Implement a keep-alive timer for /sync requests

When a /sync request fails, we spin up a keep-alive poll to /_matrix/client/r0
which 400s. We treat any HTTP response code as a success for the purposes of
polling the server. When a successful poll is done, we shoot the current /sync
request in the head immediately (via a hacky abort() on the promise) and retry
the /sync.

lib/http-api.js

@@ -43,6 +43,8 @@ module.exports.PREFIX_V2_ALPHA = "/_matrix/client/v2_alpha";
  */
 module.exports.PREFIX_IDENTITY_V1 = "/_matrix/identity/api/v1";
 
+module.exports.PREFIX_R0 = "/_matrix/client/r0";
+
 /**
  * Construct a MatrixHttpApi.
  * @constructor
@@ -416,8 +418,10 @@ module.exports.MatrixHttpApi.prototype = {
             }, localTimeoutMs);
         }
 
+        var reqPromise = defer.promise;
+
         try {
-            this.opts.request(
+            var req = this.opts.request(
                 {
                     uri: uri,
                     method: method,
@@ -425,6 +429,7 @@ module.exports.MatrixHttpApi.prototype = {
                     qs: queryParams,
                     body: data,
                     json: true,
+                    timeout: localTimeoutMs,
                     _matrix_opts: this.opts
                 },
                 function(err, response, body) {
@@ -438,6 +443,9 @@ module.exports.MatrixHttpApi.prototype = {
                     handlerFn(err, response, body);
                 }
             );
+            // FIXME: This is EVIL, but I can't think of a better way to expose
+            // abort() operations on underlying HTTP requests :(
+            reqPromise.abort = req.abort.bind(req);
         }
         catch (ex) {
             defer.reject(ex);
@@ -445,7 +453,7 @@ module.exports.MatrixHttpApi.prototype = {
                 callback(ex);
             }
         }
-        return defer.promise;
+        return reqPromise;
     }
 };