Add single host inspector state assertion over CDP

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlags.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<01feab16132bc07b79b359178e322327>>
+ * @generated SignedSource<<862c5a78fec94408ca78ef2349627a02>>
  */
 
 /**
@@ -372,6 +372,12 @@ public object ReactNativeFeatureFlags {
   @JvmStatic
   public fun fixMappingOfEventPrioritiesBetweenFabricAndReact(): Boolean = accessor.fixMappingOfEventPrioritiesBetweenFabricAndReact()
 
+  /**
+   * Enable system assertion validating that Fusebox is configured with a single host. When set, the CDP backend will dynamically disable features (Perf and Network) in the event that multiple hosts are registered (undefined behaviour), and broadcast this over `ReactNativeApplication.systemStateChanged`.
+   */
+  @JvmStatic
+  public fun fuseboxAssertSingleHostState(): Boolean = accessor.fuseboxAssertSingleHostState()
+
   /**
    * Flag determining if the React Native DevTools (Fusebox) CDP backend should be enabled in release builds. This flag is global and should not be changed across React Host lifetimes.
    */

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxAccessor.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<405bf283e4631e166cd57f5dfe30d5f9>>
+ * @generated SignedSource<<67b008ecdc29278a7019f60e24673fc1>>
  */
 
 /**
@@ -77,6 +77,7 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
   private var enableVirtualViewWindowFocusDetectionCache: Boolean? = null
   private var enableWebPerformanceAPIsByDefaultCache: Boolean? = null
   private var fixMappingOfEventPrioritiesBetweenFabricAndReactCache: Boolean? = null
+  private var fuseboxAssertSingleHostStateCache: Boolean? = null
   private var fuseboxEnabledReleaseCache: Boolean? = null
   private var fuseboxNetworkInspectionEnabledCache: Boolean? = null
   private var hideOffscreenVirtualViewsOnIOSCache: Boolean? = null
@@ -618,6 +619,15 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
     return cached
   }
 
+  override fun fuseboxAssertSingleHostState(): Boolean {
+    var cached = fuseboxAssertSingleHostStateCache
+    if (cached == null) {
+      cached = ReactNativeFeatureFlagsCxxInterop.fuseboxAssertSingleHostState()
+      fuseboxAssertSingleHostStateCache = cached
+    }
+    return cached
+  }
+
   override fun fuseboxEnabledRelease(): Boolean {
     var cached = fuseboxEnabledReleaseCache
     if (cached == null) {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxInterop.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<bffd645aa55b941acff92ca4efe6192a>>
+ * @generated SignedSource<<553d71b2c9e8e89b2e5d48723f3009b4>>
  */
 
 /**
@@ -142,6 +142,8 @@ public object ReactNativeFeatureFlagsCxxInterop {
 
   @DoNotStrip @JvmStatic public external fun fixMappingOfEventPrioritiesBetweenFabricAndReact(): Boolean
 
+  @DoNotStrip @JvmStatic public external fun fuseboxAssertSingleHostState(): Boolean
+
   @DoNotStrip @JvmStatic public external fun fuseboxEnabledRelease(): Boolean
 
   @DoNotStrip @JvmStatic public external fun fuseboxNetworkInspectionEnabled(): Boolean

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsDefaults.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<a25d191472f7777804175ef9f56521d6>>
+ * @generated SignedSource<<bf1a3a96ae311f186f7fffacc466407e>>
  */
 
 /**
@@ -137,6 +137,8 @@ public open class ReactNativeFeatureFlagsDefaults : ReactNativeFeatureFlagsProvi
 
   override fun fixMappingOfEventPrioritiesBetweenFabricAndReact(): Boolean = false
 
+  override fun fuseboxAssertSingleHostState(): Boolean = true
+
   override fun fuseboxEnabledRelease(): Boolean = false
 
   override fun fuseboxNetworkInspectionEnabled(): Boolean = false

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsLocalAccessor.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<e8531e8c374d0ea1e604a2f3d5000078>>
+ * @generated SignedSource<<7a2517498558f2c0f69831d5466ddec3>>
  */
 
 /**
@@ -81,6 +81,7 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
   private var enableVirtualViewWindowFocusDetectionCache: Boolean? = null
   private var enableWebPerformanceAPIsByDefaultCache: Boolean? = null
   private var fixMappingOfEventPrioritiesBetweenFabricAndReactCache: Boolean? = null
+  private var fuseboxAssertSingleHostStateCache: Boolean? = null
   private var fuseboxEnabledReleaseCache: Boolean? = null
   private var fuseboxNetworkInspectionEnabledCache: Boolean? = null
   private var hideOffscreenVirtualViewsOnIOSCache: Boolean? = null
@@ -679,6 +680,16 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
     return cached
   }
 
