Avoid double-sending Fastify replies in @orpc/nest

packages/nest/src/implement.test.ts

@@ -9,13 +9,15 @@ import { FastifyAdapter } from '@nestjs/platform-fastify'
 import { Test } from '@nestjs/testing'
 import { oc, ORPCError } from '@orpc/contract'
 import { implement, lazy } from '@orpc/server'
+import * as StandardServerFastify from '@orpc/standard-server-fastify'
 import * as StandardServerNode from '@orpc/standard-server-node'
 import supertest from 'supertest'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 import * as z from 'zod'
 import { Implement } from './implement'
 import { ORPCModule } from './module'
 
+const sendStandardFastifyResponseSpy = vi.spyOn(StandardServerFastify, 'sendStandardResponse')
 const sendStandardResponseSpy = vi.spyOn(StandardServerNode, 'sendStandardResponse')
 
 beforeEach(() => {
@@ -311,6 +313,8 @@ describe('@Implement', async () => {
   })
 
   it('partial working on fastify', async () => {
+    const capturedFastifyLogs: string[] = []
+
     @Controller()
     class FastifyController {
       @Implement(contract.ping)
@@ -324,7 +328,16 @@ describe('@Implement', async () => {
       controllers: [FastifyController],
     }).compile()
 
-    const app = moduleRef.createNestApplication(new FastifyAdapter())
+    const app = moduleRef.createNestApplication(new FastifyAdapter({
+      logger: {
+        level: 'info',
+        stream: {
+          write: (message: string) => {
+            capturedFastifyLogs.push(message)
+          },
+        },
+      },
+    }))
     await app.init()
     await app.getHttpAdapter().getInstance().ready()
 
@@ -357,6 +370,8 @@ describe('@Implement', async () => {
     expect(req).toBeDefined()
     expect(req!.method).toEqual('POST')
     expect(req!.url).toEqual('/ping?param=value&param2[]=value2&param2[]=value3')
+    expect(sendStandardFastifyResponseSpy).not.toHaveBeenCalled()
+    expect(capturedFastifyLogs.join('')).not.toContain('Reply was already sent')
   })
 
   it('should pass correct signal and lastEventId', async () => {

packages/nest/src/implement.ts

@@ -163,15 +163,29 @@ export class ImplementInterceptor implements NestInterceptor {
         })
 
         if (result.matched) {
+          const sendResponseInterceptors = toArray(this.config.sendResponseInterceptors)
+
           return intercept(
-            toArray(this.config.sendResponseInterceptors),
+            sendResponseInterceptors,
             { request: req, response: res, standardResponse: result.response },
             async ({ response, standardResponse }) => {
               if (isHono) {
                 const fetchResponse = StandardServerFetch.toFetchResponse(standardResponse, this.config)
                 return (response as HonoContext).newResponse(fetchResponse.body, fetchResponse)
               }
               else if (isFastify) {
+                if (sendResponseInterceptors.length === 0) {
+                  const headers = { ...standardResponse.headers }
+                  const body = StandardServerNode.toNodeHttpBody(standardResponse.body, headers, this.config)
+                  const fastifyReply = response as FastifyReply
+
+                  fastifyReply
+                    .status(standardResponse.status)
+                    .headers(StandardServerNode.toNodeHttpHeaders(headers))
+
+                  return body
+                }
+
                 await StandardServerFastify.sendStandardResponse(response as FastifyReply, standardResponse, this.config)
               }
               else {