Use XHR onprogress to debounce http._request timeout (#392)

Instead of just using a timeout to reject ongoing requests, reset the timeout when progress is observed (at least when requests are done from browsers).

This is to fix https://github.com/vector-im/riot-web/issues/2737

src/http-api.js

@@ -631,7 +631,12 @@ module.exports.MatrixHttpApi.prototype = {
         let timedOut = false;
         let req;
         const localTimeoutMs = opts.localTimeoutMs || this.opts.localTimeoutMs;
+
+        const resetTimeout = () => {
             if (localTimeoutMs) {
+                if (timeoutId) {
+                    callbacks.clearTimeout(timeoutId);
+                }
                 timeoutId = callbacks.setTimeout(function() {
                     timedOut = true;
                     if (req && req.abort) {
@@ -644,6 +649,8 @@ module.exports.MatrixHttpApi.prototype = {
                     }));
                 }, localTimeoutMs);
             }
+        };
+        resetTimeout();
 
         const reqPromise = defer.promise;
 
@@ -679,6 +686,17 @@ module.exports.MatrixHttpApi.prototype = {
                     handlerFn(err, response, body);
                 },
             );
+            // This will only work in a browser, where opts.request is the
+            // `browser-request` import. Currently `request` does not support progress
+            // updates - see https://github.com/request/request/pull/2346.
+            // `browser-request` returns an XHRHttpRequest which exposes `onprogress`
+            if ('onprogress' in req) {
+                req.onprogress = (e) => {
+                    // Prevent the timeout from rejecting the deferred promise if progress is
+                    // seen with the request
+                    resetTimeout();
+                };
+            }
             if (req && req.abort) {
                 // FIXME: This is EVIL, but I can't think of a better way to expose
                 // abort() operations on underlying HTTP requests :(