fix: generate correct import path when 'src' directory is used and middleware imports wasm module

src/build/functions/edge.ts

@@ -1,5 +1,6 @@
 import { cp, mkdir, readFile, rm, writeFile } from 'node:fs/promises'
-import { dirname, join } from 'node:path'
+import { dirname, join, relative, sep } from 'node:path'
+import { sep as posixSep } from 'node:path/posix'
 
 import type { Manifest, ManifestFunction } from '@netlify/edge-functions'
 import { glob } from 'fast-glob'
@@ -8,6 +9,8 @@ import { pathToRegexp } from 'path-to-regexp'
 
 import { EDGE_HANDLER_NAME, PluginContext } from '../plugin-context.js'
 
+const toPosixPath = (path: string) => path.split(sep).join(posixSep)
+
 const writeEdgeManifest = async (ctx: PluginContext, manifest: Manifest) => {
   await mkdir(ctx.edgeFunctionsDir, { recursive: true })
   await writeFile(join(ctx.edgeFunctionsDir, 'manifest.json'), JSON.stringify(manifest, null, 2))
@@ -107,10 +110,19 @@ const copyHandlerDependencies = async (
 
   const parts = [shim]
 
+  const outputFile = join(destDir, `server/${name}.js`)
+
   if (wasm?.length) {
-    parts.push(
-      `import { decode as _base64Decode } from "../edge-runtime/vendor/deno.land/std@0.175.0/encoding/base64.ts";`,
+    const base64ModulePath = join(
+      destDir,
+      'edge-runtime/vendor/deno.land/std@0.175.0/encoding/base64.ts',
     )
+
+    const base64ModulePathRelativeToOutputFile = toPosixPath(
+      relative(dirname(outputFile), base64ModulePath),
+    )
+
+    parts.push(`import { decode as _base64Decode } from "${base64ModulePathRelativeToOutputFile}";`)
     for (const wasmChunk of wasm ?? []) {
       const data = await readFile(join(srcDir, wasmChunk.filePath))
       parts.push(
@@ -126,9 +138,9 @@ const copyHandlerDependencies = async (
     parts.push(`;// Concatenated file: ${file} \n`, entrypoint)
   }
   const exports = `const middlewareEntryKey = Object.keys(_ENTRIES).find(entryKey => entryKey.startsWith("middleware_${name}")); export default _ENTRIES[middlewareEntryKey].default;`
-  await mkdir(dirname(join(destDir, `server/${name}.js`)), { recursive: true })
+  await mkdir(dirname(outputFile), { recursive: true })
 
-  await writeFile(join(destDir, `server/${name}.js`), [...parts, exports].join('\n'))
+  await writeFile(outputFile, [...parts, exports].join('\n'))
 }
 
 const createEdgeHandler = async (ctx: PluginContext, definition: NextDefinition): Promise<void> => {

tests/fixtures/wasm-src/next.config.js

@@ -0,0 +1,30 @@
+const { platform } = require('process')
+const fsPromises = require('fs/promises')
+
+// Next.js uses `fs.promises.copyFile` to copy files from `.next`to the `.next/standalone` directory
+// It tries copying the same file twice in parallel. Unix is fine with that, but Windows fails
+// with "Resource busy or locked", failing the build.
+// We work around this by memoizing the copy operation, so that the second copy is a no-op.
+// Tracked in TODO: report to Next.js folks
+if (platform === 'win32') {
+  const copies = new Map()
+
+  const originalCopy = fsPromises.copyFile
+  fsPromises.copyFile = (src, dest, mode) => {
+    const key = `${dest}:${src}`
+    const existingCopy = copies.get(key)
+    if (existingCopy) return existingCopy
+
+    const copy = originalCopy(src, dest, mode)
+    copies.set(key, copy)
+    return copy
+  }
+}
+
+/** @type {import('next').NextConfig} */
+module.exports = {
+  output: 'standalone',
+  eslint: {
+    ignoreDuringBuilds: true,
+  },
+}

