Controller/Adminhtml/FastlyCdn/Vcl/Upload.php
private function validateCustomSnippet($customSnippet)
    {
        $snippetName = str_replace(' ', '', $customSnippet);
        $snippetNameData = explode('_', $snippetName, 3);
        $containsEmpty = in_array("", $snippetNameData, true);
        $types = ['init', 'recv', 'hit', 'miss', 'pass', 'fetch', 'error', 'log', 'deliver', 'hash', 'none'];
        $exception = 'Failed to upload VCL snippets. Please make sure the custom VCL snippets 
            follow this naming convention: [vcl_snippet_type]_[priority]_[short_name_description].vcl';

        if (count($snippetNameData) < 3) {
            throw new LocalizedException(__($exception));
        }

        $inArray = in_array($snippetNameData[0], $types);
        $isNumeric = is_numeric($snippetNameData[1]);
        $isAlphanumeric = preg_match('/^[\w]+$/', $snippetNameData[2]);

        if ($containsEmpty || !$inArray || !$isNumeric || !$isAlphanumeric) {
            throw new LocalizedException(__($exception));
        }
        return $snippetNameData;
    }
private function validateCustomSnippet($customSnippet)
    {
        $snippetName = str_replace(' ', '', $customSnippet);
        $snippetNameData = explode('_', $snippetName, 3);
        $containsEmpty = in_array("", $snippetNameData, true);
        $types = ['init', 'recv', 'hit', 'miss', 'pass', 'fetch', 'error', 'log', 'deliver', 'hash', 'none'];
        $exception = 'Failed to upload VCL snippets. Please make sure the custom VCL snippets 
            follow this naming convention: [vcl_snippet_type]_[priority]_[short_name_description].vcl';

        if (count($snippetNameData) < 3) {
            throw new LocalizedException(__($exception));
        }

        $inArray = in_array($snippetNameData[0], $types);
        $isNumeric = is_numeric($snippetNameData[1]);
        $isAlphanumeric = preg_match('/^[\w]+$/', $snippetNameData[2]);

        if ($containsEmpty || !$inArray || !$isNumeric || !$isAlphanumeric) {
            throw new LocalizedException(__($exception));
        }
        return $snippetNameData;
    }
Validate custom snippet naming convention
[vcl_snippet_type]_[priority]_[short_name_description].vcl

@param $customSnippet
@return array
@throws LocalizedException