Swagg::Blogg

mojolicious

So I mentioned in my previous post that, with the powers granted to me by Mojolicious, I have migrated from the venerable Apache server with all my server-side fancy stuff being CGI to Docker containers. Awesome! This morning my buddy n4vn33t shared with me an interesting blog post; I'll let the post speak for itself but my takeaway was essentially, sure that upstream Docker image I'm using ought to be patched and ready to rock but... What if it's not? It would help to add RUN apt-get -y upgrade to my Dockerfile to make sure I've got the latest and greatest stuff. And so I did. And then I ran my container locally to give it a quick test and now my remaining CGI scripts are returning 404s. If I run the app locally with morbo www-swagg.pl it “just works” so I must've borked my Docker container!

To troubleshoot, I comment out the apt-get -y upgrade stuff and rebuild. That should yield the same result as prior to the change right? Well, no it didn't. At this point I'm lost so I begin removing all traces of previous images, re-pulling and re-building things. Still got 404s for my beloved guestbook which I think goes without saying, is completely unacceptable! Then I thought about this line in my Dockerfile:

RUN cpanm RJBS/Getopt-Long-Descriptive-0.105.tar.gz

Why run that instead of cpanm Getopt::Long::Descriptive? You see, this module isn't one that I'm using in my scripts but rather it's a dependency; a module I'm using is using this module. One day (prior to this) my Docker container refused to build and I narrowed the problem down to v0.106 of Getopt::Long::Descriptive building and, as it's not a module I'm much concerned with (I just need it so the module I do need will build) I enter the command as you see above to force installation of the prior version that I know will build just fine. So I start by checking out the changelogs for my modules that I'm using in my scripts. Thankfully it didn't take me long to see this in the changelog for Mojolicious (first module I checked 🙃):

9.11 2021-03-20 – This release contains fixes for security issues, everybody should upgrade! – Disabled format detection by default to fix vulnerabilities in many Mojolicious applications. That means some of your routes that previously matched “/foo” and “/foo.json”, will only match “/foo” after upgrading. From now on you will have to explicitly declare the formats your routes are allowed to handle. # /foo # /foo.html # /foo.json $r->get('/foo')–>to('bar#yada'); becomes $r->get('/foo' => [format => ['html', 'json']])–>to('bar#yada', format => undef); And if you are certain that your application is not vulnerable, you also have the option to re-enable format detection for a route and all its nested routes. Due to the high risk of vulnerabilities, this feature is going to be removed again in a future release however. my $active = $r->any([format => 1]); $active->get('/foo')–>to('Test#first'); $active->put('/bar')–>to('Test#second'); ...

Ahh that's right... I'm doing this:

plugin 'Config';

# CGI scripts
plugin CGI => ['/cgi-bin/guest'  => './cgi-bin/guest_mm.cgi'];
plugin CGI => ['/cgi-bin/whoami' => './cgi-bin/whoami.cgi'  ];

The .cgi file extension wasn't technically necessary but I want that to still work because:

  1. I already have hyperlinks all over the place that use the extension
  2. It's a CGI script and I want it to “look” like that... Petty I know

So here's my v9.11+ compliant way of using the extension:

plugin CGI => ['/cgi-bin/guest.cgi'  => './cgi-bin/guest_mm.cgi'];
plugin CGI => ['/cgi-bin/whoami.cgi' => './cgi-bin/whoami.cgi'  ];

Excellent, we're back in business! Fighting issues like this can sometimes feel like a “waste” of an afternoon because at the end of the day... My site hasn't really changed. I gained no new fun buttons or GIFs but I can sleep easy tonight knowing that my site is just a bit more “hardened” against script kiddies who never cease to make our lives just a little bit more complicated. Let's that tag this puppy, push it to my cloud provider and call it a day:

# After we've run: docker build -t www-swagg .
docker tag www-swagg gcr.io/www-swagg/www-swagg
docker push gcr.io/www-swagg/www-swagg
# Bunch of output follows...

