Sample using then-busboy

sample.js

// For each part, create a promise that captures the input
// Promises are put in the promises array so that we can wait on them all
const onFulfilled = (body) => {
    let promises = [];
    let parts = [];

    let partPromise = null;
    for (let partName in body) {
      if (isFile(body[partName])) {
        partPromise =
          body[partName].read()
            .then((buffer) => {
              parts.push({
                name: partName,
                'content-type': body[partName].mime,
                raw: buffer,
              });
            })
            .catch(err => next(err));
        promises.push(partPromise);
      } else { // !isFile
        // TODO: Assuming type is JSON until the gateway switches to using files.
        parts.push({
          name: partName,
          'content-type': 'application/json',
          raw: Buffer.from(body[partName]),
        });
      }
    }

    // once they are all read, we can do processing that requires all content
    Promise.all(promises)
      .then(() => {
        // Validate parts based on mimetype (Validate JSON, XML)
      })
      .then(() => {
        // Check for required parts...
       })