fix: append .plain.html in redirects if needed (#452)

fixes #451

src/steps/fetch-content.js

@@ -37,10 +37,13 @@ export default async function fetchContent(state, req, res) {
   const ret = await state.s3Loader.getObject(bucketId, key);
 
   // check for redirect
-  const redirectLocation = ret.headers.get('x-amz-meta-redirect-location');
+  let redirectLocation = ret.headers.get('x-amz-meta-redirect-location');
   if (redirectLocation) {
     res.status = 301;
     res.body = '';
+    if (redirectLocation.startsWith('/') && state.info.selector === 'plain') {
+      redirectLocation += '.plain.html';
+    }
     res.headers.set('location', redirectLocation);
     res.headers.set('x-surrogate-key', await computeSurrogateKey(`${contentBusId}${info.path}`));
     res.error = 'moved';

test/rendering.test.js

@@ -394,6 +394,12 @@ describe('Rendering', () => {
       assert.strictEqual(ret.headers.get('location'), 'https://www.adobe.com');
     });
 
+    it('appends .plain.html in redirects', async () => {
+      loader.headers('one-section.md', 'x-amz-meta-redirect-location', '/foo');
+      const ret = await render(new URL('https://localhost/one-section'), '.plain', 301);
+      assert.strictEqual(ret.headers.get('location'), '/foo.plain.html');
+    });
+
     it('respect folder mapping: skip if no config', async () => {
       loader.rewrite('helix-config.json', 'helix-config-no-head.json');
       loader.status('products.md', 404);