Merge pull request #2107 from micalevisk/improve-exception-filter-example

doc: replace 'catch everything' example with a platform-agnostic one

Author: kamilmysliwiec

content/exception-filters.md

@@ -284,6 +284,8 @@ You can add as many filters with this technique as needed; simply add each to th
 
 In order to catch **every** unhandled exception (regardless of the exception type), leave the `@Catch()` decorator's parameter list empty, e.g., `@Catch()`.
 
+In the example below we have a code that is platform-agnostic because it uses the [HTTP adapter](./faq/http-adapter) to deliver the response, and doesn't use any of the platform-specific objects (`Request` and `Response`) directly:
+
 ```typescript
 import {
   ExceptionFilter,
@@ -292,30 +294,35 @@ import {
   HttpException,
   HttpStatus,
 } from '@nestjs/common';
+import { HttpAdapterHost } from '@nestjs/core';
 
 @Catch()
 export class AllExceptionsFilter implements ExceptionFilter {
-  catch(exception: unknown, host: ArgumentsHost) {
+  constructor(private readonly httpAdapterHost: HttpAdapterHost) {}
+
+  catch(exception: unknown, host: ArgumentsHost): void {
+    // In certain situations `httpAdapter` might not be available in the
+    // constructor method, thus we should resolve it here.
+    const { httpAdapter } = this.httpAdapterHost;
+
     const ctx = host.switchToHttp();
-    const response = ctx.getResponse();
-    const request = ctx.getRequest();
 
-    const status =
+    const httpStatus =
       exception instanceof HttpException
         ? exception.getStatus()
         : HttpStatus.INTERNAL_SERVER_ERROR;
 
-    response.status(status).json({
-      statusCode: status,
+    const responseBody = {
+      statusCode: httpStatus,
       timestamp: new Date().toISOString(),
-      path: request.url,
-    });
+      path: httpAdapter.getRequestUrl(ctx.getRequest()),
+    };
+
+    httpAdapter.reply(ctx.getResponse(), responseBody, httpStatus);
   }
 }
 ```
 
-In the example above the filter will catch each exception thrown, regardless of its type (class).
-
 #### Inheritance
 
 Typically, you'll create fully customized exception filters crafted to fulfill your application requirements. However, there might be use-cases when you would like to simply extend the built-in default **global exception filter**, and override the behavior based on certain factors.