CODEWITHSUNDEEP
nestjsfastify
saulotoledo
saulotoledo

Reputation: 1982

How to set a custom Content-Type with fastify in NestJS?

I have an application in NestJS using Fastify. I want to set a the Content-Type to application/hal+json in my responses. I have the following code in a NestJS interceptor:

@Injectable()
export class SampleInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {

    context.switchToHttp().getResponse()
      .header('Content-Type', 'application/hal+json; charset=utf-8');

    return next.handle().pipe(
      map((data) => {
        const serializer = MyCustomSerializer();
        return serializer.serialize(data);
      })
    );
  }
}

However, I have the following error because I defined the Content-Type:

FastifyError [FST_ERR_REP_INVALID_PAYLOAD_TYPE]: FST_ERR_REP_INVALID_PAYLOAD_TYPE: Attempted to send payload of invalid type 'object'. Expected a string or Buffer.
    at onSendEnd (/home/user/Projects/nestjs-fastify-sample/node_modules/fastify/lib/reply.js:363:11)
    at onSendHook (/home/user/Projects/nestjs-fastify-sample/node_modules/fastify/lib/reply.js:325:5)
    at _Reply.Reply.send (/home/user/Projects/nestjs-fastify-sample/node_modules/fastify/lib/reply.js:151:3)
    at FastifyAdapter.reply (/home/user/Projects/nestjs-fastify-sample/node_modules/@nestjs/platform-fastify/adapters/fastify-adapter.js:37:25)
    at RouterResponseController.apply (/home/user/Projects/nestjs-fastify-sample/node_modules/@nestjs/core/router/router-response-controller.js:10:36)
    at /home/user/Projects/nestjs-fastify-sample/node_modules/@nestjs/core/router/router-execution-context.js:163:48
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
    at async /home/user/Projects/nestjs-fastify-sample/node_modules/@nestjs/core/router/router-execution-context.js:46:13
    at async Object.<anonymous> (/home/user/Projects/nestjs-fastify-sample/node_modules/@nestjs/core/router/router-proxy.js:8:17)

After some investigation, I noticed that if I do not define the Content-Type, the payload is a string representation of my JSON response. If not, the payload is an object. This happens because this code in fastify never runs and never serializes the payload as string.

Here is a repository for you to easily replicate the issue.

Is there a way to solve this issue?

Upvotes: 0

Views: 3517

Answers (1)

Jay McDoniel
Jay McDoniel

Reputation: 70412

To my understanding, so long as what you return from the interceptor is a string, Nest (and Fastify) will treat it like a string and return it however you want. I have an example where I'm returning an XML string so long as an incoming accept header is setup to ask for XML data back (content negotiation) and Fastify is returning it just fine, so as long as you strinigfy whatever your serializer returns, you shouldn't have a problem with a custom (different) header

Upvotes: 1

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