Add SingleLogSource to system_logs sources

chrome/browser/chromeos/system_logs/single_log_source.cc

Index: chrome/browser/chromeos/system_logs/single_log_source.cc
diff --git a/chrome/browser/chromeos/system_logs/single_log_source.cc b/chrome/browser/chromeos/system_logs/single_log_source.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4359af8d3703f45942d4643130db28845447574c
--- /dev/null
+++ b/chrome/browser/chromeos/system_logs/single_log_source.cc
@@ -0,0 +1,88 @@
+// 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),
+      weak_ptr_factory_(this) {}
+
+SingleLogSource::~SingleLogSource() {}
+
+void SingleLogSource::Fetch(const SysLogsSourceCallback& callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);

[afakhry, 2017/05/11 00:56:54]

It's failing because of this DCHECK.

+  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