And now we're safe. Until tomorrow when the next round of vulnerabilities gets discovered anyways 🤦‍♂️

Until next time bug,

Dan B

#docker #perl #mojolicious

I've been spending the past few weekends with Mojolicious, a Perl web framework. There's plenty of great web frameworks out there; several of them for Perl if you're a Perl programmer like me (e.g. Dancer2, Catalyst, etc). I plan on making my next few posts about Mojolicious as it really has made web programming fun for me, trying new things and learning new things (sometimes breaking new things). In the process I've been migrating my homepage from Apache/CGI to Mojolicious::Lite.

One thing my website has had is an awesome MIDI (technically an mp3 now) soundtrack, which is great but has merely presented itself as a little player in the upper left corner of the page via this HTML:

<!-- Soundtrack -->
<!-- <embed> doesn't work anymore SAD
<embed src="/misc/Smashmouth_-_All_Star.mid" width="100%" height="60">-->
<audio src="/Music/Smashmouth-All-Star.mp3" autoplay controls
       preload="auto"></audio>

Using <embed> with a MIDI file is NFG nowadays so I've replaced it with an <audio> tag. The controls attritube lets you manually play the song since no modern browser will honor the autoplay attribute. I pieced together via some Stackoverflow posts such as this one that generally a browser won't play media without the user clicking on something. I decided one way to do this is with a fake GDPR compliance banner. People click accept on these all the time without even thinking about it the same way we do with software EULAs. This of course makes them completely useless and society would be better off without them but since they're seemingly here to stay we can at least try to make something useful out of them. What I came up with is some Javascript to play it like so:

<!-- Soundtrack -->
<audio id="soundtrack" src="/Music/Smashmouth-All-Star.mp3" preload="auto">
</audio>
<!-- "GDPR" banner -->
<div id="gdpr">
  <b>Notice:</b> This site uses kickass MIDI technology instead of cookies.
  <img alt="a compact disc playing music" src="/Pictures/Music_CD.gif"
       style="vertical-align: bottom"><br>
  <br>
  <button class="win95button" onclick="playIt();"><u>O</u>K</button>
  <button class="win95button" onclick="closeIt();"><u>C</u>ancel</button>
</div>
<script>
  function closeIt() {
      document.getElementById("gdpr").style.display = "none";
  }

  function playIt() {
      document.getElementById("soundtrack").play();
      closeIt();
  }
</script>

The way this works is the user clicks on “OK” (they always do!), then document.getElementById("soundtrack").play(); reliably triggers the music playback. Mission accomplished but now I have a new grievance: The banner keeps coming back no matter what. The real GDPR banner wouldn't do this even with all its own aggrivations. This is happening because HTTP is a stateless protocol. The irony in my fake GDPR banner is that I'll need to leverage session cookies to maintain state; to tell my homepage, “This user has already heard the joke.” I started by just adding another line to the closeIt() function:

function closeIt() {
    document.getElementById("gdpr").style.display = "none";
    document.cookie = "banner=seen; max-age=600;";
}

This sets my cookie as a plain-text cookie plus I set a max-age so it doesn't linger forever (I'll explain why in a bit). This is fine but because Mojolicious has a more sophisticated way of handling the session I wanted to let Mojolicious set the cookie. That posed a new challenge: HTTP is also a request/response conversation, thus Mojo would want to set its session cookie via a Set-Cookie: response header. However by the time the user sees the banner, the request is completed. I thought of two ways to get around this: Create a new route, let's say /session, then have my accept button point to that. The /session route could then redirect the user back to the value of the Referer: request header (that's the actual spelling) with the Set-Cookie: header in the 301 or 302 response.

