Add SingleLogSource to system_logs sources

chrome/browser/chromeos/system_logs/single_log_source.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 "base/bind.h"
+#include "base/files/file_path.h"
+#include "base/task_scheduler/post_task.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace system_logs {
+
+namespace {
+
+// Converts a logs source type to the corresponding filename. In the future, if
+// non-file source types are added, this function should return an empty string.
+std::string GetLogFileSourceFilename(SingleLogSource::SupportedSource source) {
+  switch (source) {
+    case SingleLogSource::SupportedSource::kMessages:
+      return "/var/log/messages";
+    case SingleLogSource::SupportedSource::kUiLatest:
+      return "/var/log/ui/ui.LATEST";
+  }
+}
+
+}  // namespace
+
+SingleLogSource::SingleLogSource(SupportedSource source)
+    : SystemLogsSource(GetLogFileSourceFilename(source)), num_bytes_read_(0) {}
+
+SingleLogSource::~SingleLogSource() {}
+
+void SingleLogSource::Fetch(const SysLogsSourceCallback& callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  DCHECK(!callback.is_null());
+
+  SystemLogsResponse* response = new SystemLogsResponse;
+  base::PostTaskWithTraitsAndReply(
+      FROM_HERE,
+      base::TaskTraits().MayBlock().WithPriority(
+          base::TaskPriority::BACKGROUND),
+      base::Bind(&SingleLogSource::ReadFile, base::Unretained(this), response),

[afakhry, 2017/05/09 00:39:23]

This is unsafe! Sorry for not spotting this earlier.

You cannot use base::Unretained(this) here, The lifetimes of the system running
PostTaskWithTraitsAndReply() might be different than the lifetime of this
object.

Please add a WeakPtrFactory as the last member of this class, and use it here by
calling GetWeakPtr() instead of base::Unretained(this).

[Simon Que, 2017/05/09 02:06:22]

Done.

+      base::Bind(callback, base::Owned(response)));
+}
+
+void SingleLogSource::ReadFile(SystemLogsResponse* result) {
+  // Attempt to open the file if it was not previously opened.
+  if (!file_.IsValid()) {
+    file_.Initialize(base::FilePath(source_name()),
+                     base::File::FLAG_OPEN | base::File::FLAG_READ);
+    if (!file_.IsValid())
+      return;
+  }
+
+  // Check for file size reset.
+  const size_t length = file_.GetLength();
+  if (length < num_bytes_read_) {
+    num_bytes_read_ = 0;
+    file_.Seek(base::File::FROM_BEGIN, 0);
+  }
+
+  // Read from file until end.
+  const size_t size_to_read = length - num_bytes_read_;
+  std::vector<char> read_result(size_to_read);
+  const size_t size_read =
+      file_.ReadAtCurrentPos(read_result.data(), size_to_read);
+  read_result.resize(size_read);
+
+  // Create a string from the read results.
+  std::string result_string;
+
+  // The reader may only read complete lines.
+  if (!read_result.empty() && read_result.back() == '\n') {
+    result_string.reserve(read_result.size());
+    result_string.assign(read_result.begin(), read_result.end());
+    num_bytes_read_ += size_read;
+  } else {
+    // If an incomplete line was read, reset the file read offset to before the
+    // most recent read.
+    file_.Seek(base::File::FROM_CURRENT, -size_read);
+  }
+
+  // Pass it back to the callback.
+  result->emplace(source_name(), anonymizer_.Anonymize(result_string));
+}
+
+}  // namespace system_logs