fix: ensure internal x-middleware-set-cookie header is not passed on to lambda (#2891)

* fix: ensure internal x-middleware-set-cookie header is not set when setting cookies in middleware

* fix: make environment variables for draft mode available at edge

Author: mrstork

edge-runtime/lib/middleware.ts

@@ -67,6 +67,10 @@ export function mergeMiddlewareCookies(middlewareResponse: Response, lambdaReque
   const middlewareCookies = middlewareResponse.headers.get('x-middleware-set-cookie')
 
   if (middlewareCookies) {
+    // Next expects internal headers to be omitted when cookies are set by the middleware
+    // See: https://github.com/vercel/next.js/blob/005db43079c7b59fd8c2594e8362761dc4cb3211/test/e2e/app-dir/app-middleware/app-middleware.test.ts#L197-L207
+    middlewareResponse.headers.delete('x-middleware-set-cookie')
+
     // Targets commas that are not followed by whitespace
     // See: https://github.com/vercel/next.js/blob/e6145d3a37bb4c7b481fd58e05cdff9046ace8ad/packages/next/src/server/web/spec-extension/response.ts#L58-L66
     const regex = new RegExp(/,(?!\s)/)

src/build/functions/edge.ts

@@ -119,7 +119,7 @@ const writeHandlerFile = async (ctx: PluginContext, { matchers, name }: NextDefi
 
 const copyHandlerDependencies = async (
   ctx: PluginContext,
-  { name, files, wasm }: NextDefinition,
+  { name, env, files, wasm }: NextDefinition,
 ) => {
   const srcDir = join(ctx.standaloneDir, ctx.nextDistDir)
   const destDir = join(ctx.edgeFunctionsDir, getHandlerName({ name }))
@@ -132,6 +132,11 @@ const copyHandlerDependencies = async (
 
   const outputFile = join(destDir, `server/${name}.js`)
 
+  // Prepare environment variables for draft-mode (i.e. __NEXT_PREVIEW_MODE_ID, __NEXT_PREVIEW_MODE_SIGNING_KEY, __NEXT_PREVIEW_MODE_ENCRYPTION_KEY)
+  for (const [key, value] of Object.entries(env)) {
+    parts.push(`process.env.${key} = '${value}';`)
+  }
+
   if (wasm?.length) {
     for (const wasmChunk of wasm ?? []) {
       const data = await readFile(join(srcDir, wasmChunk.filePath))
@@ -161,16 +166,16 @@ const buildHandlerDefinition = (
   ctx: PluginContext,
   { name, matchers, page }: NextDefinition,
 ): Array<ManifestFunction> => {
-  const fun = getHandlerName({ name })
-  const funName = name.endsWith('middleware')
+  const functionHandlerName = getHandlerName({ name })
+  const functionName = name.endsWith('middleware')
     ? 'Next.js Middleware Handler'
     : `Next.js Edge Handler: ${page}`
   const cache = name.endsWith('middleware') ? undefined : ('manual' as const)
   const generator = `${ctx.pluginName}@${ctx.pluginVersion}`
 
   return augmentMatchers(matchers, ctx).map((matcher) => ({
-    function: fun,
-    name: funName,
+    function: functionHandlerName,
+    name: functionName,
     pattern: matcher.regexp,
     cache,
     generator,
@@ -183,10 +188,7 @@ export const clearStaleEdgeHandlers = async (ctx: PluginContext) => {
 
 export const createEdgeHandlers = async (ctx: PluginContext) => {
   const nextManifest = await ctx.getMiddlewareManifest()
-  const nextDefinitions = [
-    ...Object.values(nextManifest.middleware),
-    // ...Object.values(nextManifest.functions)
-  ]
+  const nextDefinitions = [...Object.values(nextManifest.middleware)]
   await Promise.all(nextDefinitions.map((def) => createEdgeHandler(ctx, def)))
 
   const netlifyDefinitions = nextDefinitions.flatMap((def) => buildHandlerDefinition(ctx, def))