feat: filter upload (#716)

README.md

@@ -357,6 +357,10 @@ See it's defaults in [src/Formidable.js DEFAULT_OPTIONS](./src/Formidable.js)
 - `options.filename` **{function}** - default `undefined` Use it to control
   newFilename. Must return a string. Will be joined with options.uploadDir.
 
+- `options.filter` **{function}** - default function that always returns true.
+  Use it to filter files before they are uploaded. Must return a boolean.
+
+
 #### `options.filename`  **{function}** function (name, ext, part, form) -> string
 
 _**Note:** If this size of combined fields, or size of some file is exceeded, an
@@ -372,6 +376,20 @@ form.bytesReceived;
 form.bytesExpected;
 ```
 
+#### `options.filter`  **{function}** function ({name, originalFilename, mimetype}) -> boolean
+
+**Note:** use an outside variable to cancel all uploads upon the first error 
+
+```js
+const options {
+  filter: function ({name, originalFilename, mimetype}) {
+    // keep only images
+    return mimetype && mimetype.includes("image");
+  }
+};
+```
+
+
 ### .parse(request, callback)
 
 Parses an incoming Node.js `request` containing form data. If `callback` is

examples/with-http.js

@@ -10,16 +10,21 @@ const server = http.createServer((req, res) => {
       multiples: true,
       uploadDir: `uploads`,
       keepExtensions: true,
-      filename(/*name, ext, part, form*/) {
-        /* name basename of the http originalFilename
-          ext with the dot ".txt" only if keepExtension is true
-         */
-        // slugify to avoid invalid filenames
-        // substr to define a maximum length
-        // return `${slugify(name).${slugify(ext, separator: '')}`.substr(0, 100);
-        return 'yo.txt'; // or completly different name
-        // return 'z/yo.txt'; // subdirectory
-      },
+      // filename(/*name, ext, part, form*/) {
+      //   /* name basename of the http originalFilename
+      //     ext with the dot ".txt" only if keepExtension is true
+      //    */
+      //   // slugify to avoid invalid filenames
+      //   // substr to define a maximum length
+      //   // return `${slugify(name).${slugify(ext, separator: '')}`.substr(0, 100);
+      //   return 'yo.txt'; // or completly different name
+      //   // return 'z/yo.txt'; // subdirectory
+      // },
+      filter: function ({name, originalFilename, mimetype}) {
+        // keep only images
+        return mimetype && mimetype.includes("image");
+      }
+
     });
 
     form.parse(req, (err, fields, files) => {

src/Formidable.js

@@ -27,6 +27,9 @@ const DEFAULT_OPTIONS = {
   enabledPlugins: ['octetstream', 'querystring', 'multipart', 'json'],
   fileWriteStreamHandler: null,
   defaultInvalidName: 'invalid-name',
+  filter: function () {
+    return true;
+  },
 };
 
 const PersistentFile = require('./PersistentFile');
@@ -316,6 +319,10 @@ class IncomingForm extends EventEmitter {
       return;
     }
 
+    if (!this.options.filter(part)) {
+      return;
+    }
+
     this._flushing += 1;
 
     const newFilename = this._getNewName(part);