Correct Cache-Control Behavior for GS(S)P

packages/next/build/webpack/loaders/next-serverless-loader.ts

@@ -205,6 +205,7 @@ const nextServerlessLoader: loader.Loader = function() {
     const {renderToHTML} = require('next/dist/next-server/server/render');
     const { tryGetPreviewData } = require('next/dist/next-server/server/api-utils');
     const {sendHTML} = require('next/dist/next-server/server/send-html');
+    const {sendPayload} = require('next/dist/next-server/server/send-payload');
     const buildManifest = require('${buildManifest}');
     const reactLoadableManifest = require('${reactLoadableManifest}');
     const Document = require('${absoluteDocumentPath}').default;
@@ -328,21 +329,15 @@ const nextServerlessLoader: loader.Loader = function() {
 
         let result = await renderToHTML(req, res, "${page}", Object.assign({}, getStaticProps ? {} : parsedUrl.query, nowParams ? nowParams : params, _params, isFallback ? { __nextFallback: 'true' } : {}), renderOpts)
 
-        if (_nextData && !renderMode) {
-          const payload = JSON.stringify(renderOpts.pageData)
-          res.setHeader('Content-Type', 'application/json')
-          res.setHeader('Content-Length', Buffer.byteLength(payload))
-
-          res.setHeader(
-            'Cache-Control',
-            isPreviewMode
-              ? \`private, no-cache, no-store, max-age=0, must-revalidate\`
-              : getServerSideProps
-              ? \`no-cache, no-store, must-revalidate\`
-              : \`s-maxage=\${renderOpts.revalidate}, stale-while-revalidate\`
-          )
-          res.end(payload)
-          return null
+        if (!renderMode) {
+          if (_nextData || getStaticProps || getServerSideProps) {
+            sendPayload(res, _nextData ? JSON.stringify(renderOpts.pageData) : result, _nextData ? 'json' : 'html', {
+              private: isPreviewMode,
+              stateful: !!getServerSideProps,
+              revalidate: renderOpts.revalidate,
+            })
+            return null
+          }
         } else if (isPreviewMode) {
           res.setHeader(
             'Cache-Control',

packages/next/next-server/server/next-server.ts

@@ -52,6 +52,7 @@ import Router, {
   Route,
 } from './router'
 import { sendHTML } from './send-html'
+import { sendPayload } from './send-payload'
 import { serveStatic } from './serve-static'
 import {
   getFallback,
@@ -932,11 +933,11 @@ export default class Server {
           sendPayload(
             res,
             JSON.stringify(renderResult?.renderOpts?.pageData),
-            'application/json',
+            'json',
             !this.renderOpts.dev
               ? {
-                  revalidate: -1,
-                  private: isPreviewMode, // Leave to user-land caching
+                  private: isPreviewMode,
+                  stateful: true, // non-SSG data request
                 }
               : undefined
           )
@@ -955,11 +956,11 @@ export default class Server {
         sendPayload(
           res,
           JSON.stringify(props),
-          'application/json',
+          'json',
           !this.renderOpts.dev
             ? {
-                revalidate: -1,
-                private: isPreviewMode, // Leave to user-land caching
+                private: isPreviewMode,
+                stateful: true, // GSSP data request
               }
             : undefined
         )
@@ -971,11 +972,12 @@ export default class Server {
         ...opts,
       })
 
-      if (html && isServerProps && isPreviewMode) {
-        sendPayload(res, html, 'text/html; charset=utf-8', {
-          revalidate: -1,
+      if (html && isServerProps) {
+        sendPayload(res, html, 'html', {
           private: isPreviewMode,
+          stateful: true, // GSSP request
         })
+        return null
       }
 
       return html
@@ -1000,9 +1002,16 @@ export default class Server {
       sendPayload(
         res,
         data,
-        isDataReq ? 'application/json' : 'text/html; charset=utf-8',
-        cachedData.curRevalidate !== undefined && !this.renderOpts.dev
-          ? { revalidate: cachedData.curRevalidate, private: isPreviewMode }
+        isDataReq ? 'json' : 'html',
+        !this.renderOpts.dev
+          ? {
+              private: isPreviewMode,
+              stateful: false, // GSP response
+              revalidate:
+                cachedData.curRevalidate !== undefined
+                  ? cachedData.curRevalidate
+                  : /* default to minimum revalidate (this should be an invariant) */ 1,
+            }
           : undefined
       )
 
@@ -1105,7 +1114,12 @@ export default class Server {
         query.__nextFallback = 'true'
         if (isLikeServerless) {
           prepareServerlessUrl(req, query)
-          html = await (components.Component as any).renderReqToHTML(req, res)
+          const renderResult = await (components.Component as any).renderReqToHTML(
+            req,
+            res,
+            'passthrough'
+          )
+          html = renderResult.html
         } else {
           html = (await renderToHTML(req, res, pathname, query, {
             ...components,
@@ -1114,7 +1128,7 @@ export default class Server {
         }
       }
 
-      sendPayload(res, html, 'text/html; charset=utf-8')
+      sendPayload(res, html, 'html')
     }
 
     const {
@@ -1125,9 +1139,13 @@ export default class Server {
       sendPayload(
         res,
         isDataReq ? JSON.stringify(pageData) : html,
-        isDataReq ? 'application/json' : 'text/html; charset=utf-8',
+        isDataReq ? 'json' : 'html',
         !this.renderOpts.dev
-          ? { revalidate: sprRevalidate, private: isPreviewMode }
+          ? {
+              private: isPreviewMode,
+              stateful: false, // GSP response
+              revalidate: sprRevalidate,
+            }
           : undefined
       )
     }
@@ -1348,38 +1366,6 @@ export default class Server {
   }
 }
 
