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POWhat character replacements should be performed to make base 64 encoding URL safe?
 

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  1. POWhat character replacements should be performed to make base 64 encoding URL safe?
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    <p>In looking at URL safe base 64 encoding, I've found it to be a very non-standard thing. Despite the copious number of built in functions that PHP has, there isn't one for URL safe base 64 encoding. On the manual page for <a href="http://us.php.net/base64_encode" rel="nofollow noreferrer"><code>base64_encode()</code></a>, most of the comments suggest using that function, wrapped with <code>strtr()</code>:</p> <pre><code>function base64_url_encode($input) { return strtr(base64_encode($input), '+/=', '-_,'); } </code></pre> <p>The only Perl module I could find in this area is <a href="http://search.cpan.org/~kazuho/MIME-Base64-URLSafe-0.01/lib/MIME/Base64/URLSafe.pm" rel="nofollow noreferrer">MIME::Base64::URLSafe</a> (<a href="http://cpansearch.perl.org/src/KAZUHO/MIME-Base64-URLSafe-0.01/lib/MIME/Base64/URLSafe.pm" rel="nofollow noreferrer">source</a>), which performs the following replacement internally:</p> <pre><code>sub encode ($) { my $data = encode_base64($_[0], ''); $data =~ tr|+/=|\-_|d; return $data; } </code></pre> <p>Unlike the PHP function above, this Perl version drops the '=' (equals) character entirely, rather than replacing it with ',' (comma) as PHP does. Equals is a padding character, so the Perl module replaces them as needed upon decode, but this difference makes the two implementations incompatible.</p> <p>Finally, the Python function <a href="http://docs.python.org/library/base64.html#base64.urlsafe_b64encode" rel="nofollow noreferrer">urlsafe_b64encode(s)</a> keeps the '=' padding around, prompting someone to put up <a href="http://snipplr.com/view/15110/urlsafe-base64-functions/" rel="nofollow noreferrer">this function</a> to remove the padding which shows prominently in Google results for <a href="http://www.google.com/search?hl=en&amp;q=python%20base64%20url%20safe&amp;btnG=Google+Search" rel="nofollow noreferrer">'python base64 url safe'</a>:</p> <pre><code>from base64 import urlsafe_b64encode, urlsafe_b64decode def uri_b64encode(s): return urlsafe_b64encode(s).strip('=') def uri_b64decode(s): return urlsafe_b64decode(s + '=' * (4 - len(s) % 4)) </code></pre> <p>The desire here is to have a string that can be included in a URL without further encoding, hence the ditching or translation of the characters '+', '/', and '='. Since there isn't a defined standard, <strong>what is the right way?</strong></p>
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