Merge pull request #18738 from github/add-layouts-middleware

Extract layout handling into separate middleware

Author: sarahs

middleware/contextualizers/layout.js

@@ -0,0 +1,25 @@
+const layouts = require('../../lib/layouts')
+
+module.exports = function layoutContext (req, res, next) {
+  if (!req.context.page) return next()
+
+  let layoutName
+
+  if (req.context.page.layout) {
+    // Layouts can be specified with a `layout` frontmatter value.
+    // Any invalid layout values will be caught by frontmatter schema validation.
+    layoutName = req.context.page.layout
+    // A `layout: false` value means use no layout.
+  } else if (req.context.page.layout === false) {
+    layoutName = ''
+    // If undefined, use either the default layout or the generic-toc layout.
+  } else if (req.context.page.layout === undefined) {
+    layoutName = 'default'
+  }
+
+  // Attach to the context object
+  req.context.currentLayoutName = layoutName
+  req.context.currentLayout = layouts[layoutName]
+
+  return next()
+}

middleware/index.js

@@ -110,6 +110,7 @@ module.exports = function (app) {
   app.use(instrument('./contextualizers/rest'))
   app.use(instrument('./contextualizers/webhooks'))
   app.use(asyncMiddleware(instrument('./contextualizers/whats-new-changelog')))
+  app.use(instrument('./contextualizers/layout'))
   app.use(asyncMiddleware(instrument('./breadcrumbs')))
   app.use(asyncMiddleware(instrument('./early-access-breadcrumbs')))
   app.use(asyncMiddleware(instrument('./enterprise-server-releases')))

middleware/render-page.js

@@ -136,15 +136,8 @@ module.exports = async function renderPage (req, res, next) {
     }
   }
 
-  // Layouts can be specified with a `layout` frontmatter value
-  // If unspecified, `layouts/default.html` is used.
-  // Any invalid layout values will be caught by frontmatter schema validation.
-  const layoutName = context.page.layout || 'default'
-
-  // Set `layout: false` to use no layout
-  const layout = context.page.layout === false ? '' : layouts[layoutName]
-
-  const output = await liquid.parseAndRender(layout, context)
+  // currentLayout is added to the context object in middleware/contextualizers/layouts
+  const output = await liquid.parseAndRender(req.context.currentLayout, context)
 
   // First, send the response so the user isn't waiting
   // NOTE: Do NOT `return` here as we still need to cache the response afterward!