parsers.js

const _ = require('lodash');
const Busboy = require('busboy');

const getContentType = (event) => {
  // Serverless offline is passing 'Content-Type', AWS is passing 'content-type'
  let contentType = _.get(event, 'headers.content-type');
  if (!contentType) contentType = _.get(event, 'headers.Content-Type');

  return contentType;
};

exports.parseForm = (event) => new Promise((resolve, reject) => {
  const busboy = new Busboy({
    headers: {
      'content-type': getContentType(event),
    },
  });

  const result = {};

  busboy.on('file', (fieldname, file, filename, encoding, mimetype) => {
    file.on('data', data => {
      result.file = data;
    });

    file.on('end', () => {
      result.filename = filename;
      result.contentType = mimetype;
    });
  });

  busboy.on('field', (fieldname, value) => {
    result[fieldname] = value;
  });

  busboy.on('error', error => reject(`Parse error: ${error}`));
  busboy.on('finish', () => resolve(_.set(event, 'body', result)));

  busboy.write(event.body, event.isBase64Encoded ? 'base64' : 'binary');
  busboy.end();
});

exports.fromJson = (event) => {
  if (event && event.body && _.isString(event.body)) {
    return _.set(event, 'body', JSON.parse(event.body));
  }
};

exports.toJson = (event, context, response) => {
  if (response && response.body) {
    return _.set(response, 'body', JSON.stringify(response.body));
  }
};

exports.parseRequest = (options) => {
  const defaults = _.assign({}, {
    json: true,
    forms: true,
  }, options);

  // Return the parse handler -> (event, context, response)
  return (event) => {
    if (!event || !event.body) return;

    const contentType = getContentType(event);

    // Mutate the event based on the content type
    if (_.includes(contentType, '/json') && defaults.json) {
      return exports.fromJson(event);
    }

    if (_.includes(contentType, 'multipart/form-data') && defaults.forms) {
      return exports.parseForm(event);
    }
  };
};