api: measure elapsed time

return it in objects

source/git-api.js

@@ -163,14 +163,22 @@ exports.registerApi = (env) => {
     { maxWait: 2000 }
   );
 
-  const jsonResultOrFailProm = (res, promise) =>
-    // TODO shouldn't this be a boolean instead of an object?
-    promise
-      .then((o) => res.json(o == null ? {} : o))
-      .catch((err) => {
-        winston.warn('Responding with ERROR: ', JSON.stringify(err));
-        res.status(400).json(err);
-      });
+  const jsonResultOrFailProm = (res, promise) => {
+    const now = Date.now();
+    return (
+      // TODO shouldn't this be a boolean instead of an object?
+      promise
+        .then((o) => {
+          const elapsed = Date.now() - now;
+          if (o && typeof o === 'object') o._elapsed = elapsed;
+          return res.json(o == null ? {} : o);
+        })
+        .catch((err) => {
+          winston.warn('Responding with ERROR: ', JSON.stringify(err));
+          res.status(400).json(err);
+        })
+    );
+  };
 
   const w = (fn) => (req, res) =>
     new Promise((resolve) => resolve(fn(req, res))).catch((err) => {