Function which runs on the pyboard. Matches up with send_file_to_remote.

def recv_file_from_host(src_file, dst_filename, filesize, dst_mode='wb'):
    """Function which runs on the pyboard. Matches up with send_file_to_remote."""
    import sys
    import ubinascii
    if HAS_BUFFER:
        try:
            import pyb
            usb = pyb.USB_VCP()
        except:
            try:
                import machine
                usb = machine.USB_VCP()
            except:
                usb = None
        if usb and usb.isconnected():
            # We don't want 0x03 bytes in the data to be interpreted as a Control-C
            # This gets reset each time the REPL runs a line, so we don't need to
            # worry about resetting it ourselves
            usb.setinterrupt(-1)
    try:
        with open(dst_filename, dst_mode) as dst_file:
            bytes_remaining = filesize
            if not HAS_BUFFER:
                bytes_remaining *= 2  # hexlify makes each byte into 2
            buf_size = BUFFER_SIZE
            write_buf = bytearray(buf_size)
            read_buf = bytearray(buf_size)
            while bytes_remaining > 0:
                # Send back an ack as a form of flow control
                sys.stdout.write('\x06')
                read_size = min(bytes_remaining, buf_size)
                buf_remaining = read_size
                buf_index = 0
                while buf_remaining > 0:
                    if HAS_BUFFER:
                        bytes_read = sys.stdin.buffer.readinto(read_buf, read_size)
                    else:
                        bytes_read = sys.stdin.readinto(read_buf, read_size)
                    if bytes_read > 0:
                        write_buf[buf_index:bytes_read] = read_buf[0:bytes_read]
                        buf_index += bytes_read
                        buf_remaining -= bytes_read
                if HAS_BUFFER:
                    dst_file.write(write_buf[0:read_size])
                else:
                    dst_file.write(ubinascii.unhexlify(write_buf[0:read_size]))
                bytes_remaining -= read_size
        return True
    except:
        return False