[node-bridge] Support streaming response for Serverless Function (#8795)

Adds streaming response support for React Server Components with Next 13.
2025-12-06 04:22:01 +00:00 · 2022-11-01 19:16:37 -07:00
parent 11d0091393
commit 301bcf58fb
17 changed files with 588 additions and 183 deletions
--- a/packages/build-utils/src/lambda.ts
+++ b/packages/build-utils/src/lambda.ts
@@ -23,6 +23,7 @@ export interface LambdaOptionsBase {
  regions?: string[];
  supportsMultiPayloads?: boolean;
  supportsWrapper?: boolean;
+  experimentalResponseStreaming?: boolean;
 }

 export interface LambdaOptionsWithFiles extends LambdaOptionsBase {
@@ -60,6 +61,7 @@ export class Lambda {
  zipBuffer?: Buffer;
  supportsMultiPayloads?: boolean;
  supportsWrapper?: boolean;
+  experimentalResponseStreaming?: boolean;

  constructor(opts: LambdaOptions) {
    const {
@@ -72,6 +74,7 @@ export class Lambda {
      regions,
      supportsMultiPayloads,
      supportsWrapper,
+      experimentalResponseStreaming,
    } = opts;
    if ('files' in opts) {
      assert(typeof opts.files === 'object', '"files" must be an object');
@@ -132,6 +135,7 @@ export class Lambda {
    this.zipBuffer = 'zipBuffer' in opts ? opts.zipBuffer : undefined;
    this.supportsMultiPayloads = supportsMultiPayloads;
    this.supportsWrapper = supportsWrapper;
+    this.experimentalResponseStreaming = experimentalResponseStreaming;
  }

  async createZip(): Promise<Buffer> {
--- a/packages/next/src/server-build.ts
+++ b/packages/next/src/server-build.ts
@@ -338,6 +338,7 @@ export async function serverBuild({

    const apiPages: string[] = [];
    const nonApiPages: string[] = [];
+    const streamingPages: string[] = [];

    lambdaPageKeys.forEach(page => {
      if (
@@ -359,6 +360,8 @@ export async function serverBuild({

      if (pageMatchesApi(page)) {
        apiPages.push(page);
+      } else if (appDir && lambdaAppPaths[page]) {
+        streamingPages.push(page);
      } else {
        nonApiPages.push(page);
      }
@@ -546,7 +549,12 @@ export async function serverBuild({
    const compressedPages: {
      [page: string]: PseudoFile;
    } = {};
-    const mergedPageKeys = [...nonApiPages, ...apiPages, ...internalPages];
+    const mergedPageKeys = [
+      ...nonApiPages,
+      ...streamingPages,
+      ...apiPages,
+      ...internalPages,
+    ];
    const traceCache = {};

    const getOriginalPagePath = (page: string) => {
@@ -704,6 +712,27 @@ export async function serverBuild({
      pageExtensions,
    });

+    const streamingPageLambdaGroups = await getPageLambdaGroups({
+      entryPath: requiredServerFilesManifest.appDir || entryPath,
+      config,
+      pages: streamingPages,
+      prerenderRoutes,
+      pageTraces,
+      compressedPages,
+      tracedPseudoLayer: tracedPseudoLayer.pseudoLayer,
+      initialPseudoLayer,
+      lambdaCompressedByteLimit,
+      initialPseudoLayerUncompressed: uncompressedInitialSize,
+      internalPages,
+      pageExtensions,
+    });
+
+    for (const group of streamingPageLambdaGroups) {
+      if (!group.isPrerenders) {
+        group.isStreaming = true;
+      }
+    }
+
    const apiLambdaGroups = await getPageLambdaGroups({
      entryPath: requiredServerFilesManifest.appDir || entryPath,
      config,
@@ -733,13 +762,23 @@ export async function serverBuild({
            pseudoLayerBytes: group.pseudoLayerBytes,
            uncompressedLayerBytes: group.pseudoLayerUncompressedBytes,
          })),
+          streamingPageLambdaGroups: streamingPageLambdaGroups.map(group => ({
+            pages: group.pages,
+            isPrerender: group.isPrerenders,
+            pseudoLayerBytes: group.pseudoLayerBytes,
+            uncompressedLayerBytes: group.pseudoLayerUncompressedBytes,
+          })),
          nextServerLayerSize: initialPseudoLayer.pseudoLayerBytes,
        },
        null,
        2
      )
    );
-    const combinedGroups = [...pageLambdaGroups, ...apiLambdaGroups];
+    const combinedGroups = [
+      ...pageLambdaGroups,
+      ...streamingPageLambdaGroups,
+      ...apiLambdaGroups,
+    ];

    await detectLambdaLimitExceeding(
      combinedGroups,
@@ -832,6 +871,7 @@ export async function serverBuild({
        memory: group.memory,
        runtime: nodeVersion.runtime,
        maxDuration: group.maxDuration,
+        isStreaming: group.isStreaming,
      });

      for (const page of group.pages) {
--- a/packages/next/src/utils.ts
+++ b/packages/next/src/utils.ts
@@ -748,6 +748,7 @@ export async function createPseudoLayer(files: {

 interface CreateLambdaFromPseudoLayersOptions extends LambdaOptionsWithFiles {
  layers: PseudoLayer[];
+  isStreaming?: boolean;
 }

