Multer: Calculating a hash of the file's content while it uploads

[nickretallack]

I want to generate a hash of the file's content while it is being uploaded. Can I hook in and observe the file stream somehow? And then possibly stow this information somewhere? This other issue is asking for something similar.

Here's what I'd like to do with the stream:

var crypto = require('crypto');
var path = require('path');
// ...
var hash = crypto.createHash('sha256');
file.stream.on('data', function(chunk) { hash.update(chunk) })
file.stream.on('end', function() {
  var sha256 = hash.digest('hex');
  // ... look it up in the database, etc
})

[OmgImAlexis]

+1

[suhaotian]

Write your own, just change multer/storage/disk.js：

var fs = require('fs')
var os = require('os')
var path = require('path')
var crypto = require('crypto')
var mkdirp = require('mkdirp')

function getFilename (req, file, cb) {
  crypto.pseudoRandomBytes(16, function (err, raw) {
    cb(err, err ? undefined : raw.toString('hex'))
  })
}

function getDestination (req, file, cb) {
  cb(null, os.tmpdir())
}

function DiskStorage (opts) {
  this.getFilename = (opts.filename || getFilename)

  if (typeof opts.destination === 'string') {
    mkdirp.sync(opts.destination)
    this.getDestination = function ($0, $1, cb) { cb(null, opts.destination) }
  } else {
    this.getDestination = (opts.destination || getDestination)
  }
}

DiskStorage.prototype._handleFile = function _handleFile (req, file, cb) {
  var that = this
  var hash = crypto.createHash('md5')
  that.getDestination(req, file, function (err, destination) {
    if (err) return cb(err)

    that.getFilename(req, file, function (err, filename) {
      if (err) return cb(err)

      var finalPath = path.join(destination, filename)
      var outStream = fs.createWriteStream(finalPath)

      file.stream.pipe(outStream)
      outStream.on('error', cb)
      outStream.on('data', function (chunk) {
        hash.update(chunk)
      })
      outStream.on('finish', function () {
        cb(null, {
          destination: destination,
          filename: filename,
          path: finalPath,
          size: outStream.bytesWritten,
          hash: hash.digest('hex')
        })
      })
    })
  })
}

DiskStorage.prototype._removeFile = function _removeFile (req, file, cb) {
  var path = file.path

  delete file.destination
  delete file.filename
  delete file.path

  fs.unlink(path, cb)
}

module.exports = function (opts) {
  return new DiskStorage(opts)
}

[microacup]

The right code is:

DiskStorage.prototype._handleFile = function _handleFile (req, file, cb) {
...
  file.stream.on('data', function (chunk) {
      hash.update(chunk)
  })

...

instead of

DiskStorage.prototype._handleFile = function _handleFile (req, file, cb) {
...
  outStream.on('data', function (chunk) {
      hash.update(chunk)
  })

...

because data event only trigger on ReadStream. Then rename the file when data finished.

      outStream.on('finish', function () {
        const md5 = hash.digest('hex').toLowerCase();
        const fileFormat = (file.originalname).split('.');
        const filename = md5 + '.' + fileFormat[fileFormat.length - 1];
        const oldPath = finalPath;
        finalPath = path.join(destination, filename)

        // 计算完成了md5，把文件重命名
        fs.rename(oldPath, finalPath, () => {
          cb(null, {
            destination: destination,
            filename: filename,
            path: finalPath,
            size: outStream.bytesWritten
          })
        })
      })

full solution see: how to use md5 as file name

[jonchurch]

Seems like https://github.com/expressjs/multer/pull/399 would make this easier, I believe.