Allow for no embedder provided library tag handler

runtime/vm/service.cc

 // Copyright (c) 2013, the Dart 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 file.
 
 #include "vm/service.h"
 
 #include "include/dart_api.h"
 #include "platform/globals.h"
 
 #include "vm/compiler.h"
@@ skipping 284 matching lines @@
       return entry.function;
     }
   }
   return NULL;
 }
 
 
 EmbedderServiceHandler* Service::isolate_service_handler_head_ = NULL;
 EmbedderServiceHandler* Service::root_service_handler_head_ = NULL;
 Isolate* Service::service_isolate_ = NULL;
-Dart_LibraryTagHandler Service::default_handler_ = NULL;
+Dart_LibraryTagHandler Service::embedder_provided_handler_ = NULL;
 Dart_Port Service::port_ = ILLEGAL_PORT;
 uint32_t Service::event_mask_ = 0;
 
 
 static Dart_Port ExtractPort(Dart_Handle receivePort) {
   HANDLESCOPE(Isolate::Current());
   const Object& unwrapped_rp = Object::Handle(Api::UnwrapHandle(receivePort));
   const Instance& rp = Instance::Cast(unwrapped_rp);
   // Extract RawReceivePort port id.
   if (!rp.IsReceivePort()) {
@@ skipping 94 matching lines @@
   Isolate::SetCurrent(isolate);
   {
     // Install the dart:vmservice library.
     StackZone zone(isolate);
     HANDLESCOPE(isolate);
     Library& library =
         Library::Handle(isolate, isolate->object_store()->root_library());
     // Isolate is empty.
     ASSERT(library.IsNull());
     // Grab embedder tag handler.
-    default_handler_ = isolate->library_tag_handler();
-    ASSERT(default_handler_ != NULL);
+    embedder_provided_handler_ = isolate->library_tag_handler();
     // Temporarily install our own.
     isolate->set_library_tag_handler(LibraryTagHandler);
     // Get script resource.
     const char* resource = NULL;
     const char* path = "/vmservice.dart";
     intptr_t r = Resources::ResourceLookup(path, &resource);
     ASSERT(r != Resources::kNoSuchInstance);
     ASSERT(resource != NULL);
     const String& source_str = String::Handle(
         String::FromUTF8(reinterpret_cast<const uint8_t*>(resource), r));
     ASSERT(!source_str.IsNull());
     const String& url_str = String::Handle(Symbols::DartVMService().raw());
     library ^= Library::LookupLibrary(url_str);
     ASSERT(library.IsNull());
     // Setup library.
     library = Library::New(url_str);
     library.Register();
     const Script& script = Script::Handle(
       isolate, Script::New(url_str, source_str, RawScript::kLibraryTag));
     library.SetLoadInProgress();
     Dart_EnterScope();  // Need to enter scope for tag handler.
     const Error& error = Error::Handle(isolate,
                                        Compiler::Compile(library, script));
     ASSERT(error.IsNull());
     Dart_ExitScope();
     library.SetLoaded();
     // Install embedder default library tag handler again.
-    isolate->set_library_tag_handler(default_handler_);
-    default_handler_ = NULL;
+    isolate->set_library_tag_handler(embedder_provided_handler_);
+    embedder_provided_handler_ = NULL;
     library.set_native_entry_resolver(VmServiceNativeResolver);
   }
   {
     // Boot the dart:vmservice library.
     Dart_EnterScope();
     Dart_Handle result;
     Dart_Handle url_str =
         Dart_NewStringFromCString(Symbols::Name(Symbols::kDartVMServiceId));
     Dart_Handle library = Dart_LookupLibrary(url_str);
     ASSERT(Dart_IsLibrary(library));
@@ skipping 102 matching lines @@
   if (!Dart_IsString(url)) {
     return Dart_NewApiError("url is not a string");
   }
   const char* url_string = NULL;
   Dart_Handle result = Dart_StringToCString(url, &url_string);
   if (Dart_IsError(result)) {
     return result;
   }
   if (tag == Dart_kImportTag) {
     // Embedder handles all requests for external libraries.
-    ASSERT(default_handler_ != NULL);
-    return default_handler_(tag, library, url);
+    if (embedder_provided_handler_ == NULL) {
+      return Dart_NewApiError("Unable to import module as no library tag "
+                              "handler has been provided by embedder");
+    }
+    return embedder_provided_handler_(tag, library, url);
   }
   ASSERT((tag == Dart_kSourceTag) || (tag == Dart_kCanonicalizeUrl));
   if (tag == Dart_kCanonicalizeUrl) {
     // url is already canonicalized.
     return url;
   }
   Dart_Handle source = GetSource(url_string);
   if (Dart_IsError(source)) {
     return source;
   }
@@ skipping 1796 matching lines @@
   while (current != NULL) {
     if (strcmp(name, current->name()) == 0) {
       return current;
     }
     current = current->next();
   }
   return NULL;
 }
 
 }  // namespace dart