Persist multiple files temporary with apollo-upload-server for sending out attachments as part of an email message.

persistMultipleFiles.js

const fs = require('fs')
const tmp = require('tmp')

/**
 *
 * @param stream
 * @return {Promise<any>}
 */
const storeFS = ({stream}) => {
  const tmpObj = tmp.fileSync()
  const path = tmpObj.name
  // const path = `${uploadDir}/${id}-${filename}`
  return new Promise((resolve, reject) =>
    stream
      .on('error', error => {
        if (stream.truncated)
        // Delete the truncated file
          fs.unlinkSync(path)
        reject(error)
      })
      .pipe(fs.createWriteStream(path))
      .on('error', error => reject(error))
      .on('close', (...args) => {
        console.log(...args)
      })
      .on('finish', () => resolve(tmpObj))
  )
}

/**
 *
 * @param upload
 * @return {Promise<{data: ReadStream, removeCallback: fileCallback, filename: *, contentType: *, knownLength: number}>}
 */
const processUpload = async upload => {
  const {stream, filename, mimetype} = await upload
  const tmpFile = await storeFS({stream})
  return {
    data: fs.createReadStream(tmpFile.name),
    removeCallback: tmpFile.removeCallback,
    filename,
    contentType: mimetype,
    knownLength: fs.statSync(tmpFile.name).size
  }
}

/**
 * @description need to check on apollo-upload-server v6 to circumvent the issue with await File in a loop
 * @param files
 * @return {Promise<any[]>}
 */
const prepareMailGunAttachments = async files => {
  const persistedFiles = await Promise.all(
    files.map(processUpload)
  )
  return persistedFiles
}

module.exports = prepareMailGunAttachments

resolver.js

sendMail: async (parent, {message, attachments}) => {
      let files = []
      let tmpFiles = null
      if (attachments && attachments.length) {
        tmpFiles = await prepareMailGunAttachments(attachments)
        files = tmpFiles.map(item => {
          const obj = Object.assign({}, item)
          delete obj.removeCallback
          return obj
        })
      }
      try {
        // sending out email with message and file attachments
        const r = await sendMailgunMail(message,files)
        // cleanup
        if(tmpFiles){
         tmpFiles.forEach(f => f.removeCallback()) 
        }
        return r
      }
}