Parsoid: Add fallback for transforms to the proxy

Marko Obrovac · Marko Obrovac · commit 36d1d4ace75c · 2019-10-15T16:46:12.000+02:00
When we are in split mode, we need to account for the transition period
of each domain, during which time some transform requests will actually
need to be handled by Parsoid/JS since the clients retrieved the JS
variant of the HTML. Thefore, for transform end points provide a
fallback in case of a 404 which happens if RESTBase can't retrieve the
stashed content.

Bug: T230791
diff --git a/sys/parsoid.js b/sys/parsoid.js
@@ -157,6 +157,22 @@ class ParsoidProxy {
             res.headers = res.headers || {};
             res.headers['x-parsoid-variant'] = variant;
             return P.resolve(res);
+        }).catch({ status: 404 }, (e) => {
+            // if we are in split mode, provide a fallback for
+            // transforms for the non-default variant
+            if (this.mode === 'split' && /transform/.test(operation) &&
+                        variant !== this.default_variant) {
+                if (setHdr) {
+                    req.headers['x-parsoid-variant'] = this.default_variant;
+                }
+                return this.mods[this.default_variant][operation](hyper, req)
+                .then((res) => {
+                    res.headers = res.headers || {};
+                    res.headers['x-parsoid-variant'] = this.default_variant;
+                    return P.resolve(res);
+                });
+            }
+            throw e;
         });
     }
 
