Allow embedders to respond to platform messages from the Dart application. (#4361)

This updated the native embedder API in a non-ABI breaking way.

shell/platform/embedder/embedder.cc

@@ -55,6 +55,10 @@ class PlatformViewHolder {
   FXL_DISALLOW_COPY_AND_ASSIGN(PlatformViewHolder);
 };
 
+struct _FlutterPlatformMessageResponseHandle {
+  fxl::RefPtr<blink::PlatformMessage> message;
+};
+
 FlutterResult FlutterEngineRun(size_t version,
                                const FlutterRendererConfig* config,
                                const FlutterProjectArgs* args,
@@ -101,6 +105,25 @@ FlutterResult FlutterEngineRun(size_t version,
     return ptr(user_data);
   };
 
+  shell::PlatformViewEmbedder::PlatformMessageResponseCallback
+      platform_message_response_callback = nullptr;
+  if (SAFE_ACCESS(args, platform_message_callback, nullptr) != nullptr) {
+    platform_message_response_callback =
+        [ ptr = args->platform_message_callback,
+          user_data ](fxl::RefPtr<blink::PlatformMessage> message) {
+      auto handle = new FlutterPlatformMessageResponseHandle();
+      const FlutterPlatformMessage incoming_message = {
+          .struct_size = sizeof(FlutterPlatformMessage),
+          .channel = message->channel().c_str(),
+          .message = message->data().data(),
+          .message_size = message->data().size(),
+          .response_handle = handle,
+      };
+      handle->message = std::move(message);
+      return ptr(&incoming_message, user_data);
+    };
+  }
+
   std::string icu_data_path;
   if (SAFE_ACCESS(args, icu_data_path, nullptr) != nullptr) {
     icu_data_path = SAFE_ACCESS(args, icu_data_path, nullptr);
@@ -128,7 +151,9 @@ FlutterResult FlutterEngineRun(size_t version,
       .gl_make_current_callback = make_current,
       .gl_clear_current_callback = clear_current,
       .gl_present_callback = present,
-      .gl_fbo_callback = fbo_callback};
+      .gl_fbo_callback = fbo_callback,
+      .platform_message_response_callback = platform_message_response_callback,
+  };
 
   auto platform_view = std::make_shared<shell::PlatformViewEmbedder>(table);
   platform_view->Attach();
@@ -274,3 +299,25 @@ FlutterResult FlutterEngineSendPlatformMessage(
       });
   return kSuccess;
 }
+
+FlutterResult FlutterEngineSendPlatformMessageResponse(
+    FlutterEngine engine,
+    const FlutterPlatformMessageResponseHandle* handle,
+    const uint8_t* data,
+    size_t data_length) {
+  if (data_length != 0 && data == nullptr) {
+    return kInvalidArguments;
+  }
+
+  auto response = handle->message->response();
+
+  if (data_length == 0) {
+    response->CompleteEmpty();
+  } else {
+    response->Complete({data, data + data_length});
+  }
+
+  delete handle;
+
+  return kSuccess;
+}

shell/platform/embedder/embedder.h

@@ -50,36 +50,6 @@ typedef struct {
   };
 } FlutterRendererConfig;
 
-typedef struct {
-  // The size of this struct. Must be sizeof(FlutterProjectArgs).
-  size_t struct_size;
-  // The path to the FLX file containing project assets. The string can be
-  // collected after the call to |FlutterEngineRun| returns. The string must be
-  // NULL terminated.
-  const char* assets_path;
-  // The path to the Dart file containing the |main| entry point. The string can
-  // be collected after the call to |FlutterEngineRun| returns. The string must
-  // be NULL terminated.
-  const char* main_path;
-  // The path to the |.packages| for the project. The string can be collected
-  // after the call to |FlutterEngineRun| returns. The string must be NULL
-  // terminated.
-  const char* packages_path;
-  // The path to the icudtl.dat file for the project. The string can be
-  // collected after the call to |FlutterEngineRun| returns. The string must
-  // be NULL terminated.
-  const char* icu_data_path;
-  // The command line argument count used to initialize the project. The string
-  // can be collected after the call to |FlutterEngineRun| returns. The string
-  // must be NULL terminated.
-  int command_line_argc;
-  // The command line arguments used to initialize the project. The strings can
-  // be collected after the call to |FlutterEngineRun| returns. The strings must
-  // be NULL terminated.
-  const char* const* command_line_argv;
-
-} FlutterProjectArgs;
-
 typedef struct {
   // The size of this struct. Must be sizeof(FlutterWindowMetricsEvent).
   size_t struct_size;
@@ -107,14 +77,64 @@ typedef struct {
   double y;
 } FlutterPointerEvent;
 
+struct _FlutterPlatformMessageResponseHandle;
+typedef struct _FlutterPlatformMessageResponseHandle
+    FlutterPlatformMessageResponseHandle;
+
 typedef struct {
   // The size of this struct. Must be sizeof(FlutterPlatformMessage).
   size_t struct_size;
   const char* channel;
   const uint8_t* message;
   const size_t message_size;
+  // The response handle on which to invoke
+  // |FlutterEngineSendPlatformMessageResponse| when the response is ready. This
+  // field is ignored for messages being sent from the embedder to the
+  // framework. If the embedder ever receives a message with a non-null response
+  // handle, that handle must always be used with a
+  // |FlutterEngineSendPlatformMessageResponse| call. If not, this is a memory
+  // leak. It is not safe to send multiple responses on a single response
+  // object.
+  const FlutterPlatformMessageResponseHandle* response_handle;
 } FlutterPlatformMessage;
 
