From https://jgraph.github.io/drawio-tools/tools/convert.html
var diagrams = node.getElementsByTagName('diagram');
data = atob(data);
data = bytesToString(pako.inflateRaw(data));
data = decodeURIComponent(data);
document.getElementById('textarea').value = data;
https://stackoverflow.com/questions/46351275/using-pako-deflate-with-python