@middy/http-multipart-body-parser/index.js

import BusBoy from '@fastify/busboy'
import { createError } from '@middy/util'

const mimePattern = /^multipart\/form-data(;.*)?$/
const fieldnamePattern = /(.+)\[(.*)]$/

const defaults = {
  // busboy options as per documentation: https://www.npmjs.com/package/busboy#busboy-methods
  busboy: {},
  charset: 'utf8',
  disableContentTypeError: false
}

const httpMultipartBodyParserMiddleware = (opts = {}) => {
  const options = { ...defaults, ...opts }

  const httpMultipartBodyParserMiddlewareBefore = async (request) => {
    const { headers } = request.event

    const contentType = headers?.['Content-Type'] ?? headers?.['content-type']

    if (!mimePattern.test(contentType)) {
      if (options.disableContentTypeError) {
        return
      }
      throw createError(415, 'Unsupported Media Type', {
        cause: { package: '@middy/multipart-body-parser', data: contentType }
      })
    }

    return parseMultipartData(request.event, options)
      .then((multipartData) => {
        // request.event.rawBody = body
        request.event.body = multipartData
      })
      .catch((err) => {
        // UnprocessableEntity
        throw createError(
          415,
          'Invalid or malformed multipart/form-data was provided',
          { cause: { package: '@middy/multipart-body-parser', data: err } }
        )
      })
  }

  return {
    before: httpMultipartBodyParserMiddlewareBefore
  }
}

const parseMultipartData = (event, options) => {
  const multipartData = {}
  const charset = event.isBase64Encoded ? 'base64' : options.charset
  // header must be lowercase (content-type)
  const busboy = BusBoy({
    ...options.busboy,
    headers: {
      'content-type':
        event.headers?.['Content-Type'] ?? event.headers?.['content-type']
    }
  })

  return new Promise((resolve, reject) => {
    busboy
      .on('file', (fieldname, file, filename, encoding, mimetype) => {
        const attachment = {
          filename,
          mimetype,
          encoding
        }

        const chunks = []

        file.on('data', (data) => {
          chunks.push(data)
        })
        file.on('end', () => {
          attachment.truncated = file.truncated
          attachment.content = Buffer.concat(chunks)
          if (!multipartData[fieldname]) {
            multipartData[fieldname] = attachment
          } else {
            const current = multipartData[fieldname]
            multipartData[fieldname] = [attachment].concat(current)
          }
        })
      })
      .on('field', (fieldname, value) => {
        const matches = fieldname.match(fieldnamePattern)
        if (!matches) {
          multipartData[fieldname] = value
        } else {
          if (!multipartData[matches[1]]) {
            multipartData[matches[1]] = []
          }
          multipartData[matches[1]].push(value)
        }
      })
      .on('finish', () => resolve(multipartData))
      .on('error', (e) => reject(e))

    busboy.write(event.body, charset)
    busboy.end()
  })
}
export default httpMultipartBodyParserMiddleware