type custom, for redirect and rewrite has

docs/api-reference/next.config.js/redirects.md

@@ -129,9 +129,10 @@ To only match a redirect when header, cookie, or query values also match the `ha
 
 `has` items have the following fields:
 
-- `type`: `String` - must be either `header`, `cookie`, `host`, or `query`.
+- `type`: `String` - must be either `header`, `cookie`, `host`, `query`, or `custom`.
 - `key`: `String` - the key from the selected type to match against.
 - `value`: `String` or `undefined` - the value to check for, if undefined any value will match. A regex like string can be used to capture a specific part of the value, e.g. if the value `first-(?<paramName>.*)` is used for `first-second` then `second` will be usable in the destination with `:paramName`.
+- `check`: `Function` - when the `type` is `custom`, `check` is a function that accepts `req` and returns `false` when it should not redirect, `true` when it should redirect, or a parameters object, with parameters to be used in the redirection.
 
 ```js
 module.exports = {
@@ -198,6 +199,18 @@ module.exports = {
         ],
         destination: '/another-page',
       },
+      // if a custom check matches (the cookie foo should be equal to the query parameter foo),
+      // this redirect will be applied
+      {
+        source: '/some-page',
+        has: [
+          {
+            type: 'custom',
+            check: req => req.cookies.foo === req.query.foo
+          },
+        ],
+        destination: '/another-page',
+      },
     ]
   },
 }

docs/api-reference/next.config.js/rewrites.md

@@ -222,9 +222,10 @@ To only match a rewrite when header, cookie, or query values also match the `has
 
 `has` items have the following fields:
 
-- `type`: `String` - must be either `header`, `cookie`, `host`, or `query`.
+- `type`: `String` - must be either `header`, `cookie`, `host`, `query`, or `custom`.
 - `key`: `String` - the key from the selected type to match against.
 - `value`: `String` or `undefined` - the value to check for, if undefined any value will match. A regex like string can be used to capture a specific part of the value, e.g. if the value `first-(?<paramName>.*)` is used for `first-second` then `second` will be usable in the destination with `:paramName`.
+- `check`: `Function` - when the `type` is `custom`, `check` is a function that accepts `req` and returns `false` when it should not rewrite, `true` when it should redirect, or a parameters object, with parameters to be used in the redirection.
 
 ```js
 module.exports = {
@@ -288,6 +289,18 @@ module.exports = {
         ],
         destination: '/another-page',
       },
+      // if a custom check matches (the cookie foo should be equal to the query parameter foo),
+      // this redirect will be applied
+      {
+        source: '/some-page',
+        has: [
+          {
+            type: 'custom',
+            check: (req) => req.cookies.foo === req.query.foo,
+          },
+        ],
+        destination: '/another-page',
+      },
     ]
   },
 }

packages/next/lib/load-custom-routes.ts

@@ -1,4 +1,5 @@
 import chalk from 'chalk'
+import { IncomingMessage } from 'http'
 import { parse as parseUrl } from 'url'
 import { NextConfig } from '../server/config'
 import * as pathToRegexp from 'next/dist/compiled/path-to-regexp'
@@ -13,11 +14,19 @@ export type RouteHas =
       type: 'header' | 'query' | 'cookie'
       key: string
       value?: string
+      check?: undefined
     }
   | {
       type: 'host'
       key?: undefined
       value: string
+      check?: undefined
+    }
+  | {
+      type: 'custom'
+      key?: undefined
+      value?: undefined
+      check: (req: IncomingMessage) => boolean | { [param: string]: any }
     }
 
 export type Rewrite = {

packages/next/shared/lib/router/utils/prepare-destination.ts

@@ -71,6 +71,24 @@ export function matchHas(
         value = hostname
         break
       }
+      case 'custom': {
+        if (typeof hasItem.check !== 'function') {
+          return false
+        }
+        try {
+          const result = hasItem.check(req)
+          if (!result) {
+            return false
+          }
+          if (typeof result === 'object') {
+            Object.assign(params, result)
+          }
+          return true
+        } catch (e) {
+          console.error(e)
+          return false
+        }
+      }
       default: {
         break
       }