 // measured with 1, 2, 5, 10, and `os.cpus().length || 5`
@@ -757,6 +758,7 @@ const createLambdaSema = new Sema(1);
 export async function createLambdaFromPseudoLayers({
  files: baseFiles,
  layers,
+  isStreaming,
  ...lambdaOptions
 }: CreateLambdaFromPseudoLayersOptions) {
  await createLambdaSema.acquire();
@@ -791,6 +793,11 @@ export async function createLambdaFromPseudoLayers({

  return new NodejsLambda({
    ...lambdaOptions,
+    ...(isStreaming
+      ? {
+          experimentalResponseStreaming: true,
+        }
+      : {}),
    files,
    shouldAddHelpers: false,
    shouldAddSourcemapSupport: false,
@@ -1273,6 +1280,7 @@ export type LambdaGroup = {
  pages: string[];
  memory?: number;
  maxDuration?: number;
+  isStreaming?: boolean;
  isPrerenders?: boolean;
  pseudoLayer: PseudoLayer;
  pseudoLayerBytes: number;
--- a/packages/next/test/fixtures/00-app-dir-static/app/dashboard/index/lazy.js
+++ b/packages/next/test/fixtures/00-app-dir-static/app/dashboard/index/lazy.js
@@ -1,9 +0,0 @@
-'use client';
-
-export default function LazyComponent() {
-  return (
-    <>
-      <p>hello from lazy</p>
-    </>
-  );
-}
--- a/packages/next/test/fixtures/00-app-dir-static/app/dashboard/index/page.js
+++ b/packages/next/test/fixtures/00-app-dir-static/app/dashboard/index/page.js
@@ -1,10 +0,0 @@
-import { ClientComponent } from './test.js';
-
-export default function DashboardIndexPage() {
-  return (
-    <>
-      <p>hello from app/dashboard/index</p>
-      <ClientComponent />
-    </>
-  );
-}
--- a/packages/next/test/fixtures/00-app-dir-static/app/dashboard/index/test.js
+++ b/packages/next/test/fixtures/00-app-dir-static/app/dashboard/index/test.js
@@ -1,15 +0,0 @@
-'use client';
-
-import { useState, lazy } from 'react';
-
-const Lazy = lazy(() => import('./lazy.js'));
-
-export function ClientComponent() {
-  let [state] = useState('use client');
-  return (
-    <>
-      <Lazy />
-      <p className="hi">hello from modern the {state}</p>
-    </>
-  );
-}
--- a/packages/next/test/fixtures/00-app-dir/app/dashboard/index/lazy.js
+++ b/packages/next/test/fixtures/00-app-dir/app/dashboard/index/lazy.js
@@ -1,9 +0,0 @@
-'use client';
-
-export default function LazyComponent() {
-  return (
-    <>
-      <p>hello from lazy</p>
-    </>
-  );
-}
--- a/packages/next/test/fixtures/00-app-dir/app/dashboard/index/page.js
+++ b/packages/next/test/fixtures/00-app-dir/app/dashboard/index/page.js
@@ -1,10 +0,0 @@
-import { ClientComponent } from './test.js';
-
-export default function DashboardIndexPage() {
-  return (
-    <>
-      <p>hello from app/dashboard/index</p>
-      <ClientComponent />
-    </>
-  );
-}
--- a/packages/next/test/fixtures/00-app-dir/app/dashboard/index/test.js
+++ b/packages/next/test/fixtures/00-app-dir/app/dashboard/index/test.js
@@ -1,15 +0,0 @@
-'use client';
-
-import { useState, lazy } from 'react';
-
-const Lazy = lazy(() => import('./lazy.js'));
-
-export function ClientComponent() {
-  let [state] = useState('use client');
-  return (
-    <>
-      <Lazy />
-      <p className="hi">hello from modern the {state}</p>
-    </>
-  );
-}
--- a/packages/next/test/integration/index.test.js
+++ b/packages/next/test/integration/index.test.js
@@ -7,77 +7,80 @@ const runBuildLambda = require('../../../../test/lib/run-build-lambda');

 jest.setTimeout(360000);

