Files services library: Add an "output stream" file impl helper class.

mojo/services/files/public/cpp/output_stream_file.h

Index: mojo/services/files/public/cpp/output_stream_file.h
diff --git a/mojo/services/files/public/cpp/output_stream_file.h b/mojo/services/files/public/cpp/output_stream_file.h
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+// Copyright 2015 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.
+
+// This is a helper class for implementing a |mojo::files::File| that behaves
+// like an "output stream" ("output" from the point of view of the client --
+// i.e., the client can write/stream output to it, but not read or seek).
+
+#ifndef MOJO_SERVICES_FILES_PUBLIC_CPP_OUTPUT_STREAM_FILE_H_
+#define MOJO_SERVICES_FILES_PUBLIC_CPP_OUTPUT_STREAM_FILE_H_
+
+#include <stddef.h>
+
+#include <memory>
+
+#include "mojo/public/cpp/bindings/binding.h"
+#include "mojo/public/cpp/bindings/interface_request.h"
+#include "mojo/public/cpp/system/macros.h"
+#include "mojo/services/files/public/interfaces/file.mojom.h"
+#include "mojo/services/files/public/interfaces/types.mojom.h"
+
+namespace files_impl {
+
+class OutputStreamFile : public mojo::files::File {
+ public:
+  // The |Client| receives data written to the stream "file" as well as other
+  // notifications (e.g., of the "file" being closed). From any of the methods
+  // below, the client may choose to destroy the |OutputStreamFile|.
+  class Client {
+   public:
+    // Called when we receive data from the stream "file".
+    // TODO(vtl): Maybe add a way to throttle (e.g., for the client to not
+    // accept all the data).
+    virtual void OnDataReceived(const void* bytes, size_t num_bytes) = 0;
+
+    // Called when the stream "file" is closed, via |Close()| or due to the
+    // other end of the message pipe being closed. (This will not be called due
+    // the |OutputStreamFile| being destroyed.)
+    virtual void OnClosed() = 0;
+
+   protected:
+    virtual ~Client() {}
+  };
+
+  // Static factory method. |client| may be null, but if not it should typically
+  // outlive us (see |set_client()|).
+  static std::unique_ptr<OutputStreamFile> Create(
+      Client* client,
+      mojo::InterfaceRequest<mojo::files::File> request);
+
+  ~OutputStreamFile() override;
+
+  // Sets the client (which may be null, in which case all |Write()|s to the
+  // stream "file" will just succeed). If non-null, |client| must be valid
+  // whenever the run (a.k.a. message) loop is run, i.e., whenever a client
+  // method may be called.
+  void set_client(Client* client) { client_ = client; }
+
+ private:
+  OutputStreamFile(Client* client,
+                   mojo::InterfaceRequest<mojo::files::File> request);
+
+  // We should only be deleted by "ourself" (via the strong binding).
+  friend class mojo::Binding<mojo::files::File>;
+
+  // |mojo::files::File| implementation:
+  void Close(const CloseCallback& callback) override;
+  void Read(uint32_t num_bytes_to_read,
+            int64_t offset,
+            mojo::files::Whence whence,
+            const ReadCallback& callback) override;
+  void Write(mojo::Array<uint8_t> bytes_to_write,
+             int64_t offset,
+             mojo::files::Whence whence,
+             const WriteCallback& callback) override;
+  void ReadToStream(mojo::ScopedDataPipeProducerHandle source,
+                    int64_t offset,
+                    mojo::files::Whence whence,
+                    int64_t num_bytes_to_read,
+                    const ReadToStreamCallback& callback) override;
+  void WriteFromStream(mojo::ScopedDataPipeConsumerHandle sink,
+                       int64_t offset,
+                       mojo::files::Whence whence,
+                       const WriteFromStreamCallback& callback) override;
+  void Tell(const TellCallback& callback) override;
+  void Seek(int64_t offset,
+            mojo::files::Whence whence,
+            const SeekCallback& callback) override;
+  void Stat(const StatCallback& callback) override;
+  void Truncate(int64_t size, const TruncateCallback& callback) override;
+  void Touch(mojo::files::TimespecOrNowPtr atime,
+             mojo::files::TimespecOrNowPtr mtime,
+             const TouchCallback& callback) override;
+  void Dup(mojo::InterfaceRequest<mojo::files::File> file,
+           const DupCallback& callback) override;
+  void Reopen(mojo::InterfaceRequest<mojo::files::File> file,
+              uint32_t open_flags,
+              const ReopenCallback& callback) override;
+  void AsBuffer(const AsBufferCallback& callback) override;
+  void Ioctl(uint32_t request,
+             mojo::Array<uint32_t> in_values,
+             const IoctlCallback& callback) override;
+
+  Client* client_;
+  bool is_closed_;
+
+  mojo::Binding<mojo::files::File> binding_;
+
+  MOJO_DISALLOW_COPY_AND_ASSIGN(OutputStreamFile);
+};
+
+}  // namespace files_impl
+
+#endif  // MOJO_SERVICES_FILES_PUBLIC_CPP_OUTPUT_STREAM_FILE_H_