Allow passthrough redirects

example.js

@@ -5,10 +5,15 @@ const proxy = require('.')
 
 async function startOrigin () {
   const origin = Fastify()
+
   origin.get('/', async (request, reply) => {
     return 'this is root'
   })
 
+  origin.get('/redirect', async (request, reply) => {
+    return reply.redirect(302, 'https://fastify.io')
+  })
+
   origin.get('/a', async (request, reply) => {
     return 'this is a'
   })

index.js

@@ -1,9 +1,9 @@
 'use strict'
-
 const From = require('fastify-reply-from')
 const WebSocket = require('ws')
 
 const httpMethods = ['DELETE', 'GET', 'HEAD', 'PATCH', 'POST', 'PUT', 'OPTIONS']
+const urlPattern = /^https?:\/\//
 
 function liftErrorCode (code) {
   if (typeof code !== 'number') {
@@ -31,6 +31,10 @@ function waitConnection (socket, write) {
   }
 }
 
+function isExternalUrl (url = '') {
+  return urlPattern.test(url)
+};
+
 function proxyWebSockets (source, target) {
   function close (code, reason) {
     closeWebSocket(source, code, reason)
@@ -125,7 +129,7 @@ async function httpProxy (fastify, opts) {
 
   function rewriteHeaders (headers) {
     const location = headers.location
-    if (location) {
+    if (location && !isExternalUrl(location)) {
       headers.location = location.replace(rewritePrefix, fastify.prefix)
     }
     if (oldRewriteHeaders) {

test/test.js

@@ -17,6 +17,10 @@ async function run () {
     return 'this is a'
   })
 
+  origin.get('/redirect', async (request, reply) => {
+    return reply.redirect(302, 'https://fastify.io')
+  })
+
   origin.post('/this-has-data', async (request, reply) => {
     if (request.body.hello === 'world') {
       reply.header('location', '/something')
@@ -58,6 +62,27 @@ async function run () {
     t.equal(resultA.body, 'this is a')
   })
 
+  test('redirects passthrough', async t => {
+    const server = Fastify()
+    server.register(proxy, {
+      upstream: `http://localhost:${origin.server.address().port}`
+    })
+
+    await server.listen(0)
+    t.tearDown(server.close.bind(server))
+
+    const {
+      headers: { location },
+      statusCode
+    } = await got(
+      `http://localhost:${server.server.address().port}/redirect`, {
+        followRedirect: false
+      }
+    )
+    t.equal(location, 'https://fastify.io')
+    t.equal(statusCode, 302)
+  })
+
   test('no upstream will throw', async t => {
     const server = Fastify()
     server.register(proxy)