base/trace_event/trace_buffer.h

// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.


#ifndef BASE_TRACE_EVENT_TRACE_BUFFER_H_
#define BASE_TRACE_EVENT_TRACE_BUFFER_H_

#include <stddef.h>
#include <stdint.h>

#include "base/base_export.h"
#include "base/check.h"
#include "base/functional/callback.h"

namespace base {
namespace trace_event {

// TraceResultBuffer collects and converts trace fragments returned by TraceLog
// to JSON output.
class BASE_EXPORT TraceResultBuffer {
 public:
  using OutputCallback = base::RepeatingCallback<void(const std::string&)>;

  // If you don't need to stream JSON chunks out efficiently, and just want to
  // get a complete JSON string after calling Finish, use this struct to collect
  // JSON trace output.
  struct BASE_EXPORT SimpleOutput {
    OutputCallback GetCallback();
    void Append(const std::string& json_string);

    // Do what you want with the json_output_ string after calling
    // TraceResultBuffer::Finish.
    std::string json_output;
  };

  TraceResultBuffer();
  ~TraceResultBuffer();

  // Set callback. The callback will be called during Start with the initial
  // JSON output and during AddFragment and Finish with following JSON output
  // chunks. The callback target must live past the last calls to
  // TraceResultBuffer::Start/AddFragment/Finish.
  void SetOutputCallback(OutputCallback json_chunk_callback);

  // Start JSON output. This resets all internal state, so you can reuse
  // the TraceResultBuffer by calling Start.
  void Start();

  // Call AddFragment 0 or more times to add trace fragments from TraceLog.
  void AddFragment(const std::string& trace_fragment);

  // When all fragments have been added, call Finish to complete the JSON
  // formatted output.
  void Finish();

 private:
  OutputCallback output_callback_;
  bool append_comma_;
};

}  // namespace trace_event
}  // namespace base

#endif  // BASE_TRACE_EVENT_TRACE_BUFFER_H_