Allow custom path for preview mode cookies

docs/advanced-features/preview-mode.md

@@ -194,10 +194,12 @@ Then, send a request to `/api/clear-preview-mode-cookies` to invoke the API Rout
 `setPreviewData` takes an optional second parameter which should be an options object. It accepts the following keys:
 
 - `maxAge`: Specifies the number (in seconds) for the preview session to last for.
+- `path`: Specifies the path the cookie should be applied under. Defaults to `/` enabling preview mode for all paths.
 
 ```js
 setPreviewData(data, {
   maxAge: 60 * 60, // The preview mode cookies expire in 1 hour
+  path: '/about', // The preview mode cookies apply to paths with /about
 })
 ```
 

packages/next/server/api-utils/node.ts

@@ -469,6 +469,7 @@ function setPreviewData<T>(
   data: object | string, // TODO: strict runtime type checking
   options: {
     maxAge?: number
+    path?: string
   } & __ApiPreviewProps
 ): NextApiResponse<T> {
   if (isNotValidData(options.previewModeId)) {
@@ -522,6 +523,9 @@ function setPreviewData<T>(
       ...(options.maxAge !== undefined
         ? ({ maxAge: options.maxAge } as CookieSerializeOptions)
         : undefined),
+      ...(options.path !== undefined
+        ? ({ path: options.path } as CookieSerializeOptions)
+        : undefined),
     }),
     serialize(COOKIE_NAME_PRERENDER_DATA, payload, {
       httpOnly: true,
@@ -531,6 +535,9 @@ function setPreviewData<T>(
       ...(options.maxAge !== undefined
         ? ({ maxAge: options.maxAge } as CookieSerializeOptions)
         : undefined),
+      ...(options.path !== undefined
+        ? ({ path: options.path } as CookieSerializeOptions)
+        : undefined),
     }),
   ])
   return res

packages/next/shared/lib/utils.ts

@@ -252,6 +252,11 @@ export type NextApiResponse<T = any> = ServerResponse & {
        * when the client shuts down (browser is closed).
        */
       maxAge?: number
+      /**
+       * Specifies the path for the preview session to work under. By default,
+       * the path is considered the "default path", i.e., any pages under "/".
+       */
+      path?: string
     }
   ) => NextApiResponse<T>
   clearPreviewData: () => NextApiResponse<T>

test/integration/prerender-preview/pages/api/preview.js

@@ -6,14 +6,12 @@ export default (req, res) => {
       return res.status(500).end('too big')
     }
   } else {
-    res.setPreviewData(
-      req.query,
-      req.query.cookieMaxAge
-        ? {
-            maxAge: req.query.cookieMaxAge,
-          }
-        : undefined
-    )
+    res.setPreviewData(req.query, {
+      ...(req.query.cookieMaxAge
+        ? { maxAge: req.query.cookieMaxAge }
+        : undefined),
+      ...(req.query.cookiePath ? { path: req.query.cookiePath } : undefined),
+    })
   }
 
   res.status(200).end()

test/integration/prerender-preview/test/index.test.js

@@ -121,6 +121,26 @@ function runTests(startServer = nextStart) {
     expect(cookies[1]).toHaveProperty('__next_preview_data')
     expect(cookies[1]['Max-Age']).toBe(expiry)
   })
+  it('should set custom path cookies', async () => {
+    const path = '/path'
+    const res = await fetchViaHTTP(appPort, '/api/preview', {
+      cookiePath: path,
+    })
+    expect(res.status).toBe(200)
+
+    const originalCookies = res.headers.get('set-cookie').split(',')
+    const cookies = originalCookies.map(cookie.parse)
+
+    expect(originalCookies.every((c) => c.includes('; Secure;'))).toBe(true)
+
+    expect(cookies.length).toBe(2)
+    expect(cookies[0]).toMatchObject({ Path: path, SameSite: 'None' })
+    expect(cookies[0]).toHaveProperty('__prerender_bypass')
+    expect(cookies[0]['Path']).toBe(path)
+    expect(cookies[0]).toMatchObject({ Path: path, SameSite: 'None' })
+    expect(cookies[1]).toHaveProperty('__next_preview_data')
+    expect(cookies[1]['Path']).toBe(path)
+  })
   it('should not return fallback page on preview request', async () => {
     const res = await fetchViaHTTP(
       appPort,

test/unit/split-cookies-string.test.ts

@@ -44,6 +44,16 @@ describe('splitCookiesString', () => {
       expect(result).toEqual(expected)
     })
 
+    it('should parse path', () => {
+      const { joined, expected } = generateCookies({
+        name: 'foo',
+        value: 'bar',
+        path: '/path',
+      })
+      const result = splitCookiesString(joined)
+      expect(result).toEqual(expected)
+    })
+
     it('should parse with all the options', () => {
       const { joined, expected } = generateCookies({
         name: 'foo',
@@ -111,6 +121,23 @@ describe('splitCookiesString', () => {
       expect(result).toEqual(expected)
     })
 
+    it('should parse path', () => {
+      const { joined, expected } = generateCookies(
+        {
+          name: 'foo',
+          value: 'bar',
+          path: '/path',
+        },
+        {
+          name: 'x',
+          value: 'y',
+          path: '/path',
+        }
+      )
+      const result = splitCookiesString(joined)
+      expect(result).toEqual(expected)
+    })
+
     it('should parse with all the options', () => {
       const { joined, expected } = generateCookies(
         {