Re-added file extension restriction ACP option

Closes #3918

src/controllers/uploads.js

@@ -125,6 +125,14 @@ function uploadFile(uid, uploadedFile, callback) {
 		return callback(new Error('[[error:file-too-big, ' + meta.config.maximumFileSize + ']]'));
 	}
 
+	if (meta.config.hasOwnProperty('allowedFileExtensions')) {
+		var allowed = meta.config.allowedFileExtensions.split(',').filter(Boolean);
+		var extension = path.extname(uploadedFile.name).slice(1);
+		if (allowed.length > 0 && allowed.indexOf(extension) === -1) {
+			return callback(new Error('[[error:invalid-file-type, ' + allowed.join(', ') + ']]'));
+		}
+	}
+
 	var filename = uploadedFile.name || 'upload';
 
 	filename = Date.now() + '-' + validator.escape(filename).substr(0, 255);

src/views/admin/settings/post.tpl

@@ -132,13 +132,18 @@
 					<span class="mdl-switch__label"><strong>Allow users to upload regular files</strong></span>
 				</label>
 			</div>
+
 			<div class="checkbox">
 				<label class="mdl-switch mdl-js-switch mdl-js-ripple-effect">
 					<input class="mdl-switch__input" type="checkbox" data-field="privateUploads">
 					<span class="mdl-switch__label"><strong>Make uploaded files private</strong></span>
 				</label>
 			</div>
-			<strong>Maximum File Size</strong><br /> <input type="text" class="form-control" value="2048" data-field="maximumFileSize"><br />
+			
+			<div class="form-group">
+				<label for="maximumFileSize">Maximum File Size</label>
+				<input type="text" class="form-control" value="2048" data-field="maximumFileSize">
+			</div>
 
 			<div class="checkbox">
 				<label class="mdl-switch mdl-js-switch mdl-js-ripple-effect">
@@ -146,7 +151,20 @@
 					<span class="mdl-switch__label"><strong>Allow users to upload topic thumbnails</strong></span>
 				</label>
 			</div>
-			<strong>Topic Thumb Size</strong><br /> <input type="text" class="form-control" value="120" data-field="topicThumbSize"> <br />
+
+			<div class="form-group">
+				<label for="topicThumbSize">Topic Thumb Size</label>
+				<input type="text" class="form-control" value="120" data-field="topicThumbSize"> 
+			</div>
+
+			<div class="form-group">
+				<label for="allowedFileExtensions">Allowed File Extensions</label>
+				<input type="text" class="form-control" value="" data-field="allowedFileExtensions" />
+				<p class="help-block">
+					Enter comma-separated list of file extensions here (e.g. <code>pdf,xls,doc</code>).
+					An empty list means all extensions are allowed.
+				</p>
+			</div>
 		</form>
 	</div>
 </div>