SingleLogSource handles rotation of log files

chrome/browser/chromeos/system_logs/single_log_source_unittest.cc

 // Copyright 2017 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 "chrome/browser/chromeos/system_logs/single_log_source.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
@@ skipping 54 matching lines @@
     return base::WriteFile(log_dir_.GetPath().Append(relative_path),
                            input.data(),
                            input.size()) == static_cast<int>(input.size());
   }
   bool AppendToFile(const base::FilePath& relative_path,
                     const std::string& input) {
     return base::AppendToFile(log_dir_.GetPath().Append(relative_path),
                               input.data(), input.size());
   }
 
+  // Moves source file to destination path, then creates an empty file at the
+  // path of the original source file.
+  //
+  // |src_relative_path|: Source file path relative to |log_dir_|.
+  // |dest_relative_path|: Destination path relative to |log_dir_|.
+  bool RotateFile(const base::FilePath& src_relative_path,
+                  const base::FilePath& dest_relative_path) {
+    return base::Move(log_dir_.GetPath().Append(src_relative_path),
+                      log_dir_.GetPath().Append(dest_relative_path)) &&
+           WriteFile(src_relative_path, "");
+  }
+
   // Calls source_.Fetch() to start a logs fetch operation. Passes in
   // OnFileRead() as a callback. Runs until Fetch() has completed.
   void FetchFromSource() {
     source_->Fetch(
         base::Bind(&SingleLogSourceTest::OnFileRead, base::Unretained(this)));
     scoped_task_environment_.RunUntilIdle();
   }
 
   // Callback for fetching logs from |source_|. Overwrites the previous stored
   // value of |latest_response_|.
@@ skipping 187 matching lines @@
   EXPECT_EQ(2, num_callback_calls());
   EXPECT_EQ("", latest_response());
 
   EXPECT_TRUE(AppendToFile(base::FilePath("ui/ui.LATEST"), "D:99:EF:77\n"));
   FetchFromSource();
 
   EXPECT_EQ(3, num_callback_calls());
   EXPECT_EQ("Your MAC address is: ab:88:cd:00:00:02\n", latest_response());
 }
 
+TEST_F(SingleLogSourceTest, HandleLogFileRotation) {
+  InitializeSource(SingleLogSource::SupportedSource::kMessages);
+
+  EXPECT_TRUE(AppendToFile(base::FilePath("messages"), "1st log file\n"));
+  FetchFromSource();
+  EXPECT_EQ(1, num_callback_calls());
+  EXPECT_EQ("1st log file\n", latest_response());
+
+  // Rotate file. Make sure the rest of the old file and the contents of the new
+  // file are both read.
+  EXPECT_TRUE(AppendToFile(base::FilePath("messages"), "More 1st log file\n"));
+  EXPECT_TRUE(
+      RotateFile(base::FilePath("messages"), base::FilePath("messages.1")));
+  EXPECT_TRUE(AppendToFile(base::FilePath("messages"), "2nd log file\n"));
+
+  FetchFromSource();
+  EXPECT_EQ(2, num_callback_calls());
+  EXPECT_EQ("More 1st log file\n2nd log file\n", latest_response());
+
+  // Rotate again, but this time omit the newline before rotating.
+  EXPECT_TRUE(AppendToFile(base::FilePath("messages"), "No newline here..."));
+  EXPECT_TRUE(
+      RotateFile(base::FilePath("messages"), base::FilePath("messages.1")));
+  EXPECT_TRUE(AppendToFile(base::FilePath("messages"), "3rd log file\n"));
+  EXPECT_TRUE(AppendToFile(base::FilePath("messages"), "Also no newline here"));
+
+  FetchFromSource();
+  EXPECT_EQ(3, num_callback_calls());
+  // Make sure the rotation didn't break anything: the last part of the new file
+  // does not end with a newline; thus the new file should not be read.
+  EXPECT_EQ("No newline here...3rd log file\n", latest_response());
+
+  // Finish the previous read attempt by adding the missing newline.
+  EXPECT_TRUE(AppendToFile(base::FilePath("messages"), "...yet\n"));
+  FetchFromSource();
+  EXPECT_EQ(4, num_callback_calls());
+  EXPECT_EQ("Also no newline here...yet\n", latest_response());

[afakhry, 2017/06/13 17:39:21]

Nice test! Thanks!

+}
+
 }  // namespace system_logs