def _format(command, body, headers):
    """
    Return a formatted STOMP frame as a bytestring.
    """
    bits = [command, '\n']
    if body:
        bits.extend(('content-length:', str(len(body)), '\n'))

    for key, value in headers.iteritems():
        bits.extend((key.replace('_', '-'), ':', str(value), '\n',))
    bits.extend((
        '\n',
        body or '',
        '\x00'
    ))
    return ''.join(bits)