title: PHP Heroku - Call undefined function mb_detect_encoding()
body: <p>I'm trying to deploy a PHP project to Heroku. I use composer with to install <code>slim framework</code> and <code>simple_http_dom</code> dependencies. Here content of my <code>composer.json</code>:</p>
  <pre><code>{
      &quot;require&quot;: {
          &quot;slim/slim&quot;: &quot;2.4.3&quot;,
          &quot;shark/simple_html_dom&quot;: &quot;dev-master&quot;
      }
  }
  </code></pre>
  <p>when I run the app locally, it's working fine. Then I tried to push it to Heroku, and it seems successful, I saw no error message.</p>
  <p>However, there is a problem when I tried to access it from the browser. nothing shows up. Below is the log from <code>heroku logs</code> command.</p>
  <pre><code>[Sun Aug 31 00:14:37.566291 2014] [proxy_fcgi:error] [pid 60:tid 140467698300672] [client 10.2.162.208:58783] AH01071: Got error 'PHP message: PHP Fatal error:  Call to undefined function mb_detect_encoding() in /app/vendor/shark/simple_html_dom/simple_html_dom.php on line 1234\n', referer: http://myapp.herokuapp.com/index.php/scrap/all
  [31/Aug/2014:00:14:37 +0000] &quot;POST /index.php/scrap/all/do HTTP/1.1&quot; 500 - &quot;http://myapp.herokuapp.com/index.php/scrap/all&quot; &quot;Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.94 Safari/537.36&quot;
  [31-Aug-2014 00:14:37] WARNING: [pool www] child 58 said into stderr: &quot;NOTICE: PHP message: PHP Fatal error:  Call to undefined function mb_detect_encoding() in /app/vendor/shark/simple_html_dom/simple_html_dom.php on line 1234&quot;
  </code></pre>
  <p>One piece from the error that might be interesting:</p>
  <pre><code>Got error 'PHP message: PHP Fatal error:  Call to undefined function mb_detect_encoding() in /app/vendor/shark/simple_html_dom/simple_html_dom.php on line 1234\n', referer: http://myapp.herokuapp.com/index.php/scrap/all
  </code></pre>
  <p>This is the first time I got the above error. I have another app running on Heroku using the same dependencies (but without composer) and it's working fine, but this one isn't.</p>
  <p>what should I do to fix this problem?</p>