tests/fixtures/wasm-src/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "og-api",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "postinstall": "next build",
+    "dev": "next dev",
+    "build": "next build"
+  },
+  "dependencies": {
+    "@vercel/og": "latest",
+    "next": "latest",
+    "react": "18.2.0",
+    "react-dom": "18.2.0"
+  }
+}

tests/fixtures/wasm-src/src/app/og-node/route.js

@@ -0,0 +1,8 @@
+import { ImageResponse } from '@vercel/og'
+
+export async function GET() {
+  return new ImageResponse(<div>hi</div>, {
+    width: 1200,
+    height: 630,
+  })
+}

tests/fixtures/wasm-src/src/app/og/route.js

@@ -0,0 +1,10 @@
+import { ImageResponse } from '@vercel/og'
+
+export async function GET() {
+  return new ImageResponse(<div>hi</div>, {
+    width: 1200,
+    height: 630,
+  })
+}
+
+export const runtime = 'edge'

tests/fixtures/wasm-src/src/middleware.js

@@ -0,0 +1,16 @@
+import wasm from './add.wasm?module'
+const instance$ = WebAssembly.instantiate(wasm)
+
+async function increment(a) {
+  const { instance } = await instance$
+  return instance.exports.add_one(a)
+}
+export default async function middleware(request) {
+  const input = Number(request.nextUrl.searchParams.get('input')) || 1
+  const value = await increment(input)
+  return new Response(null, { headers: { data: JSON.stringify({ input, value }) } })
+}
+
+export const config = {
+  matcher: '/wasm',
+}

tests/fixtures/wasm-src/src/pages/api/og-wrong-runtime.js

@@ -0,0 +1,22 @@
+// /pages/api/og.jsx
+import { ImageResponse } from '@vercel/og'
+
+export default function () {
+  return new ImageResponse(
+    (
+      <div
+        style={{
+          width: '100%',
+          height: '100%',
+          display: 'flex',
+          alignItems: 'center',
+          justifyContent: 'center',
+          fontSize: 128,
+          background: 'lavender',
+        }}
+      >
+        Hello!
+      </div>
+    ),
+  )
+}

tests/fixtures/wasm-src/src/pages/api/og.js

@@ -0,0 +1,26 @@
+// /pages/api/og.jsx
+import { ImageResponse } from '@vercel/og'
+
+export const config = {
+  runtime: 'edge',
+}
+
+export default function () {
+  return new ImageResponse(
+    (
+      <div
+        style={{
+          width: '100%',
+          height: '100%',
+          display: 'flex',
+          alignItems: 'center',
+          justifyContent: 'center',
+          fontSize: 128,
+          background: 'lavender',
+        }}
+      >
+        Hello!
+      </div>
+    ),
+  )
+}

tests/fixtures/wasm-src/src/pages/index.js

@@ -0,0 +1,3 @@
+export default function Page() {
+  return <p>hello world</p>
+}

tests/integration/wasm.test.ts

@@ -21,7 +21,10 @@ beforeEach<FixtureTestContext>(async (ctx) => {
   await startMockBlobStore(ctx)
 })
 
-describe('WASM', () => {
+describe.each([
+  { fixture: 'wasm', edgeHandlerFunction: '___netlify-edge-handler-middleware' },
+  { fixture: 'wasm-src', edgeHandlerFunction: '___netlify-edge-handler-src-middleware' },
+])('$fixture', ({ fixture, edgeHandlerFunction }) => {
   beforeEach<FixtureTestContext>(async (ctx) => {
     // set for each test a new deployID and siteID
     ctx.deployID = generateRandomObjectID()
@@ -33,7 +36,7 @@ describe('WASM', () => {
 
     await startMockBlobStore(ctx)
 
-    await createFixture('wasm', ctx)
+    await createFixture(fixture, ctx)
     await runPlugin(ctx)
   })
 
@@ -58,7 +61,7 @@ describe('WASM', () => {
   test<FixtureTestContext>('should work in middleware', async (ctx) => {
     const origin = new LocalServer()
     const response = await invokeEdgeFunction(ctx, {
-      functions: ['___netlify-edge-handler-middleware'],
+      functions: [edgeHandlerFunction],
       origin,
       url: '/wasm?input=3',
     })