function formatJSON(req, res, body) {
    var data = 'null';
    if (body !== undefined) {
        try {
            data = JSON.stringify(body);
        } catch (e) {
            throw new errors.InternalServerError(
                { cause: e, info: { formatter: 'json' } },
                'could not format response body'
            );
        }
    }

    // Setting the content-length header is not a formatting feature and should
    // be separated into another module
    res.setHeader('Content-Length', Buffer.byteLength(data));

    return data;
}
JSON formatter. Will look for a toJson() method on the body. If one does not
exist then a JSON.stringify will be attempted.

@public
@function formatJSON
@param    {Object} req - the request object (not used)
@param    {Object} res - the response object
@param    {Object} body - response body
@returns  {String} data