Mojo: Fix data pipe ALL_OR_NONE write capacity check.

Fixes a bug where ALL_OR_NONE writes to data pipes were checking the
total capacity of the pipe, rather than the available capacity. The bug
allowed ALL_OR_NONE writes to succeed (MOJO_RESULT_OK), but in actuality
only a portion of the data was written.

Updated unit test with a case that fails w/o the fix, but passes with
the fix.

Review-Url: https://codereview.chromium.org/2341633005
Cr-Commit-Position: refs/heads/master@{#418929}

mojo/edk/system/data_pipe_producer_dispatcher.cc

@@ -137,9 +137,8 @@ MojoResult DataPipeProducerDispatcher::WriteData(const void* elements,
   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;

mojo/edk/system/data_pipe_unittest.cc

@@ -799,7 +799,7 @@ TEST_F(DataPipeTest, AllOrNone) {
   ASSERT_EQ(MOJO_RESULT_OK, Create(&options));
   MojoHandleSignalsState hss;
 
-  // Try writing way too much.
+  // Try writing more than the total capacity of the pipe.
   uint32_t num_bytes = 20u * sizeof(int32_t);
   int32_t buffer[100];
   Seq(0, arraysize(buffer), buffer);
@@ -834,12 +834,11 @@ TEST_F(DataPipeTest, AllOrNone) {
   ASSERT_EQ(MOJO_RESULT_OK, QueryData(&num_bytes));
   ASSERT_EQ(5u * sizeof(int32_t), num_bytes);
 
-  /* TODO(jam): enable if we end up observing max capacity
-  // Too much.
+  // Try writing more than the available capacity of the pipe, but less than the
+  // total capacity.
   num_bytes = 6u * sizeof(int32_t);
   Seq(200, arraysize(buffer), buffer);
   ASSERT_EQ(MOJO_RESULT_OUT_OF_RANGE, WriteData(buffer, &num_bytes, true));
-  */
 
   // Try reading too much.
   num_bytes = 11u * sizeof(int32_t);