+typedef void (*FlutterPlatformMessageCallback)(
+    const FlutterPlatformMessage* /* message*/,
+    void* /* user data */);
+
+typedef struct {
+  // The size of this struct. Must be sizeof(FlutterProjectArgs).
+  size_t struct_size;
+  // The path to the FLX file containing project assets. The string can be
+  // collected after the call to |FlutterEngineRun| returns. The string must be
+  // NULL terminated.
+  const char* assets_path;
+  // The path to the Dart file containing the |main| entry point. The string can
+  // be collected after the call to |FlutterEngineRun| returns. The string must
+  // be NULL terminated.
+  const char* main_path;
+  // The path to the |.packages| for the project. The string can be collected
+  // after the call to |FlutterEngineRun| returns. The string must be NULL
+  // terminated.
+  const char* packages_path;
+  // The path to the icudtl.dat file for the project. The string can be
+  // collected after the call to |FlutterEngineRun| returns. The string must
+  // be NULL terminated.
+  const char* icu_data_path;
+  // The command line argument count used to initialize the project. The string
+  // can be collected after the call to |FlutterEngineRun| returns. The string
+  // must be NULL terminated.
+  int command_line_argc;
+  // The command line arguments used to initialize the project. The strings can
+  // be collected after the call to |FlutterEngineRun| returns. The strings must
+  // be NULL terminated.
+  const char* const* command_line_argv;
+  // The callback invoked by the engine in order to give the embedder the chance
+  // to respond to platform messages from the Dart application. The callback
+  // will be invoked on the thread on which the |FlutterEngineRun| call is made.
+  FlutterPlatformMessageCallback platform_message_callback;
+} FlutterProjectArgs;
+
 FLUTTER_EXPORT
 FlutterResult FlutterEngineRun(size_t version,
                                const FlutterRendererConfig* config,
@@ -140,6 +160,13 @@ FlutterResult FlutterEngineSendPlatformMessage(
     FlutterEngine engine,
     const FlutterPlatformMessage* message);
 
+FLUTTER_EXPORT
+FlutterResult FlutterEngineSendPlatformMessageResponse(
+    FlutterEngine engine,
+    const FlutterPlatformMessageResponseHandle* handle,
+    const uint8_t* data,
+    size_t data_length);
+
 #if defined(__cplusplus)
 }  // extern "C"
 #endif

shell/platform/embedder/platform_view_embedder.cc

@@ -47,4 +47,22 @@ void PlatformViewEmbedder::RunFromSource(const std::string& assets_directory,
   FXL_LOG(INFO) << "Hot reloading is unsupported on this platform.";
 }
 
+void PlatformViewEmbedder::HandlePlatformMessage(
+    fxl::RefPtr<blink::PlatformMessage> message) {
+  if (!message) {
+    return;
+  }
+
+  if (!message->response()) {
+    return;
+  }
+
+  if (dispatch_table_.platform_message_response_callback == nullptr) {
+    message->response()->CompleteEmpty();
+    return;
+  }
+
+  dispatch_table_.platform_message_response_callback(std::move(message));
+}
+
 }  // namespace shell

shell/platform/embedder/platform_view_embedder.h

@@ -7,17 +7,22 @@
 
 #include "flutter/shell/common/platform_view.h"
 #include "flutter/shell/gpu/gpu_surface_gl.h"
+#include "flutter/shell/platform/embedder/embedder.h"
 #include "lib/fxl/macros.h"
 
 namespace shell {
 
 class PlatformViewEmbedder : public PlatformView, public GPUSurfaceGLDelegate {
  public:
+  using PlatformMessageResponseCallback =
+      std::function<void(fxl::RefPtr<blink::PlatformMessage>)>;
   struct DispatchTable {
-    std::function<bool(void)> gl_make_current_callback;
-    std::function<bool(void)> gl_clear_current_callback;
-    std::function<bool(void)> gl_present_callback;
-    std::function<intptr_t(void)> gl_fbo_callback;
+    std::function<bool(void)> gl_make_current_callback;   // required
+    std::function<bool(void)> gl_clear_current_callback;  // required
+    std::function<bool(void)> gl_present_callback;        // required
+    std::function<intptr_t(void)> gl_fbo_callback;        // required
+    PlatformMessageResponseCallback
+        platform_message_response_callback;  // optional
   };
 
   PlatformViewEmbedder(DispatchTable dispatch_table);
@@ -47,6 +52,10 @@ class PlatformViewEmbedder : public PlatformView, public GPUSurfaceGLDelegate {
                      const std::string& main,
                      const std::string& packages) override;
 
+  // |shell::PlatformView|
+  void HandlePlatformMessage(
+      fxl::RefPtr<blink::PlatformMessage> message) override;
+
  private:
   DispatchTable dispatch_table_;