multer 基础教程(英文版)
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
).
Translations
This README is also available in other languages:
- 简体中文 (Chinese)
- 한국어 (Korean)
- Русский язык (Russian)
Installation
$ npm install --save multer
Usage
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.
<form action="/profile" method="post" enctype="multipart/form-data">
<input type="file" name="avatar" />
</form>
var express = require('express')
var multer = require('multer')
var upload = multer({ dest: 'uploads/' }) var 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
}) var cpUpload = upload.fields([{ name: 'avatar', maxCount: 1 }, { name: 'gallery', maxCount: 8 }])
app.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 should use the .none()
method:
var express = require('express')
var app = express()
var multer = require('multer')
var upload = multer() app.post('/profile', upload.none(), function (req, res, next) {
// req.body contains the text fields
})
API
File information
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 |
preservePath |
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.
var 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.
.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.
storage
DiskStorage
The disk storage engine gives you full control on storing files to disk.
var storage = multer.diskStorage({
destination: function (req, file, cb) {
cb(null, '/tmp/my-uploads')
},
filename: function (req, file, cb) {
cb(null, file.fieldname + '-' + Date.now())
}
}) var 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.
MemoryStorage
The memory storage engine stores the files in memory as Buffer
objects. It doesn't have any options.
var storage = multer.memoryStorage()
var 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.
limits
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 bytes |
fieldSize |
Max field value size (in bytes) | 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.
fileFilter
Set this to a function to control which files should be uploaded and which should be skipped. The function should look like this:
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!')) }
Error handling
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
).
var multer = require('multer')
var 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.
})
})
Custom storage engine
For information on how to build your own storage engine, see Multer Storage Engine.
License
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