305 lines
11 KiB
Python
305 lines
11 KiB
Python
import struct
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from pathlib import Path
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from app.fit.crc import fit_crc
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from app.fit.models import (
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DeviceFieldValue,
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FieldDefinition,
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FitConversionResult,
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GarminDevice,
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LocalDefinition,
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)
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FILE_ID_MESG_NUM = 0
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DEVICE_INFO_MESG_NUM = 23
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class FitFormatError(ValueError):
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pass
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def _validate_fit_container(data: bytearray) -> None:
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if len(data) < 14:
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raise FitFormatError("FIT file is too small")
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header_size = data[0]
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if header_size not in {12, 14}:
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raise FitFormatError(f"Unsupported FIT header size: {header_size}")
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if len(data) < header_size + 2:
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raise FitFormatError("FIT file is shorter than its header")
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if bytes(data[8:12]) != b".FIT":
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raise FitFormatError("Missing .FIT signature")
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data_size = struct.unpack_from("<I", data, 4)[0]
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expected_size = header_size + data_size + 2
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if len(data) != expected_size:
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raise FitFormatError(f"FIT size mismatch: header says {expected_size} bytes, file has {len(data)}")
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if header_size == 14:
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expected_header_crc = struct.unpack_from("<H", data, 12)[0]
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if expected_header_crc != fit_crc(data[:12]):
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raise FitFormatError("FIT header CRC check failed")
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expected_file_crc = struct.unpack_from("<H", data, len(data) - 2)[0]
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if expected_file_crc != fit_crc(data[:-2]):
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raise FitFormatError("FIT file CRC check failed")
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def _read_definition(
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data: bytearray,
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offset: int,
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has_developer_fields: bool,
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end_offset: int,
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) -> tuple[LocalDefinition, int]:
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if offset + 5 > end_offset:
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raise FitFormatError("Truncated FIT definition message")
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offset += 1 # reserved byte
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architecture = data[offset]
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offset += 1
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if architecture not in {0, 1}:
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raise FitFormatError(f"Unsupported FIT architecture: {architecture}")
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endian = ">" if architecture == 1 else "<"
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global_message_num = struct.unpack_from(f"{endian}H", data, offset)[0]
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offset += 2
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field_count = data[offset]
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offset += 1
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fields: list[FieldDefinition] = []
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for _ in range(field_count):
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if offset + 3 > end_offset:
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raise FitFormatError("Truncated FIT field definition")
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fields.append(FieldDefinition(data[offset], data[offset + 1], data[offset + 2]))
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offset += 3
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developer_field_size = 0
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if has_developer_fields:
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if offset >= end_offset:
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raise FitFormatError("Truncated FIT developer field count")
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developer_count = data[offset]
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offset += 1
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for _ in range(developer_count):
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if offset + 3 > end_offset:
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raise FitFormatError("Truncated FIT developer field definition")
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developer_field_size += data[offset + 1]
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offset += 3
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return LocalDefinition(global_message_num, endian, tuple(fields), developer_field_size), offset
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def _collect_field_offsets(
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definition: LocalDefinition,
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offset: int,
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end_offset: int,
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) -> tuple[list[tuple[FieldDefinition, int]], int]:
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result: list[tuple[FieldDefinition, int]] = []
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current = offset
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for field in definition.fields:
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if current + field.size > end_offset:
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raise FitFormatError("Truncated FIT data record")
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result.append((field, current))
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current += field.size
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if current + definition.developer_field_size > end_offset:
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raise FitFormatError("Truncated FIT developer field payload")
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current += definition.developer_field_size
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return result, current
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def _iter_data_fields(
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data: bytearray,
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) -> list[tuple[LocalDefinition, list[tuple[FieldDefinition, int]]]]:
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header_size = data[0]
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data_size = struct.unpack_from("<I", data, 4)[0]
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offset = header_size
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end_offset = header_size + data_size
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definitions: dict[int, LocalDefinition] = {}
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records: list[tuple[LocalDefinition, list[tuple[FieldDefinition, int]]]] = []
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while offset < end_offset:
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record_header = data[offset]
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offset += 1
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if record_header & 0x80:
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local = (record_header >> 5) & 0x03
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definition = definitions.get(local)
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if definition is None:
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raise FitFormatError(f"Compressed timestamp record used unknown local definition {local}")
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field_offsets, offset = _collect_field_offsets(definition, offset, end_offset)
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records.append((definition, field_offsets))
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continue
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local = record_header & 0x0F
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is_definition = bool(record_header & 0x40)
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has_developer_fields = bool(record_header & 0x20)
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if is_definition:
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definition, offset = _read_definition(data, offset, has_developer_fields, end_offset)
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definitions[local] = definition
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continue
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definition = definitions.get(local)
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if definition is None:
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raise FitFormatError(f"Data record used unknown local definition {local}")
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field_offsets, offset = _collect_field_offsets(definition, offset, end_offset)
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records.append((definition, field_offsets))
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if offset != end_offset:
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raise FitFormatError("FIT parser did not end on data boundary")
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return records
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def is_fit_file(path: Path) -> bool:
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try:
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data = bytearray(path.read_bytes())
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_validate_fit_container(data)
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_iter_data_fields(data)
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except (OSError, FitFormatError):
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return False
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return True
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def convert_fit_device(
