Implement a MOJO_READ_DATA_FLAG_PEEK flag for data pipes.

mojo/edk/system/core_unittest.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/core.h"
 
 #include <stdint.h>
 
 #include <limits>
 
@@ skipping 1066 matching lines @@
   EXPECT_EQ(2u, num_bytes);
 
   // Consumer should now be readable.
   hss = kEmptyMojoHandleSignalsState;
   EXPECT_EQ(
       MOJO_RESULT_OK,
       core()->Wait(ch, MOJO_HANDLE_SIGNAL_READABLE, 0, MakeUserPointer(&hss)));
   EXPECT_EQ(MOJO_HANDLE_SIGNAL_READABLE, hss.satisfied_signals);
   EXPECT_EQ(MOJO_HANDLE_SIGNAL_READABLE, hss.satisfiable_signals);
 
+  // Peek one character.
+  elements[0] = -1;
+  elements[1] = -1;
+  num_bytes = 1u;
+  EXPECT_EQ(MOJO_RESULT_OK,
+            core()->ReadData(
+                ch,
+                UserPointer<void>(elements),
+                MakeUserPointer(&num_bytes),
+                MOJO_READ_DATA_FLAG_NONE | MOJO_READ_DATA_FLAG_PEEK));
+  EXPECT_EQ('A', elements[0]);
+  EXPECT_EQ(-1, elements[1]);
+
   // Read one character.
   elements[0] = -1;
   elements[1] = -1;
   num_bytes = 1u;
   EXPECT_EQ(MOJO_RESULT_OK,
             core()->ReadData(ch,
                              UserPointer<void>(elements),
                              MakeUserPointer(&num_bytes),
                              MOJO_READ_DATA_FLAG_NONE));
   EXPECT_EQ('A', elements[0]);
@@ skipping 27 matching lines @@
 
   // Query how much data we have.
   num_bytes = 0;
   EXPECT_EQ(MOJO_RESULT_OK,
             core()->ReadData(ch,
                              NullUserPointer(),
                              MakeUserPointer(&num_bytes),
                              MOJO_READ_DATA_FLAG_QUERY));
   EXPECT_EQ(4u, num_bytes);
 
+  // Try to query with peek. Should fail.
+  num_bytes = 0;
+  EXPECT_EQ(MOJO_RESULT_INVALID_ARGUMENT,
+            core()->ReadData(
+                ch,
+                NullUserPointer(),
+                MakeUserPointer(&num_bytes),
+                MOJO_READ_DATA_FLAG_QUERY | MOJO_READ_DATA_FLAG_PEEK));
+  EXPECT_EQ(0u, num_bytes);
+
   // Try to discard ten characters, in all-or-none mode. Should fail.
   num_bytes = 10;
   EXPECT_EQ(MOJO_RESULT_OUT_OF_RANGE,
             core()->ReadData(
                 ch,
                 NullUserPointer(),
                 MakeUserPointer(&num_bytes),
                 MOJO_READ_DATA_FLAG_DISCARD | MOJO_READ_DATA_FLAG_ALL_OR_NONE));
 
+  // Try to discard two characters, in peek mode. Should fail.
+  num_bytes = 2;
+  EXPECT_EQ(MOJO_RESULT_INVALID_ARGUMENT,
+            core()->ReadData(
+                ch,
+                NullUserPointer(),
+                MakeUserPointer(&num_bytes),
+                MOJO_READ_DATA_FLAG_DISCARD | MOJO_READ_DATA_FLAG_PEEK));
+
   // Discard two characters.
   num_bytes = 2;
   EXPECT_EQ(MOJO_RESULT_OK,
             core()->ReadData(
                 ch,
                 NullUserPointer(),
                 MakeUserPointer(&num_bytes),
                 MOJO_READ_DATA_FLAG_DISCARD | MOJO_READ_DATA_FLAG_ALL_OR_NONE));
 
+  // Try a two-phase read of the remaining two bytes with peek. Should fail.
+  const void* read_ptr = nullptr;
+  num_bytes = 2;
+  ASSERT_EQ(MOJO_RESULT_INVALID_ARGUMENT,
+            core()->BeginReadData(ch,
+                                  MakeUserPointer(&read_ptr),
+                                  MakeUserPointer(&num_bytes),
+                                  MOJO_READ_DATA_FLAG_PEEK));
+
   // Read the remaining two characters, in two-phase mode (all-or-none).
-  const void* read_ptr = nullptr;
   num_bytes = 2;
   ASSERT_EQ(MOJO_RESULT_OK,
             core()->BeginReadData(ch,
                                   MakeUserPointer(&read_ptr),
                                   MakeUserPointer(&num_bytes),
                                   MOJO_READ_DATA_FLAG_ALL_OR_NONE));
   // Note: Count on still being able to do the contiguous read here.
   ASSERT_EQ(2u, num_bytes);
 
   // Discarding right now should fail.
@@ skipping 313 matching lines @@
   EXPECT_EQ(MOJO_RESULT_OK, core()->Close(h_passing[1]));
   EXPECT_EQ(MOJO_RESULT_OK, core()->Close(ph));
   EXPECT_EQ(MOJO_RESULT_OK, core()->Close(ch));
 }
 
 // TODO(vtl): Test |DuplicateBufferHandle()| and |MapBuffer()|.
 
 }  // namespace
 }  // namespace system
 }  // namespace mojo