style(event-handler): apply stricter linting

packages/event-handler/src/appsync-events/Router.ts

@@ -1,6 +1,9 @@
 import type { GenericLogger } from '@aws-lambda-powertools/commons/types';
 import { isRecord } from '@aws-lambda-powertools/commons/typeutils';
-import { getStringFromEnv, isDevMode } from '@aws-lambda-powertools/commons/utils/env';
+import {
+  getStringFromEnv,
+  isDevMode,
+} from '@aws-lambda-powertools/commons/utils/env';
 import type {
   OnPublishHandler,
   OnSubscribeHandler,
@@ -31,7 +34,7 @@ class Router {
    * Whether the router is running in development mode.
    */
   protected readonly isDev: boolean = false;
- 
+
   public constructor(options?: RouterOptions) {
     const alcLogLevel = getStringFromEnv({
       key: 'AWS_LAMBDA_LOG_LEVEL',

packages/event-handler/src/appsync-graphql/AppSyncGraphQLResolver.ts

@@ -152,11 +152,7 @@ class AppSyncGraphQLResolver extends Router {
    * @param context - The AWS Lambda context object.
    * @param options - Optional parameters for the resolver, such as the scope of the handler.
    */
-  public async resolve(
-    event: unknown,
-    context: Context,
-    options?: ResolveOptions
-  ): Promise<unknown> {
+  public resolve(event: unknown, context: Context, options?: ResolveOptions) {
     if (Array.isArray(event)) {
       if (event.some((e) => !isAppSyncGraphQLEvent(e))) {
         this.logger.warn(
@@ -194,10 +190,10 @@ class AppSyncGraphQLResolver extends Router {
    * @param options - Optional resolve options for customizing resolver behavior.
    */
   async #withErrorHandling(
-    fn: () => Promise<unknown>,
+    fn: () => Promise<unknown> | unknown,
     event: AppSyncResolverEvent<Record<string, unknown>>,
     options?: ResolveOptions
-  ): Promise<unknown> {
+  ) {
     try {
       return await fn();
     } catch (error) {
@@ -377,11 +373,11 @@ class AppSyncGraphQLResolver extends Router {
    * @param options - Optional parameters for the resolver, such as the scope of the handler.
    * @throws {ResolverNotFoundException} If no resolver is registered for the given field and type.
    */
-  async #executeSingleResolver(
+  #executeSingleResolver(
     event: AppSyncResolverEvent<Record<string, unknown>>,
     context: Context,
     options?: ResolveOptions
-  ): Promise<unknown> {
+  ): Promise<unknown> | unknown {
     const { fieldName, parentTypeName: typeName } = event.info;
 
     const resolverHandlerOptions = this.resolverRegistry.resolve(

packages/event-handler/src/appsync-graphql/index.ts

@@ -1,7 +1,7 @@
 export { AppSyncGraphQLResolver } from './AppSyncGraphQLResolver.js';
 export {
-  ResolverNotFoundException,
   InvalidBatchResponseException,
+  ResolverNotFoundException,
 } from './errors.js';
 export {
   awsDate,

packages/event-handler/src/bedrock-agent/BedrockAgentFunctionResolver.ts

@@ -146,7 +146,7 @@ class BedrockAgentFunctionResolver {
   public tool<TParams extends Record<string, ParameterValue>>(
     fn: ToolFunction<TParams>,
     config: Configuration
-  ): undefined {
+  ) {
     const { name } = config;
     if (this.#tools.has(name)) {
       this.#logger.warn(

packages/event-handler/src/rest/converters.ts

@@ -36,11 +36,11 @@ export const proxyEventToWebRequest = (
   const { domainName } = event.requestContext;
 
   const headers = new Headers();
-  for (const [name, value] of Object.entries(event.headers ?? {})) {
-    if (value != null) headers.set(name, value);
+  for (const [name, value] of Object.entries(event.headers)) {
+    if (value !== undefined) headers.set(name, value);
   }
 
