gistfile1.txt

Components.utils.import("resource://services-sync/main.js");
Components.utils.import("resource://services-sync/engines/clients.js");
Components.utils.import("resource://services-sync/resource.js");

function getClient() {
  let r = new Resource(Weave.Service.storageURL + "clients/" + Clients.localID);
  return r.get();
}

let ts = null;
function tryUpload(resp) {
  let p = new Resource(Weave.Service.storageURL + "clients/" + Clients.localID);
  p.setHeader("X-If-Unmodified-Since", ts);
  let out = p.put(resp);
  if (out != out.headers["x-weave-timestamp"]) {
    throw "NOOO: " + out + " != " + out.headers["x-weave-timestamp"];
  }
  ts = out;
  return out;
}
  
let r = getClient();
ts = r.headers["x-weave-timestamp"]
for (let i = 0; i < 10; ++i) {
  console.log(i);
  tryUpload(r);
}