perf: download and save mkcert in stream (#63527)

Previously, Next.js would buffer the `mkcert` binary in memory and write
it to disk all at once. The pull request changes this to pipe the
download stream to the disk. This improves memory consumption by
avoiding having to load the entire `mkcert` binary into memory.

---------

Co-authored-by: JJ Kasper <[email protected]>

packages/next/src/lib/mkcert.ts

@@ -3,6 +3,9 @@ import path from 'path'
 import { getCacheDirectory } from './helpers/get-cache-directory'
 import * as Log from '../build/output/log'
 import { execSync } from 'child_process'
+const { WritableStream } = require('node:stream/web') as {
+  WritableStream: typeof global.WritableStream
+}
 
 const MKCERT_VERSION = 'v1.4.4'
 
@@ -53,10 +56,37 @@ async function downloadBinary() {
 
     Log.info(`Download response was successful, writing to disk`)
 
-    const arrayBuffer = await response.arrayBuffer()
-    const buffer = Buffer.from(arrayBuffer)
+    const binaryWriteStream = fs.createWriteStream(binaryPath)
+
+    await response.body.pipeTo(
+      new WritableStream({
+        write(chunk) {
+          return new Promise((resolve, reject) => {
+            binaryWriteStream.write(chunk, (error) => {
+              if (error) {
+                reject(error)
+                return
+              }
+
+              resolve()
+            })
+          })
+        },
+        close() {
+          return new Promise((resolve, reject) => {
+            binaryWriteStream.close((error) => {
+              if (error) {
+                reject(error)
+                return
+              }
+
+              resolve()
+            })
+          })
+        },
+      })
+    )
 
-    await fs.promises.writeFile(binaryPath, buffer)
     await fs.promises.chmod(binaryPath, 0o755)
 
     return binaryPath