pre-calculate response type as save on request context

Author: svozza

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

@@ -217,6 +217,8 @@ class Router {
       throw new InvalidEventError();
     }
 
+    const responseType = isAPIGatewayProxyEventV2(event) ? 'v2' : 'v1';
+
     let req: Request;
     try {
       req = proxyEventToWebRequest(event);
@@ -231,6 +233,7 @@ class Router {
           req: new Request('https://invalid'),
           res: new Response('', { status: HttpStatusCodes.METHOD_NOT_ALLOWED }),
           params: {},
+          responseType,
         };
       }
       throw err;
@@ -244,6 +247,7 @@ class Router {
       // it means something went wrong with the middleware chain
       res: new Response('', { status: HttpStatusCodes.INTERNAL_SERVER_ERROR }),
       params: {},
+      responseType,
     };
 
     try {
@@ -346,7 +350,7 @@ class Router {
     options?: ResolveOptions
   ): Promise<APIGatewayProxyResult | APIGatewayProxyStructuredResultV2> {
     const reqCtx = await this.#resolve(event, context, options);
-    return webResponseToProxyResult(reqCtx.res, reqCtx.event);
+    return webResponseToProxyResult(reqCtx.res, reqCtx.responseType);
   }
 
   /**
@@ -380,7 +384,7 @@ class Router {
   ) {
     const { headers } = webHeadersToApiGatewayHeaders(
       reqCtx.res.headers,
-      reqCtx.event
+      reqCtx.responseType
     );
     const resStream = HttpResponseStream.from(responseStream, {
       statusCode: reqCtx.res.status,

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

@@ -11,12 +11,13 @@ import type {
   ExtendedAPIGatewayProxyResult,
   ExtendedAPIGatewayProxyResultBody,
   HandlerResponse,
+  ResponseType,
+  ResponseTypeMap,
   V1Headers,
 } from '../types/rest.js';
 import { COMPRESSION_ENCODING_TYPES } from './constants.js';
 import { InvalidHttpMethodError } from './errors.js';
 import {
-  isAPIGatewayProxyEventV1,
   isAPIGatewayProxyEventV2,
   isExtendedAPIGatewayProxyResult,
   isHttpMethod,
@@ -194,27 +195,19 @@ const webHeadersToApiGatewayV2Headers = (webHeaders: Headers) => {
   return { headers };
 };
 
-function webHeadersToApiGatewayHeaders(
+const webHeadersToApiGatewayHeaders = <T extends ResponseType>(
   webHeaders: Headers,
-  event: APIGatewayProxyEventV2
-): { headers: Record<string, string> };
-function webHeadersToApiGatewayHeaders(
-  webHeaders: Headers,
-  event: APIGatewayProxyEvent
-): V1Headers;
-function webHeadersToApiGatewayHeaders(
-  webHeaders: Headers,
-  event: APIGatewayProxyEvent | APIGatewayProxyEventV2
-): { headers: Record<string, string> } | V1Headers;
-function webHeadersToApiGatewayHeaders(
-  webHeaders: Headers,
-  event: APIGatewayProxyEvent | APIGatewayProxyEventV2
-): { headers: Record<string, string> } | V1Headers {
-  if (isAPIGatewayProxyEventV1(event)) {
-    return webHeadersToApiGatewayV1Headers(webHeaders);
+  responseType: T
+): T extends 'v1' ? V1Headers : { headers: Record<string, string> } => {
+  if (responseType === 'v1') {
+    return webHeadersToApiGatewayV1Headers(webHeaders) as T extends 'v1'
+      ? V1Headers
+      : { headers: Record<string, string> };
   }
-  return webHeadersToApiGatewayV2Headers(webHeaders);
-}
+  return webHeadersToApiGatewayV2Headers(webHeaders) as T extends 'v1'
+    ? V1Headers
+    : { headers: Record<string, string> };
+};
 
 /**
  * Converts a Web API Response object to an API Gateway V1 proxy result.
@@ -320,27 +313,15 @@ const webResponseToProxyResultV2 = async (
   return result;
 };
 
-function webResponseToProxyResult(
+const webResponseToProxyResult = <T extends ResponseType>(
   response: Response,
-  event: APIGatewayProxyEventV2
-): Promise<APIGatewayProxyStructuredResultV2>;
-function webResponseToProxyResult(
-  response: Response,
-  event: APIGatewayProxyEvent
-): Promise<APIGatewayProxyResult>;
-function webResponseToProxyResult(
-  response: Response,
-  event: APIGatewayProxyEvent | APIGatewayProxyEventV2
-): Promise<APIGatewayProxyResult | APIGatewayProxyStructuredResultV2>;
-function webResponseToProxyResult(
-  response: Response,
-  event: APIGatewayProxyEvent | APIGatewayProxyEventV2
-): Promise<APIGatewayProxyResult | APIGatewayProxyStructuredResultV2> {
-  if (isAPIGatewayProxyEventV1(event)) {
-    return webResponseToProxyResultV1(response);
+  responseType: T
+): Promise<ResponseTypeMap[T]> => {
+  if (responseType === 'v1') {
+    return webResponseToProxyResultV1(response) as Promise<ResponseTypeMap[T]>;
   }
-  return webResponseToProxyResultV2(response);
-}
+  return webResponseToProxyResultV2(response) as Promise<ResponseTypeMap[T]>;
+};
 
 /**
  * Adds headers from an ExtendedAPIGatewayProxyResult to a Headers object.

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

@@ -7,19 +7,28 @@ import type {
   APIGatewayProxyEvent,
   APIGatewayProxyEventV2,
   APIGatewayProxyResult,
+  APIGatewayProxyStructuredResultV2,
   Context,
 } from 'aws-lambda';
 import type { HttpStatusCodes, HttpVerbs } from '../rest/constants.js';
 import type { Route } from '../rest/Route.js';
 import type { HttpResponseStream } from '../rest/utils.js';
 import type { ResolveOptions } from './common.js';
 
+type ResponseType = 'v1' | 'v2';
+
+type ResponseTypeMap = {
+  v1: APIGatewayProxyResult;
+  v2: APIGatewayProxyStructuredResultV2;
+};
+
 type RequestContext = {
   req: Request;
   event: APIGatewayProxyEvent | APIGatewayProxyEventV2;
   context: Context;
   res: Response;
   params: Record<string, string>;
+  responseType: ResponseType;
 };
 
 type ErrorResolveOptions = RequestContext & ResolveOptions;
@@ -237,6 +246,8 @@ export type {
   Middleware,
   Path,
   RequestContext,
+  ResponseType,
+  ResponseTypeMap,
   RestRouterOptions,
   RouteHandler,
   ResolveStreamOptions,