Source code for mcap_protobuf.writer

import time
from io import BufferedWriter
from typing import IO, Any, Dict, Optional, Tuple, Union

import mcap
from mcap.well_known import MessageEncoding
from mcap.writer import CompressionType
from mcap.writer import Writer as McapWriter

from . import __version__
from .schema import register_schema

def _library_identifier():
    """the default value written into MCAP headers by this library."""
    mcap_version = getattr(mcap, "__version__", "<=0.0.10")
    return f"python mcap-protobuf-support {__version__}; mcap {mcap_version}"

[docs]class Writer: """Writer provides a higher-level abstraction for writing Protobuf messages to an MCAP file. """ def __init__( self, output: Union[str, IO[Any], BufferedWriter], chunk_size: int = 1024 * 1024, compression: CompressionType = CompressionType.ZSTD, enable_crcs: bool = True, ): self._writer = McapWriter( output, chunk_size=chunk_size, compression=compression, enable_crcs=enable_crcs, ) self._schemas: Dict[str, Tuple[int, str]] = {} self._channels: Dict[str, int] = {} self._finished = False self._writer.start(library=_library_identifier())
[docs] def write_message( self, topic: str, message: Any, log_time: Optional[int] = None, publish_time: Optional[int] = None, sequence: int = 0, ): """Writes a message to an MCAP file. :param topic: the topic that this message was originally published on. :param message: a Protobuf object to write into the MCAP. :param log_time: unix nanosecond timestamp of when this message was written to the MCAP. :param publish_time: unix nanosecond timestamp of when this message was originally published. :param sequence: an optional sequence count for messages on this topic. """ msg_typename: str = type(message).DESCRIPTOR.full_name if topic in self._channels: channel_id = self._channels[topic] schema_id, schema_name = self._schemas[topic] if msg_typename != schema_name: raise ValueError( f"topic '{topic}' has type {schema_name}, cannot write a {msg_typename}" ) else: schema_id = register_schema(self._writer, type(message)) self._schemas[topic] = (schema_id, msg_typename) channel_id = self._writer.register_channel( topic=topic, message_encoding=MessageEncoding.Protobuf, schema_id=schema_id, ) self._channels[topic] = channel_id if log_time is None: log_time = time.time_ns() if publish_time is None: publish_time = time.time_ns() self._writer.add_message( channel_id=channel_id, log_time=log_time, data=message.SerializeToString(), # type: ignore publish_time=publish_time, sequence=sequence, )
[docs] def finish(self): """Writes the index and footer to the MCAP file.""" if not self._finished: self._writer.finish() self._finished = True
def __enter__(self): return self def __exit__(self, exc_: Any, exc_type_: Any, tb_: Any): self.finish()