First step towards asynchronous loading of sources

runtime/bin/builtin.dart

Index: runtime/bin/builtin.dart
===================================================================
--- runtime/bin/builtin.dart	(revision 36309)
+++ runtime/bin/builtin.dart	(working copy)
@@ -5,6 +5,7 @@
 library builtin;
 import 'dart:io';
 import 'dart:async';
+import 'dart:convert';
 // import 'root_library'; happens here from C Code
 
 // The root library (aka the script) is imported into this library. The
@@ -107,6 +108,47 @@
 }
 
 
+void _httpGet(Uri uri, loadCallback(List<int> data)) {
+  var httpClient = new HttpClient();
+  try {
+    httpClient.getUrl(uri)
+      .then((HttpClientRequest request) {
+        request.persistentConnection = false;
+        return request.close();
+      })
+      .then((HttpClientResponse response) {
+        // Only create a ByteBuilder if multiple chunks are received.
+        var builder = new BytesBuilder(copy: false);
+        response.listen(
+            builder.add,
+            onDone: () {
+              if (response.statusCode != 200) {
+                var msg = 'Failure getting $uri: '
+                          '${response.statusCode} ${response.reasonPhrase}';
+                _asyncLoadError(uri.toString(), msg);
+              }
+
+              List<int> data = builder.takeBytes();
+              httpClient.close();
+              loadCallback(data);
+            },
+            onError: (error) {
+              _asyncLoadError(uri.toString(), error);
+            });
+      })
+      .catchError((error) {
+        _asyncLoadError(uri.toString(), error);
+      });
+  } catch (error) {
+    _asyncLoadError(uri.toString(), error);
+  }
+  // TODO(floitsch): remove this line. It's just here to push an event on the
+  // event loop so that we invoke the scheduled microtasks. Also remove the
+  // import of dart:async when this line is not needed anymore.
+  Timer.run(() {});
+}
+
+
 // Are we running on Windows?
 var _isWindows = false;
 var _workingWindowsDrivePrefix;
@@ -266,6 +308,59 @@
 }
 
 
+void _loadScript(String uri, List<int> data) native "Builtin_LoadScript";
+
+void _asyncLoadError(uri, error) native "Builtin_AsyncLoadError";
+
+
+// Asynchronously loads script data (source or snapshot) through
+// an http or file uri.
+_loadDataAsync(String uri) {
+  uri = _resolveScriptUri(uri);
+  Uri sourceUri = Uri.parse(uri);
+  if (sourceUri.scheme == 'http') {
+    _httpGet(sourceUri, (data) {
+      _loadScript(uri, data);
+    });
+  } else {
+    _loadDataFromFileAsync(uri);;
+  }
+}
+
+_loadDataFromFileAsync(String uri) {
+  var sourceFile = new File(_filePathFromUri(uri));
+  sourceFile.readAsBytes().then((data) {
+    _loadScript(uri, data);//native

[Ivan Posva, 2014/05/21 22:02:07]

The comment here is unnecessary.

[hausner, 2014/05/21 23:53:08]

Left-overs. Removed.

+  },
+  onError: (e) {
+    _asyncLoadError(uri, e);
+  });
+}
+
+
+void _loadLibrarySource(tag, uri, libraryUri, text)

[Ivan Posva, 2014/05/21 22:02:07]

I am wondering why we do not unify the loading of the script source with the
rest of the library sources and only deal with List<int> as part of this
interface. Granted that you will need to invent a special "tag" such as -1 for
the script loading, but then you do not need to duplicate the loading code.

[hausner, 2014/05/21 23:53:08]

This can be done, but on the C++ side we save nothing. The price we pay is that
for every load, we'd copy the data two more times, from a dart list to a C
buffer, and then from that C buffer into a Dart string. That would mean, we copy
source code at least 4 times:

- from read buffers into a List<int>
- sending the data from service isolate to the loading isolate
- in the C callback code from dart list to external C buffer
- in the C callback code from external buffer to Dart string

Also, loading the script source is handled slightly differently in dartutils
because the URI is resolved differently. Some global state is set when resolving
the script URI that is then used to resolve library and part uris.

+    native "Builtin_LoadLibrarySource";
+
+_loadSourceAsync(int tag, String uri, String libraryUri) {
+  var filePath = _filePathFromUri(uri);
+  Uri sourceUri = Uri.parse(filePath);
+  if (sourceUri.scheme == 'http') {
+    _httpGet(sourceUri, (data) {
+      var text = UTF8.decode(data);
+      _loadLibrarySource(tag, uri, libraryUri, text);
+    });
+  } else {
+    var sourceFile = new File(filePath);
+    sourceFile.readAsString().then((text) {
+      _loadLibrarySource(tag, uri, libraryUri, text);//native

[Ivan Posva, 2014/05/21 22:02:07]

ditto.

[hausner, 2014/05/21 23:53:08]

Done.

+    },
+    onError: (e) {
+      _asyncLoadError(uri, e);
+    });
+  }
+}
+
+
 // 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.