TraceSubscriber implementation that writes to a file.

content/browser/trace_subscriber_stdio.cc

+// Copyright (c) 2011 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 "content/browser/trace_subscriber_stdio.h"
+
+#include "base/logging.h"
+
+TraceSubscriberStdio::TraceSubscriberStdio(const FilePath& path) {
+  LOG(INFO) << "Logging performance trace to file: " << path.value();
+  m_file = file_util::OpenFile(path, "w+");
+  if (IsValid()) {
+    // FIXME: the file format expects it to start with "[".
+    fputc('[', m_file);
+  } else {
+    LOG(ERROR) << "Failed to open performance trace file: " << path.value();
+  }
+}
+
+TraceSubscriberStdio::~TraceSubscriberStdio() {
+  OnEndTracingComplete();
+}
+
+bool TraceSubscriberStdio::IsValid() {
+  return m_file && (0 == ferror(m_file));
+}
+
+void TraceSubscriberStdio::OnEndTracingComplete() {
+  if (m_file) {
+    // FIXME: the file format expects it to end with "]".
+    fputc(']', m_file);
+    fclose(m_file);
+    m_file = 0;
+  }
+}
+
+void TraceSubscriberStdio::OnTraceDataCollected(
+    const std::string& json_events) {
+  if (!IsValid()) {
+    return;
+  }
+
+  // FIXME: "json_events" currently comes with "[" and "]". But the file doesn't
+  // expect them. So remove them when writing to the file.
+  CHECK_GE(json_events.size(), 2);
+  const char* data = json_events.data() + 1;
+  size_t size = json_events.size() - 2;
+
+  size_t written = fwrite(data, 1, size, m_file);
+  if (written != size) {
+    LOG(ERROR) << "Error " << ferror(m_file) << " when writing to trace file";
+    fclose(m_file);
+    m_file = 0;
+  }
+  fputc(',', m_file);
+}