-  for (const [name, values] of Object.entries(event.multiValueHeaders ?? {})) {
+  for (const [name, values] of Object.entries(event.multiValueHeaders)) {
     for (const value of values ?? []) {
       const headerValue = headers.get(name);
       if (!headerValue?.includes(value)) {

packages/event-handler/src/rest/middleware/cors.ts

@@ -35,6 +35,7 @@ import {
  * }));
  * ```
  *
+ * @param options - Configuration options for CORS
  * @param options.origin - The origin to allow requests from
  * @param options.allowMethods - The HTTP methods to allow
  * @param options.allowHeaders - The headers to allow

packages/event-handler/src/rest/utils.ts

@@ -5,7 +5,9 @@ import type {
   HandlerResponse,
   HttpMethod,
   Middleware,
+  NextFunction,
   Path,
+  RequestContext,
   ValidationResult,
 } from '../types/rest.js';
 import {
@@ -149,8 +151,14 @@ export const isAPIGatewayProxyResult = (
  * //   -> middleware1 end
  * ```
  */
-export const composeMiddleware = (middleware: Middleware[]): Middleware => {
-  return async ({ reqCtx, next }): Promise<HandlerResponse | void> => {
+export const composeMiddleware = (middleware: Middleware[]) => {
+  return async ({
+    reqCtx,
+    next,
+  }: {
+    reqCtx: RequestContext;
+    next: NextFunction;
+  }) => {
     let index = -1;
     let result: HandlerResponse | undefined;
 
@@ -193,6 +201,6 @@ export const composeMiddleware = (middleware: Middleware[]): Middleware => {
     };
 
     await dispatch(0);
-    return result;
+    if (result !== undefined) return result;
   };
 };

packages/event-handler/src/types/bedrock-agent.ts

@@ -51,7 +51,10 @@ type ToolFunction<TParams = Record<string, ParameterValue>> = (
     event: BedrockAgentFunctionEvent;
     context: Context;
   }
-) => Promise<JSONValue | BedrockFunctionResponse>;
+) =>
+  | Promise<JSONValue | BedrockFunctionResponse>
+  | JSONValue
+  | BedrockFunctionResponse;
 
 /**
  * Tool in the Bedrock Agent Function Resolver.
@@ -159,7 +162,7 @@ type ResolverOptions = {
    *
    * When no logger is provided, we'll only log warnings and errors using the global `console` object.
    */
-  logger?: GenericLogger;
+  logger?: Pick<GenericLogger, 'debug' | 'warn' | 'error'>;
 };
 
 export type {

packages/event-handler/src/types/rest.ts

@@ -24,6 +24,7 @@ type ErrorHandler<T extends Error = Error> = (
 ) => Promise<HandlerResponse>;
 
 interface ErrorConstructor<T extends Error = Error> {
+  // biome-ignore lint/suspicious/noExplicitAny: this is a generic type that is intentionally open
   new (...args: any[]): T;
   prototype: T;
 }
@@ -53,11 +54,11 @@ interface CompiledRoute {
 
 type DynamicRoute = Route & CompiledRoute;
 
-type HandlerResponse = Response | JSONObject;
+type HandlerResponse = Response | JSONObject | undefined;
 
 type RouteHandler<TReturn = HandlerResponse> = (
   reqCtx: RequestContext
-) => Promise<TReturn>;
+) => Promise<TReturn> | TReturn;
 
 type HttpMethod = keyof typeof HttpVerbs;
 
@@ -78,12 +79,16 @@ type RestRouteOptions = {
   middleware?: Middleware[];
 };
 
-type NextFunction = () => Promise<HandlerResponse | void>;
+type NextFunction = () =>
+  | Promise<HandlerResponse>
+  | HandlerResponse
+  | Promise<void>
+  | void;
 
 type Middleware = (args: {
   reqCtx: RequestContext;
   next: NextFunction;
-}) => Promise<void | HandlerResponse>;
+}) => NextFunction;
 
 type RouteRegistryOptions = {
   /**
@@ -176,4 +181,5 @@ export type {
   RouteRegistryOptions,
   ValidationResult,
   CompressionOptions,
+  NextFunction,
 };

packages/event-handler/tests/unit/appsync-events/AppSyncEventsResolver.test.ts

@@ -87,7 +87,7 @@ describe('Class: AppSyncEventsResolver', () => {
         public scope = 'scoped';
 
