Name: multer
Owner: Particle
Description: Node.js middleware for handling `multipart/form-data`.
Forked from: expressjs/multer
Created: 2017-01-24 19:43:41.0
Updated: 2017-01-24 19:43:44.0
Pushed: 2018-01-03 18:34:38.0
Size: 4946
Language: JavaScript
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Multer is a node.js middleware for handling multipart/form-data, which is primarily used for uploading files. It is written
on top of busboy for maximum efficiency.
NOTE: Multer will not process any form which is not multipart (multipart/form-data).
This README is also available in other languages:
m install --save multer
Multer adds a body object and a file or files object to the request object. The body object contains the values of the text fields of the form, the file or files object contains the files uploaded via the form.
Basic usage example:
express = require('express')
multer = require('multer')
upload = multer({ dest: 'uploads/' })
app = express()
post('/profile', upload.single('avatar'), function (req, res, next) {
req.file is the `avatar` file
req.body will hold the text fields, if there were any
post('/photos/upload', upload.array('photos', 12), function (req, res, next) {
req.files is array of `photos` files
req.body will contain the text fields, if there were any
cpUpload = upload.fields([{ name: 'avatar', maxCount: 1 }, { name: 'gallery', maxCount: 8 }])
post('/cool-profile', cpUpload, function (req, res, next) {
req.files is an object (String -> Array) where fieldname is the key, and the value is array of files
e.g.
req.files['avatar'][0] -> File
req.files['gallery'] -> Array
req.body will contain the text fields, if there were any
In case you need to handle a text-only multipart form, you can use any of the multer methods (.single(), .array(), fields()). Here is an example using .array():
express = require('express')
app = express()
multer = require('multer')
upload = multer()
post('/profile', upload.array(), function (req, res, next) {
req.body contains the text fields
Each file contains the following information:
Key | Description | Note
— | — | —
fieldname | Field name specified in the form |
originalname | Name of the file on the user's computer |
encoding | Encoding type of the file |
mimetype | Mime type of the file |
size | Size of the file in bytes |
destination | The folder to which the file has been saved | DiskStorage
filename | The name of the file within the destination | DiskStorage
path | The full path to the uploaded file | DiskStorage
buffer | A Buffer of the entire file | MemoryStorage
multer(opts)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 files will be kept in memory and never written to disk.
By default, Multer will rename the files so as to avoid naming conflicts. The renaming function can be customized according to your needs.
The following are the options that can be passed to Multer.
Key | Description
— | —
dest or storage | Where to store the files
fileFilter | Function to control which files are accepted
limits | Limits of the uploaded data
In an average web app, only dest might be required, and configured as shown in
the following example.
upload = multer({ dest: 'uploads/' })
If you want more control over your uploads, you'll want to use the storage
option instead of dest. Multer ships with storage engines DiskStorage
and MemoryStorage; More engines are available from third parties.
.single(fieldname)Accept a single file with the name fieldname. The single file will be stored
in req.file.
.array(fieldname[, maxCount])Accept an array of files, all with the name fieldname. Optionally error out if
more than maxCount files are uploaded. The array of files will be stored in
req.files.
.fields(fields)Accept a mix of files, specified by fields. An object with arrays of files
will be stored in req.files.
fields should be an array of objects with name and optionally a maxCount.
Example:
name: 'avatar', maxCount: 1 },
name: 'gallery', maxCount: 8 }
.none()Accept only text fields. If any file upload is made, error with code
“LIMIT_UNEXPECTED_FILE” will be issued. This is the same as doing upload.fields([]).
.any()Accepts all files that comes over the wire. An array of files will be stored in
req.files.
WARNING: Make sure that you always handle the files that a user uploads. Never add multer as a global middleware since a malicious user could upload files to a route that you didn't anticipate. Only use this function on routes where you are handling the uploaded files.
storageDiskStorageThe disk storage engine gives you full control on storing files to disk.
storage = multer.diskStorage({
stination: function (req, file, cb) {
cb(null, '/tmp/my-uploads')
lename: function (req, file, cb) {
cb(null, file.fieldname + '-' + Date.now())
upload = multer({ storage: storage })
There are two options available, destination and filename. They are both
functions that determine where the file should be stored.
destination is used to determine within which folder the uploaded files should
be stored. This can also be given as a string (e.g. '/tmp/uploads'). If no
destination is given, the operating system's default directory for temporary
files is used.
Note: You are responsible for creating the directory when providing
destination as a function. When passing a string, multer will make sure that
the directory is created for you.
filename is used to determine what the file should be named inside the folder.
If no filename is given, each file will be given a random name that doesn't
include any file extension.
Note: Multer will not append any file extension for you, your function should return a filename complete with an file extension.
Each function gets passed both the request (req) and some information about
the file (file) to aid with the decision.
Note that req.body might not have been fully populated yet. It depends on the
order that the client transmits fields and files to the server.
MemoryStorageThe memory storage engine stores the files in memory as Buffer objects. It
doesn't have any options.
storage = multer.memoryStorage()
upload = multer({ storage: storage })
When using memory storage, the file info will contain a field called
buffer that contains the entire file.
WARNING: Uploading very large files, or relatively small files in large numbers very quickly, can cause your application to run out of memory when memory storage is used.
limitsAn object specifying the size limits of the following optional properties. Multer passes this object into busboy directly, and the details of the properties can be found on busboy's page.
The following integer values are available:
Key | Description | Default
— | — | —
fieldNameSize | Max field name size | 100 bytes
fieldSize | Max field value size | 1MB
fields | Max number of non-file fields | Infinity
fileSize | For multipart forms, the max file size (in bytes) | Infinity
files | For multipart forms, the max number of file fields | Infinity
parts | For multipart forms, the max number of parts (fields + files) | Infinity
headerPairs | For multipart forms, the max number of header key=>value pairs to parse | 2000
Specifying the limits can help protect your site against denial of service (DoS) attacks.
fileFilterSet this to a function to control which files should be uploaded and which should be skipped. The function should look like this:
tion fileFilter (req, file, cb) {
The function should call `cb` with a boolean
to indicate if the file should be accepted
To reject this file pass `false`, like so:
(null, false)
To accept the file pass `true`, like so:
(null, true)
You can always pass an error if something goes wrong:
(new Error('I don\'t have a clue!'))
When encountering an error, multer will delegate the error to express. You can display a nice error page using the standard express way.
If you want to catch errors specifically from multer, you can call the middleware function by yourself.
upload = multer().single('avatar')
post('/profile', function (req, res) {
load(req, res, function (err) {
if (err) {
// An error occurred when uploading
return
}
// Everything went fine
For information on how to build your own storage engine, see Multer Storage Engine.