Make Directory.list pull-based, making it possible to pause, resume and cancel directory listing.

sdk/lib/io/directory_impl.dart

Index: sdk/lib/io/directory_impl.dart
diff --git a/sdk/lib/io/directory_impl.dart b/sdk/lib/io/directory_impl.dart
index cdb6df479a6914240df87f22c7736de07ca9bb02..f63ab8593ce574a03702c966f9f0b2b9783a0603 100644
--- a/sdk/lib/io/directory_impl.dart
+++ b/sdk/lib/io/directory_impl.dart
@@ -9,8 +9,10 @@ class _Directory implements Directory {
   static const DELETE_REQUEST = 1;
   static const EXISTS_REQUEST = 2;
   static const CREATE_TEMP_REQUEST = 3;
-  static const LIST_REQUEST = 4;
-  static const RENAME_REQUEST = 5;
+  static const LIST_START_REQUEST = 4;
+  static const LIST_NEXT_REQUEST = 5;
+  static const LIST_STOP_REQUEST = 6;
+  static const RENAME_REQUEST = 7;
 
   _Directory(String this._path);
   _Directory.fromPath(Path path) : this(path.toNativePath());
@@ -251,55 +253,113 @@ class _Directory implements Directory {
     const int RESPONSE_COMPLETE = 1;
     const int RESPONSE_ERROR = 2;
 
-    var controller = new StreamController<FileSystemEntity>(sync: true);
-
-    List request = [ _Directory.LIST_REQUEST, path, recursive, followLinks ];
-    ReceivePort responsePort = new ReceivePort();
-    // Use a separate directory service port for each listing as
-    // listing operations on the same directory can run in parallel.
-    _Directory._newServicePort().send(request, responsePort.toSendPort());
-    responsePort.receive((message, replyTo) {
-      if (message is !List || message[RESPONSE_TYPE] is !int) {
-        responsePort.close();
-        controller.addError(new DirectoryException("Internal error"));
+    int id;
+
+    Function next;
+    Function close;
+
+    void onResume() {
+      if (id != null) next();
+    }
+
+    bool nextRunning = false;
+    bool canceled = false;
+
+    void onCancel() {
+      canceled = true;
+      // If we are active, but not requesting, close.
+      if (id != null && !nextRunning) {
+        close();
+      }
+    }
+
+    var controller = new StreamController<FileSystemEntity>(sync: true,
+                                                            onResume: onResume,
+                                                            onCancel: onCancel);
+
+    bool closed = false;
+    close = () {
+      if (closed) return;
+      closed = true;
+      _Directory._newServicePort().call([_Directory.LIST_STOP_REQUEST, id])
+          .then((_) {
+            controller.close();
+          });
+    };
+
+    void error(message) {
+      var errorType =
+          message[RESPONSE_ERROR][_ERROR_RESPONSE_ERROR_TYPE];
+      if (errorType == _ILLEGAL_ARGUMENT_RESPONSE) {
+        controller.addError(new ArgumentError());
+      } else if (errorType == _OSERROR_RESPONSE) {
+        var responseError = message[RESPONSE_ERROR];
+        var err = new OSError(
+            responseError[_OSERROR_RESPONSE_MESSAGE],
+            responseError[_OSERROR_RESPONSE_ERROR_CODE]);
+        var errorPath = message[RESPONSE_PATH];
+        if (errorPath == null) errorPath = path;
+        controller.addError(
+            new DirectoryException("Directory listing failed",
+                                   errorPath,
+                                   err));
+      } else {
+        controller.addError(
+            new DirectoryException("Internal error"));
+      }
+    }
+
+    next = () {
+      if (canceled) {
+        close();
         return;
       }
-      switch (message[RESPONSE_TYPE]) {
-        case LIST_FILE:
-          controller.add(new File(message[RESPONSE_PATH]));
-          break;
-        case LIST_DIRECTORY:
-          controller.add(new Directory(message[RESPONSE_PATH]));
-          break;
-        case LIST_LINK:
-          controller.add(new Link(message[RESPONSE_PATH]));
-          break;
-        case LIST_ERROR:
-          var errorType =
-              message[RESPONSE_ERROR][_ERROR_RESPONSE_ERROR_TYPE];
-          if (errorType == _ILLEGAL_ARGUMENT_RESPONSE) {
-            controller.addError(new ArgumentError());
-          } else if (errorType == _OSERROR_RESPONSE) {
-            var responseError = message[RESPONSE_ERROR];
-            var err = new OSError(
-                responseError[_OSERROR_RESPONSE_MESSAGE],
-                responseError[_OSERROR_RESPONSE_ERROR_CODE]);
-            var errorPath = message[RESPONSE_PATH];
-            if (errorPath == null) errorPath = path;
-            controller.addError(
-                new DirectoryException("Directory listing failed",
-                                         errorPath,
-                                         err));
+      if (nextRunning) return;
+      nextRunning = true;
+      _Directory._newServicePort().call([_Directory.LIST_NEXT_REQUEST, id])
+          .then((result) {
+            if (result is List) {
+              for (var message in result) {
+                if (message == null) break;
+                switch (message[RESPONSE_TYPE]) {
+                  case LIST_FILE:
+                    controller.add(new File(message[RESPONSE_PATH]));
+                    break;
+                  case LIST_DIRECTORY:
+                    controller.add(new Directory(message[RESPONSE_PATH]));
+                    break;
+                  case LIST_LINK:
+                    controller.add(new Link(message[RESPONSE_PATH]));
+                    break;
+                  case LIST_ERROR:
+                    error(message);
+                    break;
+                  case LIST_DONE:
+                    close();
+                    return;
+                }
+              }
+            } else {
+              controller.addError(new DirectoryException("Internal error"));
+            }
+            nextRunning = false;
+            if (!controller.isPaused) {
+              next();
+            }
+          });
+    };
+
+    var request = [_Directory.LIST_START_REQUEST, path, recursive, followLinks];
+    _Directory._newServicePort().call(request)
+        .then((response) {
+          if (response is int) {
+            id = response;
+            next();
           } else {
-            controller.addError(new DirectoryException("Internal error"));
+            error(response);
+            controller.close();
           }
-          break;
-        case LIST_DONE:
-          responsePort.close();
-          controller.close();
-          break;
-      }
-    });
+        });
 
     return controller.stream;
   }