resolve piper on complete shell

packages/next/build/entries.ts

@@ -162,6 +162,7 @@ export function createEntrypoints(
           page,
           absoluteAppPath: pages['/_app'],
           absoluteDocumentPath: pages['/_document'],
+          absoluteErrorPath: pages['/500'] || pages['/_error'],
           absolutePagePath,
           isServerComponent: isFlight,
           buildId,

packages/next/build/webpack/loaders/next-middleware-ssr-loader/index.ts

@@ -5,6 +5,7 @@ export default async function middlewareRSCLoader(this: any) {
     absolutePagePath,
     absoluteAppPath,
     absoluteDocumentPath,
+    absoluteErrorPath,
     basePath,
     isServerComponent: isServerComponentQuery,
     assetPrefix,
@@ -14,13 +15,15 @@ export default async function middlewareRSCLoader(this: any) {
   const isServerComponent = isServerComponentQuery === 'true'
   const stringifiedAbsolutePagePath = stringifyRequest(this, absolutePagePath)
   const stringifiedAbsoluteAppPath = stringifyRequest(this, absoluteAppPath)
+  const stringifiedAbsoluteErrorPath = stringifyRequest(this, absoluteErrorPath)
   const stringifiedAbsoluteDocumentPath = stringifyRequest(
     this,
     absoluteDocumentPath
   )
 
-  let appDefinition = `const App = require(${stringifiedAbsoluteAppPath}).default`
-  let documentDefinition = `const Document = require(${stringifiedAbsoluteDocumentPath}).default`
+  const appDefinition = `const App = require(${stringifiedAbsoluteAppPath}).default`
+  const documentDefinition = `const Document = require(${stringifiedAbsoluteDocumentPath}).default`
+  const errorDefinition = `const ErrorPage = require(${stringifiedAbsoluteErrorPath}).default`
 
   const transformed = `
         import { adapter } from 'next/dist/server/web/adapter'
@@ -40,6 +43,7 @@ export default async function middlewareRSCLoader(this: any) {
 
         ${appDefinition}
         ${documentDefinition}
+        ${errorDefinition}
         
         const {
           default: Page,
@@ -134,6 +138,7 @@ export default async function middlewareRSCLoader(this: any) {
               : ''
           }
 
+          const req = { url: pathname }
           const renderOpts = {
             Component,
             pageConfig: config || {},
@@ -162,32 +167,36 @@ export default async function middlewareRSCLoader(this: any) {
           const transformStream = new TransformStream()
           const writer = transformStream.writable.getWriter()
           const encoder = new TextEncoder()
-          
+          let result
+          let statusCode = 200
           try {
-            const result = await renderToHTML(
-              { url: pathname },
+            result = await renderToHTML(
+              req,
               {},
               pathname,
               query,
               renderOpts
             )
-            result.pipe({
-              write: str => writer.write(encoder.encode(str)),
-              end: () => writer.close()
-            })
-            .catch(() => writer.close())
           } catch (err) {
-            return new Response(
-              (err || 'An error occurred while rendering ' + pathname + '.').toString(),
-              {
-                status: 500,
-                headers: { 'x-middleware-ssr': '1' }
-              }
+            statusCode = 500
+            const errorRes = { statusCode, err }
+            result = await renderToHTML(
+              req,
+              errorRes,
+              pathname,
+              query,
+              { ...renderOpts, Component: ErrorPage }
             )
           }
 
+          result.pipe({
+            write: str => writer.write(encoder.encode(str)),
+            end: () => writer.close()
+          })
+
           return new Response(transformStream.readable, {
-            headers: { 'x-middleware-ssr': '1' }
+            headers: { 'x-middleware-ssr': '1' },
+            status: statusCode
           })
         }
 

packages/next/server/dev/hot-reloader.ts

@@ -528,6 +528,7 @@ export default class HotReloader {
                     page,
                     absoluteAppPath: this.pagesMapping['/_app'],
                     absoluteDocumentPath: this.pagesMapping['/_document'],
+                    absoluteErrorPath: this.pagesMapping['/_error'],
                     absolutePagePath,
                     isServerComponent,
                     buildId: this.buildId,

packages/next/server/render.tsx

@@ -1433,44 +1433,48 @@ function renderToNodeStream(
 
 function renderToReadableStream(
   element: React.ReactElement
-): NodeWritablePiper {
-  return (res, next) => {
-    let bufferedString = ''
-    let shellCompleted = false
-
-    const readable = (ReactDOMServer as any).renderToReadableStream(element, {
-      onCompleteShell() {
-        shellCompleted = true
-        if (bufferedString) {
-          res.write(bufferedString)
-          bufferedString = ''
-        }
-      },
-    })
-    const reader = readable.getReader()
-    const decoder = new TextDecoder()
-    const process = () => {
-      reader.read().then(
-        ({ done, value }: any) => {
-          if (!done) {
-            const s = typeof value === 'string' ? value : decoder.decode(value)
-            if (shellCompleted) {
+): Promise<NodeWritablePiper> {
+  return new Promise((resolve, reject) => {
+    let reader: any = null
+    let resolved = false
+    const doResolve = (getReader: () => any) => {
+      if (resolved) return
+      resolved = true
+      const piper: NodeWritablePiper = (res, next) => {
+        const process = async () => {
+          const reader: ReadableStreamDefaultReader = getReader()
+          const decoder = new TextDecoder()
+          reader.read().then(({ done, value }) => {
+            if (!done) {
+              const s =
+                typeof value === 'string' ? value : decoder.decode(value)
               res.write(s)
+              process()
             } else {
-              bufferedString += s
+              next()
             }
-            process()
-          } else {
-            next()
-          }
-        },
-        (err: any) => {
-          next(err)
+          })
         }
-      )
+        process()
+      }
+      resolve(piper)
     }
-    process()
-  }
+
+    const readable = (ReactDOMServer as any).renderToReadableStream(element, {
+      onError(err: Error) {
+        if (!resolved) {
+          resolved = true
+          reject(err)
+        }
+      },
+      onCompleteShell() {
+        doResolve(() => reader)
+      },
+    })
+    // Start reader and lock stream immediately to consume readable,
+    // Otherwise the bytes before `onCompleteShell` will be missed.
+    reader = readable.getReader()
+  })
 }
 
 function chainPipers(pipers: NodeWritablePiper[]): NodeWritablePiper {