+  override fun fuseboxAssertSingleHostState(): Boolean {
+    var cached = fuseboxAssertSingleHostStateCache
+    if (cached == null) {
+      cached = currentProvider.fuseboxAssertSingleHostState()
+      accessedFeatureFlags.add("fuseboxAssertSingleHostState")
+      fuseboxAssertSingleHostStateCache = cached
+    }
+    return cached
+  }
+
   override fun fuseboxEnabledRelease(): Boolean {
     var cached = fuseboxEnabledReleaseCache
     if (cached == null) {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsProvider.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<2325f5410537941e25998ca8c59bf51d>>
+ * @generated SignedSource<<0efef5db3ded62f312486ac2fb04bcdb>>
  */
 
 /**
@@ -137,6 +137,8 @@ public interface ReactNativeFeatureFlagsProvider {
 
   @DoNotStrip public fun fixMappingOfEventPrioritiesBetweenFabricAndReact(): Boolean
 
+  @DoNotStrip public fun fuseboxAssertSingleHostState(): Boolean
+
   @DoNotStrip public fun fuseboxEnabledRelease(): Boolean
 
   @DoNotStrip public fun fuseboxNetworkInspectionEnabled(): Boolean

packages/react-native/ReactAndroid/src/main/jni/react/featureflags/JReactNativeFeatureFlagsCxxInterop.cpp

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<95ebd4929bf0f98aa059ad4b8139f7b3>>
+ * @generated SignedSource<<09f32ad880a470e45d3e5ba67a6e5831>>
  */
 
 /**
@@ -381,6 +381,12 @@ class ReactNativeFeatureFlagsJavaProvider
     return method(javaProvider_);
   }
 
+  bool fuseboxAssertSingleHostState() override {
+    static const auto method =
+        getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("fuseboxAssertSingleHostState");
+    return method(javaProvider_);
+  }
+
   bool fuseboxEnabledRelease() override {
     static const auto method =
         getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("fuseboxEnabledRelease");
@@ -832,6 +838,11 @@ bool JReactNativeFeatureFlagsCxxInterop::fixMappingOfEventPrioritiesBetweenFabri
   return ReactNativeFeatureFlags::fixMappingOfEventPrioritiesBetweenFabricAndReact();
 }
 
+bool JReactNativeFeatureFlagsCxxInterop::fuseboxAssertSingleHostState(
+    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
+  return ReactNativeFeatureFlags::fuseboxAssertSingleHostState();
+}
+
 bool JReactNativeFeatureFlagsCxxInterop::fuseboxEnabledRelease(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
   return ReactNativeFeatureFlags::fuseboxEnabledRelease();
@@ -1169,6 +1180,9 @@ void JReactNativeFeatureFlagsCxxInterop::registerNatives() {
       makeNativeMethod(
         "fixMappingOfEventPrioritiesBetweenFabricAndReact",
         JReactNativeFeatureFlagsCxxInterop::fixMappingOfEventPrioritiesBetweenFabricAndReact),
+      makeNativeMethod(
+        "fuseboxAssertSingleHostState",
+        JReactNativeFeatureFlagsCxxInterop::fuseboxAssertSingleHostState),
       makeNativeMethod(
         "fuseboxEnabledRelease",
         JReactNativeFeatureFlagsCxxInterop::fuseboxEnabledRelease),

packages/react-native/ReactAndroid/src/main/jni/react/featureflags/JReactNativeFeatureFlagsCxxInterop.h

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<155f615584a7738dc5b89205c2ecad8b>>
+ * @generated SignedSource<<414ebc294bc434bdf5f9eca094eac268>>
  */
 
 /**
@@ -201,6 +201,9 @@ class JReactNativeFeatureFlagsCxxInterop
   static bool fixMappingOfEventPrioritiesBetweenFabricAndReact(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
 
+  static bool fuseboxAssertSingleHostState(
+    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
+
   static bool fuseboxEnabledRelease(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
 