-it('should build with app-dir correctly', async () => {
-  const { buildResult } = await runBuildLambda(
-    path.join(__dirname, '../fixtures/00-app-dir')
-  );
+// experimental appDir currently requires Node.js >= 16
+if (parseInt(process.versions.node.split('.')[0], 10) >= 16) {
+  it('should build with app-dir correctly', async () => {
+    const { buildResult } = await runBuildLambda(
+      path.join(__dirname, '../fixtures/00-app-dir')
+    );

-  const lambdas = new Set();
+    const lambdas = new Set();

-  for (const key of Object.keys(buildResult.output)) {
-    if (buildResult.output[key].type === 'Lambda') {
-      lambdas.add(buildResult.output[key]);
+    for (const key of Object.keys(buildResult.output)) {
+      if (buildResult.output[key].type === 'Lambda') {
+        lambdas.add(buildResult.output[key]);
+      }
    }
-  }

-  expect(lambdas.size).toBe(2);
-  expect(buildResult.output['dashboard']).toBeDefined();
-  expect(buildResult.output['dashboard/another']).toBeDefined();
-  expect(buildResult.output['dashboard/changelog']).toBeDefined();
-  expect(buildResult.output['dashboard/deployments/[id]']).toBeDefined();
+    expect(lambdas.size).toBe(2);
+    expect(buildResult.output['dashboard']).toBeDefined();
+    expect(buildResult.output['dashboard/another']).toBeDefined();
+    expect(buildResult.output['dashboard/changelog']).toBeDefined();
+    expect(buildResult.output['dashboard/deployments/[id]']).toBeDefined();

-  // prefixed static generation output with `/app` under dist server files
-  expect(buildResult.output['dashboard'].type).toBe('Prerender');
-  expect(buildResult.output['dashboard'].fallback.fsPath).toMatch(
-    /server\/app\/dashboard\.html$/
-  );
-  expect(buildResult.output['dashboard.rsc'].type).toBe('Prerender');
-  expect(buildResult.output['dashboard.rsc'].fallback.fsPath).toMatch(
-    /server\/app\/dashboard\.rsc$/
-  );
-  expect(buildResult.output['dashboard/index/index'].type).toBe('Prerender');
-  expect(buildResult.output['dashboard/index/index'].fallback.fsPath).toMatch(
-    /server\/app\/dashboard\/index\.html$/
-  );
-  expect(buildResult.output['dashboard/index.rsc'].type).toBe('Prerender');
-  expect(buildResult.output['dashboard/index.rsc'].fallback.fsPath).toMatch(
-    /server\/app\/dashboard\/index\.rsc$/
-  );
-});
+    // prefixed static generation output with `/app` under dist server files
+    expect(buildResult.output['dashboard'].type).toBe('Prerender');
+    expect(buildResult.output['dashboard'].fallback.fsPath).toMatch(
+      /server\/app\/dashboard\.html$/
+    );
+    expect(buildResult.output['dashboard.rsc'].type).toBe('Prerender');
+    expect(buildResult.output['dashboard.rsc'].fallback.fsPath).toMatch(
+      /server\/app\/dashboard\.rsc$/
+    );
+    expect(buildResult.output['dashboard/index/index'].type).toBe('Prerender');
+    expect(buildResult.output['dashboard/index/index'].fallback.fsPath).toMatch(
+      /server\/app\/dashboard\/index\.html$/
+    );
+    expect(buildResult.output['dashboard/index.rsc'].type).toBe('Prerender');
+    expect(buildResult.output['dashboard/index.rsc'].fallback.fsPath).toMatch(
+      /server\/app\/dashboard\/index\.rsc$/
+    );
+  });

-it('should build with app-dir in edge runtime correctly', async () => {
-  const { buildResult } = await runBuildLambda(
-    path.join(__dirname, '../fixtures/00-app-dir-edge')
-  );
+  it('should build with app-dir in edge runtime correctly', async () => {
+    const { buildResult } = await runBuildLambda(
+      path.join(__dirname, '../fixtures/00-app-dir-edge')
+    );

-  const edgeFunctions = new Set();
+    const edgeFunctions = new Set();

-  for (const key of Object.keys(buildResult.output)) {
-    if (buildResult.output[key].type === 'EdgeFunction') {
-      edgeFunctions.add(buildResult.output[key]);
+    for (const key of Object.keys(buildResult.output)) {
+      if (buildResult.output[key].type === 'EdgeFunction') {
+        edgeFunctions.add(buildResult.output[key]);
+      }
    }
-  }

-  expect(edgeFunctions.size).toBe(3);
-  expect(buildResult.output['edge']).toBeDefined();
-  expect(buildResult.output['index']).toBeDefined();
-  expect(buildResult.output['index/index']).toBeDefined();
-});
+    expect(edgeFunctions.size).toBe(3);
+    expect(buildResult.output['edge']).toBeDefined();
+    expect(buildResult.output['index']).toBeDefined();
+    expect(buildResult.output['index/index']).toBeDefined();
+  });

