Yii2 How to modify file validator for new extension type?

Question

I have file with extension .edoc and mimetype is application/zip. When I try to upload files with this extension, file validator gives me a standard error - that only given (in rules) extensions is possible to upload. Here is my rules:

return array_merge($parent_rules,[
            [
                ['file'],
                'file',
                'maxSize' => 5242880,  // limit 5mb => 5(mb) * 1024(kb) * 1024(b)

                'extensions' => ['pdf','doc','docx','xls','xlsx','png','jpeg','jpg','gif','tiff','tif','avi','flv',
                'wmv','mov','mp4','mkv','ogg','xml','zip','rar','7z','ods','odt','txt','edoc','msg'],
            ],
        ]);

I found that in vendor\yiisoft\yii2\helpers\mimeTypes.php there is an array of rules where extension ".edoc" is not described. When I added key=>value pair

'edoc' => 'application/zip'

File upload is working.

How/is its possible to modify or add this rule without modifying vendor files?

Answer 1

@Michal Hynčica in first answer gave me a good start for this problem, but for avoid load modified file in memory on every request in the sytem, I modified a little bit his code.

So... I made my own magic file like Michal

<?php
// load mime types from original magic file
$originalMagicFile = Yii::getAlias('@yii/helpers/mimeTypes.php');
$mimeTypes = require $originalMagicFile;

$mimeTypes['edoc'] => 'application/zip';
return $mimeTypes;

Then I created custom behavior class for this custom magic file

class MimeTypesBehavior extends Behavior
{
    public function events(): array
    {
        return [
            ActiveRecord::EVENT_BEFORE_VALIDATE => 'beforeValidate',
        ];
    }

    public function beforeValidate()
    {
        FileHelper::$mimeMagicFile = dirname(__DIR__, 2) .'/backend/models/edocMimeTypes.php';
    }

}

and added this behavior to my model form

class FileForm extends File
{
    public $file;

    public function behaviors(): array
    {
        return [
            MimeTypesBehavior::class,
        ];
    }


    /**
     * @return array the validation rules.
     */
    public function rules(): array
    {
        $parent_rules = parent::rules();
        return array_merge($parent_rules,[
            [
                ['file'],
                'file',
                'maxSize' => 5242880,  //  limit 5mb => 5(mb) * 1024(kb) * 1024(b)
                'extensions' => ['pdf','doc','docx','xls','xlsx','png','jpeg','jpg','gif','tiff','tif','avi','flv',
                    'wmv','mov','mp4','mkv','ogg','xml','zip','rar','7z','ods','odt','txt','edoc','msg']
            ],
        ]);
    }

And everything works perfect.