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";
+  }
+}

[James Cook, 2017/05/12 19:32:53]

I think this needs a NOTREACHED(); return;

+
+}  // namespace
+
+SingleLogSource::SingleLogSource(SupportedSource source)
+    : SystemLogsSource(GetLogFileSourceFilename(source)),
+      num_bytes_read_(0),
+      weak_ptr_factory_(this) {}
+
+SingleLogSource::~SingleLogSource() {}
+
+void SingleLogSource::Fetch(const SysLogsSourceCallback& callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);

[afakhry, 2017/05/11 15:42:28]

The real question is why do you need to force this to be on the UI thread?

[rkc, 2017/05/11 19:51:13]

Requiring the fetch call to be on the UI thread seems reasonable. For all the
applications we know of, only UI should be making fetch calls.
The actual ReadFile should not be, which it isn't.

+  DCHECK(!callback.is_null());
+
+  SystemLogsResponse* response = new SystemLogsResponse;
+  base::PostTaskWithTraitsAndReply(
+      FROM_HERE,
+      base::TaskTraits(base::MayBlock(), base::TaskPriority::BACKGROUND),
+      base::Bind(&SingleLogSource::ReadFile, weak_ptr_factory_.GetWeakPtr(),
+                 response),
+      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::string result_string;
+  result_string.resize(size_to_read);
+  const size_t size_read =
+      file_.ReadAtCurrentPos(&result_string[0], size_to_read);
+  result_string.resize(size_read);
+
+  // The reader may only read complete lines.
+  if (result_string.empty() || result_string.back() != '\n') {
+    // 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);
+    result->emplace(source_name(), "");
+    return;
+  }
+
+  num_bytes_read_ += size_read;
+
+  // Pass it back to the callback.
+  result->emplace(source_name(), anonymizer_.Anonymize(result_string));
+}
+
+}  // namespace system_logs