-it('should show error from basePath with legacy monorepo build', async () => {
-  let error;
+  it('should show error from basePath with legacy monorepo build', async () => {
+    let error;

-  try {
-    await runBuildLambda(path.join(__dirname, 'legacy-monorepo-basepath'));
-  } catch (err) {
-    error = err;
-  }
-  console.error(error);
+    try {
+      await runBuildLambda(path.join(__dirname, 'legacy-monorepo-basepath'));
+    } catch (err) {
+      error = err;
+    }
+    console.error(error);

-  expect(error.message).toBe(
-    'basePath can not be used with `builds` in vercel.json, use Project Settings to configure your monorepo instead'
-  );
-});
+    expect(error.message).toBe(
+      'basePath can not be used with `builds` in vercel.json, use Project Settings to configure your monorepo instead'
+    );
+  });
+}

 it('should build using server build', async () => {
  const origLog = console.log;
--- a/packages/node-bridge/bridge.js
+++ b/packages/node-bridge/bridge.js
@@ -1,4 +1,10 @@
+const { URL } = require('url');
 const { request } = require('http');
+const { Socket } = require('net');
+const { createCipheriv } = require('crypto');
+const { pipeline, Transform } = require('stream');
+
+const CRLF = `\r\n`;

 /**
 * If the `http.Server` handler function throws an error asynchronously,
@@ -17,9 +23,23 @@ process.on('unhandledRejection', err => {
 */
 function normalizeProxyEvent(event) {
  let bodyBuffer;
-  const { method, path, headers, encoding, body, payloads } = JSON.parse(
-    event.body
-  );
+  /**
+   * @type {import('./types').VercelProxyRequest}
+   */
+  const payload = JSON.parse(event.body);
+  const {
+    method,
+    path,
+    headers,
+    encoding,
+    body,
+    payloads,
+    responseCallbackCipher,
+    responseCallbackCipherIV,
+    responseCallbackCipherKey,
+    responseCallbackStream,
+    responseCallbackUrl,
+  } = payload;

  /**
   *
@@ -28,7 +48,7 @@ function normalizeProxyEvent(event) {
   */
  const normalizeBody = b => {
    if (b) {
-      if (encoding === 'base64') {
+      if (typeof b === 'string' && encoding === 'base64') {
        bodyBuffer = Buffer.from(b, encoding);
      } else if (encoding === undefined) {
        bodyBuffer = Buffer.from(b);
@@ -42,13 +62,9 @@ function normalizeProxyEvent(event) {
  };

  if (payloads) {
-    /**
-     * @param {{ body: string | Buffer }} payload
-     */
-    const normalizePayload = payload => {
-      payload.body = normalizeBody(payload.body);
-    };
-    payloads.forEach(normalizePayload);
+    for (const p of payloads) {
+      p.body = normalizeBody(payload.body);
+    }
  }
  bodyBuffer = normalizeBody(body);

@@ -59,6 +75,11 @@ function normalizeProxyEvent(event) {
    headers,
    body: bodyBuffer,
    payloads,
+    responseCallbackCipher,
+    responseCallbackCipherIV,
+    responseCallbackCipherKey,
+    responseCallbackStream,
+    responseCallbackUrl,
  };
 }

@@ -79,11 +100,23 @@ function normalizeAPIGatewayProxyEvent(event) {
    bodyBuffer = Buffer.alloc(0);
  }

-  return { isApiGateway: true, method, path, headers, body: bodyBuffer };
+  return {
+    body: bodyBuffer,
+    headers,
+    isApiGateway: true,
+    method,
+    path,
+    responseCallbackCipher: undefined,
+    responseCallbackCipherIV: undefined,
+    responseCallbackCipherKey: undefined,
+    responseCallbackStream: undefined,
+    responseCallbackUrl: undefined,
+  };
 }

 /**
 * @param {import('./types').VercelProxyEvent | import('aws-lambda').APIGatewayProxyEvent} event
+ * @return {import('./types').VercelProxyRequest}
 */
 function normalizeEvent(event) {
  if ('Action' in event) {
@@ -176,7 +209,7 @@ class Bridge {
   *
   * @param {import('./types').VercelProxyEvent | import('aws-lambda').APIGatewayProxyEvent} event
   * @param {import('aws-lambda').Context} context
-   * @return {Promise<{statusCode: number, headers: import('http').IncomingHttpHeaders,  body: string, encoding: 'base64'}>}
+   * @return {Promise<import('./types').VercelProxyResponse>}
   */
  async launcher(event, context) {
    context.callbackWaitsForEmptyEventLoop = false;
@@ -268,6 +301,10 @@ class Bridge {
        encoding: 'base64',
      };
    } else {
+      // TODO We expect this to error as it is possible to resolve to empty.
+      // For now it is not very important as we will only pass
+      // `responseCallbackUrl` in production.
+      // @ts-ignore
      return this.handleEvent(normalizedEvent);
    }
  }
@@ -275,11 +312,21 @@ class Bridge {
  /**
   *
   * @param {ReturnType<typeof normalizeEvent>} normalizedEvent
-   * @return {Promise<{statusCode: number, headers: import('http').IncomingHttpHeaders,  body: string, encoding: 'base64'}>}
+   * @return {Promise<import('./types').VercelProxyResponse | import('./types').VercelStreamProxyResponse>}
   */
  async handleEvent(normalizedEvent) {
    const { port } = await this.listening;
-    const { isApiGateway, method, headers, body } = normalizedEvent;
+    const {
+      body,
+      headers,
+      isApiGateway,
+      method,
+      responseCallbackCipher,
+      responseCallbackCipherIV,
+      responseCallbackCipherKey,
+      responseCallbackStream,
+      responseCallbackUrl,
+    } = normalizedEvent;
    let { path } = normalizedEvent;

