Add an "append flag" to base::PlatformFile.

base/platform_file_unittest.cc

 // Copyright (c) 2012 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 "base/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/platform_file.h"
 #include "base/time.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ skipping 193 matching lines @@
     EXPECT_EQ(data_to_write[i], data_read_2[i]);
   for (int i = kTestDataSize; i < kOffsetBeyondEndOfFile; i++)
     EXPECT_EQ(0, data_read_2[i]);
   for (int i = kOffsetBeyondEndOfFile; i < file_size; i++)
     EXPECT_EQ(data_to_write[i - kOffsetBeyondEndOfFile], data_read_2[i]);
 
   // Close the file handle to allow the temp directory to be deleted.
   base::ClosePlatformFile(file);
 }
 
+TEST(PlatformFile, AppendPlatformFile) {
+  base::ScopedTempDir temp_dir;
+  ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
+  FilePath file_path = temp_dir.path().AppendASCII("append_file");
+  base::PlatformFile file = base::CreatePlatformFile(
+      file_path,
+      base::PLATFORM_FILE_CREATE |
+      base::PLATFORM_FILE_APPEND,

[jar (doing other things), 2013/06/04 23:31:50]

nit: This should fit nicely (and more readably) on line 220.

+      NULL, NULL);
+  EXPECT_NE(base::kInvalidPlatformFileValue, file);
+
+  char data_to_write[] = "test";
+  const int kTestDataSize = 4;
+
+  // Write 0 bytes to the file.
+  int bytes_written = WriteFully(file, 0, data_to_write, 0);
+  EXPECT_EQ(0, bytes_written);
+
+  // Write "test" to the file.
+  bytes_written = WriteFully(file, 0, data_to_write, kTestDataSize);
+  EXPECT_EQ(kTestDataSize, bytes_written);
+
+  base::ClosePlatformFile(file);
+  file = base::CreatePlatformFile(
+      file_path,
+      base::PLATFORM_FILE_OPEN |
+      base::PLATFORM_FILE_READ |
+      base::PLATFORM_FILE_APPEND,
+      NULL, NULL);

[jar (doing other things), 2013/06/04 23:31:50]

nit: I can see this odd style used elsewhere in this file, where sometimes the
author put one argument per line (see line 238), sometimes they wrapped args
when not really needed (lines 239-240), and sometimes they put multiple args on
a line (here in 242).

I *think* you should go with the "Arguments may optionally all be placed on
subsequent lines, with one line per argument:" rule, and then when you're forced
to wrap (line 241?), indent that by an extra 4 spaces.

I found the current mixture (even though it is just copying local style) to be
more painful to read.

You could alternatively use the style shown on lines 38 and 39 (which could
perchance be better), but I think the direction of putting each of the 4 args at
the start of a line is better.

+  EXPECT_NE(base::kInvalidPlatformFileValue, file);
+  if (file == base::kInvalidPlatformFileValue) {
+    printf("errno: %d\n", errno);
+  }
+
+  char append_data_to_write[] = "78";
+  const int kAppendDataSize = 2;
+
+  // Append "test" to the file.
+  bytes_written = WriteFully(file, 0, append_data_to_write, kAppendDataSize);
+  EXPECT_EQ(2, bytes_written);
+
+  // Read the entire file

[jar (doing other things), 2013/06/04 23:31:50]

nit: Periods at end of sentences.

+  char data_read_1[32];
+  int bytes_read = ReadFully(file, 0, data_read_1,
+                             kTestDataSize + kAppendDataSize);
+  EXPECT_EQ(6, bytes_read);
+
+  // Close the file handle to allow the temp directory to be deleted.
+  base::ClosePlatformFile(file);
+}
+
+
 TEST(PlatformFile, TruncatePlatformFile) {
   base::ScopedTempDir temp_dir;
   ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
   FilePath file_path = temp_dir.path().AppendASCII("truncate_file");
   base::PlatformFile file = base::CreatePlatformFile(
       file_path,
       base::PLATFORM_FILE_CREATE |
       base::PLATFORM_FILE_READ |
       base::PLATFORM_FILE_WRITE,
       NULL, NULL);
@@ skipping 104 matching lines @@
   EXPECT_EQ(info.last_modified.ToInternalValue(),
             new_last_modified.ToInternalValue());
 #endif
 
   EXPECT_EQ(info.creation_time.ToInternalValue(),
             creation_time.ToInternalValue());
 
   // Close the file handle to allow the temp directory to be deleted.
   base::ClosePlatformFile(file);
 }