-function sendPayload(
-  res: ServerResponse,
-  payload: any,
-  type: string,
-  options?: { revalidate: number | false; private: boolean }
-) {
-  // TODO: ETag? Cache-Control headers? Next-specific headers?
-  res.setHeader('Content-Type', type)
-  res.setHeader('Content-Length', Buffer.byteLength(payload))
-  if (options != null) {
-    if (options?.private) {
-      res.setHeader(
-        'Cache-Control',
-        `private, no-cache, no-store, max-age=0, must-revalidate`
-      )
-    } else if (options?.revalidate) {
-      res.setHeader(
-        'Cache-Control',
-        options.revalidate < 0
-          ? `no-cache, no-store, must-revalidate`
-          : `s-maxage=${options.revalidate}, stale-while-revalidate`
-      )
-    } else if (options?.revalidate === false) {
-      res.setHeader(
-        'Cache-Control',
-        `s-maxage=31536000, stale-while-revalidate`
-      )
-    }
-  }
-  res.end(payload)
-}
-
 function prepareServerlessUrl(req: IncomingMessage, query: ParsedUrlQuery) {
   const curUrl = parseUrl(req.url!, true)
   req.url = formatUrl({

packages/next/next-server/server/send-payload.ts

@@ -0,0 +1,50 @@
+import { ServerResponse } from 'http'
+import { isResSent } from '../lib/utils'
+
+export function sendPayload(
+  res: ServerResponse,
+  payload: any,
+  type: 'html' | 'json',
+  options?:
+    | { private: true }
+    | { private: boolean; stateful: true }
+    | { private: boolean; stateful: false; revalidate: number | false }
+): void {
+  if (isResSent(res)) {
+    return
+  }
+
+  // TODO: ETag headers?
+  res.setHeader(
+    'Content-Type',
+    type === 'json' ? 'application/json' : 'text/html; charset=utf-8'
+  )
+  res.setHeader('Content-Length', Buffer.byteLength(payload))
+  if (options != null) {
+    if (options.private || options.stateful) {
+      if (options.private || !res.hasHeader('Cache-Control')) {
+        res.setHeader(
+          'Cache-Control',
+          `private, no-cache, no-store, max-age=0, must-revalidate`
+        )
+      }
+    } else if (typeof options.revalidate === 'number') {
+      if (options.revalidate < 1) {
+        throw new Error(
+          `invariant: invalid Cache-Control duration provided: ${options.revalidate} < 1`
+        )
+      }
+
+      res.setHeader(
+        'Cache-Control',
+        `s-maxage=${options.revalidate}, stale-while-revalidate`
+      )
+    } else if (options.revalidate === false) {
+      res.setHeader(
+        'Cache-Control',
+        `s-maxage=31536000, stale-while-revalidate`
+      )
+    }
+  }
+  res.end(payload)
+}

test/integration/getserversideprops-preview/pages/index.js

@@ -1,4 +1,6 @@
-export function getServerSideProps({ preview, previewData }) {
+export function getServerSideProps({ res, preview, previewData }) {
+  // test override in preview mode
+  res.setHeader('Cache-Control', 'public, max-age=3600')
   return {
     props: {
       hasProps: true,

test/integration/getserversideprops/pages/custom-cache.js

@@ -0,0 +1,12 @@
+import React from 'react'
+
+export async function getServerSideProps({ res }) {
+  res.setHeader('Cache-Control', 'public, max-age=3600')
+  return {
+    props: { world: 'world' },
+  }
+}
+
+export default ({ world }) => {
+  return <p>hello: {world}</p>
+}

test/integration/getserversideprops/test/index.test.js

@@ -414,12 +414,30 @@ const runTests = (dev = false) => {
       expect(dataRoutes).toEqual(expectedManifestRoutes())
     })
 
-    it('should set no-cache, no-store, must-revalidate header', async () => {
-      const res = await fetchViaHTTP(
+    it('should set default caching header', async () => {
+      const resPage = await fetchViaHTTP(appPort, `/something`)
+      expect(resPage.headers.get('cache-control')).toBe(
+        'private, no-cache, no-store, max-age=0, must-revalidate'
+      )
+
+      const resData = await fetchViaHTTP(
         appPort,
         `/_next/data/${buildId}/something.json`
       )
-      expect(res.headers.get('cache-control')).toContain('no-cache')
+      expect(resData.headers.get('cache-control')).toBe(
+        'private, no-cache, no-store, max-age=0, must-revalidate'
+      )
+    })
+
+    it('should respect custom caching header', async () => {
+      const resPage = await fetchViaHTTP(appPort, `/custom-cache`)
+      expect(resPage.headers.get('cache-control')).toBe('public, max-age=3600')
+
+      const resData = await fetchViaHTTP(
+        appPort,
+        `/_next/data/${buildId}/custom-cache.json`
+      )
+      expect(resData.headers.get('cache-control')).toBe('public, max-age=3600')
     })
 
     it('should not show error for invalid JSON returned from getServerSideProps', async () => {