From f999bfb741f9b20cc6c29608efc5cc1a8cb71cb9 Mon Sep 17 00:00:00 2001
From: Cosmin Budinschi <budinschi.cosmin@gmail.com>
Date: Wed, 5 Feb 2020 00:09:41 +0200
Subject: [PATCH 1/2] fix: trailing slash redirect

---
 packages/gatsby/src/commands/serve.js | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/packages/gatsby/src/commands/serve.js b/packages/gatsby/src/commands/serve.js
index 8c1129af6cd20..d529d846b8a2d 100644
--- a/packages/gatsby/src/commands/serve.js
+++ b/packages/gatsby/src/commands/serve.js
@@ -40,6 +40,24 @@ const readMatchPaths = async program => {
   return JSON.parse(rawJSON)
 }
 
+/**
+ * Express middleware that adds url trailing slash in order to
+ * trick static middleware and thus preventing redirect
+ * This needs to be used before express static middleware
+ * @param {*} req
+ * @param {*} res
+ * @param {*} next
+ */
+const directoryRedirectPrevention = (req, res, next) => {
+  if (req.url == `/` || req.url.indexOf(`.`) || req.url.slice(-1) !== `/`)
+    return next()
+
+  req.originalUrl += `/` // https://expressjs.com/en/api.html#req.originalUrl
+  req.url += `/`
+
+  return next()
+}
+
 const matchPathRouter = (matchPaths, options) => (req, res, next) => {
   const { url } = req
   if (req.accepts(`html`)) {
@@ -85,6 +103,7 @@ module.exports = async program => {
   app.use(telemetry.expressMiddleware(`SERVE`))
 
   router.use(compression())
+  router.use(directoryRedirectPrevention)
   router.use(express.static(`public`))
   const matchPaths = await readMatchPaths(program)
   router.use(matchPathRouter(matchPaths, { root }))

From 43802a15174fb9bac1ea09da163084763c03e1fd Mon Sep 17 00:00:00 2001
From: Cosmin Budinschi <budinschi.cosmin@gmail.com>
Date: Wed, 12 Feb 2020 19:44:11 +0200
Subject: [PATCH 2/2] fix(static-serve): add trailing slash to url

before static middleware and prevent redirect
---
 packages/gatsby/src/commands/serve.js | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/packages/gatsby/src/commands/serve.js b/packages/gatsby/src/commands/serve.js
index d529d846b8a2d..b1e75fdeb4b9e 100644
--- a/packages/gatsby/src/commands/serve.js
+++ b/packages/gatsby/src/commands/serve.js
@@ -14,6 +14,7 @@ const telemetry = require(`gatsby-telemetry`)
 const detectPortInUseAndPrompt = require(`../utils/detect-port-in-use-and-prompt`)
 const getConfigFile = require(`../bootstrap/get-config-file`)
 const preferDefault = require(`../bootstrap/prefer-default`)
+const fileExtensionRegEx = /.+\..+$/g
 
 onExit(() => {
   telemetry.trackCli(`SERVE_STOP`)
@@ -41,17 +42,22 @@ const readMatchPaths = async program => {
 }
 
 /**
- * Express middleware that adds url trailing slash in order to
- * trick static middleware and thus preventing redirect
- * This needs to be used before express static middleware
+ * Adds trailing slash to request.url, in order to deceive static middleware
+ * into getting a directory request, thus preventing redirect.
+ * This is an express middleware to be used before static middleware
  * @param {*} req
  * @param {*} res
  * @param {*} next
  */
 const directoryRedirectPrevention = (req, res, next) => {
-  if (req.url == `/` || req.url.indexOf(`.`) || req.url.slice(-1) !== `/`)
-    return next()
-
+  // url is home page
+  if (req.url === `/`) return next()
+  // url has trailing slash, no need to intervene
+  if (req.url.slice(-1) === `/`) return next()
+  // url is a file request, no need for trailing slash
+  if (fileExtensionRegEx.test(req.url)) return next()
+
+  // turning /slug into /slug/
   req.originalUrl += `/` // https://expressjs.com/en/api.html#req.originalUrl
   req.url += `/`