mcap_writer.h

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/*
 * Copyright (C) 2026 by Thun Lu. All rights reserved.
 * Author: Thun Lu <thun.lu@zohomail.cn>
 * Repo:   https://github.com/thun-res/vlink
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 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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 */
 
/**
 * @file mcap_writer.h
 * @brief Concrete BagWriter implementation for the MCAP bag file format.
 *
 * @details
 * @c McapWriter records VLink messages to the MCAP format (@c .vcap / @c .vcapx extension).
 * It inherits all configuration, compression, and split capabilities from @c BagWriter.
 *
 * MCAP files can be opened by the Foxglove Studio visualisation tool and other
 * MCAP-compatible readers.  The file is finalised with an index footer on clean shutdown.
 *
 * @par Usage
 * @code
 * auto writer = vlink::BagWriter::create("/data/recording.vcap");
 * // or explicitly:
 * auto writer = std::make_shared<vlink::McapWriter>("/data/recording.vcap");
 * writer->async_run();
 * writer->push("dds://my/topic", "demo.proto.PointCloud", vlink::SchemaType::kProtobuf,
 *              vlink::ActionType::kPublish, data);
 * @endcode
 *
 * @see BagWriter, DatabaseWriter
 */
 
#pragma once
 
#include <memory>
#include <string>
 
#include "./bag_writer.h"
 
namespace vlink {
 
/**
 * @class McapWriter
 * @brief Concrete MCAP-format bag file recorder.
 *
 * @details
 * All virtual methods from @c BagWriter are implemented.  Prefer using
 * @c BagWriter::create() for format-agnostic construction.
 */
class VLINK_EXPORT McapWriter final : public BagWriter {
 public:
  /**
   * @brief Constructs an @c McapWriter for the given @p path.
   *
   * @param path    Path to the output @c .vcap / @c .vcapx file.  Created if it does not exist.
   * @param config  Recording configuration.
   */
  explicit McapWriter(const std::string& path, const Config& config = {});
 
  /**
   * @brief Destructor -- finalises the MCAP file footer and flushes all pending writes.
   */
  ~McapWriter() override;
 
  /**
   * @brief Registers a callback invoked when a file split occurs.
   *
   * @param callback  Called with (split_index, new_filename) on each split.
   * @param before    If @c true, fires before the new file is opened; otherwise after.
   */
  void register_split_callback(SplitCallback&& callback, bool before) override;
 
  /**
   * @brief Registers a callback that resolves serialisation type strings to @c SchemaData.
   *
   * @param callback  Function mapping (@c ser_type, @c schema_type) to @c SchemaData.
   */
  void register_schema_callback(SchemaCallback&& callback) override;
 
  /**
   * @brief Embeds a @c SchemaData into the MCAP file for offline introspection.
   *
   * @param schema_data  Schema descriptor to store.
   * @param immediate    If @c true, merges synchronously; otherwise enqueues.
   * @return             @c false only when the immediate merge fails.
   */
  bool push_schema(const SchemaData& schema_data, bool immediate = false) override;
 
  /**
   * @brief Records one message to the MCAP file.
   *
   * @param url                    VLink URL of the topic.
   * @param ser_type               Serialisation type string.
   * @param schema_type            Coarse schema family for the payload.
   * @param action_type            Action type (@c kPublish, @c kRequest, etc.).
   * @param data                   Serialized payload bytes.
   * @param microseconds_timestamp Optional custom timestamp in microseconds.
   *                               @c nullptr means use the current system time.
   * @param immediate              If @c true, writes synchronously bypassing the queue.
   * @return Sequence number of the recorded message, or a negative value on error.
   */
  int64_t push(const std::string& url, const std::string& ser_type, SchemaType schema_type, ActionType action_type,
               const Bytes& data, int64_t* microseconds_timestamp = nullptr, bool immediate = false) override;
 
  /**
   * @brief Returns @c true if the writer is actively recording to disk.
   */
  [[nodiscard]] bool is_dumping() const override;
 
  /**
   * @brief Returns @c true if split-file mode is active.
   */
  [[nodiscard]] bool is_split_mode() const override;
 
  /**
   * @brief Returns the zero-based index of the current split file.
   */
  [[nodiscard]] int get_split_index() const override;
 
  /**
   * @brief Sets the expected message loss ratio for a given URL.
   *
   * @param url   Topic URL.
   * @param loss  Loss ratio in the range [0.0, 1.0].
   */
  void set_url_loss(const std::string& url, double loss) override;
 
 protected:
  size_t get_max_task_count() const override;
 
  void on_begin() override;
 
  void on_end() override;
 
 private:
  void open(const std::string& path);
 
  void close();
 
  bool merge_schema(SchemaData& schema_data);
 
  bool load_schema(const std::string& ser_type, SchemaType& schema_type, SchemaData& schema_data);
 
  bool write(const std::string& url, const std::string& ser_type, SchemaType schema_type, ActionType action_type,
             const Bytes& data, int64_t microseconds_timestamp);
 
  bool write_filex(bool complete = true);
 
  std::unique_ptr<struct McapWriterImpl> impl_;
 
  VLINK_DISALLOW_COPY_AND_ASSIGN(McapWriter)
};
 
}  // namespace vlink