectorPageDescription> getPages() const = 0;
 
-  /// connect is called by the client to initiate a debugging session on the
-  /// given page.
+  /**
+   * Called by InspectorPackagerConnection to initiate a debugging session with
+   * the given page.
+   * \returns an ILocalConnection that can be used to send messages to the
+   * page, or nullptr if the connection has been rejected.
+   */
   virtual std::unique_ptr<ILocalConnection> connect(
       int pageId,
       std::unique_ptr<IRemoteConnection> remote) = 0;

packages/react-native/ReactCommon/jsinspector-modern/InspectorPackagerConnection.cpp

@@ -101,6 +101,16 @@ void InspectorPackagerConnection::Impl::handleConnect(
   auto& inspector = getInspectorInstance();
   auto inspectorConnection =
       inspector.connect(pageIdInt, std::move(remoteConnection));
+  if (!inspectorConnection) {
+    LOG(INFO) << "Connection to page " << pageId << " rejected";
+
+    // RemoteConnection::onDisconnect(), if the connection even calls it,  will
+    // be a no op (because the session is not added to `inspectorSessions_`), so
+    // let's always notify the remote client of the disconnection ourselves.
+    sendToPackager(folly::dynamic::object("event", "disconnect")(
+        "payload", folly::dynamic::object("pageId", pageId)));
+    return;
+  }
   inspectorSessions_.emplace(
       pageId,
       Session{

packages/react-native/ReactCommon/jsinspector-modern/tests/InspectorPackagerConnectionTest.cpp

@@ -1196,4 +1196,144 @@ TEST_F(
   EXPECT_CALL(*localConnections_[1], disconnect()).RetiresOnSaturation();
   getInspectorInstance().removePage(pageId);
 }
+
+TEST_F(InspectorPackagerConnectionTest, TestRejectedPageConnection) {
+  // Configure gmock to expect calls in a specific order.
+  InSequence mockCallsMustBeInSequence;
+
+  enum {
+    Accept,
+    RejectSilently,
+    RejectWithDisconnect
+  } mockNextConnectionBehavior;
+
+  auto pageId = getInspectorInstance().addPage(
+      "mock-title",
+      "mock-vm",
+      [&mockNextConnectionBehavior,
+       this](auto remoteConnection) -> std::unique_ptr<ILocalConnection> {
+        switch (mockNextConnectionBehavior) {
+          case Accept:
+            return localConnections_.make_unique(std::move(remoteConnection));
+          case RejectSilently:
+            return nullptr;
+          case RejectWithDisconnect:
+            remoteConnection->onDisconnect();
+            return nullptr;
+        }
+      });
+
+  packagerConnection_->connect();
+
+  ASSERT_TRUE(webSockets_[0]);
+
+  // Reject the connection by returning nullptr.
+  mockNextConnectionBehavior = RejectSilently;
+
+  EXPECT_CALL(
+      *webSockets_[0],
+      send(JsonParsed(AllOf(
+          AtJsonPtr("/event", Eq("disconnect")),
+          AtJsonPtr("/payload/pageId", Eq(std::to_string(pageId)))))))
+      .RetiresOnSaturation();
+
+  webSockets_[0]->getDelegate().didReceiveMessage(sformat(
+      R"({{
+          "event": "connect",
+          "payload": {{
+            "pageId": {0}
+          }}
+        }})",
+      toJson(std::to_string(pageId))));
+
+  webSockets_[0]->getDelegate().didReceiveMessage(sformat(
+      R"({{
+          "event": "wrappedEvent",
+          "payload": {{
+            "pageId": {0},
+            "wrappedEvent": {1}
+          }}
+        }})",
+      toJson(std::to_string(pageId)),
+      toJson(R"({
+                "method": "FakeDomain.fakeMethod",
+                "id": 1,
+                "params": ["arg1", "arg2"]
+              })")));
+
+  // Reject the connection by explicitly calling onDisconnect(), then returning
+  // nullptr.
+  mockNextConnectionBehavior = RejectWithDisconnect;
+
+  EXPECT_CALL(
+      *webSockets_[0],
+      send(JsonParsed(AllOf(
+          AtJsonPtr("/event", Eq("disconnect")),
+          AtJsonPtr("/payload/pageId", Eq(std::to_string(pageId)))))))
+      .RetiresOnSaturation();
+
+  webSockets_[0]->getDelegate().didReceiveMessage(sformat(
+      R"({{
+          "event": "connect",
+          "payload": {{
+            "pageId": {0}
+          }}
+        }})",
+      toJson(std::to_string(pageId))));
+
+  webSockets_[0]->getDelegate().didReceiveMessage(sformat(
+      R"({{
+          "event": "wrappedEvent",
+          "payload": {{
+            "pageId": {0},
+            "wrappedEvent": {1}
+          }}
+        }})",
+      toJson(std::to_string(pageId)),
+      toJson(R"({
+                "method": "FakeDomain.fakeMethod",
+                "id": 2,
+                "params": ["arg1", "arg2"]
+              })")));
+
+  // Accept a connection after previously rejecting connections to the same
+  // page.
+  mockNextConnectionBehavior = Accept;
+
+  webSockets_[0]->getDelegate().didReceiveMessage(sformat(
+      R"({{
+          "event": "connect",
+          "payload": {{
+            "pageId": {0}
+          }}
+        }})",
+      toJson(std::to_string(pageId))));
+
+  EXPECT_CALL(
+      *localConnections_[0],
+      sendMessage(JsonParsed(AllOf(
+          AtJsonPtr("/method", Eq("FakeDomain.fakeMethod")),
+          AtJsonPtr("/id", Eq(3)),
+          AtJsonPtr("/params", ElementsAre("arg1", "arg2"))))))
+      .RetiresOnSaturation();
+
+  webSockets_[0]->getDelegate().didReceiveMessage(sformat(
+      R"({{
+          "event": "wrappedEvent",
+          "payload": {{
+            "pageId": {0},
+            "wrappedEvent": {1}
+          }}
+        }})",
+      toJson(std::to_string(pageId)),
+      toJson(R"({
+                "method": "FakeDomain.fakeMethod",
+                "id": 3,
+                "params": ["arg1", "arg2"]
+              })")));
+
+  EXPECT_CALL(*localConnections_[0], disconnect()).RetiresOnSaturation();
+  getInspectorInstance().removePage(pageId);
+}
+
 } // namespace facebook::react::jsinspector_modern