feat(sse): Implement Server-Sent Events

See discussion in nestjs#4826

packages/common/constants.ts

@@ -26,3 +26,4 @@ export const HTTP_CODE_METADATA = '__httpCode__';
 export const MODULE_PATH = '__module_path__';
 export const HEADERS_METADATA = '__headers__';
 export const REDIRECT_METADATA = '__redirect__';
+export const SSE_METADATA = '__sse__';

packages/common/decorators/http/index.ts

@@ -5,3 +5,4 @@ export * from './create-route-param-metadata.decorator';
 export * from './render.decorator';
 export * from './header.decorator';
 export * from './redirect.decorator';
+export * from './sse.decorator';

packages/common/decorators/http/sse.decorator.ts

@@ -0,0 +1,28 @@
+import { SSE_METADATA, PATH_METADATA, METHOD_METADATA } from '../../constants';
+import { RequestMethod } from '../../enums/request-method.enum';
+
+/**
+ * Declares this route as a Server-Sent-Events endpoint
+ *
+ * @publicApi
+ */
+export function Sse(path?: string): MethodDecorator {
+  return (
+    target: object,
+    key: string | symbol,
+    descriptor: TypedPropertyDescriptor<any>,
+  ) => {
+    Reflect.defineMetadata(
+      PATH_METADATA,
+      path && path.length ? path : '/',
+      descriptor.value,
+    );
+    Reflect.defineMetadata(
+      METHOD_METADATA,
+      RequestMethod.GET,
+      descriptor.value,
+    );
+    Reflect.defineMetadata(SSE_METADATA, true, descriptor.value);
+    return descriptor;
+  };
+}

packages/common/http/index.ts

@@ -1,3 +1,4 @@
 export * from './http.module';
 export * from './http.service';
 export * from './interfaces';
+export { SseStream } from './sse-stream.service';

packages/common/http/sse-stream.service.ts

@@ -0,0 +1,89 @@
+import { Transform } from 'stream';
+import { IncomingMessage, OutgoingHttpHeaders } from 'http';
+import { MessageEvent } from '../interfaces';
+
+function toDataString(data: string | object): string {
+  if (typeof data === 'object') return toDataString(JSON.stringify(data));
+  return data
+    .split(/\r\n|\r|\n/)
+    .map(line => `data: ${line}\n`)
+    .join('');
+}
+
+interface WriteHeaders {
+  writeHead?(statusCode: number, headers?: OutgoingHttpHeaders): WriteHeaders;
+  flushHeaders?(): void;
+}
+
+export type HeaderStream = NodeJS.WritableStream & WriteHeaders;
+
+/**
+ * Adapted from https://raw.githubusercontent.com/EventSource/node-ssestream
+ * Transforms "messages" to W3C event stream content.
+ * See https://html.spec.whatwg.org/multipage/server-sent-events.html
+ * A message is an object with one or more of the following properties:
+ * - data (String or object, which gets turned into JSON)
+ * - type
+ * - id
+ * - retry
+ *
+ * If constructed with a HTTP Request, it will optimise the socket for streaming.
+ * If this stream is piped to an HTTP Response, it will set appropriate headers.
+ */
+export class SseStream extends Transform {
+  private lastEventId: number = null;
+
+  constructor(req?: IncomingMessage) {
+    super({ objectMode: true });
+    if (req) {
+      req.socket.setKeepAlive(true);
+      req.socket.setNoDelay(true);
+      req.socket.setTimeout(0);
+    }
+  }
+
+  pipe<T extends HeaderStream>(destination: T, options?: { end?: boolean }): T {
+    if (destination.writeHead) {
+      destination.writeHead(200, {
+        'Content-Type': 'text/event-stream; charset=utf-8',
+        'Transfer-Encoding': 'identity',
+        'Cache-Control': 'no-cache',
+        Connection: 'keep-alive',
+      });
+      destination.flushHeaders();
+    }
+
+    destination.write(':ok\n');
+    return super.pipe(destination, options);
+  }
+
+  _transform(
+    message: MessageEvent,
+    encoding: string,
+    callback: (error?: Error | null, data?: any) => void,
+  ) {
+    if (message.type) this.push(`event: ${message.type}\n`);
+    if (message.id) this.push(`id: ${message.id}\n`);
+    if (message.retry) this.push(`retry: ${message.retry}\n`);
+    if (message.data) this.push(toDataString(message.data));
+    this.push('\n');
+    callback();
+  }
+
+  writeMessage(
+    message: MessageEvent,
+    encoding?: string,
+    cb?: (error: Error | null | undefined) => void,
+  ): boolean {
+    if (!message.id) {
+      this.lastEventId = this.lastEventId === null ? 0 : this.lastEventId + 1;
+      message.id = '' + this.lastEventId;
+    }
+
+    if (!message.type) {
+      message.type = 'message';
+    }
+
+    return this.write(message, encoding, cb);
+  }
+}

packages/common/index.ts

@@ -31,6 +31,7 @@ export {
   INestApplicationContext,
   INestMicroservice,
   IntrospectionResult,
+  MessageEvent,
   MiddlewareConsumer,
   ModuleMetadata,
   NestApplicationOptions,

packages/common/interfaces/http/http-server.interface.ts

@@ -69,3 +69,10 @@ export interface HttpServer<TRequest = any, TResponse = any> {
   getType(): string;
   init?(): Promise<void>;
 }
+
+export interface MessageEvent {
+  data: string | object;
+  id?: string;
+  type?: string;
+  retry?: number;
+}

