python: Implement recv_into()

[bostonrwalker]

Implement recv_into() method in Python socket API

Useful for integrating libzt sockets anywhere that Python sockets are currently used.

Signature: def recv_into(self, buffer: bytes, n_bytes: int = 0, flags: int = 0) -> int

Expected behaviour: Read n_bytes bytes into buffer. If n_bytes > len(buffer), raise an error. Return number of bytes actually read.

Example implementation (Python):

def recv_into(self, buffer: bytes, n_bytes: int = 0, flags: int = 0) -> int:
    """Receive `n_bytes` of data, writing into `buffer`

    :param buffer: Byte buffer
    :param n_bytes: (optional) Number of bytes to read (default: length of buffer)
    :param flags: (optional) Flags
    :return: Number of bytes read
    """
    if n_bytes < 0:
        raise ValueError("negative buffersize in recv_into")

    n_bytes = n_bytes or len(buffer)

    if len(buffer) < n_bytes:
        raise ValueError("buffer too small for requested bytes")

    if n_bytes > 0:
        # TODO: This part should be replaced with a native library call
        recv_bytes = self.recv(n_bytes, flags=flags)
        buffer.join(recv_bytes)
        return len(recv_bytes)
    else:
        return 0