Re-land "Extend the mDNS package with a native extension used on Mac OS"

src/pkg/mdns/mdns_extension.cc

+// Copyright (c) 2015, the Fletch project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "include/dart_api.h"
+#include "include/dart_native_api.h"
+
+#include "mdns_extension.h"
+
+// Handle request send on the service port.
+void HandleRequest(Dart_Port port_id, Dart_CObject* message) {
+  // Messages are expected to be three item lists:
+  //  [0]: reply port
+  //  [1]: request type
+  //  [2]: request argument
+  if (message->type == Dart_CObject_kArray &&
+      message->value.as_array.length == 3) {
+    Dart_CObject* reply_port = message->value.as_array.values[0];
+    Dart_CObject* request_type = message->value.as_array.values[1];
+    Dart_CObject* argument = message->value.as_array.values[2];
+    if (reply_port->type == Dart_CObject_kSendPort) {
+      if (request_type->type == Dart_CObject_kInt32) {
+        switch (request_type->value.as_int32) {
+          case kEchoRequest:
+            HandleEcho(reply_port->value.as_send_port.id, argument);
+            return;
+
+          case kLookupRequest:
+            HandleLookup(reply_port->value.as_send_port.id,
+                         argument->value.as_string);
+            return;
+
+          default:
+            break;
+            // Ignore invalid requests.
+        }
+      }
+      Dart_CObject result;
+      result.type = Dart_CObject_kNull;
+      Dart_PostCObject(reply_port->value.as_send_port.id, &result);
+    }
+  }
+}
+
+// Handler for the echo request. Used for testing that the native extension
+// can be loaded and called.
+void HandleEcho(Dart_Port reply_port, Dart_CObject* argument) {
+  Dart_PostCObject(reply_port, argument);
+}
+
+
+Dart_Handle HandleError(Dart_Handle handle) {
+  if (Dart_IsError(handle)) Dart_PropagateError(handle);
+  return handle;
+}
+
+
+// Initialize a native port with a request handler.
+void ServicePort(Dart_NativeArguments arguments) {
+  Dart_SetReturnValue(arguments, Dart_Null());
+  Dart_Port service_port =
+      Dart_NewNativePort("MDnsService", HandleRequest, true);
+  if (service_port != ILLEGAL_PORT) {
+    Dart_Handle send_port = Dart_NewSendPort(service_port);
+    Dart_SetReturnValue(arguments, send_port);
+  }
+}
+
+
+// Resolver for the extension library.
+Dart_NativeFunction ResolveName(Dart_Handle name,
+                                int argc,
+                                bool* auto_setup_scope) {
+  const char* c_name;
+  Dart_Handle check_error;
+
+  check_error = Dart_StringToCString(name, &c_name);
+  if (Dart_IsError(check_error)) {
+    Dart_PropagateError(check_error);
+  }
+  if ((strcmp("MDnsExtension_ServicePort", c_name) == 0) && (argc == 0)) {
+    return ServicePort;
+  }
+  return NULL;
+}
+
+
+// Entry point for the extension library.
+DART_EXPORT Dart_Handle mdns_extension_lib_Init(Dart_Handle parent_library) {
+  Dart_Handle result_code;
+  if (Dart_IsError(parent_library)) {
+    return parent_library;
+  }
+
+  result_code = Dart_SetNativeResolver(parent_library, ResolveName, NULL);
+  if (Dart_IsError(result_code)) {
+    return result_code;
+  }
+
+  return parent_library;
+}