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source_path: Path, output_path: Path, device: GarminDevice | None = None
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) -> FitConversionResult:
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resolved = device or GarminDevice()
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data = bytearray(source_path.read_bytes())
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_validate_fit_container(data)
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patched_count = _patch_device_metadata(data, resolved)
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header_crc = _rewrite_header_crc(data)
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file_crc = _rewrite_file_crc(data)
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_validate_fit_container(data)
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output_path.parent.mkdir(parents=True, exist_ok=True)
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output_path.write_bytes(data)
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return FitConversionResult(source_path, output_path, patched_count, header_crc, file_crc)
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def read_device_field_values(path: Path) -> list[DeviceFieldValue]:
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data = bytearray(path.read_bytes())
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_validate_fit_container(data)
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values: list[DeviceFieldValue] = []
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for definition, field_offsets in _iter_data_fields(data):
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for field, offset in field_offsets:
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if definition.global_message_num == FILE_ID_MESG_NUM and field.num in {1, 2, 3, 8}:
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values.append(
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DeviceFieldValue(
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definition.global_message_num,
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field.num,
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_read_field_value(data, offset, field, definition.endian),
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)
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)
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if definition.global_message_num == DEVICE_INFO_MESG_NUM and field.num in {
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2,
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3,
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4,
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27,
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}:
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values.append(
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DeviceFieldValue(
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definition.global_message_num,
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field.num,
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_read_field_value(data, offset, field, definition.endian),
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)
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)
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return values
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def _patch_device_metadata(data: bytearray, device: GarminDevice) -> int:
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patched_count = 0
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eligible_field_count = 0
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for definition, field_offsets in _iter_data_fields(data):
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field_map = {field.num: (field, offset) for field, offset in field_offsets}
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if definition.global_message_num == DEVICE_INFO_MESG_NUM:
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device_index_entry = field_map.get(0)
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if device_index_entry is None:
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continue
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index_field, index_offset = device_index_entry
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device_index = _read_field_value(data, index_offset, index_field, definition.endian)
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if device_index != 0:
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continue
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for field, offset in field_offsets:
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target_value: int | str | None = None
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if definition.global_message_num == FILE_ID_MESG_NUM:
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if field.num == 1:
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target_value = device.manufacturer_id
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elif field.num == 2:
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target_value = device.product_id
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elif field.num == 3 and device.serial_number is not None:
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target_value = device.serial_number
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elif field.num == 8:
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target_value = device.product_name
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elif definition.global_message_num == DEVICE_INFO_MESG_NUM:
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if field.num == 2:
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target_value = device.manufacturer_id
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elif field.num == 3 and device.serial_number is not None:
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target_value = device.serial_number
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elif field.num == 4:
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target_value = device.product_id
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elif field.num == 27:
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target_value = device.product_name
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if target_value is not None:
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eligible_field_count += 1
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if _write_field_value(data, offset, field, definition.endian, target_value):
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patched_count += 1
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if eligible_field_count == 0:
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raise FitFormatError("No writable file_id or device_info device fields found")
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return patched_count
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def _read_field_value(data: bytearray, offset: int, field: FieldDefinition, endian: str) -> int | str:
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base_type = field.base_type & 0x1F
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if base_type in {0x03, 0x04, 0x0B} and field.size >= 2:
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return struct.unpack_from(f"{endian}H", data, offset)[0]
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if base_type in {0x05, 0x06, 0x0C} and field.size >= 4:
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return struct.unpack_from(f"{endian}I", data, offset)[0]
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if base_type == 0x07:
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raw = bytes(data[offset : offset + field.size])
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if 0 in raw:
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raw = raw[: raw.index(0)]
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return raw.decode("utf-8", errors="replace")
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raw = bytes(data[offset : offset + field.size])
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return int.from_bytes(raw, "little")
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def _write_field_value(
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data: bytearray,
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offset: int,
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field: FieldDefinition,
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endian: str,
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value: int | str,
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) -> bool:
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if isinstance(value, str):
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encoded = value.encode("utf-8")
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if not encoded or field.size == 0 or len(encoded) + 1 > field.size:
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return False
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replacement = encoded + b"\x00" + b"\x00" * (field.size - len(encoded) - 1)
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if bytes(data[offset : offset + field.size]) == replacement:
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return False
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data[offset : offset + field.size] = replacement
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return True
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if field.size == 1:
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replacement = struct.pack("B", value)
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elif field.size == 2:
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replacement = struct.pack(f"{endian}H", value)
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elif field.size == 4:
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replacement = struct.pack(f"{endian}I", value)
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else:
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return False
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if bytes(data[offset : offset + field.size]) == replacement:
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return False
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data[offset : offset + field.size] = replacement
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return True
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def _rewrite_header_crc(data: bytearray) -> int | None:
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header_size = data[0]
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if header_size != 14:
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return None
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header_crc = fit_crc(data[:12])
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struct.pack_into("<H", data, 12, header_crc)
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return header_crc
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def _rewrite_file_crc(data: bytearray) -> int:
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file_crc = fit_crc(data[:-2])
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struct.pack_into("<H", data, len(data) - 2, file_crc)
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return file_crc
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