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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def message_with_placeholders(message):
 """ Return an ASGI message, with any body-type content omitted and replaced with a placeholder. """

    new_message = message.copy()
    for attr in PLACEHOLDER_FORMAT.keys():
        if message.get(attr) is not None:
            content = message[attr]
            placeholder = PLACEHOLDER_FORMAT[attr].format(length=len(content))
            new_message[attr] = placeholder
    return new_message