Send custom CDP Event to Frontend to prepare for displaying a trace

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

@@ -41,14 +41,18 @@ class HostAgent::Impl final {
       HostTargetController& targetController,
       HostTargetMetadata hostMetadata,
       SessionState& sessionState,
-      VoidExecutor executor)
+      VoidExecutor executor,
+      std::optional<tracing::TraceRecordingState> traceRecordingToEmit)
       : frontendChannel_(frontendChannel),
         targetController_(targetController),
         hostMetadata_(std::move(hostMetadata)),
         sessionState_(sessionState),
         networkIOAgent_(NetworkIOAgent(frontendChannel, std::move(executor))),
-        tracingAgent_(
-            TracingAgent(frontendChannel, sessionState, targetController)) {}
+        tracingAgent_(TracingAgent(
+            frontendChannel,
+            sessionState,
+            targetController,
+            std::move(traceRecordingToEmit))) {}
 
   ~Impl() {
     if (isPausedInDebuggerOverlayVisible_) {
@@ -428,7 +432,8 @@ class HostAgent::Impl final {
       HostTargetController& targetController,
       HostTargetMetadata hostMetadata,
       SessionState& sessionState,
-      VoidExecutor executor) {}
+      VoidExecutor executor,
+      std::optional<tracing::TraceRecordingState> traceRecordingToEmit) {}
 
   void handleRequest(const cdp::PreparsedRequest& req) {}
   void setCurrentInstanceAgent(std::shared_ptr<InstanceAgent> agent) {}
@@ -441,14 +446,16 @@ HostAgent::HostAgent(
     HostTargetController& targetController,
     HostTargetMetadata hostMetadata,
     SessionState& sessionState,
-    VoidExecutor executor)
+    VoidExecutor executor,
+    std::optional<tracing::TraceRecordingState> traceRecordingToEmit)
     : impl_(std::make_unique<Impl>(
           *this,
           frontendChannel,
           targetController,
           std::move(hostMetadata),
           sessionState,
-          std::move(executor))) {}
+          std::move(executor),
+          std::move(traceRecordingToEmit))) {}
 
 HostAgent::~HostAgent() = default;
 

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

@@ -36,13 +36,16 @@ class HostAgent final {
    * \param hostMetadata Metadata about the host that created this agent.
    * \param sessionState The state of the session that created this agent.
    * \param executor A void executor to be used by async-aware handlers.
+   * \param traceRecordingToEmit If set, this is the trace that Host has
+   * requested to display in the Frontend.
    */
   HostAgent(
       const FrontendChannel& frontendChannel,
       HostTargetController& targetController,
       HostTargetMetadata hostMetadata,
       SessionState& sessionState,
-      VoidExecutor executor);
+      VoidExecutor executor,
+      std::optional<tracing::TraceRecordingState> traceRecordingToEmit);
 
   HostAgent(const HostAgent&) = delete;
   HostAgent(HostAgent&&) = delete;

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

@@ -34,7 +34,8 @@ class HostTargetSession {
       std::unique_ptr<IRemoteConnection> remote,
       HostTargetController& targetController,
       HostTargetMetadata hostMetadata,
-      VoidExecutor executor)
+      VoidExecutor executor,
+      std::optional<tracing::TraceRecordingState> traceRecordingToEmit)
       : remote_(std::make_shared<RAIIRemoteConnection>(std::move(remote))),
         frontendChannel_(
             [remoteWeak = std::weak_ptr(remote_)](std::string_view message) {
@@ -47,7 +48,8 @@ class HostTargetSession {
             targetController,
             std::move(hostMetadata),
             state_,
-            std::move(executor)) {}
+            std::move(executor),
+            std::move(traceRecordingToEmit)) {}
 
   /**
    * Called by CallbackLocalConnection to send a message to this Session's
@@ -206,7 +208,8 @@ std::unique_ptr<ILocalConnection> HostTarget::connect(
       std::move(connectionToFrontend),
       controller_,
       delegate_.getMetadata(),
-      makeVoidExecutor(executorFromThis()));
+      makeVoidExecutor(executorFromThis()),
+      delegate_.unstable_getTraceRecordingThatWillBeEmittedOnInitialization());
   session->setCurrentInstance(currentInstance_.get());
   sessions_.insert(std::weak_ptr(session));
   return std::make_unique<CallbackLocalConnection>(

