# Copyright (c) 2023 Boston Dynamics, Inc. All rights reserved.
#
# Downloading, reproducing, distributing or otherwise using the SDK Software
# is subject to the terms and conditions of the Boston Dynamics Software
# Development Kit License (20191101-BDSDK-SL).
"""Class for reading data from a file-like object which is seekable."""
import os
import struct
from .base_data_reader import BaseDataReader
from .common import END_MAGIC, INDEX_OFFSET_OFFSET, MAGIC, ParseError
[docs]class DataReader(BaseDataReader): # pylint: disable=too-many-instance-attributes
"""Class for reading data from a file-like object which is seekable.
Methods raise ParseError if there is a problem with the format of the file.
"""
def __init__(self, infile=None, filename=None):
"""
At least one of the following arguments must be specified.
Args:
infile: binary file-like object for reading (e.g., from open(fname, "rb")).
filename: path of input file, if applicable.
"""
super(DataReader, self).__init__(infile, filename)
self._series_index_to_descriptor = {}
self._series_index_to_block_index = {} # {series_index -> SeriesBlockIndex}
self._read_index()
[docs] def series_descriptor(self, series_index):
"""Return SeriesDescriptor for given series index, loading it if necessary."""
try:
return self._series_index_to_descriptor[series_index]
except KeyError:
pass
series_block_index = self.series_block_index(series_index)
desc = self._read_desc_block_at("series_descriptor",
series_block_index.descriptor_file_offset)
self._series_index_to_descriptor[series_index] = desc
return desc
[docs] def num_data_blocks(self, series_index):
"""Returns the number of data blocks for a given series in the file."""
return len(self.series_block_index(series_index).block_entries)
[docs] def total_bytes(self, series_index):
"""Returns the total number of bytes for data in a given series in the file."""
return self.series_block_index(series_index).total_bytes
[docs] def read(self, series_index, index_in_series):
"""Retrieves a message and related information from the file.
Args:
series_index: int selecting from which series to read the message.
index_in_series: The index number of the message within the channel.
Returns: DataTypeDescriptor for channel, timestamp_nsec (int), message-data (bytes)
Raises ParseError if there is a problem with the format of the file.
"""
series_block_index = self.series_block_index(series_index)
msg_idx = series_block_index.block_entries[index_in_series]
desc, data = self._read_data_block_at(msg_idx.file_offset)
return desc, msg_idx.timestamp.ToNanoseconds(), data
[docs] def series_block_index(self, series_index):
"""Returns the SeriesBlockIndexes for the given series_index, loading it as needed."""
try:
return self._series_index_to_block_index[series_index]
except KeyError:
pass
# Need to load the block index for this series.
offset = self.file_index.series_block_index_offsets[series_index]
block_index = self._read_desc_block_at('series_block_index', offset)
self._series_index_to_block_index[series_index] = block_index
return block_index
def _read_index(self):
self._file.seek(-len(END_MAGIC), os.SEEK_END)
end_magic = self._read(len(END_MAGIC))
if end_magic != END_MAGIC:
raise ParseError("Bad magic bytes at the end of the file.")
self._file.seek(-INDEX_OFFSET_OFFSET, os.SEEK_END)
self._index_offset, self._checksum = struct.unpack('<QQ', self._read(16))
if self._index_offset < len(MAGIC):
raise ParseError('Invalid offset to index: {})'.format(self._index_offset))
self._file_index = self._read_desc_block_at("file_index", self._index_offset)
self._spec_index = [{key: value
for key, value in desc.spec.items()}
for desc in self._file_index.series_identifiers]
def _seek_to(self, location):
if location < len(MAGIC):
raise ParseError('Invalid offset for block: {})'.format(location))
self._file.seek(location)
def _read_data_block_at(self, location):
self._seek_to(location)
return self._read_data_block()
def _read_desc_block_at(self, descriptor_type_name, location):
self._seek_to(location)
return self._read_desc_block(descriptor_type_name)