         @app.onPublish('/foo', { aggregate })
-        public async handleFoo(payloads: OnPublishAggregatePayload) {
+        public handleFoo(payloads: OnPublishAggregatePayload) {
           return payloads.map((payload) => {
             return {
               id: payload.id,
@@ -97,15 +97,15 @@ describe('Class: AppSyncEventsResolver', () => {
         }
 
         @app.onPublish('/bar')
-        public async handleBar(payload: string) {
+        public handleBar(payload: string) {
           return `${this.scope} ${payload}`;
         }
 
-        public async handler(event: unknown, context: Context) {
+        public handler(event: unknown, context: Context) {
           return this.stuff(event, context);
         }
 
-        async stuff(event: unknown, context: Context) {
+        stuff(event: unknown, context: Context) {
           return app.resolve(event, context, { scope: this });
         }
       }
@@ -146,15 +146,15 @@ describe('Class: AppSyncEventsResolver', () => {
       public scope = 'scoped';
 
       @app.onSubscribe('/foo')
-      public async handleFoo(payload: AppSyncEventsSubscribeEvent) {
+      public handleFoo(payload: AppSyncEventsSubscribeEvent) {
         console.debug(`${this.scope} ${payload.info.channel.path}`);
       }
 
-      public async handler(event: unknown, context: Context) {
+      public handler(event: unknown, context: Context) {
         return this.stuff(event, context);
       }
 
-      async stuff(event: unknown, context: Context) {
+      stuff(event: unknown, context: Context) {
         return app.resolve(event, context, { scope: this });
       }
     }
@@ -222,7 +222,7 @@ describe('Class: AppSyncEventsResolver', () => {
     async ({ error, message }) => {
       // Prepare
       const app = new AppSyncEventsResolver({ logger: console });
-      app.onSubscribe('/foo', async () => {
+      app.onSubscribe('/foo', () => {
         throw error;
       });
 
@@ -242,7 +242,7 @@ describe('Class: AppSyncEventsResolver', () => {
   it('throws an UnauthorizedException when thrown by the handler', async () => {
     // Prepare
     const app = new AppSyncEventsResolver({ logger: console });
-    app.onSubscribe('/foo', async () => {
+    app.onSubscribe('/foo', () => {
       throw new UnauthorizedException('nah');
     });
 
@@ -258,7 +258,7 @@ describe('Class: AppSyncEventsResolver', () => {
   it('returns the response of the onPublish handler', async () => {
     // Prepare
     const app = new AppSyncEventsResolver({ logger: console });
-    app.onPublish('/foo', async (payload) => {
+    app.onPublish('/foo', (payload) => {
       if (payload === 'foo') {
         return true;
       }
@@ -303,7 +303,7 @@ describe('Class: AppSyncEventsResolver', () => {
     const app = new AppSyncEventsResolver({ logger: console });
     app.onPublish(
       '/foo',
-      async (payloads) => {
+      (payloads) => {
         return payloads.map((payload) => ({
           id: payload.id,
           payload: true,
@@ -353,7 +353,7 @@ describe('Class: AppSyncEventsResolver', () => {
     const app = new AppSyncEventsResolver({ logger: console });
     app.onPublish(
       '/foo',
-      async () => {
+      () => {
         throw new Error('Error in handler');
       },
       { aggregate: true }
@@ -379,7 +379,7 @@ describe('Class: AppSyncEventsResolver', () => {
     const app = new AppSyncEventsResolver({ logger: console });
     app.onPublish(
       '/foo',
-      async () => {
+      () => {
         throw new UnauthorizedException('nah');
       },
       { aggregate: true }
@@ -400,7 +400,7 @@ describe('Class: AppSyncEventsResolver', () => {
     const app = new AppSyncEventsResolver();
     app.onPublish(
       '/foo',
-      async () => {
+      () => {
         throw new Error('Error in handler');
       },
       { aggregate: true }