Add native extensions for the Dart shell to the MacOs platform

runtime/bin/extensions_macos.cc

Index: runtime/bin/extensions_macos.cc
diff --git a/runtime/bin/extensions_macos.cc b/runtime/bin/extensions_macos.cc
index d81e670eef10218fe7bc68228faa4d0d88a9083c..6013404e42d1fa72c934bd0f8b932af1b0b411e9 100644
--- a/runtime/bin/extensions_macos.cc
+++ b/runtime/bin/extensions_macos.cc
@@ -2,13 +2,44 @@
 // 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) {
-  UNIMPLEMENTED();
-  return NULL;
+  // 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) {
+    return Dart_Error("path components not allowed in extension library name");
+  }
+  const int buffer_length = strlen(library_name) + strlen("./.bundle") + 1;
+  char* library_path = new char[buffer_length];
+  snprintf(library_path, buffer_length, "./%s.bundle", library_name);
+
+  void* lib_handle = dlopen(library_path, RTLD_LAZY);
+  if (!lib_handle) {
+    delete[] library_path;
+    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);
+  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);
+  }
+  return (*fn)(parent_library);

[siva, 2012/03/07 00:14:49]

The API could be factored as:

void* Extensions::LoadLibrary(const char* extension_name);
void* Extensions::ResolveSymbol(void* library_handle, const char* name, char**
error);

Then only the implementation of these functions would be platform specific and
the rest of the code could be in a generic file.

 }