Specify the return content type of a Controller

debugcn Published at Dev

Eric Lindsey

I have the following as a metrics.controller.ts file:

import { Controller, Get } from '@nestjs/common';
import { ApiOperation, ApiResponse, ApiUseTags, ApiModelProperty } from '@nestjs/swagger';
import { PrometheusService } from './prometheus.service';

@Controller('metrics')
@ApiUseTags('Misc')
export class MetricsController {
  constructor(private readonly prometheusService: PrometheusService) {}

  @Get('/')
  @ApiOperation({
    title: 'Prometheus metrics',
    description: 'Exposes default prometheus node metrics'
  })
  @ApiResponse({ status: 200, description: 'Prometheus metrics' })
  public getMetrics(): string {
    return this.prometheusService.getMetrics();
  }
}

However Swagger incorrectly indicates a Response content type of application/json, when the actual output is text/plain:

Screen shot of output

I have tried looking at the Swagger docs regarding describing responses, and the item I am looking for is the 'content' portion. However, that doc does not cover the TypeScript annotations. The Swagger Core 2.X documentation talks about an @Operation annotation, but I don't have a reference to that and I don't know where to get one--only @ApiOperation works.

The relevant version information from npm ls in the project directory is as follows:

+-- @nestjs/[email protected]
| +-- @nestjs/[email protected] deduped
| +-- @nestjs/[email protected] deduped
| +-- [email protected]
| +-- [email protected] deduped
| `-- [email protected]

What is the proper annotation to indicate a Response content type of text/plain?

Eric Lindsey

I found out the solution is to import ApiProduces from '@nestjs/swagger' like so:

import { ApiOperation, ApiResponse, ApiUseTags, ApiProduces } from '@nestjs/swagger'

//...

    @ApiProduces('text/plain')
    public getMetrics(): string {
        //...
    }

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