Error responses' Content-Type is always returned as text/plain for the client

[yamanaliesh92]

Environment info:

• KrakenD version:

KrakenD Version: 2.5.0
Go Version: 1.20.11
Glibc Version: MUSL-1.2.4_(alpine-3.18.4)

• System info:

Docker version 23.0.1, build a5ee5b1

• Hardware specs: 2 CPUs and 8GB of RAM allocated for the container
• Backend technology: NodeJS
• Additional environment information:

Describe what are you trying to do:

• Trying to return error responses with header Content-Type: application/json without using output_encoding: 'no-op', backend error is returned with correct status and correct message but the response header Content-Type is always text/plain

Your configuration file:

{
  "$schema": "https://www.krakend.io/schema/krakend.json",
  "version": 3,
  "name": "KrakenD - API Gateway",
  "extra_config": { "router": { "return_error_msg": true } },
  "endpoints": [
    {
      "output_encoding": "json",
      "backend": [
        {
          "url_pattern": "/api",
          "method": "GET",
          "host": ["http://backend:3000"],
          "extra_config": { "backend/http": { "return_error_code": true } }
        }
      ],

      "endpoint": "/api",
      "method": "GET"
    }
  ]
}

Configuration check output:
Result of krakend check -dtc krakend.json --lint command

0 async agent(s):
Syntax OK!

Commands used:
How did you start the software?

krakend run -d -c krakend.json

Logs:

er/login"
newbackwithkrakend-gateway-1  | [00] Error #01: {"statusCode":400,"message":"email or password is not correct","error":"Bad Request"}

Additional comments:

• I know using no-op would forward all headers of backend to the client including the Content-Type but i would like not to use no-op but still get my errors as json response

[andrewbrg]

Hi, yea we have the same issue.

Everything works fine but unless the endpoint is set as no-op the content-type header on the response when there is a non-2xx response status from the backend is completely ignored.

So Kraken, forwards the error message (JSON) from the backend to the client but then just serves it with a content-type of text/plain which causes issues with some clients.

I think return_error_code should either also forward the same header from the backend to the client or another parameter be made available on the config to achieve the same thing.