class/class_backend/node_modules/multer/index.js

var makeMiddleware = require('./lib/make-middleware')

var diskStorage = require('./storage/disk')
var memoryStorage = require('./storage/memory')
var MulterError = require('./lib/multer-error')

function allowAll (req, file, cb) {
  cb(null, true)
}

function Multer (options) {
  if (options.storage) {
    this.storage = options.storage
  } else if (options.dest) {
    this.storage = diskStorage({ destination: options.dest })
  } else {
    this.storage = memoryStorage()
  }

  this.limits = options.limits
  this.preservePath = options.preservePath
  this.fileFilter = options.fileFilter || allowAll
}

Multer.prototype._makeMiddleware = function (fields, fileStrategy) {
  function setup () {
    var fileFilter = this.fileFilter
    var filesLeft = Object.create(null)

    fields.forEach(function (field) {
      if (typeof field.maxCount === 'number') {
        filesLeft[field.name] = field.maxCount
      } else {
        filesLeft[field.name] = Infinity
      }
    })

    function wrappedFileFilter (req, file, cb) {
      if ((filesLeft[file.fieldname] || 0) <= 0) {
        return cb(new MulterError('LIMIT_UNEXPECTED_FILE', file.fieldname))
      }

      filesLeft[file.fieldname] -= 1
      fileFilter(req, file, cb)
    }

    return {
      limits: this.limits,
      preservePath: this.preservePath,
      storage: this.storage,
      fileFilter: wrappedFileFilter,
      fileStrategy: fileStrategy
    }
  }

  return makeMiddleware(setup.bind(this))
}

Multer.prototype.single = function (name) {
  return this._makeMiddleware([{ name: name, maxCount: 1 }], 'VALUE')
}

Multer.prototype.array = function (name, maxCount) {
  return this._makeMiddleware([{ name: name, maxCount: maxCount }], 'ARRAY')
}

Multer.prototype.fields = function (fields) {
  return this._makeMiddleware(fields, 'OBJECT')
}

Multer.prototype.none = function () {
  return this._makeMiddleware([], 'NONE')
}

Multer.prototype.any = function () {
  function setup () {
    return {
      limits: this.limits,
      preservePath: this.preservePath,
      storage: this.storage,
      fileFilter: this.fileFilter,
      fileStrategy: 'ARRAY'
    }
  }

  return makeMiddleware(setup.bind(this))
}

function multer (options) {
  if (options === undefined) {
    return new Multer({})
  }

  if (typeof options === 'object' && options !== null) {
    return new Multer(options)
  }

  throw new TypeError('Expected object for argument options')
}

module.exports = multer
module.exports.diskStorage = diskStorage
module.exports.memoryStorage = memoryStorage
module.exports.MulterError = MulterError