How does php base64 encode and decode URL strings?

Base64 can transcode binary into visible characters for http transmission, but when base64 transcodes, it will generate " ", "/", "=", which are transcoded by the URL. Special characters cause inconsistency in the two aspects of data.

We can replace " ", "/", and "=" with characters that will not be transcoded in the URL before sending. After receiving the data, we can replace these characters back and then decode.

1. URL safe string encoding:

    function urlsafe_b64encode($string) {
       $data = base64_encode($string);
       $data = str_replace(array('+','/','='),array('-','_',''),$data);
       return $data;
    }

2. URL safe string decoding:

    function urlsafe_b64decode($string) {
       $data = str_replace(array('-','_'),array('+','/'),$string);
       $mod4 = strlen($data) % 4;
       if ($mod4) {
           $data .= substr('====', $mod4);
       }
       return base64_decode($data);
    }

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