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

apps/moterm/moterm_driver.cc

 // 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.
 
 #include "apps/moterm/moterm_driver.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/logging.h"
@@ skipping 169 matching lines @@
   client_->OnDataReceived(translated_bytes.data(),
                           static_cast<uint32_t>(translated_bytes.size()));
 }
 
 void MotermDriver::Close(const CloseCallback& callback) {
   if (is_closed_) {
     callback.Run(mojo::files::ERROR_CLOSED);
     return;
   }
 
+  is_closed_ = true;
   callback.Run(mojo::files::ERROR_OK);
 
   // TODO(vtl): Call pending read callbacks?
 
   client_->OnClosed();
 }
 
 void MotermDriver::Read(uint32_t num_bytes_to_read,
                         int64_t offset,
                         mojo::files::Whence whence,
@@ skipping 33 matching lines @@
     // TODO(vtl): Is this the "right" behavior?
     callback.Run(mojo::files::ERROR_INVALID_ARGUMENT, 0);
     return;
   }
 
   if (!bytes_to_write.size()) {
     callback.Run(mojo::files::ERROR_OK, 0);
     return;
   }
 
-  HandleOutput(static_cast<const uint8_t*>(&bytes_to_write.front()),
-               bytes_to_write.size());
+  HandleOutput(&bytes_to_write.front(), bytes_to_write.size());
 
   // TODO(vtl): Is this OK if the client detached (and we're destroyed?).
   callback.Run(mojo::files::ERROR_OK,
                static_cast<uint32_t>(bytes_to_write.size()));
 }
 
 void MotermDriver::ReadToStream(mojo::ScopedDataPipeProducerHandle source,
                                 int64_t offset,
                                 mojo::files::Whence whence,
                                 int64_t num_bytes_to_read,
@@ skipping 227 matching lines @@
   }
   if (1 + kVEOFIdx < in_values.size()) {
     uint32_t value = in_values[1 + kVEOFIdx];
     if (value > std::numeric_limits<uint8_t>::max())
       return mojo::files::ERROR_INVALID_ARGUMENT;
     veof_ = static_cast<uint8_t>(value);
   }
 
   return mojo::files::ERROR_OK;
 }