aos/util/mcap_logger.h

#ifndef AOS_UTIL_MCAP_LOGGER_H_
#define AOS_UTIL_MCAP_LOGGER_H_

#include "aos/configuration_generated.h"
#include "aos/events/event_loop.h"
#include "aos/fast_string_builder.h"
#include "aos/flatbuffer_utils.h"
#include "single_include/nlohmann/json.hpp"

namespace aos {

// Produces a JSON Schema (https://json-schema.org/) for a given flatbuffer
// type. If recursion_level is set, will include a $schema attribute indicating
// the schema definition being used (this is used to allow for recursion).
//
// Note that this is pretty bare-bones, so, e.g., we don't distinguish between
// structs and tables when generating the JSON schema, so we don't bother to
// mark struct fields as required.
enum class JsonSchemaRecursion {
  kTopLevel,
  kNested,
};
nlohmann::json JsonSchemaForFlatbuffer(
    const FlatbufferType &type,
    JsonSchemaRecursion recursion_level = JsonSchemaRecursion::kTopLevel);

// Generates an MCAP file, per the specification at
// https://github.com/foxglove/mcap/tree/main/docs/specification
// This currently generates an uncompressed logfile with full message indexing
// available, to be able to support Foxglove fully.
class McapLogger {
 public:
  McapLogger(EventLoop *event_loop, const std::string &output_path);
  ~McapLogger();

 private:
  enum class OpCode {
    kHeader = 0x01,
    kFooter = 0x02,
    kSchema = 0x03,
    kChannel = 0x04,
    kMessage = 0x05,
    kChunk = 0x06,
    kMessageIndex = 0x07,
    kChunkIndex = 0x08,
    kAttachment = 0x09,
    kAttachmentIndex = 0x0A,
    kStatistics = 0x0B,
    kMetadata = 0x0C,
    kMetadataIndex = 0x0D,
    kSummaryOffset = 0x0E,
    kDataEnd = 0x0F,
  };
  // Stores information associated with a SummaryOffset entry (an offset to the
  // start of a section within Summary section, which allows readers to quickly
  // find all the indices/channel definitions/etc. for a given log).
  struct SummaryOffset {
    OpCode op_code;
    // Offset from the start of the file.
    uint64_t offset;
    // Total length of the section, in bytes.
    uint64_t size;
  };
  // Information needed to build a ChunkIndex entry.
  struct ChunkIndex {
    // Earliest and latest message times within the Chunk being referenced.
    aos::monotonic_clock::time_point start_time;
    aos::monotonic_clock::time_point end_time;
    // Offset from the start of the file to the start of the relevant Chunk.
    uint64_t offset;
    // Total size of the Chunk, in bytes.
    uint64_t chunk_size;
    // Total size of the records portion of the Chunk, in bytes.
    uint64_t records_size;
    // Mapping of channel IDs to the MessageIndex entry for that channel within
    // the referenced Chunk. The MessageIndex is referenced by an offset from
    // the start of the file.
    std::map<uint16_t, uint64_t> message_index_offsets;
    // Total size, in bytes, of all the MessageIndex entries for this Chunk
    // together (note that they are required to be contiguous).
    uint64_t message_index_size;
  };
  enum class RegisterHandlers { kYes, kNo };
  // Helpers to write each type of relevant record.
  void WriteMagic();
  void WriteHeader();
  void WriteFooter(uint64_t summary_offset, uint64_t summary_offset_offset);
  void WriteDataEnd();
  void WriteSchema(const uint16_t id, const aos::Channel *channel);
  void WriteChannel(const uint16_t id, const uint16_t schema_id,
                    const aos::Channel *channel);
  void WriteMessage(uint16_t channel_id, const Channel *channel,
                    const Context &context, std::ostream *output);
  void WriteChunk();

  // The helpers for writing records which appear in the Summary section will
  // return SummaryOffset's so that they can be referenced in the SummaryOffset
  // section.
  SummaryOffset WriteChunkIndices();
  SummaryOffset WriteStatistics();
  std::vector<SummaryOffset> WriteSchemasAndChannels(
      RegisterHandlers register_handlers);
  void WriteSummaryOffset(const SummaryOffset &offset);

  // Writes an MCAP record to the output file.
  void WriteRecord(OpCode op, std::string_view record, std::ostream *ostream);
  void WriteRecord(OpCode op, std::string_view record) {
    WriteRecord(op, record, &output_);
  }
  // Adds an MCAP-spec string/byte-array/map/array of pairs/fixed-size integer
  // to a buffer.
  static void AppendString(FastStringBuilder *builder, std::string_view string);
  static void AppendBytes(FastStringBuilder *builder, std::string_view bytes);
  static void AppendChannelMap(FastStringBuilder *builder,
                               const std::map<uint16_t, uint64_t> &map);
  static void AppendMessageIndices(
      FastStringBuilder *builder,
      const std::vector<std::pair<uint64_t, uint64_t>> &messages);
  static void AppendInt16(FastStringBuilder *builder, uint16_t val);
  static void AppendInt32(FastStringBuilder *builder, uint32_t val);
  static void AppendInt64(FastStringBuilder *builder, uint64_t val);

  aos::EventLoop *event_loop_;
  std::ofstream output_;
  // Buffer containing serialized message data for the currently-being-built
  // chunk.
  std::stringstream current_chunk_;
  FastStringBuilder string_builder_;

  // Earliest message observed in this logfile.
  std::optional<aos::monotonic_clock::time_point> earliest_message_;
  // Earliest message observed in the current chunk.
  std::optional<aos::monotonic_clock::time_point> earliest_chunk_message_;
  // Latest message observed.
  aos::monotonic_clock::time_point latest_message_ =
      aos::monotonic_clock::min_time;
  // Count of all messages on each channel, indexed by channel ID.
  std::map<uint16_t, uint64_t> message_counts_;
  // MessageIndex's for each message. The std::map is indexed by channel ID. The
  // vector is then a series of pairs of (timestamp, offset from start of
  // current_chunk_).
  std::map<uint16_t, std::vector<std::pair<uint64_t, uint64_t>>>
      message_indices_;
  // ChunkIndex's for all fully written Chunks.
  std::vector<ChunkIndex> chunk_indices_;
};
}  // namespace aos
#endif  // AOS_UTIL_MCAP_LOGGER_H_