Change response status

Update the response status based on fields that are present in the request body.

In this guide, you learn how to use an if else function to change the HTTP status that is returned in your response. To determine the response status, you use a JSON string that is provided in the request. If the JSON includes an error, you return a 400 HTTP response code. In all other cases, you return the response code of the :status pseudo header.

This guide uses a subset of the supported transformation template attributes. To review all the attributes that you can set, see Templating language.

Before you begin

Follow the Get started guide to install Gloo Gateway, set up a gateway resource, and deploy the httpbin sample app.

Get the external address of the gateway and save it in an environment variable.

export INGRESS_GW_ADDRESS=$(kubectl get svc -n gloo-system gloo-proxy-http -o jsonpath="{.status.loadBalancer.ingress[0]['hostname','ip']}")
echo $INGRESS_GW_ADDRESS

kubectl port-forward deployment/gloo-proxy-http -n gloo-system 8080:8080

Change the response status

Create a payload that you later send as your request body.

cat << EOF > data.json
{
  "error": {
   "message": "This is an error"
  }
}
EOF

Create a RouteOption or VirtualHostOption resource with the following transformation rules:

Extract the message field from the data.json file that is sent in the request.
If the error message is not empty, return a 400 HTTP response code in the :status pseudo header.

In all other cases, do not change the :status pseudo header.

kubectl apply -f- <<EOF
apiVersion: gateway.solo.io/v1
kind: RouteOption
metadata:
  name: transformation
  namespace: httpbin
spec:
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: HTTPRoute
    name: httpbin
  options:
    transformations:
      responseTransformation:
        transformationTemplate:
          extractors: 
            message:
              body: {}
              mode: EXTRACT
              regex: '[\s\S]*(message)[\s\S]*'
              subgroup: 1
          headers:
           # We set the response status via the :status pseudo-header based on the response code
            :status:
              text: '{% if ( message ) != "" %}400{% else %}{{ header(":status") }}{% endif %}'
EOF

kubectl apply -n gloo-system -f- <<EOF
apiVersion: gateway.solo.io/v1
kind: VirtualHostOption
metadata:
  name: transformation
  namespace: gloo-system
spec:
  options:
    transformations:
      responseTransformation:
        transformationTemplate:
          parseBodyBehavior: ParseAsJson
          headers:
           # We set the response status via the :status pseudo-header based on the response code
            ":status":
              text: '{% if {{ error }} != "" %}400{% else %}{{ header(":status") }}{% endif %}'
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: Gateway
    name: http
    namespace: gloo-system
EOF

Send a request to the httpbin app and include data.json file as your payload. Because the error.message field is not empty, a 400 HTTP response code is returned.

curl -X POST -H "host: www.example.com:8080" -w "%{http_code}" \
 -H "Content-Type: application/json" \
 http://$INGRESS_GW_ADDRESS:8080/post -d @data.json | jq

curl -vik localhost:8080/get -w "%{http_code}" \
-H "foo: bar" \
-H "host: www.example.com" \

Example output:

{
  "args": {},
  "headers": {
    "Accept": [
      "*/*"
    ],
     "Content-Length": [
      "49"
    ],
    "Content-Type": [
      "application/json"
    ],
    "Host": [
      "www.example.com:8080"
    ],
    "User-Agent": [
      "curl/8.7.1"
    ],
    "X-Envoy-Expected-Rq-Timeout-Ms": [
      "15000"
    ],
    "X-Forwarded-Proto": [
      "http"
    ],
    "X-Request-Id": [
      "e462eb36-0a36-4ffd-b37d-316737819532"
    ]
  },
  "origin": "10.0.2.124:53583",
  "url": "http://www.example.com:8080/post",
  "data": "{  \"error\": {   \"message\": \"This is an error\"  }}",
  "files": null,
 "form": null,
  "json": {
    "error": {
      "message": "This is an error"
    }
  }
}
400

Update your payload file and remove the message so that the error field is empty.
```
cat << EOF > data.json
{
  "error": {
  }
}
EOF
```

Send another request to the httpbin app. Verify that this time a 200 HTTP response code is returned.

curl -X POST -H "host: www.example.com:8080" -w "%{http_code}" \
 -H "Content-Type: application/json" \
 http://$INGRESS_GW_ADDRESS:8080/post -d @data.json | jq

curl -vik localhost:8080/get -w "%{http_code}" \
-H "foo: bar" \
-H "host: www.example.com" \

Example output:

{
  "args": {},
  "headers": {
    "Accept": [
      "*/*"
    ],
     "Content-Length": [
      "49"
    ],
    "Content-Type": [
      "application/json"
    ],
    "Host": [
      "www.example.com:8080"
    ],
    "User-Agent": [
      "curl/8.7.1"
    ],
    "X-Envoy-Expected-Rq-Timeout-Ms": [
      "15000"
    ],
    "X-Forwarded-Proto": [
      "http"
    ],
    "X-Request-Id": [
      "e462eb36-0a36-4ffd-b37d-316737819532"
    ]
  },
  "origin": "10.0.2.124:53583",
  "url": "http://www.example.com:8080/post",
  "data": "{  \"error\": {   \"message\": \"This is an error\"  }}",
  "files": null,
 "form": null,
  "json": {
    "error": {
    }
  }
}
200

Cleanup

You can remove the resources that you created in this guide.

kubectl delete virtualhostoption transformation -n gloo-system
kubectl delete routeoption transformation -n httpbin

Create redirect URLs Update response body