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

@@ -146,6 +146,19 @@ class HostTargetDelegate : public LoadNetworkResourceDelegate {
     throw NotImplementedException(
         "LoadNetworkResourceDelegate.loadNetworkResource is not implemented by this host target delegate.");
   }
+
+  /**
+   * [Experimental] Will be called at the CDP session initialization to get the
+   * trace recording that may have been stashed by the Host from the previous
+   * background session.
+   *
+   * \return the trace recording state if there is one that needs to be
+   * displayed, otherwise std::nullopt.
+   */
+  virtual std::optional<tracing::TraceRecordingState>
+  unstable_getTraceRecordingThatWillBeEmittedOnInitialization() {
+    return std::nullopt;
+  }
 };
 
 /**

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

@@ -38,10 +38,17 @@ const uint16_t PROFILE_TRACE_EVENT_CHUNK_SIZE = 1;
 TracingAgent::TracingAgent(
     FrontendChannel frontendChannel,
     SessionState& sessionState,
-    HostTargetController& hostTargetController)
+    HostTargetController& hostTargetController,
+    std::optional<tracing::TraceRecordingState> traceRecordingToEmit)
     : frontendChannel_(std::move(frontendChannel)),
       sessionState_(sessionState),
-      hostTargetController_(hostTargetController) {}
+      hostTargetController_(hostTargetController) {
+  if (traceRecordingToEmit.has_value()) {
+    frontendChannel_(
+        cdp::jsonNotification("ReactNativeApplication.traceRequested"));
+    emitTraceRecording(std::move(traceRecordingToEmit.value()));
+  }
+}
 
 TracingAgent::~TracingAgent() {
   // Agents are owned by the session. If the agent is destroyed, it means that
@@ -86,25 +93,29 @@ bool TracingAgent::handleRequest(const cdp::PreparsedRequest& req) {
     // Send response to Tracing.end request.
     frontendChannel_(cdp::jsonResult(req.id));
 
-    auto dataCollectedCallback = [this](folly::dynamic&& eventsChunk) {
-      frontendChannel_(cdp::jsonNotification(
-          "Tracing.dataCollected",
-          folly::dynamic::object("value", std::move(eventsChunk))));
-    };
-    tracing::TraceRecordingStateSerializer::emitAsDataCollectedChunks(
-        std::move(state),
-        dataCollectedCallback,
-        TRACE_EVENT_CHUNK_SIZE,
-        PROFILE_TRACE_EVENT_CHUNK_SIZE);
-
-    frontendChannel_(cdp::jsonNotification(
-        "Tracing.tracingComplete",
-        folly::dynamic::object("dataLossOccurred", false)));
-
+    emitTraceRecording(std::move(state));
     return true;
   }
 
   return false;
 }
 
+void TracingAgent::emitTraceRecording(
+    tracing::TraceRecordingState state) const {
+  auto dataCollectedCallback = [this](folly::dynamic&& eventsChunk) {
+    frontendChannel_(cdp::jsonNotification(
+        "Tracing.dataCollected",
+        folly::dynamic::object("value", std::move(eventsChunk))));
+  };
+  tracing::TraceRecordingStateSerializer::emitAsDataCollectedChunks(
+      std::move(state),
+      dataCollectedCallback,
+      TRACE_EVENT_CHUNK_SIZE,
+      PROFILE_TRACE_EVENT_CHUNK_SIZE);
+
+  frontendChannel_(cdp::jsonNotification(
+      "Tracing.tracingComplete",
+      folly::dynamic::object("dataLossOccurred", false)));
+}
+
 } // namespace facebook::react::jsinspector_modern

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

@@ -24,11 +24,18 @@ class TracingAgent {
   /**
    * \param frontendChannel A channel used to send responses to the
    * frontend.
+   * \param sessionState The state of the session that created this agent.
+   * \param hostTargetController An interface to the HostTarget that this agent
+   * is attached to. The caller is responsible for ensuring that the
+   * HostTargetDelegate and underlying HostTarget both outlive the agent.
+   * \param traceRecordingToEmit If set, this is the trace that Host has
+   * requested to display in the Frontend.
    */
   TracingAgent(
       FrontendChannel frontendChannel,
       SessionState& sessionState,
-      HostTargetController& hostTargetController);
+      HostTargetController& hostTargetController,
+      std::optional<tracing::TraceRecordingState> traceRecordingToEmit);
 
   ~TracingAgent();
 
@@ -48,6 +55,12 @@ class TracingAgent {
   SessionState& sessionState_;
 
   HostTargetController& hostTargetController_;
+
+  /**
+   * Emits the captured Trace Recording state in a series of
+   * Tracing.dataCollected events, followed by a Tracing.tracingComplete event.
+   */
+  void emitTraceRecording(tracing::TraceRecordingState state) const;
 };
 
 } // namespace facebook::react::jsinspector_modern