add option to filter which files to accept

Author: LinusU

README.md

@@ -64,6 +64,7 @@ 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
 
 Apart from these, Multer also supports more advanced [busboy options](https://github.com/mscdex/busboy#busboy-methods) like `highWaterMark`, `fileHwm`, and `defCharset`.
@@ -146,6 +147,29 @@ Key | Description | Default
 
 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:
+
+```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!'))
+
+}
+```
+
 ## License
 
 [MIT](LICENSE)

index.js

@@ -7,6 +7,10 @@ var appendField = require('./lib/append-field')
 var diskStorage = require('./storage/disk')
 var memoryStorage = require('./storage/memory')
 
+function allowAll (req, file, cb) {
+  cb(null, true)
+}
+
 function multer (options) {
   options = options || {}
 
@@ -17,6 +21,8 @@ function multer (options) {
     storage = diskStorage({ destination: options.dest })
   }
 
+  var fileFilter = (options.fileFilter || allowAll)
+
   return function multerMiddleware (req, res, next) {
     if (!is(req, ['multipart'])) return next()
 
@@ -61,35 +67,41 @@ function multer (options) {
       // don't attach to the files object, if there is no file
       if (!filename) return fileStream.resume()
 
-      // defines is processing a new file
-      pendingWrites++
-
       var file = {
         fieldname: fieldname,
         originalname: filename,
         encoding: encoding,
         mimetype: mimetype
       }
 
-      Object.defineProperty(file, 'stream', {
-        configurable: true,
-        enumerable: false,
-        value: fileStream
-      })
+      fileFilter(req, file, function (err, includeFile) {
+        if (err) return abort(err)
+        if (!includeFile) return fileStream.resume()
 
-      fileStream.on('error', abort)
-      fileStream.on('limit', function () {
-        abort('LIMIT_FILE_SIZE')
-      })
+        // defines is processing a new file
+        pendingWrites++
 
-      storage.handleFile(req, file, function (err, info) {
-        if (err) return abort(err)
+        Object.defineProperty(file, 'stream', {
+          configurable: true,
+          enumerable: false,
+          value: fileStream
+        })
+
+        fileStream.on('error', abort)
+        fileStream.on('limit', function () {
+          abort('LIMIT_FILE_SIZE')
+        })
+
+        storage.handleFile(req, file, function (err, info) {
+          if (err) return abort(err)
+
+          if (!req.files[fieldname]) req.files[fieldname] = []
+          req.files[fieldname].push(extend(file, info))
 
-        if (!req.files[fieldname]) req.files[fieldname] = []
-        req.files[fieldname].push(extend(file, info))
+          pendingWrites--
+          indicateDone()
+        })
 
-        pendingWrites--
-        indicateDone()
       })
 
     })

test/file-filter.js

@@ -0,0 +1,39 @@
+/* eslint-env mocha */
+
+var assert = require('assert')
+
+var util = require('./_util')
+var multer = require('../')
+var FormData = require('form-data')
+
+describe('File Filter', function () {
+  var parser
+
+  before(function () {
+    parser = multer({
+      storage: multer.memoryStorage(),
+      fileFilter: function (req, file, cb) {
+        cb(null, file.fieldname !== 'notme')
+      }
+    })
+  })
+
+  it('should skip some files', function (done) {
+    var form = new FormData()
+
+    form.append('notme', util.file('tiny0.dat'))
+    form.append('butme', util.file('tiny1.dat'))
+
+    util.submitForm(parser, form, function (err, req) {
+      assert.ifError(err)
+      assert.equal(req.files.notme, undefined)
+      assert.equal(req.files.butme.length, 1)
+      assert.equal(req.files.butme[0].fieldname, 'butme')
+      assert.equal(req.files.butme[0].originalname, 'tiny1.dat')
+      assert.equal(req.files.butme[0].size, 7)
+      assert.equal(req.files.butme[0].buffer.length, 7)
+      done()
+    })
+  })
+
+})