title: React-Native, iOS, XHR - XHR progress event not firing on iOS while downloading Blob/Arraybuffer response type
body: <p>as title says I've noticed a strange behaviour while trying to subscribe to the &quot;progress&quot; event that should be fired by an XHR call.</p>
  <p><em>NB: Links used below are just for testing purpose, I need to download a big file (about 100MB) and read how many bytes I've already downloaded from &quot;progress&quot; event. Sefram had some heavy file hosted online where I could test</em></p>
  <pre><code>export default function dlTest(dlCalled, nextTest, settings) {
  
    if (dlCalled) return;
  
    dlCalled = true;
  
    let xhr = new XMLHttpRequest();
  
    xhr.addEventListener(&quot;progress&quot;, (e) =&gt; console.log(&quot;progress&quot;, e.loaded));
    xhr.addEventListener(&quot;load&quot;, (e) =&gt; console.log(&quot;loaded&quot;, e.loaded));
    xhr.addEventListener(&quot;error&quot;, () =&gt; console.log(&quot;error&quot;));
  
    let zipAddress = &quot;https://www.sefram.com/images/products/photos/hi_res/BK1760A.zip&quot;;
    let jpgAddress = &quot;https://www.sefram.com/images/products/photos/hi_res/207030301.jpg&quot;;
    let documentAddress = &quot;https://www.sefram.com/en/download/high-resolution-images.html&quot;;
  
    xhr.open(&quot;GET&quot;, zipAddress, true); 
    xhr.responseType = &quot;blob&quot;;
  
    xhr.send();
  }
  </code></pre>
  <p>Basically I need to read how much bytes I've downloaded since the call started.
  To sum up my tests:</p>
  <ul>
  <li>iOS:
  <ul>
  <li><p>Call <code>documentAddress &amp;&amp; Response-Type: document</code>:
  It does fire progress event but doesn't update <code>event.loaded</code> (it remains 0).
  You can try this yourself with documentAddress.</p>
  </li>
  <li><p>Call <code>documentAddress &amp;&amp; Response-Type: blob/arraybuffer</code>:
  It doesn't fire progress event at all</p>
  </li>
  <li><p>Call <code>zipAddress &amp;&amp; Response-Type: document</code>
  It doesn't fire progress event at all</p>
  </li>
  <li><p>Call <code>zipAddress &amp;&amp; Response-Type: blob/arraybuffer</code>
  It doesn't fire progress event at all</p>
  </li>
  </ul>
  </li>
  </ul>
  <p>I can't really understand why this is happening.
  I couldn't find any other discussion about this kind of problems.
  Thanks in advance for your help.</p>
  <p>React-Native version: 0.64.3</p>
  <p><a href="https://snack.expo.dev/@lianmor/download-test" rel="nofollow noreferrer">Slack Example Download Test</a></p>