    if (this.shouldStoreEvents) {
@@ -288,41 +335,42 @@ class Bridge {
      headers['x-now-bridge-request-id'] = reqId;
    }

-    // eslint-disable-next-line consistent-return
    return new Promise((resolve, reject) => {
+      let socket;
+      let cipher;
+      let url;
+
+      if (responseCallbackUrl) {
+        socket = new Socket();
+        url = new URL(responseCallbackUrl);
+        socket.connect(parseInt(url.port, 10), url.hostname);
+        socket.write(`${responseCallbackStream}${CRLF}`);
+      }
+
+      if (
+        responseCallbackCipher &&
+        responseCallbackCipherKey &&
+        responseCallbackCipherIV
+      ) {
+        cipher = createCipheriv(
+          responseCallbackCipher,
+          Buffer.from(responseCallbackCipherKey, 'base64'),
+          Buffer.from(responseCallbackCipherIV, 'base64')
+        );
+      }
+
      // if the path is improperly encoded we need to encode it or
      // http.request will throw an error (related check: https://github.com/nodejs/node/blob/4ece669c6205ec78abfdadfe78869bbb8411463e/lib/_http_client.js#L84)
      if (path && /[^\u0021-\u00ff]/.test(path)) {
        path = encodeURI(path);
      }

-      const opts = { hostname: '127.0.0.1', port, path, method };
-      const req = request(opts, res => {
-        const response = res;
-        /**
-         * @type {Buffer[]}
-         */
-        const respBodyChunks = [];
-        response.on('data', chunk => respBodyChunks.push(Buffer.from(chunk)));
-        response.on('error', reject);
-        response.on('end', () => {
-          const bodyBuffer = Buffer.concat(respBodyChunks);
-          delete response.headers.connection;
-
-          if (isApiGateway) {
-            delete response.headers['content-length'];
-          } else if (response.headers['content-length']) {
-            response.headers['content-length'] = String(bodyBuffer.length);
-          }
-
-          resolve({
-            statusCode: response.statusCode || 200,
-            headers: response.headers,
-            body: bodyBuffer.toString('base64'),
-            encoding: 'base64',
-          });
-        });
-      });
+      const req = request(
+        { hostname: '127.0.0.1', port, path, method },
+        socket && url && cipher
+          ? getStreamResponseCallback({ url, socket, cipher, resolve, reject })
+          : getResponseCallback({ isApiGateway, resolve, reject })
+      );

      req.on('error', error => {
        setTimeout(() => {
@@ -332,16 +380,10 @@ class Bridge {
        }, 2);
      });

-      for (const [name, value] of Object.entries(headers)) {
-        if (value === undefined) {
-          console.error(
-            `Skipping HTTP request header "${name}" because value is undefined`
-          );
-          continue;
-        }
+      for (const [name, value] of getHeadersIterator(headers)) {
        try {
          req.setHeader(name, value);
-        } catch (err) {
+        } catch (/** @type any */ err) {
          console.error(`Skipping HTTP request header: "${name}: ${value}"`);
          console.error(err.message);
        }
@@ -363,4 +405,106 @@ class Bridge {
  }
 }

