def read_gzip_header_filename()

in client/securedrop_client/crypto.py [0:0]

• 21 lines of code
• 8 McCabe index (conditional complexity)

def read_gzip_header_filename(filename: str) -> str:
    """
    Extract the original filename from the header of a gzipped file.

    Adapted from Python's gzip._GzipReader._read_gzip_header.
    """
    original_filename = ""
    with open(filename, "rb") as f:
        gzip_header_identification = f.read(2)
        if gzip_header_identification != GZIP_FILE_IDENTIFICATION:
            raise OSError(f"Not a gzipped file ({gzip_header_identification!r})")

        (gzip_header_compression_method, gzip_header_flags, _) = struct.unpack("<BBIxx", f.read(8))
        if gzip_header_compression_method != 8:
            raise OSError("Unknown compression method")

        if gzip_header_flags & GZIP_FLAG_EXTRA_FIELDS:
            (extra_len,) = struct.unpack("<H", f.read(2))
            f.read(extra_len)

        if gzip_header_flags & GZIP_FLAG_FILENAME:
            fb = b""
            while True:
                s = f.read(1)
                if not s or s == b"\000":
                    break
                fb += s
            original_filename = str(fb, "utf-8")

    return original_filename