🐛 Fixed custom redirects for subdirectory setups

no-issue

This issue only occurs when using custom redirects with a subdirectory
setup, and the path to be redirected from is expressed as a regex, and
the url that is being redirected to is not an external url.

The issue has a few components:

- Redirect paths as a regex generally use the ^ to ensure that they
  match the beginning of the path.

- The path that the regex is matched against conditionally excludes the
  subdirectory, specifically, the subdirectory is excluded for external
  urls

These combined means you end up with a regex like /^\/custom-redirect/
and a path like /subdir/custom-redirect, these will not match/replace
correctly, and you'll end in an infinite redirect loop.

The fix here is to *always* remove the subdirectory when testing regex's
and then conditionally adding it back *only* for the redirect, and only
if it is an internal redirect

core/server/web/shared/middlewares/custom-redirects.js

@@ -54,17 +54,19 @@ _private.registerRoutes = () => {
             customRedirectsRouter.get(new RegExp(redirect.from, options), function (req, res) {
                 const maxAge = redirect.permanent ? config.get('caching:customRedirects:maxAge') : 0;
                 const toURL = url.parse(redirect.to);
-                const currentURL = url.parse(req.originalUrl);
+                const currentURL = url.parse(req.url);
 
-                // if the URL points to an external website, remove Ghost's base path
+                toURL.pathname = currentURL.pathname.replace(new RegExp(redirect.from, options), toURL.pathname);
-                /** @see https://github.com/TryGhost/Ghost/issues/10776 */
-                const currentPath = (toURL.hostname)
-                    ? currentURL.pathname.replace(urlUtils.getSubdir(), '')
-                    : currentURL.pathname;
-
-                toURL.pathname = currentPath.replace(new RegExp(redirect.from, options), toURL.pathname);
                 toURL.search = currentURL.search;
 
+                /**
+                 * Only if the URL is internal should we prepend the Ghost subdirectory
+                 * @see https://github.com/TryGhost/Ghost/issues/10776
+                 */
+                if (!toURL.hostname) {
+                    toURL.pathname = urlUtils.urlJoin(urlUtils.getSubdir(), toURL.pathname);
+                }
+
                 res.set({
                     'Cache-Control': `public, max-age=${maxAge}`
                 });

test/regression/site/frontend_spec.js

@@ -789,7 +789,7 @@ describe('Frontend Routing', function () {
             configUtils.set('url', 'http://localhost:2370/blog/');
             urlUtils.stubUrlUtilsFromConfig();
 
-            return ghost({forceStart: true})
+            return ghost({forceStart: true, subdir: true})
                 .then(function (_ghostServer) {
                     ghostServer = _ghostServer;
                     request = supertest.agent(config.get('server:host') + ':' + config.get('server:port'));
@@ -811,6 +811,15 @@ describe('Frontend Routing', function () {
                         doEnd(done)(err, res);
                     });
             });
+            it('should work with regex "from" redirects', function (done) {
+                request.get('/blog/capture1/whatever')
+                    .expect(302)
+                    .expect('Cache-Control', testUtils.cacheRules.public)
+                    .end(function (err, res) {
+                        res.headers.location.should.eql('/blog/whatever');
+                        doEnd(done)(err, res);
+                    });
+            });
         });
 
         describe('external url redirect', function () {

test/utils/fixtures/data/redirects.json

@@ -24,6 +24,10 @@
         "from": "^/resources\\/download(\\/?)$",
         "to": "/shubal-stearns"
     },
+    {
+        "from": "^\/(?:capture1|capture2)\/([A-Za-z0-9\\-]+)",
+        "to": "/$1"
+    },
     {
         "from": "^\\/[0-9]{4}\\/[0-9]{2}\\/([a-z0-9\\-]+)(\\.html)?(\\/)?$",
         "to": "/$1"