Mojo JS bindings: draining a DataPipe

mojo/bindings/js/drain_data.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MOJO_BINDINGS_JS_DRAIN_DATA_H_
+#define MOJO_BINDINGS_JS_DRAIN_DATA_H_
+
+#include "base/memory/scoped_vector.h"
+#include "gin/runner.h"
+#include "mojo/public/c/environment/async_waiter.h"
+#include "mojo/public/cpp/system/core.h"
+#include "v8/include/v8.h"
+
+namespace mojo {
+namespace js {
+
+// This class is the implementation of the Mojo JavaScript core module's
+// drainData() method. It is not intended to be used directly. The caller
+// allocates a DrainData on the heap and returns GetPromise() to JS. The
+// implementation deletes itself after reading as much data as possible
+// and rejecting or resolving the Promise.
+
+class DrainData {
+ public:
+  // Starts waiting for data on the specified data pipe consumer handle.
+  // See WaitForData(). The constructor does not block.
+  DrainData(v8::Isolate* isolate, mojo::Handle handle);
+
+  // Returns a Promise that will be settled when no more data can be read.
+  // Should be called just once on a newly allocated DrainData object.
+  v8::Handle<v8::Value> GetPromise();
+
+ private:
+  ~DrainData();
+
+  // Registers an "async waiter" that calls DataReady() via WaitCompleted().
+  void WaitForData();
+  static void WaitCompleted(void* self, MojoResult result) {
+    static_cast<DrainData*>(self)->DataReady(result);
+  }
+
+  // Use ReadData() to read whatever is availble now on handle_ and save
+  // it in data_buffers_.
+  void DataReady(MojoResult result);
+  MojoResult ReadData();
+
+  // When the remote data pipe handle is closed, or an error occurs, deliver
+  // all of the buffered data to the JS Promise and then delete this.
+  void DeliverData(MojoResult result);
+
+  typedef std::vector<char> DataBuffer;
+
+  v8::Isolate* isolate_;
+  ScopedDataPipeConsumerHandle handle_;
+  MojoAsyncWaitID wait_id_;
+  base::WeakPtr<gin::Runner> runner_;
+  v8::UniquePersistent<v8::Promise::Resolver> resolver_;
+  ScopedVector<DataBuffer> data_buffers_;
+};
+
+}  // namespace js
+}  // namespace mojo
+
+#endif  // MOJO_BINDINGS_JS_DRAIN_DATA_H_