index.js

function getValueIgnoringKeyCase(obj, lookedKey) {
    return Object.keys(obj)
        .map(presentKey => presentKey.toLowerCase() === lookedKey.toLowerCase() ? obj[presentKey] : null)
        .filter(item => item)[0];
}

module.exports.parse = (event, spotText) => {
    const boundary = getValueIgnoringKeyCase(event.headers, 'Content-Type').split('=')[1];
    const body = (event.isBase64Encoded ? Buffer.from(event.body, 'base64').toString('binary') : event.body)
        .split(boundary)
        .filter(item => item.match(/Content-Disposition/))
        .map((item) => {
            if (item.match(/filename/)) {
                const result = {};
                result[
                    item
                        .match(/name="[a-zA-Z_]+([a-zA-Z0-9_]*)"/)[0]
                        .split('=')[1]
                        .match(/[a-zA-Z_]+([a-zA-Z0-9_]*)/)[0]
                ] = {
                        type: 'file',
                        filename: item.match(/filename="([^"]+)"/)[1],
                        contentType: item
                            .match(/Content-Type: .+\r\n\r\n/)[0]
                            .replace(/Content-Type: /, '')
                            .replace(/\r\n\r\n/, ''),
                        content: (spotText && item
                            .match(/Content-Type: .+\r\n\r\n/)[0]
                            .replace(/Content-Type: /, '')
                            .replace(/\r\n\r\n/, '')
                            .match(/text/)
                        ) ? item
                            .split(/\r\n\r\n/)[1]
                            .replace(/\r\n\r\n\r\n----/, '') : Buffer.from(item
                                .split(/\r\n\r\n/)[1]
                                .replace(/\r\n\r\n\r\n----/, ''), 'binary'),
                    };
                return result;
            }
            const result = {};
            result[
                item
                    .match(/name="[a-zA-Z_]+([a-zA-Z0-9_]*)"/)[0]
                    .split('=')[1]
                    .match(/[a-zA-Z_]+([a-zA-Z0-9_]*)/)[0]
            ] = item
                .split(/\r\n\r\n/)[1]
                .split(/\r\n--/)[0];
            return result;
        })
        .reduce((accumulator, current) => Object.assign(accumulator, current), {});
    return body;
};