Class _ExtendedHeader

exir/_serialize/_program.py:150–265

@dataclass
class _ExtendedHeader:
    # Class constants

    # The magic bytes that should be at the beginning of the header.
    EXPECTED_MAGIC: ClassVar[bytes] = b"eh00"
    MINIMUM_LENGTH: ClassVar[int] = (
        # Header magic
        4
        # Header length
        + 4
        # Flatbuffer data size
        + 8
        # Segment base offset
        + 8
    )
    # The length of the header in bytes.
    EXPECTED_LENGTH: ClassVar[int] = (
        MINIMUM_LENGTH
        # Segment data size
        + 8
    )

    # To find the header, callers should provide at least this many bytes of
    # the head of the serialized Program data. Keep this in sync with
    # kNumHeadBytes in //executorch/schema/extended_header.cpp
    NUM_HEAD_BYTES: ClassVar[int] = 64

    # Instance attributes. @dataclass will turn these into ctor args.

    # The size of the serialized program data in bytes.
    program_size: int
    # Offset to the start of the first segment, or zero if there
    # are no segments.
    segment_base_offset: int
    # Size of the segment data, in bytes, or zero if there are no segments, or
    # if the this field isn't populated in the PTE file.
    segment_data_size: int

    # The magic bytes read from or to be written to the binary header.
    magic: bytes = EXPECTED_MAGIC
    # The header length, in bytes, read from or to be written to the binary
    # header.
    length: int = EXPECTED_LENGTH

    @staticmethod
    def from_bytes(data: bytes) -> "_ExtendedHeader":
        """Tries to read an extended header from the provided data.

        Does not validate that the header is well-formed. Callers should
        use is_valid().

        Args:
            data: The data to read from.
        Returns:
            The contents of the extended header.
        Raises:
            ValueError: If not enough data is provided.
        """