+/**
+ * Generates the streaming response callback which writes in the given socket client a raw
+ * HTTP Request message to later pipe the response body into the socket. It will pass request
+ * headers namespace and an additional header with the status code. Once everything is
+ * written it will destroy the socket and resolve to an empty object. If a cipher is given
+ * it will be used to pipe bytes.
+ *
+ * @type {(params: {
+ *  url: import('url').URL,
+ *  socket: import('net').Socket,
+ *  cipher: import('crypto').Cipher
+ *  resolve: (result: (Record<string, never>)) => void,
+ *  reject: (err: Error) => void
+ * }) => (response: import("http").IncomingMessage) => void}
+ */
+function getStreamResponseCallback({ url, socket, cipher, resolve, reject }) {
+  return response => {
+    const chunked = new Transform();
+    chunked._transform = function (chunk, _, callback) {
+      this.push(Buffer.byteLength(chunk).toString(16) + CRLF);
+      this.push(chunk);
+      this.push(CRLF);
+      callback();
+    };
+
+    let headers = `Host: ${url.host}${CRLF}`;
+    headers += `transfer-encoding: chunked${CRLF}`;
+    headers += `x-vercel-status-code: ${response.statusCode || 200}${CRLF}`;
+    for (const [name, value] of getHeadersIterator(response.headers)) {
+      if (!['connection', 'transfer-encoding'].includes(name)) {
+        headers += `x-vercel-header-${name}: ${value}${CRLF}`;
+      }
+    }
+
+    cipher.write(`POST ${url.pathname} HTTP/1.1${CRLF}${headers}${CRLF}`);
+
+    pipeline(response, chunked, cipher, socket, err => {
+      if (err) return reject(err);
+      resolve({});
+    });
+  };
+}
+
+/**
+ * Generates the normal response callback which waits until the body is fully
+ * received before resolving the promise. It caches the entire body and resolve
+ * with an object that describes the response.
+ *
+ * @type {(params: {
+ *  isApiGateway: boolean,
+ *  resolve: (result: (import('./types').VercelProxyResponse)) => void,
+ *  reject: (err: Error) => void
+ * }) => (response: import("http").IncomingMessage) => void}
+ */
+function getResponseCallback({ isApiGateway, resolve, reject }) {
+  return response => {
+    /**
+     * @type {Buffer[]}
+     */
+    const respBodyChunks = [];
+    response.on('data', chunk => respBodyChunks.push(Buffer.from(chunk)));
+    response.on('error', reject);
+    response.on('end', () => {
+      const bodyBuffer = Buffer.concat(respBodyChunks);
+      delete response.headers.connection;
+
+      if (isApiGateway) {
+        delete response.headers['content-length'];
+      } else if (response.headers['content-length']) {
+        response.headers['content-length'] = String(bodyBuffer.length);
+      }
+
+      resolve({
+        statusCode: response.statusCode || 200,
+        headers: response.headers,
+        body: bodyBuffer.toString('base64'),
+        encoding: 'base64',
+      });
+    });
+  };
+}
+
+/**
+ * Get an iterator for the headers object and yield the name and value when
+ * the value is not undefined only.
+ *
+ * @type {(headers: import('http').IncomingHttpHeaders) =>
+ *  Generator<[string, string | string[]], void, unknown>}
+ */
+function* getHeadersIterator(headers) {
+  for (const [name, value] of Object.entries(headers)) {
+    if (value === undefined) {
+      console.error(
+        `Skipping HTTP request header "${name}" because value is undefined`
+      );
+      continue;
+    }
+
+    yield [name, value];
+  }
+}
+
 module.exports = { Bridge };
--- a/packages/node-bridge/package.json
+++ b/packages/node-bridge/package.json
@@ -23,6 +23,8 @@
  "devDependencies": {
    "@types/aws-lambda": "8.10.19",
    "@types/node": "*",
+    "jsonlines": "0.1.1",
+    "test-listen": "1.1.0",
    "typescript": "4.3.4"
  }
 }
--- a/packages/node-bridge/test/bridge.test.js
+++ b/packages/node-bridge/test/bridge.test.js
@@ -1,6 +1,10 @@
 const assert = require('assert');
+const crypto = require('crypto');
+const jsonlines = require('jsonlines');
 const { Server } = require('http');
 const { Bridge } = require('../bridge');
+const { runServer } = require('./run-test-server');
+const { runTcpServer } = require('./run-test-server');

 test('port binding', async () => {
  const server = new Server();
@@ -184,7 +188,7 @@ test('multi-payload handling', async () => {
 });

 test('consumeEvent', async () => {
-  const mockListener = jest.fn((req, res) => {
+  const mockListener = jest.fn((_, res) => {
    res.end('hello');
  });

@@ -222,7 +226,7 @@ test('consumeEvent', async () => {
 });

 test('consumeEvent and handle decoded path', async () => {
-  const mockListener = jest.fn((req, res) => {
+  const mockListener = jest.fn((_, res) => {
    res.end('hello');
  });

