Refactor native extension shared library lookup.

runtime/bin/builtin.dart

Index: runtime/bin/builtin.dart
diff --git a/runtime/bin/builtin.dart b/runtime/bin/builtin.dart
index 2a9bd3014d886ff412086023c815603b12b94c01..70abc70fbe3b613c72cff6db54fbcf7ccba32fc0 100644
--- a/runtime/bin/builtin.dart
+++ b/runtime/bin/builtin.dart
@@ -221,9 +221,6 @@ String _resolveUri(String base, String userString) {
 
 // Returns either a file path or a URI starting with http:, as a String.
 String _filePathFromUri(String userUri) {
-  if (userUri.startsWith(_DART_EXT)) {
-    userUri = userUri.substring(_DART_EXT.length);
-  }
   var uri = Uri.parse(userUri);
   _logResolution('# Getting file path from: $uri');
 
@@ -262,3 +259,50 @@ String _filePathFromPackageUri(Uri uri) {
                     _packageRoot;
   return _filePathFromUri(packageRoot.resolve(uri.path).toString());
 }
+
+
+// Returns the directory part, the filename part, and the name
+// of a native extension URL as a list [directory, filename, name].
+// The directory part is either a file system path or an HTTP(S) URL.
+// The filename part is the extension name, with the platform-dependent
+// prefixes and extensions added.
+String _extensionPathFromUri(String userUri) {

[Ivan Posva, 2014/03/04 20:03:56]

Please remove the types in this file. They will only serve the purpose of
causing checked mode failures as can be seen here where we are returning a List
but the function is typed to return a String.

+  if (!userUri.startsWith(_DART_EXT)) {
+    throw 'Unexpected internal error: Extension URI $userUri missing dart-ext:';
+  }
+  userUri = userUri.substring(_DART_EXT.length);
+
+  if (userUri.contains('\\')) {
+    throw 'Unexpected internal error: Extension URI $userUri contains \\';
+  }
+
+  String filename;
+  String name;
+  String path;  // Will end in '/'.
+  int index = userUri.lastIndexOf('/');
+  if (index == -1) {
+    name = userUri;
+    path = './';
+  } else if (index == userUri.length - 1) {
+    throw 'Extension name missing in $extensionUri';
+  } else {
+    name = userUri.substring(index + 1);
+    path = userUri.substring(0, index + 1);
+  }
+
+  path = _filePathFromUri(path);
+
+  if (Platform.isLinux || Platform.isAndroid) {
+    filename = 'lib$name.so';

[Ivan Posva, 2014/03/04 20:03:56]

We will also have to have a plan to deal with different OS and architecture
combinations being served from the same location.

This didn't use to be as much of an issue as the extensions were only available
locally.

+  } else if (Platform.isMacOS) {
+    filename = 'lib$name.dylib';
+  } else if (Platform.isWindows) {
+    filename = '$name.dll';
+  } else {
+    _logResolution(
+        'Native extensions not supported on ${Platform.operatingSystem}');
+    throw 'Native extensions not supported on ${Platform.operatingSystem}';
+  }
+
+  return [path, filename, name];
+}