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

@@ -10,6 +10,7 @@
 
 #ifdef REACT_NATIVE_DEBUGGER_ENABLED
 #include "InspectorFlags.h"
+#include "InspectorInterfaces.h"
 #include "NetworkIOAgent.h"
 #include "SessionState.h"
 #include "TracingAgent.h"
@@ -216,6 +217,11 @@ class HostAgent::Impl final {
           cdp::jsonNotification(
               "ReactNativeApplication.metadataUpdated",
               createHostMetadataPayload(hostMetadata_)));
+      auto& inspector = getInspectorInstance();
+      bool isSingleHost = inspector.getSystemState().registeredPagesCount <= 1;
+      if (!isSingleHost) {
+        emitSystemStateChanged(isSingleHost);
+      }
 
       auto stashedTraceRecording =
           targetController_.getDelegate()
@@ -374,6 +380,17 @@ class HostAgent::Impl final {
     tracingAgent_.emitExternalTraceRecording(std::move(traceRecording));
   }
 
+  void emitSystemStateChanged(bool isSingleHost) {
+    frontendChannel_(
+        cdp::jsonNotification(
+            "ReactNativeApplication.systemStateChanged",
+            folly::dynamic::object("isSingleHost", isSingleHost)));
+
+    if (!isSingleHost) {
+      frontendChannel_(cdp::jsonNotification("Network.disable"));
+    }
+  }
+
  private:
   enum class FuseboxClientType { Unknown, Fusebox, NonFusebox };
 
@@ -480,6 +497,7 @@ class HostAgent::Impl final {
   }
   void emitExternalTraceRecording(tracing::TraceRecordingState traceRecording) {
   }
+  void emitSystemStateChanged(bool isSingleHost) {}
 };
 
 #endif // REACT_NATIVE_DEBUGGER_ENABLED
@@ -519,6 +537,10 @@ void HostAgent::emitExternalTraceRecording(
   impl_->emitExternalTraceRecording(std::move(traceRecording));
 }
 
+void HostAgent::emitSystemStateChanged(bool isSingleHost) const {
+  impl_->emitSystemStateChanged(isSingleHost);
+}
+
 #pragma mark - Tracing
 
 HostTracingAgent::HostTracingAgent(tracing::TraceRecordingState& state)

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

@@ -79,6 +79,12 @@ class HostAgent final {
    */
   void emitExternalTraceRecording(tracing::TraceRecordingState traceRecording) const;
 
+  /**
+   * Emits a system state changed event when the number of ReactHost instances
+   * changes.
+   */
+  void emitSystemStateChanged(bool isSingleHost) const;
+
  private:
   // We use the private implementation idiom to ensure this class has the same
   // layout regardless of whether REACT_NATIVE_DEBUGGER_ENABLED is defined. The

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

@@ -326,6 +326,11 @@ class JSINSPECTOR_EXPORT HostTarget : public EnableExecutorFromThis<HostTarget>
    */
   void emitTraceRecordingForFirstFuseboxClient(tracing::TraceRecordingState traceRecording) const;
 
+  /**
+   * Emits a system state changed event to all active sessions.
+   */
+  void emitSystemStateChanged(bool isSingleHost) const;
+
  private:
   /**
    * Constructs a new HostTarget.

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

@@ -17,6 +17,10 @@ InspectorFlags& InspectorFlags::getInstance() {
   return instance;
 }
 
+bool InspectorFlags::getAssertSingleHostState() const {
+  return loadFlagsAndAssertUnchanged().assertSingleHostState;
+}
+
 bool InspectorFlags::getFuseboxEnabled() const {
   if (fuseboxDisabledForTest_) {
     return false;
@@ -48,6 +52,8 @@ void InspectorFlags::dangerouslyDisableFuseboxForTest() {
 const InspectorFlags::Values& InspectorFlags::loadFlagsAndAssertUnchanged()
     const {
   InspectorFlags::Values newValues = {
+      .assertSingleHostState =
+          ReactNativeFeatureFlags::fuseboxAssertSingleHostState(),
       .fuseboxEnabled =
 #if defined(REACT_NATIVE_DEBUGGER_ENABLED)
           true,

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

@@ -19,6 +19,12 @@ class InspectorFlags {
  public:
   static InspectorFlags &getInstance();
 
+  /**
+   * Flag determining if the inspector backend should strictly assert that only
+   * a single host is registered.
+   */
+  bool getAssertSingleHostState() const;
+
   /**
    * Flag determining if the modern CDP backend should be enabled.
    */
@@ -54,6 +60,7 @@ class InspectorFlags {
 
  private:
   struct Values {
+    bool assertSingleHostState;
     bool fuseboxEnabled;
     bool isProfilingBuild;
     bool networkInspectionEnabled;