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import ctypes

try:

    from . import bser

except ImportError:

    from . import pybser as bser

EMPTY_HEADER = b"\x00\x01\x05\x00\x00\x00\x00"

def _read_bytes(fp, buf):

    """Read bytes from a file-like object

    @param fp: File-like object that implements read(int)

    @type fp: file

    @param buf: Buffer to read into

    @type buf: bytes

    @return: buf

    """

    # Do the first read without resizing the input buffer

    offset = 0

    remaining = len(buf)

    while remaining > 0:

        l = fp.readinto((ctypes.c_char * remaining).from_buffer(buf, offset))

        if l is None or l == 0:

            return offset

        offset += l

        remaining -= l

    return offset

def load(fp, mutable=True, value_encoding=None, value_errors=None):

    """Deserialize a BSER-encoded blob.

    @param fp: The file-object to deserialize.

    @type file:

    @param mutable: Whether to return mutable results.

    @type mutable: bool

    @param value_encoding: Optional codec to use to decode values. If

                           unspecified or None, return values as bytestrings.

    @type value_encoding: str

    @param value_errors: Optional error handler for codec. 'strict' by default.

                         The other most common argument is 'surrogateescape' on

                         Python 3. If value_encoding is None, this is ignored.

    @type value_errors: str

    """

    buf = ctypes.create_string_buffer(8192)

    SNIFF_BUFFER_SIZE = len(EMPTY_HEADER)

    header = (ctypes.c_char * SNIFF_BUFFER_SIZE).from_buffer(buf)

    read_len = _read_bytes(fp, header)

    if read_len < len(header):

        return None

    total_len = bser.pdu_len(buf)

    if total_len > len(buf):

        ctypes.resize(buf, total_len)

    body = (ctypes.c_char * (total_len - len(header))).from_buffer(

        buf, len(header)

    )

    read_len = _read_bytes(fp, body)

    if read_len < len(body):

        raise RuntimeError("bser data ended early")

    return bser.loads(

        (ctypes.c_char * total_len).from_buffer(buf, 0),

        mutable,

        value_encoding,

        value_errors,

    )