@@ -295,3 +299,180 @@ test('invalid request headers', async () => {

  server.close();
 });
+
+test('`NowProxyEvent` proxy streaming with a sync handler', async () => {
+  const cipherParams = {
+    cipher: 'aes-256-ctr',
+    cipherIV: crypto.randomBytes(16),
+    cipherKey: crypto.randomBytes(32),
+  };
+
+  const effects = {
+    callbackPayload: undefined,
+    callbackStream: undefined,
+  };
+
+  const { deferred, resolve } = createDeferred();
+
+  const httpServer = await runServer({
+    handler: (req, res) => {
+      const chunks = [];
+      req.on('data', chunk => {
+        chunks.push(chunk.toString());
+      });
+      req.on('close', () => {
+        effects.callbackPayload = chunks;
+        res.writeHead(200, 'OK', { 'content-type': 'application/json' });
+        res.end();
+        resolve();
+      });
+    },
+  });
+
+  const tcpServerCallback = await runTcpServer({
+    cipherParams,
+    effects,
+    httpServer,
+  });
+
+  const server = new Server((req, res) => {
+    res.setHeader('content-type', 'text/html');
+    res.end('hello');
+  });
+
+  const bridge = new Bridge(server);
+  bridge.listen();
+  const context = { callbackWaitsForEmptyEventLoop: true };
+  const result = await bridge.launcher(
+    {
+      Action: 'Invoke',
+      body: JSON.stringify({
+        method: 'POST',
+        responseCallbackCipher: cipherParams.cipher,
+        responseCallbackCipherIV: cipherParams.cipherIV.toString('base64'),
+        responseCallbackCipherKey: cipherParams.cipherKey.toString('base64'),
+        responseCallbackStream: 'abc',
+        responseCallbackUrl: String(tcpServerCallback.url),
+        headers: { foo: 'bar' },
+        path: '/nowproxy',
+        body: 'body=1',
+      }),
+    },
+    context
+  );
+
+  await deferred;
+
+  expect(result).toEqual({});
+  expect(context.callbackWaitsForEmptyEventLoop).toEqual(false);
+  expect(effects.callbackStream).toEqual('abc');
+  expect(effects.callbackPayload).toEqual(['hello']);
+
+  server.close();
+  await httpServer.close();
+  await tcpServerCallback.close();
+});
+
+test('`NowProxyEvent` proxy streaming with an async handler', async () => {
+  const effects = {
+    callbackHeaders: undefined,
+    callbackMethod: undefined,
+    callbackPayload: undefined,
+    callbackStream: undefined,
+  };
+
+  const cipherParams = {
+    cipher: 'aes-256-ctr',
+    cipherIV: crypto.randomBytes(16),
+    cipherKey: crypto.randomBytes(32),
+  };
+
+  const { deferred, resolve } = createDeferred();
+  const jsonParser = jsonlines.parse();
+  const httpServer = await runServer({
+    handler: (req, res) => {
+      const chunks = [];
+      req.pipe(jsonParser);
+      jsonParser.on('data', chunk => {
+        chunks.push(chunk);
+      });
+      req.on('close', () => {
+        effects.callbackMethod = req.method;
+        effects.callbackHeaders = req.headers;
+        effects.callbackPayload = chunks;
+        res.writeHead(200, 'OK', { 'content-type': 'application/json' });
+        res.end();
+        resolve();
+      });
+    },
+  });
+
+  const tcpServerCallback = await runTcpServer({
+    cipherParams,
+    httpServer,
+    effects,
+  });
+
+  const jsonStringifier = jsonlines.stringify();
+  const server = new Server((req, res) => {
+    res.setHeader('x-test', 'hello');
+    res.setHeader('content-type', 'text/html');
+    jsonStringifier.pipe(res);
+    jsonStringifier.write({ method: req.method });
+    jsonStringifier.write({ path: req.url });
+    setTimeout(() => {
+      jsonStringifier.write({ headers: req.headers });
+      res.end();
+    }, 100);
+  });
+
+  const bridge = new Bridge(server);
+  bridge.listen();
+  const context = { callbackWaitsForEmptyEventLoop: true };
+  const result = await bridge.launcher(
+    {
+      Action: 'Invoke',
+      body: JSON.stringify({
+        method: 'POST',
+        responseCallbackCipher: cipherParams.cipher,
+        responseCallbackCipherIV: cipherParams.cipherIV.toString('base64'),
+        responseCallbackCipherKey: cipherParams.cipherKey.toString('base64'),
+        responseCallbackStream: 'abc',
+        responseCallbackUrl: String(tcpServerCallback.url),
+        headers: { foo: 'bar' },
+        path: '/nowproxy',
+        body: 'body=1',
+      }),
+    },
+    context
+  );
+
+  await deferred;
+
+  expect(result).toEqual({});
+  expect(context.callbackWaitsForEmptyEventLoop).toEqual(false);
+  expect(effects.callbackStream).toEqual('abc');
+  expect(effects.callbackMethod).toEqual('POST');
+  expect(effects.callbackHeaders).toMatchObject({
