feat(event-handler): add function to convert Lambda proxy event to web response object

Author: svozza

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

@@ -24,6 +24,7 @@ import {
 } from './errors.js';
 import { Route } from './Route.js';
 import { RouteHandlerRegistry } from './RouteHandlerRegistry.js';
+import { isAPIGatewayProxyEvent } from './utils.js';
 
 abstract class BaseRouter {
   protected context: Record<string, unknown>;

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

@@ -0,0 +1,48 @@
+import type { APIGatewayProxyEvent } from 'aws-lambda';
+
+function createBody(body: string | null, isBase64Encoded: boolean) {
+  if (body === null) return null;
+
+  if (!isBase64Encoded) {
+    return body;
+  }
+  return Buffer.from(body, 'base64').toString('utf8');
+}
+
+export function proxyEventToWebRequest(event: APIGatewayProxyEvent) {
+  const { httpMethod, path, domainName } = event.requestContext;
+
+  const headers = new Headers();
+  for (const [name, value] of Object.entries(event.headers ?? {})) {
+    if (value != null) headers.append(name, value);
+  }
+
+  for (const [name, values] of Object.entries(event.multiValueHeaders ?? {})) {
+    for (const value of values ?? []) {
+      headers.append(name, value);
+    }
+  }
+  const hostname = headers.get('Host') ?? domainName;
+  const protocol = headers.get('X-Forwarded-Proto') ?? 'http';
+
+  const url = new URL(path, `${protocol}://${hostname}/`);
+
+  for (const [name, value] of Object.entries(
+    event.queryStringParameters ?? {}
+  )) {
+    if (value != null) url.searchParams.append(name, value);
+  }
+
+  for (const [name, values] of Object.entries(
+    event.multiValueQueryStringParameters ?? {}
+  )) {
+    for (const value of values ?? []) {
+      url.searchParams.append(name, value);
+    }
+  }
+  return new Request(url.toString(), {
+    method: httpMethod,
+    headers,
+    body: createBody(event.body, event.isBase64Encoded),
+  });
+}

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

@@ -1,3 +1,5 @@
+import { isRecord, isString } from '@aws-lambda-powertools/commons/typeutils';
+import type { APIGatewayProxyEvent } from 'aws-lambda';
 import type { CompiledRoute, Path, ValidationResult } from '../types/rest.js';
 import { PARAM_PATTERN, SAFE_CHARS, UNSAFE_CHARS } from './constants.js';
 
@@ -43,3 +45,26 @@ export function validatePathPattern(path: Path): ValidationResult {
     issues,
   };
 }
+
+/**
+ * Type guard to check if the provided event is an API Gateway Proxy event.
+ *
+ * We use this function to ensure that the event is an object and has the
+ * required properties without adding a dependency.
+ *
+ * @param event - The incoming event to check
+ */
+export const isAPIGatewayProxyEvent = (
+  event: unknown
+): event is APIGatewayProxyEvent => {
+  if (!isRecord(event)) return false;
+  return (
+    isString(event.httpMethod) &&
+    isString(event.path) &&
+    isString(event.resource) &&
+    isRecord(event.headers) &&
+    isRecord(event.requestContext) &&
+    typeof event.isBase64Encoded === 'boolean' &&
+    (event.body === null || isString(event.body))
+  );
+};

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

@@ -53,7 +53,6 @@ interface CompiledRoute {
 
 type DynamicRoute = Route & CompiledRoute;
 
-// biome-ignore lint/suspicious/noExplicitAny: we want to keep arguments and return types as any to accept any type of function
 type RouteHandler<
   TParams = Record<string, unknown>,
   TReturn = Response | JSONObject,

packages/event-handler/tests/unit/rest/BaseRouter.test.ts

@@ -3,12 +3,14 @@ import type { APIGatewayProxyEvent, Context } from 'aws-lambda';
 import { beforeEach, describe, expect, it, vi } from 'vitest';
 import { BaseRouter } from '../../../src/rest/BaseRouter.js';
 import { HttpErrorCodes, HttpVerbs } from '../../../src/rest/constants.js';
+import { proxyEventToWebRequest } from '../../../src/rest/converters.js';
 import {
   BadRequestError,
   InternalServerError,
   MethodNotAllowedError,
   NotFoundError,
 } from '../../../src/rest/errors.js';
+import { isAPIGatewayProxyEvent } from '../../../src/rest/utils.js';
 import type {
   HttpMethod,
   Path,
@@ -43,39 +45,19 @@ describe('Class: BaseRouter', () => {
       this.logger.error('test error');
     }
 
-    #isEvent(obj: unknown): asserts obj is APIGatewayProxyEvent {
-      if (
-        typeof obj !== 'object' ||
-        obj === null ||
-        !('path' in obj) ||
-        !('httpMethod' in obj) ||
-        typeof (obj as any).path !== 'string' ||
-        !(obj as any).path.startsWith('/') ||
-        typeof (obj as any).httpMethod !== 'string' ||
-        !Object.values(HttpVerbs).includes(
-          (obj as any).httpMethod as HttpMethod
-        )
-      ) {
-        throw new Error('Invalid event object');
-      }
-    }
-
     public async resolve(
       event: unknown,
       context: Context,
       options?: any
     ): Promise<unknown> {
-      this.#isEvent(event);
+      if (!isAPIGatewayProxyEvent(event))
+        throw new Error('not an API Gateway event!');
       const { httpMethod: method, path } = event;
       const route = this.routeRegistry.resolve(
         method as HttpMethod,
         path as Path
       );
-      const request = new Request(`http://localhost${path}`, {
-        method,
-        headers: event.headers as Record<string, string>,
-        body: event.body,
-      });
+      const request = proxyEventToWebRequest(event);
       try {
         if (route == null)
           throw new NotFoundError(`Route ${method} ${path} not found`);
@@ -838,9 +820,9 @@ describe('Class: BaseRouter', () => {
         statusCode: HttpErrorCodes.BAD_REQUEST,
         error: 'Bad Request',
         message: error.message,
-        hasRequest: options.request instanceof Request,
-        hasEvent: options.event === testEvent,
-        hasContext: options.context === context,
+        hasRequest: options?.request instanceof Request,
+        hasEvent: options?.event === testEvent,
+        hasContext: options?.context === context,
       }));
 
       app.get('/test', () => {