Or, since I already have my plain-text cookie in place, why not just look for the presence of this cookie in subsequent requests and if we find it, then include our session cookie in the response? My max-age of 10 min means the plain-text cookie will eventually “roll off” if you will but the fancy, cryptographically signed session cookie will live on with its lifetime of an hour:

# Handle the session
under sub {
    my ($c) = @_;

    if ($c->cookie('banner') eq 'seen') {
        $c->session->{banner} //= 'seen'
    }

    1;
};

I'm using under in my Perl code (the controller) to save myself from having to repeat this logic in every route. Here's the end result according to the response headers:

[daniel@threadlake ~]$ curl -I -k -b 'banner=seen' https://www.swagg.net
HTTP/2 200
content-type: text/html;charset=UTF-8
set-cookie: mojolicious=eyJiYW5uZXIiOiJzZWVuIiwiZXhwaXJlcyI6MTYxNTc2Mjc0OX0---22455b29015766360fe791cb13cd16778e4fb197; expires=Sun, 14 Mar 2021 22:59:09 GMT; path=/; HttpOnly; SameSite=Lax
x-cloud-trace-context: 06fdb28b1bbd08a2b04c3d5d668a5afd;o=1
content-length: 5529
date: Sun, 14 Mar 2021 21:59:09 GMT
server: Google Frontend
via: 1.1 google
alt-svc: clear

We can decode the bit of the session cookie to the left of the three hyphens with, what else, perl:

[daniel@threadlake ~]$ perl -MMIME::Base64 -e 'print decode_base64("eyJiYW5uZXIiOiJzZWVuIiwiZXhwaXJlcyI6MTYxNTc2Mjc0OX0"), "\n";'
{"banner":"seen","expires":1615762749}

Expires in an hour rather than the 600 seconds (aka 10 minutes) of our plain-text cookie:

[daniel@threadlake ~]$ date -d @1615762749; echo "it is now: `date`"
Sun Mar 14 06:59:09 PM EDT 2021
it is now: Sun Mar 14 06:04:13 PM EDT 2021

That “stuff” to the right of the three hyphens is currently still a mystery to me. I imagine it has something to do with the HMAC-SHA1 signature that makes the session cookie tamper-proof. That's about all I can say about session cookies for one weekend. One last thing I want to share is another bonus use I found for my newfangled session. I can look for it in my templates/layouts to save the client from even having to download the mp3 file or GDPR banner resources on subsequent requests as well, sparing them some bandwidth:

<% unless (session('banner') eq 'seen') { %>
<!-- Soundtrack -->
<!-- <embed> doesn't work anymore SAD
<embed src="/misc/Smashmouth_-_All_Star.mid" width="100%" height="60">-->
<audio id="soundtrack" src="/Music/Smashmouth-All-Star.mp3" preload="auto">
</audio>
<!-- "GDPR" banner -->
<div id="gdpr">
  <b>Notice:</b> This site uses kickass MIDI technology instead of cookies.
  <img alt="a compact disc playing music" src="/Pictures/Music_CD.gif"
       style="vertical-align: bottom"><br>
  <br>
  <button class="win95button" onclick="playIt();"><u>O</u>K</button>
  <button class="win95button" onclick="closeIt();"><u>C</u>ancel</button>
</div>
<script>
  function closeIt() {
      document.getElementById("gdpr").style.display = "none";
      document.cookie = "banner=seen; max-age=600;";
  }

  function playIt() {
      document.getElementById("soundtrack").play();
      closeIt();
  }
</script>
<% } %>

Layouts and templates are also fun Mojo things I'll want to say more about in later posts. I look forward to sharing how I've actually deployed this thing via Docker container as I was pleasantly surprised on how painless this can be for someone who cut their teeth on Apache and CGI. Diving into Mojo has exposed me to newfangled concepts that I frankly wasn't particulary excited about before (I still maintain that “serverless” is a damn oxymoron!). I find myself more open to exploring them now and hopefully will give me cool things to muse on here in the future.

Source code for my cool new web 2.0 page is on my Codeberg and is, as always, “under construction”.

Happy GDPR-compliant cookie acceptance,

Dan

EDIT: Fixed some markdown formatting errors

#perl #mojolicious