+    'x-vercel-status-code': '200',
+    'x-vercel-header-x-test': 'hello',
+    'x-vercel-header-content-type': 'text/html',
+  });
+  expect(effects.callbackPayload).toMatchObject([
+    { method: 'POST' },
+    { path: '/nowproxy' },
+    { headers: { foo: 'bar' } },
+  ]);
+
+  server.close();
+  httpServer.close();
+  tcpServerCallback.close();
+});
+
+function createDeferred() {
+  let resolve;
+  const deferred = new Promise(_resolve => {
+    resolve = _resolve;
+  });
+  return { deferred, resolve };
+}
--- a/packages/node-bridge/test/run-test-server.js
+++ b/packages/node-bridge/test/run-test-server.js
@@ -0,0 +1,78 @@
+const { createServer } = require('net');
+const { Server } = require('http');
+const { Socket } = require('net');
+const { URL } = require('url');
+const crypto = require('crypto');
+const listen = require('test-listen');
+
+exports.runServer = async function runServer({ handler }) {
+  const server = new Server(handler);
+  const url = await listen(server);
+  return { url: new URL(url), close: getKillServer(server) };
+};
+
+function getKillServer(server) {
+  let sockets = [];
+
+  server.on('connection', socket => {
+    sockets.push(socket);
+    socket.once('close', () => {
+      sockets.splice(sockets.indexOf(socket), 1);
+    });
+  });
+
+  return () => {
+    return new Promise((resolve, reject) => {
+      server.close(err => {
+        if (err) {
+          return reject(err);
+        }
+        resolve();
+      });
+
+      sockets.forEach(function (socket) {
+        socket.destroy();
+      });
+
+      sockets = [];
+    });
+  };
+}
+
+exports.runTcpServer = async function runTcpServer({
+  effects,
+  httpServer,
+  cipherParams,
+}) {
+  const server = createServer();
+  server.on('connection', connection => {
+    const socket = new Socket();
+    socket.connect(parseInt(httpServer.url.port, 10), httpServer.hostname);
+    const decipher = crypto.createDecipheriv(
+      cipherParams.cipher,
+      cipherParams.cipherKey,
+      cipherParams.cipherIV
+    );
+
+    decipher.pipe(socket);
+
+    const CRLF = Buffer.from('\r\n');
+    let accBuffer = Buffer.from([]);
+    connection.on('data', function onConnectionData(chunk) {
+      accBuffer = Buffer.concat([accBuffer, chunk]);
+      const idx = accBuffer.indexOf(CRLF);
+      if (idx !== -1) {
+        effects.callbackStream = accBuffer.slice(0, idx).toString();
+        connection.off('data', onConnectionData);
+        decipher.write(accBuffer.slice(idx + 2));
+        connection.pipe(decipher);
+        decipher.on('close', () => {
+          socket.end();
+        });
+      }
+    });
+  });
+
+  const url = await listen(server);
+  return { url: new URL(url), close: getKillServer(server) };
+};
--- a/packages/node-bridge/types.ts
+++ b/packages/node-bridge/types.ts
@@ -1,5 +1,6 @@
 /// <reference types="node" />
-import {
+import type { CipherCCMTypes } from 'crypto';
+import type {
  Server,
  IncomingHttpHeaders,
  OutgoingHttpHeaders,
@@ -11,12 +12,18 @@ export interface VercelProxyEvent {
  body: string;
 }
 export interface VercelProxyRequest {
-  isApiGateway?: boolean;
+  isApiGateway: boolean;
  method: string;
  path: string;
  headers: IncomingHttpHeaders;
  body: Buffer;
+  encoding?: string;
  payloads?: Array<VercelProxyRequest>;
+  responseCallbackCipher?: CipherCCMTypes;
+  responseCallbackCipherIV?: string;
+  responseCallbackCipherKey?: string;
+  responseCallbackStream?: string;
+  responseCallbackUrl?: string;
 }
 export interface VercelProxyResponse {
  statusCode: number;
@@ -24,6 +31,7 @@ export interface VercelProxyResponse {
  body: string;
  encoding: BufferEncoding;
 }
+export type VercelStreamProxyResponse = Record<string, never>;
 export interface ServerLike {
  timeout?: number;
  listen: (
--- a/packages/node/src/index.ts
+++ b/packages/node/src/index.ts
@@ -465,6 +465,9 @@ export const build: BuildV3 = async ({
      config.helpers === false || process.env.NODEJS_HELPERS === '0'
    );

+    const experimentalResponseStreaming =
+      staticConfig?.experimentalResponseStreaming === true ? true : undefined;
+
    output = new NodejsLambda({
      files: preparedFiles,
      handler,
@@ -472,6 +475,7 @@ export const build: BuildV3 = async ({
      shouldAddHelpers,
      shouldAddSourcemapSupport,
      awsLambdaHandler,
+      experimentalResponseStreaming,
    });
  }

--- a/test/lib/deployment/now-deploy.js
+++ b/test/lib/deployment/now-deploy.js
@@ -1,3 +1,4 @@
+// bust cache
 const assert = require('assert');
 const { createHash } = require('crypto');
 const path = require('path');