Update exception-filters.md

There are differences in fastify response api

Author: ufec

content/exception-filters.md

@@ -182,6 +182,56 @@ export class HttpExceptionFilter {
 
 > info **Hint** All exception filters should implement the generic `ExceptionFilter<T>` interface. This requires you to provide the `catch(exception: T, host: ArgumentsHost)` method with its indicated signature. `T` indicates the type of the exception.
 
+you can use `response.send()` instead of `response.json()` when using `platform-fastify`, and use `import { FastifyReply as Response, FastifyRequest as Request } from 'fastify';` instead of `import { Request, Response } from 'express';`
+
+like this:
+
+```typescript
+@@filename(http-exception.filter)
+import { ExceptionFilter, Catch, ArgumentsHost, HttpException } from '@nestjs/common';
+import { FastifyReply as Response, FastifyRequest as Request } from 'fastify';
+
+@Catch(HttpException)
+export class HttpExceptionFilter implements ExceptionFilter {
+  catch(exception: HttpException, host: ArgumentsHost) {
+    const ctx = host.switchToHttp();
+    const response = ctx.getResponse<Response>();
+    const request = ctx.getRequest<Request>();
+    const status = exception.getStatus();
+
+    response
+      .status(status)
+      .send({
+        statusCode: status,
+        timestamp: new Date().toISOString(),
+        path: request.url,
+      });
+  }
+}
+@@switch
+import { Catch, HttpException } from '@nestjs/common';
+
+@Catch(HttpException)
+export class HttpExceptionFilter {
+  catch(exception, host) {
+    const ctx = host.switchToHttp();
+    const response = ctx.getResponse();
+    const request = ctx.getRequest();
+    const status = exception.getStatus();
+
+    response
+      .status(status)
+      .send({
+        statusCode: status,
+        timestamp: new Date().toISOString(),
+        path: request.url,
+      });
+  }
+}
+```
+
+> info **Hint** you must install `fastify`
+
 The `@Catch(HttpException)` decorator binds the required metadata to the exception filter, telling Nest that this particular filter is looking for exceptions of type `HttpException` and nothing else. The `@Catch()` decorator may take a single parameter, or a comma-separated list. This lets you set up the filter for several types of exceptions at once.
 
 #### Arguments host