Mojo: Fix data pipe ALL_OR_NONE write capacity check.

mojo/edk/system/data_pipe_producer_dispatcher.cc

 // Copyright 2013 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 "mojo/edk/system/data_pipe_producer_dispatcher.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <utility>
@@ skipping 119 matching lines @@
     return MOJO_RESULT_BUSY;
 
   if (peer_closed_)
     return MOJO_RESULT_FAILED_PRECONDITION;
 
   if (*num_bytes % options_.element_num_bytes != 0)
     return MOJO_RESULT_INVALID_ARGUMENT;
   if (*num_bytes == 0)
     return MOJO_RESULT_OK;  // Nothing to do.
 
-  bool all_or_none = flags & MOJO_WRITE_DATA_FLAG_ALL_OR_NONE;
-  uint32_t min_num_bytes_to_write = all_or_none ? *num_bytes : 0;
-  if (min_num_bytes_to_write > options_.capacity_num_bytes) {
+  if ((flags & MOJO_WRITE_DATA_FLAG_ALL_OR_NONE) &&
+      (*num_bytes > available_capacity_)) {
     // Don't return "should wait" since you can't wait for a specified amount of
     // data.
     return MOJO_RESULT_OUT_OF_RANGE;

[miu, 2016/09/14 22:40:23]

Should this instead be:

1. MOJO_RESULT_SHOULD_WAIT if available_capacity_ is insufficient.
and
2. MOJO_RESULT_OUT_OF_RANGE if options_.capacity_num_bytes is insufficient.

Let me know if I should change this behavior.

[jam, 2016/09/15 17:08:34]

the canonical documentation is in
https://cs.chromium.org/chromium/src/mojo/public/c/system/data_pipe.h?rcl=0&l...,
which says 

"//   |MOJO_RESULT_SHOULD_WAIT| if no data can currently be written (and the
//       consumer is still open) and |flags| does *not* have
//       |MOJO_WRITE_DATA_FLAG_ALL_OR_NONE| set."

so your current implementation is good

   }
 
   DCHECK_LE(available_capacity_, options_.capacity_num_bytes);
   uint32_t num_bytes_to_write = std::min(*num_bytes, available_capacity_);
   if (num_bytes_to_write == 0)
     return MOJO_RESULT_SHOULD_WAIT;
 
   HandleSignalsState old_state = GetHandleSignalsStateNoLock();
 
   *num_bytes = num_bytes_to_write;
@@ skipping 385 matching lines @@
   }
 
   if (peer_closed_ != was_peer_closed ||
       available_capacity_ != previous_capacity) {
     awakable_list_.AwakeForStateChange(GetHandleSignalsStateNoLock());
   }
 }
 
 }  // namespace edk
 }  // namespace mojo