Add File::Duplicate to duplicate a file handle.

base/files/file_unittest.cc

Index: base/files/file_unittest.cc
diff --git a/base/files/file_unittest.cc b/base/files/file_unittest.cc
index 3bc2db60f0e4fd85b24aacc1efc583a41ce4f457..8fed7926a6cadd8fa4955b52dade0ee0026034f4 100644
--- a/base/files/file_unittest.cc
+++ b/base/files/file_unittest.cc
@@ -443,6 +443,51 @@ TEST(FileTest, Seek) {
   EXPECT_EQ(kOffset, file.Seek(base::File::FROM_END, -kOffset));
 }
 
+TEST(FileTest, Duplicate) {
+  base::ScopedTempDir temp_dir;
+  ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
+  FilePath file_path = temp_dir.path().AppendASCII("file");
+  File file(file_path,(base::File::FLAG_CREATE |
+                       base::File::FLAG_READ |
+                       base::File::FLAG_WRITE));
+  ASSERT_TRUE(file.IsValid());
+
+  File file2(file.Duplicate());
+  ASSERT_TRUE(file2.IsValid());
+
+  // Write through one handle, close it, read through the other.
+  static const char kData[] = "now is a good time.";
+  static const int kDataLen = sizeof(kData) - 1;
+
+  ASSERT_EQ(0, file.Seek(base::File::FROM_CURRENT, 0));
+  ASSERT_EQ(0, file2.Seek(base::File::FROM_CURRENT, 0));
+  ASSERT_EQ(kDataLen, file.WriteAtCurrentPos(kData, kDataLen));
+  ASSERT_EQ(kDataLen, file.Seek(base::File::FROM_CURRENT, 0));
+  ASSERT_EQ(kDataLen, file2.Seek(base::File::FROM_CURRENT, 0));
+  file.Close();
+  char buf[kDataLen];
+  ASSERT_EQ(kDataLen, file2.Read(0, &buf[0], kDataLen));
+  ASSERT_EQ(std::string(kData, kDataLen), std::string(&buf[0], kDataLen));
+}
+
+TEST(FileTest, DuplicateDeleteOnClose) {
+  base::ScopedTempDir temp_dir;
+  ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
+  FilePath file_path = temp_dir.path().AppendASCII("file");
+  File file(file_path,(base::File::FLAG_CREATE |
+                       base::File::FLAG_READ |
+                       base::File::FLAG_WRITE |
+                       base::File::FLAG_DELETE_ON_CLOSE));
+  ASSERT_TRUE(file.IsValid());
+  ASSERT_TRUE(base::PathExists(file_path));

[grt (UTC plus 2), 2015/03/19 04:07:09]

This fails on ios_dbg_simulator_ninja. Is this expected to not work there? I
notice that other tests in this file don't use PathExists after opening a file
to make sure it exists. Should I simply remove this line, #if !defined(OS_IOS)
around it, or something else?

[grt (UTC plus 2), 2015/03/19 15:26:27]

Ah, I'd misunderstood how DELETE_ON_CLOSE worked on posix. I've fixed the test
and the doc comment in files.h.

+  File file2(file.Duplicate());
+  ASSERT_TRUE(file2.IsValid());
+  ASSERT_TRUE(base::PathExists(file_path));
+  file.Close();
+  file2.Close();
+  ASSERT_FALSE(base::PathExists(file_path));
+}
+
 #if defined(OS_WIN)
 TEST(FileTest, GetInfoForDirectory) {
   base::ScopedTempDir temp_dir;