packages/common/test/decorators/sse.decorator.spec.ts

@@ -0,0 +1,16 @@
+import { expect } from 'chai';
+import { Sse } from '../../decorators/http/sse.decorator';
+import { HTTP_CODE_METADATA, SSE_METADATA } from '../../constants';
+
+describe('@Sse', () => {
+  const prefix = '/prefix';
+  class Test {
+    @Sse(prefix)
+    public static test() {}
+  }
+
+  it('should enhance method with expected http status code', () => {
+    const metadata = Reflect.getMetadata(SSE_METADATA, Test.test);
+    expect(metadata).to.be.eql(prefix);
+  });
+});

packages/core/helpers/handler-metadata-storage.ts

@@ -17,9 +17,10 @@ export interface HandlerMetadata {
     contextId?: ContextId,
     inquirerId?: string,
   ) => (ParamProperties & { metatype?: any })[];
-  fnHandleResponse: <TResult, TResponse>(
+  fnHandleResponse: <TResult, TResponse, TRequest>(
     result: TResult,
     res: TResponse,
+    req?: TRequest,
   ) => any;
 }
 

packages/core/router/router-execution-context.ts

@@ -13,6 +13,7 @@ import {
   REDIRECT_METADATA,
   RENDER_METADATA,
   ROUTE_ARGS_METADATA,
+  SSE_METADATA,
 } from '@nestjs/common/constants';
 import { RouteParamMetadata } from '@nestjs/common/decorators';
 import { RouteParamtypes } from '@nestjs/common/enums/route-paramtypes.enum';
@@ -160,7 +161,7 @@ export class RouterExecutionContext {
         handler(args, req, res, next),
         contextType,
       );
-      await fnHandleResponse(result, res);
+      await fnHandleResponse(result, res, req);
     };
   }
 
@@ -265,6 +266,10 @@ export class RouterExecutionContext {
     return Reflect.getMetadata(HEADERS_METADATA, callback) || [];
   }
 
+  public reflectSse(callback: (...args: unknown[]) => unknown): string {
+    return Reflect.getMetadata(SSE_METADATA, callback);
+  }
+
   public exchangeKeysForValues(
     keys: string[],
     metadata: Record<number, RouteParamMetadata>,
@@ -410,6 +415,16 @@ export class RouterExecutionContext {
         await this.responseController.redirect(result, res, redirectResponse);
       };
     }
+    const isSse = !!this.reflectSse(callback);
+    if (isSse) {
+      return async <TResult, TResponse, TRequest>(
+        result: TResult,
+        res: TResponse,
+        req: TRequest,
+      ) => {
+        await this.responseController.sse(result, res, req);
+      };
+    }
     return async <TResult, TResponse>(result: TResult, res: TResponse) => {
       result = await this.responseController.transformToResult(result);
       !isResponseHandled &&

packages/core/router/router-response-controller.ts

@@ -1,5 +1,12 @@
-import { HttpServer, HttpStatus, RequestMethod } from '@nestjs/common';
+import {
+  HttpServer,
+  HttpStatus,
+  RequestMethod,
+  SseStream,
+  MessageEvent,
+} from '@nestjs/common';
 import { isFunction } from '@nestjs/common/utils/shared.utils';
+import { Observable } from 'rxjs';
 
 export interface CustomHeader {
   name: string;
@@ -78,4 +85,28 @@ export class RouterResponseController {
   ) {
     this.applicationRef.status(response, statusCode);
   }
+
+  public async sse<TInput = unknown, TResponse = unknown, TRequest = unknown>(
+    result: any,
+    response: any,
+    request: any,
+  ) {
+    if (!isFunction(result.subscribe)) {
+      throw new ReferenceError(
+        'You should use an observable to use server-sent events.',
+      );
+    }
+
+    const stream = new SseStream(request);
+    stream.pipe(response);
+
+    const subscription = result.subscribe((message: MessageEvent) => {
+      stream.writeMessage(message);
+    });
+
+    request.on('close', () => {
+      response.end();
+      subscription.unsubscribe();
+    });
+  }
 }

sample/28-sse/.eslintrc.js

@@ -0,0 +1,24 @@
+module.exports = {
+  parser: '@typescript-eslint/parser',
+  parserOptions: {
+    project: 'tsconfig.json',
+    sourceType: 'module',
+  },
+  plugins: ['@typescript-eslint/eslint-plugin'],
+  extends: [
+    'plugin:@typescript-eslint/eslint-recommended',
+    'plugin:@typescript-eslint/recommended',
+    'prettier',
+    'prettier/@typescript-eslint',
+  ],
+  root: true,
+  env: {
+    node: true,
+    jest: true,
+  },
+  rules: {
+    '@typescript-eslint/interface-name-prefix': 'off',
+    '@typescript-eslint/explicit-function-return-type': 'off',
+    '@typescript-eslint/no-explicit-any': 'off',
+  },
+};

sample/28-sse/.gitignore

@@ -0,0 +1,34 @@
+# compiled output
+/dist
+/node_modules
+
+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+lerna-debug.log*
+
+# OS
+.DS_Store
+
+# Tests
+/coverage
+/.nyc_output
+
+# IDEs and editors
+/.idea
+.project
+.classpath
+.c9/
+*.launch
+.settings/
+*.sublime-workspace
+
+# IDE - VSCode
+.vscode/*
+!.vscode/settings.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json

sample/28-sse/.prettierrc

@@ -0,0 +1,4 @@
+{
+  "singleQuote": true,
+  "trailingComma": "all"
+}