Add native extensions for the Dart shell to mac and windows

runtime/bin/extensions.cc

 // Copyright (c) 2012, 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 "bin/extensions.h"
+
 #include <stdio.h>
-#include <dlfcn.h>
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/globals.h"
-#include "bin/extensions.h"
 #include "bin/dartutils.h"
 
 Dart_Handle Extensions::LoadExtension(const char* extension_url,
                                       Dart_Handle parent_library) {
-  // TODO(whesse): Consider making loading extensions lazy, so the
-  // dynamic library is loaded only when first native function is called.
   ASSERT(DartUtils::IsDartExtensionSchemeURL(extension_url));
   const char* library_name =
       extension_url + strlen(DartUtils::kDartExtensionScheme);
-  if (strchr(library_name, '/') != NULL) {
+  if (strchr(library_name, '/') != NULL ||
+      strchr(library_name, '\\') != NULL) {
     return Dart_Error("path components not allowed in extension library name");
   }
-  const int buffer_length = strlen(library_name) + strlen("./lib.so") + 1;
-  char* library_path = new char[buffer_length];
-  snprintf(library_path, buffer_length, "./lib%s.so", library_name);
-
-  void* lib_handle = dlopen(library_path, RTLD_LAZY);
-  if (!lib_handle) {
-    delete[] library_path;
+  void* library_handle = LoadExtensionLibrary(library_name);
+  if (!library_handle) {
     return Dart_Error("cannot find extension library");
   }
-  // Reuse library_path buffer for intialization function name.
-  char* library_init_function = library_path;
-  snprintf(library_init_function, buffer_length, "%s_Init", library_name);
+
+  char* init_function_name = MakeString("%s_Init", library_name);
   typedef Dart_Handle (*InitFunctionType)(Dart_Handle import_map);
   InitFunctionType fn = reinterpret_cast<InitFunctionType>(
-      dlsym(lib_handle, library_init_function));
-  delete[] library_path;
-  char *error = dlerror();
-  if (error != NULL) {
-    return Dart_Error(error);
+      ResolveSymbol(library_handle, init_function_name));
+  delete[] init_function_name;
+
+  if (fn == NULL) {
+    return Dart_Error("cannot find initialization function in extension");
   }
   return (*fn)(parent_library);
 }
+
+// Returns a newly allocated string by printing name using format.
+// The string must be deleted by the caller.
+char* Extensions::MakeString(const char* format, const char* name) {
+  const int buffer_length = strlen(name) + strlen(format) + 1;
+  char* new_string = new char[buffer_length];
+  snprintf(new_string, buffer_length, format, name);
+  return new_string;
+}