In bin.html, some tags don't have quotes in their keyword arguments. Like type, id, method, charset arguments ; example :

<meta charset=utf-8>
<form method=POST>
<textarea name=code id=code
<input type=submit id=submit>

even though html is not sensitive, charset by example stay sensitive, code have to be converted to :

<meta charset="utf-8">
<form method="POST">
<textarea name="code" id="code">
<input type="submit" id="submit">

It would be nice to store the bins compressed in memory and to stream them as-is. Having them compressed in memory would reduce the memory usage. Streaming them as-is (with the suited http header) would reduce bandwidth usage. I know reverse-proxies are capable to compress the data on-the-fly but this is not CPU efficient, best is to have the data compressed already.

If we write a long text on the / route, where the main <textarea> is, there is no problem, the scrollbar is here :

but when we eventually click on submit, we are redirected to the paste we wrote, but the text is cut at the bottom of the page without scrollbar, we can't scroll the paste :

The encoding problem seems to be related to the way it is stored, as long as it doesn't come from the HTML meta charset tag.

When I wrote:

Ceci est un texte de test permettant de détecter un problème d'encodage certain

It then outputs:

Ceci est un texte de test permettant de détecter un problème d'encodage certain

And the HTML is:

<pre><code id="hlcode" class="lang-plaintext hljs">Ceci est un texte de test permettant de détecter un problème d'encodage certain</code></pre>

which confirms that the problem is not from the HTML meta charset tag

P.S.: Sorry for the stupid dummy text, I was not inspired