Middleware for handling `multipart/form-data`.
npm install multerMulter 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).
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``sh`
$ npm install 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:
Don't forget the enctype="multipart/form-data" in your form.
`html`
`javascript
const express = require('express')
const multer = require('multer')
const upload = multer({ dest: 'uploads/' })
const app = express()
app.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
})
app.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
})
const uploadMiddleware = upload.fields([{ name: 'avatar', maxCount: 1 }, { name: 'gallery', maxCount: 8 }])
app.post('/cool-profile', uploadMiddleware, 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 should use the .none() method:
`javascript
const express = require('express')
const app = express()
const multer = require('multer')
const upload = multer()
app.post('/profile', upload.none(), function (req, res, next) {
// req.body contains the text fields
})
`
Here's an example on how multer is used in a HTML form. Take special note of the enctype="multipart/form-data" and name="uploaded_file" fields:
`html`
Then in your javascript file you would add these lines to access both the file and the body. It is important that you use the name field value from the form in your upload function. This tells multer which field on the request it should look for the files in. If these fields aren't the same in the HTML form and on your server, your upload will fail:
`javascript`
const multer = require('multer')
const upload = multer({ dest: './public/data/uploads/' })
app.post('/stats', upload.single('uploaded_file'), function (req, res) {
// req.file is the name of your file in the form above, here 'uploaded_file'
// req.body will hold the text fields, if there were any
console.log(req.file, req.body)
});
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 | The name of the file within the destination | DiskStorage | The full path to the uploaded file | DiskStorage | A Buffer of the entire file | MemoryStorage
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 filesfileFilter | Function to control which files are acceptedlimits | Limits of the uploaded datapreservePath | Keep the full path of files instead of just the base name
In an average web app, only dest might be required, and configured as shown in
the following example.
`javascript`
const upload = multer({ dest: 'uploads/' })
If you want more control over your uploads, you'll want to use the storage
option instead of . Multer ships with storage engines DiskStorage
and ; More engines are available from third parties.
#### .single(fieldname)
Accept a single file with the name fieldname. The single file will be storedreq.file
in .
#### .array(fieldname[, maxCount])
Accept an array of files, all with the name fieldname. Optionally error out ifmaxCount
more than files are uploaded. The array of files will be stored inreq.files.
#### .fields(fields)
Accept a mix of files, specified by fields. An object with arrays of filesreq.files
will be stored in .
fields should be an array of objects with name and optionally a maxCount.
Example:
`javascript`
[
{ 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.
#### .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.
#### DiskStorage
The disk storage engine gives you full control on storing files to disk.
`javascript
const storage = multer.diskStorage({
destination: function (req, file, cb) {
cb(null, '/tmp/my-uploads')
},
filename: function (req, file, cb) {
const uniqueSuffix = Date.now() + '-' + Math.round(Math.random() * 1E9)
cb(null, file.fieldname + '-' + uniqueSuffix)
}
})
const 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 shouldstring
be stored. This can also be given as a (e.g. '/tmp/uploads'). If nodestination 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.filename
If no 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 a file extension.
Each function gets passed both the request (req) and some information aboutfile
the 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.
For understanding the calling convention used in the callback (needing to pass
null as the first param), refer to
Node.js error handling
#### MemoryStorage
The memory storage engine stores the files in memory as Buffer objects. It
doesn't have any options.
`javascript`
const storage = multer.memoryStorage()
const 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.
An 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 bytesfieldSize | Max field value size (in bytes) | 1MBfields | Max number of non-file fields | InfinityfileSize | For multipart forms, the max file size (in bytes) | Infinityfiles | For multipart forms, the max number of file fields | Infinityparts | For multipart forms, the max number of parts (fields + files) | InfinityheaderPairs | 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.
Set this to a function to control which files should be uploaded and which
should be skipped. The function should look like this:
`javascript
function 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:
cb(null, false)
// To accept the file pass true, like so:
cb(null, true)
// You can always pass an error if something goes wrong:
cb(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. Also, if you want to catch only the Multer errors, you can use the MulterError class that is attached to the multer object itself (e.g. err instanceof multer.MulterError).
`javascript
const multer = require('multer')
const upload = multer().single('avatar')
app.post('/profile', function (req, res) {
upload(req, res, function (err) {
if (err instanceof multer.MulterError) {
// A Multer error occurred when uploading.
} else if (err) {
// An unknown error occurred when uploading.
}
// Everything went fine.
})
})
``
For information on how to build your own storage engine, see Multer Storage Engine.
[ci-image]: https://github.com/expressjs/multer/actions/workflows/ci.yml/badge.svg
[ci-url]: https://github.com/expressjs/multer/actions/workflows/ci.yml
[test-url]: https://coveralls.io/r/expressjs/multer?branch=main
[test-image]: https://badgen.net/coveralls/c/github/expressjs/multer/main
[npm-downloads-image]: https://badgen.net/npm/dm/multer
[npm-url]: https://npmjs.org/package/multer
[npm-version-image]: https://badgen.net/npm/v/multer
[ossf-scorecard-badge]: https://api.scorecard.dev/projects/github.com/expressjs/multer/badge
[ossf-scorecard-visualizer]: https://ossf.github.io/scorecard-visualizer/#/projects/github.com/expressjs/multer