feat(federation): graphql gateway module

lib/graphql-gateway.module.ts

@@ -0,0 +1,88 @@
+import { DynamicModule, Inject, Module, OnModuleInit, Optional } from '@nestjs/common';
+import { ApolloServer } from 'apollo-server-express';
+import { HttpAdapterHost } from '@nestjs/core';
+import { GRAPHQL_GATEWAY_BUILD_SERVICE, GRAPHQL_GATEWAY_MODULE_OPTIONS } from './graphql.constants';
+import { GatewayBuildService, GatewayModuleOptions } from './interfaces';
+import { loadPackage } from '@nestjs/common/utils/load-package.util';
+
+@Module({})
+export class GraphQLGatewayModule implements OnModuleInit {
+  private apolloServer: ApolloServer;
+
+  constructor(
+    @Optional()
+    private readonly httpAdapterHost: HttpAdapterHost,
+    @Optional() @Inject(GRAPHQL_GATEWAY_BUILD_SERVICE)
+    private readonly buildService: GatewayBuildService,
+    @Inject(GRAPHQL_GATEWAY_MODULE_OPTIONS)
+    private readonly options: GatewayModuleOptions,
+  ) {}
+
+  static forRoot(options: GatewayModuleOptions): DynamicModule {
+    return {
+      module: GraphQLGatewayModule,
+      providers: [
+        {
+          provide: GRAPHQL_GATEWAY_MODULE_OPTIONS,
+          useValue: options,
+        },
+      ],
+    };
+  }
+
+  async onModuleInit() {
+    if (!this.httpAdapterHost) return;
+    const { httpAdapter } = this.httpAdapterHost;
+
+    if (!httpAdapter) return;
+
+    const { ApolloGateway } = loadPackage('@apollo/gateway', 'ApolloGateway');
+    const app = httpAdapter.getInstance();
+
+    const {
+      options: {
+        __exposeQueryPlanExperimental,
+        debug,
+        serviceList,
+        path,
+        disableHealthCheck,
+        onHealthCheck,
+        cors,
+        bodyParserConfig,
+        installSubscriptionHandlers,
+      },
+      buildService,
+    } = this;
+
+    const gateway = new ApolloGateway({
+      __exposeQueryPlanExperimental,
+      debug,
+      serviceList,
+      buildService,
+    });
+
+    const { schema, executor } = await gateway.load();
+
+    this.apolloServer = new ApolloServer({
+      executor,
+      schema,
+    });
+
+    this.apolloServer.applyMiddleware({
+      app,
+      path,
+      disableHealthCheck,
+      onHealthCheck,
+      cors,
+      bodyParserConfig,
+    });
+
+    if (installSubscriptionHandlers) {
+      // TL;DR <https://github.com/apollographql/apollo-server/issues/2776>
+      throw new Error('No support for subscriptions yet when using Apollo Federation');
+      /*this.apolloServer.installSubscriptionHandlers(
+        httpAdapter.getHttpServer(),
+      );*/
+    }
+  }
+}

lib/graphql.constants.ts

@@ -8,6 +8,9 @@ export const SCALAR_TYPE_METADATA = 'graphql:scalar_type';
 export const PARAM_ARGS_METADATA = '__routeArguments__';
 export const SUBSCRIPTION_OPTIONS_METADATA = 'graphql:subscription_options;';
 
+export const GRAPHQL_GATEWAY_MODULE_OPTIONS = 'graphql:gateway_module_options';
+export const GRAPHQL_GATEWAY_BUILD_SERVICE = 'graphql:gateway_build_service';
+
 export const FIELD_TYPENAME = '__resolveType';
 export const GRAPHQL_MODULE_OPTIONS = 'GqlModuleOptions';
 export const GRAPHQL_MODULE_ID = 'GqlModuleId';

lib/index.ts

@@ -8,3 +8,4 @@ export * from './interfaces';
 export * from './services/gql-arguments-host';
 export * from './services/gql-execution-context';
 export * from './tokens';
+export * from './graphql-gateway.module';