Multer is a node.js middleware for handling multipart/form-data.

It is written on top of busboy for maximum efficiency.

$ npm install multer

var express = require('express')
var multer  = require('multer')

var app = express()
app.use(multer({ dest: './uploads/'}))

You can access the fields and files in the request object:

console.log(req.body)
console.log(req.files)

IMPORTANT: Multer will not process any form which is not multipart/form-data submitted via the POST or PUT methods.

A multer file object is a JSON object with the following properties.

1. fieldname - Field name specified in the form
2. originalname - Name of the file on the user's computer
3. name - Renamed file name
4. encoding - Encoding type of the file
5. mimetype - Mime type of the file
6. path - Location of the uploaded file
7. extension - Extension of the file
8. size - Size of the file in bytes
9. truncated - If the file was truncated due to size limitation

Multer accepts an options object, the most basic of which is the dest property, which tells Multer where to upload the files. In case you omit the options object, the file will be renamed and uploaded to the temporary directory of the system.

By the default, Multer will rename the files so as to avoid name conflicts. The renaming function can be customized according to your needs.

The following are the options that can be passed to Multer.

• dest
• limits
• rename(fieldname, filename)
• onFileUploadStart(file)
• onFileUploadData(file, data)
• onFileUploadComplete(file)
• onParseStart()
• onParseEnd()
• onError()
• onFilesLimit()
• onFieldsLimit()
• onPartsLimit()

Apart from these, Multer also supports more advanced busboy options like highWaterMark, fileHwm, and defCharset.

In an average web app, only dest and rename might be required, and configured as shown in the example.

app.use(multer({
  dest: './uploads/',
  rename: function (fieldname, filename) {
    return filename.replace(/\W+/g, '-').toLowerCase() + Date.now()
  }
}))

The details of the properties of the options object is explained in the following sections.

The destination directory for the uploaded files.

dest: './uploads/'

An object specifying the size limits of the following optional properties. This object is passed to busboy directly, and the details of properties can be found on busboy's page

• fieldNameSize - integer - Max field name size (Default: 100 bytes)
• fieldSize - integer - Max field value size (Default: 1MB)
• fields - integer - Max number of non-file fields (Default: Infinity)
• fileSize - integer - For multipart forms, the max file size (in bytes) (Default: Infinity)
• files - integer - For multipart forms, the max number of file fields (Default: Infinity)
• parts - integer - For multipart forms, the max number of parts (fields + files) (Default: Infinity)
• headerPairs - integer - For multipart forms, the max number of header key=>value pairs to parse Default: 2000 (same as node's http).

limits: {
  fieldNameSize: 100,
  files: 2,
  fields: 5
}

Specifying the limits can help protect your site against denial of service (DoS) attacks.

Function to rename the uploaded files. Whatever the function returns will become the new name of the uploaded file (extension is not included). The fieldname and filename of the file will be available in this function, use them if you need to.

rename: function (fieldname, filename) {
  return fieldname + filename + Date.now()
}

Event handler triggered when a file starts to be uploaded. A file object with the following properties are available to this function: fieldname, originalname, name, encoding, mimetype, path, extension.

onFileUploadStart: function (file) {
  console.log(file.fieldname + ' is starting ...')
}

Event handler triggered when a chunk of buffer is received. A buffer object along with a file object is available to the function.

onFileUploadData: function (file, data) {
  console.log(data.length + ' of ' + file.fieldname + ' arrived')
}

Event handler trigger when a file is completely uploaded. A file object is available to the function.

onFileUploadComplete: function (file) {
  console.log(file.fieldname + ' uploaded to  ' + file.path)
}

Event handler triggered when the form parsing starts.

onParseStart: function () {
  console.log('Form parsing started at: ', new Date())
}

Event handler triggered when the form parsing completes.

onParseStart: function () {
  console.log('Form parsing completed at: ', new Date())
}

Event handler for any errors encountering while processing the form. The error object and the next object is available to the function. If you are handling errors yourself, make sure to terminate the request or call the next() function, else the request will be left hanging.

onError: function (error, next) {
  console.log(error)
  next(error)
}

Event handler triggered when the number of files exceed the specification in the limit object. No more files will be parsed after the limit is reached.

onFilesLimit: function () {
  console.log('Crossed file limit!')
}

Event handler triggered when the number of fields exceed the specification in the limit object. No more fields will be parsed after the limit is reached.

onFieldsLimit: function () {
  console.log('Crossed fields limit!')
}

Event handler triggered when the number of parts exceed the specification in the limit object. No more files or fields will be parsed after the limit is reached.

onPartsLimit: function () {
  console.log('Crossed parts limit!')
}

Copyright (c) 2014 Hage Yaapa <http://www.hacksparrow.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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