def _read_to_buffer(self):
        """Reads from the socket and appends the result to the read buffer.

        Returns the number of bytes read.  Returns 0 if there is nothing
        to read (i.e. the read returns EWOULDBLOCK or equivalent).  On
        error closes the socket and raises an exception.
        """
        try:
            chunk = self.read_from_fd()
        except (socket.error, __HOLE__, OSError) as e:
            # ssl.SSLError is a subclass of socket.error
            if e.args[0] == errno.ECONNRESET:
                # Treat ECONNRESET as a connection close rather than
                # an error to minimize log spam  (the exception will
                # be available on self.error for apps that care).
                self.close(exc_info=True)
                return
            self.close(exc_info=True)
            raise
        if chunk is None:
            return 0
        self._read_buffer.append(chunk)
        self._read_buffer_size += len(chunk)
        if self._read_buffer_size >= self.max_buffer_size:
            gen_log.error("Reached maximum read buffer size")
            self.close()
            raise IOError("Reached maximum read buffer size")
        return len(chunk)
dataset/ETHPy150Open D-L/SimpleBookMarks/src/tornado/iostream.py/BaseIOStream._read_to_buffer