Pad HID output reports on Windows to the maximum output report size.

device/hid/hid_connection_win.cc

 // Copyright (c) 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.
 
 #include "device/hid/hid_connection_win.h"
 
 #include <cstring>
 
 #include "base/bind.h"
 #include "base/files/file.h"
@@ skipping 119 matching lines @@
       ReadFile(file_.Get(),
                buffer->data(),
                static_cast<DWORD>(buffer->size()),
                NULL,
                transfer->GetOverlapped()));
 }
 
 void HidConnectionWin::PlatformWrite(scoped_refptr<net::IOBuffer> buffer,
                                      size_t size,
                                      const WriteCallback& callback) {
-  // The Windows API always wants either a report ID (if supported) or
-  // zero at the front of every output report.
+  size_t expected_size = device_info()->max_output_report_size() + 1;
+  DCHECK(size <= expected_size);
+  // The Windows API always wants either a report ID (if supported) or zero at
+  // the front of every output report and requires that the buffer be equal to

[Ken Rockot(use gerrit already), 2015/02/20 02:31:46]

nit: "requires that the buffer be equal to"
                              ^__ missing word: "size"?

+  // the maximum output report supported by this collection.
+  if (size < expected_size) {
+    scoped_refptr<net::IOBuffer> tmp_buffer = new net::IOBuffer(
+        base::checked_cast<int>(expected_size));
+    memcpy(tmp_buffer->data(), buffer->data(), size);
+    memset(tmp_buffer->data() + size, 0, expected_size - size);
+    buffer = tmp_buffer;
+    size = expected_size;
+  }
   scoped_refptr<PendingHidTransfer> transfer(new PendingHidTransfer(
       buffer, base::Bind(&HidConnectionWin::OnWriteComplete, this, callback)));
   transfers_.insert(transfer);
   transfer->TakeResultFromWindowsAPI(WriteFile(file_.Get(),
                                                buffer->data(),
                                                static_cast<DWORD>(size),
                                                NULL,
                                                transfer->GetOverlapped()));
 }
 
@@ skipping 90 matching lines @@
   if (GetOverlappedResult(
           file_.Get(), transfer->GetOverlapped(), &bytes_transferred, FALSE)) {
     callback.Run(true);
   } else {
     VPLOG(1) << "HID write failed";
     callback.Run(false);
   }
 }
 
 }  // namespace device